On the surface sites Of MOP/SiO2 catalyst under sulfiding conditions: IR spectroscopy and catalytic reactivity studies

Abstract The surface sites of MoP/SiO 2 catalysts and their evolution under sulfiding conditions were characterized by IR spectroscopy using CO as the probe molecule. The HDS activities of thiophene were measured on the MoP/SiO 2 catalyst that was subjected to different sulfidation and reactivation pretreatments. Cus Mo δ + (0 δ ⩽2) sites are probed on the surface of fresh MoP/SiO 2 by molecularly adsorbed CO, exhibiting a characteristic IR band at 2045 cm −1 . The surface of MoP/SiO 2 is gradually sulfided in HDS reactions, as revealed by the shift of the IR band at 2045 to ca. 2100 cm −1 . Although the surface of a MoP/SiO 2 catalyst becomes partially sulfided, the HDS activity tests show that MoP/SiO 2 is fairly stable in the initial stage of the HDS reaction, providing further evidence that molybdenum phosphide is a promising catalytic material for industrial HDS reactions. Two kinds of surface sulfur species are formed on the sulfided catalyst: reversibly and irreversibly bonded sulfur species. The MoP/SiO 2 catalyst remains stable in the HDS of thiophene because most sulfur species formed under HDS conditions are reversibly bonded on the catalyst surface. A detrimental effect of presulfidation on the HDS activity is observed for the MoP/SiO 2 catalyst treated by H 2 S/H 2 at temperatures higher than 623 K, which is ascribed to the formation of a large amount of the irreversibly bonded sulfur species. The irreversibly sulfided catalyst can be completely regenerated by an oxidation and a subsequent reduction under mild conditions.