Identification by X-ray diffraction of MoS/sub 2/ in used Co-Mo-Al/sub 2/O/sub 3/ desulfurization catalysts

The nature of the molybdenum species in supported molybdena hydrodesulfurization (HDS) catalysts is still a matter of controversy. The primary controversy is whether the molybdenum exists as a monolayer across the support surface or in three-dimensional units. This note reports the results of an x-ray diffraction study of a commercial, Harshaw 0402T, Co-Mo-SiO/sub 2/-Al/sub 2/O/sub 3/ catalyst untreated, sulfided, and after use as a hydrodesulfurization catalyst for coal. The patterns for the sulfided show the absence of nordstrandite and CaMoO/sub 4/, and the presence of eta-alumina and poorly crystalline MoS/sub 2/. It is difficult to assess the exact role of the MoS/sub 2/ crystalites in regard to the HDS function of the catalyst. It is possible that two- or three-dimensional or amorphous MoS/sub 2/ has activity and that the noted deactivation of the catalyst occurred through a mechanism independent of the structure of the active (molybdenum) components. The molybdenum-sulfur species could still be catalytically active for HDS reactions, but are precluded from so functioning because of diffusional limitations resulting from deposited metals or mineral matter from the coal or formed intractable carbinaceous materials (coke). On the other hand, it is possible that change in the MoS/sub 2/ crystallites is symptomaticmore » of the actual deactivation mechanism. 1 figure, 2 tables.« less