Chemical Looping Technology in Mild‐Condition Ammonia Production: A Comprehensive Review and Analysis

Abstract

Ammonia is an efficient and clean hydrogen carrier that promises to tackle the increasing energy and environmental problems. However, more than 90% of ammonia is produced by the Haber–Bosch process, and its enormous energy consumption and CO2 emissions require the development of novel alternatives. Chemical looping technology can decouple the one‐step ammonia synthesis reaction into separated nitridation and hydrogenation processes at atmospheric pressure, thereby achieving the mild ammonia synthesis based on renewable energy. The strategy of stepwise reactions circumvents the problem of competing adsorption of N2 and H2/H2O at the active sites and provides additive freedom for optimal regulation of sub‐reactions. This review introduces the concept and mechanism of chemical looping ammonia production (CLAP), and comprehensively summarizes the state‐of‐art research from the perspective of reaction pathways and nitrogen carriers. The challenges faced by CLAP and strategies to address them in terms of nitrogen carriers, methods, equipment, and technological processes are also proposed.

Towards green and efficient chemical looping ammonia synthesis: design principles and advanced redox catalysts

“…Although there have been some excellent reviews and books covering chemical looping ammonia synthesis, 27,[33][34][35][36][37][38][39][40][41][42][43][44][45][46] they tend to focus on the materials development of nitrogen or hydrogen carriers in CLAS. In this review, to propose and discuss strategies and advances for lowering reaction temperatures and increasing ammonia productivity towards green CLAS.…”

Ammonia Energy: Synthesis and Utilization

“…20 Overall, the nitrogen carriers in CLAS technology consist of metal nitrides and hydrides, which in combination with two hydrogen sources constitute three viable CLAS pathways (Figure 7b). 93 H 2 O-CL and MN-CL typically use metal nitrides as nitrogen carriers. Ammonia production is achieved by forming metal nitrides to activate N 2 , which are then hydrolyzed or hydrogenated.…”

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

“…It is one of the most significant chemical processes developed in the 20 th century and has had a profound impact on agriculture and the global food supply . The thermodynamics of the Haber-Bosch process involve nitrogen fixation from the atmosphere, a low-energy process; hydrogen production from hydrocarbon sources, an energy-intensive and endothermic step; and ammonia synthesis from nitrogen and hydrogen, an exothermic reaction requiring high temperatures and pressures . The overall process is energy-intensive, with the hydrogen production step being a major energy input, while the ammonia synthesis step releases heat.…”