Suppression of NO ₂ Generation During One‐Step Deep Oxidation of NO at a Semi‐Artificial Photoenzyme Based on Cytochrome <i>c</i>

ABSTRACT Solar‐driven catalysis holds promise in molecular oxygen activation and low‐concentration NO x elimination but achieving highly selective conversion of NO to nontoxic nitrate (NO 3 − ), while suppressing toxic NO 2 formation remains challenging. Here, we report a semi‐artificial photoenzyme catalyst constructed by immobilizing mono‐heme cytochrome c (cyt c ) on carbon nitride (CN) to refine reactive species generation for deep NO oxidation. The hybrid photoenzyme catalyst establishes localized internal electric fields (IEF) between cyt c and CN that promote exciton dissociation, and creates polarized active sites on cyt c that preferentially adsorb O 2 , and activate O 2 to active peroxides (•O 2 − and *O 2 2− ) via an electron transfer pathway with inhibiting 1 O 2 formation. The one‐step NO oxidation to NO 3 − is boosted over cyt c /CN, showing exceptional 97.4% NO conversion with ultralow NO 2 selectivity (1.5%, 6.5 ppb) and long‐term stability (98.1% after 300 min) at a weight hourly space velocity (WHSV) of 850 L g −1 ·h −1 across wide humidity ranges. The undesirable NO 2 generation is significantly lower than that of bare CN (17.0%, 104.7 ppb) and reported catalysts. The catalyst exhibits high activity in direct NO 2 removal (92.9%) and rapidly reduces NO levels to below the safe concentration (52 ppb) in a simulated environment chamber.