Paper EN+SS-FrM2
Photochemical Hole Scavenging Reactions of Methanol on TiO₂: Identification of Active Species and Water Coadsorption Study

Friday, November 2, 2012, 8:40 am, Room 15

Molecular and dissociative forms of adsorbed methanol were prepared on the rutile TiO₂(110) surface to study their relative photocatalytic activity for hole-mediated oxidation. Molecular methanol is the dominant surface species on the vacuum-annealed TiO₂(110) surface in ultrahigh vacuum (UHV). Coadsorption of methanol with oxygen results in ~ 20% of the adsorbed methanol decomposing to methoxy and OH. Subsequent heating of the surface to 350 K leaves a surface with only adsorbed methoxy groups. Using temperature-programmed desorption, we show that adsorbed methoxy is at least an order of magnitude more reactive than molecularly adsorbed methanol for hole-mediated photooxidation. Methoxy photodecomposes through cleavage of a C-H bond forming adsorbed formaldehyde and a surface OH group. These results suggest that methoxy, and not molecular methanol, is the effective hole scavenger in photochemical reactions of methanol on TiO₂. Same reactions were also studied with water coadsorption.