Selectivity Change and Deactivation in Photocatalytic CO ₂ Reduction Induced by SO ₂

Industrial flue gas is a major source of CO2 emissions, but the effects of its contaminants on CO2 photoreduction remain unclear. Here, we investigated the influence of SO2 on the photocatalytic performance of CO2 photoreduction using Pt/TiO2 as a model photocatalyst. SO2 enhanced the yield of CO2 photoreduction within 2.5 h, accompanied by a selectivity change from 100% CH4 to predominantly CO, followed by a gradual deactivation of the catalyst. Gaseous SO2 hindered the proton supply for CH4 generation by suppressing H2O adsorption. SO2 was oxidized into SO42–, which occupied the step sites of Pt NPs and formed a new Pt–O–SO3 species, weakening the π-electron back-bonding in the Pt(5d)-Co(2π*) bonds and thus facilitating *CO desorption. Lastly, the excessive accumulation of SO42– led to catalyst poisoning. This work sheds light on the role of SO2 during the photoreduction of CO2 and provides a theoretical foundation for the direct photocatalytic conversion of CO2 from industrial flue gas.