In Situ Studies on Temperature-Dependent Photocatalytic Reactions of Methanol on TiO2(110)

We studied the photocatalytic reaction of methanol on the TiO2(110) surface in situ by surface sum frequency generation vibrational spectroscopy. The in situ vibrational spectra of the photo-oxidation product, formaldehyde and methyl formate, on TiO2(110) was unambiguously assigned and identified. The temperature-dependent photocatalytic reaction efficiency was observed and suggested that the thermal diffusion might be important for the photocatalytic reaction. Scanning tunneling microscopy combined with ultraviolet light was used to investigate the photocatalytic reaction efficiency on the hydroxylated TiO2(110) surface, which shows that the neighboring hydroxyl group on the bridge-bonded oxygen site dramatically inhibits the photo-oxidation of methanol because of the repulsion between hydroxyl groups. Our results provide direct vibrational spectral evidence of photo-oxidation products of methanol on TiO2(110), show the importance of thermal processes in surface photocatalytic reactions, and deepen our understanding on photochemistry on this surface. Copyright © 2019 American Chemical Society.