The Role of Cobalt in Unsupported MoS2 Hydrodesulfurization Catalysts

Abstract

Crystalline MoS2 catalysts were impregnated with cobalt over the total composition range, and their catalytic activity in the hydrodesulfurization of thiophene tested in a microreactor at 400° and near atmospheric pressure. Three principal composition regions could be distinguished in the sulfided catalysts: (1) Co/(Co + Mo) compositions 0–0.4. In this region intercalated Co enhances the intrinsic activity which reaches a maximum near a Co content of 0.25. The region is sulfur "deficient" with respect to MoS2 + Co9S8 and there is no evidence for the presence of Co9S8. (2) Compositions 0.4–0.65. This region is characterized by the exact stoichiometry MoS2 + Co9S8 and by the appearance of a Co9S8 phase. Surface area experiences a fivefold increase, as does percent conversion, but intrinsic activity changes very little. (3) Compositions > 0.65. A region of lesser interest, it is sulfur "deficient", possibly through the formation of Co4S3, and surface area decreases steeply with Co content.