Unravelling the C C coupling in CO2 photocatalytic reduction with H2O on Au/TiO2-x: Combination of plasmonic excitation and oxygen vacancy

CO2 photocatalytic conversion with H2O is an attractive technology to convert green-house gas into value-added chemicals. However, the main limitation of this process is the low selectivity to products higher than C1. The reaction mechanism, especially CC coupling mechanism, is still ambiguous. In this work, the photocatalytic CO2 reduction with H2O is investigated on oxygen-deficient Au/TiO2-x driven by UV or visible light under continuous flow condition. Notably, an exceptional high selectivity of 20 % towards C2H6 is achieved over 2.76 wt% Au/TiO2-x under plasmonic excitation with the essential involvement of oxygen vacancy (VO). The reaction pathway is reasonably proposed based on a series of in-situ characterization results: the in-situ DRIFTS determined key reaction intermediates, electronic property of Au under excitation state and the critical role of VO. The high selectivity towards C2H6 is explained by the slightly positive-charged Au in Au/TiO2-x under plasmonic excitation and the enhanced *CO stability.