The use of mild conditions for the synthesis of NH₃ from N₂ from air and H₂ from H₂O would allow its coupling with renewable energy. To meet this goal, new catalysts and new approaches for activating the reactants have been investigated recently to meet this goal. These efforts are revised here to guide further research

Abstract

Ammonia is one of the most important chemicals in the world because it is a feedstock for fertilizer production and, moreover, it has been proposed as a convenient storage media for renewable H₂. Currently, it is produced by Haber-Bosch process, which entails harsh operation conditions and a high carbon footprint, rendering the process difficult to be run by renewable energy. Therefore, substituting the conventional Haber-Bosch process by other approach less energy-intensive and carbon-free is an urgent need. A milder process for ammonia synthesis will enable the implementation of smaller distributed plants more aligned with renewable energies. For this reason, there is a plethora of current research focusing on the development of suitable catalysts with higher activity and selectivity for nitrogen reduction and processes that will work under less severe operating conditions or even at ambient conditions. Some of the most relevant research approaches are here revised and compared.