Plasma/catalyst system for reduction of NO_x in lean conditions

NO_x conversion to N₂ was investigated by a plasma/catalyst system in rich oxygen similar to a lean-burn engine exhaust. Catalytic activity was enhanced by the assistance of plasma, and the plasma/catalyst system showed higher NO_x conversion over a wider temperature window than did catalyst alone. The plasma/catalyst (Ag/Al₂O₃) system showed a remarkable improvement in NO_x conversion in the lower temperature range under 400 °C. The NO_x conversion of plasma/catalyst (Ag/Al₂O₃) was 40%-50%, and its selectivity to N₂ was over 96% under the conditions that the hydrocarbon (C1 base) to NO_x ratio was about 3 and 10% O₂ existed over the temperature range of 300-500 °C. Ag/Al₂O₃ showed a better performance than Al₂O₃ when assisted by plasma. Helium was used as a balance gas to measure N₂ formation by gas chromatography, and NO_x conversion was measured by a chemiluminescence NO_x analyzer in N₂ balance as well as He balance. The result in N₂ balance gas was compared with the result in helium balance gas at the 300 °C where the largest enhancement by plasma was observed. The NO_x conversion in N₂ balance gas was similar to that in helium balance gas, which verified that the plasma effect obtained in helium balance gas is consistent with that of N₂ balance gas, which is the largest component of the real exhaust gas.