NH<sub>3</sub> Synthesis from N<sub>1</sub> Compounds by Photocatalytic Technology: Promotion Mechanism, Reaction Pathways, and Efficiency Evaluation Criteria
Chunling Zhang, Jieyuan Li, Ruimin Chen, Shujie Shen, Jielin Wang, Yanjuan Sun, Fan Dong
Abstract
Ammonia (NH 3 ) is one of the most important chemicals in high demand in human society. Given the high-energy consumption and environmental impact associated with the Haber–Bosch process, an environmentally friendly method for NH 3 synthesis under ambient conditions should be developed. The reduction of N 1 compounds, including nitrate (NO 3 – ), nitrite (NO 2 – ), and nitric oxide (NO x ), are more energetically favorable than that of nitrogen (N 2 ), avoiding the activation of inert N≡N bonds. Photocatalytic NH 3 synthesis from N 1 compounds’ reduction, which utilizes sunlight to convert contaminants into value-added chemicals, offers an intriguing approach to NH 3 synthesis. This review offers a comprehensive overview of the progress of research in photocatalysis technology for reduction of N 1 compounds to NH 3 synthesis. Insight into the efficiency promotion mechanism is provided, particularly focusing on the optimization of the photocatalyst, the activation and mass transfer of reactants, and the redox synergistic promotion. Moreover, the reaction pathways are summarized. The efficiency evaluation criteria, including accurate quantification of the NH 3 yield, comprehensive performance evaluation indicators, and NH 3 separation and recovery, are discussed to guide systematic and reliable NH 3 synthesis. Finally, the current achievements and future challenges of photocatalytic N 1 compounds to NH 3 synthesis are critically discussed.