Dissertations / Theses on the topic 'Catalyst ink'

Despite the benefits of fuel cell technology its advancement to being commercially functional is hindered by a number of crucial factors. These factors are often associated with the lack of appropriate materials or manufacturing routes that would enable the cost of electricity per kWh to compete with existing technology. Whilst most research efforts have been directed towards developing more active catalysts, the amount of catalyst required in the fuel cell can be further reduced by improving the platinum utilisation in the membrane electrode assembly. The platinum utilisation is a strong function of the catalyst layer preparation step and there remains significant scope for optimisation of this step. Whereas significant work has been conducted into the different components of the catalyst ink there is limited work and understanding on the influence of the mixing method of the catalyst ink. This study will focus on the influence of the mixing technique on the catalyst ink properties and on the final fuel cell performance. Specifically, the study will investigate the effect of the three different mixing techniques on (i) catalyst ink quality (ii) the physical properties of the resultant catalyst layer and (iii) the in-situ electrochemical performance of the membrane electrode assembly. A large set of characterisation techniques were chosen to effectively study the step wise processing of the catalyst layer, and fuel cell performance. The results presented here include a comparison of the various mixing techniques and a comprehensive 2 x 2 factorial design into the individual techniques. The results suggest that high energy mixing is required for effective distribution of catalyst layer components, an even catalyst layer topography and a highly functional ionomer network which consequently, enhances performance. The mixing energy referred to involves prolonged mixing time, enhanced mixing intensity or a combination of the two. During bead milling of catalyst inks, high intensity mixing seems to be beneficial however, prolonged mixing time appears to be detrimental to the ionomer film structure. During high shear stirring and ultrasonic homogenisation of catalyst inks, the ink mixture significantly heats up. It has been observed that at higher temperatures, Nafion elongates and the contact with catalyst agglomerates is enhanced. High shear stirring of catalyst inks seems to be most effective at high agitation rates. High mixing energies result in high shear forces and in addition, high mixing temperatures which appear to be beneficial to establishing an effective catalyst/Nafion interface, enhancing the three phase boundary observed during in-situ testing. Ultrasonic homogenisation seems to be more effective at prolonged sonication times. Due to the erosive nature of ultrasonic dispersion, sufficient time is required to establish a well dispersed and distributed catalyst ink. However, the nature of particle size distribution resulting from ultrasonication shows that inks are unstable and is not recommended for high throughput processing. Overall, fuel cell performance is not significantly affected by the mixing step however; mixing does have an observable impact on catalyst layer formulation. Generally, when optimizing membrane electrode assembly fabrication, mixing parameters should be carefully chosen. This goes without saying that parameters need to be effectively studied before foregoing catalyst ink processing.

The aim of this thesis work is focused on the development and characterization of nanostructured catalysts, in order to exploit them in two different reactions: the Oxygen Reduction Reaction (ORR) and the CO2 Reduction Reaction (CO2RR). The objective of this research is to find economical and ecological materials that could replace platinum as catalyst of the two reactions, while maintaining comparable performance. Considering the ORR, the study is concentrated on the manganese oxide family (MnxOy), structured in the form of nanofibers by electrospinning technique and subsequent thermal treatment. The aim is to demonstrate that the MnxOy nanofibers own all the necessary properties, e.g. cheapness, efficiency and environmental-friendliness, revealing themselves as promising and innovative structures as catalysts for ORR. This material is studied in terms of morphology, composition and electrochemical activity by varying the final calcination temperature of the nanofibers. Thanks to this study, it is possible to describe the thermal evolution of the catalyst, comparing the electrochemical performance to a precise nanostructure and crystalline composition. The ceramic nanofibers, in fact, catalyze efficiently the ORR, granting a cheaper and more eco-friendly material than platinum, which is the most used today in energy production devices, as Microbial Fuel Cells (MFCs). The MnxOy catalyst is also coupled with a conductive substrate in an MFC device, revealing its capability of successfully reduce oxygen after the direct integration onto the electrode, without changing its catalytic performance. Considering the CO2RR, the attention is focused on the titanium dioxide nanotubes (TiO2 NTs) and copper oxide nanofibers (CuxO NWs) -based catalysts. Vertically oriented TiO2 NTs are obtained by anodic oxidation of a titanium foil and studied, by their own, in terms of morphology and composition. Further they are coupled with a copper and a copper oxide layers, characterizing the electrochemical properties, catalytic performance and selectivity toward CO2RR. As a competitive alternative to TiO2 NTs, CuxO NWs are obtained by thermally oxidizing the copper foils at different temperatures and characterizing them in terms of morphology, composition catalytic activity and selectivity, analyzing both the liquid and gaseous byproducts. Lastly, the CuxO NWs are coupled with and titanium dioxide upper layer, exploiting the same in characterizations of the former substrate in order to be comparable. All the studied substrate show some catalytic activity toward CO2 reduction, but the highest efficiency is associated to the CuxO NWs, revealing formation of byproducts both in liquid and in gaseous form.

Numerous efforts have been made for the development of renewable energies to replace fossil fuels and thus reduce greenhouse gas emissions. Renewable energy has the advantage of having a limitless supply over time and is clean. This thesis reports on novel transition metal-based electrocatalysts for acidic water splitting and CO2 reduction, which are two significant technologies to produce chemical fuels (i.e. H2 and C-based compounds) from renewable electricity. The target is to develop and investigate cost-effective, stable, and efficient electrocatalysts for acidic water splitting and CO2 reduction, replacing noble metals and achieving performances above the current state of the art. In the first part, the preparation and oxygen evolution properties of the oxygen plasma-treated and acid-activated carbon paper are investigated. This part also presents the Ru incorporated Carbon paper, as an efficient, stable, and self-standing catalyst for OER in acid. This catalyst shows an overpotential of 230 mV vs. RHE at 1 mA cm−2, comparable to the other carbon-based materials. It shows a small Tafel slope of 74 mV dec-1 and 20 hours of stability at 10 mA cm−2. In the second part, the template-assisted wet synthesis and electrochemical OER studies of yolk-shell Co3O4/Co1−xRuxO2 hollow microspheres (MSs) are discussed. It demonstrates a lower overpotential of 240 mV at 10 mA cm-2 and a small Tafel slope of 70 mV dec−1. Also, the MSs exhibit high mass activity of 600 A g−1 and show high stability for 24 hours Chronopotentiometry tests at constant current densities of 10 and 20 mA cm−2 in 0.5 M H2SO4. Finally, nanostructured CdSe/Cu3P/CdSe heterostructures (in the form of nanocoral and sandwiches), obtained through colloidal synthesis, were used as efficient electrocatalysts for CO2 reduction. The nanocoral and Sandwich structured catalyst demonstrated higher CO2-to- HCOO– conversion giving a FEHCOO– of about 60% and 40% at –1.4 V vs RHE, respectively in 0.5 M KCl.

This thesis illustrates catalytic activity, stability and intrinsic kinetics of methane steam reforming (MSR) reaction over noble metal catalysts. The main objective of this thesis is to evaluate a best performing catalyst based on the maximization of H2 production and minimization of CO in the synthesis gas produced from MSR reaction. The noble metal catalysts tested towards MSR reaction were Rh, Ru and Pt supported on different reducible and irreducible oxides. The oxides (CeO2, MgO and Al2O3) used in this work were synthesized from their nitrite precursor by Simultaneous combustion synthesis (SCS) while Nb2O5 was prepared by heat treatment of Niobic acid obtained from Companhia Brasileira de Metalurgia e Mineracão (CBMM, Brasil). In all the catalysts the noble metals were deposited on the support by wetness impregnation method, except Pt/CeO2 which was prepared by one shoot SCS method. All the prepared catalysts were calcined under different calcination regimes. The best performing catalysts were characterized by different techniques BET, CO chemisorption, porosiometery, XRD, XPS, ICP, TEM and SEM analyses. Efforts have been made to correlate the catalytic activity with the physical characterization. All the catalysts prepared were initially screened by MSR reaction in a tubular fixed bed quartz reactor of 4mm ID containing 30mg of catalyst diluted with 50mg of inert. For catalytic screening and stability test the feed was introduced at a weight hourly space velocity of 20 NLh-1g-1cat and steam to carbon ratio 3-4 depending upon the catalyst. The results obtained from basic screening of the catalysts were analyzed in terms of methane conversion, H2 produced in dry reformate and CO2 selectivity. Among all the catalysts tested towards MSR only two were chosen based on initial screening, Rh/CeO2 and Pt/CeO2, for the further test concerning catalyst stability. The stability of Rh/CeO2 and Pt/CeO2 catalysts was determined based on daily start up and shut down cycle (DSS) with a 6h performance period. The Pt/CeO2 catalyst was tested for a total of 150 h in which 100h performance was with DSS in N2 environment while 50h of catalyst activity with DSS in reaction environment. The Rh/CeO2 catalyst was tested for a total of 25 h catalyst activity with DSS in N2 environment. Additionally the Rh/CeO2 catalyst was also tested in 100h continuous ageing. Both the catalysts showed good results in terms of catalyst activity and stability during the time period. As Rh/CeO2 catalyst showed good activity during 100h continuous endurance this catalysts was chosen to evaluate the intrinsic kinetics of methane steam reforming. For the kinetics test firstly the heat and mass transfer limitations were evaluated both experimentally and theoretically. The reactor was operated in an integral mode and no inert was used in feed for the kinetic experiments. The effect of WHSV at constant S/C 3 on the methane conversion and product composition was also determined. The partial pressures of the reactants were varied by varying the steam-to-carbon ratio of the feed. An attempt was made to fit kinetic data obtained using the models available in literature. The kinetic data obtained was perfect fit for the model proposed by Berman, and the activation energy of Rh/CeO2 was found to be 38.6 kJ/mol.

Les piles à combustible à membrane échangeuse d'anions (AEMFC) ont récemment attiré l'attention en tant que piles à combustible alternatives à faible coût aux piles à combustible à membrane échangeuse de protons traditionnelles en raison de l'utilisation possible d'électrocatalyseurs non-nobles. Bien que l'AEMFC ressemble à la PEMFC, les problèmes de gestion de l'eau sont plus prégnants dans une AEMFC car l'ORR en milieu alcalin nécessite de l'eau, tandis qu'en même temps, de l'eau est produite en grande quantité du côté de l'anode. Pour mieux comprendre la gestion de l'eau dans ce type de pile à combustible, il faut d'abord développer et acquérir de l'expérience avec ce type de pile à combustible à l'échelle du laboratoire. Puisque les matériaux prêts à l'emploi n'existaient pas au commencement de la thèse, nous avons dû fabriquer nos propres assemblages électrode-membranes (AMEs) à partir des matériaux disponibles dans le commerce. Etant donné que la thématique de fabrication des AMEs est nouvelle pour les chercheurs du LEMTA, cette thèse est articulée en deux parties, une dédiée à la formulation, la préparation et l'optimisation des AMEs pour PEMFC ; et une autre dédiée au développement d'AEMFC. Les résultats ont indiqué que la composition et préparation de l'encre, ainsi que la manière de déposer l'encre modifient systématiquement la structure de l'électrode, de même que ses performances en piles à combustible. En outre, l'étude fournit des informations sur les procédures et les méthodes pour les tests en AEMFC. Ici, nous souhaiterions partager notre savoir-faire avec les nouveaux venus dans le domaine de la préparation des AMEs pour piles à combustibles à membranes échangeuses d'ions
Anion exchange membrane fuel cells (AEMFCs) have recently attracted significant attention as low-cost alternative fuel cells to traditional proton exchange membrane fuel cells as a result of the possible use of platinum-group metal-free electrocatalysts. Although AEMFC is a mimic of PEMFC but working in an alkaline medium, water management issues are more severe in AEMFC because ORR in alkaline media requires water, while at the same time water is produced at the anode side. To better understand water management in this type of fuel cell, it is necessary first to develop and gain experience with this kind of fuel cell on the laboratory scale. Since no ready-to-use materials are available at the beginning of the project, the necessity of fabricating homemade MEAs from commercially available materials becomes a reality that we must face. As MEA fabrication is a new topic to LEMTA's researchers, this is why this thesis was divided into two parts: one part dedicated to the formulation, preparation, and optimization of MEAs for PEMFC through physico-chemical and electrochemical characterizations; another part dedicated to the development of AEMFC. The results indicated that ink deposition, composition, and preparation systematically change the electrode structure and thus affect fuel cells performance. Furthermore, the study provides information on the AEMFC procedures and methods. Here, we would like to share our know-how with newcomers in the field of preparation of MEA in ion exchange membrane fuel cells

The aim of this work is an investigation on a series of Pd-doped cobalt spinels catalysts for the lean CH4 combustion reaction. All the catalysts were synthesized and fully characterized from the structural and surface point of view (XRD, XRF, RS, BET, XPS, and FESEM) and then tested towards the oxidation of CH4 in lean conditions. The work was divided into two parts. In the first part, different catalysts at powder level were screened to optimize the design of Pd-doped cobalt spinel catalysts. In the second part, the best performing Pd-based catalysts previously selected were coated on structures of various nature (ceramic monoliths and foams) and tested towards the lean methane combustion to simulate a possible real applications (abatement of unburned CH4 residues from compressed natural gas vehicles or ventilation air methane emissions in coal mines). This thesis is organized as a collection of papers, either published during the Ph.D. or submitted for publications. In the first part (catalysts at powder level), the influence of different synthesis methods on the preparation of Pd/Co3O4 catalysts was evaluated (Paper I). Next, the role of the Pd doping on Co3O4 was investigated to determine the optimal Pd loading (Paper II). Then the Pd/Co3O4 catalyst formulation was optimized: the important catalysts’ features determining the reactivity were exploited in a technologically relevant methane concentration range (Paper III). In the end, a series of cobalt iron spinels was investigated to synthesize active catalysts, with a lower content of Co, with the aim of reducing the production costs (Fe cheaper than Co) (Paper IV). As main results, the synthesis method influences the catalytic activity. Indeed, the undoped spinels synthesized by solution combustion synthesis exhibit a better activity respect to the undoped spinel synthesized via precipitation. Thus, evaluating all the informations coming from the various characterizations, the influence of the synthesis method on the catalytic activity of cobalt oxide seems to be related with its redox state. Palladium doping improves the catalytic activity independently of the synthesis method, palladium load, and CH4 inlet concentration. Indeed a complete CH4 oxidation can be reached at a temperature lower than 430 °C for undoped spinels. The addition of palladium led to the formation of a reduced cobalt oxide phase which could contribute to a generation of active oxygen species under reaction conditions. The optimal Pd load is 3wt.%, calculated as PdO. The benefit was due to the existence of well-dispersed Pd nanocrystals. At lower Pd concentrations (0.5% Pd) the amount of Pd was insufficient to catalyze CH4 combustion effectively in the applied conditions, while the specific activity was lost for higher Pd concentrations (5% Pd) because of the agglomeration of Pd nanoparticles. Finally, the addition of Fe to Co3O4 did not affect the catalytic activity of undoped catalysts, supposedly because the rate-determining step of the reaction is the activation of the C–H bond in the CH4 molecule, and apparently, Fe is not influencing the lattice oxygen stability. In the second part of the work, undoped and 3 wt.% Pd-doped cobalt spinel catalysts were deposited on monoliths and open cell foams via solution combustion synthesis using glycine as precursors. The catalyzed structures were impregnated with Pd via wetness impregnation. The catalytic activity were tested toward the methane oxidation in lean conditions, in a gas mixture containing 0.5 vol.% or 1 vol.% CH4 at three different weight hourly space velocity (30, 60, and 90 NL h–1 gcat–1). The addition of Pd improved the catalytic activity of all structures independently on the test conditions. The pressure drop and heat transfer properties were evaluated for monoliths and foams as well. The results show that the foams exhibit an higher catalytic activity than the monolith. Moreover, all the catalysts show better activity at lower weight hourly space velocity. The open cell foam based on zirconia, with the biggest average pore diameter, exhibits the best catalytic activity. In general, zirconia-based foams show a better activity than alumina and silicon carbide ones for all test conditions. In order to well understand the different behavior of the foams, pressure drop measurements and thermal conductivity tests were carried out. From these measurements, the zirconia-based foams have lower pressure drop and lower overall heat exchange coefficients than the monolith and alumina and silicon carbide foams. This aspect can be explained by the higher thermal conductivity of alumina and silicon carbide materials. In conclusion, the obtained results represent a promising scientific advance because they demonstrate the good and stable performance of a 3% Pd/Co3O4 catalyst on a zirconia-based structured support for methane combustion in adiabatic or quasi-adiabatic applications (Papers V and VI). Finally, the basic Co3O4 spinel, synthesized with different methods, was tested as an alternative anodic catalyst for the electrochemical oxygen evolution reaction, the typical reaction of an electrolyzer (Paper VII).

Orientador: Gustavo Paim Valença
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-20T14:34:27Z (GMT). No. of bitstreams: 1 CarrenoGonzalez_IvonMaritza_M.pdf: 7134932 bytes, checksum: acf616348074122010d96651cd1436a7 (MD5) Previous issue date: 2012
Resumo: Sólidos monometálicos e bimetálicos de níquel e molibdênio suportado em alumina foram impregnados com 3% de teor metálico variando a ordem de impregnação até umidade incipiente, os quais podem ter efeitos significativos sobre o seu desempenho. As amostras foram calcinadas e caracterizadas, e utilizadas na desoxigenação catalítica do etilenoglicol. Esses materiais apresentaram áreas superficiais entre 177 e 160 m²g-¹. Os difratogramas de raios X de todos os sólidos obtidos exibiram a fase 'gama'-alumina e mediante o detector de energia dispersiva de raios X se confirmou a presença dos metais nos sólidos. Os testes catalíticos foram realizados em um reator de leito fixo, nas temperaturas de 533, 553, 573, 593 e 613 K e pressões de vapor do etilenoglicol de 13148 e 8662 Pa; a massa dos sólidos utilizada foi 35mg. Os compostos identificados foram a água, hidrogênio, metano, etano, éter etílico, acetaldeído e etanol. Foi realizado o balanço de mols do sistema e os valores dos graus de avanço de cada reação. Os cálculos dos efeitos difusivos demonstraram que as transferências de massa interna e externa e a transferência de energia externa não foram limitantes nas reações. Seis reações principais foram observadas e mediante os graus de avanço permitiu a avaliação de cada reação na formação dos determinados produtos de reação. Baseados na literatura se utilizaram expressões da taxa de reação para as reações propostas neste estudo. A seletividade aos produtos e conversão na desoxigenação do etilenoglicol apresentou mudanças baseadas na forma da ordem de impregnação dos sólidos. Igualmente foram realizados os cálculos das energias de ativação, fatores préexponenciais e as constantes da taxa
Abstract: Monometallic and bimetallic catalysts of nickel and molybdenum supported on alumina were prepared by incipient wetness with 3% metal content by varying the order of impregnation. The samples were calcined, characterized and used in the catalytic deoxygenation of ethylene glycol. The surface areas of the solids varied between 177 and 160 m²g-¹. The X-ray diffraction patterns of all solids had only 'gamma'-alumina phase. Analysis by X-ray dispersive energy confirmed the presence of both Ni and Mo in the solids. The catalytic tests were carried out in a fixed bed reactor and the reaction temperatures varied between 533 and 613 K while the vapor pressures of ethylene glycol were 8662 and 13148 Pa. The mass of the catalyst was kept constant at ca. 35mg. The identified compounds were water, hydrogen, methane, ethane, diethyl ether, acetaldehyde and ethanol. A mass balance for the reaction system was carried out and the extent of reaction was calculated for each reaction. The effect of diffusion was calculated and the results suggest that no internal or external mass transfer and external energy transfer were limiting in the reaction conditions used in this work. Rate expressions from the literature were used in this work. The results of conversion and selectivity to products in the deoxygenation of ethylene glycol reaction suggest that changes in the order of impregnation of the solid are important
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química

Energia é um recurso que historicamente apresenta tendência de crescimento de demanda. Projeções indicam que, para suprir as necessidades energéticas do futuro, será necessário um uso massivo do hidrogênio como combustível. O uso de sistemas de célula a combustível baseada no uso de membrana polimérica condutora de prótons (PEMFC) tem características que permitem sua aplicação para geração de energia elétrica em aplicações estacionárias, automotivas e portáteis. O uso de hidrogênio como combustível para PEMFC apresenta a vantagem de resultar em baixa emissão de poluentes quando comparado às dos combustíveis fósseis. Para que ocorram as reações em uma PEMFC é necessária a construção de conjuntos eletrodo-membrana-eletrodo (MEA), sendo o processo de produção de MEAs e os materiais utilizados, relevantes no custo final do kW instalado para geração de energia por sistemas de célula a combustível, o que é, atualmente, uma barreira tecnológica e financeira para a aplicação em grande escala desta tecnologia. Nesse trabalho foi desenvolvido um processo de produção de MEAs por impressão a tela que apresenta alta reprodutibilidade, rapidez e baixo custo. Foram desenvolvidos o processo de impressão a tela e a composição de uma tinta precursora da camada catalisadora (TPCC), que permitem o preparo de eletrodos para confecção de MEAs com a aplicação da massa exata de eletrocatalisador adequada para cátodos 0,6 miligramas de platina por centímetro quadrados (mgPt.cm-2) e ânodos 0,4 mgPt.cm-2 em apenas uma aplicação por eletrodo. A TPCC foi desenvolvida, produzida, aplicada e caracterizada, apresentando características semelhantes a de tintas de impressão a tela para outras aplicações. Os MEAs produzidos apresentaram desempenho de até 712 mA.cm-2 a 600 mV para MEAs de 25 cm2 e o custo para produção de MEAs de 247,86 cm2 capazes de gerar 1 kW de energia foi estimado em R$ 13.939,45, considerando custo de equipamentos, materiais e mão de obra.
Energy is a resource that presents historical trend of growth in demand. Projections indicate that future energy needs will require a massive use of hydrogen as fuel. The use of systems based on the use of proton exchange membrane fuel cell (PEMFC) has features that allow its application for stationary applications, automotive and portable power generation. The use of hydrogen as fuel for PEMFC has the advantage low pollutants emission, when compared to fossil fuels. For the reactions in a PEMFC is necessary to build membrane electrode assembly (MEA). And the production of MEAs and its materials are relevant to the final cost of kW of power generated by systems of fuel cell. This represent currently a technological and financial barriers to large-scale application of this technology. In this work a process of MEAs fabrication were developed that showed high reproducibility, rapidity and low cost by sieve printing. The process of sieve printing and the ink composition as a precursor to the catalyst layer were developed, which allow the preparation of electrodes for MEAs fabrication with the implementation of the exact catalyst loading, 0.6 milligrams of platinum per square centimeters (mgPt.cm-2) suitable for cathodes and 0.4 mgPt.cm-2 for anode in only one application step per electrode. The ink was developed, produced, characterized and used with similar characteristics to ink of sieve printing build for other applications. The MEAs produced had a performance of up to 712 mA.cm-2 by 600 mV to 25 cm2 MEA area. The MEA cost production for MEAs of 247.86 cm2, that can generate 1 kilowatt of energy was estimated to US$ 7,744.14 including cost of equipment, materials and labor.

In 2006 the global demand for primary energy amounted to nearly 12 million tons of oil equivalent (Mtoe), to a large extent (over 80%) supplied by fossil fuels, i.e. coal, oil, and natural gas. According to the scenario suggested by the International Energy Agency (IEA), energy demand will rise in 2030 to about 17 Mtoe. Fossil fuels will remain largely dominant. Over 70% of the expected demand for the period 2008-2030 will be due to the developing countries (China, India, Middle East, Africa, Latin America). Approximately 50% of this energy demand will involve the generation of electricity, but a significant proportion (20%) will be linked to the transport sector, while the remaining 30% will be distributed between industry, services and residential use. Obviously, predictions of growth in energy demand suggested some problems: if the availability of primary sources, mainly fossil fuels, will be sufficient to meet the demand in quantity, quality and distribution; whether the progressive increase in the use of fossil sources will be compatible with environmentally sustainable development, what role other sources of energy such as nuclear and renewables can play in the future landscape and economical development?. In this scenario, the hydrogen plays a key role as an energy carrier. But the hydrogen is not available in its free form; hydrogen atoms are only available linked to other natural resources, and it must extracted somehow. Currently, most of the hydrogen on the planet is produced by steam reforming of methane, as it is the most abundant gas among the fossil fuels, at an acceptable cost and easily available through the dense network of distribution (pipelines). However, there are also other techniques of syngas production such as the partial oxidation (CPOX), the oxy steam reforming (OSR), which has the characteristic of being able to be made autothermal (ATR) and the dry reforming (DR). The dry reforming is particularly interesting because it uses as a reagent mixture methane and carbon dioxide, two gases with particular heavy greenhouse effect. In this regard the biogas (mixture of carbon dioxide and methane), produced by anaerobic digestion basically from biomass, is particularly suitable for this process since it allows avoiding the preventive separation of CO2 from methane in the production process of syngas. The main aim of this doctoral thesis is the study of the process of syngas production from methane and biogas on catalysts supported on ceramic monoliths made of cordierite, using the steam reforming (SR) process and oxy-steam reforming (OSR) process. The tests were carried out in collaboration with the Institute of Advanced Techniques for Energy "Nicola Giordano" (CNR -ITAE) in Messina (Italy). This thesis is constituted by an introductory part that covers topics related to the production and storage of hydrogen (Chapter 1, “Introduction”); a central part which describes the pilot plant used to carry on tests on steam reforming and oxy steam reforming of methane and biogas, and the preparation of the various tested structured catalysts (Chapter 2, “Experimental part”); and a final part which consists of four papers describing the various experimental works carried out (Chapters 3 to 6). Finally, conclusions on the work done are reported (Chapter 7, “Conclusions”). Chapter 3, “Methane oxy-steam reforming reaction: performances of Ru/γ-Al2O3 catalysts loaded on structured cordierite monoliths”, reports the process of production of syngas via oxy-steam reforming of methane on Ru structured catalyst supported on γ-Al2O3 as carrier. In particular, the influence of the catalyst loading, the influence of the O/C and S/C ratios, the influence of the reaction temperature and the space velocity, were specifically addressed. Chapter 4, “Syngas production by methane oxy-steam reforming: performance of Me/CeO2 (Me = Rh, Pt, Ni) catalyst lined on cordierite monoliths”, presents the process of production of syngas via oxy-steam reforming comparing the performances of three structured catalysts, based on noble and non-noble metals (Rh, Pt and Ni) supported on CeO2 as carrier, focusing on the comparison of the influence of reaction temperature and space velocity on the reactor performance. Chapter 5, “Comparative Study on Steam and Oxydative Steam Reforming of Methane with Ru and Rh Based Catalysts supported on Cordierite Monoliths”, shows the comparison between the processes of steam reforming and oxy-steam reforming of methane on two structured catalysts (Ru/γ-Al2O3 and Rh/CeO2). The two different processes on the two catalysts were studied separately, and then compared. Moreover, an energy requirement discussion on the two processes was addresses (with the support of a series of Aspen Plus® simulations), with specific reference to the energy required for the vaporization of water (the only liquid reagent), and the energy required by the reforming reaction with respect to the moles of methane fed to the process. Chapter 6, “Biogas Steam and Oxy-Steam Reforming processes over structured catalysts based on Me/CeO2 (Me = Rh, Pt, Ni) coated on cordierite monoliths”, describes the comparison between the processes of steam reforming and oxy-steam reforming of biogas on three structured catalysts, based on noble and non-noble metals (Rh, Pt and Ni) supported on CeO2 as carrier . At the time of the submission of the present doctoral thesis to the external Commission, December 2013, the first paper, presented on Chapter 3, has been submitted to the peer reviewed “International Journal of Hydrogen Energy” (manuscript nr. HE-S-13-04515-2), while the other three papers, Chapters 4 to 6, are almost ready for the submission to other international peer reviewed journals (“Applied Catalysis B: Environment”, “Applied Energy”, and “Industrial Engineering and Chemistry Research”).

2012 - 2013
In the early decade, a rapid increase in oil consumption was recorded, that led to a widening between the predicted demand for oil and the known oil reserves. Such trend, mainly due to the growing new economies, is causing a quick increasing in oil price, that effect on European chemical industry competitiveness. In this dramatic scenario, characterized by higher cost of naphtha from crude oil, the ability to exploit novel feeds such as natural gas, coal and biomass may be the keystone for the chemical industry revival. Innovating chemical processes are thus essential for the future of the chemical industry to make use of alternative feedstock in the medium and long term future. In this direction, to open new direct routes with rarely used and less reactive raw feedstock such as short-chain alkanes and CO2 appears one of the most promising breakthrough, since in one hand it may reduce the current dependency of European chemical industry on naphtha, in the other hand may reduce the energy use and environmental footprint of industry. Despite light alkanes (C1–C4) and CO2 are stable molecules hard to activate and transform directly and selectively to added-value products, these challenges could be overcome thanks to relevant process intensifications along with the smart implementation of catalytic membrane reactors. Process intensification consists of the development of novel apparatuses and techniques, as compared to the present state-of-art, to bring dramatic improvements in manufacturing and processing, substantially decreasing equipment size/production capacity ratio, energy consumption, or waste production. The past decade has seen an increase in demonstration of novel membrane technology. Such developments are leading to a strong industrial interest in developing membrane reactors for the chemical industry. The main target of the CARENA is to address the key issues required to pave the way to marketing CMRs in the European chemical industry. The UNISA contribution in CARENA project is to study and optimize supported and unsupported catalysts in order to match to membrane reactors aimed to methane reforming and propane dehydrogenation processes. The guideline of this work was fully jointed to the UNISA involving in CARENA project. The methane reforming routes (steam- and/or auto-thermal-) are processes widely analyzed in the literature, and many studies identified Ni and Pt-group as most active catalysts, as well as the benefits of bimetallic formulation. Moreover, the crucial role of ceria and zirconia as chemical supports was demonstrated, due to their oxygen-storage capacity. In this work, great effort was spent in the reforming process intensification, in order to maximize catalyst exploit in reforming process. In order to minimize mass transfer limitations, without precluding the catalyst-membrane coupling, several foams were selected as catalytic support, and were activated with a catalytic slurry. The performances of such catalysts in the auto-thermal reforming and steam reforming of methane were investigated. Catalytic tests in methane auto-thermal reforming conditions were carried out in an adiabatic reactor, investigating the effect of feed ration and reactants mass rate. Tested catalysts showed excellent performances, reaching thermodynamic equilibrium even at very low contact time. By comparing foams catalyst performances to a commercial honeycomb catalyst, the advantages due to the foam structure was demonstrated. The complex foam structure in one hand promotes a continuous mixing of the reaction stream, in the other hand allows conductive heat transfer along the catalyst resulting in a flatter thermal profile. As a result, the reaction stream quickly reaches a composition close to the final value. Steam reforming catalytic tests were carried out on foam catalysts at relatively low temperature (550°C) and at different steam-to carbon ratios and GHSV values. The catalytic tests evidenced the relevance of heat transfer management on the catalytic performances, since the samples characterized by the highest thermal conductivity showed the best results in terms of methane conversion and hydrogen yield. The beneficial effect was more evident in the more extreme conditions (higher S/C ratios, higher reactants rates), in which the heat transfer limitations are more evident. The selective propane dehydrogenation (PDH) was one of the most attractive challenges of the CARENA project, that points to insert a membrane-assisted PDH process in a wider scheme characterized by the process stream recirculation. This approach requires to minimize inerts utilization and side-products formation. Moreover, no papers are present in literature on the concentrated-propane dehydrogenation, due to the severe thermodynamic limitations. A wide study is present in this work aimed to identify and select an optimal catalytic formulation and the appropriate operating conditions that allows the process intensification for the PDH reaction by means of a membrane reactor. In a first stage, the relevance of side-reactions in the catalytic volume and in the homogeneous gas phase was analyzed, resulting in the optimization of the reaction system. Platinum-tin catalysts were prepared, in order to study the role of each compound on the catalytic performances and lifetime. Preliminary studies have defined the optimal operating conditions, able to minimize the coke formation and then to slow down catalyst deactivation. Several studies on catalyst support highlighted the requirement to use a basic supports with a high specific surface, able to minimize cracking phenomena. Basing on such indications, CARENA partners provided two catalytic formulations optimized with respect the indicated operating conditions, that showed excellent activity ad selectivity. On these catalyst, the effect of the water dilution, the operating pressure and the presence of CO and CO2 was investigated, in order to understand the catalytic formulation behavior in the real scheme conditions. [edited by author]
XII n.s.

The research activities reported in this PhD thesis focus on one class of time-depending input variables: temperature and reactant concentration. Specifically, reactivity parameters (reagents conversion and products formation) were recorded as a function of temperature in temperature-programmed experiments with variable feed conditions (reducing or oxidizing atmospheres) and spent materials were characterized with surface analyses (SEM, EDS) to correlate their activity to chemical (mass and heat transfer) and physical (aggregation, segregation) phenomena. Also, the common feature between the catalytic materials investigated is the oxygen-storage capacity, i.e. their ability to store and release oxygen in oxygen-lean conditions, that represents a critical feature for more flexible operations, highly-selective oxidations and safer working conditions. Two model materials were selected as oxygen-donors for two distinct applications: CuO was chosen to correlate the effect of different reaction parameters to its morphological features, long-time stability during redox cycles (H2-O2) and formation of peculiar superficial nanostructures while LaFeO3 (perovskite) was identified as a possible candidate for the oxidative function, in automotive converter by taking advantage of oxygen diffusion in the lattice to transform CO into CO2. The last class of materials (CuY zeolites) was studied in CH4 activation to assess their potential application to an industrial-relevant reaction (methane-to-methanol, MTM) in which the oxygen provided by the zeolites selectively reduces the extent of over-oxidation products in favour of the partial oxidation to methanol.
The research activities reported in this PhD thesis focus on one class of time-depending input variables: temperature and reactant concentration. Specifically, reactivity parameters (reagents conversion and products formation) were recorded as a function of temperature in temperature-programmed experiments with variable feed conditions (reducing or oxidizing atmospheres) and spent materials were characterized with surface analyses (SEM, EDS) to correlate their activity to chemical (mass and heat transfer) and physical (aggregation, segregation) phenomena. Also, the common feature between the catalytic materials investigated is the oxygen-storage capacity, i.e. their ability to store and release oxygen in oxygen-lean conditions, that represents a critical feature for more flexible operations, highly-selective oxidations and safer working conditions. Two model materials were selected as oxygen-donors for two distinct applications: CuO was chosen to correlate the effect of different reaction parameters to its morphological features, long-time stability during redox cycles (H2-O2) and formation of peculiar superficial nanostructures while LaFeO3 (perovskite) was identified as a possible candidate for the oxidative function, in automotive converter by taking advantage of oxygen diffusion in the lattice to transform CO into CO2. The last class of materials (CuY zeolites) was studied in CH4 activation to assess their potential application to an industrial-relevant reaction (methane-to-methanol, MTM) in which the oxygen provided by the zeolites selectively reduces the extent of over-oxidation products in favour of the partial oxidation to methanol.

2014 - 2015
Today, the increasingly serious lack of resources and the obsolescence of the plants present on the whole planet led to develop new ways that go beyond “traditional” chemical engineering. The research is now focusing on novel equipment and techniques that potentially could change the concept of chemical plants and lead to compact, safe, energy-efficient, and environment-friendly sustainable processes. These developments share a common focus on “process intensification” — an approach that has truly emerged in the past few years as a special and interesting discipline of chemical engineering, because of the reasons enounced above. Process intensification tends its aim to the reduction of the total costs (fixed and operating) in an industrial plant. This “saving” in economic terms is possible not only by making a minimization of the equipment’s volume, but it’s also related to both chemical and physical aspects of one industrial process. The principle targets of a process intensification are: 1. Improved control of reactor kinetics giving higher selectivity/reduced waste products. 2. Higher energy efficiency. 3. Reduced capital costs. 4. Reduced inventory/improved intrinsic safety/fast response times. In order to reach all of these targets, it must be considered that transport phenomena play a very important role for the process intensification of an industrial reactor. Also improvements in environmental impact is another aspect that is constantly faced today, regarding all the processes in which there is the need of eliminating one dangerous chemical species. Taking into accounts all these reasons, one possible candidate for process intensification is represented by the Water Gas Shift process (WGS). It is the first purification stage of a hydrogen production plant, and involves the conversion of CO in CO2, while at the same time there is an increase in H2 yield in syngas. It also provides a H2/N2 mixtures with the appropriate ratio for the production of an important chemical product, such as ammonia. The WGS is an exothermic reaction, thermodynamically favored at low temperature, however kinetic limitations make it convenient to work with a two-stage process, i.e. two different catalytic systems: a first stage (HTS), carried out in the temperature range 350-600°C, where the most of the CO conversion is obtained (but thermodynamic limitations effect the theoretically reachable conversion); a second stage (LTS) carried out in the temperature range of 180-350°C, with slow kinetics (the thermodynamic conditions allow to obtain very low CO concentration, less than 10 ppm). Although this type of configuration is very effective, it shows several disadvantages: as a first, the global system kinetics is very slow, requiring a high mass of catalyst, that in turn results in long activation time; moreover, the presence of the inter-cooling unit increases not only the energy requirements of the process, but also the plant cost itself; furthermore, the LTS catalyst shows pyrophoricity, resulting not able to sustain frequent start up and shut down stages, and then not suitable for mobile fuel cell applications. Definitely, the actual WGS plant configuration would be of course the biggest unity of an integrated fuel processor. For these reasons, a process intensification is needed. Considering a conventional adiabatic reactor, the exothermicity and the equilibrium characteristics of the WGS reaction, together with the catalysts performances, reflects negatively on the CO conversion, disfavoring the reaction rate at the inlet of the catalytic bed, where the temperature is low, and limiting the very high conversion values at the outlet, where the temperature is high. So, a process intensification for this type of process should accounts for a modification both of the catalytic phase and the catalyst bed thermal profile. In order to reach the first target, it is necessary to find a good catalytic formulation that is able to be efficient in the low temperature range. Moreover, by considering the influence of the heat transport on the whole system, the use of a high conductive catalyst could play a crucial role, with the possibility of redistributing the heat of reaction along the catalytic bed to obtain a flatter thermal profile with a lower outlet temperature and, consequently, a higher CO conversion. The aim of this PhD thesis was to investigate the influence of the catalyst thermal properties on the Water Gas Shift (WGS) process, by using a structured carrier with high thermal conductivity. The research line was followed in order to verify if it is possible to increase the backdiffusion of the reaction heat throughout the structured catalyst bed, modifying the adiabatic temperature profile, obtaining, with respect to a typical packed bed reactor, a higher temperature at the inlet section and a lowered temperature at the outlet bed section, overcoming respectively, the kinetic and thermodynamic limits, achieving so an increased CO conversion. Accordingly, this approach would ensure that a conventional double staged WGS reactors with intermediate heat exchange could be replaced with a single WGS reactor, characterized by a "quasi isothermal" temperature profile. In this context, during the PhD project different phases have been followed to reach the intended objective. 1. CHOICE OF THE STRUCTURED CARRIER In order to reach the desired heat transfer properties, metal foams were chosen as structured carriers. They are open-cell structures that may be fabricated in a variety of shapes from a wide range of materials, and they exhibit very high porosities with good interconnectivity. These characteristics result in a lower pressure drop than that observed with packed beds and high convection in the tortuous megapores, which, in turn, enhances mass and heat transfer. Moreover, they are also easily coated with high-surface-area catalytic components, using well-established techniques. In general, mainly two parameters effect on overall heat transfer coefficient: the void fraction (or porosity) and the pore density (PPI), in addition to the bulk thermal conductivity. The first two parameters can highly influence the third one, because the first one is related to the amount of solid material and the second one to the way in which the solid material is distributed in the structured carrier. Moreover, the conventionally applicable foams for a catalytic process must be highly porous, otherwise pressure drops can increase dramatically. In order to find an efficient open cell foam for the purposes of this PhD project, the heat transfer through different structured metal foams was investigated. The thermal properties, in particular the thermal conductivity and the gas phase heat transfer coefficient of the structured supports were estimated by means of a mathematical model, developed on the basis of other similar heat transfer models accounted for honeycomb monoliths. An experimental set up was built, including an oven for heating the whole system at different temperatures, a quartz tube in which the metal foam was inserted, and a set of thermocouples to measure temperature in different points of the carrier. The experimental results were used to optimize the mathematical model and validate it, and the thermal properties estimated were used as basis for a comparison between the carriers and the choice of the best one in terms of heat transfer. 2. CHOICE OF THE CATALYTIC PHASES The literature research revealed that reducible oxides supported platinum based catalysts are today the best choice for obtaining a highly active and efficient catalytic system for the WGS reaction. These types of catalysts, instead of gold ones, are more stable and, if high dispersed on a reducible oxide, can prevent phenomena such as sintering of the active metal particles. On the basis of this review, different platinum based catalysts, supported on ceria, ceria-zirconia and ceria-alumina were prepared, through the wet impregnation method, followed by drying at 120°C and calcination in muffle. A wide characterization of the samples was done, including the specific surface area estimation (BET method), the XRF and XRD analysis, the use of the Raman shift and the study on the reducibility properties of the samples, through the technique of the temperature programmed reduction (TPR). The Water Gas Shift tests were made by fixing the operative conditions, in order to have a benchmark for this initial screening. The CO concentration was set to 5%, water at 25% and helium balance, as inert component. These activity and selectivity tests were made at atmospheric pressure, in a range of temperature between 150°C and 400°C, with a gas hourly space velocity of 5000 h-1. All the samples were reduced to particles with a size between 180 and 355 m. the aim of this experimental campaign was to find a good and efficient catalytic formulation, active in a very low temperature range. The best catalyst, from those investigated, was also tested by increasing the space velocity of one order of magnitude and by verifying its durability, in order to investigate about possible critical issue to be corrected. 3. DEPOSITION OF THE CATALYTIC PHASES ON THE STRUCTURED CARRIER In order to anchor the catalytic phases to the structured carrier, it is necessary to formulate a good washcoat. A washcoat is a chemical species that in catalysis is used to disperse the materials over a large surface area. Washcoat materials must form a rough surface, which greatly increases the surface area compared to the smooth surface of the bare structured carrier. This in turn maximizes the catalytically active surface available to react. So, the washcoat was formulated on the basis of what enounced above. The catalyst preparation was divided into three stages. All these stages were followed by drying at 120°C and calcination at 450°C for 3 hours. Firstly, the washcoat was anchored to the foam surface by using the dip-coating procedure. Then, chemical support was added to the washcoat by the wet impregnation method. Finally, the sample was impregnated with a solution of the platinum precursor. The same catalyst formulation was also prepared in powder form, and employed as reference. The stability of the washcoat on the foam surface was tested via sonication, to verify the adhesion of the chemical species on the structured support. The specific surface area (SSA) was determined by the BET method. The Scanning Electron Microscope (SEM) was used to study the morphology of the foams and to check the washcoat on the surface of the foam. It was possible to estimate the pores average diameter and the fibers diameter, and it was also verified that the washcoating procedure led to a homogeneous deposition on the surface of the structured carrier. The temperature programmed reduction (TPR) was performed in a stainless steel tube with an internal diameter of 22 mm. A 5% H2/N2 gas mixture (flow rate: 1000 Ncm3/min) was fed to the reactor, and temperature was raised up to 400°C with a heating rate of 10°C/min. The WGS catalytic tests were performed at atmospheric pressure, in typical conditions for the LTS process (a temperature range of 200-400°C). The reacting mixture consisted of 8% CO, 30% H2O and N2 balance. The catalysts activity was tested in the same reactor as the TPR. The gas hourly space velocity (GHSV) was set up to 10000 h-1. 4. DEVELOPMENT OF A “QUASI” ADIABATIC SYSTEM: COMPARISON BETWEEN PACKED BED AND STRUCTURED FOAM CATALYST An important phase of the PhD was dedicated to the development of a “quasi” adiabatic system, in order to exploit the high conduction of the structured catalyst, prepared in the previous phase, with respect to a conventional packed bed catalyst. In order to evaluate the influence of the thermal transport properties of the foams on the WGS reaction, a laboratory system able to avoid thermal dispersions was set up. This target was reached by increasing the total flow rate, keeping constant the L/D ratio of the structured foam catalyst. The experimental set up was used to drive a WGS reaction in the following conditions: inlet T = 260 °C, P = 1 atm, CO molar fraction = 8 vol%, H2O molar fraction = 30 vol%, N2 balance, WHSV = 2.4 gCO/gcat-1/h-1, linear flow velocity = 18.2 cm/s-1. In order to compare the performances of the different samples, two thermocouples were installed, one at the inlet section of the catalyst and the other one at the outlet section, while the CO conversion was continuously monitored with the aid of an ABB detector. After making a comparison between the performances of a foam catalyst with those of a packed bed catalyst, the developed experimental set up was used to perform different WGS tests on different types of foam. The aim of these tests was to investigate how the void fraction and the pore density can influence the heat transfer, and so the performances of the structured catalyst. 5. MODELING OF THE WGS ADIABATIC REACTOR In order to validate the results obtained by the tests made with the “quasi” adiabatic system, the model of the adiabatic reactor was developed with the aid of the finite element software COMSOL Multiphysics 5.0 (License number: No.13073437,00-0f-fe-0a-73-34). The comparison has been done between the structured foam catalyst and a conventional packed bed adiabatic reactor. The process has been modeled coupling transport phenomena and reaction kinetics. The reactor model was implemented exclusively with the CFD. A simplified geometry of the real system was built. By assuming no dependence of the transport parameters with the tangential coordinate, it was possible to reduce the volume domain to ¼ of the real one. In particular, the simulated geometry was built as follows. The gas stream flows axially, along the z-coordinate, through the reactor (internal diameter of 22 mm, tickness of 2.5 mm). The catalytic zone was put in the middle of the reactor (catalyst diameter of 16.5 mm). The length of the catalytic zone was set to 88 mm, while the total length of the reactor was 400 mm. The use of COMSOL allowed to simulate the packed bed adiabatic reactor and the structured foam catalyst, in order to exploit the high thermal properties of the latter in view of an intensification of the Water Gas Shift process. The developed model will be the basis for the design of an industrial reactor, where the catalyzed structured foam technology is applied. [edited by author]
XIV n.s.

Many environmental problems are caused when fossil fuels are used in engines. Biodiesel is a promising option to substitute these fuels because it is renewable, biodegradable and not toxic. The most used process to prepare biodiesel is by homogeneous transesterification of vegetable oils, using NaOH or KOH, but it produces a high concentration of impurities in the product. To overcome this, the use of heterogeneous catalysts is being increasingly studied. Geopolymer (GP) is an inorganic material with a chemical composition similar to zeolite and a variable microstructure, obtained by the reaction of aluminosilicates with a highly alkaline medium forming a continuous 3D network. It can be used as a heterogeneous catalyst, due to the high content of metals such as Na and/or K, as well as high basicity and specific surface area. The great advantage of using heterogeneous catalysts is that they can be recovered by filtration and reused in the process, making the biodiesel production more economical and generating fewer effluents to be treated. This work investigated GP acting as heterogeneous catalysts to produce biodiesel by transesterification reaction of soybean oil with methanol. Three types of GP powder were produced mixing metakaolin with an activating alkaline solution: Na-based, K-based GP and a mixture between them; they were treated at 110, 300, 500 and 700 °C, then lattice-shaped GPs were designed and produced by DIW, adding PEG and filler in the previous formulation and then, they were dried at 110 °C. Porous structures with Ø ~24 mm x 9,6 mm height and unsupported parts were produced. All materials were characterized. The transesterification reaction was carried out using all the samples as a heterogeneous catalyst to evaluate the yield of biodiesel concerning the GP composition, reaction conditions and morphology of samples. According to the results obtained in this study, it was verified that using GP both in powder and structure as catalyst, it was possible to obtain biodiesel from the transesterification of soybean oil. Comparing the materials with the same molar ratios, Na.K_GP treated at 500°C (powder) achieved the highest conversion (~98%). For the 3D structure tested in the reaction (3D_Na_GP1, 110 °C) a conversion was observed, but lower (~41%) compared to Na.K_GP, even in its powdered version (~53%). To verify the conversion efficiency of the other structures (3D_K_GP1, Na.K_GP) further studies are needed.
Molti problemi ambientali sono causati dall'uso dei combustibili fossili nei motori. Il biodiesel è un'opzione promettente per sostituire questi carburanti perché è rinnovabile, biodegradabile e non tossico. Il processo più utilizzato per preparare il biodiesel è la transesterificazione omogenea degli oli vegetali, utilizzando NaOH o KOH, ma produce un'alta concentrazione di impurità nel prodotto. Per superare questo, l'uso di catalizzatori eterogenei viene sempre più studiato. Geopolymer (GP) è un materiale inorganico con una composizione chimica simile alla zeolite e una microstruttura variabile, ottenuta dalla reazione di alluminosilicati con un mezzo altamente alcalino che forma una rete 3D continua. Può essere usato come catalizzatore eterogeneo, a causa dell'elevato contenuto di metalli come Na e/o K, nonché di un'elevata basicità e di una superficie specifica. Il grande vantaggio dell'utilizzo di catalizzatori eterogenei è che possono essere recuperati mediante filtrazione e riutilizzati nel processo, rendendo la produzione di biodiesel più economica e generando meno effluenti da trattare. Questo lavoro ha indagato su GP che agisce come catalizzatori eterogenei per produrre biodiesel mediante la reazione di transesterificazione dell'olio di soia con metanolo. Sono stati prodotti tre tipi di polvere GP miscelando metacaolino con una soluzione alcalina attivante: GP a base di Na, a base di K e una miscela tra loro; sono stati trattati a 110, 300, 500 e 700 °C, quindi i GP a forma di reticolo sono stati progettati e prodotti da DIW, aggiungendo PEG e filler nella precedente formulazione e quindi, sono stati essiccati a 110 °C. Sono state prodotte strutture porose con Ø ~ 24 mm x 9,6 mm di altezza e parti non supportate. Tutti i materiali sono stati caratterizzati. La reazione di transesterificazione è stata effettuata utilizzando tutti i campioni come catalizzatore eterogeneo per valutare la resa di biodiesel riguardante la composizione GP, le condizioni di reazione e la morfologia dei campioni. In base ai risultati ottenuti in questo studio, è stato verificato che l'utilizzo di GP sia in polvere sia nella struttura come catalizzatore, è stato possibile ottenere biodiesel dalla transesterificazione dell'olio di soia. Confrontando i materiali con gli stessi rapporti molari, Na.K_GP trattato a 500 °C (polvere) ha ottenuto la conversione più alta (~98%). Per la struttura 3D testata nella reazione (3D_Na_GP1, 110 °C) è stata osservata una conversione, ma inferiore (~41%) rispetto a Na.K_GP, anche nella sua versione in polvere (~53%). Per verificare l'efficienza di conversione delle altre strutture (3D_K_GP1, Na.K_GP) sono necessari ulteriori studi.

For political and environmental concerns about fossil fuels, today it is imperative to develop economical and energy-efficient processes for the sustainable production of fuels and chemicals. Fischer Tropsch synthesis is a well-established industrial process able to utilize for these objectives syngas (mixture of H2, CO, CO2) manufactured from CH4, coal or, as a new tendency, from biomass. In particular, for the utilization of syngas from biomass it is necessary to use iron-based catalysts. The PhD work has performed an optimization study of particular iron based supported catalysts loaded with high amount of iron, in order to obtain a new kind of Fischer Tropsch catalysts having good performance and great mechanical resistance. The research has dealt with different studies: the catalyst composition (concerning both the loading of iron on silica and the quantity of promoters), the catalysts activation procedure before the FT runs, the calculation of the catalysts activation energy, the influence of many parameters as the temperature and the pressure of the reactor, the composition of the feeding gas, the influence of the calcination temperature of the used catalysts. Moreover, a deep catalysts characterization has been made using different techniques (BET, TPR, SEM, TEM, IR, micro-Raman, XRD, ICP) to correlate the FT results with the catalysts properties. All the catalysts have been prepared using the impregnation method and in some case an innovative procedure with the help of Ultrasound (US) has been tested. Moreover a project of a new membrane reactor has been made, in collaboration with Genoa University, to increase at maximum the stability and the optimization of the process.

In this thesis, the growth dynamics and mechanisms of III-V semiconductor nanowires (NWs) and their heterostructures are studied. III-V NWs are realized by self-catalyzed and catalyst-free growth methods on Si (111) substrates by means of chemical beam epitaxy. The Au-free growth approach is particularly important for the integration of III-V semiconductors on silicon toward a CMOS-compatible electronics. The morphological and structural properties of the grown NWs are investigated by scanning (SEM) and transmission electron microscopy (TEM). These NWs exhibit very high aspect ratio and good material quality, which makes them useful to be employed for fundamental studies as well as for application in electronics and optoelectronics. The first part of the thesis is focused on the growth of InAs/InP/GaAsSb core-dual-shell (CDS) NWs. Detailed morphological, structural, and compositional analyses of the NWs as a function of growth parameters are carried out by SEM, TEM, and by energy-dispersive X-ray spectroscopy. Furthermore, by combining the scanning transmission electron microscopy-Moiré technique with geometric phase analysis, we studied the residual strain and the relaxation mechanisms in this system. We found that InP shell facets are well-developed along the crystallographic <110> and <112> directions only when the nominal thickness is above 1 nm, suggesting an island-growth mode. Moreover, the crystallographic analysis indicates that both InP and GaAsSb shells grow almost coherently to the InAs core along the ⟨112⟩ direction and elastically compressed along the ⟨110⟩ direction. For an InP shell thickness above 8 nm, some dislocations and roughening occur at the interface. This study provides useful general guidelines for the fabrication of high-quality devices based on these CDS NWs. Indeed, we investigated the tunnel coupling between the outer p-type GaAsSb shell and the n-type InAs core in InAs/InP/GaAsSb CDS NWs. Low-temperature (4.2 K) transport measurements in the shell-shell configuration in CDS NWs with 5 nm-thick InP barrier reveal a weak negative differential resistance. Differently, when the InP barrier thickness is increased to 10 nm, this negative differential resistance is fully quenched. The electrical resistance between the InAs core and the GaAsSb shell, measured in core-shell configuration, is significantly higher with respect to the resistance of the InAs core and of the GaAsSb shell. The field effect, applied via a back-gate, has an opposite impact on the electrical transport in the core and in the shell portions. Our results show that electron and hole free carriers populate the InAs and GaAsSb regions respectively and indicate InAs/InP/GaAsSb CDS NWs as an ideal system for the investigation of the physics of interacting electrons and holes at the nanoscale. The second part of this thesis is dedicated to the growth of self-catalyzed InAs/InSb axial heterostructures. The growth mechanisms of these heterostructures are thoroughly investigated as a function of the In and Sb line pressures, and growth time. Some interesting phenomena are observed and analysed. In particular, the presence of an In droplet on top of the InSb segment is shown to be essential to form axial heterostructures in the self-catalyzed vapor-liquid-solid mode. Axial versus radial growth rates of InSb segments are investigated under different growth conditions and described within a dedicated model containing no free parameters. It is shown that a widening of the InSb segment with respect to the InAs stem is caused by the vapor-solid growth on the nanowire sidewalls rather than by the droplet swelling. The In droplet can even shrink smaller than the nanowire facet under Sb-rich conditions. The third part of the thesis is focused on the realization of self-catalyzed InSb quantum dot (QD) embedded into InAs NW. A systematic study on the influence of the growth parameters on the morphology of such NWs is performed. Radial and axial growth rates are studied as a function of growth parameters in order to realize InSb QD NW with controlled morphology. In particular, we have explored different growth conditions to minimize the InAs shell around the InSb QD. We found that the shell thickness around the InSb QD decreases with increasing growth temperature while it increases with an increase of the As line pressure. Furthermore, from the high resolution-TEM analysis, we observed that InAs-stem and InAs-top segment have a wurtzite (WZ) crystal structure with several defects such as stacking faults and twins perpendicular to the growth direction. It is commonly observed that the InAs NWs grown by catalyst-free and self-catalyzed growth methods show highly defective (or mixed WZ/ZB) crystal structure. By contrast, here the InSb QD shows a defect-free zincblende (ZB) crystal structure without any stacking faults, consistently with the energetically preferred cubic structure of the InSb crystals generally attributed to the low ionicity of group III to Sb bonds. This study gives useful information for the realization of InSb QDs with controlled morphology and optimized quality embedded in InAs NWs in the self-catalyzed regime.

The PhD thesis involves one or more articles that are either published,submitted or in the process of manuscript preparation. These all chapters are eloborated in context to the understandings and advancements involved during the PhD period. The whole thesis involves insights about synthesis and characterization of BiVO4 in the form of powder as well as thin films. It also describes the ability of BiVO4 powders and thin films in water splitting and volatile organic compound degradation.

Heterogeneous catalysts, especially when nanostructured, can play a crucial role to minimize byproducts and to stabilize the catalyst itself, thanks to its tailored properties. The efforts of my PhD have been focused to synthetize new nanostructured catalysts for the acetaldehyde production from ethanol via oxidative and non-oxidative dehydrogenation reactions. For oxidative dehydrogenation process Mo-based catalysts, supported on alumina, silica-alumina or silica, have been synthesized and tested. High acetaldehyde yield was obtained in the temperature range 573-673 K even if at higher temperatures dehydration products are formed. Catalytic activity was enhanced when a small amount of silica was introduced in the alumina support, thus obtaining more stable catalysts. Thus, other two different catalytic systems have been tested: Nb-P-Si oxides and copper-based catalysts, but the first presents low selectivity to acetaldehyde while the second catalyses the total oxidation to CO2. For non-oxidative dehydrogenation, the research activity started with the synthesis of copper supported (Al2O3, Mg2Al2O4 and ZnAl2O4 as supports) catalysts by means of conventional impregnation method. Even if these materials are active to produce acetaldehyde they suffer of deactivation and several by products were detected. To improve the catalytic performances of the best catalyst identified, the CuO-ZnAl2O4 one, new synthetic procedures were investigated and optimized. Moreover, during the period abroad, another innovative technique based on Aerosol Assisted Sol Gel process, was employed to synthesize CuO-SiO2 catalysts. All the synthetized catalysts were tested on a laboratory plant and deeply morphologically and structurally characterized. Particular attention was also dedicated to the characterization of exhaust catalysts to enlighten deactivation causes and regeneration possibilities.

Abstract In this Ph.D. project, the effective parameters in the sol-immobilization method which can affect catalytic reactivity including: capping agent, solvent of synthesis, and support were studied. The synthesized catalysts were employed in the liquid phase hydrogenation reactions of two biomass derived molecules namely furfural and vanillin. In this regard, the role of protective agents, which are used to stabilize colloidal nanoparticles (NPs) in solutions, for Pd NPs supported on carbon support in the liquid phase hydrogenation of furfural was explored. The use of Pd as a hydrogenation catalyst is well documented, as hydrogenation reactions can only be performed by metals that can easily chemisorb hydrogen. Pd is one of such metals capable of dissociate hydrogen even at room temperature. The capping agent adsorbed on the surface of the NPs can alter their activity and selectivity, by modifying the particle size, size distribution, morphology, and stability against leaching and agglomeration. Besides, the effect of the amount of protective agent and the synthesis solvents have been investigated, allowing better insight into the metal-support interaction in Pd/TiO2 catalysts for the hydrogenation of furfural. Then, the effect of using different carbonaceous supports with various chemical-physical properties on the activity and selectivity towards the hydrodeoxygenation of vanillin as a lignin model compound was explored. To better understand the role of the capping agents in controlling the activity and the selectivity of the furfural hydrogenation, a series of carbon-supported Pd nanoparticles were prepared through controlled sol-immobilization method using different capping agents, including polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly(diallyldimethylammonium) chloride (PDDA) containing oxygen and/or nitrogen groups. The catalysts were characterized by different techniques. UV-Vis and Fourier-transform infrared (FTIR) spectroscopy were used to evaluate the interaction between capping agents and Pd precursor, while transmission electron microscopy (TEM) was performed to study the final morphology of the catalyst. Finally, X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface chemistry of the carbon support, the chemical state, and the exposure of supported palladium species. The UV-Vis spectra of the system composed of Pd precursor plus capping agent demonstrated the interaction of the metal with PVA and PVP. In the case of PDDA, changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. The disappearance of the peaks associated with Pd2+ and the observed scattering indicated a complete reduction to Pd0 and the formation of metal nanoparticles. The interaction of the capping agents with the Pd precursor was studied by FTIR spectroscopy. For PVA, the peaks corresponding to the stretching vibrations of C–O–C linkage were observed, which suggested the presence of cross-linked PVA molecules, and the slight modification observed for the peaks in the spectrum of PVA + Na2PdCl4 suggested a weak interaction between the metal precursor and the –OH groups present in PVA. In the case of PVP, a decrease in the intensity of the peak after the addition of Pd was observed which confirmed that both O and N groups are present in PVP interaction with the metal precursor. For PDDA, after the addition of Pd, the intensity of the peaks decreased, which indicated that the activity of the vibrational modes is modified in the mixture, probably due to PDDA–Pd interaction. The morphological characteristics of the synthesized catalysts were evaluated by HRTEM. We noticed that the capping agent has a major effect on the size and distribution of Pd NPs when using activated carbon as the support. All catalysts had an average particle size of 3–4 nm, with the presence of isolated larger particles in the case of PdPDDA/C. The XPS survey data revealed that only Pd, C, N, and O species were present on the surface of the catalysts. Depending on the capping agent used, substantial differences were observed in the relative amount of Pd on the surface: PdPVA/C (1.30 %) > PdPDDA/C (0.76 %) > PdPVP/C (0.50 %). The data also showed a different oxygen content in the samples. PdPVA/C displayed the highest relative amount of O (14.7 % compared to PdPDDA/C (9.70 %) and PdPVP/C (9.10 %)), respectively. The highest oxygen content on the surface of PdPVA/C catalyst is probably due to the presence of –OH groups in PVA. PdPVP/C exhibited the highest N content (2.95 %), higher than PdPDDA/C (1.86 %) due to the presence of a pyrrole-type N species in PVP and dimethyl-ammonium groups in PDDA, while in the PdPVA/C N was not detected on the surface, as expected. The performance of the prepared catalysts was examined for the liquid-phase hydrogenation of furfural (furfural 0.3 M; furfural/metal ratio 500 mol/mol, 5 bar H2, temperature range of 25–75 °C) with 2-propanol as solvent. The catalytic results revealed that the activity of catalysts is correlated to the relative amount of Pd at the surface: PdPVA/C (1.3%) > PdPDDA/C (0.76%) > PdPVP/C (0.50%). At 75 °C the catalysts exhibit similar reactivity. We ascribed this effect to the partial removal of a capping agent during the reaction, thereby exposing a higher number of active sites to the reactant. In the next step, since the best results were obtained using PVA, this latter was chosen as the protective agent, focusing on the effects that its amount and the change of the solvent of synthesis to methanol-water mixtures might have on the preparation of Pd/TiO2 catalysts. This new approach indicates the necessity of using the capping agent, and results also show that the acidification step, which lowers the isoelectric point (IEP) to afford anchoring of the NPs to the surface of the support, can be eliminated while still maintaining the same degree of Pd immobilization (≥ 96%) and particle size control (< 2 nm). These samples were evaluated for furfural hydrogenation; there was an improvement in selectivity towards furfuryl alcohol and tetrahydrofurfuryl alcohol, whereas ether by-products were suppressed. Supported Pd NPs were prepared in accordance with the standard sol-immobilization method, in which the temperature of the chemical reduction was maintained at 1 °C. This temperature was chosen as earlier research in our workgroup reviled the formation of smaller nanoparticles when lower temperatures were used. UV-Vis spectroscopy was performed to characterize the precursor salt and colloidal solutions during NPs preparation. Changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. Catalysts prepared with increasing volumes of MeOH showed shifts in the distinctive ligand to metal charge transfer (LMCT) and d-d transitions. This confirms a change to the Pd metal precursor complex when it is solvated in either the MeOH/H2O mixture or in pure MeOH. One reason for this is the exchange of ligands between the Pd salt complex and the solvent synthesis. The Pd % loading of each catalyst was measured using microwave plasma – atomic emission spectroscopy (MP-AES). All catalysts were characterized using TEM, in order to get information of their average NP sizes and particle size distributions/dispersions. An initial comparison of catalysts, showed that an acidified immobilization step increases the average NP size. The bigger NP size and dispersion was found for the sample prepared by H2O as the solvent, PVA, and acidification step, which it can be ascribed to the interaction of the stabilizer agent (PVA) with acid during the immobilization step. XAFS was performed to investigate both changes to Pd oxidation state (XANES) and the local structural environment with respect to Pd (EXAFS). The results confirmed that by using PVA in the solvent system, the Pd oxidation state contains a greater quantity of Pd2+. Interestingly, by removing the acidification step during the synthesis, an increase in the oxidized Pd state was observed. This was consistent with the TEM data indicating this increase in Pd2+ is related to the observed particle sizes. Pd surfaces are known to form passivating oxide layers when exposed to air with an increase in the temperature needed to form a bulk oxide structure. Therefore, the Pd2+ fraction refers to the quantity of the available Pd surface and hence the particle size. Fitting of the 1st shell Pd K edge EXAFS data was consistent with the trends observed through TEM and XANES characterization. The presence of small Pd NPs is confirmed by the decreased magnitude of Pd-Pd scattering, signified by smaller CNPd-Pd. All catalysts were tested for the hydrogenation of furfural at 50°C. Although the XANES, EXAFS, and TEM data have all confirmed that sample prepared by the pure MeOH contains smaller NPs than the sample prepared by pure H2O, the initial catalytic activity showed that the sample synthesized by H2O has a significant increase in initial TOF h-1. In addition, furfural hydrogenation performed over the bare TiO2 support displayed 98.4 % selectivity to the acetal product (2-(diisopropoxymethyl) furan), at isoconversion, while sample prepared by H2O revealed less selectivity to the acetal (18.8%). To understand these differences in activity/selectivity we performed further HRTEM investigations of the fresh samples. These studies have identified a 'halo' of PVA around NPs produced using MeOH (e.g. PdMeP) and at the interface between NPs and support. We suggest that the poor solubility of PVA in methanol is responsible for this increase in PVA clustering on the catalytic surface/support interface identified with HRTEM. We also propose that the active sites on TiO2 are formed through the spillover of hydrogen onto the support and accounts for the superior yield of acid catalysed products for Pd/TiO2 compared to TiO2 alone. In the case of Pd/TiO2, the catalysts prepared using MeOH result in aggregation of PVA at the Pd-TiO2 interface, which restrict spillover effects and decreases the amount of acid catalysed products. For the catalysts prepared without the addition of PVA, we observed a higher proportion of ethers than for the analogous catalysts prepared with PVA. This further supports our hypothesis that PVA at the metal-support interface limits the spillover of hydrogen. Catalyst recycle tests were carried out over six consecutive hydrogenation cycles. The catalysts prepared without PVA quickly deactivated with almost negligible performance by the sixth consecutive run. The TEM analysis of the spent sample confirmed that when PVA is not present the samples quickly agglomerate and effective surface area of Pd rapidly diminishes. Finally, the effect of support on both activity and selectivity of the catalyst in the hydrogenation of vanillin to vanillyl alcohol and the subsequent hydrodeoxygenation (HDO) to creosol was studied. Four types of carbonaceous materials (three activated carbon: Norit, KB, G60, and a carbon nanofiber: HHT) were used as support for Pd nanoparticles. Catalysts were synthesized with sol immobilisation method using PVA as the capping agent, and tested in the hydrodeoxygenation reaction of vanillin under mild reaction conditions (50 °C, 5 bar H2 and isopropanol as solvent). Catalysts have been extensively characterized by TEM, XPS and BET in order to correlate the surface properties with the catalytic behaviour and selectivity to the target products. In the end, recycle tests were carried out on the most active catalyst to determine the reusability of the material used. BET analysis was conducted on Pd-supported catalysts. Pd/Norit catalyst has the highest surface area (2000 m2/g), whereas Pd/HHT has the lowest surface area (40 m2/g). The average pore radius of all samples was in the range of 2 nm for Pd/KB to 25,4 nm for Pd/HHT. XPS analysis were performed on the synthesized catalysts to determine the oxidation state of the Pd, the graphitization order and the presence and abundance of oxygen functionality. Pd/Norit, Pd/KB and Pd/G60 had a similar amount of C1s species (84.4 %, 87.3 % and 91.1 %, respectively), while Pd/HHT had the highest number of C 1s (98.8 %). Evaluation of O1s species revealed that the Pd/HHT catalyst has the lowest amount of functionalisation (0.9 %), while Pd/Norit the highest one (14.3 %). The results showed that the Pd/HHT catalyst has the highest amount of C=C (82.1 %), therefore the support can be considered highly graphitised. TEM analysis were performed to determine the mean particle size and size distribution. In all samples, the nanoparticles are homogeneously distributed on the support. Pd/Norit and Pd/KB had similar mean Pd particle sizes (2.5 and 2.7 nm respectively). Whereas, Pd/G60 and Pd/HHT displayed higher mean Pd nanoparticle diameters (3.5 and 3.9 nm, respectively). The catalysts were tested in the vanillin HDO reaction. The reaction profile shows the features of a typical consecutive reaction, with vanillyl alcohol as the intermediate product, and creosol as the final product. Interesting, an additional product was detected in the reaction mixture, namely vanillyl isopropyl ether. The ether is produced by reaction of vanillyl alcohol with a molecule of solvent (isopropanol) and it is consumed with time since it is in equilibrium with the alcohol. The results revealed that the rate of conversion of vanillin enhances with increasing degree of graphitisation. These results can be explained by the strong interaction between the graphitic plane of the support and the aromatic ring of the substrate that allows a better interaction with the active metal nanoparticles. At the same time, the activity in the vanillin hydrogenation reaction decreases with an increase in oxygen content at the carbon surface. The support-substrate interaction is responsible for the change in activity; the increase in oxygen functionality actually disrupts the graphical plane structure of the support. The support affected the selectivity at the lower conversion. In fact, at 50 % of conversion, vanillyl alcohol was the main product of Pd/Norit, Pd/HHT and Pd/KB (selectivity in the 73-82 %), while Pd/G60 provided high levels of both vanillyl isopropyl ether and creosol (23 and 21 %, respectively). The formation of ether was associated with the amount of carboxylic support functionality (COOH groups). The recycling tests were carried out on the most active catalyst: Pd/HHT. After five consecutive reactions, the conversion did not significantly decrease, demonstrating the high stability of the catalyst. Comparably, the selectivity of vanillyl alcohol remained almost unchanged.

Polymer electrolyte membrane fuel cells (PEMFC) are electrochemical devices which can directly convert the chemical energy of a fuel (such as hydrogen or a low-molecular weight alcohol) and an oxidant (i.e. oxygen) into electrical energy with high efficiency. Moreover, due their low operating temperature, they are suitable for automotive or portable applications. However, the slow kinetics of oxygen reduction reaction (ORR) requires the use of costly Pt-based catalysts at the cathode in order to obtain the desired power density values. Nevertheless, the cathode is still responsible for the main voltage loss in the cell. The overall objective of the research carried out in this Ph.D. thesis was the development of Pt-free ORR catalysts starting from different carbon, nitrogen and transition metals precursors. Different synthesis approaches were used in order to obtain an improvement of the activity, and to understand the influence of the synthesis process variables. In particular, the influence of carbon supports (commercial and synthesized in the lab), nitrogen and transition metals precursors, templating agents, number and temperature of pyrolysis were examined. The catalysts produced were characterized by means of several instrumental techniques such as N2 physisorption, XRD, XPS, EDX, SEM, FESEM, TEM, Raman and FTIR. The effect of the presence of different transition metals on the pyrolysis process was investigated by TGA coupled with a mass spectroscopy analysis, in order to have an insight on their influence in the formation of ORR active sites. The activity toward ORR was assessed by RDE-RRDE (rotating disk electrode - rotating ring disk electrode) analysis and by gas-diffusion electrode in a 3-electrodes electrochemical cell configuration. The electrochemical techniques used were cyclic voltammetry (CV), linear sweep voltammetry (LSV), staircase voltammetry (SV), chronoamperometry and electrochemical impedance spectroscopy (EIS). These electrochemical tests were performed in both acid and alkaline conditions, with reference to the potential applications in both H+ and OH– conducing polymer electrolyte membrane fuel cells. This first part of research was carried out in the laboratories of the Gre.En2 (Green Energy and Engineering) Group in the Department of Applied Science and Technology (DISAT) at Politecnico di Torino. Then, in the second part, some of the most promising electrocatalysts in terms of ORR activity were in different types of single PEMFC. In particular, using acidic electrolyte membrane, the tests were performed using H2 or methanol as fuels. In the case of direct methanol fuel cell (DMFC) tests, short-term durability tests were done in order to compare the durability performance of our catalysts with a standard Pt-based catalysts. The tests with alkaline electrolyte membrane were performed using ethanol as fuel. This second part of research was carried out at the Universidad Autonoma de Madrid in the laboratories of the Department of Applied Physical-Chemistry. Here the structure of the thesis: Chapter 1 is a general introduction about the PEMFC fuel cell technology, particularly focusing on the non-noble metal catalysts for ORR as potential alternative to Pt. Chapter 2 is focused on the use of different types of reduced graphene oxide as support for the synthesis of Fe-N/C catalysts. In Chapter 3, a complex between Co ions and a N-containing ligand molecule is impregnated on multi walled carbon nanotubes and pyrolyzed one or two times for producing a Co-N-C catalyst, and the influence of the second pyrolysis on the activity improvement was investigated. Chapter 4 deals the optimization of the synthesis process of a Fe-N-C catalyst using polypyrrole as N source and mesoporous carbon a C-support. In Chapter 5 the study of the influence of different silica templates on the morphology on the ORR activity of a Fe-N-C catalyst synthesized using Fe-phthalocyanine as precursor is presented. In Chapter 6, different Me-phthalocyanines (Me = Fe, Co, Cu, Zn) were used as precursor for the synthesis of Me-N-C catalysts using SBA-15 silica as hard template. The influence of the different transition metals on the pyrolysis process and on the ORR activity and selectivity toward a complete 4 e- oxygen reduction was investigated in both acid and alkaline conditions. A detailed kinetic analysis in acid conditions is also presented. The most active catalyst was tested in different types of PEMFCs. Finally, in Chapter 7, the influence of four different carbon supports on the ORR activity of Fe-N/C catalysts in acid and alkaline conditions as well as the performance in single PEMFC is examined. The general conclusions of the thesis are presented in Chapter 8.

Mankind makes extensive use of crude oil to fuel its insatiable demands for energy and hydrocarbon derivatives. The refining of crude oil is based on a process known as cracking, where long-chain hydrocarbons are systematically broken into smaller chain hydrocarbons known as fractions with each fraction allowing for the production of a specific material. The maximum efficiency of cracking can be achieved in the petroleum refining processes by controlling the operating parameters of the units, and over the years many studies have attempted to optimize the cracking conditions such as temperatures, pressures and the use of a variety of catalysts to reach maximum productivity. Catalysts such as the Y-type zeolite catalysts are often used because their acidity and thermal stability makes them an ideal cracking catalyst; however the developments of enhanced catalytic properties for zeolite-Y catalysts are essential to increase the production yields. Optimization of the Y-type zeolite catalyst is the focus of this research and accordingly the synthesis, characterization, modifications and catalysis have been studied in depth. A review of the literature has shown that there are three main techniques used to improve the zeolite properties following the synthesis process; (Cation exchange, Dealumination and Desilication), since the crystalline structure of a Y-type zeolite is prepared from an alkaline aluminosilicates gel. However, the literature focuses mainly on the reaction variables used in the modifications. As such this study focuses on the effects of treatment processes on the composition, behaviour and catalytic properties of the synthesized Y-zeolite framework. Laboratory experimental data has confirmed that a synthesis process using 24 h aging for crystal nuclei at 25 °C and 18 h crystallization time for crystal growth at 100 °C produced the desired zeolite NaY morphology, and NaNH4Y zeolite forms with various cation contents (3, 1.5 and 0.5 wt% Na+) were obtained by subjecting the NaY form to a multi-stage ion exchange using 0.5 M NH4NO3 at 80 °C, while the HY form was obtained by the calcination of NH4Y form under high temperature. Calcination temperatures above 450 °C were shown to indicate a removal of the framework hydroxyl groups via dehydroxylation, which led to a collapse of zeolite-Y structure, whereas raising the level of Na+ inside the zeolite lattice throughout the calcination was led to a delay in the starting point of the dehydroxylation region as confirmed via TG and DSC-analyses. This finding was also used in the preparation of the USY form by steaming the HY form, as the former is a traditional zeolite-Y form utilized in the refining units. It was found that Na-ions hindered the extraction of Al-atoms from the Y-lattice thus reducing the rate of dehydroxylation, and minimising rapid contraction of the unit cells and Y-structure collapse, which helped make a rigid structure and a more resilient lattice for steaming at high temperature. In addition, analyses data confirmed that the extraction of EFAl-species from the USY-structures using an EDTA chemical treatment led to an increase in the acidity of treated catalyst and the introduction of mesopores. Lower lattice Si/Al ratio and larger porosity were also found using the dealuminated-desilicated rather than the desilicated-dealuminated leaching method in the treatment of both Y and USY structures via dislodgement of both Si and Al-atoms in NaOH and HCl solution. Cracking was performed on deactivated catalysts (450 °C) in a PFTR using nC7 in N2 at 325 - 425 °C and W/F = 22 - 44 g.h.mol-1, and confirmed that the tuned steaming/leaching conditions succeeded in modifying the catalytic properties of the in house made catalysts, as they possess superior performance when compared to the industrial catalysts typically used.

During this PhD project different Fe and Co-based catalysts active in the FT reaction have been synthesized, characterized and tested, in particular: 1- An impregnated synthesized Fe-based catalyst supported on SiO2 and promoted with K and Cu (30 %wt of Fe, 2 %wt of K and 3.75 %wt of Cu) named Fe30K2Cu3.75. In particular, potassium improves CO ad-sorption while Cu promotes the reduction of the iron oxides species. The loading of active metal and promoters have been already determined elsewhere in recent studies. 2- Three different Co-based catalysts synthesized by flame spray pyrolysis (FSP) and supported on SiO2, and eventually promoted with Ru (5 %wt of Co; 10 %wt of Co; 10 %wt of Co and 0.4 %wt of Ru). The catalysts are named as 5Co, 10Co and 10Co-0.4Ru. FSP technique allows to obtain single or mixed metal oxides characterized by a high surface area and high thermal stability due to the instantaneous dispersion, vaporization and flame-decomposition (pyrolysis) of an organic solution composed by the precursors of the catalyst. 3- Three different Fe-based samples supported on SiO2 and promoted with K and Cu, prepared with the use of ultrasound (US) (10 %wt of Fe; 30 %wt of Fe; 30 %wt of Fe, 2 %wt of K and 3.75 %wt of Cu). Cata-lysts are named as Fe10US, Fe30US and Fe30K2Cu3.75US. In particular US allows to synthesize materials with better morphological properties with respect to traditional impregnated samples. Fe30K2Cu3.75 (1) sample is active for the FT conversion even if syngas with a H2/CO ratio similar to the ratio of bio-syngas (H2/CO= 1) is fed to the reactor. The catalyst presents a satisfactory stability as a function of TOS and selec-tivity toward the reaction products remains essentially unchanged at different syngas ratios at the same temperature tested. The developed kinetic model is in fully agreement with the ones fundable in the recent literature for iron-based catalysts tested in fixed bed FT reactor. 10Co and 10Co-0.4Ru (2) samples are active in the FT synthesis in the range of temperatures tested with a H2/CO= 2 syngas fed to the reactor. 5Co did not show any activity to FT reaction in the experimental condi-tion tested. 10Co sample showed a great stability in function of TOS at T= 250 °C, reactants conversion and selectivity towards the reaction products were stable for the whole duration of the durability test (TOS= 200 h). The addition of 0.4 %wt of Ru improved significantly catalyst activity in terms of reactant conversion. All the US synthesized samples (3) are suitable catalysts for the FT reaction at the different tested conditions and with a H2/CO ratio equal to 2. Both Fe10US and Fe30US catalysts showed excellent stability as a function of TOS at all the tested reaction temperatures. The sonochemically prepared catalysts showed good results in terms of selectivity toward the reaction products.

This Ph.D. thesis deals with the synthesis, immobilization of bismuth-based nanostructures and their photocatalytic evaluation for degradation of organic pollutants mainly dyes, with the aim to optimize synthesis and photo-evaluation conditions by focusing the practical application of heterogeneous photocatalysis. Initially, various bismuth based single structures α-Bi2O3, Bi5O7NO3 and heterostructures α/β-Bi2O3, β-Bi2O3/Bi5O7NO3 were synthesized by a simple and scalable route i.e. thermal decomposition of precursor salt. Properties such as crystallinity, composition, morphology and optical parameters were tuned by simply varying the calcination temperature. Heterostructures of α/β-Bi2O3, β-Bi2O3/Bi5O7NO3 are well crystallized, formed stable composites (originated from single precursor salt) and eventually improved the stability of β-Bi2O3 (a metastable form) in the heterojunction structure. Single structures and heterostructures were evaluated for photodegradation of various dyes (differ in chemical structures and ionic behaviors) under visible and UV light. Test were conducted on single dyes or mixed solution of 2/3 dyes to assess the photocatalytic mechanism and kinetics when dealing the mixed effluent. From the obtained results, it was observed that α/β-Bi2O3 and β-Bi2O3/Bi5O7NO3 heterostructures have higher photocatalytic response due to efficient cascade of electrons and holes within the tuned heterojunction and band alignments. Moreover, different dyes interact differently with the photocatalyst and resulted in changed kinetics, while mechanism of degradation depended upon their ionic behavior. Furthermore, during degradation of mixed solution; dyes that have higher interaction (with photocatalyst) and low absorptivity preferentially degraded earlier. Afterwards, α/β-Bi2O3 were used to investigate and distinguish coexisting processes during photocatalysis: (i) intense adsorption, (ii) dye photobleaching and sensitization assisted photodegradation and (iii) partial or complete mineralization. It was found that some dyes with Azo (N=N) and sulphonic groups have intense adsorption over photocatalyst surface and discoloration could occur without photocatalysis. Further, it was revealed that under controlled conditions, the other coexisted processes hardly occur during photocatalysis. Moreover, indigo carmine (IC) dye was found appropriate for preliminary photo-evaluation because its discoloration/removal process could be directly associated with photocatalytic oxidation by analyzing some identified spectral changes in UV-vis absorbance spectrum. Moreover, it was highlighted that dye chromophoric groups react readily and are easily attacked by the originated photocatalytic reactive species and partially mineralized, while further degradation of resulted intermediates containing phenyl groups, became more difficult to oxidize or reduce to achieve complete mineralization. In addition, to investigate and identify the mechanism and the path of photodegradation of the investigated dyes, two approaches were used: 1) the photo-evaluation of dyes in presence of quenchers of hole, atomic oxygen and hydroxyl radical i.e. triethyl amine (TEA), P-benzoquinone (BQ) isopropanol (IP) and, respectively and 2) Evolution of O2 after water oxidation. From the experimental results it was observed, that the photocatalytic activity eventually reduced in presence of quenchers as they quench the originated reactive radical species. Moreover, evolved O2 during water splitting confirmed that electrons and holes are well separated and able to generate reactive oxygen and radical species for photodegradation and partial mineralization of dyes. Thereafter, the work was focused to tackle the challenges of powder photocatalyst recovery and to explore a competing route, i.e. immobilized fixed support. Glass, steel mesh and sintered silica were used for photocatalyst immobilization to solve the problems associated to photocatalyst recovery, mass limitation and low interaction of pollutants with fixed photocatalyst supports. The immobilization/deposition of β-Bi2O3 over each support, was achieved by pneumatic spray pyrolysis and subsequent calcination at 450 °C. During photo-evaluation of different β-Bi2O3 immobilized supports; deposited sintered silica exhibited higher activity and competing response to β-Bi2O3 powder. The improved activity of sintered silica was associated to the rough, porous and hydrophilic nature of silica that have facilitated in providing higher interaction of deposited β-Bi2O3 films with dye molecules. Furthermore, β-Bi2O3 deposited sintered silica exhibited improved performance for photodegradation and mineralization of various dyes of different chemical structures and ionic behaviors and cyclic stability up to 3 cycles. Then, the work was focused to obtain single structure ferromagnetic bismuth ferrite (BiFeO3) and its heterostructure (BiFeO3/Fe2O3/Bi2Fe4O9); as they have the advantage of easy magnetic separation from aqueous solution. The single structure BiFeO3 and its heterostructures were obtained by using Sol-Gel method, in which precursor solution, containing dissolved Bi(NO3)3:5H2O and Fe(NO3)3:9H2O were preheated and calcined at 500°C with and without addition of Polyethylene Glycol (PEG) and NaOH in the precursor solution. From the XRD and UV-vis DRS analysis it was observed that addition of PEG and NaOH, assisted to obtain single nanostructure BiFeO3, simply by enabling the particles polymerization and inhibiting the formation of other compounds like Fe2O3 and Bi2Fe4O9. It was revealed that single phase BiFeO3 is antiferromagnetic in nature and have very low photocatalytic response, due to the low energy band gap and high electron and holes recombination rate. On the other hand, BiFeO3/Fe2O3/Bi2Fe4O9 heterostructure displayed high magnetic saturation and exhibited improved photoactivity. This is due to a low electrons and holes recombination rate because of tuned band alignment and charge transfer within the heterojunction interfaces. Cyclic stability and photocatalytic performance of BiFeO3/Fe2O3/Bi2Fe4O9 were found almost similar during photodegradation of various dyes up to 3 cycles. At the end, detailed analyses of the efficient heterostructure α/β-Bi2O3 and promising β-Bi2O3 immobilized silica were made, for the evaluation of bulk single and mixed dye solutions under natural sunlight and at varying IC dye concentrations. It was found that the mechanism and the photodegradation kinetics were almost similar amongst lab conditions and during sunlight irradiation and for bulk solutions of single and mixed dyes. Moreover, the experienced phenomena of the degradation and achieved kinetic rate at varying IC concentration were almost alike for both α/β-Bi2O3 and deposited β-Bi2O3 sintered silica. These results revealed that deposited β-Bi2O3 sintered silica could have the promising potential over α/β-Bi2O3 or any other powder photocatalyst under solar light irradiation. Moreover, cyclic stability and the photoactivity of both α/β-Bi2O3 and deposited β-Bi2O3 silica were almost identical up to 3 cycles.

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Neste trabalho, foi estudada a influência da adição de TiO2 na atividade catalítica para a reação de oxidação de etanol sobre nanocatalisadores PtRu e PtSn. O efeito da quantidade de TiO2 adicionado também foi investigado para os catalisadores bimetálicos de PtSn. Os estudos foram realizados de modo comparativo para catalisadores suportados em carbono com a mesma parte metálica (Pt, PtRu ou PtSn), com e sem modificação com TiO2. A síntese das nanopartículas de PtRu e PtSn de composição nominal 50:50 e 70:30 (em átomos), respectivamente, foi realizada pelo método do poliol modificado, enquanto o TiO2 foi sintetizado separadamente pelo processo sol-gel. Com o intuito de avaliar as diferenças na atividade catalítica promovidas pela presença do óxido, mantendo idênticas as propriedades da parte metálica, as nanopartículas em estado coloidal foram separadas em frações: uma foi utilizada para a preparação do catalisador sem óxido e as outras para a preparação dos materiais contendo TiO2. Os nanocatalisadores preparados foram caracterizados por difração de raios X (DRX), microscopia eletrônica de transmissão (TEM), espectroscopia de fotoelétrons excitados por raios X (XPS) e espectroscopia de absorção de raios X (XAS) in situ. O comportamento eletroquímico geral foi avaliado por voltametria cíclica em solução ácida ou alcalina e as atividades eletrocatalíticas para a oxidação de etanol foram estudadas por varreduras de potencial e cronoamperometria. De maneira geral, os resultados mostram que a presença do TiO2 promove um aumento da atividade catalítica para a oxidação de etanol em meio ácido que, em baixos potenciais, resultaria das mudanças na vacância da banda 5d da Pt promovida pelas interações metal-óxido. Os estudos realizados variando a quantidade de TiO2 mostraram que os efeitos do teor de óxido são significativos tanto em meio ácido quanto em meio alcalino. Experimentos utilizando a...
In this work, the influence of the addition of TiO2 on the catalytic activity toward ethanol oxidation reaction on PtRu and PtSn nanocatalysts was studied. The effect of the amount of TiO2 added was also investigated for the PtSn bimetallic catalysts. The studies were comparatively performed for carbon-supported catalysts with the same metallic component (Pt, PtRu or PtSn) with and without modification with TiO2. The synthesis of PtRu and PtSn nanoparticles with nominal composition equal to 50:50 and 70:30 (in atoms), respectively, was carried out by a modified polyol method, while TiO2 was synthesized separately by a sol-gel process. In order to evaluate the differences in the catalytic activity promoted by the presence of the oxide, while maintaining the same properties of the metallic part, the colloid of nanoparticles was separated into fractions: one was used to prepare the catalyst without oxide and the others were used for preparation of the TiO2 containing materials. Nanocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption spectroscopy (XAS). The general electrochemical behavior was evaluated by cyclic voltammetry in acidic or alkaline solution and the electrocatalytic activity for ethanol oxidation was studied by potential sweeps and chronoamperometry. Overall, the results show that the presence of TiO2 enhances the catalytic activity for ethanol oxidation in acid medium in the low potential region, because of the changes in the Pt 5d band vacancy promoted by metal-oxide interactions. The studies involving the variation of the amount of TiO2 showed that the effects of oxide content are significant both in acidic and in alkaline medium. Experiments using in situ Fourier transform infrared reflection-absorption spectroscopy (FTIRAS) were performed in order to analyze qualitatively the products of alcohol oxidation at each...

Orientador: Hebe de las Mercedes Villullas
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Banca: Joelma Perez
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Banca: Flávio Colmati Júnior
Resumo: Neste trabalho, foi estudada a influência da adição de TiO2 na atividade catalítica para a reação de oxidação de etanol sobre nanocatalisadores PtRu e PtSn. O efeito da quantidade de TiO2 adicionado também foi investigado para os catalisadores bimetálicos de PtSn. Os estudos foram realizados de modo comparativo para catalisadores suportados em carbono com a mesma parte metálica (Pt, PtRu ou PtSn), com e sem modificação com TiO2. A síntese das nanopartículas de PtRu e PtSn de composição nominal 50:50 e 70:30 (em átomos), respectivamente, foi realizada pelo método do poliol modificado, enquanto o TiO2 foi sintetizado separadamente pelo processo sol-gel. Com o intuito de avaliar as diferenças na atividade catalítica promovidas pela presença do óxido, mantendo idênticas as propriedades da parte metálica, as nanopartículas em estado coloidal foram separadas em frações: uma foi utilizada para a preparação do catalisador sem óxido e as outras para a preparação dos materiais contendo TiO2. Os nanocatalisadores preparados foram caracterizados por difração de raios X (DRX), microscopia eletrônica de transmissão (TEM), espectroscopia de fotoelétrons excitados por raios X (XPS) e espectroscopia de absorção de raios X (XAS) in situ. O comportamento eletroquímico geral foi avaliado por voltametria cíclica em solução ácida ou alcalina e as atividades eletrocatalíticas para a oxidação de etanol foram estudadas por varreduras de potencial e cronoamperometria. De maneira geral, os resultados mostram que a presença do TiO2 promove um aumento da atividade catalítica para a oxidação de etanol em meio ácido que, em baixos potenciais, resultaria das mudanças na vacância da banda 5d da Pt promovida pelas interações metal-óxido. Os estudos realizados variando a quantidade de TiO2 mostraram que os efeitos do teor de óxido são significativos tanto em meio ácido quanto em meio alcalino. Experimentos utilizando a...
Abstract: In this work, the influence of the addition of TiO2 on the catalytic activity toward ethanol oxidation reaction on PtRu and PtSn nanocatalysts was studied. The effect of the amount of TiO2 added was also investigated for the PtSn bimetallic catalysts. The studies were comparatively performed for carbon-supported catalysts with the same metallic component (Pt, PtRu or PtSn) with and without modification with TiO2. The synthesis of PtRu and PtSn nanoparticles with nominal composition equal to 50:50 and 70:30 (in atoms), respectively, was carried out by a modified polyol method, while TiO2 was synthesized separately by a sol-gel process. In order to evaluate the differences in the catalytic activity promoted by the presence of the oxide, while maintaining the same properties of the metallic part, the colloid of nanoparticles was separated into fractions: one was used to prepare the catalyst without oxide and the others were used for preparation of the TiO2 containing materials. Nanocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption spectroscopy (XAS). The general electrochemical behavior was evaluated by cyclic voltammetry in acidic or alkaline solution and the electrocatalytic activity for ethanol oxidation was studied by potential sweeps and chronoamperometry. Overall, the results show that the presence of TiO2 enhances the catalytic activity for ethanol oxidation in acid medium in the low potential region, because of the changes in the Pt 5d band vacancy promoted by metal-oxide interactions. The studies involving the variation of the amount of TiO2 showed that the effects of oxide content are significant both in acidic and in alkaline medium. Experiments using in situ Fourier transform infrared reflection-absorption spectroscopy (FTIRAS) were performed in order to analyze qualitatively the products of alcohol oxidation at each...
Doutor

The present work highlights well-defined nanostructured ceria; a morphology that bestows exceptional catalytic activity on ceria towards soot oxidation. The work includes also introduction of promoting foreign metals, such as praseodymium and zirconium, to well-defined nanostructured ceria as a means of improving reducibility, thermal stability and oxygen storage capacity of the catalyst. Temperature-programmed oxidation (TPO) has been used for analyzing catalytic activity. At the first stage of the research, nanostructured equimolar ceria-praseodymia (denoted as Ce50Pr50-NP) was found to have the highest amount of surface oxygen, the highest reducibility and the highest catalytic activity towards soot oxidation. The nanostructured morphology has been proven to raise the functionality of praseodymia as the foreign metal in ceria. The work also introduces small, silane-stabilized Pt nanoparticles. Upon calcination, silyl ligands are transformed into siliceous patches that prevent the particle from migrating/coalescing. Cu nanoparticles have been prepared the same way as Pt nanoparticles; however, they sinter even under milder thermal treatment. The small Pt-NPs are proven active towards all pollutant oxidations, including NOx-assisted soot oxidation, and they function better with nanostructured ceria as the support. Unexpectedly, Ce50Pr50-NP gives higher activity towards NOx-assisted soot oxidation than Pt catalysts. Intense NO conversion and NO2 adsorption on the surface of Ce50Pr50-NP are the reason behind its high activity.

In the last century the amino alcohol serinol (2-amino-1,3-propanediol) has become a common intermediate for several chemical processes. Since the 40's serinol was used as precursor for synthesis of antibiotics (e.g. chloramphenicol). In the last years, new scopes of application were discovered. Serinol is used as building block in the synthesis of X-ray contrast agents, pharmaceuticals (anti-inflammatory or analgesic drugs) or in the cosmetics industry. It can either be obtained by chemical processes based on 2-nitro-1,3-propanediol, dihydroxiacetone (1,3-Dihydroxypropan-2-one or simply DHA) and ammonia [59]. One way to synthesize Serinol, in fact, is reacting DHA in a catalyzed reaction using Pt supported on carbon as catalyst. The DHA can be synthesized from Glycerol (1,2,3-propanetriol or glycerine) with a selective oxydation of the secondary carbon. The reaction from Glycerol to DHA must be catalyzed and nowadays only one method is well known. The method to obtain DHA uses gluconobacter oxydans as catalyst for the selective glycerol oxydation. Anyway the method presents many drawbacks cost not yet solved such as low productivity and high production. It is fundamental to underline how nowadays glycerol plants are closing and others are opening that use glycerol as a raw material as a result of the large surplus of glycerol that is formed as a byproduct in manufacturing biodiesel fuel by transesterification of seed oils with methanol. Over the last twenty years, indeed, biodiesel emerged as a viable fuel and as a fossil diesel additive to replace sulfur, whose content is being progressively lowered according to tighter environmental legislation. However, the increasing production of biodiesel is not artificially sustained and is predicted to spread and increase, as biodiesel provides sufficient advantages to merit subsidy. Besides the closure of production plants, industry reacted to this situation stimulating research to find new applications of glycerol as a low-cost feedstock for functional derivatives either for mass consumption, such as additives for concrete, or as a precursor of valued fine chemicals [60]. One investigated application of glycerol is exact its possible use as starting material for DHA synthesis (figure 1.4, chapter 1). The aim of this work was to investigate for new possibilities to transform glycerol into DHA, avoinding gluconobacter oxydans utilisation. In particular the attention was posed on new catalytic solutions investigating inorganic catalysts for the selective oxydation of glycerol. Two catalytic system were investigated. An heterogenous solution using noble metal nanoparticles supported on carbonious supports (mono- and bi-metallic systems) and an homogeneous one using an organometallic catalyst based on Pd. The study was approach from experimental and theoretical point of view becasue the reaction mechanism is not still clear. The research bring us to investigate deeply many weakness of the reaction and not still clear in literature, such as an efficient analytical method, problems linked to the catalysts aging, their deactivation and synthesis.

Gli argomenti di questa tesi hanno riguardato l’elettrolisi cloro-soda e l’elettrolisi dell’acqua mediante sistemi basati su membrane a scambio protonico (PEM). • Elettrolisi cloro-soda. Il cloro è oggi essenzialmente ottenuto mediante i processi industriali di elettrolisi di cloro-soda ed, in minore quantità, dall’elettrolisi dell’acido cloridrico. Il principale problema di questi processi è l’elevato consumo di energia elettrica che, solitamente, rappresenta una parte sostanziale del costo totale di produzione. Per l’ottimizzare di tale processo è necessario, quindi, ridurre il consumo energetico. La sostituzione del tradizionale catodo ad evoluzione di idrogeno, con un elettrodo a diffusione gassosa ad ossigeno, comporta una nuova reazione che riduce il potenziale termodinamico di cella e questo si traduce in un risparmio energetico del 30-40%. L’attività di ricerca è stata indirizzata verso lo studio di elettrodi a diffusione gassosa per la reazione di riduzione di ossigeno con particolare attenzione all’analisi superficiale e morfologica degli elettrocatalizzatori. In particolare l’attenzione è stata focalizzata sui fenomeni di deattivazione che coinvolgono questo tipo di elettrodi. Test di durata sono stati condotti sugli elettrodi in cella cloro-soda. Analisi di tipo comparativo sugli stessi sono state condotte, prima e dopo il loro funzionamento, nelle condizioni operative di interesse. La superficie degli elettrodi è stata analizzata mediante microscopio elettronico a scansione e spettroscopia fotoelettronica a raggi X. Analisi di bulk sono state effettuate mediante diffrattometria a raggi X ed analisi termogravimetrica. • Elettrolisi dell’acqua (PEM). L’idrogeno può essere prodotto a partire da sorgenti energetiche rinnovabili come fotovoltaico, eolico mediante l’elettrolisi dell’acqua. In particolare, l’elettrolisi, mediante l’utilizzo di un elettrolita polimerico (PEM), è considerata una promettente metodologia per la produzione di idrogeno, alternativa al convenzionale processo di elettrolisi il cui elettrolita è un liquido alcalino, altamente tossico e corrosivo. Un elettrolizzatore PEM possiede certamente dei vantaggi confrontato con il classico processo alcalino in termini di semplicità, sicurezza ed alta efficienza energetica. Questo sistema utilizza la già affermata tecnologia delle celle a combustibile ad elettrolita polimerico. Sfortunatamente il processo di scissione elettrochimica dell’acqua è associata ad un elevato consumo energetico, principalmente dovuto agli alti sovrapotenziali nella reazione anodica di evoluzione di ossigeno. Risulta quindi di fondamentale importanza trovare elettrocatalizzatori per l’evoluzione di ossigeno ottimali in modo da minimizzare le perdite. Il platino è utilizzato al catodo per la reazione di evoluzione di idrogeno (HER) e gli ossidi di iridio o rutenio sono usati all’anodo per la reazione di evoluzione di ossigeno (OER). Questi ossidi metallici sono richiesti perché, confrontati al platino metallico, offrono alta attività catalitica, una migliore stabilità a lungo termine ed una minore perdita di efficienza dovuta alla corrosione o all’inquinamento. Il lavoro è stato principalmente indirizzato verso: 1) la sintesi e caratterizzazione di anodi a base di RuO2 e IrO2; 2) la sintesi di supporti conduttori a base di subossidi di titanio con alta area superficiale. 1) Catalizzatori nanostrutturati a base di RuO2 e IrO2 sono stati preparati mediante un processo colloidale a 100°C; gli idrossidi così ottenuti sono stati calcinati a differenti temperature. L’attenzione è stata focalizzata sugli effetti che il trattamento termico produce sulla struttura cristallografica e sulla dimensione delle particelle di questi catalizzatori e come queste proprietà possono influenzare le performance degli elettrodi per la reazione di evoluzione di ossigeno. Caratterizzazioni elettrochimiche sono state fatte mediante curve di polarizzazioni, spettroscopia d’impedenza, e misure di crono-amperometria. 2) Una nuova metodologia di sintesi per la preparazione dei subossidi di titanio con fase Magneli (TinO2n-1) è stata sviluppata. Le caratteristiche di questi materiali sono state valutate sotto condizioni operative, in elettrolizzatori di tipo SPE, e confrontate con la polvere commerciale Ebonex. La stessa fase attiva a base di IrO2 è stata usata, come elettrocatalizzatore, per entrambi i sistemi.
The topics of this PhD thesis are concerning with Chlor alkali electrolysis and PEM water electrolysis. • Chlor alkali electrolysis. The industrial production of chlorine is today essentially achieved through sodium chloride electrolysis, with only a minor quantity coming from hydrochloric acid electrolysis. The main problem of all these processes is the high electric energy consumption which usually represents a substantial part of the total production cost. Therefore, in order to improve the process, it is necessary to reduce the power consumption. The substitution of the traditional hydrogen-evolving cathodes with an oxygen-consuming gas diffusion electrode (GDE) involves a new reaction that reduces the thermodynamic cell voltage and leads to an energy savings of 30-40%. My research activity was addressed to the investigation of the oxygen reduction at gas-diffusion electrodes as well as to the surface and morphology analysis of the electrocatalysts. Specific attention was focused on deactivation phenomena involving this type of GDE configuration. The catalysts used in this study were based on a mixture of micronized silver particles and PTFE binder. In this study, fresh gas diffusion electrodes were compared with electrodes tested at different times in a chlor-alkali cell. Electrode stability was investigated by life-time tests. The surface of the gas diffusion electrodes was analyzed for both fresh and used cathodes by scanning electron microscopy and X-ray photoelectron spectroscopy. The bulk of gas diffusion electrodes was investigated by X-ray diffraction and thermogravimetric analysis. • PEM water electrolysis. Water electrolysis is one of the few processes where hydrogen can be produced from renewable energy sources such as photovoltaic or wind energy without evolution of CO2. In particular, an SPE electrolyser is considered as a promising methodology for producing hydrogen as an alternative to the conventional alkaline water electrolysis. A PEM electrolyser possesses certain advantages compared with the classical alkaline process in terms of simplicity, high energy efficiency and specific production capacity. This system utilizes the well know technology of fuel cells based on proton conducting solid electrolytes. Unfortunately, electrochemical water splitting is associated with substantial energy loss, mainly due to the high over-potentials at the oxygen-evolving anode. It is therefore important to find the optimal oxygen-evolving electro-catalyst in order to minimize the energy loss. Typically, platinum is used at the cathode for the hydrogen evolution reaction (HER) and Ir or Ru oxides are used at the anode for the oxygen evolution reaction (OER). These metal oxides are required, compared to the metallic platinum, because they offer a high activity, a better long-term stability and less efficiency losses due to corrosion or poisoning. My work was mainly addressed to a) the synthesis and characterisation of IrO2 and RuO2 anodes; b) conducting Ti-suboxides support based on a high surface area. a) Nanosized IrO2 and RuO2 catalysts were prepared by using a colloidal process at 100°C; the resulting hydroxides were then calcined at various temperatures. The attention was focused on the effect of thermal treatments on the crystallographic structure and particle size of these catalysts and how these properties may influence the performance of oxygen evolution electrode. Electrochemical characterizations were carried out by polarization curves, impedance spectroscopy and chrono-amperometric measurements. b) A novel chemical route for the preparation of titanium suboxides (TinO2n−1) with Magneli phase was developed. The relevant characteristics of the materials were evaluated under operating conditions, in a solid polymer electrolyte (SPE) electrolyser, and compared to those of the commercial Ebonex®. The same IrO2 active phase was used in both systems as electrocatalyst.

This thesis investigates both hydrogen combustion and production, focusing on fundamentals of Pt-catalysed oxidation and steam methane reforming on nickelbased catalysts. On the first aspect, we started reporting and investigating discrepancies on the structure and predictions of detail surface kinetic models from Literature, for H2-O2 reaction on Pt. Quantitative comparisons have been carried out through a closed-vessel, well-stirred reactor model with catalytic internal surface. Discrepancies in the predictions of the microkinetic models apparently comes from disagreement in the experimental date they are based on. Differences in experimental set-ups and Pt surface structure prompted us to develop own data, using plane Pt surface in suitable reactors. A novel laboratory reactor to investigate hydrogen oxidation on Pt surfaces has been designed, based on modelling, and built. Experimental catalytic activity test proved that Pt activity can vary dramatically. Catalyst pretreatments with H2 and O2 revealed the mechanism of competition for surface sites as well as restructuring of the surface. Significantly long transformation was measured, particularly after catalyst O2 pretreatment, that are not included in the elementary chemistry models from Literature. Reaction lightoff at H2 lean compositions have been measured and compared with Literature experimental data, providing explanations for the differences among published data. Subsequently, transient simulation of hydrogen combustion in platinumcoated channel has been adopted to evaluate the behavior under heterogeneous and hetero-/homogeneous chemistries. Effects of catalyst support material properties, FeCr-alloy and cordierite, have been compared. Implication for the operation of various practical catalytic reactors are finally drawn. Concerning H2 production, we investigated the catalytic reforming of natural gas, by steam, both theoretically and experimentally. We identified relevant ranges of operative variables to study the catalyst at industrially relevant conditions. We designed by scaling down from industrial plants an original set-up to investigate the reaction kinetics at high-pressure (10 bars). We compared three nickel-based catalysts at low steam-to-carbon conditions, approaching S/C = 1, to collect activity and coking data for validation and development of detailed surface chemistry model.
Questa tesi investiga sia la combustion che la produzione di idrogeno, con particolare attenzione verso aspetti fondamentali della ossidazione catalizzata da platino e la reazione di steam reforming del metano su catalizzatori a base di nickel. Per quanto riguarda il primo aspetto, siamo partiti dall’osservare ed approfondire discrepanze sulla struttura e sui risultati di modelli cinetici di reazioni superficiali presenti in Letteratura, per la reazione di H2 e O2 su Pt. I confronti quantitativi sono stati fatti utilizzando un Modello di reattore chiuso ben mescolato con le superfici interne catalitiche. Le differenze nelle perizie dei diversi modelli sembrano discendere da differenze nei dati sperimentali su cui sono stati calibrati. Il fatto che se non state utilizzate diverse configurazioni sperimentali, e probabilmente strutture delle superfici di Pt , ci ha stimolato a intraprendere una campagna sperimentale per ottenere dati propri, utilizzando superfici di platino planari in opportuni reattori. Un nuovo reattore di laboratorio, a flusso stagnante, per indagare reazioni su Pt in forma di dischi e stato progettato sulla base di una` modellazione dettagliata e realizzato in laboratorio. I risultati sperimentali hanno dimostrato che l’attivita del Pt può variare enormemente. Pretrattamenti con H2 o O2 Hanno chiarito il meccanismo della competizione per siti superficiali e la possibilita di ristrutturazione la superficie. Sono state misurate trasformazioni di lunga durata, soprattutto dopo pretrattamenti con O2, che non trova una spiegazione in nessuno dei modelli cineticidettagliati di letteratura. Mediante misure in rampa di temperatura si e studiato` l’innesco di miscele povere di H2 in aria. Il confronto con dati di letteratura suggerisce una plausibile interpretazione della discrepanza dei dati riportati. Successivamente simulazioni transitorie della combustione di idrogeno in canali rivestiti di platino e stato utilizzato per valutare il comportamento della`reazione eterogenea con e senza reazione omogenea. L’effetto delle proprieta`del supporto del catalizzatore sono stati confrontati, considerando leghe Fe-Cre cordierite. Le implicazioni pratiche per l’operativita di questi reattori sono state`delineate. Per quanto riguarda la produzione di idrogeno abbiamo studiato sia dal punto di vista teorico che sperimentale la reazione di reforming di gas naturale mediante7 vapore. Abbiamo identificato intervalli significativi da un punto di vista industriale per le variabili operative, per studiare la cinetica dei catalizzatori. Abbiamo progettato un reattore di laboratorio mediante regole di scala rispetto a un impianto modello industriale di riferimento, con l’obiettivo di studiare la reazione a pressioni elevate (10bars). Abbiamo confrontato tre catalizzatori basati su Nickel con formulazioni diverse, modificando rapporto vapore/carbonio in alimentazione, per avvicinarsi alle condizioni stechiometriche. Si sono raccolti numerosi ,dati sia di attivita cataliticha che di formazione di carbone, utili per uno sviluppo di modelli` cinetici dettagliati della reazione superficiale.

1. Introduction Biodiesel (BD) is a liquid biofuel that is defined as a fatty acid methyl ester fulfilling standards such as the ones set by European (EN 14214) and the American (ASTM 6751) regulations. BD is obtained by the transesterification (Scheme 1.1) or alcoholysis of natural triglycerides contained in vegetable oils, animal fats, waste fats and greases, waste cooking oils (WCO) or side-stream products of refined edible oil production with short-chain alcohols, usually methanol or ethanol and using an alkaline homogeneous catalyst (Perego and Ricci, 2012). Scheme 1.1. Transesterification reaction. BD presents several advantages over petroleum-based diesel such as: biodegradability, lower particulate and common air pollutants (CO, SOx emissions, unburned hydrocarbons) emissions, absence of aromatics and a closed CO2 cycle. Refined, low acidity oilseeds (e.g. those derived from sunflower, soy, rapeseed, etc.) may be easily converted into BD, but their exploitation significantly raises the production costs, resulting in a biofuel that is uncompetitive with the petroleum-based diesel (Santori et al., 2012; Lotero et al., 2005). Moreover, the use of the aforementioned oils generated a hot debate about a possible food vs. fuel conflict, i.e. about the risk of diverting farmland or crops at the expense of food supply. It is so highly desirable to produce BD from crops specifically selected for their high productivity and low water requirements (Bianchi et al., 2011; Pirola et al., 2011), or from low-cost feedstock such as used frying oils (Boffito et al., 2012a) and animal fats (Bianchi et al., 2010). The value of these second generation biofuels, i.e. produced from crop and forest residues and from non-food energy crops, is acknowledged by the European Community, which states in its RED directive (European Union, RED Directive 2009/28/EC): ‘‘For the purposes of demonstrating compliance with national renewable energy obligations […], the contribution made by biofuels produced from wastes, residues, non-food cellulosic material, and ligno-cellulosic material shall be considered to be twice that made by other biofuels’’. However, the presence of free fatty acids in the feedstock, occurring in particular in the case of not refined oils, causes the formation of soaps as a consequence of the reaction with the alkaline catalyst. This hinders the contact between reagents and the catalyst and makes difficult the products separation. Many methods have been proposed to eliminate FFA during or prior to transesterification (Pirola et al., 2011; Santori et al., 2012). Among these the FFA pre-esterification method is a very interesting approach to lower the acidity since it allows to lower the acid value as well as to obtain methyl esters already in this preliminary step (Boffito et al., 2012a, 2012b; 2012c Bianchi et al., 2010, 2011; Pirola et al., 2010, 2011). Aims of the work The aims of this work are framed in the context of the entire biodiesel production chain, ranging from the choice of the raw material, through its standardization to the actual biodiesel production. The objectives can be therefore summarized as follows: Assessing the potential of some vegetable or waste oils for biodiesel production by their characterization, deacidification and final transformation into biodiesel; To test different ion exchange resins and sulphated inorganic systems as catalysts in the FFA esterification; To assess the use of ultrasound to assist the sol-gel synthesis of inorganic sulphated oxides to be used as catalysts in the FFA esterification reaction; To assess the use of sonochemical techniques such as ultrasound and microwave to promote both the FFA esterification and transesterification reaction. 2. Experimental details 2.1 Catalysts In this work, three kinds of acid ion exchange resins were used as catalysts for the FFA esterification: Amberlyst®15 (A15), Amberlyst®46 (A46) (Dow Chemical) and Purolite®D5081 (D5081). Their characteristic features are given in Tab. 2.1. Various sulphated inorganic catalysts, namely sulphated zirconia, sulphated zirconia+titania and sulphated tin oxide were synthesized using different techniques. Further details will be given as the results inherent to these catalysts will be presented. Catalyst A15 A46 D5081 Physical form opaque beads Type Macroreticular Matrix Styrene-DVB Cross-linking degree medium medium high Functional group -SO3H Functionalization internal external external external Form dry wet wet Surface area (m2 g-1) 53 75 514a Ave. Dp (Ǻ) 300 235 37a Total Vp (ccg-1) 0.40 0.15 0.47 Declared Acidity (meq H+g-1) 4.7 0.43 0.90-1.1 Measured acidity (meq H+g-1) 4.2 0.60 1.0 Moisture content (%wt) 1.6 26-36 55-59 Shipping weight (g l-1) 610 600 1310a Max. operating temp (K) 393 393 403 Tab. 2.1. Features of the ion exchange resins used as catalysts. The acidity of all the catalysts was determined by ion exchange followed by pH determination as described elsewhere (López et al., 2007; Boffito et al., 2012a; 2012b). Specific surface areas were determined by BET (Brunauer, Emmett and Teller, 1938) and pores sizes distribution with BJH method (Barrett, Joyner and Halenda, 1951). XRD, XPS SEM-EDX and HR-TEM analyses were performed in the case of catalysts obtained with the use of ultrasound (Boffito et al. 2012a). Qualitative analyses of Lewis and Brønsted acid sites by absorption of a basic probe followed by FTIR analyses was also carried out for this class of catalysts (Boffito et al, 2012a). 2.2 Characterization of the oils Oils were characterized for what concerns acidity (by acid-base titrations) as reported by Boffito et al. (2012a, 2012b; 2012c), iodine value (Hannus method (EN 14111:2003)), saponification value (ASTM D5558), peroxide value and composition by GC analyses of the methyl ester yielded by the esterification and transesterification. Cetane number and theoretical values of the same properties were determined using equations already reported elsewhere (Winayanuwattikun et al., 2008). 2.3 Esterification and transesterification reactions In Tab. 2.2, the conditions adopted in both the conventional and sonochemically-assisted esterification are reported. For all these experiments a temperature of 336 K was adopted. Vials were used to test the sulphated inorganic oxides, while Carberry reactor (confined catalyst) (Boffito et al., 201c) was used just for the FFA esterification of cooking oil. Rector oil (+ FFA) (g) MeOH (g) catalyst amount vial 21 3.4 5%wt/gFFA sulphated inorganic catalysts slurry 100 16 - 10 g ion exchange resins - 5%wt/gF FA sulphated inorganic catalysts Carberry 300 48 10 g (5 g in each basket) Tab. 2.2. Free fatty acids esterification reaction conditions for conventional and sonochemically-assisted experiments. All the sonochemically-assisted experiments were performed in a slurry reactor. FFA conversions were determined by acid-base titrations of oil samples withdrawn from the reactors at pre-established times and calculated as follows: "FFA conversion (%)=" (〖"FFA" 〗_"t=0" "-" 〖"FFA" 〗_"t" )/〖"FFA" 〗_"t=0" " x 100" In Tab. 2.3, the conditions of both the conventional and ultrasound (US)-assisted transesterification are reported. KOH and CH3ONa were used for conventional experiments, while just KOH for the US-assisted experiments. The BD yield was determined by GC (FID) analysis of the methyl esters. Method Reactor Step gMeOH/100 goil gKOH/100 goil Temp. (K) Time (min) traditional batch step 1 20 1.0 333 90 step 2 5.0 0.50 60 US-assisted batch step 1 20 1.0 313, 333 30 US-assisted continuos step 1 20 1.0 338 30 Tab. 2.3. Transesterification reaction conditions. 3. Results and Discussion 3.1 Characterization and deacidification of different oils by ion exchange resins: assessment of the potential for biodiesel production In Tab. 3.1 the results of the characterization of the oils utilized in this work are displayed. The value in parentheses indicate the theoretical value of the properties, calculated basing on the acidic composition. The acidity of all the oils exceeds 0.5%wt (~0.5 mgKOH/g), i.e. the acidity limit recommended by both the European normative (EN 14214) and American standard ASTM 6751 on biodiesel (BD). The iodine value (IV) is regulated by the EN 14214, which poses an upper limit of 120 gI2/100 g. The number of saturated fatty chains in the fuel determines its behaviour at low temperatures, influencing parameters such as the cloud point, the CFPP (cold filter plugging point) and the freezing point (Winayanuwattikun et al., 2008). The IV are in most of the cases similar to the ones calculated theoretically. When the experimental IV differs from the theoretical one, it is in most of the cases underestimated. This can be explained considering the peroxide numbers (PN), which indicates the concentration of O2 bound to the fatty alkyl chains and is therefore an index of the conservation state of oil. Oils with high IV usually have a high concentration of peroxides, whereas fats with low IV have a relatively low concentration of peroxides at the start of rancidity (King et al., 1933). Moreover, although PN is not specified in the current BD fuel standards, it may affect cetane number (CN), a parameter that is regulated by the standards concerning BD fuel. Increasing PN increases CN, altering the ignition delay time. Saponification number (SN) is an index of the number of the fatty alkyl chains that can be saponified. The long chain fatty acids have a low SN because they have a relatively fewer number of carboxylic functional groups per mass unit of fat compared to short chain fatty acids. In most of the cases the experimental SN are lower than the ones calculated theoretically. This can be explained always considering the PN, indicating a high concentration of oxygen bound to the fatty alkyl chains. Oil Acidity (%wt) IV1 (gI2/ 100 g) PN2 (meqO2 /kg) SN3 (mg KOH/g) CN4 Fatty acids composition (%wt) animal fat (lard)* 5.87 51 2.3 199 62.3 n.d. soybean* 5.24 138 3.8 201 42.4 n.d. tobacco1 1.68 143 (149) 21.9 199 (202) 41.6 (39.8) C14:0 (2.0) C16:0 (8.3) C18:0 (1.5) C18:1 (12.0) C18:2 (75.3) C18:3 (0.6) C20:0 (0.1) C22:0 (0.2) sunflower* 3.79 126 3.7 199 45.4 n.d. WSO5 0.50 118 (129) 71.3 187 (200) 48.9 (44.6) C16:0 (6.9) C18:0 (0.9) C18:1 (40.1) C18:2 (50.9) C18:3 (0,3) C20:0 (0.1) C20:1 (0.4) C22:0 (0.4) palm 2.71 54.0 (53.0) 12.3 201 (208) 61.3 (60.6) 16:0 (43.9) 18:0 (5.6) 18:1 (40.5) 18:2 (8.6) WCO6 2.10 53.9 (50.7) 11.0 212 (196) 59.9 (62.7) C16:0 (38.8) C18:0 (4.1) C18:1 (47.9) C18:2 (4.2) WCO:CRO =3:1 2.12 69.0 (75.5) 30.1 200 (212) 58.1 (55.1) C16:0 (30.1) C18:0 (3.1) C18:1 (51.9) C18:2 (12.0) C18:3 (2.%) C20:0 (0.2) C22:0 (0.1) WCO:CRO =1:1 2.19 76.8 (90.7) 51.3 188 (203) 58.1 (52.8) C16:0 (21.5) C18:0 (2.1) C18:1 (55.8) C18:2 (14.7) C18:3 (5.1) C20:0 (0.8) C22:0 (0.1) WCO:CRO =1:3 2.24 84.5 (104) 62.4 177 (202) 58.1 (49.9) 14:0 (0.1) 16:0 (14.7) 16:1 (0.7) 18:0 (6.85) 18:1 (40.0) 18:2 (37.0) 18:3 (0.25) 20:0 (0.25) 22:0 (0.15) rapeseed (CRO7) 2.20 118 (123) 71.6 165 (200) 52.8 (45.9) C16:0 (4.1) C18:0 (0.1) C18:1 (63.7) C18:2 (20.2) C18:3 (10.2) C20:0 (1.5) C22:0 (0.2) rapeseed* 4.17-5.12 108 (107) 3.5 203 (200) 48.9 (49.5) C16:0 (7.6) C18:0 (1.3) C18:1 (64.5) C18:2 (23.7) C18:3 (2.4) C20:0 (0.5) Brassica juncea 0.74 109 (110) 178 (185) 52.4 (51.1) C16:0 (2.4) C18:0 (1.1) C18:1 (19.9) C18:2 (19.2) C18:3 (10.9) C20:0 (7.2) C20:1 (1.7) C22:0 (0.9) C22:1 (34.8) 24:0 (1.9) safflower 1.75 139 48.9 170 47.1 n.d. WCO: tobacco2 =1:1 4.34 119 (112) 56.0 191 (203) 48.1 (48.0) C16:0 (22.5) C18:0 (3.2) C18:1 (32.0) C18:2 (42.1) C18:3 (0.2) tobacco2 6.17 141 (151) 33.4 183 (201) 44.4 (39.5) C16:0 (8.7) C18:0 (1.6) C18:1 (12.8) C18:2 (76.0) C18:3 (0.7) C20:0 (0.1) C22:0 (0.1) 1Iodine value; 2Peroxide number; 3Saponification number; 4Cetane number; 5Winterized sunflower oil, 6Waste cooking oil; 7Crude rapeseed oil; * refined, commercial oils acidified with pure oleic acid up to the indicated value. Tab. 3.1. Results of the characterization of the oils. The results of the FFA esterification performed on the different oils are given in Fig. 3.1. Fig. 3.1. Results of the FFA esterification reaction on different oils. The dotted line represents a FFA concentration equal to 0.5%wt, i.e. the limit required by both the European and American directives on BD fuel and to perform the transesterification reaction avoiding excessive soaps formation. The FFA esterification method is able to lower the acidity of most of the oils using the ion exchange resins A46 and D5081 as catalysts in the adopted reaction conditions. High conversion was obtained with A15 at the first use of the catalyst, but then its catalytic activity drastically drops after each cycle. The total loss of activity was estimated to be around 30% within the 5 cycles (results not shown for the sake of brevity). A possible explanation concerning this loss of activity may be related to the adsorption of the H2O yielded by the esterification on the internal active sites, which makes them unavailable for catalysis. When H2O molecules are formed inside the pores, they are unable to give internal retro-diffusion due to their strong interaction with H+ sites and form an aqueous phase inside the pores. The formation of this phase prevents FFA from reaching internal active sites due to repulsive effects. What appears to influence the FFA conversion is the refinement degree of the oil. WCO is in fact harder to process in comparison to refined oils (Bianchi et al., 2010; Boffito et al., 2012c), probably due to its higher viscosity which results in limitations to the mass transfer of the reagents towards the catalyst. Indeed, the required acidity limit is not achieved within 6 hours of reaction. A FFA concentration lower than 0.5%wt is not achieved also in the case of WCO mixture 3:1 with CRO and 1:1 with tobacco oil and in the case of the second stock of tobacco oil (tobacco2). This is attributable to the very low quality of these feedstocks due to the waste nature of the oil itself, in the case of WCO, or to the poor conservation conditions in the case of tobacco oilseed. In this latter case, the low FFA conversion was also ascribed to the presence of phospholipids, responsible for the deactivation of the catalyst. BD yields ranging from 90.0 to 95.0 and from 95.0 to 99.9% were obtained from deacidified raw oils using KOH and NaOCH3 as a catalyst, respectively. In Fig. 3.2, the comparison between A46 and D5081 at different temperatures and in absence of drying pretreatment (wet catalyst) is displayed. As expected, D5081 performs better than A46 in all the adopted conditions. Nevertheless, the maximum conversion within a reaction time of 6 hours is not achieved by any of the catalysts both operating at 318 K and in the absence of drying pretreatment. A more detailed study on the FFA esterification of WCO and its blends with rapeseed oil and gasoline was carried out. In Tab. 3.2 a list of all the experiments performed with WCO is reported together with the FFA conversion achieved in each case, while in Fig. 3.3 the influence of the viscosity of the blends of WCO is shown. Fig. 3.2. Comparison between the catalysts. D5081 and A46 at a) different catalysts amounts and b) temperatures and treatments. The results show that Carberry reactor is unsuitable for FFA esterification since a good contact between reagents and catalyst is not achieved due to its confinement. A15 deactivated very rapidly, while A46 and D5081 maintained their excellent performance during all the cycles of use due to the reasons already highlighted previously. The blends of WCO and CRO show an increase of the reaction rate proportional to the content of the CRO, that is attributable to the decreases viscosity (Fig. 3.3), being all the blend characterized by the same initial acidity. Also the use of diesel as a solvent resulted in a beneficial effect for the FFA esterification reaction, contributing to the higher reaction rate. Feedstock %wtFFAt=0 Reactor Cat. gcat/100 goil gcat/100 g feedstock Number of cat. re-uses FFA conv. (%), 1st use, 6 hr 1 WCO 2.10 Carberry A15 3.3 3.3 6 15.4 2 WCO 2.10 slurry A15 10 10 6 71.7 3 WCO 2.10 Carberry A46 3.3 3.3 6 7.7 4 WCO 2.10 slurry A46 10 10 6 62.0 5 WCO 2.10 slurry D5081 10 10 6 63.7 6 CRO 2.20 slurry A46 10 10 10 95.9 7 CRO 2.20 slurry D5081 10 10 10 93.7 8 WCO 2.10 slurry A46 10 10 0 62.0 9 WCO 75 CRO 25 2.12 7.5 71.3 10 WCO 50 CRO 50 2.19 5.0 79.9 11 WCO 25 CRO 75 2.24 2.5 86.1 12 CRO 2.20 10 95.9 13 WCO 75 DIESEL 25 1.74 7.5 76.8 14 WCO 50 DIESEL 50 1.17 5.0 58.7 15 WCO 25 DIESEL 75 0.65 2.5 40.4 16 WCO 25 DIESEL 75 (higher FFA input) 2.44 2.5 63.5 Tab. 3.2. Experiments performed with waste cooking oil. . Fig. 3.3. FFA conversions and viscosities of the blend of WCO with rapeseed oil. 3.2. Sulphated inorganic oxides as catalysts for the free fatty acid esterification: conventional and ultrasound assisted synthesis Conventional syntheses In Tab. 3.3, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Catalyst Composition Prep. method precursors T calc. SSA (m2g-1) Vp (cm3g-1) meq H+g-1 1 SZ1 SO42-/ZrO2 one-pot sol-gel ZTNP1, (NH4)2SO4 893 K O2 107 0.09 0.90 2a SZ2a SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 893 K 102 0.10 0.11 2b SZ2b SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 653 K 110 0.10 0.12 3 SZ3 SO42-/ZrO2 Physical mixing ZrOCl2.8H2O (NH4)2SO4 873 K 81 0.11 1.3 4 SZ4 Zr(SO4)2/SiO2 Impregnation Zr(SO4)2.4H2O SiO2 873 K 331 0.08 1.4 5 SZ5 Zr(SO4)2/Al2O3 Impregnation Zr(SO4)2.4H2O Al2O3 873 K 151 0.09 0.67 6 ZS Zr(SO4)2.4H2O (commercial) - - - 13 0.12 9.6 7 STTO_0 SO42-/SnO2 Physical mixing + impregnation SnO2 TiO2 P25 H2SO4 773 K 16.8 0.10 3.15 8 STTO_5 SO42-/95%SnO2-5%TiO2 773 K 15.9 0.11 3.43 9 STTO_10 SO42-/ 90%SnO2-10%TiO2 773 K 16.5 0.09 5.07 10 STTO_15 SO42-/ 85%SnO2-15%TiO2 773 K 14.9 0.11 7.13 11 STTO_20 SO42-/ 80%SnO2-20%TiO2 773 K 16.9 0.09 7.33 Tab. 3.3. Sulphated inorganic catalysts synthesized with conventional techniques. The FFA conversions of the sulphated Zr-based systems are provided in Fig. 3.4a and show that Zr-based sulphated systems do not provide a satisfactory performance in the FFA esterification, probably due to their low acid sites concentration related to their high SSA. Even if catalysts such as SZ3 and SZ4 exhibit higher acidity compared to other catalysts, it is essential that this acidity is located mainly on the catalyst surface to be effectively reached by the FFA molecules, as in the case of ZS. In Figure 3.4b, the results of the FFA esterification tests of the sulphated Sn-Ti systems are shown. Other conditions being equal, these catalysts perform better than the sulphated Zr-based systems just described. This is more likely due to the higher acidity along with a lower surface area. With increasing the TiO2 content, the acidity increases as well. This might be ascribable to the charge imbalance resulting from the heteroatoms linkage for the generation of acid centres, (Kataota and Dumesic, 1988). As a consequence, the activity increases with the TiO2 content along with the acidity of the samples. For the sake of clarity, in Fig. 3.4c the FFA esterification conversion is represented as a function of the number of active sites per unit of surface area of the samples. Ultrasound- assisted synthesis In Tab. 3.4, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Samples SZ and SZT refer to catalysts obtained with traditional sol-gel method, while samples termed USZT refer to US-obtained sulphated 80%ZrO2-20%TiO2. The name is followed by the US power, by the length of US pulses and by the molar ratio of water over precursors. For example, USZT_40_0.1_30 indicates a sample obtained with 40% of the maximum US power, on for 0.1 seconds (pulse length) and off for 0.9 seconds, using a water/ZTNP+TTIP molar ratio equal to 30. SZT was also calcined at 773 K for 6 hours, employing the same heating rate. This sample is reported as SZT_773_6h in entry 2a. Further details about the preparation can be found in a recent study (Boffito et al., 2012b). Entry Catalyst Acid capacity (meq H+/g) SSA (m2g-1) Vp (cm3g-1) Ave. BJH Dp (nm) Zr:Ti weight ratio S/(Zr+Ti) atomic ratio 1 SZ 0.30 107 0.20 6.0 100 0.090 2 SZT 0.79 152 0.19 5.0 79:21 0.085 2a SZT_773_6h 0.21 131 0.20 5.0 n.d.1 n.d 3 USZT_20_1_30 0.92 41.7 0.12 12.5 80:20 0.095 4 USZT_40_0.1_30 1.03 47.9 0.11 9.5 81:19 0.067 5 USZT_40_0.3_30 1.99 232 0.27 4.5 81:19 0.11 6 USZT_40_0.5_7.5 1.70 210 0.20 5.0 78:22 0.086 7 USZT_40_0.5_15 2.02 220 0.20 5.0 80:20 0.13 8 USZT_40_0.5_30 2.17 153 0.20 5.0 78:22 0.12 9 USZT_40_0.5_60 0.36 28.1 0.10 10 79:21 0.092 10 USZT_40_0.7_30 1.86 151 0.16 5.0 78:22 0.11 11 USZT_40_1_15 3.06 211 0.09 7.0 80:20 0.15 12 USZT_40_1_30 1.56 44.1 0.09 7.0 80:20 0.17 Tab. 3.4. Sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel technique. Some of the results of the characterizations are displayed in Tab. 3.4. The results of the catalytic tests are shown in Fig. 3.5 a, b and c. In Fig. 3.5a and 3.5b the FFA conversions are reported for the samples synthesized using the same or different H2O/precursors ratio, respectively. Fig. 3.5. FFA conversions of sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel for a) the same amount of H2O, b) different amount of H2O used in the sol-gel synthesis, c) in function of the meq of H+/g of catalyst Both the addition of TiO2 and the use of US during the synthesis are able to improve the properties of the catalysts and therefore the catalytic performance in the FFA esterification. The addition of TiO2 is able to increase the Brønsted acidity and, as a consequence, the catalytic activity (compare entries 1 and 2 in Tab. 3.4). The improvement in the properties of the catalysts due the use of US is probably caused by the effects generated by acoustic cavitation. Acoustic cavitation is the growth of bubble nuclei followed by the implosive collapse of bubbles in solution as a consequence of the applied sound field. This collapse generates transient hot-spots with local temperatures and pressures of several thousand K and hundreds of atmospheres, respectively (Sehgal et al., 1979). Very high speed jets (up to 100 m/s) are also formed. As documented by Suslick and Doktycz (Suslick and Doktycz, 1990), in the presence of an extended surface, such as the surface of a catalyst, the formation of the bubbles occurs at the liquid-solid interface and, as a consequence of their implosion, the high speed jets are directed towards the surface. The use of sonication in the synthesis of catalysts can therefore improve the nucleation production rate (i.e. sol-gel reaction production rate) and the production of surface defects and deformations with the formation of brittle powders (Suslick and Doktycz, 1990). For the samples obtained with the US pulses with on/off ratio from 0.3/0.7 on, the conversion does not increase much more compared to the one achieved with the sample obtained via traditional sol-gel synthesis. Their conversion is in fact comparable (see samples USZ_40_0.3_30, USZ_40_0.5_30, USZ_40_0.7_30 and SZT in Fig. 3.5a. The similarity in the catalytic performance of these catalysts may be ascribable to the fact that they are characterized by comparable values of SSA (entries 2, 5, 8, 10 in Tab. 3.4) and, in the case of the catalysts obtained with pulses, also by comparable acidities (entries 5, 8, 10 in Tab. 3.4). A high SSA may in fact be disadvantageous for the catalysis of the reaction here studied for the reasons already highlighted in the previous sections. The best catalytic performance is reached by the sample USZT_40_1_30, i.e. the one obtained using continuous US at higher power. This catalyst results in fact in a doubled catalytic activity with respect to the samples prepared either with the traditional synthesis or with the use of pulsed US. In spite the acidity of this catalyst is lower than that of the samples obtained with the US pulses, it is characterized by a rather low surface area (entry 12 in Tab. 3.4) that can be associated with a localization of the active sites mainly on its outer surface. As evidenced by the FTIR measurements (not reported for the sake of brevity), it is also important to highlight, that only in the case of the USZT_40_1_30 sample, a not negligible number of medium-strong Lewis acid sites is present at the surface, together with a high number of strong Brønsted acid centres. The XRD patterns of the samples were typical of amorphous systems, due to the low calcination temperatures. Samples calcined for a long time (SZT_773_6h) exhibit almost no catalytic activity (results not reported for the sake of brevity). This catalytic behaviour might be ascribable to the loss of part of the sulphates occurred during the calcinations step that result also in a very low acid capacity (see Tab. 3.4). For the sake of clarity, in Fig. 3.5c the FFA conversions as a function of the concentration of the acid sites normalized to the surface area are reported for the most significant samples. For what concerns how the water/precursors ratio affects the catalysts acidity, some general observations can be made: increasing it up to a certain amount increases the H+ concentration (compare entries from 6 to 9 and 11 to 12 in Tab. 3.4) because the rate of the hydrolysis and the number of H2O molecules that can be chemically bounded increases. Nevertheless, increasing the water/precursor ratio over a certain amount (30 for pulsed and 15 for continuous US, entries 8 and 11 in Tab. 3.4, respectively), seems to have a negative effect on the acidity concentration. In fact, the risk of the extraction of acid groups by the excess of water increases as well and the US power density decreases. 3.3 Sonochemically-assisted esterification and transesterification Esterification In Tab. 3.5 a list of the sonochemically-assisted esterification experiments is displayed together with the final acidities achieved after 4 hours of reaction. The reactor used for these experiments, provided with both an US horn (20 kHz) and a MW emitter (2450 MHz) is described elsewhere in detail (Ragaini et al., 2012). Standard calorimetric measurements were carried out to measure the actual emitted power (Suslick and Lorimer, 1989). Considering entries from 1 to 6 (rapeseed oil with high acidity), a final acidity lower than 0.5%wt is achieved within 4 hours operating at the conventional temperature of 336 K with all the methods, while this does not happen operating at lower temperatures. In particular, the lowest acidity is achieved at 336 K with MW. Considering entries from 7 to 12, inherent to the raw tobacco oilseed, final acidities lower than 0.5%wt are achieved only with the use of US. It is remarkable that at the temperature of 293 K the FFA esterification reaction rate results 6X faster than the conventional process at the same temperature. In the case of the rapeseed oil with low acidity (entries from 13 to 20), the use of MW increases the FFA conversion at 293 K and 313 K but not at 336 K. Moreover, the higher the applied power, the higher the FFA conversion. Oil Initial acidity (%wt) Cat. Technique Temp. (K) Emitted power (W) Tthermostat (K) Final acidity (%wt), 4 hr 1 Rapeseed oil (5)* 4.2-5.0 A46 conventional 313 - 315 1.18 2 336 338 0.50 3 ultrasound 313 38.5 293 0.55 4 336 313 0.48 5 microwaves 313 61.4 293 0.69 6 336 313 0.32 7 Tobacco 1.17 A46 conventional 293 - 293 0.97 8 313 315 0.55 9 336 338 0.45 10 ultrasound 293 38.5 277 0.48 11 313 293 0.46 12 336 313 0.30 13 Rapeseed oil (2)* 2.0-2.3 D5081 conventional 293 - 277 0.82 14 313 315 0.44 15 336 338 0.25 16 microwaves 293 31.7 277 0.73 17 313 31.7 293 0.34 18 61.4 293 0.37 19 336 31.7 313 0.29 20 61.4 313 0.25 Tab. 3.5. Sonochemically-assisted esterification experiments. The positive effects of acoustic-cavitation in liquid-solid systems are ascribable to the asymmetric collapse of the bubbles in the vicinity of the solid surface. When a cavitation bubble collapses violently near a solid surface, liquid jets are produced and high-speed jets of liquid are driven into the surface of a particle. These jets and shock waves improve both the liquid–solid and liquid-liquid mass transfer (Mason and Lorimer, 1988). MW is considered as a non-conventional heating system: when MW pass through a material with a dipole moment, the molecules composing the material try to align with the electric field (Mingos et al., 1997). Polar molecules have stronger interactions with the electric field. Polar ends of the molecules tend in fact to align themselves and oscillate in step with the oscillating electric field. Collisions and friction between the moving molecules results in heating (Toukoniitty et al., 2005). The increase of the FFA conversion as the power increases may be attributed to the fact that more power is delivered to the system and, therefore, the enhanced temperature effects caused by electromagnetic irradiation are increased with respect to lower powers. Differently the reason why a too high power was detrimental at the temperature of 336 K could be accounted for by two factors: i) the acoustic cavitation is enhanced at lower temperatures due to the higher amount of gas dissolved; ii) possible generation of too high temperatures inside the reaction medium that could have caused the removal of methanol from the system through constant evaporation or pyrolysis. Transesterification Transesterification experiments were performed on rapeseed oil both in batch and continuous mode. For the batch experiments two kinds of reactors were used: a traditional reaction vessel and a Rosett cell reactor, both with two ultrasound horns with different tip diameters (13 and 20 mm), and operating powers. A Rosett cell is a reactor designed to promote hydrodynamic cavitation through its typical loops placed at the bottom of vessel. Sonicators used in this work were provided by Synetude Company (Chambery, France). In Fig. 3.6, results from the conventional and the US-assisted batch experiments are compared. The US methods allows to attain very high yields in much shorter times than the traditional method and using less reagents (see Tab. 2.3) in just one step. The beneficial effects given by the US are attributable to the generation of acoustic cavitation inside the reaction medium leading to the phenomena already described in the case of esterification reaction. In particular, with the use of the Rosett cell reactor, BD yields of 96.5% (dotted lined) are achieved after 10 minutes of reaction. This is likely due to the combined approach exploiting acoustic cavitation along with hydrodynamic cavitation, which is able to provide a very efficient mixing inside the system. The use of the Rosett cell reactor provided transesterification reaction rates up to 15X faster than the conventional process. Continuous experiments were performed using two tubular reactors with different volumes (0.070 L at 35 KHz and 0.700 L at 20 kHz) and different US powers (19.3 and 68.3 W, respectively). The volume of the treated reagents was varied to obtain the same power density in both the reactors. Results are presented in Fig. 3.7. BD yields higher than 96.5% were obtained in the case of the small reactor within a reaction time of ~5 minutes. It is remarkable that BD yields higher than 90% were obtained using pulsed US (2 seconds on, 2 seconds off) after only 18 seconds, corresponding to just one passage in the reactor. In this case the transesterification reaction rate was 300X faster than the conventional process. The beneficial effects of pulses for the reactivity of the transesterification have been extensively reported (Chand et al., 2010; Kumar et al., 2010). In particular, as reported by Chand, when pulses are adopted, excessive heating of the reaction medium is not promoted, so preventing the loss of the gases dissolved in the system that are necessary for the acoustic cavitation to occur. Moreover, excessive heating during the transesterification reaction might lead to evaporation followed by pyrolysis of methanol and its subsequent removal from the reaction environment. 4. Conclusions As a conclusion to this work, some final remarks can be claimed: Feedstocks with a high potential for biodiesel (BD) production are Brassica juncea oilseed, which can be used as feedstock for BD100, Carthamus tinctorus, tobacco, animal fat and waste cooking oil to be used in BD blends with other oils or in diesel blends. However, blending different oils among them or with diesel already during the free fatty acids (FFA) esterification reaction may increase the reaction rate due to the lowered viscosity. Free fatty acids esterification over acid ion exchange resins in slurry reactors remains the preferred method of oils deacidification due to the optimal contact between the reagents and the catalyst and the good durability over time. The final high BD yields obtained for the oils de-acidified with the pre-esterification method over sulphonic ion exchange resins demonstrate its effectiveness in lowering the acidity and the possibility of obtaining high quality biodiesel from the selected feedstocks. Surface acidity and specific surface area of sulphated inorganic systems can be increased by both adding TiO2 and using ultrasound (US) in precise experimental conditions to assist the sol-gel synthesis of the catalysts. Changing the experimental conditions of US during the sol-gel synthesis makes also possible to tune the properties of the catalysts. In spite of not satisfying FFA conversions were obtained, US-assisted sol-gel synthesis turns out to be an extremely interesting method to obtain catalysts with high acidity and surface area. Both US and microwaves (MW) enhanced the FFA esterification reaction rate at temperatures lower than the one used conventionally (336 K). The positive effects of US are attributable to the phenomena generated inside the reaction medium by the acoustic cavitation, while MW are able to generate temperature effects localized in the proximity of the catalyst surface and to increase MeOH-oil solubility. US-assisted transesterification reaction is much faster than conventional transesterification: BD yields higher than 96.5% were achieved in most of the cases within 10 minutes of reaction, whereas the conventional method requires 150 minutes, besides higher reagents amount and higher temperatures. In particular, BD yields higher than 90% were obtained using a continuous reactor and pulsed US within 18 seconds, corresponding to just one passage in the reactor. In this case the transesterification reaction rate resulted to be 300X faster than the conventional process. Suggestions for the continuations of the work concern the further study of the synthesis of sulphated inorganic systems such as SO42-/ZrO2 or SnO2 or TiO2 with US and MW. Future work should also be devoted to the optimization of the experimental variables related to the use of MW and US to promote both FFA esterification and transesterification reactions. References Barrett E.P., Joyner L.G., Halenda P.P., “The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms”, J. Am. Chem. Soc. 1951, 73, 373. Bianchi C.L., Boffito D.C., Pirola C., Ragaini V., “Low temperature de-acidification process of animal fat as a pre-step to biodiesel production”, Catal. Lett., 2010, 134, 179. Bianchi C.L., Pirola C., Boffito D.C., Di Fronzo A., Carvoli G., Barnabè D., A. Rispoli, R. Bucchi, “Non edible oils: raw materials for sustainable biodiesel”, in Stoytcheva M., Montero G. (Eds.): Biodiesel Feedstocks and Processing Technologies, Intech, 2011, pp. 3-22. Boffito D.C., Pirola C., Galli F., Di Michele A., Bianchi C.L., “Free Fatty Acids Esterification of Waste Cooking Oil and its mixtures with Rapeseed Oil and Diesel”, Fuel, 2012a, accepted on 19th October 2012, DOI: 10.1016/j.fuel.2012.10.069. Boffito D.C., Crocellà V., Pirola C., Neppolian B., Cerrato G., Ashokkumar M., Bianchi C.L., “Ultrasonic enhancement of the acidity, surface area and free fatty acids esterification catalytic activity of sulphated ZrO2-TiO2 systems”, J. Catal., 2012b, http://dx.doi.org/10.1016/j.jcat.2012.09.013 Boffito D.C., Pirola C., Bianchi C.L., “Heterogeneous catalysis for free fatty acids esterification rea.ction as a first step towards biodiesel production”, Chem, Today, 2012c, 30, 14. Brunauer S., Hemmett P., Teller E., “Adsorption of Gases in Multimolecular Layers”, J. Am. Chem. Soc. 1938, 60, 309. López D. E., Suwannakarn K., Bruce D. A., Goodwin JG. “Esterification and transesterification on tungstated zirconia: Effect of calcination temperature”, J Catal 2007, 247, 43. Mason T.J., Lorimer J.P., “Sonochemistry, Theory, Applications and Uses of Ultrasound in Chemistry“, Efford, J. Wiley, New York, 1988. Mingos D.M.P.,Baghurst D.R., “Applications of Microwave Dielectric Heating Effects to Synthetic Problems in Chemistry“, Microwave-Enhanced Chemistry, American Chemical Society,Washington, DC, USA, 1997. Perego C., Ricci, M., “Diesel fuel from biomass”, Catal. Sci. Technol., 2012, 1, 1776. Pirola C., Boffito D.C., Carvoli G., Di Fronzo A., Ragaini V., Bianchi C.L., “Soybean oil deacidification as a first step towards biodiesel production”, in D. Krezhova (Ed.): Recent Trends for Enhancing the Diversity and Quality of Soybean Products, Intech, 2011, pp. 321-44. Pirola C., Bianchi C.L., Boffito D.C., Carvoli G., Ragaini V., “Vegetable oil deacidification by Amberlyst : study of catalyst lifetime and a suitable reactor configuration”, Ind. Eng. Chem. Res., 2010, 49, 4601. Ragaini V., Pirola C., Borrelli S., Ferrari C., Longo I., “Simultaneous ultrasound and microwave new reactor: Detailed description and energetic considerations”, Ultrasonics Sonochemistry 2012, 19, 872 Sehgal C., Steer R.P., Sutherland R.G., Verrall R.E., “Sonoluminescence of argon saturated alkali metal salt solutions as a probe of acoustic cavitation”, J. Chem. Phys., 1979, 70, 2242. Suslick K. S., Doktycz, S. J., "The Effects of Ultrasound on Solids" in Mason, T.J.: Advances in Sonochemistry, JAI Press: New York, 1990, vol.1, pp. 197-230. Toukoniitty B., Mikkola J.P., Murzin D.Yu., Salmi T., “Utilization of electromagnetic and acoustic irradiation in enhancing heterogeneous catalytic reactions”, Appl. Catal. A 2005, 279, 1 Winayanuwattikun P., Kaewpiboon C., Piriyakananon K., Tantong S., Thakernkarnkit W., Chulalaksananukul W. et al. “Potential plant oil feedstock for lipase-catalyzed biodiesel production in Thailand”, Biomass. and Bioen. 2008, 32, 1279.

Hydrogen production from solar-driven water splitting (WS) reaction is considered a promising way to store solar energy. This process can be achieved directly by means of a photo-electrochemical cell (PEC), where light absorption, charge separation and WS occur in a single device; or indirectly, by coupling a photovoltaic device to an electrolyzer. WS is a thermodynamically uphill reaction, formed by two half reactions, i.e. the reduction of protons into H2 and the oxidation of water into O2. From a kinetic point of view, the latter is the most challenging one, being generally considered as the bottleneck for a widespread use of WS for hydrogen production. Thus, regardless of whether WS is carried out in direct or indirect configurations, the efficiency of the water oxidation catalyst (WOC) is a key determinant of the overall energy storage efficiency. The present thesis fits within this context, being focused on the study of different WOCs based on earth abundant elements (i.e. Mn and Co). Different heterogeneous Mn-based WOCs were studied, including: (i) different crystal structures of Mn oxides, both commercial and lab-made (i.e. MnO2, Mn3O4 and Mn2O3); (ii) a calcium manganese oxide (containing Ca2Mn3O8 and CaMn2O4) and (iii) lanthanum manganites (LaMnO3) prepared via sol-gel (SG) and flame spray pyrolysis (FP). On the other hand, the heterogenization of a homogeneous Co based WOC, i.e. the polyoxometalate Na10[Co4(H2O)2(PW9O34)2] (CoPOM), was investigated, as well. CoPOM is known to be a highly active WOC, comprising an active {Co4O4} core stabilized by oxidatively resistant polytungstate ligands. Transferring its solution reactivity to solid substrates is a fundamental step in the realization of a PEC.

Nowadays it is imperative to develop economical and energy-efficient processes for the sustainable production of fuels and chemicals alternative to the ones deriving from petroleum. Climate change and air quality are major environmental concerns because they directly affect the way we live and breathe. In order to meet the present and future threats generated by emissions to the atmosphere, environmental agencies around the world have issued more stringent regulations. One of them is the control of residual sulfur in diesel fuel and emission standards for particulates from diesel vehicles. All these facts have recently aroused renewed interest in the Fischer–Tropsch Synthesis (FTS) because it can produce super clean diesel oil fraction with high cetane number (typically above 70) without any sulfur and aromatic compounds, using syngas - (mixture of H2, CO, CO2) - from natural gas, CH4, coal or, as a new tendency, from biomass. The essential target of FTS is to produce paraffins and olefins with different molecular weight and to limit the maximum formation of methane and CO2. FTS usually requires catalysts based on iron or cobalt. Iron catalysts are often preferred over cobalt–based ones especially when converting syngas with molar H2/CO ratio lower than 2 (corresponding to the stoichiometry required by the FTS reaction). This is also the typical H2/CO ratio of syngas produced from biomass or coal. In fact, iron-based catalysts are active towards the Water Gas Shift reaction (WGS: CO + H2O-> CO2 + H2), increasing the H2/CO ratio. On the other hand when feeding a syngas mixture with a H2/CO ratio close to 2, cobalt catalysts are preferred due to their high selectivity towards heavy hydrocarbons and their low activity in WGS reaction limiting the CO2 formation. Moreover Co-based catalysts exhibit longer life-time and higher CO conversion compared with Fe based catalyst. In this wide and well-known situation it is nowadays imperative to develop new innovative kind of catalysts in order to make possible the conversion of syngas and biosyngas (i.e. syngas produced from biomass) to useful hydrocarbon by FTS process. Considering very recent research results the aim of the PhD’s research was addressed toward the development of three particular kind of catalysts: The first group of catalysts tested were the Co-based hydrotalcites (HTlc) with different amount of Co in two different pilot plants. HTlc-based materials have been recently reported as good catalysts for several processes in the energy field. Up to now the only study reported in literature on the use of synthetic HTlc as FTS catalysts concerns their use as inert supports for the catalytically active metal. According to this study, hydrotalcite-supported catalysts result in higher activity than Co/Al2O3, even in absence of reduction promoters. The second group of catalysts tested were the Co-based catalysts and bimetallic Co-Ru based catalyst synthesized with the help of ultrasound, because the ultrasound are presented in literature as an innovative way to synthesize new kind of materials. Finally, were synthesized and tested samples of Fe-based catalysts supported on silica with the variation of the H2/CO ratio (with the aim to evaluate the performance of biomass) and with the results propose a kinetic model. Concerning the results obtained in this PhD’s research work, it is clear that all the samples tested have given good results. The Co-based catalysts, synthesized using the traditional impregnation method, with an additional step of ultrasound have given good results in comparison with the results in the current literature. The hydrotalcites have given lower results, if compared with the Co-based catalysts synthesized with the help of ultrasound, but they have opened an alternative and innovative way, that has never been tried before. Iron based catalysts allow a direct conversion of the biosyngas, and the results have shown how our catalysts are active with an H2/CO ratio ≤2. Furthermore, trends have been modeled with success. In conclusion, the PhD’s research work, has given a serious contribution to the current state of the art on catalysis in the Fischer-Tropsch synthesis either with cobalt and iron based catalysts. With cobalt has been optimized a traditional synthesis procedure with the introduction of ultrasound, furthermore has been created a completely new kind of catalyst. With iron has continued an optimization’s work of iron supported with high loading metals, so to develop a suitable kinetic model able to work not only with syngas, but also with biosyngas.

Mycobacterium tuberculosis catalase-peroxidase (KatG) is a bifunctional hemoprotein which activates isoniazid (INH), a pro-drug that is integral to frontline antituberculosis treatments. The activated species, an isonicotinoyl radical, couples to NAD+/NADH forming an isoniazid-NADH adduct that ultimately confers anti-tubercular activity. In order to better understand the mechanisms of isoniazid activation as well as the origins of KatG-derived INH-resistance, we have compared the catalytic properties of the wild-type enzyme to twenty-three KatG mutants which have been associated with isoniazid resistance in clinical M. tuberculosis isolates. Neither catalase nor peroxidase activities, the two inherent enzymatic functions of KatG, were found to correlate with isoniazid resistance. Furthermore, catalase function was lost in mutants which lacked the Met-Tyr-Trp crosslink, the biogenic cofactor in KatG which has been previously shown to be integral to this activity. The presence or absence of the crosslink itself, however, was also found to not correlate with INH resistance. The KatG resistance-conferring mutants were then assayed for their ability to generate the INH-NADH adduct in the presence of peroxide (t-BuOOH and H2O2), superoxide, and no exogenous oxidant (air-only). The results demonstrate that residue location plays a critical role in determining INH-resistance mechanisms associated with INH activation; however, different mutations at the same location can produce vastly different reactivities that are oxidant-specific. Furthermore, the data can be interpreted to suggest the presence of a second mechanism of INH-resistance that is not correlated with the formation of the INH-NADH adduct.

The methanol-to-olefins reaction is an important industrial process for the production of light olefins (C2-C4). Silicoaluminophosphates are the most common catalysts for this process with SAPO-34 (CHA), SAPO-18 (AEI) and their intergrowths being considered the most catalytically active and selective. Understanding the crystal growth of such materials is important for control of the structure and defect incorporation, which can have a large effect on the catalytic behaviour. In this thesis, the synthesis, characterisation, catalysis and crystal growth of such materials are investigated. A series of CHA/AEI intergrowth materials were synthesised by sequential increases in silicon content, where low silicon content led to formation of AEI and higher silicon content led to CHA and intergrowth formation. X-ray diffraction and MAS-NMR were used to quantify the amount of intergrowth and there was a strong correlation between both techniques. Atomic Force Microscopy (AFM) revealed the mechanism by which these intergrowth structures grow. There is competition at the surface between the spiral-growth and layer-growth mechanisms, which has a significant effect on the resulting intergrowth, as intergrowth formation is only permitted with a layer-growth mechanism. Intergrowth on screw dislocations is not allowed, and thus discrete blocks of pure-phase AEI or CHA form. These intergrowth materials were tested for their performance in the methanol-to-olefins reaction. With a higher level of silicon, the catalysts had a larger acid site density but equivalent acid strength. The conversion of methanol over the catalysts correlated with the acid site density, where a greater acid site density led to higher conversion and faster deactivation. The selectivity over time was similar for all catalysts, with a high selectivity to ethylene and propylene. However, at the same percentage conversion, the C2/C3 ratio showed a strong correlation to the cage shape. Catalysts with a higher ratio of AEI cages had a higher selectivity to C3 and C4 products than the other catalysts, owing to the larger size of the internal AEI cage compared to the CHA cage. The crystal growth mechanism on SAPO-18 was investigated in detail to interrogate the complex spiral pattern that forms on the surface. Spirals form in a triangular type pattern due to differences in growth rates in different crystallographic directions. Interlaced terraces were also present. The unit cell and the relative orientation of the AEI cages define the different growth rates. In-situ AFM was used to investigate the dissolution behaviour of SAPO-18 and SAPO-34. In both cases, dissolution occurred via classical step retreat. The similarity in the layer stacking in both materials led to equivalent structure dissolution in both cases. The 0.9 nm layers dissolved first to 0.7 nm (closed cages) then to 0.4 nm (unstable intermediates). Dissolution of SAPO-18 revealed unusual spiral dissolution pits near the core of the dislocations. CHA/AEI intergrowth materials were also prepared using a dual-template method, where two templates, morpholine for CHA and N,N-diisopropylethylamine for AEI, were combined during synthesis. The phase transition from CHA to AEI occurred at different molar ratios with different synthesis procedures. XRD modelling confirmed the synthesis of an intergrowth phase at a molar ratio of 70% morpholine and 30% DPEA. Changes in chemical shift in the 13C MAS-NMR were used to observe the different template interactions with the framework as the ratio of CHA and AEI cages changed.

The present Ph.D. thesis deals with the hydrogen production via a novel process involving a biogas autothermal reforming (ATR) unit with the adoption of a catalytic wall-flow filter located downstream from the ATR processor to effectively filter and in-situ gasify the carbon emissions eventually generated. This work was aimed to produce 50 Nm3/h of green hydrogen from the ATR of a model biogas (60:40 Vol ratio) by using catalytic structured supports. Moreover, a solution for the eventual carbon formation during the biogas ATR was addressed. A nanostructured delafossite catalyst to ensure the gasification of soot in absence of O2 was synthesized. In addition, a Life Cycle Assessment (LCA) and a techno-economic analysis for the hydrogen production from biogas were also carried out. Concerning the identification of the suitable support structure to improve the coupling of exothermic and endothermic reactions during the hydrogen production from biogas ATR, homogenous SiSiC lattices composed of Cubic, Octet and Kelvin cells and the Conventional Foam structure coated with Ni based catalysts doped with noble metals were investigated. The different catalytic geometries were tested using a model biogas composed of clean methane and carbon dioxide (60:40 Vol ratio) with a steam to carbon ratio (S/C) fixed at 2.0. The effect of the space velocity, inlet temperature and oxygen to carbon ratio (O/C) on methane conversion and hydrogen yield were studied for each catalytic support. The O/C ratios evaluated was equal to 1.0, 1.1 and 1.2. Space velocity (GHSV) values from 2000 to 20000 h-1 in standard conditions (equivalent to 5000- 85000 h-1 in operating conditions), and, inlet temperatures of 500, 600 and 700°C were employed. The combined effect of chemical reaction and some properties and parameters such as: pressure drop and specific surface area on the steady-state performances of an adiabatic reactor at high flow rates has been analyzed. ASPEN simulations were performed to calculate the thermodynamic equilibrium at the different boundary conditions to validate the data and to determine the hydrodynamic properties. This study has demonstrated that the rotated cubic cell support shows the best performance in transforming the biogas into hydrogen with high CH4 conversion (<95%) and an H2 yield higher of 2.1 using an O/C ratio of 1.0, 1.1 and 1.2, S/C ratio of 2 and GHSV of 20000 h-1. Besides, this support can ensure a high reliability of the ATR process due to its lower pressure drop (6-40 Pa/m) with the lower specific surface area comparing to the other structures tested. The conventional foam has presented also good performances for all the GHSV values in terms of CH4 conversion but it is less selective for hydrogen production. With respect to the catalyst for gasification of carbon in a reducing atmosphere (H2, CO, H2O, CO2), nano-materials based on transition metal were synthesized via a solution combustion synthesis (SCS) method. LiFeO2 catalyst was selected as the most promising candidate for the soot gasification catalyst on the soot trap application close coupled to the ATR reactor for syngas post-treatment process. Afterwards, some issues in mixed atmosphere, i.e., when simultaneous carbon gasification with CO2 and steam in the presence of H2 and CO take place, were studied. It was demonstrated that the carbon gasification is inhibited during an isothermal reaction at 650°C for 40 minutes when CO and H2 are used as co-reagents. But even in these extreme reduced conditions, the LiFeO2-catalyst gasified 32.9% of the initial carbon, compared to 8% for the non-catalytic case. when H2 is used as co-reagent in the steam carbon gasification, the reaction is inhibited, the carbon conversion decreases from 73.1% to 46.6%. Analogously, when CO is a co-reactant in the carbon gasification with CO2, the reaction is inhibited, the soot conversion declines from 70.2% to 31.6 %. However, it was observed that in mixed atmosphere gasification reactions, when CO2 and H2O simultaneously reacts with carbon, there is a passive combination of steam and carbon dioxide in the gasification reaction. This means that the two gases operate on separated active sites without influencing each other. LiFeO2 was also coated on the monoliths (15/20 μm mean pore size and 45% porosity) and the coated filters’ performance was evaluated during the soot particles loading. The pressure drop across the filters was very low (<8 mbar) during loading showing that the applied coated method on the filters was successfully. On the other hand, the catalytic filter coupled with the rotated cube cell was tested at the pilot plant to examine their interaction, the effect of the coating method and the penalty in pressure drop of all system. A pressure drop of 0 – 68 mbar obtained during the test proves that the coating method did not alter the operation of the plant. As for testing at the demonstration plant, firstly, a monolith (Rh/Pt) was tested close coupled with an uncoated filter using an O/C ratio from 0.9 to 1.3, S/C ratio equal to 2.0, an inlet temperature (Tin) of 450°C with a GHSV from 5000 to 14000 h-1. The overall result fully agrees with the prediction from the simulation. The thermodynamic equilibrium was reached during the testing time with a methane conversion of 98% and hydrogen yield of 2.0. Moreover, tests with the integration of the catalyzed conventional foam and the catalytic trap downstream of the reforming reactor were performed. The boundary conditions were a space velocity of 4000, S/C= 2 and O/C=1.1. A thermodynamic equilibrium and a methane conversion higher than 98% were achieved. The plant was able to reach the predicted conversions and concentrations at nominal capacities corresponding to 50 Nm3/h (100 Kg/day) of pure hydrogen, creating a negligible pressure drop during the operation time of the processor. Finally, this thesis also deals with a comparative LCA of three different hydrogen production process from biogas. The investigated processes are: the biogas ATR, the biogas steam reforming (SR) and the water hydrolysis (a biogas-fueled internal combustion engine (ICE) followed by an electrolyzer). They were compared using environmental (GWP) and energetic (GER) impacts in order to highlight their weaknesses and strengths. H2 from biogas ATR has been demonstrated to be the most promising process in terms of the emissions reduction and energetic efficiency considering its life cycle from the extraction and processing of raw materials to the production of high purity hydrogen. The ICE + Electrolyzer process require a large amount of energy and biogas to sustain the electrochemical reactions. This feature makes such system the least energetically efficient with the most negative environmental impact. With a process efficiency of 65%, 63% and 25% for ATR, steam reforming and electrolysis process, respectively. Lastly, the economic analysis was performed to evaluate the H2 final cost. On the one hand, it was found that the process is economically favorable for H2 production higher than 100 Nm3/h. On the other hand, in 10 years of amortization using this technology, the final cost for H2 production of 100 Nm3/h from biogas is 3€/Kg H2, lower than the European target (5€/kg H2). The longer the plant life is, the more affordable the initial investment is.

The present Ph.D. thesis provides some examples of innovative 2nd generation catalytic processes for the conversion of renewable raw materials into green value-added chemicals. In particular, D-glucose and some its derivatives, all ideally representing waste materials of dedicated biomasses, agricultural residues, or solid organic urban waste exploitation in the biorefinery plant, were converted into useful chemical building-blocks. After a brief introduction to the topic and the description of the experimental method, each chapter of the work is based on one or more scientific articles either published or submitted. Among the possible catalytic reactions, the hydrogenation, oxidation and hydrodeoxygenation were investigated: for this purpose, several novel catalysts were synthetized, tested and characterized. The catalysts were made from precursor solutions with the incipient wet impregnation method or with the solution combustion synthesis, depending by the catalyst type. The conversion of glucose and some glucose-derivatives was typically performed under gentle operative conditions and in aqueous mean. Pt-based catalysts were tested for glucose conversion to adipic acid in a two-step process carried out in water solution without any pH control by investigating the effect of a series of supporting materials (active carbon, alumina, silica and ceria). The process consisted in the D-saccharic acid (SacA) production by D-glucose catalytic wet air oxidation followed by a hydrodeoxygenation treatment of SacA to adipic acid (AA) with the same catalyst. The main limit of using Pt for D-glucose oxidation is represented by the catalyst inhibition operated by the first product of the reaction, the gluconic acid (GluA), which prevents the consecutive reaction of SacA formation, but a deeper investigation of the reaction scheme allowed us to assess that over Pt/alumina the consecutive oxidation of gluconic acid to SacA is slightly favored under uncontrolled pH too.We have demonstrated that a 5.2 wt.% Pt on γ-alumina sample, the catalysts presenting the larger amount of strong Brønsted acid sites, was the best material for obtaining SacA (with a molar yield of about 13.5%); afterward, by performing the halogen-promoted hydrodeoxygenation of the resulting solution, the SacA was quantitatively converted into AA (and thus the overall adipic acid molar yield from glucose was about 13.0%). Effectively, The efficient conversion of common biomass derivatives, as D-glucose, into value-added chemicals has received a great deal of attention in the last few years. Several heterogeneous catalytic systems, characterized by noble metals, have already been investigated for the Catalytic Wet Air Oxidation (CWAO) of derived biomass. Nevertheless, the redox effect of such catalysts on biobased compounds has not been described in detail. In the present thesis, some perovskite type oxides (Fe, Co, Mn) that present high redox properties and stability under hydrothermal conditions have been tested to establish their ability to convert D-glucose into C6 aldaric acid, lactic acid (LacA) and levulinic acid (LevA). The influence of the reaction temperature, and the affinity of the catalysts to hydrogen and oxygen on the distribution of the liquid products have been investigated. In the best conditions, 50.3 mol.% and 69.5 mol.% of lactic and levulinic acid have been obtained by employing LaCoO3 and LaMnO3, respectively. Apart from the oxidative effect, which has led to several oxidation products, a high reductive effect of the catalysts has enabled the conversion of some key intermediates, such as pyruvic acid (PyrA) and hydroxymethylfurfural (HMF), into the desired products. LaMnO3, which has resulted to be the most oxidizable/reducible catalyst over a low temperature range, has shown the best performance of the studied perovskite type oxides; it has been found to promote the conversion of hydroxymethylfurfural to levulinic acid and to give the highest overall molar yield. Moreover, performing catalysts have been synthetized through incipient wet impregnation and tested for cis,cis-muconic acid (ccMA) hydrogenation to adipic acid. Before the hydrogenation, the investigation on the solubility of ccMA dissolution in different polar solvents has been carried out by characterizing and modelling the dissolution as a function of temperature. Water, ethanol, 2-propanol and acetic acid have been investigated as solvents in the range temperatures from a 298.15 to 348.15 K. Owing to the absence of ccMA solubility data, the reliability of the adopted experimental set-up was validated comparing published and experimental solubility data of a similar compound, that is, AA. From the results, it has emerged that the employed system is appropriate for the determination of molar fractions of an organic compound dissolved in polar solvents. The molar fraction and temperature were correlated using the Apelblat equation model, which is applied for the mathematic fitting of experimental data. A total relative average deviation of 3.54% was obtained for the experimental results and the solubility data obtained with the model, thus attesting the adequacy for this study. The use of Apelblat equation also allowed to determine the apparent molar enthalpy and molar entropy of dissolution. The dissolution of ccMA in water, ethanol, 2-propanol and acetic acid, over temperatures ranging from 298.15 to 348.15 K, has been shown to be endothermic. The activity of Pt-based catalysts has been compared with a Ni-based catalyst at a gentle condition. A supported 14.2 wt.% Ni on γ-alumina converted 100% of muconic acid, yielding 99.4 mol.% of AA. Finally, the oxidative cracking of 5-keto-L-aldonic acids to tartaric acid (TarA) was successfully performed at room temperature and atmospheric pressure in a carbonate buffer (pH = 10.34), by employing various V-based catalysts. The performance of the novel heterogeneous V-based catalysts was compared with the one of a conventional homogeneous system. The effect of the catalysts was obvious and 2%VOx/ZrO2 was found to be the best catalyst for the 5-keto-aldonic acids conversion to tartaric acid. The tartaric acid selectivity was equal to 74.5% and 44.3% starting from the 5-keto-D-gluconic acid (5kGl) and 5-keto-L-galactonic acid (5kGa), respectively. The best performances in terms of tartaric acid selectivity were obtained at the beginning of reaction, and about one fourth of the carbon moles were converted into tartaric acid after 24 h of reaction. The substrate was entirely converted after 24 h indicating that several by-products were also produced during the reaction. So, an overall reaction pathway was supposed and the effect of the vanadium structure to the catalytic activity was hypothesized. Moreover, the reaction mechanism of the 5-keto-aldonic acids conversion to tartaric acid promoted by the anchoring VOx-support bond was described.

Seven β-triketimine nickel complexes C1-C7 with composition [L1-7Ni(μ-Br)2NiL1- 7][BArF4]2, where L1 = HC{C(Me)=N(2,4,6-Me3C6H2)}3, L2 = HC{C(Me)=N(2,6- Me2C6H3)}3, L3 = HC{C(Me)=N(2,4-Me2C6H3)}3, L4 = HC{C(Me)=N(2-MeC6H4)}3, L5 = HC{C(Me)=N(2,4,6-Me3C6H2)}2{C(Me)=N(2,6-Me2C6H3)}, L6 = HC{C(Me)=N(2,4,6-Me3C6H2)}{C(Me)=N(2,6-Me2C6H3)}2, and L7 = HC{C(Me)=N(2,4,6-Me3C6H2)}{C(Me)=N(2,6-iPr2C6H3)}2 were synthesized from the interaction of nickel(II) bromide with L1-7 in the presence of NaBArF (BArF = [(3,5- (CF3)2C6H3)4B]−). These complexes were then fully characterized by single-crystal X- ray diffraction (XRD), MALDI-MS and elemental analysis. From XRD results, they were found to be five-coordinated dimeric bromide-bridged species [LNi(μ- Br)2NiL][BArF]2. The geometry at nickel was distorted square pyramidal, with the τ parameter in the range 0.05 to 0.28. In addition, an enamine-diimine nickel complex C8: (L2-NiBr2) was synthesized from triketimine ligand L2 and nickel dibromide in THF, thus lacking the weakly co-ordinating BArF anion. This complex was found to be pseudotetrahedral, where only two of the three imine nitrogen atoms co-ordinated. These two nitrogen atoms and two bromine atoms formed the coordination shell of Ni(II). The six-membered ring [Co-N1-C2-C3-C4-N2] adopted a boat conformation. These complexes (C1-C7) were screened in the polymerization of ethylene monomer using methylaluminoxane (MAO) as cocatalyst in toluene as solvent at 30°C. It was observed that the steric and electronic variations conferred on the complexes by ligands L1-7 had a strong influence on the activity and also on the properties of the produced polyethylene. The catalytic activity decreased in the order C2 > C1 > C6 > C5 > C7 in the range 3229 to 271 kg PE (mol Ni)-1 h-1 for a standard set of conditions (3 bar ethylene, 30 ̊C, Al:Ni 2000), while the catalysts C3 and C4, bearing only a single ortho substituents, were inactive under identical conditions. Those conditions also had strong influences on catalyst activity and polymer properties: Al:Ni ratio in the range 500 to 3000 maximized activity at 2000. For the polymerization temperature in the range 20 to 50 °C, the activity was maximized at 30 °C, while the number of branches increased with temperature while Mn decreased due to increased chain transfer. Increasing the polymerization pressure resulted in fewer branches while the molecular weight increased because of high concentration of ethylene monomer. The effect of the nature of the counterion on polymerization activity and on the polymer properties was investigated when ethylene was polymerized by C8 (N,N-Ni) and C2 (N,N,N-Ni). It was found that polyethylene produced by C8 had significantly greater crystallinity (Tm 59 ̊C, 35 branches per 1000 carbons) than that produced by C2 (Tm 36 ̊C, 53 branches per 1000 carbons). The presence of the weakly nucleophilic counterion (BArF) as in C2, may have facilitated chain walking, resulting in a branched polymer, whereas [MeMAO]- (C8) was a slightly more nucleophilic counterion impeding chain walking. Furthermore, activity was also much greater for C2 than for C8. This is the first report of an anion effect on branching.

L’intégration monolithique de matériaux semi-conducteurs III-V sur substrat de Silicium est essentielle pour le développement de la photonique sur Silicium. L’objectif est de réaliser une micro-source optique à base d’un réseau ordonné de Nanofils (NFs) III-V (InAsP/InP) placés sur un guide d’onde Si. De par leur aptitude à relaxer les contraintes, les NFs sont d’un grand intérêt. C’est dans ce contexte que s’est déroulée cette thèse axée sur la croissance autocatalysée de NFs InP sur Silicium par épitaxie directe. Nous avons ainsi montré que la croissance auto-catalysée de NFs InP denses et verticaux dépend directement de la nature de l’oxyde de surface du substrat Si. Une distribution monomodale ou bimodale de NFs ont été achevées en fonction des conditions de formation des gouttelettes d’indium ou des paramètres de croissance. Une pression critique et une température critique ont permis de délimiter des domaines favorables à la croissance. Les propriétés optiques intrinsèques des NFs ont été déterminées suffisantes pour l’objectif visé. Enfin, des résultats sur la simulation optique et la polarisation de la lumière émise dans les NFs et le guide d’onde ont permis d’établir un cahier des charges pour la croissance des NFs verticaux sur SOI pour que le couplage/partage de leurs modes optiques soit le plus efficace possible aux longueurs d’onde télécom
Monolithic integration of III-V semiconductors materials on Si substrate is essential for the Si photonic development. We aim at achieving an optical microsource based on a regular array of III-V (InAsP/InP) nanowires (NWs) standing on top a Si waveguide. Due to their ability to be fully relaxed, nanowires growth is of deep interest. This PhD thesis has been oriented towards such context especially among self-catalyzed InP NWs growth by epitaxy. Thus we have shown that highly dense and vertical self-catalyzed InP NWs accomplishment is related to Si substrate surface oxide. A monomodal or bimodal NWs distribution have been reached through a control of indium droplets formation or growth parameters. A critical pressure and a critical temperature have been found to delimit favorable growth regime. Intrinsic optical properties have been determined to be goal sufficient. Optical simulation modeling and characterization of the polarization light state in NWs and in the Si waveguide have led us to establish functional specifications to grow vertical NWs on SOI as way that their optical modes could be coupled efficiently at telecommunications wavelength