Highly Selective Photocatalytic CO ₂ -to-CH ₄ Conversion in Water Vapor via CeO ₂ /Carbon Nitride Nanosheet Heterojunctions

Solar-driven CO2 reforming in water vapor to produce high-value-added chemical fuels offers significant potential for renewable energy. Achieving this conversion under mild conditions can be efficiently realized through multielectron-coupled proton transfer (M-ECPT) photocatalysis. This work introduces CeO2/CNs-NKM, a composite synthesized by firmly anchoring highly dispersed cerium oxide (CeO2) onto crystalline carbon nitride nanosheets (CNs-NKM). Experimental and theoretical studies confirm that this material possesses an optimized S-scheme heterojunction structure. This structure enables high efficiency in electron excitation, storage, and release, which critically promotes the highly selective M-ECPT conversion of CO2 to CH4 in water vapor. Consequently, the optimized CeO2/CNs-NKM catalyst achieves CO2 reduction rates to CO and CH4 of 6.58 and 14.91 μmol·g–1·h–1, respectively, with a calculated CH4 selectivity of 90.06%. Computational simulations validate the proposed reaction pathway, providing insights into photocatalytic strategies for deep CO2 reduction, akin to artificial photosynthesis.