Exploring the Origin of Synergistic Effect in Plasma-Assisted Ammonia Synthesis over a Ni Catalyst

Plasma-assisted ammonia synthesis is generally perceived as a promising alternative to the Haber-Bosch process under milder conditions. However, the synergistic effect in plasma catalysis has not yet been thoroughly understood. Herein, the plasma-assisted ammonia synthesis over Ni-based catalysts was investigated on a double dielectric barrier discharge (DDBD) coupled temperature-programmed surface reaction system. It is found that the chemical enhancement of the synergistic effect possibly originates from the adsorption of plasma-activated nitrogen species on the surface, which suggests a Langmuir-Hinshelwood (L-H) process. The physical promotion is sourced from the catalyst-modulated discharge. The overall performance is integrally affected by (I) temperature-dependent plasma chemistry in gas phase, (II) decomposition of NH₃ (>600 K), and (III) thermal catalysis (>700 K). This study offers fundamental understandings and theoretical insights on plasma-assisted ammonia synthesis over Ni-based catalysts.