Exploring the enhancement effects of hetero-metal doping in CeO₂ on CO₂ photocatalytic reduction performance

Doping hetero-metal ions in semiconductors, especially metal oxides, is a common practice to elevate their photocatalytic reduction activity. However, the underlying enhancement mechanism of doping different metal ions into the host lattice on photocatalytic CO₂ reduction has been rarely explored and thus remains unclear. In this work, CeO₂ nanoparticles doped with three different metal ions (CeM, M = Y, La, Mo) have been synthesized, which exhibited significantly improved photo-reduction CO₂ activity. According to the analysis of Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), Y and Mo doping results in increased oxygen vacancy concentration in CeO₂, which promotes the absorption of UV–visible light and the separation/transfer of electrons and holes, consequently elevating the catalytic activity. More importantly, through in-situ FT-IR, CO₂ adsorption/activation and the intermediates generated on catalyst surface during CO₂ photoreduction reaction were investigated and discussed in-depth. Similar carbonates and hydrocarbonates, such as HCO₃⁻, b-CO₃²⁻ and m-CO₃²⁻, have been found to be produced on CeO₂ and CeM, while these intermediates accumulated and strongly covered on the catalyst surface have been revealed to be responsible for the gradually declined CO₂ reduction activity and stability.