Methyl Formate Production on TiO2(110), Initiated by Methanol Photocatalysis at 400 nm

Previous observations of methyl formate (HCOOCH3) during the photo-oxidation of methanol (CH3OH) on TiO2 catalysts suggested that photocatalysis on TiO2 could be used to build up complex molecules from a single precursor. We have investigated the mechanism of HCOOCH3 formation by irradiating a CH3OH-adsorbed TiO2(110) surface with 400 nm light at low surface temperatures. Through the detection of volatile products after irradiation by temperature programmed desorption, we have found, as previously reported [Phillips et al. J. Am. Chem. Soc. 2013, 135, 574-577] that HCOOCH3 is formed by the cross-coupling reaction of CH3O and CH2O, which are products of the first and second dissociation steps, respectively, in the stepwise photocatalysis of CH3OH on TiO2(110). Unlike the previous study, we have observed the photocatalytic production of HCOOCH3 without preoxidation of the surface, and we have concluded that the final reaction step to produce HCOOCH3 (i.e., the Cross-coupling reaction of CH2O with CH3O) does not involve a transient HCO intermediate.