Dissertations / Theses on the topic 'Nanocatalysi'

L’univers de la nanocatalyse reste encore un domaine peu exploré notamment à cause de la difficulté de pouvoir synthétiser de manière simple et contrôlée les nanoparticules et de la mise en place d’un système réactionnel adaptable à ce type de catalyse hétérogène. Dans ces travaux de thèse nous montrons qu’il est possible d’obtenir des nanoparticules de cobalt hc en partant du complexe CoCl(PPh3)3 facile d’accès et en le chauffant simplement dans l’oléylamine. Le mécanisme de synthèse basé sur la dismutation de ce complexe de cobalt(I) a été prouvé par des études expérimentales et théoriques. Nous montrons également qu’il est possible de contrôler la taille et la forme de ces nanoparticules en changeant certains paramètres de réactions comme la durée ou la nature du précurseur métallique. De plus, en appliquant ce protocole à d’autres métaux (notamment le nickel) nous avons réussi à obtenir des nanoparticules et également à former des alliages bimétalliques CoxNi1-x. Nos nanoparticules ont été utilisées dans des réactions d’hydrogénations et de transferts d’hydrogène en présence de NH3BH3 (principalement sur des alcynes) et ont montré leur efficacité tant au niveau des conversions que sur la sélectivité. Nous avons pu comparer ces résultats avec ceux obtenus en phase homogène en partant de différents complexes de cobalt. Une étude approfondie de cette catalyse homogène a été faite, montrant une fois encore l’efficacité du cobalt (tant sous la forme de nanoparticules que de complexes) sur les réactions d’hydrogénation et de transfert d’hydrogène. Ces résultats ouvrent de grandes perspectives quant à l’utilisation des métaux non nobles pour le stockage et l’utilisation du dihydrogène, permettant un accès plus simple vers des applications dans le domaine de l’énergie
Nanocatalysis universe is a field which is yet to be explored, especially because of the difficult access to simple and well-controlled nanoparticles and their uses in heterogeneous catalyzed reactions. In this work, we show that it is possible to obtain hcp cobalt nanoparticles starting from the easily accessible CoCl(PPh3)3 and by simply heating it in oleylamine. The mechanism of this reaction based on the disproportionation of the cobalt(I) was proved by experimental and theoretical studies. We also demonstrate that it is possible to control the size and the shape of those nanoparticles by changing some parameters like the reaction time or the nature of the organometallic precursor. Moreover, by using the same protocol with other metals (especially nickel) we were able to obtain nanoparticles and then to form CoxNi1-x bimetallic alloys. Our nanoparticles were used for hydrogenation and hydrogen transfer reactions in presence of NH3BH3 (mainly on alkynes) giving good conversions and selectivities. We then compare those results with homogeneous catalysis, using different cobalt complexes. We made an in-depth study of this homogeneous catalysis which shows once again the efficiency of cobalt (as nanoparticles or organometallic complexes) on hydrogenations and hydrogen transfers. Those results offer new opportunities concerning the use of non-noble metals for the storage and the use of dihydrogen, allowing easier access towards energy applications

L'élaboration de méthodes de synthèse, basées sur l’utilisation d’espèces métalliques a été un sujet de tous les instances en chimie organique. Malgré l’efficacité des métaux utilisés en catalyse homogènes, leurs procédures de recyclage restent limitées. Ce pourquoi, une contrainte supplémentaire a été placée dans la conception de catalyseurs, pouvant offrir à la fois l'efficacité de la catalyse homogène et le recyclage de l’hétérogène. Dans ce contexte, les nanoparticules métalliques sont apparues comme objet phare, en raison de leurs propriétés physico-chimiques inégalées. On a découvert que les nanoparticules de métaux nobles présentaient des propriétés catalytiques similaires dans certains cas, aux complexes monoatomiques. De plus, les Au NPs ont montré une activité catalytique remarquable dans l'oxydation d’alcools activés sous O2. Nous avons donc envisagé des procédures multicatalytiques, basées sur les NPs d’Au. Notre choix d'utiliser des catalyseurs solides était pertinent, puisque les nano-catalyseurs, pour lesquels la fraction de sites actifs se trouve en surface, limitent les risques de cross-quenching. Ici, nous présentons trois nouveaux procédés bicatalytiques permettant l’accès, à des chromenes/quinoléines (53-93%) via une oxydation / Michael Addition/ aldolisation, combinant nanocatalyse et catalyse basique, l’accès à des ortho-THC (50-81%) via oxydation / arylation / cyclisation, combinant nanocatalyse et catalyse supportée, ainsi qu’une une oxydation / hydrolyse en cascade, pour accéder à l’HMLA (86%, sel 93%), un grand panel de produits d'activité biologique reconnue, utilisé en parfumerie ou visant une pré-industrialisation via la chimie en flux continu
Elaboration of synthetic methods based on metal-catalyzed reactions has been a hot topic in organic chemistry. Despite good efficiency, catalysis proceeding homogeneously, are limited in the operation of recovering/recycling of the catalysts. An important stress was placed to design catalysis, offering both the efficiency of homogeneous catalysts and the recyclability of heterogeneous catalysts. In this context, metal nanoparticles merged as a key tool, due to their unique physical and chemical properties. Notably, Au NPs have shown remarkable catalytic activity in the oxidation of activated alcohols under O2 atmosphere. Since now, the access to more complex molecules is the next step forward for this field, we envisioned multicatalytic roads, based on the oxidation of activated alcohols via supported Au NPs. Our choice of using solid catalysts was relevant, since nanostructured catalysts for which the fraction of active sites are located on the surface, limit the risk of cross-quenching. The latter carbonyl formed, could be further converted in situ, via tandem protocol. Herein, we developed novel, atom- and step-economical bicatalytic one-pot processes, to access substituted chromenes/quinolines (53-93%) by tandem oxidation/hetero-Michael addition/aldolisation combining nanocatalysis and base catalysis, ortho-THCs (50-81%) via tandem oxidation/arylation/cyclisation combining nanocatalysis and supported catalysts and a tandem cascade oxidation/hydrolysis to access HMLA (86%, sel 93%). A large panel of products of biological activity relevance, pertaining to the fragrance chemistry or aiming in some cases, pre-industrial scalability via continuous flow applications

Metal nanoparticles have a large surface area to volume ratio compared to their bulk counterparts, which makes them attractive to use as catalysts. Atoms on the surface of metal nanoparticles are very active due to their high surface energy resulting from their unsatisfied valency. First synthesis of gold nanoparticles with different shapes and bimetallic structure are explored in detail. Then an experimental method which could distinguish between the two mechanisms (homogeneous or heterogeneous) by using hollow plasmonic gold nanocatalyst is developed. Furthermore the catalytic activity of gold nanocages was changed by adding an inner platinum or palladium nanoshell. Results suggested that adding palladium inner shell increased the activity of gold nanocages towards the reduction nitro groups to amino groups. Controlling the selectivity of the catalyst is an important goal of catalysis research. Lastly selectivity of the plasmonic nanocatalyst (Gold sphere-Gold shell Nanorattles) with multiple plasmon modes was studied for photo-dimerization of nitro groups into azo dimers were studied on gold nanocatalyst surface. Results showed that selectivity can be controlled by changing the wavelength of the light exciting surface plasmon.

The key aim of this thesis was to develop titanium-containing mesoporous catalysts (Ti-MCM-41) and supported Pt catalysts on mesoporous materials (Pt/Al-MCM-41) with specific functionality to direct the target reactions by a green method. Both catalysts have high surface area and size-confined nano-pore to enhance the activity for oxidation reactions. A one-pot room-temperature direct synthesis method was developed for a series of amorphous Ti-MCM-41 with and without Brønsted acid sites (BAS). The investigation was focused on the relationship between the acidity and the formation of surface active sites for cyclohexene oxidation using hydrogen peroxide. The formation of intermediates peroxo-titanium and superoxo-titanium was confirmed by diffuse reflectance UV-visible spectroscopy and electron paramagnetic resonance (EPR) spectroscopic studies. The relationships between Ti precursors and the local coordination structure of Ti-MCM-41 were investigated and evaluated in cyclohexene oxidation. DRUV-visible and EPR spectroscopies investigation have provided evidence that the nature of the oxo intermediates formed on contact with H2O2 depends on the intrinsic local structure and environment of the Ti ions. Well dispersed and size-confined Pt nanoparticles into Al-MCM-41 were successfully prepared and evaluated in benzyl alcohol oxidation. With a small amount of acidic OH groups covered by Pt particles over Pt/Al-MCM-41 exhibited excellent conversion and selectivity due to the electron transfer between Pt and the supports. The influence of the alkali-treatment of Pt/Al-MCM-41 on the mesoporous structure for benzyl alcohol oxidation was investigated. Alkali-treatment apparently influenced the pore properties and the surface area of the catalysts. The catalysts prepared with acidic supports had higher conversion than those with alkali-treated catalysts.

Metal nanoparticles have received much interest for their application in catalysis due to high surface-to-volume ratios resulting in more available active sites. Ideally these catalysts are heterogeneous and allow for facile separation from the catalytic reaction mixture making them ideal for industrial application. Dispersed metal nanoparticles are explored due to their high reactivity in solution and are stabilized by surfactants and polymers. However, it is difficult to determine whether or not a catalyst is truly heterogeneous as a certain degree of leaching from the metal nanoparticle is inevitable. Determining the mechanisms involved in nanocatalysis is also a challenge. In this study, a series of dispersed palladium nanocatalysts in the Suzuki reaction with phenylboronic acid and bromobenzene were characterized before and after catalysis to determine what changes occur. Samples where characterized before and after the catalytic reaction by XPS, SEM, and EDS to monitor changes in particle size and composition. Reaction mixtures after catalysis were analyzed by ICP-MS for leached palladium species to determine if concentrations were high enough for homogeneous catalysis to take place. The dispersed palladium nanoparticles studied experienced growth during the catalytic process and a significant amount of leaching. XPS analysis indicates the presence of aromatic species on the particle surface after the catalytic reaction. The aromatic species is likely biphenyl, the product of the catalytic reaction, as the presence of boron and bromine was not found in XPS and EDS analysis.

L’ús de catalitzadors actius y selectius en processos industrials pot minimitzar la formació de residus no reciclables. Entre els procesos catalítics més comuns, la semi-hidrogenació d’alquins en alquens ha sigut objecte d’especial atenció per la seva rellevància en les indústries petroquímica, de polímers i de química fina. La selecció de catalitzadors heterogenis adequats pot millorar la productivitat i evitar problemes de sobre hidrogenació i/o oligomerització. Aquesta tesi tracta de la síntesi i caracterització de nous catalitzadors col•loïdals per la seva aplicació en reaccions d’hidrogenació selectiva utilitzant disseny d’experiments (DOE). Es proposen noves síntesis de nanopartícules de Pd, així com metodologies eficients per la planificació d’experiments, demostració de reproductibilitat i tractament analític de dades de TEM. Es va estudiar la relació estructura-síntesis de nanopartícules utilitzant DOE i es va avaluar l’efecte de diversos paràmetres sobre la mida, distribució i forma de les nanopartícules així com sobre l’eficàcia de la síntesis. Els paràmetres i iteracions clau es van ressaltar obtenint una recepta de nanopartícules col•loïdals ben definides. La impregnació d’aquestes nanopartícules en diversos suports catalítics es va fer utilitzant síntesis d’una i dos etapes, i es va estudiar l’efecte de la immobilització, els paràmetres de síntesis, el suport catalític, el contingut de Pd i la relació de síntesis sobre la mida i dispersió de les nanopartícules. Finalment, es va realitzar un estudi cinètic de la hidrogenació amb 1-octí sobre quatre catalitzadors suportats utilitzant DOE. La concentració de 1-octí, la pressió d’hidrògen i la temperatura es van modificar segons els experiments dissenyats, i tan sols van ser necessaris 24 proves catalítiques per obtenir expressions cinètiques robustes que van permetre comparar el rendiment dels catalitzadors. Aquesta tesi ofereix un anàlisis profund del disseny de nous nanocatalitzadors basats en Pd per a la seva aplicació en reaccions de semi-hidrogenació d’alquins utilitzant metodologies pràctiques i efectives.
El uso de catalizadores activos y selectivos en procesos industriales puede minimizar la formación de residuos no reciclables. Entre los procesos catalíticos más comunes, la semi-hidrogenación de alquinos en alquenos ha sido objeto de especial atención por su relevancia en las industrias petroquímica, de polímeros y de química fina. La selección de catalizadores heterogéneos apropiados puede mejorar la productividad y evitar problemas de sobre hidrogenación y/o oligomerización. Esta tesis trata de la síntesis y caracterización de nuevos catalizadores coloidales para su aplicación en reacciones de hidrogenación selectiva utilizando diseño de experimentos (DOE). Se proponen nuevas síntesis de nanopartículas de Pd, así como metodologías eficientes para la planificación de experimentos, demostración de reproducibilidad y tratamiento analítico de datos de TEM. Se estudió la relación estructura-síntesis de nanopartículas utilizando DOE y se evaluó el efecto de varios parámetros sobre el tamaño, distribución y forma de las nanopartículas así como sobre la eficacia de la síntesis. Los parámetros e interacciones clave se resaltaron obteniendo una receta de nanopartículas coloidales bien definidas. La impregnación de estas nanopartículas en diferentes soportes catalíticos se realizó utilizando síntesis de una y dos etapas y se estudió el efecto de la inmovilización, los parámetros de síntesis, el soporte catalítico, el contenido de Pd y la relación de síntesis sobre el tamaño y dispersión de las NPs. Finalmente, se realizó un estudio cinético de la hidrogenación con 1-octino sobre cuatro catalizadores soportados usando DOE. La concentración de 1-octino, la presión de hidrógeno y la temperatura se modificaron según los experimentos diseñados, y solo fueron necesarias 24 pruebas catalíticas para obtener expresiones cinéticas robustas que permitieron comparar el rendimiento de los catalizadores. Esta tesis ofrece un análisis profundo del diseño de nuevos nanocatalizadores basados en Pd para su aplicación en reacciones de semi-hidrogenación de alquinos utilizando metodologías prácticas y efectivas.
Heterogeneous catalysts offer an essential tool to achieve a suitable use of energy and chemicals. Indeed, the use of active and selective catalysts in industrial processes can minimize the formation of non-recyclable waste. Among the most commonly applied catalytic processes, the semi-hydrogenation of alkynes into alkenes has been the object of particular attention for its relevance in the petrochemicals, polymer and fine chemical industries. Indeed the selection of proper heterogeneous catalysts derives in productivity improvements preventing over-hydrogenation and/or oligomerization issues. The thesis dealt with the synthesis and characterization of novel catalysts prepared by colloidal approach for application in selective hydrogenation reactions using design of experiments methodology (DOE). Novel synthesis of colloidal Pd NPs was proposed as well as efficient methodologies for the experiment planning, reproducibility demonstration and analytical treatment of TEM data. Two NPs structure-synthesis relationship studies were performed using DOE. The effect of several parameters on the NPs size, distribution, shape and synthesis efficiency were assessed. The key parameters and interactions were highlighted and recipe of well-defined colloidal NPs were delivered. Impregnation of these NPs on different catalytic supports was performed using one pot and two-step syntheses. The effect of the immobilization process, parameter of synthesis, catalytic support, Pd content and scale of the synthesis on the NPs size and dispersion were studied. Finally, a kinetic study of the 1-octyne hydrogenation over four supported catalysts was performed using DOE. The 1-octyne concentration, hydrogen pressure and temperature were varied according to designed experiments: only 24 catalytic tests were performed to obtain robust kinetic expressions for the four catalysts. Thanks to these kinetic data, their performances were compared. This thesis offers a deeper analysis on the design of new Pd-based nanocatalysts for application in alkyne semi-hydrogenation reactions using practical and effective methodologies.

Propylene is the second most important starting chemical in the petrochemical industry after ethylene. Unlike ethylene, propylene readily undergoes substitution reactions including polymerisation, oxidation, halogenation, hydrohalogenation, alkylation, hydration, oligomerization and hydroformylation, which lead to a wide variety of important downstream products. One of the principal uses of propylene is to produce key chemicals from selective oxidation. In 2016, the world annual production of propylene is about 94 million tonnes, and the global proportion used to produce selective oxidation product is over 18%. They constitute a key part of the chemical industry and contribute towards substantial economic benefits. The application of Ag based heterogeneous catalysts to selective propylene oxidation is a key factor in the synthesis of nearly all downstream chemicals, however billions of pounds are lost every year due to unplanned reactor shutdown, safety control and environment unfriendly emission control as a results of inefficiency catalytic selectivity and activity. Despite, both theoretical and experimental research works have been intensively involved, the fundamental reason leading to these effects are not yet well understood. The work presented in this thesis explores a range of novel modification techniques that alter the activity of Ag nanocatalysts for selective propylene oxidation, especially in propylene epoxidation. Particular focus is placed on developing surface modified Ag catalysts through morphology control, surface architecture engineering with another sublayer metal. Using a combination of modelling, novel and traditional materials characterisation methods, it is found that these modification result in some significant electronic and/or geometric alterations to the Ag nanoparticles surface. The Ag-Ag bond distance can be dramatically enlarged by exposing a high-index Ag surface or a core-shell structure with monolayer Ag shell. When interacting with molecular oxygen, the molecular oxygen adsorption and dissociation behaviour is sensitive to the geometric changes in Ag surface. This leads to an enhanced selectivity toward propylene epoxidation than combustion resulting from preventing a C-H bond cleavage. Finally, be creating atomically dispersed Ag on zeolite, a completely different interaction between molecular oxygen and single atom Ag were discovered comparing to on a extensive silver surface. This leads to the observation of an excitingly new propylene oxidation reaction producing ethanol and CO₂ resulting from C=C bond cleavage. Overall, the research presented within this thesis demonstrated a number of methods for the intelligent design of novel heterogeneous Ag catalysts with remarkable activity and selectivity toward specific selective propylene oxidation. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions.

We report on the fabrication of a new complex catalytic system composed of silica-supported silver nanoparticles (AgNP) encapsulated inside polymer microcapsules (MC)s. The silver nanocatalyst itself was obtained by reduction of silver salt in the presence of SiO₂ particles acting as AgNP carriers, to provide a complex Ag/SiO₂ catalyst with the Ag surface completely free of capping agents. Ag/SiO₂ particles were enclosed inside the interior of polymer microcapsules. Due to the presence of the hydrophobic shell on the MC surface, catalytic reactions become feasible in an organic solvent environment. On the other hand, the hydrophilic nature of the MC interior forces the water-soluble reactants to concentrate inside the capsules which act as microreactors. Based on the example of catalytically driven reduction of 4-nitrophenol we demonstrate that encapsulated Ag/SiO₂ particles possess enhanced catalytic activity as compared to the catalyst being freely dispersed in reaction medium.

La catalisi ha profondamento modificato la nostra società e giocherà un ruolo chiave nella risoluzione della crisi energetica ed ambientale che stiamo affrontando in questo secolo. Il grande vantaggio nello sviluppo dei nanomateriali nel regno della nanotecnologia ha portato a possibilità impreviste anche per la progettazione di nuovi catalizzatori. La produzione e la comprensione del funzionamento di catalizzatori ad alta efficienza basati su materiali nanostrutturati è lo sforzo del campo emergente della nanocatalisi. Negli ultimi anni, i nanocatalizzatori sono stati ampiamente studiati e si è registrato un costante progresso nella loro produzione su larga scala. La tecnologia è tuttora in evoluzione ed ulteriore ricerca è necessaria per capitalizzare appieno il suo potenziale. I metodi computazionali sono molto adatti a studiare il funzionamento dei nanocatalizzatori e a fornire importanti informazioni da un punto di vista atomistico. Un accurato ed efficiente metodo è rappresentato dalla teoria del funzionale della densità (DFT). In questa tesi, abbiamo esplorato le caratteristiche chimiche e fisiche di clusters metallici supportati e di film sottili di ossidi utilizzando principalmente il metodo basato su DFT. Questi materiali sono di particolare interesse nella catalisi e in molte altre applicazioni, a causa delle loro caratteristiche uniche che derivano dalla nanostrutturazione. In particolare, abbiamo studiato la geometria, lo stato di carica, l’interazione cluster-supporto, e la reattività di clusters metallici sub-nanometrici supportati su ossidi. In un caso particolare abbiamo inoltre affrontato il ruolo della dimensione in nanoparticelle metalliche più grandi. Per quanto riguarda i clusters supportati, abbiamo verificato che le forze di dispersione di van-der-Waals sono molto importanti per la corretta descrizione dell’interazione cluster-supporto. Inoltre, abbiamo stabilito che difetti e dopanti presenti sulla superfice del supporto ossido hanno un'influenza determinante sui cluster, determinandone intrinsecamente la reattività. Anche la modifica dei cluster attraverso la formazione di leghe altera l’interazione metallo-supporto, e può essere sfruttata per evitare l’agglomerazione dei clusters. La nanostrutturazione del supporto a base di ossido può generare nuove proprietà del materiale e in questo contesto abbiamo esaminato le caratteristiche di un film ultrasottile di ossido supportato su metallo. Infine, abbiamo eseguito studi meccanicistici che hanno contribuito a chiarire il meccanismo di reazione dell’ossidazione di CO su catalizzatori a base di Au/TiO2 e dell’idrogenazione di CO2 su catalizzatori a base di Ru/TiO2 and Cu/TiO2.
Catalysis has largely shaped society and will play a key part in the resolution of the energy and environment crisis we are facing in this century. The great advancements in the development of nanomaterials in the realm of nanotechnology have brought forth unforeseen possibilities also for the design of novel catalysts. The production and understanding of highly efficient catalysts based on nanostructured materials is the endeavor of the emerging field of nanocatalysis. In the last years, nanocatalysts have been studied extensively and progress in their large-scale fabrication has been demonstrated. Still, the technology is immature and further research is necessary to capitalize its full potential. Computational approaches are well suited to investigate the functioning of nanocatalysts and provide valuable atomistic insights. An accurate and efficient method is density functional theory (DFT). In this thesis, we explored the physical and chemical characteristics of supported metal clusters and oxide thin films using mainly DFT. These materials are of special interest in catalysis and many other applications, because of their unique features emerging from the nanostructuring. In particular, we investigated the geometry, the charge state, the cluster-support interaction, and the reactivity of sub-nanometer metal clusters supported on oxides. In a case study, we also addressed size-effects on larger metal nanoparticles. Regarding the supported clusters, we find that van-der-Waals dispersion forces are important for the correct description of the cluster-support interaction. Furthermore, we establish that defects and dopants present on the supporting oxide surface have a determining influence on the clusters, inherently affecting their reactivity. Also the modification of the clusters via alloying alters the metal-support interaction which can be exploited against cluster agglomeration. Nanostructuring of the oxide support engenders new material properties and in this context we examined the features of metal-supported oxide ultrathin films. Finally, we performed mechanistic studies contributing to elucidate the reaction mechanism of CO oxidation on Au/TiO2, as well as CO2 hydrogenation on Ru/TiO2 and Cu/TiO2.

This work contributes to the development of electrocatalysts for use in polymer electrolyte fuel cells, specifically for the cathodic oxygen reduction reaction (ORR). To achieve this, electrochemical analysis was conducted using biofabricated platinum (bio-Pt) catalyst. Bio-Pt per se was found to be a poor catalyst for the ORR, attributed to the platinum being inaccessible to the reactants. Various ‘cleaning’ techniques were tested to partially remove biomass, providing improved catalytic activity.

We develop a theoretical framework for a priori estimation of catalytic activity of metal nanoparticles using geometry-based reactivity descriptors of surface atoms and kinetic analysis of reaction pathways at various types of active sites. We show that orbitalwise coordination numbers 𝐶𝑁^α (α = 𝑠 or 𝑑) can be used to predict chemical reactivity of a metal site (e.g., adsorption energies of critical reaction intermediates) by being aware of the neighboring chemical environment, outperforming their regular (𝐶𝑁) and generalized (𝐶̅𝑁̅) counterparts with little added computational cost. Here we include two examples to illustrate this method: CO oxidation on Au (5𝑑¹⁰6𝑠¹) and O₂ reduction on Pt (5𝑑⁹6𝑠¹). We also employ Bayesian learning and the Newns-Anderson model to advance the fundamental understanding of adsorbate-surface interactions on metal nanocatalysts, paving the path toward adsorbate-specific tuning of catalysis.
Doctor of Philosophy
The interactions between reaction intermediates and catalysts should be neither too strong nor too weak for catalytic optimization. This Sabatiers principle arising from the scaling relations among the energetics of reacting species at geometrically similar sites, provides the conceptual basis for designing improved catalysts, but imposes volcano-type limitations on the attainable catalytic activity and selectivity. One of the greatest challenges faced by the catalysis community today is how to develop design strategies and ultimately predictive models of catalytic systems that could circumvent energy scaling relations. This work brings the quantum-chemical modeling and machine learning technique together and develops a novel stochastic modeling approach to rationally design the catalysts with desired properties and bridges our knowledge gap between the empirical kinetics and atomistic mechanisms of catalytic reactions.

The aim of this project was to develop a new preparative route leading to the synthesis of bimetallic precious metal catalysts to be used in, the anode of fuel cells. These catalysts required high metal dispersion and good interaction between the metals used. Control over high metal loading onto the support was also desirable. / Current preparative methods in industry involve the eo-precipitation of mixed metal oxides onto supports together with subsequent high temperatures treatments to achieve the desired bimetallic structure. The final catalysts generally present agglomeration and segregation of the metals when high loadings are required and high temperature applied. As a result, they show poor surface area and low activity. The method studied in this project consisted of two steps: the preparation of mixed metal oxides nanoparticles stabilised by surfactants and the solution reduction of these species under H2. Both the oxide and reduced particles can be isolated in a powder form and easily re-dispersed into an appropriate solvent to give stable dispersions. The oxide and reduced nanoparticles were absorbed onto carbon supports. Using this method, PtRu catalysts for fuel cell applications were prepared. Cyclic voltammetry was used to determine the surface area of the metal particles onto supports and also gave an indication of surface compositions. Preparative variables were investigated in order to manipulate the characteristics of the particles obtained. Firstly, the nature of the stabiliser was examined, showing that the use of a non-ionic stabiliser yielded high dispersions and narrow size distribution. However, the presence of stabiliser in the final products proved to be an issue for their use as catalysts and a firing stage was then introduced. The resulting catalysts showed higher surface areas than their equivalent standard catalysts but surprisingly performance was not increased. Additionally, it was found that no particle growth was observed at high loading; for instance, good dispersion and high surface areas were still obtained at 60wt% metal onto carbon.

Surface catalysed reactions play an important role in chemical productions. Developments of catalyst requiring high activity whilst improving on product selectivity can potentially have a profound effect in the chemical industry. Traditional catalyst modifications were focused on tuning the size, shape and foreign metal doping to form well defined metal nanoparticles of unique functionalities. Here, we show new approach to engineering of metal nanocatalysts via a subsurface approach can modify the chemisorption strength of adsorbates on the surface. Carbon modified nanoparticles were synthesised using glucose to stabilise Pd nanoparticles at a molecular level. Upon heat treatment, the carbonised glucose encapsulated the Pd nanoparticles with carbon atoms take residence in the octahedral holes (15 at.%). These materials were tested in liquid phase stereoselective hydrogenations of 3-hexyn-1-ol and 4-octyne. The former has importance in the fragrance industry towards the production of leaf fragrance alcohol. It was shown for the first time that the geometrically and electronically modified Pd with interstitial carbon atoms reduced the adsorption energy of alkenes, ultimately leading to higher reaction selectivity. Boron modified Pd nanoparticles was synthesised using BH₃.THF in the liquid phase. The material possess high B interstitial saturation (20 at.%), which can be synthesised for the first time below 100°C. These materials were tested in the liquid phase selective hydrogenation of various alkynes and 2-chloronitrobenzene, of which the latter has importance in the pesticides industry. Kinetic modelling on the hydrogenation of 4-octyne suggests these subsurface occupied B does play a pivotal role on increasing the reaction selectivity, as removal of these species lead to decreased selectivity. Au nanoparticles were synthesised and characterised using H¹³COOH NMR. The new liquid NMR characterisation method is successfully applied to examine the chemisorption strength of metal nanoparticles. An attempt to synthesise PVP capped B modified Pd nanoparticles with the above NMR characterisation was investigated. It is believed the examples of subsurface atom modifications as shown here may offer future catalyst developments in this area.

“Una alternativa per aconseguir una font d’energia lliure en carboni és la fotoproducció d’H2 mitjançant el trencament catalític de l’aigua (water splitting, WS, Eq. 1) fent servir la llum solar. 2H2O + hv --> 2H2 + O2 (Eq. 1) WS és un procés en el qual l’aigua és oxidada a dioxigen a l’ànode (reacció d’evolució d’oxigen, REO, Eq. 2), constituent llavors la font d’electrons per reduir protons a H2 al càtode (reacció d’evolució d’hidrogen, REH, Eq. 3). 2H2O --> O2 + 4H+ + 4e- (Eq. 2) 2H+ + 2e- --> H2 (Eq. 3) El desenvolupament de catalitzadors altament actius i eficients és essencial per a aconseguir una cinètica òptima d’aquestes dues semireaccions. Les nanopartícules (NPs) són veritables potencials catalitzadors gràcies a la seva alta estabilitat i rati superfície/volum, exposant grans quantitats de centres actius. En aquesta tesi, diferents nanocatalitzadors han estat sintetitzats mitjançant el mètode organometàl·lic, el qual és avantatjós per obtenir nanomaterials amb una superfície neta. Per tal d’entendre els factors que afecten a l’activitat electrocatalítica dels nanomaterials, s’han realitzat càlculs teòrics per DFT basats en conceptes ben acceptats (energia lliure d’adsorció d’hidrogen, δGH*, i gràfics “volcano”). Degut a que la presència de lligands a la superfície de les NPs pot influenciar l’activitat electrocatalítica, s’han realitzat càlculs DFT per determinar els modes més favorables de coordinació de diferents lligands i obtenint també els valor de δGH*, trobant-se una correlació satisfactòria entre les dades experimentals i les dades DFT. Diferents estudis confirmen que els suports de carboni conductors milloren l’activitat electrocatalítica restringint l’agregació dels nanocatalitzadors i millorant la transferència electrònica des del nanocatalitzador metàl·lic cap a l’elèctrode. En aquesta tesi, dos materials de carboni diferents, òxid de grafè reduït (OGr) i microfibres de carboni (FC) han estat utilitzats com a suports de NPs metàl·liques. A més a més, s’ha estudiat l’efecte del dopatge de N o P en OGr en la REH, obtenint un efecte sinergètic positiu entre els heteroàtoms i NPs de Ru. Contràriament al grafè, les FC són més fàcils de manipular i poden fer-se servir directament com a elèctrodes. Llavors, s’han sintetitzat NPs de Ru i de Co sobre dos tipus diferents de FC, diferenciant-se en la presencia o no de grups –COOH a la superfície de la fibra. Dues metodologies han estat utilitzades, in situ i ex situ, per tal de modificar la interfase entre les NPs i el suport de carboni, afegint diferents solvents (THF o 1-heptanol) en les NPs de Co, o lligands (4-fenilpiridina, 4PP) en les NPs de Ru. Els resultats evidencien que una interacció adequada entre les NPs i la superfície del suport és un element clau per obtenir una millorada activitat electrocatalítica, obtenint millor resultats en sistemes on tenen lloc interaccions π-π entre les NPs (Ru-4PP) i les estructures de carboni o enllaços d’hidrogen entre Co(OH)2 i els grups COOH a les FC. Una altra estratègia prometedora és l’adició d’un segon metall a una estructura metàl·lica, obtenint efectes electrònics sinergètics beneficiosos degut a canvis en l’entorn químic dels centres metàl·lics i disminuint l’energia d’adsorció dels reactius. En aquest sentit, sistemes bimetàl·lics, Ru@Ni-foam i NPs de RuCo han estat sintetitzats. La influencia en l’activitat catalítica en OER de diferents percentatges de dopatge de Ru en el sistemes Ru@Ni-foam ha estat estudiada. Finalment, els sistemes bimetàl·lics basats en NPs de RuCo han estat sintetitzats fent servir tres lligands diferents, 4’-(4-metilfenil)-2,2’:6’,2”-terpiridina, 4-PP i 1-heptanol. S’ha examinat la influencia del lligand i el rati entre metalls Ru/Co en la mida i morfologia de les NPs. Els estudis electrocatalítics obren noves portes per explorar l’interès dels sistemes bimetàl·lics com a catalitzadors per WS i la producció d’hidrogen.
Una solución para conseguir una fuente de energía libre de carbono es la fotoproducción de H2 mediante la división catalítica del agua (Water splitting, WS, Ecuación 1) utilizando la luz solar. 2H2O + hv --> 2H2 + O2 (Ecuación 1) WS es un proceso en el que el agua se oxida a dioxígeno en el ánodo (reacción de evolución del oxígeno, REO, Ecuación 2), constituyendo así la fuente de electrones para reducir los protones a H2 en el cátodo (reacción de evolución del hidrógeno, REH, Ecuación 3). 2H2O --> O2 + 4H+ + 4e- (Ecuación 2) 2H+ + 2e- --> H2 (Ecuación 3) El desarrollo de catalizadores de WS altamente activos y eficientes es esencial para la correcta cinética de estas dos semireacciones. Las nanopartículas (NPs) son verdaderos catalizadores potenciales debido a su alta estabilidad y relación superficie/volumen, exponiendo altas cantidades de sitios activos. En esta tesis doctoral se han sintetizado diferentes nanoelectrocatalizadores siguiendo el método organometálico, que resulta ventajoso para obtener nanomateriales de superficie limpia. Para entender los factores que afectan a la actividad electrocatalítica de los nanomateriales, se han realizado cálculos teóricos sobre la base de conceptos bien aceptados (energía libre de adsorción de hidrógeno, δGH*, y diagramas de volcán). Dado que los ligandos presentes en la superficie de las NPs metálicas pueden influir en la actividad electrocatalítica, se realizaron cálculos DFT para determinar los modos de coordinación más favorables de diferentes ligandos y obtener los valores de δGH*, obteniéndose correlaciones satisfactorias entre los datos experimentales y los de DFT. Diferentes estudios confirman que los soportes conductores de carbono mejoran la actividad electrocatalítica al restringir la agregación de los nanocatalizadores y mejorar la transferencia de electrones desde el nanocatalizador metálico al electrodo. En esta tesis doctoral se han utilizado dos materiales de carbono, el óxido de grafeno reducido (OGr) y las microfibras de carbono (FC), como soportes de NPs metálicas. Además, se ha estudiado el efecto del dopaje de N y P sobre el OGr en la REH, obteniendo un efecto sinérgico positivo entre heteroátomos y NPs de Ru. A diferencia del grafeno, las microfibras de carbono son más fáciles de manipular y pueden utilizarse directamente como electrodos. Así, se han sintetizado NPs de Ru y Co sobre dos microfibras diferentes, que difieren en la presencia o no de grupos -COOH en la superficie. Además, se han empleado dos metodologías diferentes, in situ y ex situ, para modificar la interfaz entre las NPs y el soporte de carbono mediante la adición de diferentes disolventes (THF o 1-heptanol) o ligandos (4-fenilpiridina, 4PP). Los resultados evidencian que una adecuada interacción entre las NPs y la superficie del soporte es clave para una mejor actividad catalítica, obteniéndose mejores resultados en los sistemas en los que tienen lugar interacciones π-π entre las estructuras Ru-4PP NPs/C o enlaces H entre las NPs de Co(OH)2 y -COOH en la FC. Otra estrategia prometedora es la adición de otro metal a una nanoestructura metálica, lo que conduce a efectos electrónicos beneficiosos al cambiar el entorno químico de los centros metálicos. En este sentido, se sintetizaron sistemas bimetálicos de Ru@Ni-espuma y NPs de RuCo. Se ha estudiado la influencia de diferentes porcentajes de dopaje de Ru en los sistemas de Ru@Ni-espuma sobre la actividad catalítica hacia la REO. Finalmente, se sintetizaron NPs de RuCo utilizando tres ligandos diferentes, 4’-(4-metilfenil)-2,2’:6’,2””-terpiridina, 4-PP y 1-heptanol, con el fin de determinar la influencia del ligando y de la ratio Ru/Co en el tamaño y la morfología de las NPs. Los estudios electrocatalíticos realizados abren una nueva puerta para explorar el interés de los nanocatalizadores bimetálicos en WS y la producción de hidrógeno.
One solution to achieve a carbon free energy source is the photoproduction of H2 by the catalytic water splitting (WS, Eq. 1) using sunlight. 2H2O + hv --> 2H2 + O2 (Eq. 1) WS is a process in which water is oxidized to dioxygen in the anode (oxygen evolution reaction, OER, Eq. 2), thus constituting the source of electrons to reduce protons to H2 in the cathode (hydrogen evolution reaction, HER, Eq. 3). 2H2O --> O2 + 4H+ + 4e- (Eq. 2) 2H+ + 2e- --> H2 (Eq. 3) Developing highly efficient and active WS catalysts is essential for the proper kinetics of these two reactions. Nanoparticles (NPs) are true potential catalysts due to their high stability and surface per volume ratio, exposing high amounts of active sites. In this PhD, different nanoelectrocatalysts have been synthesized by following the organometallic approach which is advantageous for obtaining clean-surface nanomaterials compared to other synthesis methodologies. To understand the factors affecting the electrocatalytic activity of the nanomaterials, theoretical DFT calculations have been performed on the basis of well accepted concepts (hydrogen adsorption free energy, δGH*, and volcano plots). Given that the ligands present on the surface of metal NPs can influence the electrocatalytic activity, DFT calculations were performed to determine the most favorable coordination modes of different ligands and to obtain the δGH* values of the resulting NPs. Successful correlations between experimental and DFT data have been obtained. Conductive C-based supports are known to enhance the electrocatalytic activity by restraining the aggregation of the nanocatalysts and improving the electron transfer from the metal nanocatalyst to the electrode. In this PhD, two different carbon materials, reduced graphene oxide (rGO) and carbon microfibers (CF) have been used as supports for metal NPs. Furthermore, the effect of N and P doping onto rGO has been studied towards the HER, obtaining a positive synergistic effect between the heteroatoms and Ru NPs. In contrast to graphene, CF are easier to handle and can be directly used as electrodes, thus avoiding the issues related to the NPs deposition onto macroscopic electrodes (GC, FTO). Thus, Ru and Co NPs have been synthesized on top of two different CF, differing in the presence or not of –COOH moieties onto the surface. Two different methodologies, in-situ and ex-situ, have been employed in order to tune the interface between the NPs and the C support by adding different solvents (THF or 1-heptanol) for Co NPs or ligands (4-phenylpyridine, 4PP) for Ru NPs. The results evidence that a proper interaction between the NPs and the support surface is key for an improved catalytic activity of the hybrid materials, obtaining better results in the systems where π-π interactions between Ru-4PP NPs/C structures or H-bonds between Co(OH)2 and COOH moieties in the CF take place. Another promising strategy is the addition of another metal onto a metallic nanostructure, leading to beneficial synergistic electronic effects by changing the chemical environment of the metal centers and decreasing the adsorption energy of the reactants. In this sense, bimetallic Ru@Ni-foam and RuCo NPs systems were synthesized. The influence on the catalytic activity towards OER of different percentages of Ru-doping in Ru@Ni-foam systems has been studied. Finally, RuCo bimetallic systems were synthesized by using three different ligands, 4’-(4-methylphenyl)-2,2’:6’,2”-terpyridine, 4-PP and 1-heptanol. The influence of the ligand and the Ru/Co metal ratio on the size and morphology of the NPs has been determined. Preliminary electrocatalytic tests have been performed, opening a new door to explore the interest of bimetallic nanocatalysts for the water-splitting and the production of hydrogen.
Universitat Autònoma de Barcelona. Programa de Doctorat en Química

Fibrous catalysts were prepared by an eggshell membrane-templating process and an electrospinning process. The microstructure and catalytic performances in methane reforming were studied as functions of preparation parameters. The fibrous catalysts combines the advantages of porous catalysts and non-porous catalysts, and the high dispersion at high catalyst loadings and fast mass transfer can be achieved, showing high potential for industrial applications.

La preparazione di nanoparticelle (NPs) metalliche risulta complessa per via della loro instabilità termodinamica. Per questo motivo, la ricerca di nuove tecnologie sintetiche e di stabilizzazione atte a controllarne la morfologia, rappresenta uno dei temi di maggior interesse scientifico per la chimica della catalisi. La tecnica di sol immobilization permette di ottenere catalizzatori nanostrutturati composti da nanoparticelle stabilizzate da polimeri. Inoltre, le proprietà dei polimeri hanno mostrato particolari caratteristiche nel modulare l’attività catalitica del metallo in forma nanoparticellare. Questa attività di ricerca è finalizzata alla sintesi di copolimeri idrosolubili contenenti fosforo in grado di stabilizzare nanoparticelle di oro supportate su carbone attivo. Differenti tecniche di caratterizzazione sono state impiegate per correlare le proprietà dei polimeri sintetizzati con la dimensione delle nanoparticelle. Inoltre, mediante la riduzione del 4-nitrofenolo, scelta come reazione modello, è stata valutata l’attività catalitica dei materiali nanostrutturati e l’influenza dei parametri di reazione (temperatura, agitazione e quantità di catalizzatore) sulle loro performance catalitiche.

This thesis focuses on the understanding the effect of various factors, such as physical structures of metal particles, chemical composition of supports and metal-support interactions, on the catalytic performance of Pd or Pt nanocatalysts for hydrodeoxygenation (HDO) of bio-oil model compounds. The first part of the thesis addressed the alternative catalyst synthesis strategy based on emerging double-flame spray pyrolysis method (FSP), which was able to tune the catalytic properties of nanocatalysts without changing their precursors and chemical compositions during the synthesis. A series of Pd catalysts on the silica-alumina supports, SiO2- , and Al2O3 supports have been synthesized with the tunable surface properties within micro-seconds. The characterization results showed that various flow rates of precursors and gases used for the synthesis of catalysts influenced the formation of the catalyst structures and further change the surface acidity of catalysts due to the correlation between acidity and structure, but, the flow rates did not influence the electronic properties of Pd particles. Therefore, the higher conversion but the similar chemoselectivity have been reached in the hydrogenation of the bio-oil model ketone compound-acetophenone The second part is to identify the dominant effects from size of metal catalysts (under uniform shape and face) or the support acidity in the hydrodeoxygenation of the bio-oil model compounds of acetophenone, benzaldehyde, and butyrophenone. The uniform cubic Pd particles with different size (8, 13, and 21 nm) have been synthesized and loaded on the most popular supports (SiO2-, Al2O3-, and silica-alumina) with various functional groups and acidity. The results showed different acidities on the supports (Brønsted acidic site for Silica-alumina, Lewis acidic site for Al2O3-, and non/weak silanol OH group for SiO2- support) could not influence the chemoselectivity of the reaction but effected the conversion obviously. The particle size has more significant influence than the acidity. The smallest (8nm) Pd particle catalysts regardless of kinds of supports revealed the highest conversion for the hydrogenation the bio-oil model compounds. The third part focused on the influence of various types of catalysts with different acidities, chemical composition, and metal-support interaction on enantioselective hydrogenation of several model compounds in two reaction systems: 1). Pt-cinchrona modified system, and 2). Pd-(S) proline modified system. The result indicated acidic supports promoted the both conversion and enantioselectivity. Specially, Pd/SA made by double-FSP method, which has the highest Brønsted acid sites, showed 100 % conversion of isopherone on 60 min with 99% ee values.

This thesis centres on the development of colloidal nanoparticles for the hydrogenation of carbon dioxide to methanol. Chapter two focusses on the synthesis of zinc oxide (ZnO) nanoparticles through the hydrolysis of diethylzinc in the presence of sub-stoichiometric quantities of organic ligands. Characterisation of the product, through a range of spectroscopic, diffraction and electron microscopy techniques, reveals small (3-4 nm), equiaxial, mono-disperse ZnO nanoparticles coordinated to alkyl-carboxylate, phosphinate and sulfinate ligands. Detailed investigation of the dioctyl-phosphinate capped-zinc oxide nanoparticles reveals that increasing the loading of ligand into the reaction (from 0.05-0.33 equivalents of ligand to zinc) does not affect the size or morphology of the nanoparticles, rather influencing the ligand density and coverage of the nanoparticle surface. In chapter three, these partially capped ZnO nanoparticles, mixed with copper nanoparticles, demonstrate catalytic activity for CO2 hydrogenation. Post-reaction analysis showed significant nanoparticle rearrangement, with an interface forming between the copper and the ZnO. In some cases, a self-assembled nanostructure is observed, consisting of a copper nanoparticle sandwiched between two pyramidal zinc oxide nanoparticles. The ligand has a significant effect on the activity of the catalyst; more reductively stable di-alkyl phosphinate ligands show superior activity to carboxylates. Decreasing the ligand loading on the zinc oxide nanoparticles, results in a higher peak activity due to the decreased ligand density exposing more of the catalyst surface, however the stability of the catalyst is also reduced. In chapter four, the interface between nanoparticles is targeted, with the goal of depositing copper onto the ZnO colloids through reduction and thermolysis reactions to form hybrid Cu/ZnO nanostructures. The most effective route entails the hydrogenolysis of mesitylcopper(I) on to the ZnO nanoparticles, the resulting nanocatalyst displays superior peak activity to both the mixed nanoparticle catalyst described above and a suspension of the commercial catalyst run under the same conditions.

El trabajo realizado en esta tesis ha seguido dos líneas de investigación principales: por un lado, el uso de electrodos monocristalinos de Pt ha permitido realizar estudios fundamentales de la interfase electrodo│disolución, así como de la electrocatálisis de moléculas orgánicas simples (C2) bifuncionalizadas, y por otro lado, el efecto que la estructura superficial ejerce sobre la electrocatálisis de ciertas reacciones se ha aplicado a la síntesis y caracterización de nanopartículas de Pt con forma controlada. Este campo se ha ampliado al estudio de nanocatalizadores bimetálicos y trimetálicos para la ORR. El estudio que aquí se presenta ha profundizado en el conocimiento sobre las relaciones que hay entre estructura superficial – actividad – y estabilidad morfológica y composicional de electrocatalizadores basados en Pt destinados a PEMFCs.

There is a rising concern about energy and environment for future. Transition from current fossil fuels to green fuels and building of cleaner environment to lead sustainable life is at enormous task. Hydrogen gas is recognized as a clean fuel and may be a sustainable solution. Hydrogen can be directly used as clean fuel in fuel cells with no harmful by-products. Chemical hydrides with high hydrogen storage capacity in terms of gravimetric and volumetric efficiencies are the most promising candidates to supply pure hydrogen at room temperature. Among them, Ammonia Borane (NH3BH3, AB) and Sodium borohydride (NaBH4, SBH) have drawn a lot of interest as they are stable, non-flammable, and nontoxic. Large amount of pure hydrogen gas is released during the hydrolysis of these hydrides in presence of certain catalysts and the by-products are non-toxic, environmentally safe and can be recycled. Co based catalysts are considered as good candidates for catalyzed hydrolysis owing to their good catalytic activity, low cost and effortless synthesis. In favor of environmental concern, especially the air pollution (conversion of CO to CO2) and water pollutions (organic pollutants) are vital problems and there is a serious need to mitigate these problems. Cobalt (Co) based materials are with high catalytic activity for hydrolysis, organic pollutants degradation and CO oxidation. So, a single Co based catalysts as powders and as immobilized coatings prepared by chemical reduction method and pulsed laser deposition (PLD) were studied for hydrogen production by hydrolysis of AB and SBH and thin film coatings Co3O4 were studied for CO oxidation and organic pollutants degradation. On the basis of characterization results, the role of catalyst to enhance catalytic activity is discussed in hydrolysis, CO oxidation and pollutants degradation reactions. The stability and re-usability of these catalysts have also been investigated.

There is a rising concern about energy and environment for future. Transition from current fossil fuels to green fuels and building of cleaner environment to lead sustainable life is at enormous task. Hydrogen gas is recognized as a clean fuel and may be a sustainable solution. Hydrogen can be directly used as clean fuel in fuel cells with no harmful by-products. Chemical hydrides with high hydrogen storage capacity in terms of gravimetric and volumetric efficiencies are the most promising candidates to supply pure hydrogen at room temperature. Among them, Ammonia Borane (NH3BH3, AB) and Sodium borohydride (NaBH4, SBH) have drawn a lot of interest as they are stable, non-flammable, and nontoxic. Large amount of pure hydrogen gas is released during the hydrolysis of these hydrides in presence of certain catalysts and the by-products are non-toxic, environmentally safe and can be recycled. Co based catalysts are considered as good candidates for catalyzed hydrolysis owing to their good catalytic activity, low cost and effortless synthesis. In favor of environmental concern, especially the air pollution (conversion of CO to CO2) and water pollutions (organic pollutants) are vital problems and there is a serious need to mitigate these problems. Cobalt (Co) based materials are with high catalytic activity for hydrolysis, organic pollutants degradation and CO oxidation. So, a single Co based catalysts as powders and as immobilized coatings prepared by chemical reduction method and pulsed laser deposition (PLD) were studied for hydrogen production by hydrolysis of AB and SBH and thin film coatings Co3O4 were studied for CO oxidation and organic pollutants degradation. On the basis of characterization results, the role of catalyst to enhance catalytic activity is discussed in hydrolysis, CO oxidation and pollutants degradation reactions. The stability and re-usability of these catalysts have also been investigated.

The thesis focuses on synthesis and characterization of nanocatalysts for applications in wastewater treatment and hydrogen production through electrochemical water splitting. Different photocatalysts and electrocatalysts are synthesized using wet chemistry techniques as well as Pulsed Laser Deposition (PLD). The synthesized catalysts pave demonstrate excellent catalytic activity thereby paving way for their use on an industrial scale.

The thesis focuses on synthesis and characterization of nanocatalysts for applications in wastewater treatment and hydrogen production through electrochemical water splitting. Different photocatalysts and electrocatalysts are synthesized using wet chemistry techniques as well as Pulsed Laser Deposition (PLD). The synthesized catalysts pave demonstrate excellent catalytic activity thereby paving way for their use on an industrial scale.

Les procédés catalytiques ont été largement étudiés comme une approche prometteuse pour fournir une énergie durable et subvenir au besoin eau potable. Parmi ceux-ci, les procédés photocatalytiques et sonocatalytiques ont été adaptés comme des méthodes efficaces pour atteindre ces deux objectifs. Le facteur clé de ces procédés est l'utilisation de matériaux actifs capables d'éliminer les molécules nocives des eaux usées et de transformer les autres constituants en produits à haute valeur ajoutée. Les matériaux considérés pour les procédés photocatalytiques doivent être actifs sous l'effet de la lumière solaire. A l’heure actuelle, l'accent est mis sur la préparation de photocatalyseurs efficaces et respectueux de l'environnement en utilisant des matières premières abondantes sur Terre. L'un des objectifs de cette thèse est donc de préparer des nanoparticules cœur-coquille Ti@TiO2 exemptes de métaux nobles par traitement sonohydrothermal dans l'eau pure de nanoparticules de titane disponibles dans le commerce. Les propriétés structurelles, chimiques et optiques des nanoparticules cœur-coquille ainsi préparées ont été soigneusement étudiées et comparées à celles des nanoparticules de titane initiales. L'activité de ces particules a été testée pour la production photocatalytique d'hydrogène assistée par la chaleur ainsi que pour la dégradation des polluants sous irradiation lumineuse ou ultrasonore. La production d'hydrogène avec ces particules a été étudiée à partir de solutions aqueuses composées de différents réactifs sacrificiels (alcools, mélange acide carboxylique/amine, et glucose) sous atmosphère inerte et températures contrôlées. Une amélioration de l'activité photocatalytique des nanoparticules de Ti@TiO2 avec l'augmentation de la température du milieu réactionnel (25 °C -95 °C) a été observée dans tous les systèmes étudiés. Le mécanisme du processus photocatalytique a été discuté en considérant les énergies d'activation apparentes ainsi que l'effet isotopique cinétique H/D. En outre, une étude comparative de l'activité de Ti@TiO2 et des nanoparticules initiales de Ti0 pour la dégradation de certains polluants par la lumière et par les ultrasons a également été menée. Nous avons ainsi pu montrer que la présence de la coquille de TiO2 à la surface des nanoparticules de Ti permettait d’augmenter la vitesse de dégradation des molécules complexantes (EDTA) ainsi que celle des colorants organiques (RhB) sous irradiation lumineuse et atmosphère Ar/20% O2. Au contraire, les nanoparticules de Ti0 passivées uniquement sous air ont présenté une activité plus élevée au cours de la dégradation sonocatalytique de l’EDTA que pour les particules cœur-coquille. De plus, à haute fréquence ultrasonore et sous atmosphère Ar/O2, une dégradation sonochimique efficace de la rhodamine B a été observée même sans catalyseur
Catalytic processes have been widely investigated as a promising approach for providing sustainable energy and clean water resources. Among such, photocatalytic and sonocatalytic processes have been adapted as successful methods for fulfilling those two objectives. The key factor to these processes is the use of active materials capable of eliminating harmful molecules from wastewater and transforming others into products of high-added value. Those integrated in photocatalytic processes must be active under solar light. Today’s major focus is the preparation of effective environmentally friendly photocatalysts using earth-abundant raw materials. One of the objectives of this thesis is to prepare noble-metal free Ti@TiO2 core-shell nanoparticles throughout the sonohydrothermal treatment of commercially available titanium nanoparticles in pure water. Structural, chemical and optical properties of the prepared core-shell nanoparticles have been carefully studied and further compared to those of the initial titanium nanoparticles. The activity of these particles has been tested for the thermal-assisted photocatalytic hydrogen production and the degradation of pollutants with either light or ultrasound. Hydrogen production with those particles was tested from aqueous solutions composed of different sacrificial reagents (alcohols, carboxylic acid/amine mixture, and glucose) under controlled temperatures and inert atmosphere. Improved photocatalytic activity of Ti@TiO2 nanoparticles with the increase of temperature (25 °C - 95 °C) was observed in all studied systems. The mechanism of the photocatalytic process has been discussed in terms of apparent activation energies and H/D kinetic isotope effects. In addition, comparative study of the activity of Ti@TiO2 and initial Ti0 nanoparticles towards the degradation of certain pollutants by light and by ultrasound was investigated herein. The presence of TiO2 shell on the surface of Ti nanoparticle s showed enhanced degradation of complexing molecules (EDTA) and organic dyes (RhB) under light in the presence of Ar/20% O2 while higher activity towards sonocatalytic EDTA degradation was observed with air-passivated Ti0 nanoparticles. At high-frequency ultrasound and in the presence of Ar/O2 atmosphere, efficient sonochemical degradation of Rhodamine B has been observed even without catalyst

This thesis focuses on the synthesis of nanocatalysts for the electroreduction of CO¬2 to useful fuels such as formic acid, methanol, methane and carbon monoxide. Copper-based materials were synthesised via a continuous hydrothermal flow synthesis process (CHFS). This method involved mixing pressurised precursor solutions with supercritical water to rapidly form ultra-fine nanocatalysts. CuO synthesis was investigated by varying experimental parameters, such as mixer types, temperature, pH, metal salt precursor and H¬2O¬2. Particle size was modulated by controlling these parameters and sub-15 nm particle sizes were possible. This has not been previously observed or reported in the literature in flow synthesis for CuO. The as-prepared CuO nanoparticles were formulated into Nafion based inks. The influence of the Nafion fraction on the Faradaic efficiencies and overpotential was explored. The highest Faradaic efficiency for formic acid production (61%) was observed with the optimum Nafion fraction. Insights into the significant increase in the Faradaic efficiency with the optimum Nafion content was elucidated with electrochemical impedance spectroscopy (EIS). Ni doped CuO synthesised via CHFS, was reported here for the first time, where higher inclusion of Ni was possible compared to co-precipitation. The Ni doped CuO samples were evaluated for their electrocatalytic properties and showed higher Faradaic efficiency at lower overpotential (< 1.2 V) and below 11 at % Ni, compared to the undoped CuO. The catalysts were evaluated by EIS, Tafel analysis and structural characterisation. Rotating Ring Disk Electrode (RRDE), a hydrodynamic technique, was validated as a high-throughput tool to screen catalysts prior to bulk electrolysis. The Pt ring was successfully used to electrochemically detect formic acid, as it was formed in situ on copper-based catalysts. This was confirmed by conducting product calibration and understanding the oxidation behaviour on Pt as a function of rotation and scan rate.

In the present study the methods of synthesis and characterization of metal nanoparticles structures of a given size and surface topology on the non-metallic surfaces are described. The main application of such particles can be selective heterogeneous catalysis of chemical reactions or their usage as nucleus of growth centers for different nanostructures (tubes, whiskers, etc.). The formation of nanoparticles systems on the surface was carried out by two ways: by "thin cutoff plate" method and by vacuum annealing of ultrathin solid films. Metal was deposited on the substrate by thermal evaporation (deposition) in vacuum. Studies of the samples were carried out using the methods of Auger analysis and scanning electron microscopy. AES detects intense peaks of deposited metals with weak tungsten (the evaporator material), oxygen, carbon and the substrate material elements peaks in chemical composition of the films. The SEM studies reveal the presence of well-defined islet metallic structures on the samples obtained by both methods. For vacuum annealing method a clear correlation between annealing and obtained structures parameters is demonstrated. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/20565
In the present study the methods of synthesis and characterization of metal nanoparticles structures of a given size and surface topology on the non-metallic surfaces are described. The main application of such particles can be selective heterogeneous catalysis of chemical reactions or their usage as nucleus of growth centers for different nanostructures (tubes, whiskers, etc.). The formation of nanoparticles systems on the surface was carried out by two ways: by "thin cutoff plate" method and by vacuum annealing of ultrathin solid films. Metal was deposited on the substrate by thermal evaporation (deposition) in vacuum. Studies of the samples were carried out using the methods of Auger analysis and scanning electron microscopy. AES detects intense peaks of deposited metals with weak tungsten (the evaporator material), oxygen, carbon and the substrate material elements peaks in chemical composition of the films. The SEM studies reveal the presence of well-defined islet metallic structures on the samples obtained by both methods. For vacuum annealing method a clear correlation between annealing and obtained structures parameters is demonstrated. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/20565

Surface science investigations of model catalysts have contributed significantly to heterogeneous catalysis over the past several decades. The unique properties of nanomaterials are being exploited in catalysis for the development of highly active and selective catalysts. Surface science investigations of model catalysts such as inorganic fullerene-like (IF) nanoparticles (NP), inorganic nanotubes (INT), and the oxide-supported nanoclusters are included in this dissertation. Thermal desorption spectroscopy and molecular beam scattering were respectively utilized to study the adsorption kinetics and dynamics of gas phase molecules on catalyst surfaces. In addition, ambient pressure kinetics experiments were performed to characterize the catalytic activity of hydrodesulfurization (HDS) nanocatalysts. The nanocatalysts were characterized with a variety of techniques, including Auger electron spectroscopy, x-ray photoelectron spectroscopy, electron microscopy, and x-ray diffraction. The adsorption kinetics studies of thiophene on novel HDS catalysts provided the first evidence for the presence of different adsorption sites on INT-WS2. Additionally, the adsorption sites on IF- MoS2 NP and silica-supported Mo clusters (Mo/silica) were characterized. Furthermore, the C-S bond activation energy of thiophene on Mo/silica was determined. These studies finally led to the fabrication of Ni/Co coated INT-WS2, which showed good catalytic activity towards HDS of thiophene. The studies of methanol synthesis catalysts include the adsorption kinetics and dynamics studies of CO and CO2 on Cu/silica and silica-supported EBL-fabricated Cu/CuOx nanoclusters. The adsorption dynamics of CO on Cu/silica are modeled within the frame work of the capture zone model (CZM), and the active sites of the silica-supported Au/Cu catalysts are successfully mapped. Studies on EBL model catalysts identify the rims of the CuOx nanoclusters as catalytically active sites. This observation has implications for new methanol catalyst design.
NSF Grant
DOE Grant

In this dissertation, research efforts mainly focused on exploring the applications of superparamagnetic iron oxide nanoparticles (SPIONs) in MR imaging and nanocatalysis via surface functionalization. A dopamine-based surface-functionalization strategy was established. The Simanek dendrons (G1 to G3), oligonucleotides and amino acids were loaded onto SPION surfaces via this approach to develop pH-sensitive MRI contrast agents, specific-DNA MR probes and a biomimetic hydrolysis catalyst. Dendron-SPION conjugates (G1 to G3) have good aqueous solubilities and high transverse relaxivities (>300 s-1*mM-1). They also showed interesting strong pH-sensitive R2 and R2* relaxivities, which were governed by the clustering states of dendron-SPIONs in different pH environments. Values of R2m and R2* m/R2m varied by over an order of magnitude around pH 5. The efficient cell-uptake (~3 million/cell) and low cytotoxicity of G1 to G3-SPIONs were demonstrated on HeLa cell cultures. The strong R2* effects were observed indicating the SPION clustering in HeLa cells. Two SPION-oligonuleotide conjugates were synthesized by coupling two half-match oligonucleotides onto domapine-capped SPIONs via SPDP linkers. They served as MR probes to detect a single-strand DNA with the same sequence to miRNA-21 based on the change of R2 values due to the DNA-bridged SPION clustering. The detection limit of the DNA could reach to 16.5 nM. A biomimetic hydrolysis nanocatalyst (i.e., Fe2O3-Asp-His complex) was developed by loading Asp and His-dopamine derivatives onto SPIONs. Paraoxon and nitrophenyl acetate were hydrolyzed under a mild condition (neutral pH, 37 °C) catalyzed by the Fe2O3-Asp-His complex. The two amino acids Asp and His cooperated with each other on the SPION surfaces to catalyze hydrolysis reactions. This catalyst could be recycled by a magnet and reused for four times without a significant loss of catalytic activity.

This research focuses on the synthesis, characterization, and capability of the metal organic frameworks (MOFs) as a candidate adsorbent for storage and separation of greenhouses gases. The performance and effectiveness of various synthesized MOFs were explored for the selectivity of CO2/N2 and CO2/CH4. The research contributes to the advances in synthesis of different MOFs and their application for gas uptake. This has potential advantages than other materials for future environmental science and materials applications.

This thesis reports a computational discovery and design of highly efficient electrocatalysts for various of electrochemical reactions. The method is based on the Density Functional Theory (DFT) by using Vienna ab initio simulation package (VASP). This project is a step forward in developing the low-cost, high activity, selectivity, stability and scalability for the electrochemical reactions, which could make a contribution to the global-scale green energy system for a clean and sustainable energy future.

In this research, SMFs panels were applied for further deposition of CNFs, ZnO and Al2O3 to hydro-genate selectively acetylene to ethylene. To understand the role of different structures of the examined supports, the characterization methods of SEM, ASAP, NH3-TPD and N2 adsorption-desorption isotherms were used. Following the characterization of green oil by FTIR, the presence of more unsaturated constitu-ents and then, more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO was confirmed, which in turn, could block the pores mouths. Besides the limited hydrogen transfer, the lowest pore diameters of Al2O3 / SMFs close to the sur-face, supported by N2 adsorption-desorption isotherms could explain the fast deactivation of this catalyst, compared to the other ones. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35216

Fuel Cells are important forms of sustainable power generation and Biofuel Cells utilize the use of bio-compatible/biodegradable molecules as fuels. Glucose is an ideal candidate to serve this purpose. In this project, a Glucose Fuel Cell (GFC) has been fabricated using the nanomaterials developed in the lab. The skeletal system of this GFC is a three-layered structure; a Membrane Electrode Assembly (MEA) composed of carbon electrodes (anode and cathode) and a Poly Vinyl Alcohol/Poly Acrylic Acid (PVA/PAA) polymer electrolyte. Gold and Silver (Au and Ag) nanoparticles are utilized as catalyst on the anode and cathode respectively, which are prepared by the use of green chemistry practice. One of the GFC has been compacted under hot press and the other non-hot pressed. ,which led to different surface areas. For the validation of the GFC stacks, the glucose concentration was selected around biologically available levels, i.e at 400 mg/dL in both the cases. One trial on hot pressed membrane with 200 mg/dL of glucose is also studied. Short Circuit Current (SCC) and Open Circuit Voltage (OCV) were measured following which the voltages and currents were measured across load resistances. The Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) studies were carried out on the membrane while the electrodes were characterized by Scanning Electron Microscopy (SEM). UV-Vis studies were carried out on the Au and Ag nanoparticle suspension before and after impregnation of carbon cloth electrodes. Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) has been utilized to estimate the concentration and thus the number of nanoparticles adsorbed on the surface of the carbon cloth. The variations of output current with the thickness of the membranes were studied. The assembly containing the catalytic particles showed power levels ranging between 128.7 nW-332.2 nW in the glucose concentration of 400 mg/dL. Rigorous efforts are under process to scale down the power consumption of electronics to extremely low levels. GFCs could be used as power generators in such devices. The inexpensiveness of the fuel is a remarkable factor.

The primary aim of this study was to develop mesoporous nanocatalysts for (i) hydrogen production via steam reforming of methanol (SRM) in a tubular reactor, and (ii) syngas conversion to hydrocarbons via Fisher-Tropsch synthesis using silicon microchannel microreactors. The mesoporous catalysts for SRM were prepared by an optimized one-pot hydrothermal synthesis procedure. The catalysts were investigated for SRM activity in a packed bed tubular reactor using metals, namely, Cu, Co, Ni, Pd, Zn, and Sn. The metals were incorporated in different supports -MCM-41, SBA-15, CeO₂, TiO₂, and ZrO₂ to investigate the influence of support on catalyst properties. A sharp contrast in catalyst performance was noticed depending on the type of support employed. For example, in SRM at 250 °C, Cu supported on amorphous silica SBA-15 and MCM-41 produced significantly less CO (< 7%) compared to other crystalline supports Cu-TiO₂ and Cu/ZrO₂ that showed high CO selectivity of ∼56% and ∼37%, respectively. Amongst all the metals studied for SRM activity using 1:3 methanol:water mole ratio at 250 °C, 10%Cu-MCM-41 showed the best performance with 68% methanol conversion, 100% H₂ , ∼6 % CO, 94% CO₂ selectivities, and no methane formation. Furthermore, 10%Cu-CeO₂ yielded the lowest CO selectivity of 1.84% and the highest CO2 selectivity of ∼98% at 250 °C. Stability studies of the catalysts conducted for time-on-stream of 40 h at 300 °C revealed that Cu-MCM41 was the most stable and displayed consistent steady state conversion of ∼74%. Our results indicate that, although coking played an influential role in deactivation of most catalysts, thermal sintering and changes in MCM-41 structure can be responsible for the catalyst deactivation. For monomtetallic systems, the MCM-41 supported catalysts especially Pd and Sn showed appreciable hydrothermal stability under the synthesis and reaction conditions. While bimetallic Pd-Co-MCM-41 and Cu-Ni-MCM-41 catalysts produced more CO, Cu-Zn-MCM-41 and Cu-Sn-MCM-41exhibited better SRM activity, and produced much less CO and CH4. In spite of the improved the stability and dispersion of the monometallic active sites in the support, no noticeable synergistic activity was observed in terms of H₂ and CO selectivities in the multimetallic catalysts. For the Fisher-Tropsch (F-T) studies, Co-TiO ₂, Fe-TiO₂ and Ru-TiO₂ catalysts were prepared by the sol-gel method and coated on 116 microchannels (50μm wide x 100μm deep) of a Si-microreactor. The F-T process parameters such as temperature, pressure and flow rates were controlled by an in-house setup programmed by LabVIEW^®. The effect of temperature on F-T activity in the range of 150 to 300°C was investigated at 1 atm, a flow rate of 6 ml/min and a constant H₂:CO molar ratio of 2:1. In our initial studies at 220 °C, 12%Ru-TiO₂ showed higher CO conversion of 74% and produced the highest C₂-C₄ hydrocarbon selectivity-of ∼11% ethane, 22% propane and ∼17% butane. The overall catalyst stability and performance was in the order of 12%Ru-TiO₂>> 12%Fe-TiO₂ > 12%Co-TiO₂.

Magnetic separation has received a lot of attention as a robust, highly efficient and rapid catalyst separation technology. Many studies have focused on developing methodologies for the immobilization of catalytic active species, but the development of magnetic supports has been mainly limited to silica, polymer or carbon-coated magnetic nanoparticles (NPs). The design of magnetic nanocomposites and the incorporation of other oxides are highly welcome to broaden the application of this separation technology in the field of catalysis. In this context, studies of the thermal stability of silica-coated magnetite (Fe3O4@SiO2) were performed to evaluate the possibility of calcining it without losing the magnetic properties of the support. The calcination would permit the deposition of different oxides on the silica surface, such as ceria and titania. The calcined Fe3O4@SiO2 material preserved the core-shell morphology and magnetic properties, but increased its surface area six times. New magnetic supports were developed by using post-coating process for the deposition of ceria and titania onto silica-coated magnetite. Magnetically recoverable Rh, Pd and Ru nanocatalysts were prepared. The catalysts were employed in hydrogenation of cyclohexene, benzene or phenol and the study of the influence of each support on the catalytic activity was a main objective of this thesis. The catalysts were prepared by two different approaches: the impregnation and the sol-immobilization of pre-formed metal NPs. The colloidal metal NPs were prepared by reduction of metal salts and also by decomposition of organometallic complexes. Rhodium catalysts prepared by impregnation of rhodium(III) chloride and reduction with H2 showed some reproducibility issues that were surpassed by using NaBH4 or hydrazine as reducing agents. The preparation of catalysts by the immobilization of colloidal NPs is an interesting alternative to obtain reproducible and very active catalysts. Nanoparticles of Pd, Rh and Ru were prepared by an organometallic approach and immobilized on calcined Fe3O4@SiO2, Fe3O4@SiO2CeO2 and Fe3O4@SiO2TiO2. The elimination of the stabilizing agent leads to more active catalysts upon recycling. Rhodium catalysts supported on ceria support was the most active catalyst in the hydrogenation of cyclohexene (TOF 125,000 h-1). Palladium catalysts were the most selective catalyst for the hydrogenation of phenol to cyclohexanone, no matter the support used. The formation of cyclohexanol is enhanced with titania and the hydrodeoxygenation to produce cyclohexane occurred mainly with silica.
A separação magnética tem recebido muita atenção como uma tecnologia robusta, altamente eficiente e rápida para recuperar catalisadores sólidos após uso em reações em fase líquida. Muitos estudos têm focado nas metodologias para a imobilização de espécies cataliticamente ativas, mas o desenvolvimento de suportes magnéticos tem se limitado a nanopartículas magnéticas revestidas com sílica, polímeros ou carbono. O desenvolvimento de nanocompósitos magnéticos com a incorporação de outros óxidos é muito desejável para ampliar a aplicação dessa tecnologia de separação em catálise. Nesse contexto, estudos da estabilidade térmica de magnetita revestida com sílica (Fe3O4@SiO2) foram realizados para avaliar a possibilidade de calcina-la sem perder as propriedades magnéticas do suporte. Uma etapa de calcinação é necessária para a deposição de diferentes óxidos na superfície da sílica, tais como céria e titânia. O Fe3O4@SiO2 calcinado preservou a morfologia \"core-shell\" e as propriedades magnéticas, porém apresentou um aumentou de seis vezes na área superficial. Novos suportes magnéticos foram desenvolvidos pela deposição de céria e titânia sobre magnetita previamente revestida com sílica. Nanocatalisadores magneticamente recuperáveis de Rh, Pd e Ru foram preparados. Os catalisadores foram utilizados na hidrogenação de ciclo-hexano, benzeno ou fenol e o principal objetivo dessa tese foi o estudo da influência de cada suporte na atividade catalítica. Os catalisadores foram preparados de duas formas diferentes: impregnação-redução e imobilização de nanopartículas (NPs) metálicas pré-formadas. As NPs coloidais foram preparadas pela redução de sais metálicos e, também, pela decomposição de complexos organometálicos. Catalisadores de ródio preparados pela impregnação de cloreto de ródio(III) e redução com H2 mostraram alguns problemas de reprodutibilidade, que foram superados utilizando NaBH4 ou hidrazina como agentes redutores. A preparação de catalisadores pela imobilização de NPs coloidais é uma alternativa interessante para obter catalisadores reprodutíveis e muito ativos. Nanopartículas de Pd, Rh e Ru foram preparadas a partir de organometálicos e imobilizadas em Fe3O4@SiO2 calcinada, Fe3O4@SiO2CeO2 e Fe3O4@SiO2TiO2. A eliminação do agente estabilizante torna os catalisadores mais ativos durante os reusos. O catalisador de Rh sobre o suporte de céria foi o catalisador mais ativo na hidrogenação de ciclohexeno (TOF 125000 h-1). O catalisador de Pd foi o catalisador mais seletivo para a hidrogenação de fenol em ciclo-hexanona, independente do suporte usado. A formação de ciclo-hexanol é favorecida pelo suporte de titânia e a hidrodesoxigenação para produzir ciclo-hexano ocorreu principalmente no suporte de sílica.

Palladium-catalyzed carbon-carbon cross-coupling reactions have emerged a broadly useful, selective and widely applicable method to synthesize pharmaceutical active ingredients. As currently practiced in the pharmaceutical industry, homogeneous Pd catalysts are typically used in cross-coupling reactions. The rational development of heterogeneous catalysts for cross-coupling reactions is critical for overcoming the major drawbacks of homogeneous catalysis including difficulties in the separation, purification, and quality control process in drug production. In order to apply heterogeneous catalysis to flow reactors that may overcome this limitation, the catalyst must be strongly bound to a support, highly stable with respect to leaching, and highly active. While the primary role of supports in catalysis has been to anchor metal particles to prevent sintering and leaching, supports can also activate catalytic processes. In this study, by using a xi combined theoretical and experimental method, we probed the effect of graphene as support in the complex reaction cycle of Suzuki reactions. The density functional theory study provides a fundamental understanding of how a graphene support strongly binds the Pd nanoparticles and act as both an efficient charge donor and acceptor in oxidation and reduction reaction steps. Theoretical investigations prove that the Pd-graphene interaction promotes electron flow between the metal cluster and the defected graphene to reduce reaction barrier. The ability for graphene to both accept and donate charge makes graphene an unusually suitable support for multi-step catalytic processes that involve both oxidation and reduction steps. The computer-aided catalyst design with the atomic precise accuracy demonstrates the Pd/graphene catalyst can be further optimized and the first-row transition metal nanoparticles have great potential to replace Pd to catalyze the Suzuki reaction. The corresponding experimental study shows that the method to immobilize the Pd nanoparticles on the graphene is crucial to increasing the reactivity and stability of the resulted catalyst. A comparison of the activation energy and turn over frequency for a series of supported and homogeneous catalysts indicates that exposing palladium-graphene to defect inducing microwave radiation results in dramatically lower activation energies and higher turnover frequencies. Furthermore, the heterogeneity tests demonstrate the Suzuki reactions are carried out on the surface of the immobilized Pd nanoparticle agreeing with the theoretical results. A method to engineer the 2-D graphene support to a 3-D structure to minimize the re-stacking and agglomeration of the graphene lattice will also be introduced in this study.

La present tesis va consistir en el disseny de nous nanocatalitzadors de cobalt per a la reacció de Fischer-Tropsh (FT). Les nano partícules de Cobalt van ser sintetitzades utilitzant diferents metodologies: reducció química utilitzant borohidrur de sodi com agent reductor o, descomposició tèrmica de compostos organometàl·lics tals com Co2(CO)8. Les síntesis van ser realitzades en presència de polímers com agents estabilitzants. Després de la síntesis, les nano partícules de cobalt foren aïllades, caracteritzades (utilitzant TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA i RAMAN) i provades en la reacció de Fischer-Tropsch en fase aquosa. Amb la finalitat de comparar amb catalitzadors suportats clàssics, les nano partícules de cobalt van ser immobilitzades amb TiO2 i provades en FT utilitzant un reactor de llit fix. En aquest estudi es va observar que l'activitat i la selectivitat de les nanopartícules de cobalt en ambdós sistemes catalítics depenien altament de paràmetres tals com el mètode de síntesis, el polímer estabilitzant i la mida de partícula. Aquestes diferències van ser atribuïdes a variacions en l'estructura i composició de les nano partícules que alhora eren intrínseques de cada paràmetre d'estudi.
La presente tesis consistió en el diseño de nuevos nanocatalizadores de cobalto para la reacción de Fischer-Tropsch (FT). Nanoparticulas de cobalto fueron sintetizadas usando diferentes metodologías: reducción química usando borohidruro de sodio como agente reductor o descomposición térmica of compuestos organometálicos tales como Co2(CO)8. Las síntesis fueron realizadas en presencia de polímeros como agentes estabilizantes. Después de la síntesis, las nanopartículas de cobalto fueron aisladas, caracterizadas (usando TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA and RAMAN) y probadas en la reacción de Fischer-Tropsch en fase acuosa. Con la finalidad de comparar con catalizadores soportados clásicos, las nanopartículas de cobalto fueron también inmovilizadas en TiO2 y probadas en FT usando reactores de lecho fijo. En este estudio se observó que el desempeño (actividad y selectividad) de las nanopartículas de cobalto en ambos sistemas catalíticos dependió altamente de parámetros tales como el método de síntesis, el polímero estabilizante y el tamaño de partícula. Estas diferencias fueron atribuidas a variaciones en la estructura y composición of las nanopartículas que a su vez eran intrínsecas a cada parámetro de estudio
The present thesis consisted in the design of novel cobalt nanocatalysts for the Fishcer-Tropsch (FT) synthesis. Cobalt nanoparticles were synthesized using different methodologies: chemical reduction method using sodium borohydride as reducing agent or thermal decomposition of organometallic precursors such as Co2(CO)8. The syntheses were carried out under the presence of polymer stabilizers. After the synthesis, the cobalt nanoparticles were isolated, characterized (using TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA and RAMAN) and tested in the Aqueous Phase Fischer-Tropsch synthesis. For comparison purposes with classical supported catalysts, the cobalt nanoparticles were also immobilized on TiO2 and tested in FT using fixed bed reactors. In this study was observed that the catalytic performance (activity and selectivity) of the cobalt nanoparticles in both catalytic systems were highly dependent on parameters such as the synthetic methodology, the polymer stabilizer and the particle size. These differences were attributed to variations in the structure and composition of the NPs intrinsic to each parameter under study.

In this thesis, the bioconversion of palladium and gold solutions and gold-bearing wastes into highly valuable mono- and bimetallic catalysts is described. This process relies on bioreduction; the ability of some bacteria to reduce Pd(II) and Au(III) ions at the expense of an exogenous electron donor with precipitation as zero valent metals. The resulting metallic nanoparticles (NPs) immobilised on the outer membrane and within the periplasm exhibit remarkable catalytic properties, sometimes surpassing commercially available catalyst formulations in terms of activity and/or selectivity. Previous studies in the field have mainly focused on the ability of Desulfovibrio spp. to reduce Pd(II) from both surrogate solutions and reprocessing wastes. The mechanism of Pd(II) reduction in this genus was previously shown to be enzymatic, involving hydrogenases, key enzymes of hydrogen metabolism. In this study, a detailed investigation into the mechanism of Pd(II) reduction by Escherichia coli using a genetic approach confirmed hydrogenase involvement and additionally showed that these enzymes are needed to initiate the formation of Pd(O) nuclei. Genetically engineered strains depleted of all functional hydrogenases lost their ability to produce Pd(O) NPs, which in turn greatly affected the catalytic activity of the resulting bioinorganic catalyst ("bioPd(O)"). Further studies suggested that the nature of the bacterial support also influenced the catalytic activity of bioPd(O) preparations. Seven bacterial strains, representing different Gramnegative and Gram-positive genera, were tested for Pd(II) reduction. Large differences in Pd(II) sorption and Pd(II) reduction ability were observed between strains; the combination of these factors affected the final size distribution of the cell-bound Pd(O) NPs and hence the catalytic activity of the resulting bioPd(O) preparations. Bioinorganic catalysts were shown to be active and/or selective in a wide variety of reactions, including Cr(VI) reduction, hydrogenolysis (reductive dehalogenation), Heck coupling and oxidations. The bioreductive approach was applied to demonstrate Au(III) reduction and recovery using cells of D. desulfuricans and E. coli and the first evidence of the catalytic activity of biogenic Au(O) NPs is presented. Au(III) reduction was slower than Pd(II) reduction and only partially involved hydrogenases which suggested the involvement of an additional different reduction route. However, introducing a bionanocatalyst consisting of lightly pre-palladized cells into the process greatly improved the speed of Au(III) reduction and resulted in the formation of highly ordered AulPd core/shell nanostructures which exhibited catalytic properties not seen with traditional chemical counterparts.

The application of heterogeneous catalysts to industrial processes is a key factor in the synthesis of nearly all chemicals currently produced, however billions of pounds are lost every year due to unplanned reactor shutdowns and catalyst replacement as a result of catalytic deactivation processes. Poisoning of heterogeneous catalysts by sulfur compounds is a particularly prominent class of deactivation processes, affecting a wide range of catalytic materials and catalytic reactions, including the industrially-prominent Haber-Bosch process for the synthesis of ammonia and steam reforming of methane for the synthesis of hydrogen. However, while the effects of sulfur adsorption on catalytic behaviour are often unmistakably apparent, the fundamental interactions leading to these effects are not yet well understood. The work presented in this thesis uses a combination of models systems, novel and traditional characterization techniques, and methods of modifying catalyst geometric and electronic structure to approach the topic of sulfur poisoning from a fundamental perspective. Particular focus is placed on using selective decoration of active sites to develop a system of model hydrogenation reactions to relate changes in catalytic behaviour to changes in geometric and electronic structure. Application of these model reactions to investigate the sensitivities of palladium- and ruthenium-based catalytic systems to modification by sulfur shows contrasting effects for the two metals. While both systems exhibit similar geometric effects of modification, the palladium-based catalysts are far more sensitive than the ruthenium-based catalysts to modification of electronic structure. Additionally, controlled variation in particle size for the palladium-based catalysts demonstrates that catalytic behaviour is dominated by electronic structure for small nanoparticles and geometric structure for large nanoparticles. This leads small nanoparticles to show increased sensitivity to electronic modification effects resulting from sulfur adsorption. Ultimately, the research presented within this thesis provides a basis for the intelligent design of heterogeneous catalysts for improving tolerance for sulfur poisoning, and for utilizing the effects of sulfur modification to optimize catalytic activity and selectivity for the synthesis of fine chemicals.

In this manuscript, the application of different nanocatalysts derived from metal oxides impregnated on the surface of the magnetite in different reaction of general interest in Organic Chemistry is described. In the First Chapter, a cobalt derived catalyst was used to study the hydroacylation reaction of azodicarboxylates with aldehydes. In the Second Chapter, a catalyst derived from copper was used to perform different reactions, including homocoupling of terminal alkynes and the subsequent hydration reaction to obtain the corresponding 2,5-disubstituted benzofurans, the reaction of alcohols and amines (or nitroarenes) to obtain the corresponding aromatic imines, the cross-dehydrogenative coupling reaction of N-substituted tetrahydroisoquinolines using deep eutectic solvents and air as final oxidant. Finally, the formation of benzofurans from aldehydes and alkynes through a tandem coupling-allenylation-cyclization process has been performed. In the Third Chapter, a bimetallic catalyst derived from nickel and copper was used to study the multicomponent reaction between benzyl bromides, sodium azide and alkynes to obtain the corresponding triazoles. In the Fourth Chapter, a catalyst derived from palladium was used in the direct arylation of heterocycles using iodonium salts. Also the synthesis of 4-aryl coumarins through the Heck arylation reaction and subsequent cyclization using the same catalyst is described. In the last Chapter, the use of different eutectic mixtures were studied as alternative media to perform in a single vessel the cyclation reaction of N-hydroxy imidoyl chlorides and alkynes, without any type of catalyst under oxidizing conditions.

This thesis focuses on synthesis of various types of metal-based catalysts and testing their catalytic activities for activation peroxymonosulfate for degradation of aqueous organic pollutants. Catalysts’ dimensional effects on activities were investigated by preparing catalysts in different shapes. Magnetic separable metal-based catalysts were also developed to minimize the heavy metal leaching problems. Studies further revealed that hydroxyl and sulfate radicals are the dominant reactive species for the decomposition of organic pollutants.

The thesis reports the synthesis of magnetic Mn-based nanocatalysts by different hydrothermal methods and their application in the oxidative reaction of aqueous phenol solutions for wastewater treatment. It was found that all the catalysts present high activity in peroxymonosulfate (PMS, Oxone) activation for the decomposition of phenol and good magnetic performance in separation. This research makes good contributions to materials synthesis and catalytic oxidation of organic pollutants in water.

From catalytic studies in surface science, it has been shown that the catalytic activity is dependent on the type of metal facet used. Nanocrystals of different shapes have different facets. This raises the possibility that the use of metal nanoparticles of different shapes could catalyze different reactions with different efficiencies. The catalytic activity is found to correlate with the fraction of surface atoms located on the corners and edges of the tetrahedral, cubic, and spherical platinum nanoparticles. It is observed that for nanoparticles of comparable size, the tetrahedral nanoparticles have the highest fraction of surface atoms located on the corners and edges and also have the lowest activation energy, making them the most catalytically active. Nanoparticles have a high surface-to-volume ratio, which makes them attractive to use compared to bulk catalytic materials. However, their surface atoms are also very active due to their high surface energy. As a result, it is possible that the surface atoms are so active that their size and shape could change during the course of their catalytic function. It is found that dissolution of corner and edge atoms occurs for both the tetrahedral and cubic platinum nanoparticles during the full course of the mild electron transfer reaction and that there is a corresponding change in the activation energy in which both kinds of nanoparticles strive to behave like spherical nanoparticles. When spherical palladium nanoparticles are used as catalysts for the Suzuki reaction, it is found that the nanoparticles grow larger after the first cycle of the reaction due to the Ostwald ripening process since it is a relatively harsh reaction due to the need to reflux the reaction mixture for 12 hours at 100 oC. When the tetrahedral Pt nanoparticles are used to catalyze this reaction, the tetrahedral nanoparticles transform to spherical ones, which grow larger during the second cycle. In addition, studies on the effect of the individual reactant have also provided clues to the surface catalytic process that is taking place. In the case of the electron transfer reaction, the surface catalytic process involves the thiosulfate ions binding to the nanoparticle surface and reacting with the hexacyanoferrate (III) ions in solution. In the case of the Suzuki reaction, the surface catalytic mechanism of the Suzuki reaction involves the phenylboronic acid binding to the nanoparticle surface and reacting with iodobenzene via collisional processes.

Controlling photoreactions remains a formidable challenge to chemists who have developed several approaches with varying degrees of success to achieve high reactivity/selectivity. Following nature's footprints, chemists have explored the use of confined media for controlling photoreactions. This thesis explores catalytic aspects of a water-soluble supramolecule known as a cucurbituril. Cucurbituril is a macrocyclic oligomer with a large enough cavity to sequester two guest molecules of appropriate size. The guest molecules explored in this thesis is coumarins. The model investigation involves host-guest complexes between cucurbit[8]uril (CB[8]) and coumarin to study the [2+2] photodimerization in water through various spectroscopic techniques. Our initial investigations explored the formation of host-guest complexes with coumarin guests that interacted with CB[8] host. This host guest complexation was used to explore and control photochemical reaction and photophysical properties of encapsulated coumarin guest molecules. The host-guest complexation was found to be dependent on the polarity of the coumarin and the volume constraints imparted by the CB[8] cavity. Observational insights from various coumarins provided insights into formation of host-guest complexes with CB[8]. Some coumarins do not form complexes but if they do they can form 1:1 and 1:2 host guest complexes as well as dynamic host-guest complexes (mixture of 1:1 and 1:2 host-guest complexes). Using dynamic host-guest complexes, we explored the use of CB[8] as a photocatalysts. Photodimerization of 6-methylcoumarin was explored as a model system to understand the supramolecular aspects of photocatalysis. The mechanism for photocatalysis was elucidated using various spectroscopic techniques. Both steady state and time-resolved experiments were carried to ascertain the thermodynamic and kinetic aspects of the supramolecular catalytic process. Spectroscopic investigations provided insights into vital role of dynamic complexes in the catalytic cycle as well as the extrusion of photoproduct from the cavity to enable turnover in the system. Thus this investigation provided an opportunity to build an overall picture of a novel supramolecular photocatalytic process in water. This will undoubtedly foster further development in the area of supramolecular photocatalysis.
National Science Foundation (NSF CAREER CHE- 0748525 and CHE- 1213880)
NSF ND-EPSCoR Seed Grant
NSF ND-EPSCoR Doctoral Research Fellowship

The area of methanol synthesis and utilization has been attracting research interests due to its positive impact on the environment and also from energy perspectives. Methanol synthesis from CO₂ hydrogenation not only produces methanol which is a key platform chemical and a clean fuel, but can also recycle CO₂ which is one of the major greenhouse gases causing global warming. As a mobile energy carrier (particularly as a hydrogen carrier), methanol is a versatile molecule which is able to generate H₂ via its decomposition. Catalysis plays a decisive role in the success of both methanol synthesis from CO₂ hydrogenation and its reverse decomposition reaction. Pd/Ga₂O₃ binary catalyst has recently been identified as an active catalyst for the methanol synthesis reaction. In this thesis, it is reported the shape effect of Pd promoted Ga₂O₃ for this reaction. The catalytic H₂ evolution from methanol photodecomposition has also been studied over these catalysts. Three shapes of Ga₂O3 nanomaterials (i.e. rod and plate β-Ga₂O3, and particle γ-Ga₂O₃) have been synthesized, followed by doping with Pd metal to form corresponding Pd/Ga₂O₃ nanocatalysts. It was found that a (002) polar Ga2O3 surface which was dominantly presented on the plate form was unstable, giving a higher degree of oxygen defects and mobile electrons in the conduction band than the other non-polar (111) and (110) surfaces of the rod form. It was shown that a significantly stronger metal support interaction was found between the (002) polar Ga₂O₃ on the plate form and Pd, which gave higher methanol yield and selectivity. For methanol photodecomposition, it was found that, for pure Ga₂O₃ catalysts of different shapes, the plate form with a highest degree of defects (unstable polar surface) could encourage a non-radiative catalytic recombination of electron and hole pairs upon irradiation, hence giving a highest photocatalytic activity for H₂ production. Once Pd was introduced onto these oxide surfaces, it was noted that there was a fast and readily electron transfer from the conduction band of Ga₂O₃ to Pd due to the formation of a Schottky junction between the two materials. This produces metal sites for hydrogen production and further enhances the rate of the photocatalytic reaction over the radiative recombination of excitons. However, it was also found that at higher Pd content (>1%), the significantly shortened exciton lifetimes reduce the catalytic rate hence giving an overall volcanic response of activity to increasing Pd content for each shape of Ga₂O₃. At the higher Pd content, the plate form appeared to sustain a longer lifetime for photocatalysis compared to the other forms at the equivalent Pd loading.