The CO coadsorption and reactions of sulfur, hydrogen and oxygen on clean and sulfided Mo(100) and on MoS 2(0001) crystal faces

Abstract

The chemisorption and reactivity of O 2 and H 2 with the sulfided Mo(100) surface and the basal (0001) plane of MoS 2 have been studied by means of Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). These studies have been carried out at both low (10 −8–10 −5Torr) and high (1 atm) pressures of O 2 and H 2. Sulfur desorbs from Mo(100) both as an atom and as a diatomic molecule. Sulfur adsorbed on Mo(100) blocks sites of hydrogen adsorption without noticeably changing the hydrogen desorption energies. TDS of 18O coadsorbed with sulfur on the Mo(100) surface produced the desorption of SO at 1150 K, and of S, S 2 and O, but not SO 2. A pressure of 1 × 10 −7 Torr of O 2 was sufficient to remove sulfur from Mo(100) at temperatures over 1100 K. The basal plane of MoS 2 was unreactive in the presence of 1 atm of O 2 at temperatures of 520 K. Sputtering of the MoS 2 produced a marked uptake of oxygen and the removal of sulfur under the same conditions.