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8. Hydrodeoxygenation of Phenolic Compounds by Sulfided (Co)Mo/Al2O3 Catalysts, a Combined Experimental and Theoretical Study Hydrodésoxygénation de composés phénoliques en présence de catalyseurs sulfurés (Co)Mo/Al2O3 : une étude expérimentale et théorique

Author

Badawi M., Paul J.-F., Payen E., Romero Y., Richard F., Brunet S., Popov A., Kondratieva E., Gilson J.-P., Mariey L., Travert A., and Maugé F.

Subjects
Chemical technology, TP1-1185, Energy industries. Energy policy. Fuel trade, HD9502-9502.5
Abstract

The hydrodeoxygenation of model phenol compounds (phenol and 2-ethylphenol) was carried over unpromoted Mo/Al2O3 and promoted CoMo/Al2O3 catalysts. Hydrodeoxygenation proceeds by two pathways: – hydrogenation of the aromatic ring followed by Csp3-O bond cleavage (HYD pathway, (hydrogenation of the aromatic ring followed by Csp3-O bond cleavage)); – direct cleavage of the Csp2-O bond (DDO pathway). Both routes were favored by the presence of Co on the catalyst, while the presence of the alkyl substituent on the phenolic ring favors the DDO route but inhibits the HYD pathway. IR (InfraRed) spectroscopy shows that while phenol mostly dissociates on these catalysts, a significant fraction of 2-ethylphenol remains non dissociated. The adsorption energies of both reactants and possible reaction intermediates on promoted and non-promoted sulfide phases as computed by DFT (Density-Functional Theory) confirm these findings and allow rationalizing the catalytic activity trends observed experimentally. L’hydrodésoxygénation de deux composés phénoliques modèles (phénol et 2-éthylphénol)) a été étudiée sur deux catalyseurs Mo/Al2O3 et CoMo/Al2O3 sulfurés. La désoxygénation de ces molécules fait intervenir deux voies parallèles et indépendantes, à savoir : – l’hydrogénation du noyau aromatique suivie par la rupture de la liaison Csp3-O (voie HYD, (hydrogenation of the aromatic ring followed by Csp3-O bond cleavage)); – la rupture directe de la liaison Csp2-O (voie de DésOxygénation Directe – DOD). Ces deux voies sont favorisées en présence du catalyseur promu par le cobalt (CoMo/Al2O3). La présence du groupe éthyle permet d’améliorer la voie DOD mais conduit à une diminution de la voie HYD. Les études menées par spectroscopie IR (InfraRouge) montrent que le phénol est majoritairement dissocié sur ces catalyseurs alors que le 2-éthylphénol semble plutôt adsorbé de façon non-dissociative. Les énergies d’adsorption de ces deux réactifs ainsi que celles des intermédiaires réactionnels impliqués sur les phases promues et non-promues ont été déterminées par calculs DFT (Density-Functional Theory). Elles permettent de rationnaliser les résultats expérimentaux obtenus.

Published
2013
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50. Direct Aromatic C–N Bond Cleavage Evidenced in the Hydrodenitrogenation of 2,6-Dimethylaniline over Cobalt-Promoted Mo/Al2O3Sulfide Catalysts: A Reactivity and FT-IR Study

Author

van Gestel, J, Dujardin, C, Maugé, F, and Duchet, J.C

Abstract

The hydrodenitrogenation of 2,6-dimethylaniline (DMA) was studied over a series of sulfided Co(0–4.7%)–Mo(8.7%)/Al2O3catalysts at 573 K under 4 MPa total pressure and 0–56 kPa H2S partial pressure. Two NiMo samples were tested for comparison. The reaction network presents three parallel routes: dearomatization of DMA followed by either hydrogenation–elimination to dimethylcyclohexenes and dimethylcyclohexanes, or NH3elimination to m-xylene, and disproportionation of DMA to 2-methylaniline and 2,4,6-trimethylaniline. We demonstrate that part of the xylene is formed by direct aromatic carbon–nitrogen bond cleavage through a nucleophilic substitution involving hydride species. On CoMo catalysts, in the presence of H2S, the amount of extra xylene is independent of Co content, while the dearomatization is promoted. Without H2S, this special substitution reaction is most important on the Mo catalyst, and strikingly Co acts as a poison. FT-IR spectroscopy of adsorbed carbon monoxide evidences a new type of sites on the sulfided catalysts after a mild hydrogen treatment. We propose that a site configuration located exclusively on unpromoted Mo atoms highly depleted in sulfur is responsible for the direct denitrogenation route. The NiMo couple behaves differently: xylene formation is independent of Ni content, which means that the specific Mo sites for direct C–N bond rupture are poisoned by nickel, even in the presence of H2S. The location of Co and Ni on the MoS2slabs then appears different.

Published
2001
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