Hydrocarbon Selective Reduction Of NO_x In The Presence Of Excess Oxygen

The synergistic effect between dielectric barrier discharge plasmas and catalysts on NO_x removal and the reactions of the surface intermediate species in the hydrocarbon selective catalytic reduction of NO_x in the presence of excess oxygen have been investigated. The main results presented in the dissertation have been summarized as follows:1. CH₄ activation and NO conversion by different pure discharge plasmas have beeninvestigated at atmospheric pressure. The experimental results have revealed that CH4 can be effectively activated, at the same time significant amount of NO_x can be generated from N₂ and O₂ in pulsed spark discharges and streamer discharges (needle to plane); NO can be converted effectively while CH₄ can be converted little in pulsed streamer discharges (wire to cylinder) and dielectric barrier discharges (DBD, positive pulsed and ac). Using the combined DBD plasmas and In/ZSM-5 catalysts, the lower temperature activity of CH₄-SCR of NO_x has been promoted significantly. With a reacting gas mixture of 0.03% NO, 0.05% CH₄,2% O₂ in N₂, at 300 ℃ and GHSV of 7200 h^-1, the pure plasma-induced, pure catalytic and plasma-catalytic NO_x conversion percentages are 24%, 25% and 65%.2. Using the combined DBD plasmas and Co-ZSM-5 catalysts, C₂H₂ and C₂H₄ show higher catalytic activities than CH₄ (C₂H₂ is further better than C₂H₄) in the SCR of NO_x, with 0.05% NO, 15% O₂, 0.1% HC (calculated to C1) in N₂ as reacting gas mixtures, at 150-300 ℃, and GHSV=12000 h^-1. By using C₂H₂ as reducing agent, at 150 ℃ and input discharge energy intensity of 140 J l^-1, the pure plasma-induced, pure catalytic and plasma-catalytic NO_x conversion percentages are -3%, 24%, 53%. At 200 ℃, the above corresponding data are -7.5%, 34%, 67%, respectively.3. The reactions of the surface species NC_aO_bH_c, formed by the pretreatment of Co-ZSM-5 in a NO/C₂H₄/O₂ gas mixture at 275 ℃, with the NO/O₂ flow are able to produce much more N₂ than that with the individual NO or O₂ flow, which implies that the above intermediates can only be oxidized by NO+O₂ gas mixtures to the products N₂, CO and CO₂. With the hard-determined oxygen content, the average atomic ratios of N:C:H in the above surface...