Pd─N ₄ Sites in MOFs Modulate Oxygen Reduction Pathways for 100% Selective Photocatalytic CO ₂ ‐to‐CH ₄ Conversion from Oxygenated Flue Gas

Abstract

Abstract Direct photocatalytic CO 2 reduction in flue gas is significantly challenged by the thermodynamically favored oxygen reduction reaction. While conventional approaches showed promise, the inherent O 2 affinity of transition and noble metals prevented full suppression of O 2 adsorption and activation, severely constraining the multi‐step proton‐coupled electron transfers required for the CO 2 ‐to‐CH 4 pathway. We therefore envisioned a CO‐mediated oxygen scavenging mechanism by modulating oxygen reduction pathways. Via Pd─N 4 site engineering, the resulting Pd/Cu 3 (HITP) 2 /TiO 2 composite effectively suppressed competitive oxygen reduction reaction, enabling selective CO 2 ‐to‐CH 4 conversion under aerobic conditions. Control experiments and density functional theory calculations revealed that the Pd─N 4 sites steered oxygen reduction toward CO‐mediated pathways—thermodynamically and kinetically favored over conventional oxygen reduction reaction, thereby mitigating competitive effects and simultaneously purifying the product. Consequently, such composite exhibited complete CH 4 selectivity at 6.7 µmol g −1 h −1 under simulated industrial flue gas conditions (15 vol% CO 2 , 3 vol% O 2 , 5 vol% H 2 O, balanced N 2 ). Our work highlights catalytic site modulation and advances a new strategy for photocatalytic CO 2 reduction in oxygenated flue gas via pathway‐selective oxygen reduction.