Facile synthesis of Mo-doped TiO2 for selective photocatalytic CO2 reduction to methane: Promoted H2O dissociation by Mo doping

Abstract

Noble-metal co-catalysis could increase the CH4 product selectivity for photocatalytic CO2 reduction by TiO2. However, the high cost and scarcity of noble metals are key obstacles for their extensive use. Thus, it is necessary to explore cheap alternatives. Herein, Mo-doped TiO2 with different Mo concentrations were successfully prepared via a one-pot hydrothermal method at 473 K. The activity measurements of the photocatalysts show that the CH4 selectivity is increased with the Mo concentrations increasing and reaches 54.1 % at a Mo concentration of about 0.3 wt%. With further increasing the Mo concentrations, the CH4 selectivity begins to decrease. Transient photocurrent and fluorescence emission spectroscopy measurements, IR spectra for adsorbed D2O and ·OH trapping suggest that the promoted electron-hole separation and proton supply are together responsible for the enhanced CH4 selectivity. Moreover, photocatalytic CO, formaldehyde, and methanol reductions with H2O and ·CH3 trapping show that the enhanced CH4 selectivity is not directly related with the interaction of CO2 with catalyst surfaces. These reaction results also imply that photocatalytic CO2 reduction might follow the fast-deoxygenation pathway over TiO2-based catalysts. The present work supplies a guide to explore cheap modifiers for selective photocatalytic CO2 reduction to CH4.