Electron-induced decomposition of methanol on titanium dioxide(110) single crystal surface

Electron induced decomposition (EID) of methanol adsorbed on the vacuum-annealed {dollar}rm TiOsb2(110){dollar} was studied with temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). Methanol multilayers desorbed at 165 K while the adsorbed layers desorbed above 190 K. Chemisorbed methanol desorbs from {dollar}rm TiOsb2{dollar} in three main TPD states: a molecular state at 295 K and two dissociative states at 350 and 480 K. The 350 K desorption peak was assigned to methoxyls adsorbed on non-vacancy sites and the 480 K desorption peak was attributed to methoxyls adsorbed on vacancy sites. Although methanol decomposed on the surface, no irreversible decomposition was observed and methanol was the only desorption product in TPD experiments. By preheating a multilayer precovered surface to 197 K, methanol adlayers could be prepared containing only the saturated monolayer and both types of methoxyls. The effect of 100 eV electron irradiation on chemisorbed methanol and methoxyls was examined. Methanol and formaldehyde were the only TPD products of irradiated methoxyls and methanol adlayers. The EID cross-section for molecularly adsorbed methanol and methoxyls on non-vacancy was {dollar}rm 2.3times 10sp{lcub}-16{rcub} cmsp2{dollar} and {dollar}rm 1.8times 10sp{lcub}-16{rcub} cmsp2{dollar} for methoxyls adsorbed on vacancy sites. These results demonstrate the ability of low energy electrons to activate organic compounds adsorbed on oxide surfaces, and suggest that the EID cross-section depends on the surface coverage, and chemical state of adsorbed species. Based on these results, low energy electrons produced from absorption of ionizing radiation may play a significant role in the radiocatalytic destruction of organic compounds over oxide catalyst surfaces.