AN INVESTIGATION OF THE REDUCTION BEHAVIOR OF MOS2 AL2O3 AND THE SUBSEQUENT DETECTION OF HYDROGEN ON THE SURFACE/

The reduction behaviour of a conventional MoS2/gammaAl2O3 catalyst has been studied using a combination of temperature-programmed reduction, temperature-programmed desorption, X-rav photoelectron spectroscopy, and conventional transmission electron microscopy. The quantity of hyd rogen detected on the surface of the catalyst was strongly influenced by the reduction temperature, with a maximum at 700-degrees-C (H/Mo = 0.64). Two main hydrogen desorption peaks were detected, a low-tempera ture desorption peak (300-500-degrees-C) and a high-temperature peak ( 500-800-degrees-C), with positions and intensities that depend on the reduction temperature. Reduction in hydrogen at temperatures higher th an 600-degrees-C was found to induce significant differences in the ox idation state of the molybdenum, with an oxidation number lower than 4 detected by XPS in the catalyst. The onset of the detection of molybd enum in an oxidation state lower than 4 was found to coincide with the maximum in the plot of H/Mo as a function of reduction temperature. F urther increases in the reduction temperature resulted in increased qu antities of reduced molybdenum and decreased quantities of hydrogen. A t reduction temperatures lower than 600-degrees-C, the surface contain s Mo4+, hydrogen, and sulfur species. As the electroneutrality of the MoS2 slabs must be respected, these results have been taken as indirec t evidence for the presence of a hydridic species on the MoS2 surface. (C) 1994 Academic Press, Inc.