An efficient catalyst of CuPt/TiO2 for photocatalytic direct dehydrogenation of methanol to methyl formate at ambient temperature

Abstract

To obtain high methanol conversion at high methyl formate (MF) selectivity by the thermal reaction of direct dehydrogenation of methanol is a challenging issue due to the thermodynamic restriction. Herein, a new green route of photocatalytic direct dehydrogenation of methanol to MF with high methanol conversion and high MF selectivity on CuPt/TiO₂ at ambient temperature is reported. The methanol conversion reaches 78% at 95% MF selectivity in a single pass at 30 °C, far higher than those of thermal reactions. It is found that CuPt alloy nanoparticles with different Cu : Pt ratios were formed and highly dispersed on the surface of titania. The heterojunction, i.e., the Schottky barrier or ohmic contact which was determined by the Cu : Pt ratio, was formed at the interface between the alloy nanoparticles and titania. Platinum could be doped in the lattice of titania and thus change the density of carriers and the band structure, especially the band gap and valence band edge. The charge transfer resistance was inversely proportional to the methanol conversion, the smaller the charge transfer resistance the higher the methanol conversion, but it had little influence on the MF selectivity. Both the light-induced hole oxidation step from methoxy to coordinated formaldehyde, related to the methanol conversion, and the MF formation step from the coupling of methoxy and formaldehyde, which is an exothermic process and related to the MF selectivity, readily occurred at low/room temperatures, leading to high methanol conversion and high MF selectivity at room temperatures. The photocatalytic reaction mechanism breaks the thermodynamic restriction of the thermal reactions. This study may contribute to the design of new photocatalytic systems and provide an applicable green route to MF synthesis from methanol.