The Structural Form of Cobalt and Nickel Promoters in Oxidic HDS Catalysts

Hydrodesulfurization catalysts consist of CoO and MoO 3 or NiO and MoO 3 on a γ-A1 2 O 3 carrier ( 1 - 3 ). The catalysts are produced in the oxidic form; their actual active state is obtained by sulfiding before or during usage in the reactor. Molybdenum oxide - alumina systems have been studied in detail ( 4 - 8 ). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support ( 9 - 11 ). Richardson ( 12 ) studied the structural form of cobalt in several oxidic cobalt-molybdenumalumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit ( 10 ) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% MoO 3 and 4 wt% CoO. They concluded that a cobalt aluminate