SBA-15-supported nickel phosphide hydrotreating catalysts

A series of Ni 2P and Ni 12P 5 hydrotreating catalysts supported on SBA-15 ordered mesoporous silica were prepared by impregnation of nickel phosphate precursors followed by reduction in hydrogen at 873 K. The major product was Ni 2P with additional phosphate species when a high excess of phosphorus...

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Bibliographic Details
Published in:Journal of catalysis 2008, Vol.253 (1), p.119-131
Main Authors: Korányi, Tamás I., Vít, Zdeněk, Poduval, Dilip G., Ryoo, Ryong, Kim, Hei Seung, Hensen, Emiel J.M.
Format: Article
Language:English
Subjects:
Catalysis
Catalysts
Chemical reactions
Chemistry
Colloidal state and disperse state
Dibenzothiophene
Exact sciences and technology
General and physical chemistry
Hydrodenitrogenation
Hydrodesulfurization
Nickel
Nickel phosphide
Ortho-methyl aniline
Phosphates
Porous materials
Pyridine
SBA-15
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Thiophene
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Summary:A series of Ni 2P and Ni 12P 5 hydrotreating catalysts supported on SBA-15 ordered mesoporous silica were prepared by impregnation of nickel phosphate precursors followed by reduction in hydrogen at 873 K. The major product was Ni 2P with additional phosphate species when a high excess of phosphorus was used (P/Ni = 2). When a stoichiometric amount of P was used (P/Ni = 0.5), the sole product was Ni 12P 5 without Ni 2P and phosphate byproducts. The active site density as determined by CO chemisorption for such Ni 12P 5 phases was about three times higher than typically found for Ni 2P/SiO 2 catalysts and in good accord with active site densities following from particle size. The excess phosphorus results in mesopore blocking by unreduced phosphate species, impeding the accessibility of the Ni 2P active sites as probed by CO chemisorption. The catalysts exhibited lower hydrodesulfurization (HDS) but similar or somewhat higher hydrodenitrogenation (HDN) activities than reference alumina-supported NiMo or CoMo catalysts in simultaneous thiophene HDS and pyridine HDN, as well as parallel dibenzothiophene HDS and ortho-methyl aniline HDN hydrotreating reactions. In general, the intrinsic activities of the Ni 2P catalysts were higher than those of Ni 12P 5 catalysts. The activities of these phosphide catalysts were found to be stable or increasing with reaction time. X-ray photoelectron studies of reduced catalysts exposed to a sulfiding mixture suggest that this increase is due to in situ sulfidation of the nickel phosphide to nickel phosphosulfide. Thus, it seems reasonable that surface phosphosulfides form the active catalytic surface in these catalysts.
ISSN:0021-9517
1090-2694
DOI:10.1016/j.jcat.2007.10.012