NO-to-NH₃ conversion under real flue-gas conditions: Environmental catalysis and challenges toward sustainable deployment

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.