PdCu alloy anchored defective titania for photocatalytic conversion of carbon dioxide into methane with 100% selectivity

The photoreduction of CO₂ into CH₄ with simultaneous high activity and selectivity is a promising strategy to increase energy supply and alleviate global warming. However, the absence of the active sites that is responsible for the adsorption and activation of CO₂ and the generation of CO and H₂ via side reactions often lead to poor efficiency and low selectivity of the catalyst. Herein, Cu, Pd, and PdCu metal clusters cocatalyst-anchored defective TiO₂ nanotubes (Cu/TiO₂-SBO, Pd/TiO₂-SBO, and Pd₁Cu₁/TiO₂-SBO) were designed via a simple solution impregnation reduction and applied for photocatalytic conversion of CO₂ to CH₄. The Pd₁Cu₁/TiO₂-SBO photocatalyst exhibits excellent catalytic performance among the other catalysts for photoreduction of CO₂ into CH₄. More interestingly, the product selectivity of CH₄ reaches up to 100% with a rate of 25 µmol g⁻¹ h⁻¹. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) simulations indicate that the main reasons for the high selectivity of CH₄ are attributed to the PdCu alloy and oxygen vacancies, which jointly enhance the photoinduced carrier separation and lower energy barriers of key intermediates. Moreover, due to the tunable d-band center of the Cu site in the PdCu alloy, the generated intermediates can be well prevented from poisoning and promoted to participate in further reactions. Hopefully, the current study will provide insight into the development of new, highly selective photocatalysts for the visible light-catalytic reduction of CO₂ into CH₄.