Effects of Oxygen and Sulfur on the Bonding and Reactivity of CO, H2, H2CO, and CH3OH on Tungsten Carbide Surfaces

Article abstract of DOI:10.1021/j150626a013

The surface reactivity of W(100) with adsorbed oxygen and sulfur was studied by using temperature-programmed reaction spectroscopy (TPRS).Oxygen was deposited on W(100) by the chemisorption of molecular oxygen at room temperature.A p(4*1) stucture was observed for oxygen coverages between 0.4 and 1.0 monolayer; this structure transformed into a p(2*1) structure upon heating to 1200 K.Sulfur was deposited by the cracking of H2S at 600 K to give a p(2*1) structure at a saturation coverage of one monolayer.One monolayer of either oxygen or sulfur totally inhibited the dissociative chemisorption of hydrogen and carbon monoxide on tungsten.In addition the saturation uptake of molecular CO at room temperature was reduced by about 1 order of magnitude compared to the clean and carburized surfaces.The strong modification in the reactivity of tungsten was further demonstrated by investigating the surface reactions of formaldehyde and methanol.Both the adsorption and the decomposition of these molecules were severely hindered by the presence of oxygen and sulfur.Similar detrimental effects on adsorption were found for these adatoms on W(100)-(5*1)C.Significant difference in the saturation uptake of formaldehyde was observed between the p(4*1)O and p(2*1)O surfaces indicative of a structural transformation.These two surfaces exhibited different Lewis acidities.