Conversion of dilute nitrous oxide (N2O) in N2 and N2–O2 mixtures by plasma and plasma-catalytic processes

Abstract

A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma and plasma-catalytic conversion of dilute N₂O in N₂ and N₂–O₂ mixtures at both room and high temperature (300 °C). The effects of catalyst introduction, O₂ content and inlet N₂O concentration on N₂O conversion and the mechanism involved in the conversion of N₂O have been investigated. The results show that N₂O in N₂ could be effectively decomposed to N₂ and O₂ by plasma and plasma-catalytic processes at both room and high temperature, with much higher decomposition efficiency at 300 °C than at room temperature for the same discharge power. Under an N₂–O₂ atmosphere, however, N₂O could be removed only at high temperature, producing not only N₂ and O₂ but also NO and NO₂. Production and conversion of N₂O occur simultaneously during the plasma and plasma-catalytic processing of N₂O in a N₂–O₂ mixture, with production and conversion being the dominant processes at room and high temperature, respectively. N₂O conversion increases with the increase of discharge power and decreases with the increase of O₂ content. Increasing the inlet N₂O concentration from 100 to 400 ppm decreases the conversion of N₂O under an N₂ atmosphere but increases that under an N₂–O₂ atmosphere. Concentrating N₂O in the N₂–O₂ mixture could alleviate the negative influence of O₂ by increasing the involvement of plasma reactive species (e.g., N₂(A³Σ_u⁺) and O(¹D)) in N₂O conversion. Packing the discharge zone with a RuO₂/Al₂O₃ catalyst significantly enhances the conversion of N₂O and improves the selectivity of N₂O decomposition under an N₂–O₂ atmosphere, revealing the synergy of plasma and catalyst in promoting N₂O conversion, especially its decomposition to N₂ and O₂.