Photocatalytic conversion of CO₂ into light olefins over TiO₂ nanotube confined Cu clusters with high ratio of Cu⁺

Photo-reducing carbon dioxide to light olefins with high selectivity under simulated sunlight irradiation is greatly significant but also challenging. Herein, by using Trimethylaluminium (TMA) and Bis(hexafluoroacetylacetonato) copper(II) (Cu(hfac)₂) as precursors, TiO₂ nanotubes with confined Cu cocatalysts are synthesized via template-assisted atomic layer deposition (ALD). Various characterizations revealed that the Cu species are highly dispersed in the form of cluster with several atoms. The loading content of copper is up to 3.8 wt%. This Cu/TiO₂ catalyst shows superior catalytic performance in the photocatalytic reduction of CO₂ with H₂O, with 60.4% selectivity to light olefins at 150 °C. This superior selectivity can be attributed to the ideal Cu/TiO₂ confined structure with highly dispersed Cu clusters and high ratio of surface Cu⁺ species (75.7%). The Cu⁺ species provide the active sites for the C[sbnd]C coupling reaction. By proper controlling the reaction conditions, such as low light intensity and medium temperature, the ratio of CO₂ and active hydrogen can be reasonably regulated to obtain a high selectivity of olefins.