Progress and prospects in the chemical looping ammonia synthesis
Ammonia is mainly used as a raw material for the production of nitrogen fertilizers.In recent years,it also has been seen as a promising energy carrier.Industrial ammonia synthesis is mainly based on the Haber-Bosch(H-B)process requiring a significant energy input,so it relies severely on fossil energy and leads high CO2 emissions.Therefore,there is an urgent need to develop"Green ammonia synthesis"process driven by renewable energy operating under mild conditions.Chemical looping ammonia synthesis(CLAS)is a process that decouples the ammonia synthesis reaction into multiple sub-reactions mediated by an intermediate N carrier material.It has the ad-vantages of circumventing the ubiquity scaling relationships,avoiding the competitive adsorption between N2 and H2(or H2O),and being able to operate at atmospheric pressure.In addition,this process is suitable to distributed and small-scale ammonia synthesis and is easy to couple with the utilize of renewable energy.Therefore,CLAS has received widely attention in recent years.This review was initiated by briefly defining chemical looping processes and summarizing the research of chemical looping in the area of fossil fuel conversion.The his-tory of CLAS,the development of nitrogen carrier materials,and some recent progresses were then reviewed.The discussion was concluded with future perspectives on the design of nitrogen carrier materials and the prospective advancements in CLAS.The binary metal nitrides,multi-metallic nitrides,metal imides,and metal nitrides,which were used as nitrogen carrier materials in N2-H2 and/or N2-H2O CLAS,were presented.Additionally,the CLAS process assisted by external energy such as electricity,light,plasma,and microwaves was discussed.Strategies to enhance the thermodynamic and kinetic performance of nitrogen carrier materials were also detailed.Finally,the review addressed current challenges and emerging research directions in chemical looping ammonia synthesis.
chemical loopingammonia synthesisnitrogen carriersmetal imidesmetal nitrides
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