Production of ammonia via a chemical looping process based on metal imides as nitrogen carriers

• Published in: Nature energy 2018-12, Vol.3 (12), p.1067-1075
• Main Authors: Gao, Wenbo, Guo, Jianping, Wang, Peikun, Wang, Qianru, Chang, Fei, Pei, Qijun, Zhang, Weijin, Liu, Lin, Chen, Ping
• Format: Article
• Language: English
• Subjects: 639/301/299; 639/4077/4079/4088/4058; 639/638/77/887; Alkaline earth metals; Ammonia; Current carriers; Economics and Management; Energy; Energy Policy; Energy Storage; Energy Systems; Free energy; Imides; Low temperature; Metal hydrides; Nitrogen; Oxidation; Renewable and Green Energy; Synthesis; Valence
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-018-0268-z

Ammonia is a promising carbon-free energy carrier, but is currently synthesized industrially under harsh conditions. Synthesizing ammonia using lower temperatures and pressures could therefore improve its prospects as a chemical means to store and transport energy. Here we report that alkali and alkaline earth metal imides function as nitrogen carriers that mediate ammonia production via a two-step chemical looping process operating under mild conditions. Nitrogen is first fixed through the reduction of N 2 by alkali or alkaline earth metal hydrides to form imides and, subsequently, the imides are hydrogenated to produce NH 3 and regenerate the metal hydrides. The oxidation state of hydrogen therefore switches between −1 (hydride), 0 (H 2 ) and +1 (imide and NH 3 ). Late 3d metals accelerate the reaction rates of both steps. The chemical loop mediated by BaNH and catalysed by Ni produces NH 3 at 100 °C and atmospheric pressure. Reducing the severity of the conditions required to synthesize ammonia would increase the viability of its use as a carbon-free energy carrier. Here the authors use metal imides to mediate ammonia production via a two-step chemical looping process that operates under mild conditions.