Photo-assisted thermal catalytic CO2 reduction over Ru-TiO2 catalysts.

Photothermal catalysis is a promising technology to convert CO2 into high value-added products. Here, we show that loading Ru NPs on TiO2 achieved a remarkable photothermal synergistic effect and the Ru-TiO2 demonstrated a high efficiency for the photothermal conversion of low CO2 concentration to CH4 at the gas-solid interface. The photothermal activity of the Ru-TiO2 (217.9 µmol/(g·h)) was nearly 6 times higher than pure thermal activity (38.08 µmol/(g·h)), and nearly 20 times than the photocatalytic activity (10.9 µmol/(g·h)). We revealed that the light excitation could drive the generated electrons from TiO2 to Ru particles, beneficial to CO2 reduction, while external heating showed no influence on the charge separation of the Ru-TiO2. Hence, the photothermal synergy is not a heat-assisted photocatalytic process, but a photo-assisted thermal catalytic process. We finally demonstrated that the CO2 was firstly converted to CO, and the CO was further hydrogenated to CH4. The introduction of light could promote the activation of intermediate CO species at the Ru-Ti interface sites, thus greatly accelerating CO hydrogenation to CH4. This work contributes to further understanding of the mechanism of photothermal catalytic CO2 reduction.