Synergy Study for Plasma-Facilitated C2 H4 Selective Catalytic Reduction of NOx Over Ag/γ-Al2O3 Catalyst

Synergy study is of great importance to optimize the two-stage plasma-facilitated catalysis system and also necessary to gain a mechanistic understanding of the overall reaction process. In this paper, the effects of the long-lived chemical products of plasma pretreatment on the subsequent selective catalytic reduction (SCR) of NO_x at fixed and changed energy density of dielectric-barrier-discharge plasma reactor were investigated, respectively, for the aim of the synergy study of plasma- facilitated C₂H₄-SCR (PF-SCR) of NO_x over Ag/gamma-Al₂O₃ catalyst at lower temperature. For comparison, C₂H₄-SCR of NO_x over Ag/gamma-Al₂O₃ catalyst alone was also considered. Results showed that PF-SCR for NO_x removal exhibited obvious synergistic effect at 240degC, and the NO_x removal efficiency for plasma alone, C₂H₄-SCR alone, and PF-SCR were 43.6%, 6.7%, and 90.1%, respectively. In the NO/NO₂/C₂H₄/O₂/N₂ system, the long-lived chemical products of plasma pretreatment for the synergistic link between plasma and catalysis included NO₂, aldehyde (formaldehyde and acetaldehyde), and nitrogen-contained organic compounds (methyl nitrate, nitro methyl, and ethyl nitrate). Among the nitrogen-contained chemical products of plasma pretreatment, the major synergistic link between plasma and catalysis was NO₂ at lower input energy density, transferred to the mutual action of NO₂ and nitrogen-contained organic compounds over catalyst at higher input energy density.