Organosulfur chemistry on W(211) surfaces. 1. A comparison of methanethiol and methanol

The reactions of methanol and methanethiol on clean, oxided, sulfided, and carbided W(211) surfaces were studied by LEED, AES, and TPR. Adsorption occurred by an oxidative addition in which the hydroxyl or sulfhydryl hydrogen was removed forming methoxy and methanethioxy intermediates. Clean W(211) was a very strong reductant totally decomposing the molecules. Adsorbed oxygen oxidized the surface making it a weaker reducing agent so that alkoxy and thioxy intermediates were stabilized. An epitaxial surface oxide was a mild oxidant compared to clean W(211); this surface oxidized methanol to formaldehyde. Adsorbed sulfur severely reduced methanol adsorption. Surfaces with adsorbed sulfur adsorbed methanethiol. This adsorption suggests the formation of a disulfide species. Carbided W(211) stabilized both alkoxy and thioxy intermediates as well as oxidizing methanol to formaldehyde. The adsorbed methoxy and methanethioxy intermediates decomposed by C-O or C-S bond scission forming adsorbed methyl groups which either decomposed or were hydrogenated to form methane. At temperatures above 500 K methyl groups recombined and C₂ hydrocarbon products evolved. Surface oxides and carbides oxidized methoxy to formaldehyde and CO, but no surface oxidized methanethioxy to thioformaldehyde or CS.