Methanol Adsorption on Clean and Oxygen-Predosed V(100) Single-Crystal Surfaces

Abstract

The thermal chemistry of methanol on V(100) single-crystal surfaces was investigated in ultrahigh vacuum (UHV) by temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and isotope labeling experiments. It was found that thermal activation of adsorbed methanol leads to the production of methane, ethylene, formaldehyde, and carbon monoxide. Methane desorption is seen in two states centered at 320 and 490 K, both rate-limited by the dehydrogenation steps that supply the needed extra hydrogen atoms, from the hydroxyl and methyl moieties, respectively. The presence of submonolayer coverages of oxygen on the surface enhances the yield of the high-temperature methane state at the expense of the low-temperature methane production, and delays all of the surface reactions to higher temperatures. The mechanism for the formation of ethylene in this conversion was investigated by comparing the TPD profiles of several reference molecules. The results suggest adsorbed formaldehyde as the key intermediate and methylene coupling as the most probable pathway.