Advantageous Role of Ir0 Supported on TiO2 Nanosheets in Photocatalytic CO2 Reduction to CH4: Fast Electron Transfer and Rich Surface Hydroxyl Groups

Abstract

Ir-based heterogeneous catalysts for photocatalytic CO₂ reduction have rarely been reported and are worthy of investigation. In this work, TiO₂ nanosheets with a higher specific surface area and more oxygen vacancies were employed to support Ir metal by impregnation (Imp) and ethylene glycol (EG) reduction methods. In comparison with Ir/TiO₂ (Imp) and TiO₂, Ir/TiO₂ (EG) exhibited excellent photocatalytic performance toward CO₂ reduction, especially for CH₄ production on account of the oxygen defect of TiO₂ and rich surface hydroxyl groups produced from the interaction between TiO₂ nanosheets and metallic Ir. In situ ESR suggested that the oxygen defect was significant for CO₂ adsorption/activation. Furthermore, metallic Ir was beneficial for photogenerated electron transfer, surface hydroxyl generation, and adsorption of the CO intermediate, generating more available electrons and reducing agents for CH₄ production. In situ CO₂ DRIFTS confirmed the key synergistic interaction between the oxygen defect and metallic Ir in the photoreduction from CO₂ to CH₄.

Keywords: CO2 photoreduction; Ir/TiO2; oxygen defect; surface hydroxyl; synergistic mechanism.