Catalytic photo-redox of simulated air into ammonia over bimetallic MOFs nanosheets with oxygen vacancies

作者：Zhao, Wenjun; Qin, Jiangzhou; Teng, Wei; Mu, Jincheng; Chen, Chang; Ke, Jun; Huang, Jacob C.; Liu, Baojun^*; Wang, Shaobin^*

来源：Applied Catalysis B: Environmental , 2022, 305: 121046.

DOI：10.1016/j.apcatb.2021.121046

• Oxygen vacancies
• Bimetallic organic frameworks
• Ammonia photosynthesis
• Air redox reaction (ARR)

Solar-driven conversion of nitrogen (N-2) into ammonia (NH3) is a promising alternative to the Haber-Bosch process, while still suffers from low conversion efficiency due to inactive N=N bond. Herein, a novel pathway of photocatalytic air redox reaction (ARR) to ammonia via NO is proposed and tested over an effective catalyst of oxygen-vacancy-rich bimetallic Cu-Co organic framework ultrathin nanosheets (OVR-CuCo-MOFs NS) under visible light. The catalyst with unique oxygen defective sites shows an excellent NH3 synthesis rate from air (287.76 & PLUSMN; 7.02 mu mol g-(1).h(-1)), which is 5.4-fold higher than that from pure N-2. Moreover, experiments and theoretical calculations indicate that the transformation of air mainly follows a redox pathway, in which N-2 and O-2 can be trapped at the oxygen vacancies to generate nitric oxide (*NO) and further be reduced to ammonia by visible light. The ARR process shows a lower barrier of free energies in the onset activation step (*N-2 & RARR; *N-NO,-0.08 eV) and rate-limiting step (*NO & RARR; *NHO, 1.23 eV) compared with those of traditional nitrogen reduction (*N-2 & RARR; *N-NH, 1.48 eV and H2N-NH2 & RARR; *NH2, 1.29 eV, respectively). This work provides a new and sustainable pathway for photo-driven ammonia synthesis.

• 单位
  北京大学; 贵州大学; 江苏科技大学; 武汉工程大学