Progress in design and application research of nitrogen carrier in chemical looping ammonia synthesis technology

Ammonia is not only the main raw material of nitrogen fertilizer production, but also one of the energy carriers for the storage and conversion process of renewable energy. Therefore, the development of a mild ammonia synthesis technology has become an important research topic in recent years. The chemical looping ammonia synthesis technology decouples the ammonia synthesis reaction into several steps, including the nitrogen fixation and the ammonia release, which has the advantages of easy operation, mild reaction, and low energy consumption. As the key to the chemical looping ammonia synthesis, nitrogen carriers play the role of transferring energy and nitrogen species. However, the current low nitrogen fixation efficiency of nitrogen carriers severely limits the development of the chemical looping ammonia synthesis technology. Therefore, this article reviews the research on the design, preparation and application of nitrogen carriers for the chemical looping ammonia synthesis. Firstly, the design theory of nitrogen carrier is summarized; secondly, the current research status of nitrogen carrier is introduced, with a focus on how to improve the ammonia production rate of nitrogen carrier and the utilization rate of lattice nitrogen; finally, the opportunities and challenges of chemical looping ammonia synthesis technology are discussed, which provide a reference for the design and development of nitrogen carrier in the future.