Air‐Level Oxygen Enables 100% Selectivity in Urea Synthesis via Photocatalytic C─N Coupling of CO and Ammonia

Abstract

Abstract The clean‐energy‐driven synthesis of urea from carbon‐ and nitrogen‐containing small molecules has garnered significant interest but remained great challenges to achieve with high selectivity. Herein, we present a photocatalytic pathway for the selective urea synthesis through the oxidative coupling between CO and NH 3 . The key factor in this process is the atmospheric O 2 level, which plays a crucial role in controlling both the urea production rate and its selectivity. Using oxygen‐deficient TiO 2 under an air‐level (20%) O 2 atmosphere, we achieved a urea generation rate of 54.31 mg g cat −1 h −1 with 100% selectivity. This rate is 38.52 times higher than under oxygen‐free conditions, while further increasing the O 2 level significantly reduces selectivity. Mechanistic studies reveal that the process begins with the oxidation of NH 3 to •NH 2 through oxidative radicals generated on TiO 2 , especially the oxygen‐derived O 2 •– . This •NH 2 radicals then couple with CO to form urea. The concentration of radicals is controlled by the O 2 level, with the optimal concentration under air‐level O 2 enabling efficient NH 3 oxidation to •NH 2 while preventing over‐oxidation.