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.