Adsorption and reaction of methanethiol on thin-film cerium oxide

The adsorption and reaction of methanethiol, CH3SH, have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The behavior of the CH3SH was examined as a function of the Ce oxidation state. CH3SH weakly interacts with fully oxidized CeO2(1 1 1) forming both chemisorbed CH3SH and CH3S + OH. OH forms through the reaction of the sulfhydrol H with the surface O. These species recombine and desorb near 180 K leaving the surface virtually clean. When the ceria is ca. 50% reduced, the chemisorbed CH3SH desorbs near 150 K while the CH3S + OH are stable to 400 K. These species react above 450 K to produce predominantly CH4 and CH3SH. A small amount of CH2O and water are also formed through reaction with the O in the ceria. Atomic S is left on the surface. S 2p, C 1s and O 1s soft X-ray photoelectron spectroscopy were used to identify the nature of the chemisorbed species and the adsorption site of the CH3S or S.