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 hydrogen 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-temperature 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 than 600-degrees-C was found to induce significant differences in the oxidation state of the molybdenum, with an oxidation number lower than 4 detected by XPS in the catalyst. The onset of the detection of molybdenum 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. Further increases in the reduction temperature resulted in increased quantities of reduced molybdenum and decreased quantities of hydrogen. At reduction temperatures lower than 600-degrees-C, the surface contains Mo4+, hydrogen, and sulfur species. As the electroneutrality of the MoS2 slabs must be respected, these results have been taken as indirect evidence for the presence of a hydridic species on the MoS2 surface. (C) 1994 Academic Press, Inc.