Le développement de technologies plus propres et économes en énergie amène aujourd’hui l’industrie du raffinage à modifier ses stratégies de préparation de catalyseurs et à se tourner vers l'utilisation plus massive de catalyseurs hétérogènes plus actifs, sélectifs, stables et régénérables.Récemment une méthode originale a été développée par Dufaud et al. (J. Mater. Chem., 2009, 19, 1142-1150) pour encapsuler des polyoxométallates (POMs) dans les murs des silices mésoporeuses. Le projet de thèse a visé l’élaboration de nouveaux catalyseurs basés sur cette nouvelle méthodologie qui devrait conduire à des systèmes à haute teneur en métal actif Mo/W bien dispersé, avec une meilleure proximité spatiale entre le Mo/W et son promoteur. Afin de mettre en évidence cette proximité, différentes voies ont été envisagées :i) synthèse en deux étapes comportant l'encapsulation des POMs dans les murs de SBA-15, suivie d’une imprégnation à sec des promoteurs (Ni(NO3)2 ou Co(NO3)2)ii) synthèse en une seule étape comportant l'imprégnation à sec de POMs substitués Co3PCoMo11O40H, Ni3PNiMo11O40H, Co3/2PMo12O40 ou Ni3/2PMo12O40 iii) préparation traditionnelle par co-Imprégnation à sec d’une silice SBA-15 par une solution de POMs et Ni(NO3)2 ou Co(NO3)2, afin de mettre en évidence non seulement l'intérêt de la nouvelle méthode de préparation mais aussi le gain lié à l'utilisation de supports de type SBA-15 (par rapport aux supports aluminiques conventionnels) ayant des caractéristiques texturales aussi remarquables. L’effet du traitement de sulfuration sur ces solides a été étudié et l’évaluation des propriétés catalytiques de ces matériaux a été réalisée sur des molécules modèles en hydrogénation du toluène, hydrodésulfuration du thiophène et du 4,6-DMDBT. A partir des résultats obtenus, une des stratégies de synthèse a été optimisée, en vue de l'élaboration de matériaux encore plus actifs. / Economic growth in the developing countries over the past decade has increased the global demand for crude oil. It is projected that the global crude slate will become sourer, with a sulfur content above 1.3 wt%. An overall aim of policymakers is thus to ensure that transportation fuels do not surpass a sulfur content of 10 ppm. Several solutions are possible to achieve the nowadays goals, that affect either the process or the catalyst. The latter solution, which does not involve significant additional costs for refiners, is therefore the most studied. One way to improve the nowadays catalysts would be to increase the content of active metal (eg cobalt and molybdenum in the case of CoMo systems). Nevertheless, at higher metal loadings, the formation of refractory species such as CoMoO4 or Co3O4 by sintering during calcination and/or sulfidation steps has been reported for alumina-Supported catalysts. This PhD project is based on the development of new hydrotreating catalysts, through a 2-Step one-Pot method : synthesis of polyoxometalates-Containing mesoporous SBA-15 materials, followed by incipient wetness impregnation of active phase promoter. The encapsulation of these species within the silica matrix would prevent the agglomeration of large particles during sulfidation reactions and could thus lead to systems with high content of active metal well dispersed over the support. One aim of this study was to evaluate the potential of these catalysts in the hydrotreating of several feedstocks, such as diesel oil, gasoline or vegetal oil. A second objective was the understanding of the nature of the different interactions between the active phase precursors and the support, according to each preparation technique.The non-Promoted hybrid catalyst showed a better dispersion of the metallic phase in the oxide state, compared to the catalysts prepared by incipient wetness impregnation, which can be correlated with stronger interactions between encapsulated POM and silica functionalities, such as siloxanes and silanols, as evidenced by Raman spectroscopy. However, the wide-Angle XRD showed the presence of MoO3 crystallites. HRTEM analyzes of the sulfided catalysts showed different species on this catalyst: small MoS2 slabs and metal particles (∼ 1 nm) mainly in the walls but also on the surface of pores; curved MoS2 slabs at mesopores surface leaving the entrance of the pore free; MoS2 hanks blocking the pores.This catalyst showed a relatively low sulfidation rate (determined by XPS), which could be associated with the presence of refractory species already present before activation. Thus, the toluene conversion represented per MoS2 clearly showed the interest of the catalyst prepared by this innovative method, presenting an intrinsic activity two-Fold higher than that of the catalyst prepared by dry impregnation.The subsequent impregnation of the active phase promoter of the hybrid catalyst (Pr(NO3)2, Pr = Ni or Co; 4 <pH <6), resulted in a very heterogeneous distribution of species, which could be attributed to a POM destruction by the impregnation solution, that afterward led to the sintering of large clusters. However, the hybrid catalysts promoted showed improved catalytic performances when compared to the traditional alumina-Based catalysts, when nickel is used as a promoter. However, the sulfidation and promotion rates of these catalysts must be improved: the catalyst with the highest Ni content showed (i) a high Ni/Mo atomic ratio of 0.4, which would lead to a loss of active sites by excessive decoration, and (ii) the formation of species such as NixOwSy or NixSy, which could lead to the loss of active sites, dispersion and access to the active phase.Perspectives towards an enhanced HDT catalyst based on the findings of this project are:Milder synthesis calcination conditionsSulfidationPost-Synthetic treatment in order to introduce Ni and Mo in proximal vicinityRegeneration of HDT hybrid catalysts
| Identifer | oai:union.ndltd.org:theses.fr/2013ENSL0799 |
| Date | 10 January 2013 |
| Creators | Lopes Silva, Susana |
| Contributors | Lyon, École normale supérieure, Dufaud, Véronique |
| Source Sets | Dépôt national des thèses électroniques françaises |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation, Text |
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