CO2 Promoted methanol conversion to methyl formate by photocatalysis

• The Pd and Au modified P25 photocatalyst presents a step change in methyl formate production. • 98.1 % conversion of methanol and 94.9 % methyl formate selectivity have been achieved. • Formaldehyde is identified as a critical intermediate. • Au nanoparticles act as the special charges’ separator, dramatically reducing the recombination of electrons and holes. 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 TiO 2 (P25) was designed to use a very low-cost precursor methanol with the assistance of CO 2 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 CO 2 as a reaction moderator inhibits the methanol over oxidation.