A comparison study on non-thermal plasma-assisted catalytic reduction of NO by C3H6 at low temperatures between Ag/USY and Ag/Al2O3 catalysts

A comparison study was carried out on non-thermal plasma (NTP)-assisted selective catalytic reduction (SCR) of NO_x by propene over Ag/USY and Ag/Al₂O₃ catalysts. Ag/USY was almost inactive in thermal SCR while it showed obvious activities in NTP-assisted SCR at 100 °C–200 °C. Although the NO_x conversion over Ag/Al₂O₃ was also enhanced at 300 °C–400 °C by the assistance of NTP, it was ineffective below 250 °C. The intermediates over Ag/USY and Ag/Al₂O₃ were investigated using in situ DRIFTS method. It was found that key intermediates in HC-SCR, such as NCO, CN, oxygenates and some N-containing organic species were enriched after the assistance of NTP. The differences in the behaviors of above intermediates were not found between these two kinds of catalysts. However, some evidences suggested that different properties of the absorbed NO_x species resulted in the distinction of SCR reactions over Ag/USY and Ag/Al₂O₃. TPD profiles of Ag/Al₂O₃ showed that nitrates formed over the catalyst were quite stable at low temperatures, which might occupy the active sites and were unfavorable to SCR reactions. The nitrates over Ag/USY were unstable, among which the unidentate nitrate species is probably contributed to the SCR reactions at low temperatures.