CO2 Promoted methanol conversion to methyl formate by photocatalysis

Methyl formate (MF), as an important precursor to numerous commercially significant compounds (e.g. dimethyl carbonate, methyl acetate, and ethyl glycol etc), is typically synthesised via the condensation reaction or carbonylation of methanol, requiring relatively high-value precursors (e.g. formic acid or dry CO) while with a low conversion or selectivity. Herein palladium (Pd) and gold (Au) modified TiO₂ (P25) was designed to use a very low-cost precursor methanol with the assistance of CO₂ to synthesise MF under ambient conditions. Remarkably, a high conversion of methanol (98.1 %) and selectivity to MF (94.9 %) have been achieved under an optimised reaction condition using methanol as the major reactant. In this system, Au significantly enhances charge separation and transfer, and then Pd serves as a final hole acceptor facilitating the oxidation of methanol to MF by PdAu-modified P25. This synergy boosts the MF formation rate by 15 times compared to single metal modified P25 under identical reaction conditions. Further studies reveal that formaldehyde is a pivotal intermediate in the formation of MF and employing CO₂ as a reaction moderator inhibits the methanol over oxidation.