Les glycosyltransferases sont les enzymes responsables de la synthèse d'oligosaccharides, de polysaccharides et de glycoconjugués. Elles catalysent le transfert d'un saccharide à partir d'un substrat donneur, en général un nucléotide sucre, vers un substrat accepteur. Le mécanisme de réaction des glycosyltransférases peut avoir lieu avec une inversion ou une rétention de l'anomérie de liaison du sucre transféré. De nombreuses incertitudes subsistent au sujet du mécanisme des glycosyltransférases transférant avec rétention de l'anomérie. L'élucidation de ce mécanisme aiderait à la conception d'inhibiteurs ciblés afin de soigner des maladies allant des infections virales et bactériennes au cancer. De nombreuses protéines sont actives à l'état cristallin, ce qui fait de la cristallographie aus rayons X un outil de choix pour étudier le mécanisme d'enzymes. La « cristallographie cinétique » est un terme qui regroupe l'ensemble des techniques permettant d'initier une activité biologique in crystallo pour générer et piéger une quantité significative d'un état intermédiaire de réaction, afin de résoudre sa structure par cristallogrpahie aux rayons X. Le but de mon projet était d'étudier le mécanisme catalytique d'une glycosyltransférase transférant avec rétention de l'anomérie, par cristallographie cinétique. De cette façon, j'ai étudié une enzyme du groupe sanguin responsable du transfert d'un galactose à partir d'UDP-Gal vers l'antigène H. J'ai étudié les effets de la cryoprotection sur la structure de la protéine, et j'ai effectué les études préalables nécessaires à l'application de deux techniques issues de la cristallographie cinétique à l'étude de ces enzymes : « Déclencher-tremper »et « Tremper-déclencher ». / Glycosyltransferases are a large class of enzymes responsible for the synthesis of oligosaccharides, polysaccharides and glycoconjugates. They catalyze the transfer of a saccharide from a donor substrate, usually a nucleotide sugar, to an acceptor. Glycosyltransferase reactions can occur with either retention or inversion of the anomeric configuration of the transferred sugar. Many uncertainties remain concerning the catalytic mechanisms of retaining glycosyltransferases even though the elucidation of this mechanism would help in the rationale design of potent inhibitors to treat diseases ranging from viral and bacterial infections to cancer. Many proteins function in the crystalline state which makes X-ray crystallography a potential powerful tool for studying enzymatic mechanisms. ‘Kinetic crystallography' is a term coined to name the ensemble of techniques to initiate a biological turnover in crystallo in order to generate and trap a significant amount of a given intermediate reaction state, and then solve its X-ray structure. The aim of my project was to investigate the catalytic mechanism of a retaining glycosyltransferase, by kinetic crystallography methods. In this way, I studied a human blood group synthase responsible for the transfer of a galactose from UDP-Gal to the H antigen. I investigated the effects of the cryoprotectant on the structure of the protein, and I made preliminary studies to apply two kinetic crystallography techniques to the enzyme: freeze-trigger and trigger freeze experiments.

La présente thèse s’inscrit dans un projet collaboratif de type CEFIPRA entre l’Inde (Dr. Ravi Kumar, Department of Metallurgical and Materials Engineering, Indian Institute of Technology-Madras (IIT Madras), Chennai) et la France (Dr. Samuel Bernard, Institut Européen des Membranes, CNRS, Montpellier). Les travaux de thèses se sont consacrés à la synthèse de céramiques de type non-oxyde autour de systèmes binaires (nitrure de silicium et nitrure de bore) et ternaires (Si-M-N, B-M-N (M=Ti, Zr, Hf)) à partir de précurseurs moléculaires et polymères, i.e., la voie polymères précéramiques ou PDCs. L’idée principale de ce travail est de former des structures nanocomposites à partir des systèmes ternaires dans lesquelles des nanocristaux de nitrures métalliques (M=Ti, Zr, Hf) se développent pendant la synthèse du nitrure de silicium et du nitrure de bore. Une caractérisation complète allant des polymères aux matériaux finaux a été conduite. Ces matériaux ont ensuite été préparés sous forme de composés mésoporeux (monolithes) en couplant la voie des polymères précéramiques à une approche de nanomoulage. Ces monolithes à haute surface spécifique et mésoporosité interconnectée ont alors été appliqués comme support de nanoparticules de platine pour l’hydrolyse du borohydrure de sodium pour générer de l’hydrogène. Les performances en tant que support de catalyseur ont été évaluées en termes de volume d’hydrogène libéré et de reproductibilité. Nous avons montré que les nanocomposites TiN/Si3N4 de surface spécifique très élevée présentent les meilleures performances grâce à l’activité catalytique du Si3N4 amorphe, de la présence de TiN nanométrique et de l’effet synergétique entre les nanoparticules Pt, le TiN nanostructuré et le Si3N4 amorphe. En preuve de concept, nous avons montré que ces structures nanocomposites étaient multifonctionnelles: elles peuvent être appliquées en tant que supports d’électro-catalyseurs et matériaux d’électrodes dans les piles à combustibles et les super-condensateurs, en particulier pour ceux contenant des matériaux lamellaires 2D et du carbone libre. / The thesis has been funded by a collaborative research partnership between Indian (Dr. Ravi Kumar, Department of Metallurgical and Materials Engineering, Indian Institute of Technology-Madras (IIT Madras), Chennai) and French institutes (Dr. Samuel Bernard, European Membrane Institute, CNRS, Montpellier), IFCPRA/CEFIPRA. It is focused on the synthesis, and characterization of binary (silicon nitride and boron nitride) and ternary (Si-M-N, B-M-N (M = Ti, Zr, Hf)) ceramics which are prepared through a precursor approach based on the Polymer-Derived Ceramics (PDCs) route. The idea behind the preparation of the ternary systems is to form nanocomposite structures in which metal nitrides (M = Ti, Zr, Hf) nanocrystals grow during the synthesis of silicon nitride and boron nitride. A complete characterization from the polymer to the final material is done. Then, these materials have been prepared as mesoporous monoliths coupling the PDCs route with a nanocasting approach to be applied as supports of platinum nanoparticles for the hydrolysis of liquid hydrogen carriers such as sodium borohydride. The performance as catalyst supports has been evaluated in terms of volume of hydrogen released and reproducibility. We showed that the very high specific surface area TiN/Si3N4 nanocomposites displayed the best performance because of the catalytic activity of amorphous Si3N4, the presence of nanoscaled TiN and the synergetic effect between Pt nanoparticles, nanoscaled TiN and amorphous Si3N4. Interesting, these materials are multi-functional as demonstrated as a proof of concept: they can be applied as electrocatalyst supports, electrode materials for fuel cells and supercapacitors, in particular those containing 2D layered materials and free carbon.

Nas últimas décadas, tem se intensificado a busca por novas fontes energéticas. Neste contexto, o uso do hidrogênio como combustível é profícuo porque, além de possuir um elevado poder energético, sua combustão não gera poluente algum. Sendo assim, a decomposição catalítica do metano é uma alternativa interessante, pois consiste na produção de hidrogênio puro, sem geração de COx. O objetivo deste trabalho foi estudar o efeito de diferentes teores de cobre em catalisadores contendo cobalto e alumínio na decomposição catalítica do metano. Uma série de catalisadores Co-Al modificados com cobre (com diferentes teores de cobre) foram preparados por co-precipitação e avaliados na reação de decomposição catalítica do metano. Foram testados diferentes razões molares de Co/Cu e dos metais M+2/M+3. Os catalisadores foram caracterizados por medidas de área específica SBET, TPR-H2,TGA-DTA e DRX. As amostras após a reação foram caracterizadas por DRX, TPO e MEV. Os ensaios de atividade foram conduzidos em reator tubular de leito fixo, carga de 100 mg, em temperaturas entre 500 e 750°C, utilizando-se uma razão molar N2/CH4 igual a 9 na alimentação. A influência da ativação, com passagem hidrogênio antes da reação, também foi estudada. Constatou-se uma forte influência sobre a redutibilidade de óxidos de cobalto na presença de Cu. Este metal diminui fortemente a temperatura de redução (em mais de 100°C) do CoAl2O4 devido a um efeito sinergético entre Cu e Co. Os resultados dos testes de atividade indicam que a conversão de CH4 é menor para os catalisadores que contém maior teor de cobre. Além disso, constatou-se que, quando há um pequeno aumento na substituição de cobalto pelo cobre, a atividade não é significativamete alterada. Os testes catalíticos com temperatura constante, bem como a avaliação dos catalisadores reduzidos previamente, sugerem a etapa de redução prévia com hidrogênio pode ser evitada. / In recent decades, has been intensified the search for new energy sources. In this context, the use of hydrogen as a fuel is advantageous because, besides having an high power energy, its combustion does not generate any pollutant. Thus, the catalytic decomposition of methane is an attractive alternative, because pure hydrogen without COx generation. The objective of this work was to study the effect of different amounts of copper over Co-Al catalysts in the catalytic decomposition of methane. The samples were prepared by co-precipitation and evaluated in the reaction of catalytic decomposition of methane to produce hydrogen. Tests were performed with catalysts containing different Co/Cu and M+2/M+3 ratios. Samples were characterized by SBET, TGA, DTA, XRD and TPR. The carbon produced in the reaction was characterized by XRD, SEM and TPO. Tests were performed in a tubular fixed bed reactor, between 500 and 700°C, using a N2/CH4 (9:1 molar). The influence of activation with hydrogen was also studied. The results showed that the presence of Cu strongly decreased the reduction temperature of CoAl2O4 (more than 100ºC) due to a synergistic effect between Cu and Co. The activity runs showed that CH4 conversion decreases as Cu content amount increases. A small increase in the substitution of cobalt by copper does not change significantly the CH4 conversion. Moreover, the run with temperature constant, as well the study of the reduction with H2, suggests that the activation step can be avoid. The analysis of XRD, SEM and TPO suggest that the carbon was formed mainly in the form of single-walled nanotubes.

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

This thesis presents the results of the investigation on developing and evaluating a low temperature (<150oC) non - catalytic process using a hydrogen transfer agent (instead of molecu-lar hydrogen) for coal dissolution in supercritical CO2. The main idea behind the thesis was that one hydrogen atom from water and one hydrogen atom from the hydrogen transfer agent (HTA) were used to hydrogenate the coal. The products of coal dissolution were non-polar and polar while the supercritical CO2, which enhanced the rates of hydrogenation and dissolution of the non-polar molecules and removal from the reaction site, was non-polar. The polar modifier (PM) for CO2 was added to the freed to aid in the dissolution and removal of the polar components. The addition of a phase transfer agent (PTA) allowed a seamless transport of the ions and by-product between the aqueous and organic phases. DDAB, used as the PTA, is an effective phase transfer catalyst and showed enhancement to the coal dissolution process. COAL + DH- +H2O  COAL.H2 + DHO-- This process has a great feature due to the fact that the chemicals were obtained without requir-ing to first convert coal to CO and H2 units as in indirect coal liquefaction. The experiments were conducted in a unique reactor set up that can be connected through two lines. one line to feed the reactor with supercritical CO2 and the other connected to gas chromatograph. The use of the supercritical CO2 enhanced the solvent option due to the chemical extraction, in addition to the low environmental impact and energy cost. In this thesis the experiment were conducted at five different temperatures from atmos-pheric to 140°C, 3000 - 6000 psi with five component of feed mixture, namely water, HTA, PTA, coal, and PM in semi batch vessels reactor system with a volume of 100 mL. The results show that the chemicals were obtained without requiring to first convert coal to CO and H2 units as in indirect coal liquefaction. The results show that the conversion was found to be 91.8% at opti-mum feed mixtures values of 3, 1.0 and 5.4 for water: PM, HTA: coal, water: coal respectively. With the oil price increase and growing in energy demand, the coal liquefaction remain afforda-ble and available energy alternative.

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Membrane reactor is a device that simultaneously carrying out reaction and membrane-based separation. The advantageous transport properties of the membranes can be employed to selectively remove undesired products or by-products from the reaction mixture, to break the thermodynamic barrier, and to selectively supply the reactant. In this work, membrane reactor technology has been exploited with robust H₂ selective polymeric membranes in the process of hydrogenation and dehydrogenation. A state-of-the-art 3-phase catalytic membrane contactor is utilized in the processes of soybean hydrogenation and bio-oil hydro-deoxygenation, where the membrane functions as phase contactor, H₂supplier, and catalytic support. Intrinsically skinned asymmetric Polyetherimide (PEI) membranes demonstrated predominant H₂permeance and selectivity. By using the PEI membrane in the membrane contactor, soybean oil is partially hydrogenated efficiently at relatively mild reaction conditions compared with a conventional slurry reactor. In the hydroprocessing of bio-oil using the same system, the membrane successfully removed water, an undesired component from bio-oil by pervaporation. The more industrially feasible membrane-assisted reactor is studied in the alkane dehydrogenation process. Viable polymeric materials and their stability in elevated temperatures and organic environment are examined. The blend polymeric material of Matrimid® 5218 and Polybenzimidazole (PBI) remained H₂permeable and stable with the presence of hydrocarbons, and displayed consistent selectivity of H2/hydrocarbon, which indicated the feasibility of using the material to fabricate thermally stable membrane for separation. The impact of membrane-assisted reactor is evaluated using finite parameter process simulation in the model reaction of the dehydrogenation of methylcyclohexane (MCH). By combining tested catalyst performance, measured transport properties of the material and hypothetical membrane configuration, by using a membrane assisted packed-bed reactor, the thermodynamic barrier of the reaction is predicted to be broken by the removal of H₂. The overall dehydrogenation conversion can be increased by up to 20% beyond equilibrium. The predicted results are justified by preliminary experimental validation using intrinsically skinned asymmetric Matrimid/PBI blend membrane. The conversions at varied temperatures partially exceeded equilibrium, indicating successful removal of H₂by the blend membrane as well as decent thermal stability of the membrane at elevated temperatures with the presence of hydrocarbons. The successful outcome of membrane contactor and membrane-assisted reactor using robust polymeric membranes shows the effectiveness and efficiency of membrane reactors in varied application. The future work should be focusing on two direction, to further develop durable and efficient membranes with desired properties; and to improve the reactor system with better catalytic performance, more precise control in order to harvest preferable product and greater yield.

Neste trabalho investigou-se a influência do cobre em diferentes catalisadores a base de níquel na decomposição catalítica do metano. Foram avaliados desde aspectos relacionados ao tratamento térmico das amostras até o desempenho catalítico nos testes de atividade. As amostras foram preparadas a partir de dois métodos diferentes. Um grupo foi preparado pelo método de impregnação úmida utilizando sílica como suporte, enquanto o segundo foi preparado pelo método de coprecipitação contínua, utilizando nitratos de cobre, níquel e alumínio em diferentes composições molares. Os ensaios foram realizados em reator tubular de leito fixo acoplado a um forno com controle de temperatura e conectado em linha com cromatógrafo gasoso. Utilizou-se 100 mg de amostra, numa faixa de temperatura de 500 a 750°C, utilizando como alimentação uma mistura reacional de N2:CH4 na proporção de 9:1. A caracterização das amostras foi realizada através das análises de SBET, TGA, TPR, TPO, DRX e Espectroscopia Raman. Os resultados mostraram uma significativa influência do cobre na atividade das amostras em temperaturas superiores a 500°C. A presença de cobre influenciou a área específica e a temperatura de redução das amostras calcinadas. Pequenas quantidades de cobre contribuem ao evitar a desativação do catalisador por sinterização em temperaturas superiores a 500°C. Para os catalisadores coprecipitados, além da influência do cobre, avaliou-se também a influência do gás utilizado no tratamento térmico das amostras. Foram utilizadas amostras não calcinadas, amostras calcinadas em ar por seis horas e calcinadas em N2 pelo mesmo período. Os resultados indicaram que a presença de cobre contribui para uma maior estabilidade e atividade nos ensaios realizados nas temperaturas de 600 e 650°C, principalmente para as amostras calcinadas em ar. As amostras com 11% de cobre na composição apresentaram elevada estabilidade na temperatura de 600°C, mesmo quando não calcinadas, indicando que a etapa de tratamento térmico pode ser evitada para este tipo de amostra. As análises de DRX, TPO e Espectroscopia Raman sugerem que o carbono formado, tanto para os catalisadores suportados quanto para os coprecipitados, depositou-se na forma de nanotubos de paredes múltiplas. / The effect of copper in different nickel-based catalysts in the catalytic decomposition of methane was investigated. Were evaluated aspects from the heat treatment of the samples to the catalytic performance in activity tests. Samples were prepared using two different methods. One group was prepared by the wet impregnation method using silica as the support and the second group was prepared by continuous coprecipitation method using copper nitrate, nickel and aluminum in different molar compositions. Catalytic activity runs were carried out in a tubular fixed-bed reactor coupled to an oven with temperature control and connected in line with a gas chromatograph. Samples of 100 mg were used in a temperature range of 500 to 750°C applying a reaction mixture of N2:CH4 at a ratio 9:1 as feed supply. The characterization of the samples was performed through the analysis of SBET, TGA, TPR, TPO, XRD and Raman spectroscopy. The results showed a significant effect of copper on the activity of the samples at temperatures above 500°C. The presence of copper influenced the specific area and the reduction temperature of the calcined samples. Small amounts of copper contributed to avoid catalyst deactivation by sintering at temperatures above 500°C. For the coprecipitated catalysts in addition to the influence of copper, the effect of the gas used for the thermal treatment of samples was also evaluated. Uncalcined samples and samples calcined in air and in N2 for six hours were used. The results indicated that the presence of copper contributed to a superior stability and activity in runs performed at temperatures of 600 to 650°C, especially for samples calcined in air. Samples with 11% of copper showed high stability at 600°C, even if not calcined, indicating that the thermal treatment step can be avoided for this type of sample. The XRD, TPO and Raman spectroscopy results suggest that the carbon deposited on the spent catalysts was in the form of multi-walled nanotubes, for both the supported and the coprecipitated catalysts.

Neste trabalho, foi estudada a decomposição catalítica do metano sobre catalisadores coprecipitados, à base de Co-Al, para produção de hidrogênio e nanotubos de carbono. Foram testados catalisadores com diferentes proporções de cobalto e alumínio, bem como o efeito da adição de outros metais bivalentes (Mg, Ni, Zn ou Cu) ao sistema Co-Al. Os catalisadores foram caracterizados por TGA-DTA, DRX, TPR, TPO e imagens de MEV. As reações foram conduzidas em uma termobalança operando como reator diferencial, com 10 mg de catalisador. A faixa de temperatura analisada foi de 500-750°C. Os melhores resultados em termos de atividade e estabilidade foram obtidos com o catalisador Co66Al33. A adição de outros metais bivalentes não melhorou o desempenho do catalisador, principalmente porque esses metais afetaram a redutibilidade do catalisador. Para o catalisador que apresentou os melhores resultados (Co66Al33), foram realizados testes em diferentes temperaturas e condições reacionais. Os resultados mostraram que a forma de ativação afeta o desempenho deste catalisador, de forma que o catalisador pré-ativado produziu maiores quantidades de hidrogênio, nas reações a 550, 600 e 700°C. No entanto, a 650°C, a amostra autoativada teve desempenho semelhante à pré-ativada, inclusive mostrando-se mais ativa após certo tempo de reação. A caracterização do carbono depositado mostrou que todos os catalisadores produziram nanotubos de carbono. As imagens de microscopia eletrônica por varredura (MEV) mostraram a presença de filamentos mais longos e abundantes na amostra Co50Al50. As análises de oxidação a temperatura programada (TPO) indicaram que os nanotubos de carbono são de parede simples (SWNT). Para o catalisador Co66Al33, as análises de TPO indicaram maior produção de SWNT por parte das amostras pré-ativadas. / In this work, we studied the catalytic decomposition of methane over coprecipitated Co-Al based catalysts, for production of hydrogen and carbon nanotubes. Tests were performed with catalysts containing different Co-Al molar ratios, as well as with addition of other divalent metals (Mg, Ni, Zn, or Cu) to Co-Al system. The samples were characterized by TGA-DTA, XRD, TPR, TPO and SEM images. Activity tests were carried out in a thermobalance, operating as a differential reactor, with 10 mg of catalyst. The temperature range studied was 500-750°C. The best results in terms of activity and stability were obtained with the catalyst Co66Al33. Addition of other divalent metals did not improve the catalyst performance, mainly because these metals affected the catalyst reducibility. For the best results sample (Co66Al33), additional tests were performed at different temperatures and reaction conditions. Results showed that the activation method affects the catalyst performance, so as pre-activated sample produced more hydrogen than auto-activated sample, at 550, 600 and 700°C of reaction temperature. Nevertheless, at 650°C, auto-activated sample had performance almost similar to the pre-activated sample, even showing higher activity after a period of reaction. Characterization of deposited carbon showed that all catalysts produced carbon nanotubes. The images of scanning electron microscopy (SEM) showed formation of longer and abundant filaments in the sample Co50Al50. Temperature programmed oxidation analyses indicated that filaments are single walled carbon nanotubes (SWNT). For the catalyst Co66Al33, TPO analyses indicated a higher production of SWNT by pre-activated samples.

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