On the Mechanism of Methyl Formate Production Initiated by Photooxidation of Methanol on Rutile TiO₂(110) and TiO₂(011)-(2 × 1) Surfaces

The formation of HCOOCH 3 initiated by photooxidation of CH 3 OH on TiO 2 surfaces is interesting, but the mechanism remains ambiguous. Using thermal desorption spectroscopy and X-ray photoelectron spectroscopy, we herein have comparatively studied the adsorption of HCOOCH 3 on the rutile TiO 2 (110) surface, the coadsorption and photooxidation of CH 3 OH and HCHO on the rutile TiO 2 (110) surface, and the adsorption and photooxidation of CH 3 OH on the rutile TiO 2 (011)-(2 × 1) surface. The HCOOCH 3 formation from the photooxidation of CH 3 OH was identified as a relay reaction of photocatalytic reactions, followed by thermal reactions. CH 3 OH is photocatalytically oxidized to CH 3 O and HCHO species, and HCHO is photocatalytically oxidized to HCO species, and then the CH 3 O and HCO species undergo thermal coupling reactions to produce HCOOCH 3 during the subsequent heating process. The TiO 2 surface structure was observed to affect not only the photocatalytic oxidation process of CH 3 OH to produce CH 3 O and HCO species but also the subsequent thermal coupling reaction of CH 3 O and HCO species to produce HCOOCH 3 . CH 3 OH on the TiO 2 (110) surface is more photoreactive than on the TiO 2 (011)-(2 × 1) surface. A higher fraction of HCHO is produced for CH 3 OH/TiO 2 (011)-(2 × 1) than for CH 3 OH/TiO 2 (110), while a smaller faction of HCOOCH 3 is produced. These results broaden our fundamental understanding of the reaction mechanism of CH 3 OH photocatalysis on TiO 2 surfaces.