Plasma oxidation of NO in O2:N2 mixtures: The importance of back-reaction

• Investigation of plasma oxidation of NO to NO2 in dry O2:N2 mixtures.
• Back-reaction of NO2 to NO resulted in the saturation of NO removal.
• NO reaction with O3 resulted in the decreased influence of inlet NO concentration.
• A new analytical expression was derived to explain the experimental findings.

Present study was devoted on the investigation of the NO removal by dielectric barrier discharge (DBD) in dry O2:N2 mixtures with a wide range of inlet NO concentrations and O2 fractions. The experimental results were complemented by solving a set of differential equations describing the plasma-chemistry in the used mixtures. The oxidation of NO to NO2 was a sublinear function of plasma energy. At the same input energy and at 23 °C, the oxidation efficiency was mainly determined by O2 fraction while the inlet NO concentration had smaller influence. The importance of inlet NO concentration became more pronounced at 100 °C.Analytical equations which have been previously derived to describe the plasma based removal of pollutants were not able to explain the saturation of NO removal at a certain value and relatively small influence of inlet NO concentration. The analysis of the possible reactions between nitrogen oxides and plasma species demonstrated that the presence of back-reaction NO2 + O → NO + O2 leads to the saturation of NO removal. The relative importance of O2 fraction and inlet NO concentration in the oxidation efficiency was determined by the reactions involving ozone. Based on the knowledge of most important reactions, a new analytical relationship between NO and specific input energy was derived which was consistent with the experimental findings.