Recent Advances in NH3 Synthesis with Chemical Looping Technology

Ammonia economy is expected to provide a long-term solution without carbon emission to relieve environmental burdens and tackle traditional fossil fuel depletion. NH3 synthesis with chemical loop technology is a promising NH3 production alternative with independence from fossil fuels, high product selectivity, and simplified operation under milder conditions. Looped nitrogen carriers provide a chemical looping ammonia synthesis (CLAS) process with thermodynamic and/or kinetic advantages via decoupling scaling relations and circumventing competitive chemisorption of N2 and H2/H2O. The approach has great flexibility in material and process design, and individual steps can thus be optimized separately. This review summarizes the recent progress related to the CLAS process. Four routines (i.e., H2-TM CLAS, H2-AH CLAS, H2O-2step CLAS, and H2O-3step CLAS) are analyzed and compared as well as the plant configurations using chemical looping technology to generate feedstocks for Haber–Bosch NH3 synthesis. The corresponding challenges are also presented, and potential solutions are discussed.