PHYSICOCHEMICAL CHANGES IN HYDRODESULFURIZATION CATALYSTS DURING OXIDATIVE REGENERATION

Both CoMo and Ni-CoMo catalyst supported over gamma-alumina were synth esized and compulsively deactivated by coking from 1,5-hexadiene. The coked catalysts, containing similar to 8.8 wt% carbon and similar to 7 wt% sulfur, were regenerated by oxidative burnoff at various temperat ures in the range of 300-700 degrees C. The catalyst regenerated at ea ch temperature was characterized by various techniques; i.e., BET, XRD , XPS, and TPR. During regeneration, physicochemical properties such a s surface area, crystallinity, reducibility, and metal distribution ch anged significantly with the regeneration temperature. Increase in the dispersion of promoter species (cobalt or nickel) was observed in the catalysts regenerated at low temperatures and this gave rise to the e nhancement of activity in comparison to the fresh catalyst. On the oth er hand, promoters migrated into the sublayer of alumina support at hi gher temperatures and thus resulted in the formation of PAl2O4 (P = Co or Ni) phases. Consequently, the crystallinity of the catalyst increa sed while the reducibility decreased as the regeneration temperature i ncreased. An abrupt increase in Mo dispersion and a decrease in surfac e area were observed when the coked catalyst was regenerated at 700 de grees C. (C) 1997 Academic Press.