<p>The increase in shale gas exploitation has motivated the studies towards new processes for converting light alkanes into higher valuable chemicals, including fuels. The works in this dissertation focuses on two processes: propane dehydrogenation and ethylene oligomerization. The former involves the conversion of propane into propylene and hydrogen, while the latter converts light alkenes into higher molecular weight products, such as butylene and hexene. </p> <p>The thesis project focuses on understanding the effect of geometric effects of Pt alloy catalysts for propane dehydrogenation and the methodologies for their characterization. Pt-Co bimetallic catalysts were synthesized with increasing Co loadings, characterized and evaluated for its propane dehydrogenation performance. In-situ synchrotron X-Ray Powder Diffraction (XRD) and X-Ray Absorption (XAS) were used to identify and differentiate between the intermetallic compound phases in the nanoparticle surface and core. Difference spectra between oxidized and reduced catalysts suggested that, despite the increase in Co loading, the catalytic surface remained the same, Pt₃Co in a Au₃Cu structure, while the core became richer in Co, changing from a monometallic Pt fcc core at the lowest Co loading to a PtCo phase in a AuCu structure at the highest loading. Co^II single sites were also observed on the surface, due to non-reduced Co species. The catalytic performance towards propane dehydrogenation reinforced this structure, as propylene selectivity was around 96% for all catalysts, albeit the difference in composition. The Turnover Rate (TOR) of these catalysts was also similar to that of monometallic Pt catalysts, around 0.9 s^-1, suggesting Pt was the active site, while Co atoms behaved as non-active, despite both atoms being active in their monometallic counterparts.</p> <p>In the second project, a single site Co^II catalyst supported on SiO₂ was evaluated for ethylene oligomerization activity. The catalyst was synthesized, evaluated for propane dehydrogenation, propylene hydrogenation and ethylene oligomerization activities and characterized <i>in-situ</i> by XAS and EXAFS and H₂/D₂ exchange experiments. The catalysts have shown negligible conversion at 250^oC for ethylene oligomerization, while a benchmark Ni/SiO₂ catalyst had about 20% conversion and TOR of 2.3x10^-1 s^-1. However, as the temperature increased to above 300^oC, ethylene conversion increased significantly, reaching about 98% above 425^oC. <i>In-situ</i> XANES and EXAFS characterization suggested that H₂ uptake under pure H₂ increased in about two-fold from 200^oC to 500^oC, due to the loss of coordination of Co-O bonds and formation of Co-H bonds. This was further confirmed by H₂/D₂ experiments with a two-fold increase in HD formation per mole of Co. <i>In-situ</i> XAS characterization was also performed with pure C­₂H₄ at 200^oC showed a similar trend in Co-O bond loss, suggesting the formation of Co-alkyl, similarly to that of Co-H. The <i>in-situ</i> XANES spectra showed that the oxidation state remained stable as a Co²⁺ despite the change in the coordination environment, suggesting that the reactions occurs through a non-redox mechanism. These combined results allowed the proposition of a reaction pathway for dehydrogenation and oligomerization reactions, which undergo a similar reaction intermediate, a Metal-alkyl or Metal-Hydride intermediates, activating C-H bonds at high temperatures.</p>

L’objectif de cette étude est de préparer des catalyseurs bimétalliques Ni-X/SiO2, de les caractériser, et de comparer leur activité en hydrogénation du styrène en éthylbenzène,ainsi que leur sélectivité en hydrogénation de la double liaison oléfinique du styrène, par rapport à l’hydrogénation du noyau benzénique. L’élément X est greffé de manière contrôlée sur le nickel, et est choisi selon son électronégativité, soit inférieure (Zr), soit égale (Sn), soit supérieure (Au) à celle du nickel, dans le but d’étudier les effets géométriques et/ou électroniques qu'il pourrait induire. Parmi les échantillons préparés, le catalyseur Ni-Au/SiO2s’est révélé presque aussi actif que le catalyseur non dopé et nettement plus sélectif dans l’hydrogénation du styrène en éthylbenzène. / The aim of the present study is to prepare silica-supported Ni-X bimetallic catalysts, tocharacterize them, and to compare their catalytic activity in the hydrogenation of styrene, as well as their selectivity in the hydrogenation of the styrene’s olefinic double bond instead of the hydrogenation of the aromatic ring. The element X is grafted in a controlled way on the supported nickel particles, and is chosen according to its electronegativity, which is eitherlower (Zr), or equivalent (Sn), or higher (Au) than the electronegativity of Ni, in order to study the geometrical and/or electronic effects due to the doping of Nickel. Among the prepared samples, the Ni-Au/SiO2 catalyst has exhibited high activity and high selectivity in the hydrogenation of styrene into ethylbenzene, which makes the doping of Ni by Au apromising alternative for PyGas selective hydrogenation catalysts.

Les nanoparticules bimétalliques supportées sont des catalyseurs particulièrement attractifs en raison d’une activité et d’une stabilité accrues par rapport à leurs homologues monométalliques. Dans cette thèse des solides à base d'or ont été étudiés en tant que catalyseurs de l'oxydation sélective du glucose en absence de base. Il a été mis en évidence que la variation du ratio molaire entre l’or et le second métal (Pd, Pt, or Cu) a un impact différent sur les performances catalytiques en fonction de la nature du second métal, du support et de la méthode de préparation. Les séries Au-Pd supportés sur TiO2 et préparés par la méthode de sol-immobilisation et Au-Cu supportés sur TiO2 et préparés par la méthode de précipitation-réduction ont montré un effet synergique important, en particulier lorsque le rapport entre les deux métaux était de 1. Ces catalyseurs convertissent sélectivement le glucose en acide gluconique et leur activité a été trouvée supérieure à celle des contreparties monométalliques. L'analyse XPS a démontré que les espèces Au+δ, Pd+2 et CuOH jouent alors un rôle important dans la réaction étudiée en absence de base. Le bismuth en tant que second métal n'a montré aucun effet bénéfique, au contraire du palladium et du cuivre. Les catalyseurs à base d’Au et de Pt supportés sur ZrO2 se sont avérés quant à eux très stables lorsque la teneur en or était inférieure à 0,3% en masse. La nature du support a un impact très important sur le mécanisme de la réaction conduite en absence base sur des catalyseurs à base d’or. La raison réside dans les interactions que ce support développe avec la phase bimétallique favorisant ainsi la formation des espèces actives / The supported bimetallic nanoparticles are particularly attractive catalysts due to the increased activity and stability over their monometallic counterparts. In this thesis, gold-based solids have been studied as catalysts for the selective base-free oxidation of glucose. It has been demonstrated that the variation of the molar ratio between gold and the second metal (Pd, Pt, or Cu) has a different impact on the catalytic performances depending on the nature of the second metal, the support and the method of preparation. TiO2 supported Au-Pd series prepared by the sol-immobilization method and Au-Cu series prepared by the precipitation-reduction method showed a significant synergistic effect, particularly when the ratio of the two metals was 1. Under the reaction conditions used (T = 60 °C or 80 °C, P = 5 bar air, t = 5 h), these catalysts selectivity to gluconic acid and their activity was found to be greater than that of monometallic counterparts, especially when the catalyst is supported on TiO2. XPS analysis showed that the Au+δ, Pd+2 and CuOH species played an important role in the base-free reaction. Bismuth as the second metal showed no beneficial effect, unlike palladium and copper. The Au-Pt catalysts supported on ZrO2 proved to be still active when the gold content was less than 0.3 wt.%. Ultimately, the nature of the support has a very important impact on the mechanism of the base-free reaction conducted on gold-based catalysts (formation of H2O2 in situ). The reason lies in the interactions of the support with the bimetallic phase thus favoring the formation of the active species

No description available.

No description available.

Ce travail a porté sur la conversion du méthane en hydrogène par les procédés de vaporeformage et reformage à sec, utilisant de nouvelles formulations de catalyseurs afins d'augmenter la sélectivité en produit désiré (H₂), de réduire la production du monoxyde de carbone (CO) et défavoriser la formation de coke. Deux familles de catalyseurs, à base de nickel et de ruthénium supportés par la cérine et/ou l'alumine, ont été évaluées dans ces réactions. Il a été montré que les catalyseurs à base de ruthénium supportés par l'alumine présente une bonne activité catalytique et une très bonne résistance au dépôt de coke dans les réactions de reformage du méthane. La cérine joue un rôle déterminant dans les catalyseurs à base de nickel en favorisant la dispersion de la phase active et évitant la formation des agglomérats. Parallèlement, une inhibition de la formation de coke est observée grâce aux propriétés redox du solide. Les travaux ont porté également sur l'amélioration de la formulation des catalyseurs monométalliques, et un catalyseur bimétallique (Ru-Ni/CeO₂-Al₂O₃) actif, sélectif et stable pour la production d'hydrogène à partir du méthane a été mis au point. L'ajout d'un deuxième métal en faible teneur (0,5%) aide à maintenir le Ni sous sa forme actif empêchant la formation de coke sur la surface du catalyseur. Pour les deux réactions étudiées, les excellentes performances obtenues proviennent essentiellement de l'ajustement des paramètres de réaction et les paramètres de préparation des catalyseurs, ce qui ouvre de réelles perspectives d'application industrielle. / This work has focused on the methane conversion by steam reforming and dry reforming processes, through new catalyst formulations in order to increase the selectivity of expected products (H₂), to reduce carbon monoxide production (CO) and to limit the coke formation. Two categories of catalysts were evaluated in these reactions : nickel-based catalysts and ruthenium-based catalysts supported by ceria and/or alumina. It has been reported that the ruthenium-based catalysts supported by alumina provide important catalytic activity and high resistance to coke deposition in the methane reforming reactions. Ceria played a determining role in the nickel-based catalysts by enhancing the active phase dispersion without agglomerates and coke formation. Works have also continued on the improvement of the monometallic catalyst and an active bimetallic catalyst (Ru-Ni/CeO₂-Al₂O₃), selective and stable in hydrogen production from methane has been developed. The addition of a second metal helps maintaining Ni in its active form, preventing the coke formation on the catalyst surface. For the two considered reactions, the excellent performance was largely due to the adjustment of the reactions and catalyst parameters offering a real potential industrial application.

Die vorliegende Arbeit beschreibt die Präparation von Pt-Fe/SiO2-Katalysatorproben für die selektive Flüssigphasenhydrierung von Zimtaldehyd. Während der Herstellung wurden die Proben ausschließlich einer Reduktion bei 350 °C oder einer anschließenden Reduktion bei 750 °C unterworfen. Die präparierten Materialien wurden mit den Methoden ICP-OES, Laserbeugung, N2-Physisorption, XRD, TEM, SQUID und TPR/O charakterisiert. Daneben wurden Chemisorptions-Untersuchungen mit den Adsorptiven H2, O2 und CO durchgeführt. Infolge der angewandten Reduktionstemperatur von 750 °C konnte exemplarisch die Ausbildung von Metallpartikeln der Überstrukturphase nachgewiesen werden. Die katalytische Austestung der Materialien erfolgte in diskontinuierlich betriebenen Hydrierautoklaven. Hierbei stand die wertschöpfende Umsetzung zum Zimtalkohol im Vordergrund. Die Verwendung von Katalysatorproben, die Überstrukturphasen des Systems Fe-Pt aufweisen, führte nicht zu einer signifikanten Selektivitätsverbesserung zum Zielprodukt Zimtalkohol. Optimale Zimtalkohol-Ausbeuten ließen sich für Katalysatorproben erreichen, deren Metallpartikel nominelle Fe-Anteile von 30 bis 40 Mol.-% aufwiesen.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A reaÃÃo de sÃntese de Fischer-Tropsch tem merecido grande atenÃÃo pela sua aplicaÃÃo no Ãmbito tecnolÃgico e cientÃfico. Este interesse està associado à conversÃo do gÃs natural em produtos lÃquidos de alta qualidade (gasolina e diesel) e elevado valor agregado. No presente trabalho à descrito a metodologia empregada na sÃntese e caracterizaÃÃo de catalisadores bimetÃlicos, com alto teor da fase ativa de ferro e cobalto, usados na sÃntese de Fischer-Tropsch, suportados em sÃlica promovidos com potÃssio e cobre com diferentes proporÃÃes em base molar. O uso de catalisadores de ferro utilizados na sÃntese de Fischer-Tropsch tem sido estudado por muitos pesquisadores, os resultados tÃm mostrado que estes possuem um desempenho satisfatÃrio na produÃÃo de combustÃveis lÃquidos. Entretanto, pesquisas mostram que os catalisadores de cobalto sÃo mais eficientes na produÃÃo de hidrocarbonetos de cadeia longa e linear em relaÃÃo ao ferro. Contudo, catalisadores a base de cobalto sÃo mais caros comparados aos de ferro. Uma relaÃÃo custo/benefÃcio tem que ser atingida na fabricaÃÃo de catalisadores de tal forma que tenhamos uma otimizaÃÃo da produÃÃo de combustÃveis sintÃticos de elevado peso molecular sem muitos gastos com o catalisador. Pretende-se com esta discussÃo, identificar possÃveis vias para o desenvolvimento de catalisadores mais ativos e seletivos, variando a composiÃÃo do promotor estrutural para fins de otimizar a distribuiÃÃo dos produtos (diesel e graxa). A reaÃÃo foi conduzida em um reator de leito de lama. O estudo seguiu um planejamento experimental do tipo fatorial quadrado com ponto central e os resultados foram analisados baseados na metodologia de anÃlises de superfÃcies de respostas. Os efeitos das diferentes condiÃÃes operacionais (temperatura e pressÃo) e dos diferentes teores de potÃssio e cobre na distribuiÃÃo dos produtos lÃquidos foram comparados baseados nos cromatogramas, nÃmero mÃdio de carbono (Nn). Diante dos testes realizados com os catalisadores bimetÃlicos (Fe/Co) dopados com diferentes teores de potÃssio e/ou cobre, chegou-se a uma melhor relaÃÃo entre os metais (K,Cu) para sÃntese de um catalisador mais eficiente (50Fe/50Co/12K/5Cu/139SiO2). Sendo que o objetivo desta formulaÃÃo bimetÃlica, obter vantagens de possÃveis efeitos sinergÃticos entre os dois metais (Fe/Co) e seus promotores estruturais. / The reaction of Fischer-Tropsch synthesis has received great attention for its application in technology and science. This interest is associated with conversion of natural gas into high quality liquid products (gasoline and diesel) and high added value. In the present paper describes the methodology employed in the synthesis and characterization of bimetallic catalysts with high levels of the active phase of iron and cobalt, used in the synthesis of Fischer-Tropsch, supported on silica promoted with potassium and copper with different ratios on a molar basis. The use of iron catalysts used in the Fischer-Tropsch synthesis has been studied by many researchers, the results have shown that these have a satisfactory performance in the production of liquid fuels. However, studies have shown that cobalt catalysts are most effective in producing long-chain hydrocarbons and linear with respect to iron. However, the cobalt-based catalysts are more expensive compared to iron. A cost / benefit ratio has to be reached in the manufacture of catalysts which have such an optimization of production of synthetic fuels of high molecular weight inexpensively with the catalyst. The intention with this discussion, identify possible pathways for the development of more active and selective catalysts, varying the composition of the promoter structure for purposes of optimizing the distribution of products (diesel and grease). The reaction was conducted in a reactor bed of mud. The study followed an experimental planning factorial central square and the results were analyzed based on the methodology of the analysis of response surfaces. The effects of different operating conditions (temperature and pressure) and different concentrations of potassium and copper in the distribution of liquid based on the chromatograms were compared, average carbon number (Nn). Before the tests with the bimetallic catalysts (Fe / Co) doped with different concentrations of potassium and / or copper, it was a better relationship between the metals (K, Cu) for the synthesis of a more efficient catalyst (50Fe/50Co/12K/5Cu/139SiO2). Since the goal of this formulation bimetallic take advantage of possible synergistic effects between the two metals (Fe / Co) and its structural promoters.

Die vorliegende Arbeit beschreibt die Präparation von Pt-Fe/SiO2-Katalysatorproben für die selektive Flüssigphasenhydrierung von Zimtaldehyd. Während der Herstellung wurden die Proben ausschließlich einer Reduktion bei 350 °C oder einer anschließenden Reduktion bei 750 °C unterworfen. Die präparierten Materialien wurden mit den Methoden ICP-OES, Laserbeugung, N2-Physisorption, XRD, TEM, SQUID und TPR/O charakterisiert. Daneben wurden Chemisorptions-Untersuchungen mit den Adsorptiven H2, O2 und CO durchgeführt. Infolge der angewandten Reduktionstemperatur von 750 °C konnte exemplarisch die Ausbildung von Metallpartikeln der Überstrukturphase nachgewiesen werden. Die katalytische Austestung der Materialien erfolgte in diskontinuierlich betriebenen Hydrierautoklaven. Hierbei stand die wertschöpfende Umsetzung zum Zimtalkohol im Vordergrund. Die Verwendung von Katalysatorproben, die Überstrukturphasen des Systems Fe-Pt aufweisen, führte nicht zu einer signifikanten Selektivitätsverbesserung zum Zielprodukt Zimtalkohol. Optimale Zimtalkohol-Ausbeuten ließen sich für Katalysatorproben erreichen, deren Metallpartikel nominelle Fe-Anteile von 30 bis 40 Mol.-% aufwiesen.

Made available in DSpace on 2016-06-02T19:56:47Z (GMT). No. of bitstreams: 1 4365.pdf: 6331664 bytes, checksum: 4fff8665ac587e730c995ecd4feb1665 (MD5) Previous issue date: 2012-03-30 / Universidade Federal de Sao Carlos / The effect of variation of cobalt (Co)/nickel (Ni) composition in catalysts based on these transition metals was evaluated focusing mainly in the oxi-reduction properties and their relation to carbon deposition in the Steam Reforming of Ethanol (SRE) reaction. The catalysts, with metal loading of 15 and 8 wt%, were prepared by conventional impregnation of the Co and Ni salts on the sol-gel synthesized support MgAl2O4. The characterization was performed by N2 adsorption-desorption isotherms; X-ray diffraction (XRD); temperature programed reduction (H2-TPR); thermogravimetric analysis (TGA); scanning electron microscopy (SEM) and transmission electron microscopy (TEM); X-ray absorption near edge spectroscopy (H2-XANES), in situ extended X-ray absorption on fine structure spectroscopy (SRE-EXAFS) and Raman spectroscopy. The catalytic tests were done in the temperature range of 250 to 700°C and the conversion and products distribution dependence on the metal loading and composition were evaluated. Reduction profiles and diffraction patterns lead to believe that occur the formation of a spinel NiCo2O4 in the weight ratio 1Co:1Ni during calcination. Such spinel once reduced yields an alloy Co-Ni, accordinto to TEM images and EXAFS data. The alloy formation, although it is hard to characterize, seems to be determining factor on carbon deposition resistance on the catalyst surface during SRE. Carbon deposition, as addressed by TGA and SEM, is strongly sensitive to metal loading, being severe on monometallic samples with higher metal loading; independent of the loading, the bimetallic catalysts in the proportion 1:1 are resistant to carbon deposition. SRE-EXAFS showed that these catalysts didn t oxidize during reaction, differing from Co catalysts, where the equilibrium between oxide and metallic sites controls the ethanol activation and carbon oxidation rates. / O efeito da variação da composição cobalto (Co)/níquel (Ni) em catalisadores à base destes metais de transição foi avaliado focando principalmente nas propriedades de oxirredução e sua relação com a deposição de carbono na reação de Reforma a Vapor do Etanol (RVE). Os catalisadores, com teor metálico de 15 e 8 % em massa, foram preparados por impregnação convencional dos sais de Co e Ni sobre o suporte MgAl2O4 sintetizado por método sol-gel. A caracterização foi realizada por isotermas de adsorçãodessorção de N2; difração de raios X (XRD); redução à temperatura programada (H2-TPR), análise termogravimétrica (TGA), microscopia eletrônica de varredura (SEM) e transmissão (TEM), espetroscopia de absorção de raios X próximo da borda (H2-XANES), espectroscopia de absorção de raios X estendida de estrutura fina in situ (RVE-EXAFS) e espectroscopia Raman. Os testes catalíticos foram realizados na faixa de temperatura de 250 a 700°C e a dependência da conversão e distribuição de produtos com o teor e composição metálicos foi avaliada. Os perfis de redução e difratogramas levam a crer que ocorre a formação de um espinélio NiCo2O4 na proporção 1Co:1Ni em massa durante calcinação. Este espinélio quando reduzido forma uma liga Co-Ni, conforme mostram imagens de TEM e dados de EXAFS. A formação de liga, embora difícil de ser caracterizada, parece ser fator determinante na resistência a deposição de carbono sobre a superfície do catalisador durante a RVE. A deposição de carbono, conforme averiguada por TGA e SEM, é fortemente sensível ao teor metálico, sendo severa nas amostras monometálicas com maior teor de metal; já os catalisadores bimetálicos na proporção 1:1 são resistentes à deposição de carbono independentemente do teor. RVE-EXAFS mostrou que estes catalisadores não se oxidam durante reação; diferindo de catalisadores de Co, onde o equilíbrio entre sítios óxidos e metálicos controla as taxas de ativação de etanol e oxidação do carbono.