Preparation and characterization of zeolite-supported molybdenum and cobalt-molybdenum sulfide catalysts

Preparation, characterization and catalysis of zeolite-supported Mo, Co(Ni) and Co(Ni)-Mo sulfide catalysts have been reviewed in the present article. Incomplete sulfidation of Mo oxides and poor dispersion of Mo sulfides were observed for zeolite-supported Mo catalysts prepared by impregnation methods, accompanied by a considerable crystallinity loss at a high calcination temperature. A significant migration of Mo oxide species into zeolite pores was noted during the calcination, producing Mo ore-species in tetrahedral coordinations. Incorporation of Mo into zeolite using ion-exchange techniques and solid-solid reactions is briefly described. Metal carbonyl techniques provided highly dispersed and fully sulfided intrazeolite Mo and Co sulfide clusters by use of Mo(CO)(6) and Co(CO)(3)NO, respectively. The Mo sulfide catalysts encaged in NaY exhibited much higher HDS activities than the impregnation catalysts. Go-Mo binary sulfide clusters were successfully synthesized in the pores of NaY as evidenced by EXAFS and XPS. The Co sites of the clusters were found to play important roles in hydrogenation and HDS. Thermally stable and catalytically active binary sulfide clusters for HDS are proposed to be intrazeolite Co2Mo2S6 molecular clusters. It was demonstrated that catalytic synergy between Co and Mo sulfides was generated by Co-S-Mo chemical bond formations. (C) 1997 Elsevier Science B.V.