A comparison of some catalytic, structural and textural properties of unsupported MoS 2 and WS 2 hydrodesulfurization catalysts promoted by Group VIII metals

Abstract

We compare fully sulfided unsupported systems active in hydrodesulfurization and related reactions, namely FeMo, CoMo, NiMo, CoW and NiW. The results concerning FeMo and CoW are new; for the other systems, previously published data are used. The addition of a small amount of Group VIII metal (atomic proportion r = VIII/( VIB + VIII) ≈ 0.01 −0.02) brings about a marked decrease in the specific surface area of Group VIB metal sulfides; an increase is observed for higher values. At r = 0.01 −0.02, MoS 2 and WS 2 have a better crystallinity. Catalytic activities (per unit surface area) under 30 bar pressure in the hydrogenolysis of thiophene are higher, by a factor of 1.7 − 10, for r = 0.25 than for r = 0.01 − 0.02. Except for CoMo, the same trend is observed for the hydrogenation of cyclohexene. In the range where the maximum synergy between the active sulfides is observed, MoS 2 shows comparable activity in the hydrogenolysis of thiophene, but WS 2 has a higher hydrogenating activity. Both systems show essentially the same sensitivity to the Group VIII promotors. The promoting effect of Ni in hydrogenolysis and hydrogenation is substantially higher than that of Fe or Co.