Tesi sul tema "Catalytic reforming"

Thesis (Ph. D.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains x, 174 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 155-166).

This thesis describes a study of catalysed steam methane reforming. A microreactor of 3 mm bore, operated and controlled by computer has been used. The catalyst employed was an industrial type steam reforming nickel oxide-alumina catalyst containing 15% nickel. The experiments were performed at temperatures of industrial interest in the range of 600-840°C. The pressure range was 2.5-9 bar, at hydrogen to methane ratios of 0.5-2 and steam to methane ratios of 2-3.1. The catalyst was initially activated at 700°C in a flow of steam and hydrogen (7:1) for 16 hours. Initially, the activity of the catalyst was very high then after 16 hours of operation it started to decline to reach its lowest level after 60 hours of operation despite reactivation. Subsequent activation methods including hydrogen reduction and temperature treatment were found to have dynamic effects on catalyst activity. An important improvement in the activity of the catalyst at lower temperature was established by incorporating a dynamic sequence of temperature changes that included some experiments at temperatures within the range 750-850°C. The dynamics of several such experiments were measured and recorded. The improvement in activity at lower temperature following a high temperature experiments gradually declined at a rate that was much slower than the dynamics of mass transfer and heat transfer in the system. The experimental results were used to examine a dual reaction mechanism for the reforming process. The reaction velocity coefficients established by non-linear parameter estimation were studied as function of temperature, pressure and composition.

In this work, a fundamental kinetic model for the catalytic reforming process has been developed. The complex network of elementary steps and molecular reactions occurring in catalytic reforming has been generated through a computer algorithm characterizing the various species by vectors and Boolean relation matrices. The algorithm is based on the fundamental chemistry occurring on both acid and metal sites of the catalyst. Rates are expressed for each of the elementary steps involved in the transformation of the intermediates. The Hougen-Watson approach is used to express the rates of the molecular reactions occurring on the metal sites of the catalyst. The single event approach is used to account for the effect of structure of reactant and activated complex on the rate coefficients of the elementary steps occurring on the acid sites. This approach recognizes that even if the number of elementary steps is very large they belong to a very limited number of types, and therefore it is possible to express the kinetics of elementary steps by a reduced number of parameters. In addition, the single event approach leads to rate coefficients that are independent of the feedstock, due to their fundamental chemical nature. The total number of parameters at isothermal conditions is 45. To estimate these parameters, an objective function based upon the sum of squares of the residuals was minimized through the Marquardt algorithm. Intraparticle mass transport limitations and deactivation of the catalyst by coke formation are considered in the model. Both the Wilke and the Stefan-Maxwell approaches were used to calculate the concentration gradients inside of the particle. The heterogeneous kinetic model was applied in the simulation of the process for typical industrial conditions for both axial and radial flow fixed bed reactors. The influence of the main process variables on the octane number and reformate volume was investigated and optimal conditions were obtained. Additional aspects studied with the kinetic model are the reduction of aromatics, mainly benzene. The results from the simulations agree with the typical performance found in the industrial process.

In this project, the active and stable catalysts were successfully developed for methane reforming reactions under microwave heating. The monometallic Co, Cu, and Mo catalysts supported on either AhO3 or TiO2 were inactive under all tested conditions whilst their respective bimetallic CoMo and CuMo catalysts were highly active and stable at low microwave powers to produce desirable syngas ratios. The activation mechanism of metallic­based catalysts for reforming reactions under microwave heating was explored.

Stringent legislation on control of vehicle exhaust emissions has led to consideration of alternative means of reducing emissions, with hydrogen fuel cell powered vehicles being accepted as one favoured possibility. However, the difficulties of storing and distributing hydrogen as a fuel are such that the conversion of more readily available fuels to hydrogen on board the vehicle may be required. The production of hydrogen by the partial oxidation of isooctane over Rh/Al2O3, Rh/CeO2-?l2O3 and Rh/CeO2-ZrO2 catalysts has been investigated. Oxidation was initiated at temperatures between 200 ?220 oC. The yield of hydrogen was 100%. CeO2-ZrO2 was found to be the best support. The production of hydrogen by the autothermal reforming of artificial gasoline has been studied. Part of gasoline is oxidised to produce heat and steam to promote the steam reforming of unburnt gasoline to produce hydrogen. The use of platinum impregnated on ceria supports (active for oxidation) and a commercial nickel based catalyst (Ni-com), for steam reforming of gasoline have been explored. Initiation of oxidation of artificial gasoline over unreduced platinum based catalysts occurred at temperature as low as 150 oC, depending on the oxygen:carbon ratio and the liquid hydrocarbon used. Detailed kinetic studies of the steam reforming of isooctane and artificial gasoline (a mix of cyclohexane, isooctane and octane) over pre-reduced Ni-com catalysts showed that the reaction was 0.17 order in isooctane and 0.54 order in steam, whilst the reaction was 0.08 order in artificial gasoline and 0.23 order in steam. Mechanisms have been proposed to account for the dual site surface reaction with dissociative adsorption of isooctane or artificial gasoline and steam. Combined oxidation and steam reforming systems (autothermal reforming) using Pt/CeO2 as a front catalyst bed and Ni-com as the rear bed at the feed conditions of oxygen:carbon (O:C) ratio of ca.1.2 and steam:carbon (S:C) ratio of ca.2, produces ca. 3.5 moles of hydrogen per mole of gasoline fed. The system reaction temperature could be controlled by adjusting the O:C and S:C ratios in feed.

La thèse de doctorat avait comme objectif l’étude de la production d’hydrogène par vaporeformage catalytique du glycérol. Les catalyseurs développés dans ce travail sont des oxydes mixtes cérine-zircone de structure fluorite auxquels des oxydes de métaux de transition (Co) ou des métaux nobles (Ru/Rh) ont été ajoutés. L’effet de la nature de l’élément ajouté (Ru, Rh, Co-Rh, Co-Ru), de la quantité de métaux nobles (0,5 %, 1,2%) et du rapport massique CeO2/ZrO2 (0,65/0,35; 0,8/0,2; 0,2/0,8) a été étudié. Les caractérisations des catalyseurs avant test montrent que la présence de métaux nobles favorise les propriétés re-dox de la fluorite : abaissement de la température de réduction de l’oxyde de cérium. Cependant, le pourcentage de réduction de la cérine n’augmente qu’en présence de cobalt et métal noble. Les propriétés red-ox sont les plus marquées pour des rapports Ce/Zr élevés. La présence de Rh ou de Ru augmente l’activité catalytique et la stabilité du catalyseur par rapport à Ce-Zr ou Ce-Zr-Co. Le Rh a une activité supérieure à celle du Ru et l’addition du Rh peut se limiter à 0,5 % en masse. L’augmentation du rapport Ce/Zr est aussi favorable à l’activité catalytique. En conséquence, le meilleur catalyseur de production d’hydrogène par vaporeformage du glycérol est l’oxyde mixte Ce-Zr-Co-Rh riche en cérium. La production d’hydrogène et la stabilité catalytique ont été améliorées avec ce catalyseur soit en modifiant la configuration du lit catalytique (décomposition plus importante donc vaporeformage des produits secondaires), soit par addition d’oxygène en faible quantité (gazéification du carbone présent sur la surface favorisée)
This work presents the H2 production by glycerol steam reforming (GSR) using as catalysts mixed fluorite-type oxides of Ce-Zr-(Ru/Rh) and Ce-Zr-Co-(Ru/Rh). The effect of the active phase (Ru, Rh, Co-Ru, Co-Rh), the amount of the noble metal (0. 5% wt, 1. 2 % wt), and the mass CeO2/ZrO2 ratio (0. 65/0. 35, 0. 8/0. 2, 0. 2/0. 8) were studied. The characterisation of the catalysts before test showed that the introduction noble metals favoured the redox properties of the mixed oxides by lowering the temperature of reduction. However only with the presence of Co and the noble metal the reducibility capacity of the mixed oxides increased (% Ce reduced). The redox properties were also enhanced by the higher amount of Ce in the mixed oxide. The presence of the noble metals (Ru/Rh) increases the catalytic activity and stability respect to Ce-Zr and Ce-Zr-Co catalysts. The increase in the amount of noble metal did not present a significant change but the increase in the Ce amount enhanced the stability and selectivity towards H2. The comparison between equivalent series of Ru and Rh catalysts shows that the Rh oxides exhibit a better catalytic behaviour. The catalyst with the best performance towards the production of H2 was the Ce-Zr-Co-Rh mixed oxide rich in cerium. Additional tests were performed using this catalyst and it was found that improvements of the process of GSR can be achieved by modification of the catalytic bed configuration (favour the steam reforming of glycerol decomposition by-products) and by the addition of low quantities of O2 to the reactant flow (improve carbon gasification and catalyst stability)

The utilisation of biogas as an energy source or as a feed stock for the chemical industry would help to lower the present wasteful and environmentally unfriendly venting of greenhouse gases to the atmosphere. One obstacle to this becoming a reality include finding a catalyst that is active towards carbon dioxide reforming of methane as well as resistance to carbon deposition and sulphur poisoning. As a potential alternative to supported nickel catalysts, a nickel doped perovskite has been produced via a hydrothermal synthesis method for reforming biogas. The selected perovskite, SrZrO3, was doped with 4 mol % nickel into the structure and shown to be phase pure by XRD. This material was rigorously tested catalytically using a range of biogas conditions. 4 mol% Ni doped SrZrO3 was shown to be resistant to carbon deposition under high temperature, methane rich biogas reforming conditions with no observable trend between the amount of carbon formed and the time on stream. This catalyst showed high activity and selective towards the formation of the desired products, an equimolar mixture of hydrogen and carbon monoxide. As naturally derived biogas is not a pure mixture of methane and carbon dioxide, studies into the effect that two of the other important components of biogas, water and sulphur containing compounds, were carried out. The perovskite material was seen to be stable towards continued dry reforming of methane irrespective of the inclusion of water, and at elevated reaction temperatures was able to convert the water into the required products of hydrogen and carbon monoxide. The effect of hydrogen sulphide was studied and the perovskite material was seen to be susceptible to sulphur poisoning. However the extent and the recovery from this type of deactivation was an improvement on that seen by Ni/YSZ and 5% ceria doped Ni/YSZ.

Biomass has become an increasingly important renewable source of energy forenhanced energy security and reduced CO[subscript]2 emissions. Gasification is at the core of many biomass utilisation technologies for such purposes as the generation of electricity and the production of hydrogen, liquid fuels and chemicals. However, gasification faces a number of technical challenges to become a commercially feasible renewable energy technology. The most important one is the presence of tar in the gasification product gas. The ultimate purpose of this thesis was to investigate the catalytic reforming of tar using cheap catalysts as an effective means of tar destruction.In this thesis, natural ilmenite ore and novel char-supported catalysts were studied as catalysts for the steam reforming of biomass tar derived from the pyrolysis of mallee biomass in situ in two-stage fluidised-bed/fixed-bed quartz reactors. In addition to the quantification of tar conversion, the residual tar samples were also characterised with UV-fluorescence spectroscopy. Both fresh and spent catalysts were characterised with X-ray diffraction spectroscopy, FT-Raman spectroscopy and thermogravimetric analysis.The results indicate that ilmenite has activity for the reforming of tar due to its highly dispersed iron-containing species. Both the externally added steam and low concentration oxygen affect the tar reforming on ilmenite significantly. The properties of biomass affect the chemical composition of its volatiles and therefore their reforming with the ilmenite catalyst. Compared with sintering, coke deposited on ilmenite is the predominant factor for its deactivation.During the steam reforming process, the char-supported iron/nickel catalysts exhibit very high activity for the reforming of tar. In addition, NO[subscript]x precursors could be decomposed effectively on the char-supported iron catalyst during the steam reforming process. The hydrolysis of HCN and the decomposition of NH[subscript]3 on the catalyst are the key reactions for the catalytic destruction of NO[subscript]x precursors.The kinetic compensation effects demonstrate that the reaction pathways on the char-supported catalysts are similar but different from those on ilmenite. The proprieties of catalyst support could play important roles for the activities of the catalysts and the reaction pathways on the catalysts. The char support as part of the char-supported catalysts can undergo significant structural changes during the catalytic reforming of biomass volatiles.

La energía se ha convertido en una necesidad vital para garantizar el desarrollo de las sociedades modernas. Entre las diferentes posibles alternativas para producir energía, el hidrogeno presenta varias características que lo convierten en un atractivo vector energético: primero, se trata de una tecnología más eficiente para transformar la energía química en electricidad -por ejemplo, utilizando pilas de-combustible, las cuales también reducen de manera significativa los niveles de emisión de CO2 -; en segundo lugar, el hidrogeno puede ser producido a partir de una amplia variedad de materias primas, incluyendo recursos renovables y no renovables. Sin embargo, las tecnologías para producir hidrogeno para applicaciones con pilas de combustible aun requieren de un esfuerzo en investigación y desarrollo.
El objetivo principal de esta tesis fue de evaluar técnicamente las opciones para preparar y utilizar catalizadores en placas insertados en un reactor de pared catalítica para producir hidrogeno mediante el reformado por vapor de etanol bajo condiciones de alta eficiencia térmica. Para completar el objetivo general y los objetivos específicos, se diseño un plan experimental sistemático, compuesto de tres partes: documentación, experimentación y simulación numérica. La información utilizada se puede clasificar en tres ramas: primero, una revisión detallada de las características generales que presentan las técnicas de reformado, seguido por una revisión descriptiva del reformado por vapor de etanol, enfocado en los principales aspectos de la preparación de catalizadores y la realización de la reacción química. A continuación en segundo lugar, se presenta una descripción acerca de reactores estructurados y los métodos para preparar catalizadores. Por último, en tercer lugar, se expone una explicación centrada en los materiales, equipos y métodos empleados para explorar el rendimiento de los catalizadores. Esta parte incluye la descripción de: algunas de las técnicas analíticas más comunes para caracterizar y evaluar tanto catalizadores como compuestos químicos y la descripción de las herramientas utilizadas en la simulación numérica.
El primer bloque de simulación numérica tiene como fin evaluar las posibles restricciones termodinámicas por medio de análisis específicos basados en el equilibrio termodinámico, tanto del reactor como del proceso integrado. Luego, se ejecuta un mapeo del conjunto de condiciones operacionales, compuesto por cuatro variables principales: (temperatura, relación vapor carbón, presión y factor de recobro de hidrogeno en el separador de membrana). Ello con el fin de garantizar una operación auto-térmica del procesador de combustible. Se compara la habilidad y la ventaja entre los diferentes tipos de catalizadores publicados en trabajos previos en base a las condiciones termodinámicas ideales determinadas en el análisis termodinámico.
Para los catalizadores en polvo, se realizo experimentos de caracterización y reacción mediante el empleo de un reactor de lecho fijo. Se ha efectuado un estudio sistematico para comparar la actividad y la selectividad de dos tipos de catalizadores, bajo condiciones moderadas de temperatura y relación vapor carbón. Los catalizadores basados en níquel (Ni/La2O3-Al2O3) y cobalto (Co-Fe/ZnO y Co-Mn/ZnO) han sido preparados y probados a las siguientes condiciones: temperatura en el rango de 400-500°C, relación vapor carbono entre 2 y 4, tiempo de contacto desde 4.3 hasta 1100 min·gcat molEtOH-1, cubriendo un rango de conversión de etanol desde 20 hasta 100%. Se ha efectuado un diseño de análisis multifactorial para establecer la influencia de las variables (temperatura, relación vapor carbón, tiempo de contacto y formulación del catalizador) en términos de la conversión de etanol y la selectividad hacia los diferentes productos.
Por último, se ha efectuado la caracterización, simulación y experimentación utilizando una configuración de reactor de pared catalítica. Primero, se emplea un modelo en 2D para analizar las características principales del reactor de pared catalítica diseñado y construido para realizar la reacción sobre las placas con catalizador previamente preparadas. En segundo lugar, se expone de manera detallada el método seguido para preparar dos tipos diferentes de placas catalíticas. Estas placas con catalizador son caracterizadas de manera similar al método empleado con los catalizadores en polvo. Luego, se ha realizado un estudio sistemático para comparar la actividad y la selectividad de los dos tipos de placas catalíticas. Por último, mediante un modelo 1D se revelan aspectos fundamentales de la configuración del reactor de pared catalítica utilizando una configuración con dos canales paralelos, en los cuales se ejecutan una reacción endotérmica y otra exotérmica respectivamente.
La principal conclusión de este trabajo es que el reformado por vapor de etanol puede ser realizado bajo condiciones de alta eficiencia térmica si se emplea un diseño basado en un reactor de pared catalítica con recobro de calor integrado a una unidad de separación para la purificación del hidrogeno. Las placas catalíticas han demostrado ser un elemento fundamental en este tipo de reactor porque incrementan de manera significativa el transporte de calor que se requiere para sostener las reacciones endotérmicas.
Energy has become a fundamental necessity to guarantee modern society development. Among different alternatives possible to produce energy, hydrogen presents several characteristics which make it an attractive energy vector: first, more efficient processes to transform chemical energy into electricity -such as Fuel Cells that, in addition, will help to reduce significantly CO2 emission levels-; and second, hydrogen can be produced from a large variety of feed stocks, including fossil and renewable resources. However, as hydrogen production technologies for Fuel Cell applications are not available commercially yet, it still requires additional R&D efforts.
The principal objective of this thesis was to evaluate technical feasibility for preparing and using catalytic plates in a Catalytic Wall Reactor configuration to produce hydrogen by Steam Reforming of Ethanol under conditions of high thermal efficiency. To fulfill the overall and specific objectives, a systematic experimental plan was designed and executed. It was composed of three main parts: documentation, experimentation and numerical simulation. Background information is divided into three branches, first a detailed overview of technical features for reforming technology, followed by a descriptive review of Steam Reforming of Ethanol key aspects for catalysts preparation and reaction performance. Third is presented a comprehensive examination on structured reactor and catalyst preparation methods. In this part is exposed a detailed explanation of materials, equipments, and methods employed for screening catalyst and evaluating catalytic reactor performance. Also, is presented employed techniques for catalyst characterization and fluid analysis. Finally are described tools for numerical simulation.
First component of numerical simulations evaluates possible thermodynamic constrains through specific analyses based on thermodynamic equilibrium of reactor and integrated fuel processor. Then, is performed a mapping for the set of four operational variables (temperature, steam to carbon ratio, pressure, and hydrogen recovery in the membrane separator), that allow an auto-thermal operation of the fuel processor. The suitability and advantages of the different catalysts preparations that are known from recent publications are discussed on the basis of the operation conditions determined on the thermodynamic analysis.
Experimental work is performed for powder catalyst characterization and catalytic experimentation using a Packed Bed Reactor (PBR). It has conducted a systematic study to compare the activity and selectivity of two types of catalyst at moderate temperature and steam to carbon (SC) ratios. Nickel-based catalysts (Ni/La2O3-Al2O3) and novel Co-based catalysts (Co-Fe/ZnO and Co-Mn/ZnO) have been prepared and tested at temperatures of 400 and 500 °C, Steam to Carbon (SC) molar ratios of 2 and 4, and contact times from 4.3 to 1100 min·gcat molEtOH-1, covering a range of ethanol conversion from 20 to 100%. A multifactorial design analysis has been conducted to establish the significance of temperature, SC ratio, contact time and catalyst formulation on ethanol conversion and selectivity towards the different reaction products.
At last, it is carried out the catalytic plate characterization, simulation and experimentation using a Catalytic Wall Reactor configuration. First, is used a 2D modeling to analyze main characteristics of the Catalytic Wall Reactor designed and constructed to perform reactions on the prepared catalytic plates. Prepared catalytic plates are characterize in a similar way to that employed for the powder catalysts. After that, it was conducted a systematic study to compare the activity and selectivity of two types of catalytic plates. 1D model reveals main aspects on thermal performance for a theoretical Catalytic Wall Reactor using two co-current channels with endothermic and exothermic reactions respectively.
Main conclusion from this work is that Steam Reforming of Ethanol can be performed at high thermal efficiency if the design of the fuel processor is based on structured catalytic wall reactors with integrated heat recovery coupled to a separation unit for hydrogen purification. Catalytic plates have proven to be a key component on CWR because improves significantly the heat transfer which is required to sustain endothermic reactions.

An investigation was conducted to determine the feasibility of developing a reduced order model capable of accurately predicting the behavior of steam methane reforming. An emerging model reduction technique based on examining causal relationships was applied to the reaction network developed by Xu and Froment to eliminate unnecessary intermediate species[1]. A dynamic discrepancy term was included in the reduced network to quantify the error incurred from the network reduction. This discrepancy is stochastic in nature, and a Markov Chain Monte Carlo (MCMC) sampling routine coupled with Bayesian statistical methods was used to calibrate the parameters of the discrepancy by comparison with simulated data provided by a more robust model of methane reforming.

An output distribution of discrepancy parameters was calibrated based on the transient response of a laboratory scale continuous stirred tank reactor (CSTR). Extrapolation to predictions of more complex plug flow reactor (PFR) models was also shown effective using the calculated distribution. Specifications regarding reactor geometry and operating conditions were taken from previously published studies. Traditional simplifying assumptions were specified to reduce the computation complexity of both the reactor simulation and calibration routine. Simulations were performed using a combination of MATLAB and C++ Matlab executable (MEX) files using high performance computing resources available through West Virginia University's Spruce Knob cluster.

Results of the calibration showed that the proposed modeling technique is able to reproduce the behavior of both the transient response of the single constant stirred tank reactor and the discretized plug flow reactor approximations. Convergence of the calibration routine was validated through statistical means. Additionally, computational times for both the robust model and the proposed reduced model are shown to be on the same order of magnitude. The combination of these findings verifies the ability of the proposed modeling technique to not only accurately predict the behavior of steam reforming but also indicates the potential for applying the proposed method for more complex simulations.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
Dry reforming of methane reaction was conducted in the presence of titanate nanotubes (TNTs) modified with Co, Ni and Pt. TNTs were synthesized by hydrothermal treatment and than these solids were either submitted to ion exchange for Ni and Co using hexahydrate nitrate solutions, or they were submitted to wet impregnation with H2Ptl6.6H2O (1% w/w of Pt) solution. The solids were characterized before and after the dry reforming of methane by elemental chemical analysis (CHN), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption-desorption isotherms, thermoprogrammed reduction (TPR), CO2 thermoprogrammed desorption (CO2-TPD), transmission electronic microscopy (TEM), scanning electronic microscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). Raman and XRD results showed the presence of Na2Ti3O7 phase to all sodic nanotubes, while that the nanotubes modified displayed peaks and vibrational modes relative to CoTi3O7, NiTi3O7 and PtOx/Na2Ti3O7 phases. TEM images exhibited tubular morphology composed by multi-walls, as observed by XRD and Raman. SEM-EDS results showed the nanotubes composition with M/Ti ratio lower than the theoretical (value of 0,33), due to the presence of structural water. The XPS results confirmed the presence of M(OH)2 phase (M=Co, Ni or Pt) present on nanotubes surface. TPR patterns suggested the formation of M0/MTiO3 (M = Co, Ni and Pt) after the reduction of the nanotubes at 650 ÂC. The nitrogen adsorption-desorption isotherms of sodic and modified TNTs showed isotherms type IV with an essentially mesoporous structure. CO2-TPD patterns suggested the presence of weak and moderate basic sites in all catalysts, indicating phase transformation due to the decomposition, in situ, of as-prepared nanotubes. The catalyst NiTNT exhibited the highest CO2 and methane conversion at 600 ÂC, with about 43 and 25%, respectively, and H2/CO ratio equal 1, without deactivation over time. PtTNT was lesser susceptible to coking, although sintering remarkably decreased the performance of this solid. On the other hand, PtTNT and CoTNT showed formation of coke over the PtOx/PtTiO3 and Co0/CoTiO3 active phase, respectively, so that the latter solid deactivated during the dry reforming of methane.
A reaÃÃo da reforma seca do metano foi conduzida na presenÃa de nanotubos de titanatos (TNTs) modificados com Co, Ni e Pt. Os TNTs foram sintetizados via tratamento hidrotÃrmico e, posteriormente, foram submetidos à troca iÃnica por Ni e Co, utilizando soluÃÃes de nitrato hexahidratado, ou foram submetidos à impregnaÃÃo via-Ãmida com soluÃÃo de H2PtCl6.6H2O (1% m/m de Pt). Os catalisadores foram caracterizados antes e apÃs reaÃÃo de reforma seca do metano por anÃlise quÃmica (CHN), difraÃÃo de raios-X (DRX), espectroscopia Raman, isotermas de adsorÃÃo-dessorÃÃo de nitrogÃnio, reduÃÃo termoprogramada (TPR), dessorÃÃo termoprogramada de CO2 (TPD-CO2), microscopia eletrÃnica de transmissÃo (TEM), microscopia eletrÃnica de varredura (MEV-EDS) e espectroscopia fotoeletrÃnica de raios-X (XPS). Os resultados de Raman e DRX evidenciaram a presenÃa da fase Na2Ti3O7 para os nanotubos sÃdicos, enquanto que para os nanotubos modificados foram identificados picos e modos vibracionais referentes Ãs fases CoTi3O7, NiTi3O7 e PtOx/Na2Ti3O7. As imagens de TEM exibiram morfologia tubular composta por multiparedes, corroborando com os resultados de DRX e Raman. Os resultados de MEV-EDS mostraram a composiÃÃo dos nanotubos com razÃo M/Ti menor que o teÃrico (0,33), devido à presenÃa de Ãgua estrutural. Os resultados de XPS confirmaram a existÃncia da fase M(OH)2 (M=Co, Ni ou Pt) presentes na superfÃcie dos nanotubos. As curvas de TPR sugeriram a formaÃÃo da fase M0/MTiO3 (M = Co, Ni e Pt), apÃs a reduÃÃo dos nanotubos a 650 ÂC. As isotermas de adsorÃÃo-dessorÃÃo de nitrogÃnio dos TNTs sÃdicos e modificados apresentaram isotermas do tipo IV com estrutura essencialmente formada por mesoporos. Os perfis de TPD-CO2 sugeriram a presenÃa de sÃtios bÃsicos fracos e moderados em todos os catalisadores, indicando mudanÃa de fase devido à decomposiÃÃo in situ dos nanotubos como sintetizados. O catalisador NiTNT apresentou os melhores resultados de conversÃo de CO2 e metano a 600 ÂC, com aproximadamente 43 e 25%, respectivamente, e razÃo H2/CO igual a 0,5, sem desativaÃÃo ao longo do tempo. PtTNT foi menos susceptÃvel à formaÃÃo de coque, embora o fenÃmeno de sinterizaÃÃo tenha desfavorecido o desempenho do sÃlido. Por outro lado, os sÃlidos PtTNT e CoTNT apresentaram formaÃÃo de coque sobre as fases ativas PtOx/PtTiO3 e Co0/CoTiO3, respectivamente, de modo que este Ãltimo sÃlido desativou durante a reaÃÃo da reforma seca do metano.

Hydrogen has been regarded as the most environmental friendly energy carrier due to its easily-storage and high energy concentration. A variety of technologies have been studied to generate hydrogen. Ethanol steam reforming is one of the most promising ways to generate hydrogen since its high productivity. However, the high operating temperature is the main challenge for developing the process. Metallic catalysts have been widely investigated to improve the performance of ethanol steam reforming process. Ni-based catalysts are frequently studied due to their good catalytic performance and low cost for ESR. However, quick deactivation is still a major challenge for Ni-based catalysts, which is mainly caused by coke formation or metal sintering. In this thesis, improvements of Ni-based catalysts have been studied in two approaches: introducing a second metal of Cu to form bimetallic catalysts and Optimizing Ni content in catalysts that Ni is supported on CaO modified Al2O3. Bimetallic CuNi/YSZ catalysts were synthesized by impregnation. Results showed that adding Cu to Ni-based catalysts successfully improved the catalytic stability while Cu has barely activity in ESR. The formation of Cu-Ni alloy can improve catalyst reducibility and stabilize Ni from sintering. Ni supported on CaO modified Al2O3 catalysts were synthesized by co-precipitation. Introducing of CaO to Al2O3 support successfully improved the stability of catalysts by reducing acidity sites since the acidic property of Al2O3 leads to serious coke formation in ESR. Different Ni loading ratios contribute to the formation of different Ni-containing compounds, which have various catalytic performances in ESR. Increasing Ni loading ratio has positive effect on catalytic activity. But excess Ni loading does influence the particle size, metal dispersion and reducibility.

This dissertation includes two accounts of rigorous modeling of petroleum refinery modeling using rigorous reaction and fractionation units. The models consider various process phenomena and have been extensively used during a course of a six-month study to understand and predict behavior. This work also includes extensive guides to allow users to develop similar models using commercial software tools. (1) Predictive Modeling of Large-Scale Integrated Refinery Reaction and Fractionation Systems from Plant Data: Fluid Catalytic Cracking (FCC) Process with Planning Applications: This work presents the methodology to develop, validate and apply a predictive model for an integrated fluid catalytic cracking (FCC) process. We demonstrate the methodology by using data from a commercial FCC plant in the Asia Pacific with a feed capacity of 800,000 tons per year. Our model accounts for the complex cracking kinetics in the riser-regenerator and associated gas plant phenomena. We implement the methodology with Microsoft Excel spreadsheets and a commercial software tool, Aspen HYSYS/Petroleum Refining from Aspen Technology, Inc. The methodology is equally applicable to other commercial software tools. This model gives accurate predictions of key product yields and properties given feed qualities and operating conditions. This work differentiates itself from previous work in this area through the following contributions: (1) detailed models of the entire FCC plant, including the overhead gas compressor, main fractionator, primary and sponge oil absorber, primary stripper and debutanizer columns; (2) process to infer molecular composition required for the kinetic model using routinely collected bulk properties of feedstock; (3) predictions of key liquid product properties not published alongside previous related work (density, D-86 distillation curve and flash point); (4) case studies showing industrially useful applications of the model; and (5) application of the model with an existing LP-based planning tool. (2) Predictive Modeling of Large-Scale Integrated Refinery Reaction and Fractionation Systems from Plant Data: Continuous Catalyst Regeneration (CCR) Reforming Process: This work presents a model for the rating and optimization of an integrated catalytic reforming process with UOP-style continuous catalyst regeneration (CCR). We validate this model using plant data from a commercial CCR reforming process handling a feed capacity of 1.4 million tons per year in the Asia Pacific. The model relies on routinely monitored data such ASTM distillation curves, paraffin-napthene- aromatic (PNA) analysis and operating conditions. We account for dehydrogenation, dehydrocyclization, isomerization and hydrocracking reactions that typically occur with petroleum feedstock. In addition, this work accounts for the coke deposited on the catalyst and product recontacting sections. This work differentiates itself from the reported studies in the literature through the following contributions: (1) detailed kinetic model that accounts for coke generation and catalyst deactivation; (2) complete implementation of a recontactor and primary product fractionation; (3) feed lumping from limited feed information; (4) detailed procedure for kinetic model calibration; (5) industrially relevant case studies that highlight the effects of changes in key process variables; and (6) application of the model to refinery-wide production planning.
Ph. D.

Thesis (Ph. D.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains xii, 162 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 139-150).

Pyrolysis of biomass is a promising and sustainable approach to produce value-added chemicals and biofuels. In order to achieve a high yield of hydrogen-rich syngas from pyrolysis of biomass, the microwave-enhanced pyrolysis of biomass coupled with catalytic reforming was studied systematically in this research. Firstly, microwave-enhanced pyrolysis of biomass was carried out and compared with conventional pyrolysis under the same processing conditions. Characterisations of biomass, pyrolytic char, bio-oil and biogas were conducted to investigate the differences between microwave-enhanced and conventional pyrolysis. It was found that certain types of carbon nano materials were formed on the surface of microwave pyrolytic chars. More biogas was produced via microwave heating, in which the highest H2 content reached 48.2vol.% during the course of microwave-enhanced pyrolysis of bamboo at 800°C. Most of the syngas contents produced from microwave-enhanced pyrolysis of biomass were above 80vol.% at 800°C. Generally, biomass could be converted into biofuel efficiently with microwave-enhanced process. Secondly, in order to increase hydrogen production, microwave-enhanced pyrolysis coupled with catalytic reforming (MPCCR) at 600°C was studied. In catalyst screening, Ni and Fe were applied as active compounds loaded onto different supports such as molecular sieves (13X), Al2O3 and natural minerals. In addition, activated carbon was employed as a reforming agent. It was found that Ni-13X catalyst resulted in a low yield of bio-oil and high yield of biogas around 75wt.%, which was the highest among all the catalysts investigated. It was also observed that activated carbon played a significant role in increasing biogas product and reducing bio-oil yield to less than 1wt.% in both conventional and microwave-enhanced pyrolysis coupled with reforming. MPCCR with Ni-13X and activated carbon enhanced cracking reactions of bio-oil, and subsequently lowed bio-oil yields and narrowed products distribution simultaneously. The maximum H2 content reached 55vol.% by MPCCR of bamboo using activated carbon as the reforming agent. Compared with conventional reforming, there was a sharp increase of H2 yield via microwave-enhanced reforming, resulting in a hydrogen-rich syngas with a high ratio of H2 to CO. Therefore, it is concluded that microwave irradiation enhances the reforming process. Finally, in this study, a novel method for catalyst-free synthesis of multi-walled carbon nanotubes (MWCNTs) from biomass was developed. MWCNTs with a diameter of 50 nm and a wall thickness around 5 nm have been successfully prepared via microwave-enhanced pyrolysis of gumwood at 500 °C. The mechanism for the growth of such carbon nanotubes (CNTs) was proposed as follows: volatiles were released from the biomass and left behind char particles; these char particles then acted as substrates, mineral matter in char particles (originating from biomass) acted as the catalyst, and the volatiles released act as the carbon source gas; the volatiles then underwent thermal and/or catalytic cracking on the surface of char to form amorphous carbon nanospheres; the carbon nanospheres subsequently self-assembled to form multi-walled CNTs under the effects of microwave irradiation. In summary, microwave-enhanced pyrolysis of biomass has the potential to produce high yield of hydrogen-rich syngas not only at high temperatures but also at low temperatures when it is coupled with catalytic reforming processes. It has also been demonstrated that microwave-enhanced pyrolysis of biomass could be used to produce MWCNTs at low temperatures. It can therefore be concluded that microwave-enhanced pyrolysis of biomass is an effective and efficient approach for the conversion of biomass into value-added products under mild conditions.

Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The brewing process is an energy intensive process that uses large quantities of heat and electricity. To produce this energy requires a high, mainly fossil fuel consumption and the cost of this is increasing each year due to rising fuel costs. One of the main by-products from the brewing process is Brewers Spent Grain (BSG), an organic residue with very high moisture content. It is widely available each year and is often given away as cattle feed or disposed of to landfill as waste. Currently these methods of disposal are also costly to the brewing process. The focus of this work was to investigate the energy potential of BSG via pyrolysis, gasification and catalytic steam reforming, in order to produce a tar-free useable fuel gas that can be combusted in a CHP plant to develop heat and electricity. The heat and electricity can either be used on site or exported. The first stage of this work was the drying and pre-treatment of BSG followed by characterisation to determine its basic composition and structure so it can be evaluated for its usefulness as a fuel. A thorough analysis of the characterisation results helps to better understand the thermal behaviour of BSG feedstock so it can be evaluated as a fuel when subjected to thermal conversion processes either by pyrolysis or gasification. The second stage was thermochemical conversion of the feedstock. Gasification of BSG was explored in a fixed bed downdraft gasifier unit. The study investigated whether BSG can be successfully converted by fixed bed downdraft gasification operation and whether it can produce a product gas that can potentially run an engine for heat and power. In addition the pyrolysis of BSG was explored using a novel “Pyroformer” intermediate pyrolysis reactor to investigate the behaviour of BSG under these processing conditions. The physicochemical properties and compositions of the pyrolysis fractions obtained (bio-oil, char and permanent gases) were investigated for their applicability in a combined heat power (CHP) application.

Hydrogen is considered as a clean energy carrier that can be converted to electricity by fuel cell with high efficiency. To be economically feasible and comparable, hydrogen needs to be liquefied, compressed, or adsorbed in metallic hydrides in large scale prior to the transfer. This requires very high pressure or very low temperature, which make a very high risk during transfer and delivery. Hence, it is highly beneficial to produce and consume pure hydrogen at the same place/time. The use of renewable biofuels such as bio-ethanol as a source of hydrogen is highly beneficial due to the higher H/C ratio, lower toxicity, and higher safety of storage that distinguish ethanol over other substrates. Among the reforming processes, steam reforming of ethanol delivers the highest amount of hydrogen per mole of converted ethanol. Noble metal-based catalysts are well known for very high reactivity in terms of ethanol conversion and hydrogen selectivity together with nearly zero carbon deposition over the surface of the catalyst. Ethanol steam reforming (ESR) over noble metal-based catalysts can be considered as an efficient and reliable method for hydrogen production. The application of membrane reactors (MR) -in which production and separation of hydrogen (pure hydrogen production) occurs in the same reactor vessel- is highly beneficial to omit costly and complicated unit processes for hydrogen purification. Besides, by removal of one of the products (hydrogen) via permeation through the membrane, equilibrium limitations are overcome even at unbeneficial operating conditions, leading to higher production of hydrogen and higher efficiency of the process. In case of a palladium-based membrane, highly pure hydrogen is obtained, suitable for feeding a fuel cell online. In this work, in-situ production of pure hydrogen via catalytic ethanol steam reforming (ESR) in a membrane reactor (MR) was investigated. A mixture of pure ethanol and distilled was used as the fuel. ESR experiments were carried out over Pd-Rh/CeO2 catalyst in a Pd-Ag membrane reactor -named as the fuel reformer- at variety of operating conditions regarding the operating temperature, pressure, fuel flow rate, and the molar ratio of water-ethanol (S/C ratio). The performance of the catalytic membrane reactor (CMR) was studied in terms of ethanol conversion, pure hydrogen production rate, hydrogen yield, and hydrogen recovery. Thermodynamic evaluation of the CMR was presented as a supplement to the comprehensive investigation of the overall performance of the fuel reformer. Exergy analysis was performed based on the experimental results aiming not only to understand the thermodynamic performance of the fuel reformer, but also to introduce the application of the exergy analysis in CMRs studies. Exergy analysis provided important information on the effect of operating conditions and thermodynamic losses, resulted in understanding of the best operating conditions. The exergy efficiency of the CMR was evaluated considering both an insulated reactor (without heat loss), and a non-insulated reactor (with heat loss). The simulation of the dynamics of hydrogen permeation was performed. The simulation presented in this work is similar to the hydrogen flow rate adjustments needed to set the electrical load of a fuel cell, if fed online by the studied pure hydrogen generating system. A static model for the catalytic zone was derived from the Arrhenius law to model the production rate of the ESR species. The permeation zone (membrane) was modeled based on the Sieverts' law as the physical definition of hydrogen permeation through the membrane, and a block box model as a function of the fuel flow rate and the reactor pressure. Finally, a dynamic model was proposed under ideal gas law assumptions to simulate the dynamics of pure hydrogen production rate in the case of the fuel flow rate or the operational pressure set point adjustment (transient state) at isothermal conditions.
Com a alternativa als combustibles fòssils, l'hidrogen es considera un vector energètic net que es pot convertir a electricitat amb una gran eficiència en una pila de combustible. Normalment, per ser econòmicament atractiu, cal liquar, comprimir o absorbir en metalls l'hidrogen a gran escala per a transportar-lo. Això requereix pressions molt altes o temperatures molt baixes, cosa que suposa riscos en el seu transport i emmagatzematge. Per aquest motiu resulta molt interessant el produir i consumir l'hidrogen al mateix lloc i en el mateix moment. L'ús de biocombustibles renovables com el bioetanol com a font d'hidrogen és molt avantatjós donada la seva relació H/C elevada, baixa toxicitat i elevada seguretat en l'emmagatzematge, aspectes difícils de trobar en altres substrats. Els catalitzadors que contenen metalls nobles mostren una alta activitat en la conversió d'etanol i alta selectivitat a hidrogen al temps que eviten la deposició de carboni a la seva superfície. Així, la reformació catalítica d'etanol (ESR) fent ús de catalitzadors que contenen metalls nobles es pot considerar un mètode eficient i robust per a produir hidrogen. L'ús de reactors de membrana (MR) en els que la producció i separació d'hidrogen té lloc en el mateix reactor resulta especialment útil a l'hora de simplificar i abaratir la purificació de l'hidrogen que es produeix. A més, mitjançant la separació d'un dels productes de la reacció a través de la membrana, l'hidrogen, es superen els límits termodinàmics i es pot treballar en condicions més suaus de reacció, el que comporta una producció més alta d'hidrogen i una millor eficiència del procés. En aquest treball s'investiga la producció in situ d'hidrogen pur per reformació catalítica d'etanol amb vapor d'aigua (ESR) en un reactor de membrana (MR). El combustible utilitzat ha estat una mescla d'etanol pur i aigua i els experiments s'han dut a terme amb un catalitzador Pd-Rh/CeO2 i una membrana Pd-Ag (reformador) sota diferents condicions d'operació de temperatura, pressió, cabal de combustible i relació molar d'aigua-etanol (relació S/C). El comportament del reactor catalític de membrana (CMR) s'ha avaluat en termes de conversió d¿etanol, producció d'hidrogen pur, rendiment d'hidrogen i recuperació d'hidrogen. La investigació exhaustiva del comportament del CMR s'ha complementat amb un estudi termodinàmic. S'ha dut a terme una anàlisi detallada de l'exergia en base als resultats experimentals amb la intenció, no només d'entendre el comportament del reformador, sinó també com a eina en l'estudi, per primer cop, de reactors catalítics de membrana. L'anàlisi energètica ha donat lloc a informació innovadora sobre les condicions de treball del CMR i les pèrdues termodinàmiques del sistema, cosa que permet entendre quines són les millors condicions d'operació. L'anàlisi energètica s'ha dut a terme considerant un reactor aïllat (sense pèrdues de calor) i un reactor no aïllat (amb pèrdues de calor). Per últim, s'ha modelat i simulat la dinàmica en la producció d'hidrogen (permeació) com a darrer pas en l'estudi de l'aplicabilitat del reformador. La simulació realitzada permet ajustar l'alimentació d'hidrogen pur d'una pila de combustible necessària per a garantir el subministrament elèctric en una aplicació. S'ha construït un model estàtic per a la zona catalítica del CMR a partir de la llei d'Arrhenius per a modelitzar la producció de les espècies de la ESR (CO, CO2, CH4, H2O i H2). La zona de permeació del CMR (membrana) s'ha modelitzat, bé amb la llei de Sieverts en base al fenomen físic de transport d'hidrogen a través de la membrana, o bé amb un model de caixa negre tenint en compte la producció d'hidrogen i la pressió. El model dinàmic s'ha realitzat assumint gasos ideals per a simular la dinàmica en la producció d'hidrogen pur quan hi ha canvis en l'alimentació de combustible o canvis en la pressió del CMR en condicions isotermals.

Hydrogen production from bio-resource is a promising option. In order to economically and practically derive hydrogen from biomass on a sustainable scale, novel catalysts are needed to be developed with properties of effective and inexpensive. In this study, initial works include the preparation of Ni/MgO catalysts via different methods including co-precipitation, hydrothermal treatment and wet-impregnation. These catalysts formed solid solutions after calcination at 600 ℃. It was found that hydrothermal treatment increased the specific surface area of the catalyst from 49.7 m2/g to 79.8 m2/g. In addition, the total pore volume and t-plot micropore volume of the hydrothermally treated Ni/MgO (NixMgyO-hydro) increased by a great extent. In the 20 h methanol steam reforming tests, NixMgyO solid solutions prepared via different methods were examined for their catalytic performance, stability and resistance to carbon deposition. Amongst all the catalysts tested, the NixMgyO-hydro catalyst exhibited the highest conversion rate of 97.4mol% with no carbon deposition. This was particularly true when the steam-to-carbon ratio (S/C) was 3. When S/C was 1, similarly, the NixMgyO-hydro showed the highest performance and the lowest amount of carbon deposition. Characterizations of the spent NixMgyO-hydro revealed that it had very low portion of highly ordered carbon on its surface. It is attributed to the rapid removal of atomic carbon, which led to the prevention of carbon accumulation and subsequent transformation into highly ordered structure. The carbon removal mechanism was confirmed by CO2-TPD analysis. The strong basic sites on the NixMgyO-hydro surface enhanced the reaction between deposited carbon and adsorbed CO2. In addition, the catalytic activity of NixMgyO-hydro catalyst was compared with the Ni/γ-Al2O3 catalyst and several other commercial catalysts. Its outstanding performance in steam reforming of methanol was further verified. Although the NixMgyO-hydro catalyst showed good performance in the steam reforming of methanol, it was not the case for ethanol reforming. The NixMgyO-hydro catalyst showed low hydrogen yield and serious carbon deposition during ethanol steam reforming. The low hydrogen yield was caused by the suppression of water-gas shift reaction (WGSR) at high temperatures, whilst the carbon fouling was due to the existence of C-C bonds in ethanol and high selective conversion towards ethylene. Therefore, the modification of the NixMgyO-hydro catalyst was carried out to overcome these drawbacks. Various elements, i.e., Ce, La and Co, were as catalytic promoters and individually added to the NixMgyO-hydro catalyst. Most of the modified catalysts exhibited much higher hydrogen yield at 700 ℃ due to the enhancement of WGSR. Some catalysts, such as Ce- and Co-modified catalysts, showed significant increase in hydrogen yields, which were higher than 80mol% after 30 h of reaction. It is worth mentioning that the La-modified catalysts promoted the hydrogen yield to 53mol% even at low temperature condition (500 ℃), whilst it was only 12.5mol% with the unmodified catalyst at the same temperature. The reason for this was due to the lack of suitable acid sites on La surface, which led to the accelerated formation of acetaldehyde. The advantage of acetaldehyde is it could be decomposed at very low temperature. The formation of carbon on Ce- and La-modified catalysts was also suppressed. The Ce element showed outstanding oxygen storage and release capability to improve the gasification of carbon deposition. Similarly, La2O3 would form La2O2CO3 species which could achieve carbon removal by offering CO2. Subsequently, the modified catalysts were tested with acetic acid (HAc) and phenol as feedstock, both of which are the most common-seen compounds in bio-oil. The results of these tests, such as catalytic performance and anti-carbon abilities, were consistent with the findings in ethanol steam reforming. Most of the modified catalysts showed very high hydrogen yields above 80mol%, which were only 61.9mol% and 73.7mol% for the unmodified NiMgO catalyst in the steam reforming of HAc and phenol, respectively. The better resistant abilities of the modified catalysts over carbon deposition were also confirmed in the steam reforming of HAc and phenol. In order to determine the performance of the catalysts in steam reforming of actual bio-oil, all of the modified catalysts were evaluated based on their performance in the reforming of major model compounds of bio-oil. Three hydrothermally treated catalysts, i.e., 1%Ce/NiMgO, 2%La/NiMgO and 2%Co/NiMgO, were selected and tested. All three catalysts showed carbon conversions above 90mol% and hydrogen yield in excess of 70mol% after 100 h test. The amounts of carbon deposition on these catalysts were also within an acceptable range. It can therefore be concluded that the NixMgyO solid solution with proper modification, i.e. addition of suitable promoter, could be developed as a promising catalyst for hydrogen production via the steam reforming of bio-oil.

Global energy demands are constantly increasing and fossil fuels are a finite resource. The shift towards alternative, more renewable and sustainable fuels is inevitable. Furthermore, the increased emissions of greenhouse gases have forced a pressing need to find cleaner, more environmentally friendly sources of fuel. Biomass energy is a promising alternative fuel because it offers several important advantages. It is a renewable energy form, it comes from many sources and produces biogas (CH4 and CO2). Furthermore, it can have a zero carbon footprint; this is due to the fact that the carbon produced is from the same carbon used to make the biomass. In addition, by replacing fossil fuels, the emissions of CH4 and CO2 (both greenhouse gases) is reduced. Biomass-derived syngas (H2 and CO) can be utilized as a feedstock for many important industrial processes such as methanol synthesis, ammonia synthesis and Fischer-Tropsch synthesis (FTS) to produce long chain hydrocarbon fuels. Municipal solid waste (MSW) biomass is considered as the source of the biomass for this dissertation work. MSW accounts for 20% of man-made methane emissions making it an attractive source for utilization. However, methane reforming to synthesis gas (H2 and CO) typically occurs at temperatures higher than 600°C making it economically challenging at the smaller scale of MSW conversion processes. This dissertation effort focused on formulating low precious metal loaded heterogeneous catalysts that can reform methane at low temperature (T<500°C) making the process more industrially viable. The effect of select contaminants (siloxanes) in the biogas on the reforming catalysts was studied through accelerated poisoning. Finally, the syngas ratio was improved by combining low temperature dry reforming with steam reforming (termed bi-reforming). The catalyst system used for this dissertation study was comprised of 1.34wt%Ni- 1.00wt%Mg on a Ceria-Zirconia oxide support (0.6:0.4 ratio respectively). The catalysts were doped with platinum (0-0.64% by mass) and compared to palladium doped catalysts (0-0.51% by mass). The ratio chosen for the support, Ce0.6Zr0.4, was determined to be the best ratio in terms of activity and surface area by previous studies done in this group [1]. Nickel has been widely studied as methane reforming catalyst [2-6]. Alone, nickel atoms are prone to carbon deposition especially during methane decomposition, however, coupling NiO with MgO helps to reduce carbon deposition by reducing agglomeration of Ni crystallites, thereby improving catalyst lifetime [2, 7]. Furthermore, addition of small amounts of noble metals such as Pt or Pd help to drive the reduction of the catalyst to lower temperatures and enhance catalytic activity. Different metal loadings of Pt and Pd were tested to determine the optimum catalyst that will reform methane at low temperatures, is resistant to deactivation and produces a high syngas ratio (~2:1) which is necessary for processes such as FTS. Preliminary results have shown that in general Pt is superior in this catalyst system for low temperature reforming of methane. It consistently had syngas ratios near the desired ratio compared to Pd, it did not deactivate with extended time on stream and overall had higher turnover frequencies. This catalyst system has potential to make industrial reforming of methane from biomass feedstock more economically viable.

Title from PDF of title page (University of Missouri--Columbia, viewed on March 2, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. Sunggyu Lee, Dissertation Advisor. Vita. Includes bibliographical references.

The research presented in this dissertation involved characterization of the Cu/ZnO solid catalyst system as applied to methanol/steam reformation. Thermogravimetry was used to investigate in-lab synthesized samples and a commercial product G66B (Cu/ZnO 33/67 wt. %). The 33% Cu sample contained Cu ions in the ZnO matrix. This phase required the highest temperatures (400°C) for H₂ reduction. The 50% Cu sample reduced at a lower temperature (220°C) but its complete reduction required the same maximum temperature. The higher temperature process was similar to the 33% case, while the lower one was due to the reduction of a amorphous CuO phase. The 66% Cu sample reduced in a fairly narrow low temperature (270°C) range. Therefore, its CuO phase has a amorphous structure. G55B reduced at lower temperatures than the in-lab samples. This difference is possibly due to different synthetic procedures used in the production of G66B and the in-lab samples. The CuO phase of G66B appears to be amorphous and well dispersed. Raman spectroscopy was used to identify the crystal phases of these solids. The complexity of the initial precipitate was monitored versus the Cu/Zn ratio of the system. The nature of the phases present under reduction conditions was determined. This information has provided insight into the active phases involved in methanol reformation. The role of the solids lattice oxygen was determined. The reaction was carried out on labelled ¹⁸O-containing Cu/ZnO. Incorporation of ¹⁸O into both CO₂ and H₂O clearly indicates the involvement of these oxygens in the reaction. Observation of C¹⁸O¹⁸O indicates that the C-O bond in methanol does not remain intact. XPS was used to determine the effects of oxidation, reduction, and reaction on the Cu component of G66B. Upon oxidation all Cu exists as Cu⁺². The catalyst always contains Cu⁺¹ and Cuᵒ after H₂ reduction. After methanol/steam reformation with a 50/50 vol% mxiture, all Cu is reduced to Cuᵒ. Changes in the Cu/Zn ratio of the surface are interpreted in terms of changes in surface morphology.

Le travail de doctorat avait pour objectif d’améliorer les performances de la gazéification de la biomasse en se focalisant sur deux aspects : qualité du gaz produit (élimination des goudrons) et captage de CO2 formé en vue d’une valorisation chimique ultérieure. Le travail de thèse a été divisé en quatre parties : 1. Tests de laboratoire sur la gazéification de la biomasse dans des conditions proches d’une utilisation effective avec la mise en place d’un élément catalytique filtrant dans la partie disponible du réacteur de gazéification en lit fluidisé. La présence de goudrons (hydrocarbures aromatiques lourds) est le principal obstacle à une valorisation chimique des gaz formés en plus de la valorisation énergétique. 2. Etude couplée du reformage d’hydrocarbures (méthane, aromatiques) et de la capture de CO2 avec de la dolomite (CaO, MgO) et un catalyseur à base de nickel. Les hydrocarbures testés sont représentatifs des goudrons produits lors de la gazéification de la biomasse. 3. Optimisation du solide minéral (dolomite) pour un système catalytique à double fonction : vaporeformage et captage de CO2 pour une meilleure efficacité de la dolomite modifiée pour les réactions de reformage. Etude de l’addition d’oxyde de fer et de nickel à la structure dolomite. 4. Etude du captage de CO2 par la dolomite dans un réacteur lit fluidisé à l’échelle du laboratoire. La cinétique de l’adsorption de CO2 par CaO dans les conditions réelles a été déterminée et un modèle réactionnel proposé
The objective of the Ph. D. Work was the improvement of the biomass gasification performances, focusing on two main aspects: product gas quality (tar elimination) and in situ CO2 capture, in order to carry out a further chemical valorisation. The PhD work has been developed in four main directions: 1. Laboratory tests of a biomass gasification process, at real process conditions by means of a firstly prepared catalytically activated filter element inserted in the freeboard of a fluidized bed steam gasifier. The presence of tar (heavy, aromatic hydrocarbons) is the main obstacle for a chemical and energetic valorisation of the product gas. 2. The study of simultaneous hydrocarbon (methane, aromatics) reforming and CO2 capture by means of commercial, readily available materials (a nickel catalyst mixed with calcined dolomite, CaOMgO). The model compounds used are representative of tar produced in a real biomass gasification process. 3. The study of the opportunity of optimize the granular, mineral solid material for a system performing the double function of steam reforming and CO2 capture, improving the catalytic activity of dolomite for reforming reactions. Effect of addition of iron and nickel to the dolomite structure. 4. The study of CO2 capture by particles of dolomite in a gas-fluidized in a laboratory-scale reactor. Step-response experiments have been performed to determine CaO conversion rates in the bed as a function of time and dolomite particle diameter. A simple flow-with-reaction model of the process is proposed

Hydrogen as a clean energy carrier has drawn great attention. Production of H2 from sustainable bio-oil is considered an alternative for conventional fossil fuel based energy system, since the overall process of bio-oil converting to H2 ideally is carbon-neutral and hence environmental friendly. This study focuses on developing an adequate catalyst for bio-oil steam reforming to produce H2. Ruthenium and/ or nickel based catalysts supported on alumina, ceria-alumina or ceria-silica were synthesized by sol-gel method or incipient wetness impregnation and characterized using BET Surface area analysis, Powder X-Ray diffraction (XRD), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). Steam reforming of selected model compounds, n-propanol, glycerol and acetic acid, was investigated in a fixed bed tubular flow reactor over the prepared catalysts at 450 or 500 °C. The effects of support nature, preparation method, catalyst composition and reaction temperature on the steam reforming activity and stability of catalysts were studied. Catalysts showing better performance in terms of reactant conversion and H2 yield were selected for investigating the steam reforming of an acetic acid/glycerol aqueous mixture, consisting of acetic acid and glycerol with a weight ratio of 3/7 similar to a bio-oil generated from fast pyrolysis of cellulose. The steam-to-carbon ratio (S/C) and the flow rate of feed were constant at 4 and 0.1 ml/min, respectively. The effluent gas was monitored by GC/TCD and the evolution of carbon conversion and product gas distribution as a function of time was studied. Among all catalysts investigated, the one with nominal composition A10C10N1Rnc showed the best performance in steam reforming at 500 °C as indicated by higher and more stable H2 yields achieved regardless the reactant used. In order to investigate the sorption-enhanced steam reforming, three CaO-based CO2 absorbents were synthesized: two derived from calcium acetate with or without MgO support, noted as CAM and CA, respectively, and the other MgO-supported one derived from calcium d-gluconate, denoted as CGM. Results from the 15-carbonation/regeneration-cycle test suggested that the MgO-containing absorbent CAM has the highest CaO molar conversion and stable CO2 absorption capacity. Though significantly higher CO2 absorption capacity was shown from absorbent CA in the first one cycle, CA absorbent soon lost most of the CO2 absorption capacity due to severe sintering. In addition, the CO2 absorption capacity of absorbent CGM might be underestimated due to insufficient carbonation time. The A10C10N1Rnc catalyst and the CAM absorbent were applied in the steam reforming of acetic acid/glycerol mixture at 500°C. However, no significant improvement can be observed in the presence of absorbent CAM

Abstract The energy consumption around the globe is on the rise due to the exponential population growth and urbanization. There is a need for alternative and non-conventional energy sources, which are CO2-neutral, and a need to produce less or no environmental pollutants and to have high energy efficiency. One of the alternative approaches is hydrogen economy with the fuel cell (FC) technology which is forecasted to lead to a sustainable society. Hydrogen (H2) is recognized as a potential fuel and clean energy carrier being at the same time a carbon-free element. Moreover, H2 is utilized in many processes in chemical, food, metallurgical, and pharmaceutical industry and it is also a valuable chemical in many reactions (e.g. refineries). Non-renewable resources have been the major feedstock for H2 production for many years. At present, ~50% of H2 is produced via catalytic steam reforming of natural gas followed by various down-stream purification steps to produce ~99.99% H2, the process being highly energy intensive. Henceforth, bio-fuels like biomass derived alcohols (e.g. bio-ethanol and bio-glycerol), can be viable raw materials for the H2 production. In a membrane based reactor, the reaction and selective separation of H2 occur simultaneously in one unit, thus improving the overall reactor efficiency. The main motivation of this work is to produce H2 more efficiently and in an environmentally friendly way from bio-alcohols with a high H2 selectivity, purity and yield. In this thesis, the work was divided into two research areas, the first being the catalytic studies using metal decorated carbon nanotube (CNT) based catalysts in steam reforming of ethanol (SRE) at low temperatures (<450 °C). The second part was the study of steam reforming (SR) and the water-gas-shift (WGS) reactions in a membrane reactor (MR) using dense and composite Pd-based membranes to produce high purity H2. CNTs were found to be promising support materials for the low temperature reforming compared to conventional catalyst supports, e.g. Al2O3. The metal/metal oxide decorated CNTs presented active particles with narrow size distribution and small size (~2–5 nm). The ZnO promoted Ni/CNT based catalysts showed the highest H2 selectivity of ~76% with very low CO selectivity <1%. Ethanol was shown to be a more suitable and viable source for H2 than glycerol. The dense Pd-Ag membrane had higher selectivity but a lower permeating flux than the composite membrane. The MR performance is also dependent on the active catalyst materials and thus, both the catalyst and membrane play an important role. Overall, the membrane–assisted reformer outperforms the conventional reformer and it is a potential technology in pure H2 production. The high purity of H2 gas with a CO-free reformate for fuel cell applications can be gained using the MR system
Tiivistelmä Maailman energiankulutus on kasvussa räjähdysmäisen väestönkasvun ja voimakkaan kaupungistumisen myötä. Tällä hetkellä energian tuottamisen aiheuttamat ympäristöongelmat ja taloudellinen epävarmuus ovat seikkoja, joiden ratkaisemiseksi tarvitaan vaihtoehtoisia ja ei-perinteisiä energialähteitä, joilla on korkea energiasisältö ja jotka tuottavat vähän hiilidioksidipäästöjä. Eräs vaihtoehtoisista lähestymistavoista on vetytalous yhdistettynä polttokennotekniikkaan, minkä on esitetty helpottavan siirtymistä kestävään yhteiskuntaan. Vety on puhdas ja hiilivapaa polttoaine ja energian kantaja. Lisäksi vetyä käytetään monissa prosesseissa kemian-, elintarvike-, metalli- ja lääketeollisuudessa ja se on arvokas kemikaali monissa prosesseissa (mm. öljynjalostamoissa). Uusiutumattomat luonnonvarat ovat olleet tähän saakka merkittävin vedyn tuotannon raaka-aine. Tällä hetkellä noin 50 % vedystä tuotetaan maakaasun katalyyttisellä höyryreformoinilla. Puhtaan (yli 99,99 %) vedyn tuotanto vaatii kuitenkin useita puhdistusvaiheita, jotka ovat erittäin energiaintensiivisiä. Integroimalla reaktio- ja puhdistusvaihe samaan yksikköön (membraanireaktori) saavutetaan huomattavia kustannussäästöjä. Biopolttoaineet, kuten biomassapohjaiset alkoholit (bioetanoli ja bioglyseroli), ovat vaihtoehtoisia lähtöaineita vedyn valmistuksessa. Tämän työn tavoitteena on tuottaa vetyä bioalkoholeista tehokkaasti (korkea selektiivisyys ja saanto) ja ympäristöystävällisesti. Tutkimus on jaettu kahteen osaan, joista ensimmäisessä tutkittiin etanolin katalyyttistä höyryreformointia matalissa lämpötiloissa (<450 °C) hyödyntämällä metallipinnoitettuja hiilinanoputkia. Työn toisessa osassa höyryreformointia ja vesikaasun siirtoreaktioa tutkittiin membraanireaktorissa käyttämällä vedyn tuotantoon tiheitä palladiumpohjaisia kalvoja sekä huokoisia palladiumkomposiittikalvoja. Hiilinanoputket (CNT) havaittiin lupaaviksi katalyyttien tukimateriaaleiksi verrattuna tavanomaisesti valmistettuihin tukiaineisiin, kuten Al2O3. CNT-tukiaineelle pinnoitetuilla aktiivisilla aineilla (metalli-/metallioksidit) todettiin olevan pieni partikkelikoko (~2–5 nm) ja kapea partikkelikokojakauma. Sinkkioksidin (ZnO) lisäyksellä Ni/CNT-katalyytteihin saavutettiin korkea vetyselektiivisyys (~76 %) ja erittäin alhainen hiilimoksidiselektiivisyys (<1 %). Etanolin todettiin olevan parempi vedyn raaka-aine kuin glyserolin. Tiheillä Pd-Ag-kalvoilla havaittiin olevan vedyn suhteen korkeampi selektiivisyys mutta matalampi vuo verrattuna palladiumkomposiittikalvoihin. Membraanireaktorin suorituskyky oli riippuvainen myös katalyytin aktiivisuudesta, joten sekä kalvolla että katalyyttimateriaalilla oli merkittävä rooli kyseisessä reaktorirakenteessa. Yhteenvetona voidaan todeta, että membraanierotukseen perustuva reformointiyksikkö on huomattavasti perinteistä reformeriyksikköä suorituskykyisempi mahdollistaen tehokkaan teknologian puhtaan vedyn tuottamiseksi. Membraanitekniikalla tuotettua puhdasta vetyä voidaan hyödyntää mm. polttokennojen polttoaineena

This study focuses on upgrading biomass derived syngas for the synthesis of liquid fuels using Fischer-Tropsch synthesis (FTS). The process includes novel gasification of biomass via a tri-reforming process which involves a synergetic combination of CO2 reforming, steam reforming, and partial oxidation of methane. Typical biomass-derived syngas H2:CO is 1:1 and contains tars that deactivate FT catalyst. This innovation allows for cost-effective one-step production of syngas in the required H2:CO of 2:1 with reduction of tars for use in the FTS. To maximize the performance of the tri-reforming catalyst, an attempt to control oxygen mobility, thermal stability, dispersion of metal, resistance to coke formation, and strength of metal interaction with support is investigated by varying catalyst synthesis parameters. These synthesis variables include Ce and Zr mixed oxide support ratios, amount Mg and Ni loading, and the preparation of the catalyst. Reaction conditions were also varied to determine the influences reaction temperature, gas composition, and GHSV have on the catalyst performance. Testing under controlled reaction conditions and the use of several catalyst characterization techniques (BET, XRD, TPR, XAFS, SEM-EDS, XPS) were employed to better explain the effects of the synthesis parameters. Applications of the resulting data were used to design proof of concept solar powered BTL plant. This paper highlights the performance of the tri-reforming catalyst under various reaction conditions and explains results using catalyst characterization.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xiv, 194 p.; also includes graphics Includes bibliographical references (p. 178-188). Available online via OhioLINK's ETD Center

Supported Ni and Rh catalysts were developed for the reforming of two greenhouse gases, methane and carbon dioxide to syngas (a mixture of hydrogen and carbon monoxide). This is an endothermic, equilibrium limited reaction. To overcome the thermodynamic limitations, a commercially available porous membrane (Vycor glass) was used in a combined reactor-separator configuration. This was to selectively remove one or more of the products from the reaction chamber, and consequently shift the equilibrium to the right. However, the separation mechanism in this membrane involved Knudsen diffusion, which provided only partial separations. Consequently, there was some transport of reactants across the membrane and this led to only marginal improvements in performance. To overcome this limitation, a new membrane was developed by modifying the Vycor substrate by the chemical vapor deposition of a silica precursor. This new membrane, termed Nanosil, provided high selectivity to hydrogen at permeabilities comparable to the support material. Application of this membrane in the combined reactor-separator unit provided higher conversions than that obtained using the Vycor membrane.
Ph. D.

In this work the synthesis, characterization, and gas transport properties of hydrogen selective silica membranes were studied along with the catalytic reforming of CH4 with CO2 (CH4 + CO z 2 CO + 2 H2) in a hydrogen separation membrane reactor. The silica membranes were prepared by chemical vapor deposition (CVD) of a thin SiO2 layer on porous supports (Vycor glass and alumina) using thermal decomposition of tetraethylorthosilicate (TEOS) in an inert atmosphere. These membranes displayed high hydrogen permeances (10-8 - 10-7 mol m-2 s-1 Pa-1) and excellent H2 selectivities (above 99.9 %) over other gases (CH4, CO, and CO2). The membranes were characterized using Scanning Electron Microscopy and Atomic Force Microscopy, and the mechanism of gas transport was studied applying existing theories with a newly developed treatment. The catalytic reforming of CH4 with CO2 was carried out in a membrane reactor installed with a hydrogen separation ceramic membrane. The reaction was conducted at various pressures (1 - 20 atm) and temperatures (873 K and 923 K) at non-equilibrium conditions, and the results were compared with those obtained in a packed bed reactor in order to evaluate performance of the membrane reactor for the reaction. It was found that concurrent and selective removal of hydrogen from the reaction in the membrane reactor resulted in considerable enhancements in the yields of the reaction products, H2 and CO. The enhancements in the product yields in the membrane reactor increased with pressure showing a maximum at 5 atm, and then decreased at higher pressures. This was due to a trade-off between a thermodynamic quantity (hydrogen production by the reaction) and transport property (hydrogen separation through the membrane). It was also found that the reverse water-gas shift (RWGS) reaction occurred simultaneously with the reforming reaction giving the detrimental effect on the reaction system by reducing the amount of hydrogen production in favor of water. This was particularly significant at high pressures.
Ph. D.

L’étude concerne un nouveau procédé de reformage du gaz naturel en gaz de synthèse par le dioxyde de carbone (RSM), en vue de l'utilisation rationnelle des déchets carbonés industriels pour la production d'hydrocarbures et d'hydrogène. Cette méthode utilise des systèmes à membranes catalytiques inorganiques (SMC) qui favorisent des réactions catalytiques hétérogènes en phase gazeuse dans des micro-canaux céramiques. La surface active des catalyseurs formés à l'intérieur des canaux est faible en termes de superficie, mais elle est caractérisée par une valeur élevée du facteur Surface/Volume du catalyseur, qui induit une efficacité importante de la catalyse hétérogène. Les SMC, formés à partir de dérivés alcoxy et des précurseurs métalliques complexes, contiennent de 0,008 à 0,055% en masse de nano-composants mono- et bimétalliques actifs répartis uniformément dans les canaux. Pour les systèmes [La-Ce]-MgO-Ti02/Ni-Al et Pd-Mn-Ti02/Ni-Al, les productivités de 10500 et 7500 1/h·dm3membr. ont été respectivement obtenues lors du RSM dès 450°C avec une composition de gaz de synthèse H2/?? allant de 0,63 à 1,25 et un taux de conversion de 50% de la charge CH4/CO2 (1/1). Ainsi les SMC sont d’un ordre de grandeur plus efficace qu’un réacteur à lit fixe du même catalyseur. Le RSM est initié par l'oxydation de CH4 par l'oxygène de structure des oxydes métalliques présents en surface, et le CO2 réagit avec le carbone finement divisé provenant de la dissociation de CH4. Une synergie catalytique a été mise en évidence pour le système Pd-Mn. Ces SMC de 108 pores par cm² de surface constituent un ensemble de nano réacteurs de fort potentiel industriel (synthèse d’oléfines, biomasse)
This study reports the development of a new process to convert methane and carbon dioxide (dry methane reforming - DMR) into valuable products such as syngas from non-oil resources. The practical interest is to produce syngas from carbon containing exhaust industrial gases. This process uses membrane catalytic systems (MCS) that support heterogeneous catalytic reactions in gaseous phase in ceramic micro-channels. The active surface of the catalysts formed inside the micro-channels is low in term of area, but it is characterized by a high value of the catalyst surface/volume ratio, which induces a high efficiency of heterogeneous catalysis. The SMC are formed from alkoxy derivatives and precursor metal complex containing between 0.008 and 0.055% by weight of nano-components mono-and bimetallic active distributed evenly in the channels. For systems [La-Ce] -MgO-Ti02/Ni-Al and Pd-Mn-Ti02/Ni-Al, productivities of 10500 and 7500 l/h · dm3 membr. were respectively obtained by RSM at 450°C with a composition of syngas H2/?? ranging from 0.63 to 1.25 and a conversion rate of 50% with a CH4/CO2 (1/1) feed. Thus the CMS is an order of magnitude more efficient than a fixed bed reactor of the same catalyst. The MDR is initiated by the oxidation of CH4 by structural oxygen of metal oxides available on the surface, and the CO2 reacts with the finely divided carbon arising from the dissociation of CH4. A catalytic synergy has been demonstrated for the system Pd-Mn. This CMS, having 108 pores per cm² of surface, can be considered as a set of nano reactors. Thus this new approach is very promising for industry (synthesis of olefins, uses of biomass)

The world&rsquo
s being alerted to the global warming danger and the depletion of fossil fuel resources, has increased the importance of the clean and renewable hydrogen energy. Bioethanol has high potential to be used as a resource of hydrogen since it is a non-petroleum feedstock and it is able to produce hydrogen rich mixture by steam reforming reactions. Discovery of mesoporous MCM-41 type high surface area silicate-structured materials with narrow pore size distributions (20-100 Å
) and high surface areas (up to 1500 m2/g) opened a new avenue in catalysis research. Catalytic activity of such mesoporous materials are enhanced by the incorporation of active metals or metal oxides into their structure. Nickel and copper are among the most active metals to be used in steam reforming of ethanol to produce hydrogen. In this study, copper and nickel incorporated MCM-41 type catalytic materials were tested in the steam reforming of ethanol. Two Ni-MCM-41 samples having different Ni/Si ratios were prepared by high temperature direct synthesis method and two Cu-MCM-41 samples having same Cu/Si ratios were synthesized by two different methods namely, high temperature direct synthesis method and impregnation method. The synthesized materials characterized by XRD, EDS, SEM, N2 physisorption and TPR techniques. XRD results showed that Ni-MCM-41 and Cu-MCM-41 catalysts had typical MCM-41 structure. The d100 and lattice parameter values of Ni-HT (I) (Ni-MCM-41 sample having 0.036 Ni/Si atomic ratio) was obtained as 3.96 and 4.57 nm., respectively. In addition Ni-HT (I) was found to have a surface area of 860.5 m2/g and 2.7 nm pore diameter. The d100 and lattice parameter values for a typical Cu-MCM-41 prepared by impregnation method having Cu/Si atomic ratio of 0.19 were obtained as 3.6 and 4.2 nm., respectively. This sample also has a 631 m2/g surface area and 2.5 nm pore diameter. Steam reforming of ethanol was investigated in the vapor phase by using Ni-MCM-41 and Cu-MCM-41 catalysts between 300°
C and 550°
C. Results proved that Ni incorporated MCM-41 type catalytic materials were highly active in hydrogen production by steam reforming of ethanol and actualized almost complete ethanol conversion for Ni-MCM-41 having Ni/Si atomic ratio of 0.15 over 500°
C . The side products obtained during reforming are methane and formaldehyde. Although the Cu-MCM-41 samples were not as active as Ni-MCM-41, it was observed that Cu-MCM-41 catalyst synthesized by the impregnation method showed an ethanol conversion of 0.83. However, the main product was ethylene with the copper incorporated catalysts. Effects of space time, the operating conditions (reaction temperature), metal/Si ratio of the catalyst and the preparation method on the product distributions were also investigated and best reaction conditions were searched.

A fundamental understanding of the kinetics and mechanisms of the catalytic reaction steps involved in the process of converting a fuel into hydrogen rich stream suitable for a fuel cell, as well as the electro-catalytic reactions within a fuel cell, is not only conceptually appealing, but could provide a sound basis for the design and development of efficient fuel processor/fuel cell systems. With the quantum chemical calculations on kinetics of elementary catalytic reaction steps becoming rather commonplace, and with increasing information now available in terms of electronic structures, vibration spectra, and kinetic data (activation energy and pre-exponential factors), the stage is set for development of a comprehensive approach. Toward this end, we have developed a framework that can utilize this basic information to develop a comprehensive understanding of catalytic and electrocatalytic reaction networks. The approach is based on the development of Reaction Route (RR) Graphs, which not only represent the reaction pathways pictorially, but are quantitative networks consistent with the Kirchhoff's laws of flow networks, allowing a detailed quantitative analysis by exploiting the analogy with electrical circuits. The result is an unambiguous portrayal of the reaction scheme that lays bare the dominant pathways. Further, the rate-limiting steps are identified rationally with ease, based on comparison of step resistances, as are the dominant pathways via flux analysis. In fact, explicit steady-state overall reaction (OR) rate expression can also be derived in an Ohm's law form, i.e. OR rate = OR motive force/OR resistance of an equivalent electric circuit, which derives directly from the RR graph of its mechanism. This approach is utilized for a detailed analysis of the catalytic and electro-catalytic reaction systems involved in reformer/fuel cell systems. The catalytic reaction systems considered include methanol decomposition, water gas shift, ammonia decomposition, and methane steam reforming, which have been studied mechanistically and kinetically. A detailed analysis of the electro-catalytic reactions in connection to the anode and cathode of fuel cells, i.e. hydrogen electrode reaction and the oxygen reduction reaction, has also been accomplished. These reaction systems have not so far been investigated at this level of detail. The basic underlying principles of the RR graphs and the topological analysis for these reaction systems are discussed.

[EN] Several major problems have to be solved before Solid Oxide Fuel Cells (SOFC) can operate continuously using hydrocarbon fuels such as natural gas. The risk of low catalytic behavior for fuel reforming, the carbon formation/deposition on the anode material at high operating temperatures and the presence of impurities in the fuel (in particular sulfides) can dramatically reduce the performance and durability of the cells. Taking all this into account, new anode materials with adequate (electro)catalytic properties are required. Recently, manganite compounds with Ruddlesden-Popper (RP) structure have been studied as potential new anode materials in INTERFASE group at Universidad Industrial de Santander (UIS). Their electrochemical performance have been described in previous works with promising results, but a fundamental knowledge was missing concerning the catalytic properties of such materials and the way to improve them by the addition of nickel metallic particles on the electrode surface. The current Ph.D. thesis was focused on the synthesis, characterization and catalytic study for steam reforming in SOFC anode conditions (low steam content) of a new RP manganite (La1.5Sr1.5Mn1.5Ni0.5O7±δ), which, in reducing atmosphere at high operating temperatures promotes via an exsolution mechanism the formation of two phases, i.e. an RP manganite of composition LaSrMnO4±δ decorated with metallic active Ni nanoparticles embedded in the surface; such strategy can be viewed as an original way to improve the (electro)catalytic properties of the anode materials and then a promising option for future SOFC systems operating with Colombian natural gas. The first chapter deals with the synthesis and characterization of the RP n= 2 phase La1.5Sr1.5Mn1.5Ni0.5O7±δ using the Pechini method. In agreement with SOFC operating temperature, Ni exsolution has been studied in diluted H2 at different temperatures (750, 800 and 850 °C) and reduction times. Ni nanoparticles decorating an RP n= 1 manganite is confirmed by XRD, TEM-EDS analysis and the size of the metallic particles on the oxide surface, below 100 nm, is characterized as a function of the exsolution conditions. The second chapter presents the catalytic behavior for the methane steam reforming reaction of the exsolved material applying the Gradual Internal Reforming concept adapted to SOFC operation (i.e. low water content, steam to carbon ratio equal to 0.15) at different reaction temperatures (750, 800 and 850 °C). The catalytic properties of Ni impregnated samples using a similar (La,Sr)2MnO4±δ ceramic support are also presented for comparison. The exsolved material exhibits better performance than the impregnated manganite for the reaction, especially at 850 °C, with higher conversion, conversion rate, and H2 production rate. Concerning the steam reforming of light alkane gas mixtures (CH4-C2H6, and CH4-C3H8), the behavior is affected due to the competition between the molecules and low available metallic active sites, but without affecting the H2 production. In addition, at long reaction times, the activity over the exsolved material is stable even with 100 h of reaction, without formation of carbonaceous species on the Ni particles, as confirmed by TEM and TGA/MS analysis. In the third and last chapter, the possible coke formation and sulfide poisoning are presented. Despite the high and stable catalytic behavior for methane steam reforming reaction with considerable carbon formation resistance, the exsolved material exhibits a high level of sensitivity to H2S poisoning, similar to the case of state-of-the-art Ni/YSZ anodic cermet and or Ni impregnated catalyst, with a drop of the activity to almost zero. Nevertheless, the exceptional overall results obtained for the exsolution-based material are promising for a possible use as SOFC anode operating with sulfur-free Colombian natural gas.
[ES] Muchos son los problemas que deben resolverse antes de que las celdas de combustible de óxido sólido (SOFC por sus siglas en inglés) puedan operar continuamente usando combustibles hidrocarbonados como por ejemplo el gas natural. El riesgo de una baja actividad catalítica para el reformado del combustible, la formación y depósito en el material de ánodo a elevadas temperaturas de operación y la presencia de impurezas en el combustible empleado (en particular de sulfuros) pueden reducir dramáticamente el desempeño y la durabilidad de las celdas. Teniendo todo esto en cuenta, nuevos materiales de ánodo con adecuadas propiedades (electro)catalíticas son necesarios. Recientemente, en el grupo INTERFASE de la Universidad Industrial de Santander (UIS), compuestos de tipo manganita con estructura Ruddlesden-Popper (RP) han sido estudiados como potenciales materiales de ánodo. Su desempeño electrocatalítico ha sido descrito en trabajos previos con promisorios resultados, pero el conocimiento fundamental sobre las propiedades catalíticas de dichos materiales y la forma de mejorarlos mediante la adición de partículas metálicas de níquel en la superficie del electrodo aún faltaba. La presente tesis doctoral se enfocó en la síntesis, caracterización y estudio catalítico en el reformado con vapor en condiciones de ánodo de celdas SOFC (bajo contenido de vapor) de una nueva manganita de tipo RP (La1.5Sr1.5Mn1.5Ni0.5O7±δ), la cual, en atmósfera reductora y a elevadas temperaturas de operación, promueven a través del mecanismo de exsolución la formación de dos fases: una manganita tipo RP de composición LaSrMnO4±δ decorada con nanopartículas metálicas y activas de Ni incrustadas en la superficie; dicha estrategia puede ser vista como una manera muy original de mejorar las propiedades (electro)catalíticas de los materiales de ánodo y por lo tanto ser consideradas como una opción prometedora para sistemas SOFC operados con gas natural colombiano. El primer capítulo trata sobre la síntesis de la fase RP n= 2 La1.5Sr1.5Mn1.5Ni0.5O7±δ usando el método de Pechini y su caracterización. De acuerdo con la temperatura de operación de las celdas SOFC, la exsolución del Ni en atmósfera de H2 diluido a diferentes temperaturas (750, 800 y 850 °C) y tiempos de reducción fue estudiada. Las nanopartículas de Ni decorando la manganita de estructura RP n= 1 es confirmada a través de análisis de DRX, MET-EDS y el tamaño de las partículas metálicas en la superficie del óxido, inferiores a 100 nm, es caracterizado en función de las condiciones de exsolución. El segundo capítulo presenta el comportamiento catalítico del material exsuelto en la reacción de reformado de metano aplicando el concepto de reformado interno gradual (GIR por sus siglas en inglés) adaptado a celdas SOFC (en otras palabras, bajo contenido de agua, relación vapor carbono igual a 0.15) a diferentes temperaturas de reacción (750, 800 y 850 °C). Las propiedades catalíticas de las muestras impregnadas con Ni utilizando como soporte un material cerámico similar (La,Sr)2MnO4±δ, son también presentados como comparación. El material exsuelto exhibe un mejor desempeño catalítico en la reacción de reformado que la manganita impregnada, especialmente a 850 °C, mostrando una más alta conversión, velocidad de conversión y de producción de H2. Con respecto al reformado de la mezcla de alcanos ligeros (CH4 -C2H6, y CH4 -C3H8), el comportamiento catalítico es afectado debido a la competición entre moléculas y la baja disponibilidad de sitios activos metálicos, sin afectar la producción de H2. Adicionalmente, a tiempos de reacción prolongados, la actividad en el material exsuelto es estable incluso con 100 h de reacción, sin formación de especies carbonáceas sobre las partículas de Ni como lo confirman las imágenes MET y el ATG/MS. En el tercer y último capítulo, la posible formación y depósito de carbón y el envenenamiento con sulfuros son presentados. Sin embargo, a pesar de la elevada y estable actividad catalítica en la reacción de reformado de metano con vapor con una considerable resistencia a la formación de carbón, el material exsuelto tiene un alto nivel de sensibilidad al envenenamiento con H2S, similar al Ni/YSZ (material de referencia de la literatura) o al material impregnado con Ni, con una disminución de la actividad catalítica a prácticamente cero No obstante, el excepcional resultado global obtenido en el material exsuelto es prometedor para un posible uso como material de ánodo en sistemas SOFC alimentados con gas natural colombiano libre de H2S.
[CA] Molts són els problemes que han de ser resolts abans que les cel·les de combustible d'òxid sòlid (SOFC per les seues sigles en anglès) puguen operar contínuament usant combustibles hidrocarbonats com per exemple el gas natural. El risc d'una baixa activitat catalítica per al reformat del combustible, la formació i depòsit en el material d'ànode a elevades temperatures d'operació i la presència d'impureses en el combustible emprat (en particular de sulfurs) poden reduir dramàticament l'acompliment i la durabilitat de les cel·les. Tenint tot això en compte, nous materials d'ànode amb propietats (electro)catalítiques adequades són necessaris. Recentment, en el grup d'investigació INTERFASE de la Universitat Industrial de Santander (UIS), compostos de tipus manganita amb estructura Ruddlesden-Popper (RP) han sigut estudiats com a potencials materials anòdics. El seu acompliment electroquímiques ha sigut tractades en treballs previs amb resultats promissoris, però el coneixement fonamental sobre les característiques catalítiques d'aquests materials i la manera de millorar-los mitjançant l'addició de partícules metàl·liques de níquel en la superfície de l'elèctrode encara faltava. La present tesi de doctorat es va enfocar en la síntesi, caracterització i estudi d'activitat catalítica en el reformat amb vapor en condicions d'ànode de cel·les SOFC (sota contingut de vapor) d'una nova manganita de d'estructura RP (La1.5Sr1.5Mn1.5Ni0.5O7±δ), la qual, en atmosfera reductora i a elevades temperatures d'operació, promouen, a través del mecanisme de exsolució; la formació de dues fases: una manganita de composició LaSrMnO4±δ decorada amb nanopartícules metàl·liques i actives de Ni incrustades en la superfície; aquesta estratègia pot ser vista com una manera molt original de millorar les propietats (electro)catalítiques dels materials d'ànode i per tant, ser considerades com una prometedora opció per a futurs usos en sistemes SOFC alimentats amb gas natural colombià. El primer capítol tracta sobre la síntesi de la fase RP n= 2 La1.5Sr1.5Mn1.5Ni0.5O7±δ usant el mètode de Pechini i la seua caracterització. D'acord amb la temperatura d'operació de les cel·les SOFC, la exsolució del Ni en atmosfera d'H2 diluït a diferents temperatures (750, 800 i 850 °C) i temps de reducció va ser estudiada. Les nanopartícules de Ni decorant la manganita d'estructura RP n= 1 és confirmada a través d'anàlisi de DRX, MET-EDS i la grandària de les partícules metàl·liques en la superfície de l'òxid, inferiors a 100 nm, és caracteritzat en funció de les condicions de exsolució. El segon capítol presenta el comportament catalític del material d’exsolució en la reacció de reformat de metà amb vapor aplicant el concepte de reformat gradual intern (GIR per les seues sigles en anglès) adaptat a cel·les SOFC (en altres paraules, sota contingut de vapor, relació vapor-carboni de 0.15) a diferents temperatures de reacció (750, 800 i 850 °C). Les propietats catalítiques de les mostres impregnades amb Ni utilitzant com a suport un material ceràmic similar (La,Sr)2MnO4±δ, són també presentats com a comparació. El material d’exsolució exhibeix un millor resultat catalític en la reacció de reformat que la manganita impregnada, especialment a 850 °C, mostrant una més alta conversió, velocitat de conversió i de producció d'H2. En el reformat de la mescla d'alcans lleugers (CH4 -C2H6, i CH4 -C3H8), el comportament catalític és afectat per la competició entre molècules i la baixa disponibilitat de llocs actius metàl·lics, sense afectar la producció d'H2. Addicionalment, a temps de reacció llargs, l'activitat en el material d’exsolució és estable fins i tot desprès de 100 h de reacció, sense formació d'espècies carbòniques sobre les partícules de Ni, com ho confirmen les imatges MET i el ATG/MS. En el tercer i últim capítol, la possible formació i depòsit de carbó i l'enverinament amb sulfurs són presentats. No obstant això, malgrat l'elevada i estable activitat catalítica en la reacció de reformat de metà amb vapor amb una considerable resistència a la formació de carbó, el material d’exsolució té un alt nivell de sensibilitat a l'enverinament amb H2S, similar al Ni/YSZ (material de referència de la literatura) o el material impregnat amb Ni, amb una disminució de l'activitat catalítica a pràcticament zero No obstant això, l'excepcional resultat global obtingut aquest nou material és prometedor per a un possible ús futur com a material d'ànode en sistemes SOFC alimentats amb gas natural colombià lliure d'H2S.
Al Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS) por la beca de estudios de Doctorados Nacionales Conv. 647 y el proyecto # 110265842833 “Symmetrical high temperature Fuel Cell operating with Colombian natural gas”. Al Consejo Superior de Investigaciones Científicas por el apoyo con la ayuda económica para la estancia mediante la convocatoria I-coop Project # COOPA20112.
Vecino Mantilla, JS. (2020). Nickel exsolution effect on the catalytic behavior of ruddlesden-popper manganites in sofc conditions using colombian natural gas [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149474
TESIS

The highly competitive market in the oil refining industry forces refiners look for more detailed information of both feedstocks and products to achieve the optimal economic performance. Due to stricter environmental legislations, the molecular level characterisation has been investigated by various researchers and shows promising advantages in modern refinery design and operation. Although various molecular characterisation methods have been developed, there is an unavoidable trade-off between keeping astronomical molecule details and practicality in industrial applications. In the meantime, many of these methodologies have different characteristics and different focuses according to a particular application purpose. Our aim is hence to tackle the problems of developing manageable and practical technical solutions for molecular characterisation of petroleum fractions for vary refinery processes. A pseudo-component based approach is developed within a modified MTHS (Molecular Type Homologous Series) matrix framework (Peng, 1999) to represent the molecular information of a particular refining stream. This proposed methodology incorporates both molecular type and pseudo-component information by the conjunction of homologous series and boiling points in the matrix framework. To increase the usability of this method, a 3-parameter gamma distribution function is introduced to describe the composition of each structural molecular type. Typical PIONA (paraffin, iso-paraffin, olefin, naphthene, aromatic) analysis, ratios between each homologous types and the percentage of particular carbon type are considered as well as the distillation curve and the density of a stream. More strict product specifications and environmental legislations make strong restriction to the benzene and aromatics content in gasoline products, which motivate refiners to understand, characterise and simulate gasoline catalytic reforming on molecular-level. In this work, kinetic and reactor model of naphtha catalytic reforming is developed based on the proposed MTHS method. The naphtha feedstock composition is represented by the MTHS matrix, and a kinetic network is constructed according to conversions among matrix elements. A process model proposed by Wu (2010) is employed for reforming modelling. The proposed model is then applied to a bench-scale semi-regenerative catalytic reforming unit, which contains 3 fixed-bed reactors, for validation. The influences of essential operating conditions, such as reactor inlet temperature, pressure and weight hourly space velocity (WHSV), on the product distribution and quality are explored. The developed characterisation is also applied in gasoline blending modelling. A molecular-level nonlinear gasoline blending model is developed based on proposed MTHS method with validation. Key properties such as Octane Numbers (ONs) and RVP are blended by molecular matrix elements, and the influence of molecular composition on bulk properties is obvious. A case of recipe optimisation is studied to show the applicability of the proposed method. The implementation of the developed MTHS method for catalytic reforming and gasoline blending demonstrates the compatibility when characterising different petroleum streams, and provides a common platform to simulate and optimise refining operations on the same molecular basis.

Production of high-quality syngas from biomass gasification in a dual fluidised bed gasifier (DFBG) has made a significant progress in R&D and Technology demonstration. An S&M scale bio-automotive fuel plant close to the feedstock resources is preferable as biomass feedstock is widely sparse and has relatively low density, low heating value and high moisture content. This requires simple, reliable and cost-effective production of clean and good syngas. Indirect DFBGs, with steam as the gasification agent, produce a syngas of high content H2 and CO with 12-20 MJ/mn3 heating value. The Mid Sweden University (MIUN) gasifier, built for research on synthetic fuel production, is a dual fluidised bed gasifier. Reforming of tars and CH4 (except for methanation application) in the syngas is a major challenge for commercialization of biomass fluidised-bed gasification technology towards automotive fuel production. A good syngas from DFBGs can be obtained by optimised design and operation of the gasifier, by the use of active catalytic bed material and internal reforming. This thesis presents a series of experimental tests with different operation parameters, reforming of tar and CH4 with catalytic bed material and reforming of tar and CH4 with catalytic internal reformer.   The first test was carried out to evaluate the optimal operation and performance of the MIUN gasifier. The test provides basic information for temperature control in the combustor and the gasifier by the bed material circulation rate.    After proven operation and performance of the MIUN gasifier, an experimental study on in-bed material catalytic reforming of tar/CH4 is performed to evaluate the catalytic effects of the olivine and Fe-impregnated olivine (10%wtFe/olivine Catalyst) bed materials, with reference to non-catalytic silica sand operated in the mode of dual fluidised beds (DFB). A comparative experimental test is then carried out with the same operation condition and bed-materials but when the gasifier was operated in the mode of single bubbling fluidised bed (BFB). The behaviour of catalytic and non-catalytic bed materials differs when they are used in the DFB and the BFB. Fe/olivine and olivine in the BFB mode give lower tar and CH4 content together with higher H2+CO concentration, and higher H2/CO ratio, compared to DFB mode. It is hard to show a clear advantage of Fe/olivine over olivine regarding tar/CH4 catalytic reforming.    In order to significantly reduce the tar/CH4 contents, an internal reformer, referred to as the FreeRef reformer, is developed for in-situ catalytic reforming of tar and CH4 using Ni-catalyst in an environment of good gas-solids contact at high temperature.  A study on the internal reformer filled with and without Ni-catalytic pellets was carried out by evaluation of the syngas composition and tar/CH4 content. It can be concluded that the reformer with Ni-catalytic pellets clearly gives a higher H2 content together with lower CH4 and tar contents in the syngas than the reformer without Ni-catalytic pellets. The gravimetric tar content decreases from 25 g/m3 down to 5 g/m3 and the CH4 content from 11% down below 6% in the syngas.   The MIUN gasifier has a unique design suitable for in-bed tar/CH4 catalytic reforming and continuously internal regeneration of the reactive bed material. The novel design in the MIUN gasifier increases the gasification efficiency, suppresses the tar generation and upgrades the syngas composition.
Gasification-based Biorefinery for Mechanical Pulp Mills