Effet de confinement du nickel dans des catalyseurs à base de silice mésoporeuse pour la production de gaz de synthèse par reformage du méthane avec le CO2

Although economically and environmentally advantageous, the methane dry reforming process using supported nickel based catalysts still faces problems of active phase (a transition metal) sintering and of carbon deposition, which result in catalytic activity loss. This thesis is focused on the study of the confinement effect of nickel in mesoporous silica-based catalysts for syngas production by reforming of methane with CO2. In this study, the samples were characterized by N2 sorption, XRD, TEM/SEM, TPR, in addition to Raman, XPS, TPH/MS, TGA/MS for the spent catalysts. The results indicate that a well-structured mesoporous support with high surface area and large pore volume is important for better dispersion and stabilization of the active phase inside the porosity. The mesoporous SBA-15 silica support (prepared in large quantity), composed of elongated grains, appear to be suitable for the purpose. Moreover, it is demonstrated that the formation of small nickel particles well-confined inside the pores favors carbon resistance. This can be achieved by applying hydrothermal treatment to the support, using two solvents method for Ni deposition, using direct reduction of uncalcined samples, adding Rh in small quantities or promoting with Ce, provided that Ni and Ce are in interaction.Malgré ses avantages économiques et environnementaux, le procédé de reformage à sec du méthane sur des catalyseurs au nickel supporté se heurte encore à des problèmes de frittage de la phase active (un métal de transition) et de dépôt de carbone, ce qui entraîne une diminution de l'activité catalytique. Cette thèse porte sur l'étude de l'effet de confinement du nickel dans des catalyseurs à base de silice mésoporeuse pour la production de gaz de synthèse par reformage du méthane par le CO2. Dans cette étude, les échantillons ont été caractérisés par physisorption de N2, DRX, MET/MEB, RTP, et, en plus, par Raman, SPX, HTP/SM, ATG/SM pour les catalyseurs après test catalytique. Les résultats montrent qu'un support mésoporeux bien structuré ayant une grande surface spécifique et un grand volume poreux est important pour une meilleure dispersion et stabilisation de la phase active à l'intérieur de la porosité. La silice mésoporeuse de SBA-15 (préparée en grande quantité), composée de grains allongés, semble être appropriée pour atteindre cet objectif. Il est de plus démontré que la formation de petites particules bien confinées à l'intérieur des pores favorise la résistance au dépôt de carbone. Ceci peut être obtenu en imposant un traitement hydrothermal au support, en utilisant la méthode deux solvants pour le dépôt de Ni, en passant à une réduction directe des échantillons non calcinés, en ajoutant du Rh en faibles quantités ou en utilisant du Ce comme promoteur, à condition que le Ni et Ce soient en interaction

Effet de l'ordre d'ajout du Ni et du Ce dans SBA-15 sur l'activité en reformage à sec du methane

International audienceDry reforming of methane has been carried out on SBA-15 catalysts containing 5 wt% Ni and 6 wt% Ce. The effect of the order of Ni and Ce impregnation on the catalytic activity has been studied. Both metals were added using the “two-solvent” method that favors metal dispersion inside the pores. Characterizations by XRD (low and high angles), N2 sorption, SEM and TEM of the materials after metal addition and calcination indicate good preservation of the porosities and high NiO and CeO2 dispersion inside the porous channels. Reduction was carried out before the catalytic tests and followed by TPR measurements. The most active reduced catalyst was the Ni–Ce/SBA-15 sample prepared by impregnating cerium first, then nickel. All catalysts were highly active and selective towards H2 and CO at atmospheric pressure. Full CH4 conversion was obtained below 650 °C. The higher performances compared to those reported in the literature for mesoporous silica with supported Ni and Ce catalysts are discussed.Le reformage à sec du méthane a été étudié sur des catalyseurs SBA-15 contenant 5 % en poids de Ni et 6 % en poids de Ce. L’effet de l’ordre d’imprégnation de Ni et Ce sur l’activité catalytique a été étudié. Ces deux métaux ont été ajoutés en utilisant la méthode « à deux solvants », qui favorise la dispersion du métal à l’intérieur des pores. Les caractérisations par DRX (petits et grands angles), adsorption de N2, MEB et MET des matériaux après ajout du métal et calcination montrent une bonne préservation de la porosité et une grande dispersion des nanoparticules de NiO et CeO2 à l’intérieur des pores. La réduction des catalyseurs suivie par RTP a été effectuée avant tests catalytiques. Le catalyseur le plus actif est le Ni–Ce/SBA-15 réduit, préparé par imprégnation, tout d’abord du cérium, puis du nickel. Les catalyseurs étaient très actifs et sélectifs en H2 et CO sous pression atmosphérique, avec une conversion complète de CH4 atteinte avant 650 °C. Les performances supérieures à celles décrites dans la littérature pour des catalyseurs à base de silice mésoporeuse contenant du Ni et du Ce sont discutées

Effect of pore geometry of mesoporous supports on catalytic performances in methane reforming

Catalysts prepared using three dimensional SBA-16 silica support (composed of micropores and cage-like mesopores) were tested in the reaction of methane dry reforming, in comparison with 2D hexagonal mesoporous SBA-15 support. The samples were evaluated by N2 sorption and X-Ray diffraction (XRD) for the assessment of their textural and structural properties. The reducibility was characterized by temperature programmed reduction (TPR). The catalytic performances were evaluated in methane dry reforming and spent catalysts (after reaction) were characterized for the evaluation of sintering and coke formation by TPH/MS, XRD and HR-TEM

Effect of pore geometry of mesoporous supports on catalytic performances in methane reforming

Catalysts prepared using three dimensional SBA-16 silica support (composed of micropores and cage-like mesopores) were tested in the reaction of methane dry reforming, in comparison with 2D hexagonal mesoporous SBA-15 support. The samples were evaluated by N2 sorption and X-Ray diffraction (XRD) for the assessment of their textural and structural properties. The reducibility was characterized by temperature programmed reduction (TPR). The catalytic performances were evaluated in methane dry reforming and spent catalysts (after reaction) were characterized for the evaluation of sintering and coke formation by TPH/MS, XRD and HR-TEM

Mesocellular silica foam-based Ni catalysts for dry reforming of CH4 (by CO2)

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Influence of the swelling agents of siliceous mesocellular foams on the performances of Ni-based methane dry reforming catalysts

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Sr promoted Ni/W–Zr catalysts for highly efficient CO₂ methanation: unveiling the role of surface basicity

This study explores the employment of CO2 methanation for carbon dioxide utilization and global warming mitigation. For the first time, in this work, we combine the interesting properties of the WO3–ZrO2 support and the benefits of Sr to improve the performance of Ni-based catalysts in this reaction. Sr loading on 5Ni/W–Zr samples is increased to 3 wt %, resulting in improved surface basicity through strong basic site formation. After 300 min, the 5Ni + 3Sr/W–Zr catalyst exhibits high activity and stability, achieving 90% CO2 conversion and 82% CH4 yield compared to 62 and 57% on 5Ni/W–Zr. Limited sintering and absence of carbon deposits are confirmed by temperature-programmed oxidation, XRD, Raman, and TEM analyses at 350 °C for 300 min. Sr promotion creates additional CO2 adsorption and conversion sites, enhancing the catalytic performance.<br/

High carbon-resistant nickel supported on yttria–zirconia catalysts for syngas production by dry reforming of methane: The promoting effect of cesium

Dry reforming of methane (DRM) is a highly researched process for conversion of methane into syngas that consumes the greenhouse gas (CO2). In this work, the promotional effect of cesium on yttria-zirconia-supported nickel catalysts is studied, for the first time, in DRM. Cs loading was varied from 0.5 to 4.0 wt% and fresh materials were characterized by N2 sorption, XRD, TPR, and TEM, while spent catalysts were examined by TEM, Raman spectroscopy, and TGA after catalytic testing. Interestingly, cesium improved carbon resistance of the catalysts. It was shown that addition of up to 1.0 wt% Cs resulted in formation of 13–14 nm nanoparticles in strong interaction with the support, which prevented their sintering during reaction. In this case, hydrogen yield exceeded 75% after 420 min on stream, and this value was higher than those reported in literature for the same loading of other promoters like cerium and barium. However, as the amount of cesium surpassed 1.0 wt%, catalytic performance was lowered, even below that of Cs-free sample and this can be assigned to a possible coverage of active sites by excess cesium. An optimum range of 0.5–1.0 wt% was thus determined for a good performance in dry reforming of methane