XPS AND XRD STUDIES OF FRESH AND SULFIDED MO2N

Mo surface species of molybdenum nitride and their changes under sulfi ding conditions were investigated by XRD and XPS. Mo2N was synthesized by temperature-programmed reaction of MoO3, with NH3. The decompositi on of the Mo3d spectra gave a Mo3d doubler which corresponded to Model ta+ (2 less than or equal to delta < 4), Mo4+ and Mo5+ Or Mo6+ species . The BE of the Mo species of passivated Mo2N shifted to higher energy level compared with the freshly prepared Mo2N due to the oxidation of Mo nitride during passivation. When Mo2N was contacted for 4 h with a 15% H2S-H-2 mixture at 400 degrees C, the XRD spectra did not reveal any new phase, which indicates a high stability of Mo2N against sulfid ation, but XPS data showed the presence of sulfur, including S-0 and S 2- species, and a decrease of the N/Mo atomic ratio revealed some chan ges in surface composition. More than one monolayer of Mo2N was transf ormed to sulfide. It is probable that the oxygen incorporated during p assivation reacted with sulfur and formed a thin layer of molybdenum s ulfide on the Mo2N surface. (C) 1998 Elsevier Science B.V. All rights reserved.