Photocatalytic CO₂ reduction to CH₄ using H₂O offers a sustainable route for solar fuel production but remains challenged by the lack of non-noble-metal cocatalysts that are both efficient and selective. Herein, we report a stepwise photodeposition strategy to anchor Cu-Bi alloy sub-nanoclusters (ASNCs, 0.84 ± 0.12 nm) on blue TiO₂ (BT) for CO₂ photoreduction. The optimal Bi_0.4Cu_0.6/BT catalyst achieves a CH₄ evolution rate of 94.4 μmol g^-1 h^-1 with 96.9% selectivity under simulated solar irradiation, substantially outperforming monometallic Cu/BT and Bi/BT. The synergistic interaction between Cu and Bi can inhibit the aerial oxidation of metallic Cu⁰ and Bi⁰, accelerate the separation of photogenerated electron-hole pairs, and facilitate the adsorption and activation of CO₂. Meanwhile, strong interfacial dielectric coupling between the ASNCs and BT support creates interface states (IFS), which enables visible-light-driven hot electron injection, thereby significantly enhancing the charge separation efficiency and overall photocatalytic activity. Furthermore, the Cu-Bi alloy substantially lowers the Gibbs free energy barrier for CO₂ adsorption over Cu active sites and establishes a thermodynamically favorable pathway for stepwise hydrogenation of CO₂ toward CH₄. This work establishes a non-noble-metal alloy sub-nanocluster strategy on defect-engineered TiO₂ for efficient and selective CO₂-to-CH₄ photoreduction.

The catalytic reduction of nitric oxide (NO) to ammonia (NO reduction reaction (NORR)) provides a dual-benefit environmental pathway that simultaneously mitigates harmful NO emissions and supports sustainable nitrogen management. Significant advances have been made in understanding active-site structures, orbital hybridization, and proton-coupled electron-transfer steps governing NO activation and selectivity. However, most progress has been achieved under idealized laboratory conditions, whereas real flue-gas environments pose substantial challenges to catalyst stability, competitive adsorption, reaction pathways, and system integration. This review critically evaluates mechanistic insights, catalyst design principles, and emerging reactor configurations relevant to NORR under practical conditions. By integrating environmental catalysis with process engineering considerations, we outline strategies to enhance selectivity, impurity tolerance, and operational robustness. Finally, key research priorities and sustainability implications are identified to guide the advancement and deployment of NORR technologies for resource-oriented utilization of industrial flue gas NO streams.

Defect engineering has been regarded as a versatile strategy to maneuver the photocatalytic activity. However, there are a few studies concerning how to maintain the stability of defects, which is important to ensure sustainable photocatalytic performance. Here, a novel strategy to modulate the structural properties of BiSbO₄ using light-induced dynamic oxygen vacancies is reported by us for efficient and stable photocatalytic oxidation of formaldehyde. Interestingly, the continuous consumption and replenishment of vacancies (namely dynamic vacancies) ensure the dynamic stability of oxygen vacancies, thus guaranteeing the excellent photocatalytic stability. The oxygen vacancies could also accelerate the electron migration, inhibit the photogenerated electron/hole recombination, widen the light absorption spectra, and thus improve the photocatalytic formaldehyde removal performance. Combined with the results of in situ DRIFTS, the reaction mechanism for each step of formaldehyde oxidation is revealed. As supported by DFT calculation of Gibbs free energy, the introduction of oxygen vacancies into BiSbO₄ can promote spontaneous process of formaldehyde oxidation. Our work highlights a promising approach for stabilizing the defects and proposes the photocatalytic reaction mechanism in combination with the thermodynamic functions.