Formation of Nitrogen Oxides (N2O, NO, and NO2) in Typical Plasma and Plasma-Catalytic Processes for Air Pollution Control

Effects of discharge power, O2 content, reaction temperature, catalyst introduction, and presence of NO and dichloromethane (DCM) on the formation of nitrogen oxides (N2O, NO, and NO2) by discharge in N2-O2 mixture have been systematically investigated using a dielectric barrier discharge (DBD) reactor. Results show that discharge in N2-O2 mixture always produces several to hundreds ppm of nitrogen oxides as byproducts. The production of nitrogen oxides increases with the increase of O2 content and the introduction of Al2O3 or RuO2/Al2O3 catalyst. N2O production first increases and then decreases/levels off with increasing discharge power at room temperature, but increases monotonously at 300 °C. NO and NO2 are produced only at relatively high discharge power at room temperature but are produced at all discharge power tested at 300 °C. Increasing the reaction temperature from room temperature to 300 °C significantly reduces the production of N2O but increases that of NO and NO2. The presence of hundreds ppm NO in N2-O2 mixture significantly reduces the production of N2O due to the effective quenching of the vital species for N2O formation (N2(A3Σu+)) by NO. The presence of hundreds ppm DCM, however, hardly affects the production of nitrogen oxides, demonstrating the precedence of nitrogen oxide production over DCM decomposition in N2-O2 plasma.