Strategies for avoiding the scaling relationship in ammonia synthesis with non-thermal plasma methods – the “shift” or “break” approach

Abstract

Ammonia is a zero-carbon molecule and a promising hydrogen storage material with an increasing global demand. The synthesis of ammonia still relies on the traditional Haber–Bosch method, which has high ammonia production but strict reaction conditions and high energy consumption. It is critical to develop an efficient green ammonia synthesis process. It is presented that shifting or breaking the scaling relationship between the adsorption energy and activation energy of nitrogen over transition metals in traditional catalytic methods can result in a high ammonia production efficiency under mild conditions. This work reviews the current progress in various catalytic ammonia synthesis methods based on the approach of avoiding the scaling relationship. The green plasma ammonia processes focused on N₂ and H₂/H₂O are emphasized in detail, such as plasma-coupled catalysis, plasma-coupled electrocatalysis, plasma-coupled photocatalysis, and plasma-coupled chemical looping due to the N₂ activated in plasma. These novel systems are designed to overcome the limitations of a single ammonia synthesis system and are expected to achieve green and sustainable ammonia production.