Enhanced methanol selectivity of CuxO/TiO2 photocatalytic CO2 reduction: Synergistic mechanism of surface hydroxyl and low-valence copper species

Abstract Photocatalytic CO2 reduction to methanol is a promising method to solve the energy and environmental issues. Herein, copper species with different valences loading on TiO2 via the oxidizing and reducing atmosphere treatment, denoted as Cu/Ti(air) and Cu/Ti(H2), for CO2 photoreduction. The methanol yield greatly increased on Cu/Ti(H2) with low-valence copper species, which was 17-fold higher than that of Cu/Ti(air). It showed that the reducing atmosphere generated Ti3+ species and oxygen vacancies on Cu/Ti(H2), leading to richer protons of surface hydroxyls adsorbed on surface and available photo-electrons. In addition, in-situ CO2 adsorption-DRIFTS suggested that low-valence copper species of Cu/Ti(H2) had better ability of CO2 activation and CO*, HOCO−, HCOOH active intermediates adsorption, which further hydrogenated and conversed to CH3OH, with the help of protons and photo-electrons. Therefore, owing to the synergistic effects of surface hydroxyl and low-valence copper species, Cu/Ti(H2) was provided with the superior conversion and selectivity of CO2 to methanol.