Enhanced Photo-Oxidation of Formaldehyde on Highly Reduced o-TiO2(110)

Photo-oxidation of formaldehyde is important because it is an atmospheric pollutant and a possible intermediate along the pathway for CO2 reduction to methanol. By using temperature-programmed reaction spectroscopy as the main tool, we demonstrate that the efficiency for photo-oxidation of formaldehyde to adsorbed formate on rutile TiO2(110) is strongly dependent on the degree of reduction of the surface and near-surface region. The most efficient photoreaction occurs when O adatoms are present on titania that is highly bulk reduced. These data suggest that electron–hole pairs created deep in the bulk do not play a significant role in the photo-oxidation of formaldehyde. Exposure of the material to O2 heals most bridging oxygen vacancies, creates O adatoms in the Ti five-coordinate rows, and quenches charge at the surface due to the presence of interstitial defects in the near-surface region. Under these conditions, the surface is oxidized but the bulk remains reduced. The major product of formaldehyde ph...