Promoting Effect of Cobalt on the Catalytic Properties of Molybdenum Disulfide Nanoparticle Suspensions

Abstract

The catalytic activity of suspensions of cobalt-promoted molybdenum disulfide particles in hydroconversion of the petroleum vacuum residue was studied. Catalyst particle suspensions were prepared from inverse emulsions of aqueous solutions of the precursors (ammonium paramolybdate, cobalt nitrate or acetate) directly in the feed (in situ). Two procedures were used for preparing the promoted catalyst: consecutive or simultaneous addition of the precursors to the dispersion medium. The toluene-insoluble particles (TIPs) containing the spent catalyst had the size from 380 to 410 nm and contained the MoS₂, МоО₃, and Co₉S₈ crystalline phases. The cobalt-promoted dispersed catalyst exhibits the maximal activity in hydrodesulfurization and hydrogenation at the cobalt content of 33 at. %. The effect observed is due to the formation of a variable-composition Мо–Со–S phase, which cannot be identified by X-ray diffraction, on the surface of MoS₂ particles. A further increase in the promoter concentration leads to blocking of the MoS₂ particle surface with Co₉S₈ crystals, which, in turn, leads to a decrease in the catalyst activity in hydrodesulfurization and hydrogenation of high-molecular-mass feed components, to an increase in coking, and to a decrease in the fraction of paraffin–naphthene hydrocarbons in the hydrogenation product.