Chemical looping based Low-pressure ammonia synthesis

Ammonia (NH3) is a promising alternative to fossil fuels due to its ability to store and release hydrogen without carbon emissions, with high energy density. The traditional Haber-Bosch (H-B) process for ammonia synthesis is energy-intensive, requiring extreme pressure conditions (10–20 MPa). Chemical Looping-based Ammonia Synthesis (CLAS) offers a sustainable alternative, via a cyclic process where hydrogen gas reacts with a nitrogen containing solid (termed a ‘nitrogen carrier’) at near ambient pressure to form ammonia. The nitrogen carrier is regenerated in N2 gas in a separate step. However, practical implementation of CLAS faces challenges, primarily in the development of effective nitrogen carriers. This review analyses nitrogen carrier materials for the CLAS process, focusing on material screening and fabrication techniques, as well as strategies to reduce energy consumption and increase ammonia production at reactor and system level. The latest advancements in transition metal nitrides and alkali/alkaline earth metal imides are highlighted, as well as external field-assisted technologies to apply the CLAS process at industrial scale. © 2024 The Author(s)