Advances in Nitrogen Carriers for Chemical Looping Processes for Sustainable and Carbon-Free Ammonia Synthesis

The use of ammonia as a hydrogen carrier has generated considerable interest in developing more renewable and long-lasting methods for ammonia production. Collaborative efforts among research institutes, industries, and governments are underway to produce carbon-free ammonia and achieve net-zero emissions by 2050. One largely emerging approach, namely, chemical looping ammonia production (CLAP) with high product selectivity and energy efficiency that utilizes nitrogen carrier materials under atmospheric pressure may greatly reduce this process. Despite recent advancements, several key challenges related to the thermodynamics, kinetics, mechanisms, and environmental impacts of CLAP remain unresolved. This review provides a comprehensive overview of the progression and breakthroughs in this captivating domain, contrasts the properties of nitrogen carriers deployed in assorted CLAP processes alongside thermodynamic and kinetic considerations, and offers insights into the future trajectory of CLAP.