Study on the Formation and Transformation Mechanisms of NO in Air Plasma Nitrogen Fixation

Plasma nitrogen fixation technology has demonstrated significant potential in reducing fossil energy consumption and achieving low carbon emissions. However, its high energy consumption and the complex, uncertain mechanisms underlying nitrogen fixation remain substantial challenges that limit further development. To gain deeper insight into the formation and evolution of nitrogen oxides during plasma discharge, this study employs laser-induced fluorescence diagnostics to track the temporal evolution of key reactive nitrogen species during the pulsed direct current discharge process. The experimental results show that the density of the O atom decreases rapidly within 1 ms after the discharge ends. However, the NO density exhibits a trend of first increasing and then decreasing after the discharge, with its peak occurring after the discharge ends. Moreover, the interconversion between NO and NO₂ during the nitrogen fixation process, as well as the thermal stability of NO₂, was considered. Thermal decomposition experiments reveal that the main formation pathway of NO is attributed to the thermal decomposition of NO₂ in the high-temperature environment after the discharge, which is the key factor leading to the delayed peak in NO density. Finally, the concentrations of NO and NO₂ were measured using Fourier-transform infrared spectroscopy, and the transformation relationship between the two species during the discharge process was inferred. The results reveal the critical role of NO₂ thermal decomposition in the evolution of NO, providing experimental support for further investigation into the kinetic mechanisms of NO formation during air discharge.