Study of cobalt and ruthenium supported on WC catalysts for FT reaction.

An investigation of bulk and cobalt or ruthenium supported tungsten carbide was carried out for their use in the Fischer-Tropsch reaction. Two types of WC were studied : tungsten carbide protected by free carbon and clean tungsten carbide, respectively noticed WC(A) and WC(B). XPS analysis shows that after air exposure, the WC(A) carbide surface is protected from the excess carbon whereas a surface W6+ phase is induced during the passivation step for WC(B). However WC(A) is inert towards aqueous impregnation, whereas WC(B) starts to corrode. A reduction in hydrogen at 673 K for Ru and 773K for Co supported catalysts allows obtaining Co0 and Ru0 dispersed on layers of free carbon covering the WC core for WC(A) and on a surface free of oxygen for WC(B). All the catalysts were active for the FT reaction. WC(A) produces mainly light alkanes (78%) and alcohols (22%), whereas no alcohol production is observed for WC(B). Co/WC(B) has a better activity than Co/WC(A), due to a better dispersion of cobalt on WC(B). The addition of Ru on WC(A) allow to obtain an high active catalyst with production of heavy hydrocarbons. On the contrary, formation of a Ru-W alloy could be consider to explain the low activity of Ru/WC(B) catalyst

Characterization of new Co and Ru on WC catalysts for Fischer-Tropsch reaction. Influence of the carbide surface state.

International audienceAn investigation of the performances in Fischer-Tropsch reaction of 1 wt% M/WC(X) (M = Co, Ru; X=A, B), where A is a tungsten carbide protected by free carbon and B is a clean tungsten carbide, was carried out. Supported catalysts performances were compared to those of the parent tungsten carbides at 473K and 20 bar. It was found that WC(A) produces mainly hydrocarbons but also 20–40% alcohols, whereas WC(B) activity is only towards linear alkanes. Before catalytic test, a reduction in pure hydrogen allows obtaining Co0 and Ru0 dispersed on layers of free carbon covering the WC core for the WC(A), and on a surface free of oxygen for WC(B). Co as Ru dispersions are improved on WC(B) compared to WC(A). A direct consequence is that Co/WC(B) has a better activity than Co/WC(A). Ru–W alloy formation could be responsible of the inobservance of a better activity for Ru/WC(B). On contrary, addition of Ru on WC(A) highly increases the activity and the production of heavy hydrocarbons. This beneficial effect, not observed with cobalt, could be attributed to a better dispersion of ruthenium on a carbon polymeric surface of WC

CO(2)hydrogenation using bifunctional catalysts based on K-promoted iron oxide and zeolite: influence of the zeolite structure and crystal size

[EN] In the present manuscript, the influence of the zeolite structure and crystal size on bifunctional tandem catalysts combining K-promoted iron oxide (K/Fe3O4) with different zeolites has been studied for the CO(2)hydrogenation reaction at 320 degrees C and 25 bar. First, to evaluate the influence of the zeolite structure on CO(2)conversion, three different zeolite topologies have been evaluated (BEA, MFI and CHA) with similar Si/Al molar ratios. The combination of K/Fe(3)O(4)with MFI maximizes the formation of aromatic products, while its combination with CHA and BEA increases the C-1-C(4)gas fractions, with a high olefin selectivity. In addition, aromatics and aliphatic hydrocarbons are present in the condensed liquids of the tandem catalysts containing BEA, while no aromatics are observed for those with CHA. These different product selectivities can be ascribed to the different consecutive reactions within the three zeolites, where MFI favors the aromatization of alkenes, and BEA and CHA favor oligomerization/cracking reactions leading to an increase of light olefin yield. Second, the evaluation of the nanosized form of the three proposed zeolite frameworks has also been carried out. The reduction of the particle size allows for increasing light olefin selectivity in all cases as compared to zeolites with larger crystals. Shorter intracrystalline diffusion paths facilitate the egression of light olefins before being involved in consecutive oligomerization reactions. In the particular case of the tandem catalysts with nanosized MFI zeolites, the C-2-C(4)fraction and its olefinicity are increased while maintaining the overall aromatic selectivity comparable to that obtained with micron-sized MFI zeolites.This work was supported by the Spanish Government through "Severo Ochoa" (SEV-2016-0683, MINECO) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE), by the Fundacion Ramon Areces through a research contract (CIVP18A3908) and by Generalitat Valenciana (AICO/2019/060). A. R. F. acknowledges the Spanish Government-MINECO for a FPU scholarship (FPU2017/01521). The Electron Microscopy Service of the UPV is acknowledged for their help in sample characterization.García-Hurtado, E.; Rodríguez-Fernández, A.; Moliner Marin, M.; Martínez, C. (2020). CO(2)hydrogenation using bifunctional catalysts based on K-promoted iron oxide and zeolite: influence of the zeolite structure and crystal size. 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Optimisation de catalyseurs pour la synthèse Fischer-Tropsch à partir de biosyngaz

Les travaux exposés dans ce manuscrit portent sur la préparation de catalyseurs monométalliques et bimétalliques à base de cobalt et de fer supportés sur alumine et silice pour la synthèse Fischer-Tropsch. Les catalyseurs notés xCoyFe/Al2O3 ou SiO2 ont une teneur massique globale de 10% pour différentes valeurs du rapport Co/Fe (x et y = 0 ; 2,5 ; 5 ; 7,5 ; 10 et x+y = 10%). Ainsi, ces catalyseurs ont été préparés par imprégnation à sec et caractérisés à différentes étapes de leurs préparations par différentes techniques de caractérisation physico-chimiques et spectroscopiques. L axe majeur de cette étude concerne la germination des phases oxydes et la genèse des phases actives des matériaux mixtes, les échantillons monométalliques représentant des références solides pour cette étude. Par le biais de décompositions de spectres XANES et d analyses de surface poussées, nous avons mis en avant la présence d un alliage CoFe sur certains catalyseurs mixtes après calcination pour les faibles teneurs en cobalt. L étude de la dispersion des phases oxydes a conduit à montrer que le fer est toujours mieux dispersé que le cobalt quelque soit le catalyseur ou le support utilisé. De plus, sur le support alumine les matériaux sont mieux dispersés, avec des tailles de cristallites plus faibles. L originalité de ces travaux repose sur l établissement d une étude Operando, durant laquelle nous avons pu confirmer la particularité de nos matériaux mixtes CoFe. En effet, ces derniers, présentent une faible sensibilité aux phénomènes de frittage des particules métalliques de cobalt, contrairement aux matériaux monométalliques. Par ailleurs les matériaux mixtes présentent une activité intermédiaire à celle des matériaux classiques monométalliques pour la réaction Fischer-Tropsch.The work exposed in this manuscript concerns the preparation of monometallic and bimetallic catalysts containing cobalt and iron supported on alumina and silica for the synthesis Fischer-Tropsch. The catalysts denoted xCoyFe/Al2O3 or SiO2 have a total mass content of 10% for various values of the Co/Fe ratio (x and y = 0; 2.5; 5; 7.5; 10 and x+y = 10%). Thus, these catalysts were prepared by wetness impregnation and were characterized at different stages of their preparations by various physicochemical and spectroscopic techniques of characterization. The major part of this study concerns the germination of the oxides phases and the genesis of the active phases of mixed materials. The samples monometallic represent the solid references for this study. From decompositions of XANES and XPS spectra, we proposed the presence of a CoFe alloy on mixed catalysts after calcination for the low cobalt contents. A better dispersion is observed for iron compared with cobalt whatever the support used. Moreover, on the alumina support, iron and cobalt are better dispersed with lower crystallite sizes. The originality of this work consists with the Operando study, which allowed to confirm the characteristic of our mixed materials CoFe. Indeed, the latter, have a low sensitivity of sintering of the cobalt metal particles, contrary to materials monometallic. These mixed materials present an intermediate activity compared with those of monometallic materials for the Fischer-Tropsch reaction.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Influence des précurseurs et du prétraitement des catalyseurs sur la genèse des particules de cobalt pour la synthèse Fischer-Tropsch

Cette étude porte sur les liens entre la structure de catalyseurs à base de cobalt supportés sur silice d'une part et leurs performances catalytiques dans le cadre de la synthèse Fischer-Tropsch d'autre part. Les catalyseurs ont été prépares par imprégnation à sec à partir de solutions aqueuses de nitrate et d'acétate de cobalt. Lors de certaines préparations, des métaux nobles (Ru ou Re) et du saccharose ont été aussi utilisés. Une combinaison de techniques physico-chimiques dont des techniques "in situ" a permis d'identifier et de caractériser la structure des catalyseurs à chaque étape de leur synthèse. ... Dans ces catalyseurs, les particules métalliques de cobalt ont une taille de 4 à 15 nm suivant les conditions de synthèse. Il a été démontré que la dispersion du cobalt, la réductibilité et le nombre de sites métalliques dans ces catalyseurs dépendaient de l'exothermicité de décomposition du précurseur de cobalt, de la température de calcination, de la présence de métaux nobles ainsi que de l'addition de saccharose. La mesure de la vitesse de conversion du CO et le dosage des sites actifs par chimisorption du propène ont montré une corrélation entre l'activité du catalyseur et la dispersion du cobalt métallique. Cependant, cette relation ne semble plus s'appliquer lorsque les particules sont trop petites "8 nm). La faible activité mesurée pour les catalyseurs possédant les plus petites nanoparticules de cobalt métalliques est probablement liée à une instabilité de ces dernières qui provoque une désactivation du catalyseur dans des conditions de la synthèse Fischer-TropschLILLE1-BU (590092102) / SudocSudocFranceF

Contrôle du dépôt et de la décomposition des précurseurs de cobalt dans la conception de catalyseurs Fischer-Tropsch

Cette thèse porte sur la conception de nouveaux catalyseurs à base de cobalt supportés par des matériaux aluminiques pour la synthèse Fischer-Tropsch. Ainsi, de nombreux catalyseurs ont été préparés par imprégnation à sec et par méthode sol-gel. Ils ont été étudiés à chaque étape de leur préparation par différentes techniques physico-chimiques et spectroscopiques et un certain nombre ont été testés en réacteurs à lit fixe et slurry sous pression.L axe majeur de cette étude concerne l introduction sous-stœchiométrique d additifs organiques au cours de la préparation de catalyseurs. En fonction des conditions de préparation, ces composés ont eu un impact très marqué sur la dispersion et la réductibilité du cobalt et donc, sur les performances des catalyseurs en synthèse Fischer-Tropsch. Différents paramètres influant sur les performances catalytiques ont été identifiés comme la nature chimique de ces composés, leur mode d introduction, les conditions de leur décomposition Nous avons constaté que le rôle de ces agents organiques pouvait être multiple. Ces composés, en interagissant avec les ions cobalt, sont susceptibles de modifier la nature des entités à base de cobalt déposées sur le support et ainsi, de modifier le processus de nucléation-croissance des agrégats d oxyde de cobalt lors de la décomposition du précurseur. Par ailleurs, ces molécules organiques peuvent aussi modifier les propriétés physico-chimiques du support (texture, point isoélectrique ) et par conséquent, changer la répartition du cobalt à la surface durant l imprégnation.This thesis focuses on the design of new cobalt catalysts supported by alumina for Fischer-Tropsch synthesis. A large number of catalysts were prepared by wetness impregnation and by sol-gel method. They were studied at different stages of their preparation by various physicochemical and spectroscopic methods and a certain number was tested in fixed bed and slurry reactors under pressure.The major part of this study addresses sub-stoichiometric introduction of organic additives during catalyst preparation. According to the conditions of preparation, these compounds had a major impact on the dispersion and reducibility of cobalt and therefore on the catalytic performances in Fischer-Tropsch synthesis. Various parameters affecting the catalytic behaviour were identified such as the chemical nature of these compounds, their mode of introduction, conditions of their decomposition, etc. We noticed that these organic agents can have multiple functions. These compounds, by interacting with cobalt ions, may modify the nature of cobalt precursor deposited on the support and thus modify the process of nucleation-growth of cobalt oxide aggregates during decomposition of precursor. In addition, these organic molecules can modify the physicochemical properties of support (texture, PZC point, etc.) and consequently, change the cobalt dispersion on the support during impregnation.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF