Structure of molybdenum sulfide clusters encaged in zeolites: Effect of zeolite composition

The structure and catalytic property of molybdenum sulfide clusters encaged in NaY zeolite were investigated as a function of the composition of the host zeolite. The local structure of molybdenum sulfides was studied by means of MoK-edge XAFS. The local structure of intrazeolite molybdenum sulfide clusters depended on the Si/Al ratio of the host zeolite. Molybdenum sulfide dimer species were formed in NaY zeolites with a composition of 3.5 > Si/Al > 2.1. It is proposed that the structure of dimer clusters is reversibly transformed into a tetramer structure by an H2-treatment at 673 K. The intrinsic activity of molybdenum sulfide clusters for the HDS of thiophene decreased as the Mo–Mo distance of Mo2S4 dimer clusters increased.