Transition-metal-free barium hydride mediates dinitrogen fixation and ammonia synthesis Yeqin Guan 1,2 , Chuangwei Liu 3 , Qianru Wang 1,2 , Wenbo Gao 1,2 , Heine Anton Hansen 3 , Jianping Guo 1,2 , Tejs Vegge 3 , Ping Chen 1,2 1 Dalian Institute of Chemical Physics, China, 2 University of Chinese Academy of Sciences, China, 3 Technical University of Denmark, Denmark Ammonia is crucial for the manufacture of nitrogen fertilizers and is also widely regarded as a promising energy or hydrogen carrier. 1 Due to the high energy consumption of the industrial ammonia production, the development of alternative materials and approaches for efficient N 2 reduction to ammonia under mild conditions is a long- sought goal. The employment of main group elements for this vital reaction recently aroused increasing interest because of different bonding characteristics and new dinitrogen reaction chemistry. In this work, we report ammonia synthesis via a chemical looping process mediated by a transition-metal-free barium hydride (BaH 2 ). 2 Experimental and computational studies reveal that the introduction of hydrogen vacancies is essential for creating coordinatively unsaturated multi-Ba sites for N 2 activation (Figure 1). The hydridic hydrogen acts as an electron donor and facilitates the activation of N 2 with concurrent H 2 release, which functionally resembles the molecular hydrido complexes and FeMo cofactor in nitrogenase. The BaH 2 -mediated chemical looping process has prospects for the future development toward ammonia synthesis using transition-metal-free materials.
Figure 1 Schematic diagram of the mechanism for N 2 activation on BaH 2 References 1. J. Guo, P. Chen, Chem, 2017, 3, 709-712. 2. Y. Guan, C. Liu, Q. Wang, W. Gao, H. A. Hansen, J. Guo, T. Vegge, P. Chen, Angew. Chem. Int. Ed. 2022, 61, e202205805.
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