Plasma-driven catalytic ammonia synthesis from renewable electricity has recently gained traction as an alternative to the Haber–Bosch process for decentralized applications. We summarize the state-of-the-art in literature and provide avenues for improvement.

Plasma-based NO_X synthesis can be combined with renewable electricity for decarbonized fertilizer production. Renewed research interest makes it increasingly competitive with the conventional process.

Plasma-enhanced catalytic ammonia synthesis has been proposed as an alternative pathway for green nitrogen fixation in case of medium- and small-scale operation. Recently, Mehta et al. postulated that plasma-induced vibrational excitations of N₂ decrease the dissociation barrier, without influencing the subsequent hydrogenation reactions and ammonia desorption at atmospheric conditions. In this paper, this postulation is substantiated with experimental data of unpromoted and promoted, alumina-supported ruthenium ammonia synthesis catalysts. Within the temperature regime for plasma-enhanced catalytic ammonia synthesis over ruthenium-based catalysts (>200°C), synergy is experimentally observed between the catalyst and the plasma by a lowered apparent activation energy. While the apparent activation energy for thermal-catalytic ammonia synthesis typically ranges from ~60 kJ mol^-1 to ~115 kJ mol^-1, the apparent activation energy for plasma-enhanced catalytic ammonia synthesis ranges from ~20 kJ mol^-1 to ~40 kJ mol^-1, consistent with the hypothesis that ammonia synthesis is enhanced via plasma-induced vibrational excitations of N₂. Further support follows form the observation that the effects of promotors and supports on activity are similar for thermal catalysis and plasma-enhanced catalysis. As promotor and support influence activity via enhancing dissociation of N₂, it follows that breaking the N≡N bond is still relevant in plasma-enhanced catalytic ammonia synthesis.

Synthetic ammonia, manufactured by the Haber–Bosch process and its variants, is the key to securing global food security. Hydrogen is the most important feedstock for all synthetic ammonia processes. Renewable ammonia production relies on hydrogen generated by water electrolysis using electricity generated from hydropower. This was used commercially as early as 1921. In the present work, we discuss how renewable ammonia production subsequently emerged in those countries endowed with abundant hydropower, and in particular in regions with limited or no oil, gas, and coal deposits. Thus, renewable ammonia played an important role in national food security for countries without fossil fuel resources until after the mid-20th century. For economic reasons, renewable ammonia production declined from the 1960s onward in favor of fossil-based ammonia production. However, renewable ammonia has recently gained traction again as an energy vector. It is an important component of the rapidly emerging hydrogen economy. Renewable ammonia will probably play a significant role in maintaining national and global energy and food security during the 21st century.