PREPARATION, CATALYSIS, AND CHARACTERIZATION OF HIGHLY DISPERSED MOLYBDENUM SULFIDE CATALYSTS SUPPORTED ON A NAY ZEOLITE

The structure and dispersion of the molybdenum sulfides supported on a NaY zeolite were studied using XAFS techniques. It was found that mol ybdenum sulfide species prepared by sulfiding vapor deposited Mo(CO)(6 ) or by sulfiding molybdenum oxide dimer species encaged in the zeolit e are highly dispersed and thermally stabilized against sintering or r estructuring. These molybdenum species are formed via molybdenum sulfi de dimer species as an intermediate. On the other hand, with the molyb denum sulfide catalysts prepared by an impregnation method, the sulfid ation of molybdenum oxides was incomplete. The molybdenum oxide specie s are suggested to be mainly located in the zeolite cavities after cal cination, forming isolated molybdenum oxides in tetrahedral configurat ions. The molybdenum sulfide species prepared from Mo(CO)(6) showed mu ch higher catalytic activities for thiophene hydrodesulfurization and butadiene hydrogenation than the molybdenum sulfides prepared by the i mpregnation, in conformity with a higher dispersion and higher fractio n of the molybdenum sulfide species. It is demonstrated that in combin ation with metal carbonyl techniques, zeolite supports are very suitab le for the preparation of highly dispersed molybdenum sulfides at a hi gh Mo loading.