Hydrodesulfurization over supported monometallic, bimetallic and promoted carbide and nitride catalysts

The preparation of alumina-supported beta-Mo2C, MoC1-x (x approximate to 0.5), gamma-Mo2N, Co-Mo2C, Ni2Mo3N, Co3Mo3N and Co3Mo3C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported beta-Mo2C and gamma-Mo2N catalysts (Mo2C/Al2O3 and Mo2N/Al2O3, respectively) are significantly more active than sulfided MoO3/Al2O3 catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo2C/Al2O3 catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo2C/Al2O3 and Mo2N/Al2O3 catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported beta-Mo2C and gamma-Mo2N particles under HDS conditions. Cobalt promoted catalysts, Co-Mo2C/Al2O3, have been found to be substantially more active than conventional sulfided Co-MoO3/Al2O3 catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni2Mo3N/Al2O3, Co3Mo3N/Al2O3, Co3Mo3C/Al2O3), while significantly more active for thiophene HDS than unpromoted Mo nitride and carbide catalysts, are less active than conventional sulfided Ni-Mo and Co-Mo catalysts prepared from the same oxidic precursors. (C) 2003 Elsevier B.V. All rights reserved.