Oxygen Vacancy Sites Enable Efficient Photocatalytic Oxidation of Nitric Oxide: The Role of W/Mo Valence Transition in Bi₂W(Mo)O_6‐x

Abstract Oxygen vacancy (O v ) sites play a critical role in the activation and deep oxidation of nitric oxide (NO). However, controlling the concentration and type of O v remains a significant challenge. In this study, Bi 2 W(Mo)O 6‐x is investigated as a model system and demonstrates that increasing the concentration of O v substantially enhances the efficiency of air NO removal. Increasing the O v concentrations in Bi 2 WO 6‐x and Bi 2 MoO 6‐x improves NO removal efficiency ≈12‐ and 11‐fold, respectively, compared to their low‐O v counterparts. This enhancement is attributed to improved adsorption and activation of NO/O 2 molecules, better separation and transfer of photogenerated carriers, and increased visible light absorption. Notably, Bi 2 WO 6‐x remains highly stable over ten recycling tests for continuous air NO deep photooxidation, while Bi 2 MoO 6‐x shows a 43.5% decrease in efficiency after ten runs. This sustained performance is attributed to stable O v s without changes in metal ion valence, unlike Bi 2 MoO 6‐x , where instability arises from the reduction of Mo 6+ to Mo 4+ . In situ DRIFTS reveals possible pathways for the deep photooxidation of NO to nitrate (NO 3 − ). This study provides valuable insights into designing high‐performance, durable catalysts by effectively controlling O v concentration and type, paving the way for efficient photocatalytic air purification technologies.