Warm non-equilibrium plasma-assisted catalysis for sustainable ammonia synthesis

Abstract

Ammonia is synthesized mainly through the energy-intensive Haber–Bosch process, a major source of global CO₂ emissions, exhibiting difficulty in decentralizing and utilizing renewable electricity. Plasma-assisted catalysis seems to be a suitable alternative. The authors report a systematic investigation of ammonia synthesis using a rotating gliding-arc “warm” plasma, over Fe, Ni, and Cu catalysts in a post-plasma configuration that mitigates plasma-induced degradation. Under identical hydrodynamic conditions, performance of Fe (62.7 ppm) > Ni (54.0 ppm) > Cu (40.7 ppm), indicating that the catalyst surface drives performance. A multi-manifold vibrational volcano model reveals that Fe has a “vibrational sweet spot” at moderate excitation (v ≈ 1–3), where vibrationally excited N₂ lowers the dissociation barrier without inducing desorption limitation, while Ni and Cu remain weakly bound; extension to extreme vibrational excitation (v ≥ 10) predicts weaker-binding metals becoming optimal once the dissociation barrier is fully cancelled. This preliminary investigation marks an essential first step towards the use of non-equilibrium vibrational excitation to navigate the Sabatier landscape for sustainable nitrogen fixation.