Insights on the Mechanism of Surface-Catalyzed Oxidative Nitrogen Fixation Based on Liquid-Phase Bubble Pin-Plate Discharge

In plasma-coupled catalytic oxidation of nitrogen fixation (NF), the gas–liquid phase combination and synergy with surface catalysis improve NF conversion and reduce energy consumption. However, there is a lack of studies on the synergistic reaction mechanisms of plasma and surface catalysis. Therefore, this study designed a liquid-phase bubble pin-plate discharge device providing a ground electrode as a catalytic electrode for the study of catalytic coupled mechanisms and optimized the setup parameters. The NF performance of several metal materials was investigated as catalytic electrodes. Among them, Fe foils show the best performance, with a conversion of 1.08%, and Ni foils display the most limited performance. To further study the coupled mechanism, density functional theory calculations combined with the plasma diagnostic technique were used to reveal the corresponding reaction paths and decisive steps by calculating the energies of dissociation and adsorption of nitrogen-based reactive species on the surface of Fe and Ni foils and the energies of stepwise oxidation of N• radicals. The results show that the Eley–Rideal mechanism is the optimal mechanism for NF to NO and NO2, and the Fe foils are more favorable for the formation of adsorbed state N. These findings offer significant guidance for design of the reactor and catalysts for plasma-coupled catalytic NF.