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(A³Σ_u ⁺)) 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.