Methyl formate synthesis from methanol on titania supported copper catalyst under UV irradiation at ambient condition: Performance and mechanism

Abstract

Selective oxidation of methanol to methyl formate (MF) with high MF formation rate and simple by-products at ambient conditions is a challenging process. Herein, we report the methyl formate synthesis from methanol on a titania supported copper catalyst in a flow reactor at 15–45°C under UV irradiation. The MF formation rate reaches 56.4mmolg−1h−1. Carbon dioxide is the only by-product below 30°C, and very small amount of dimethoxymethane besides carbon dioxide can be detected at 45°C. CuO on titania in the as-prepared catalyst is reduced to Cu to form an Ohmic contact between Cu and titania during the reaction under UV irradiation, which facilitates the photo-excited electron transfer from the conduction band of titania to Cu and reduces the recombination of the photo-excited electron–hole pairs. The negative charge on the Cu surfaces promotes the dissociation of oxygen. The coordinated methoxy resulted from the dissociative chemisorption of methanol on the surface of titania is oxidized by the photo-generated holes to form coordinated surface formaldehyde. The oxygen dissociation and the oxidation of coordinated methoxy are parallel reactions, and both of them are rate-controlled by light intensity. This study may contribute to design new photocatalytic systems and provide an applicable green route to MF synthesis from methanol.