The goal of this work was to establish the suitable and limiting concentrations of Zn, Cu and Mn compounds during syngas fermentation. The results showed that cells encased in polyvinylidene difluoride (PVDF) membranes had a faster accumulation of methane in reactors containing fermentation medium dosed with 5 mg/L of each heavy metal compared to free cells. It was also revealed that total inhibition of biohydrogen production occurred in medium containing 5 mg/L Cu, 30 mg/L Zn and 140 mg/L Mn while the most suitable metal concentration level was 0.1 mg/L Cu, 0.6 mg/L and 2.8 mg/L Mn. In addition, a comparison test showed that for the most suitable metal concentration in the medium, rate of performance at pH 6 and 7 was higher than at pH 5.

This work describes the application of porous metal supported Pd-membranes to the water-gas shift catalytic membrane reactor in the context of its potential application to the Integrated Gasification Combined Cycle (IGCC) process. The objective of this work was to develop a better understanding of Pd-membrane fabrication techniques, water-gas shift catalytic membrane reactor operation, and long-term behavior of the Pd-membranes under water-gas shift conditions. Thin (1.5 - 16 um) Pd-membranes were prepared by electroless deposition techniques on porous metal supports by previously developed methods. Pd-membranes were installed into stainless steel modules and utilized for mixed gas separation (H2/inert, H2/H2O, dry syngas, and wet syngas) at 350 - 450C and 14.5 atma to investigate boundary layer mass transfer resistance and surface inhibition. Pd-membranes were also installed into stainless steel modules with iron-chrome oxide catalyst and tested under water-gas shift conditions to investigate membrane reactor operation in the high pressure (5.0 - 14.6 atma) and high temperature (300 - 500C) regime. After the establishment of appropriate operating conditions, long-term testing was conducted to determine the membrane stability through He leak growth analysis and characterization by SEM and XRD. Pd and Pd/Au-alloy membranes were also investigated for their tolerance to 1 - 20 ppmv of H2S in syngas over extended periods at 400C and 14.0 atma. Water-gas shift catalytic membrane reactor operating parameters were investigated with a focus on high pressure conditions such that high H2 recovery was possible without a sweep gas. With regard to the feed composition, it was desirable to operate at a low H2O/CO ratio for higher H2 recovery, but restrained by the potential for coke formation on the membrane surface, which occurred at a H2O/CO ratio lower than 2.6 at 400C. The application of the Pd-membranes resulted in high CO conversion and H2 recovery for the high temperature (400 - 500C) water-gas shift reaction which then enabled high throughput. Operating at high temperature also resulted in higher membrane permeance and less Pd-surface inhibition by CO and H2O. The water-gas shift catalytic membrane reactor was capable of stable CO conversion and H2 recovery (96% and 88% respectively) at 400C over 900 hours of reaction testing, and 2,500 hours of overall testing of the Pd-membrane. When 2 ppmv H2S was introduced into the membrane reactor, a stable CO conversion of 96% and H2 recovery of 78% were observed over 230 hours. Furthermore, a Pd90Au10-membrane was effective for mixed gas separation with up to 20 ppmv H2S present, achieving a stable H2 flux of 7.8 m3/m2-h with a moderate H2 recovery of 44%. The long-term stability under high pressure reaction conditions represents a breakthrough in Pd-membrane utilization.

Coal gasification is currently being developed as a cleaner alternative to conventional combustion technology. To optimise H2 production in this process, a water gas shift reaction is utilised to convert all CO with H2O to produce CO2 and H2. Typically industrial processes involve a two-step reaction system followed by a downstream H2 purification system, though attracting significant inefficiencies and high capital costs. Replacing a conventional unit process with a membrane reactor in this application is foreseen to provide major advantages: • Removing H2 from the reaction in-situ, a membrane reactor can minimise downstream processing and associated capital and operational costs. • Shift the reaction to higher conversions, improving efficiencies and reducing CO in the outlet. • Provide a purified H2 stream for use in PEM fuel cells, while concentrating the CO2 stream at high pressure for possible sequestration. If the concept of membrane reactor is to be adopted in coal gasification, important material improvements and operational challenges must be overcome before commercialisation can be realised. In addition, the water gas shift reaction has only recently gained interest for membrane reactors and is currently lacking comprehensive research on the effects of operating conditions on both the conversion and separation found within the unit. To this end, these are strong motivations of this work to contribute with knowledge in this field of research. This thesis examines the effects of operating conditions such as temperature, pressure, space velocity, sweep gas rate and feed water ratio on the performance of a water gas shift membrane reactor as compared with a conventional reactor. Novel cobalt silica molecular sieve membranes were used with conventional low temperature water gas shift reaction CuZnAl2O3 catalysts. Two type of membrane reactor configuration were investigated: a small flat template with catalyst on the feed side, and a scale up tube membrane with catalyst placed also in feed stream, the inner shell of the tube membrane. The cobalt silica membranes complied with activated transport, following a flux dependency gas permeation, where He and H2 permeance increased with temperature whilst N2, CO and CO2 showed the opposite effect. Best single gas selectivities were very high, with values of 4500 (He/N2) and 1100 (H2/CO2). In addition, the energy of activation for He and H2 was also very high, in excess of 9-10 kJ.mol-1, clearly indicating the high quality of the membranes employed in this study. It was found that the MR improved CO conversions for a range of space velocities as a function of temperature, which was attributed to both activate transport property of the membrane and increased conversion. Below equilibrium limits this provided an improved H2 production of 5 – 12% at 200-250oC as the removal of H2 through the membrane allowed enhanced conversion. With a set feed rate, the optimum advantage of the MR was seen at a water ratio of 1 as the lower equilibrium limits allowed greater potential for conversion enhancement. With increasing excess water this advantage decreased from 7% down to 0.5% at 300oC. The use of pressure and sweep rate was used to optimise the membranes permeation rate and selectivity. While pressure (or driving force) provided the highest potential for increasing permeation (or flow rate), temperature in tandem with pressure provided the greatest improvement in membrane selectivity, thus increasing H2 concentration from 95 – 99% in the permeate stream. Detailed study of permeate concentrations with changing conditions was undertaken to provide an understanding of the transport properties of silica membranes. It was observed that membrane selectivity and permeation decreased with the gas composition (ie Single>Binary>Ternary). Nevertheless, for separation of a ternary mixture at increased temperatures (250oC) the membrane could provide up to 99% purified H2 while reducing CO down to 700ppm. Competitive gas permeation regimes are an industrial reality which is seldom addressed in membranes for high temperature gas separation. The effect of gas mixtures on permeation and selectivity was attributed to several factors: chemical potential (or driving force) of the feed gas mixture, blockage of micropores by large molecules (CO2 and CO) which in turn affects the percolation of H2. As a result, gas separation was reduced for higher CO and CO2 feed concentrations, leading to a significant reduction in the H2 flow rate. Temperature played a vital role in this competitive process, as H2 diffusivity and CO, CO2 adsorption followed an inverse trend. Thus, increasing temperature led to higher H2 pore diffusivity, while decreasing the competitive effect of CO and CO2 adsorption. The use of cobalt modified silica to improve the hydrothermal stability of the membranes was investigated for use in the water gas shift reaction. It was found that the addition of cobalt stabilised the silica pore network, maintaining microporosity after exposure to steam. This is validated with long term stability testing in a water gas shift membrane reactor, where it was seen that the membrane could provide up to 95% H2 concentration in the permeate for over 200hrs of MR operation. This provided novel work, establishing the feasibility of these membranes for long term testing and operation in an industrial WGS MR.

The progress in fuel cell technology has resulted in an increased interest towards hydrogen fuel. Consequently, water gas shift reaction has found a renewed significance. Even though iron- and copper-based catalysts have been used for water gas shift reaction for decades, the catalysts are not strong enough to bring carbon monoxide concentration to a level tolerable for a fuel cell working at low temperatures. This study is focused on hydrogen production from water gas shift reaction using a nickel catalyst. Literature review revealed that nickel is one of the promising catalysts for water gas shift reaction. A thermodynamic analysis proved that exothermic water gas shift reaction is thermodynamically favorable at low temperatures but kinetically limited, and vice versa at higher temperatures. Initial experiments using 12 catalysts supported over monolith alumina revealed that nickel supported on ceria-promoted monolith alumina (Ni/CeO2-Al2O3) performed best, especially at 500oC. At this temperature and steam flowrates of 0.1-0.5 ml/min, the nickel catalyst had an activity of 94-99%, H2 yield of 55-61 vol.%, and H2 selectivity of 77-99%. A second set of experiments examined nine nickel based catalysts using different supports (mostly in powder form) which also demonstrated that Ni/CeO2-Al2O3 is the most promising catalyst for high temperature (450oC) water gas shift reaction. When nickel loading was varied from 1 to 8% (w/w), it was apparent that the catalyst performance increased with the nickel loading. Powder alumina resulted in better catalysis than monolith alumina. In this experiment, it was evident that the presence of minor amounts (1% (w/w) of the nickel loading) of a dopant material that included cobalt, chromium, molybdenum, or ruthenium affected the catalytic activity of the primary catalyst. The addition of cobalt or chromium resulted in positive effect on the performance of Ni/CeO2-Al2O3 catalyst. There was no appreciable effect due to the addition of ruthenium, and there was negative effect owing to the presence of molybdenum. Undoped, cobalt-doped, or chromium-doped Ni/CeO2-Al2O3 catalyst performed much better for water gas shift reaction at 450oC than that of a commercial (control) catalyst. A kinetic study revealed that the activation energy of water gas shift reaction over Ni/CeO2-Al2O3 was to be 104.5 kJ/mol.

No description available.

Los nanoclústeres (NCs) exhiben propiedades físicas y químicas muy novedosas sensibles a su tamaño y geometría. Además, resultan muy interesantes pues tienden un puente entre el comportamiento de los átomos y el del sólido. Por otro lado, reciben gran atención por sus aplicaciones tecnológicas, como por ejemplo, los NCs de metales de transición en el campo de la catálisis heterogénea. En particular, los clústeres de Pt depositados sobre óxidos tales como rutilo TiO2, han mostrado ser eficientes como catalizadores en reacciones tales como la oxidación de CO a CO2, paso intermedio importante de la reacción de WGS (water gas shift). Es por ello que en esta tesis se realizó una caracterización exhaustiva de clústeres de Pt aislados (Ptn) y clústeres de Pt soportados (Ptn/TiO2(110)), evaluando sus propiedades estructurales, cohesivas y electrónicas a través de un estudio teórico utilizando métodos de modelado ab initio basados en la Teoría de la Funcional Densidad (DFT). Primeramente, se consideraron los clústeres de Ptn (n = 2, 4, 13, 19, 55, 79, 85 y 147) aislados. Para cada clúster se optimizó su estructura, y a partir de ella se determinaron las demás propiedades. Las densidades de estados vibracionales obtenidas en el marco de la aproximación armónica muestran un comportamiento muy diferente al del sólido, con presencia de estados discretos, que dan lugar a desviaciones del modelo de Debye para el calor específico a volumen constante a bajas temperaturas. Entre los clústeres estudiados, el Pt13 fue abordado en detalle, en particular porque las típicas configuraciones de capa cerrada resultaron inestables. Este es un resultado inesperado, puesto que muchos trabajos proponen a las estructuras (Oh) e (Ih) como las más plausibles para este tamaño de clúster. Ante este resultado, se utilizó la técnica de dinámica molecular ab initio, que incorpora efectos térmicos, con el fin de analizar la evolución de los clústeres en el tiempo y en búsqueda de nuevas configuraciones estables de menor energía. Como resultado, un nuevo isómero de baja simetría con estructura de capas apiladas es predicho para el clúster Pt13. Otro tamaño de clúster estudiado en distintas configuraciones fue el Pt4. Se consideraron las geometrías bidimensionales planar (P), romboédrica (R) y la tridimensional tetraédrica (T). De manera aislada, el clúster (T) resultó más estable, aunque esta misma tendencia no se mantuvo al momento de depositar los NCs en el sustrato de rutilo estequiométrico (TiO2). Para analizar la potencialidad del sistema Ptn/TiO2 como catalizador, fueron depositados NCs de Pt4 (P y T) y Pt13(Oh) sobre la superficie TiO2(110) tanto estequiométrica como reducida (TiO2(110)+Vo). Para ambos sustratos se estudió la estabilidad relativa de las estructuras de los clústeres, determinando las geometrías de equilibrio, las energías de adsorción, los efectos de transferencia de carga y la densidad electrónica de estados para caracterizar los diferentes aspectos de la interacción metal-óxido. En particular se evaluó la factibilidad del uso de estos sistemas en las reacciones de oxidación de CO por un átomo de oxígeno de la superficie, como paso intermedio en la reacción de WGS. / Nanoclusters exhibit novel physcial and chemical properties sensitive to their size and geometry. Besides, they are of interest since they tend to stablish a bridge between the behaviour of the atoms and the solid. On the other side, they are receiving great attention due to their technological applications, such as for example, the transition metal nanoclusters in the field of heterogeneous catalyst. In particular, Pt clusters deposited on oxides such as rutile TiO2, have shown to be efficient as catalysts in reactions such as the oxidation of CO to CO2, an important intermediate step in the WGS (water gas shift) reaction. Due to this fact in this thesis an exhaustive characterization of isolated Pt clusters (Ptn) and suppported Pt clusters is performed, evaluating their structural, cohesive and electronic properties through a theoretical study using ab initio modelling methods based on Density Functional Theory,. Firstly, the isolated Ptn (n = 2, 4, 13, 19, 55, 79, 85 y 147) clusters were considered. For each cluster its structure was optimized, and with it the other properties were determined. The vibrational densities of states, calculated in the harmonic approximation, show a behaviour very different from the bulk one, with the presence of discrete states that give rise to deviations from the Debye model for the specific heat at constant volumen and low temperatures. Among the clusters studied, the Pt13 was treated in detail, in particular because the typical close shell configurations happen to be unstable. This is an unexpected result, since various works report (Oh) e (Ih) structures as the most plausible ones for this cluster size. Considering this, we applied the ab initio molecular dynamic technique, that incorporates explicitly thermal effects, with the aim to analyse the time evolution of the cluster, and to search new stable configurations of lower energy. As a result, a new layered low symmetry stable isomer of lower energy is predicted for the Pt13 cluster. Another cluster size studied in different configurations was Pt4. The two-dimensional planar geometry (P), rombohedrical (R) and the tridimensional tetrahedrical (T) one, were considered. For the isolated clusters, the (T) one was more stable, although this trend is changed for the supported NCs on stequiometric rutile (TiO2). To analyze the potential activity of the Ptn/TiO2 as a catalyst, NCs of Pt4 (P y T) and Pt13(Oh) were deposited on the TiO2(110) stoiquiometric and reduced (TiO2(110)+Vo) surfaces. For both substrates the relative stability of the structures was studied, determining the equilibrium geometries, the adsorption energies, the effects of charge transfer and the electronic density of states to characterize different aspects of the metal-oxide interaction. In particular the feasibility of the use of these systems for the oxidation of CO by one oxygen atom of the surface, as intermediate step in the WGS reaction, was evaluated.

On the basis of our investigation of the "Aldridge" catalyst, an alkali impregnated cobalt0-molybdate on an A1 203 support, for the water-gas shift, methanation, and ethanol dehydration reactions, we can make the following conclusions: 1. The cesium-impregnated "Aldridge" catalyst is highly active for the water-gas shift reaction under sulfur tolerant conditions. 2. The activity of this catalyst is strongly dependent upon the cesium:molybdenum molar ratio. The normalized first order rate constant increases with this ratio until an optimum is reached for the full strength and half strength catalyst. 3. The transition temperatures appeared only with the cesium-impregnated full and half strength catalysts, but not with the one-fifth catalysts. 4. The potassium-impregnated cobalt-molybdate catalyst is quite active, in Comparison to lithium- and sodium-impregnated versions. 5. The cesium-impregnated zinc-molybdate catalyst is not as active as the unimpregnated cobalt-molybdate. Its activity is approximately half that of catalyst "Z" at 400°C. 6. We don't believe that the "Aldridge" catalyst is a catalytic melt. / Master of Science

L'intérêt pour la synthèse de Fischer-Tropsch (FTS) est d'actualité. Elle permet la conversion de matière première (biomasse) en combustible liquide. Comparés aux catalyseurs à base de cobalt, ceux à base de fer présentent une désactivation rapide, une activité et une sélectivité faibles en produisant une quantité non désirable de CO2. Après plusieurs décennies d'études, l'origine de ces défauts reste méconnue. Les catalyseurs classiques sont généralement fortement chargés en fer (>70 wt.%) et composés de nombreuses phases empêchant l'établissement d'une relation structure-activité. Il est nécessaire de développer des catalyseurs contenant du fer plus actifs, plus sélectifs et plus stables par une approche rationnelle. La synthèse de nanoparticules de taille contrôlée (3.5 nm) encapsulées dans les murs d'une silicalite-1 creuse (Fe@hollow-silicalite-1) est présentée. L'encapsulation empêche le frittage pendant la synthèse de Fischer-Tropsch, permettant de garder une bonne dispersion du fer. Contrairement aux autres catalyseurs, le catalyseur Fe@hollow-silicalite-1actif ne produit pas de CO2. L'hydrophobicité de la silicalite-1 est très certainement à l'origine de la non-production de CO2 par inhibition de la réaction directe du gaz à l'eau. On démontre que le catalyseur Fe@hollow-silicalite-1convertit le CO2 en CO par réaction du gaz à l'eau inversée (R-WGS). Afin d'établir une relation structure-activité, des catalyseurs à base de fer de taille bien contrôlée sont synthétisés et caractérisés (MET, in-situ XANES, in-situ Mössbauer). Deux catégories de TOF suivant la taille des particules, ~10-2 s-1 pour les plus larges (>20 nm) et ~10-3 s-1 pour les plus petites, sont observées / Fischer-Tropsch synthesis (FTS) is gaining renewed interests as it allows converting alternative feedstocks (biomass) into liquid fuels. Compared to Co-based catalysts, state of the art Fe catalysts show lower activity, faster deactivation and lower selectivity as it produces an undesirable amount of CO2. Despite decades of studies, the origins of low activity and selectivity and fast deactivation are still unclear. Typical Fe based catalysts are highly metal loaded (>70 wt.%) and composed of many different phases, which strongly impedes the establishment of structure-activity relationships. There is a need to develop more active, more selective and more stable iron FTS catalysts by rational approaches.The synthesis of well-controlled 3.5 nm iron nanoparticles encapsulated in the walls of a hollow-silicalite-1 zeolite (Fe@hollow-silicalite-1) is presented. The encapsulation prevents particle sintering under FTS conditions leading to a high and stable Fe dispersion. The catalyst Fe@hollow-silicalite-1 is active and highly selective in FTS. Most importantly, Fe@hollow-silicalite-1 does not produce CO2 in contrast to all other Fe-based catalysts. The strong hydrophobicity of the silicalite-1 is likely the origin of the lack of CO2 production by inhibition of the forward WGS reaction. We demonstrated that Fe@hollow-silicalite-1converts CO2 into CO by the reverse WGS reaction. In order to establish a structure-activity relationship, a series of Fe-based catalysts with well-controlled particle sizes were synthesized and characterized (TEM, in-situ XANES, in-situ Mössbauer, XRD). We observed two distinct categories of TOFs depending on the particle size, ~10-2 s-1 for larger (>20 nm) and ~10-3 s-1 for smaller ones

No description available.

Le reformage des gaz primaires de gazéification a été étudié à des températures de 800-1000[degrés Celsius].Le reformage thermique à ces températures a permis de convertir jusqu'à 65 % du goudron et de réduire le ratio phénol/naphtalène de 99 %, ce qui représente un avantage certain pour le traitement des eaux de lavages. L'ajout d'un lit fixe contenant du char a permis d'augmenter la conversion du goudron à 85 % et de réduire les phénols sous le seuil de détection du GC-MS. Dans ces conditions, il a été démontré que le reformage thermique convertit tous les gaz C[indice inférieur 2] -C[indice inférieur 3] , à l'exception de l'éthane, pour lequel une cinétique a été établie, et d'une légère production d'acétylène. L'ajout d'un lit fixe contenant du char a augmenté la conversion des gaz C[indice inférieur 2] -C[indice inférieur 3] et a même permis la conversion de 30 % du méthane à une température aussi basse que 925[degrés Celsius]. Par contre, l'ajout de char transporté par le gaz de synthèse à des concentrations moindres n'a pas eu d'effet observable sur la conversion des gaz C[indice inférieur 1]-C[indice inférieur 3].Le char transporté a cependant augmenté le taux de la réaction de water gas shift , ce qui permet un meilleur ajustement du ratio H2 /CO et une synthèse optimale dans les étapes catalytiques subséquentes.