Plasma/Catalyst System for Reduction of NOx in Diesel Engine Exhaust

NOx reduction by a plasma/catalyst system was tested with modeled gas and real exhaust gas. Ag/Al₂O₃ was used as the catalyst. The oxidation of NO to NO₂ by the plasma was increased as HC concentration and input energy density increase. The presence of H₂O in the reactant gas led to the production of acid by plasma. The catalytic activity for NOx reduction was enhanced by the assistance of plasma especially in the lower temperature region. This activity was a little suppressed in the presence of H₂O, but the acid was not detected in the effluent gas treated by the plasma/catalyst system. The NOx conversion to N₂ was evaluated by a gas chromatography in the model gas with helium as the balance gas. The result in helium balance gas showed the selectivity to N₂ depended on the catalyst temperature and was also enhanced by the assistance of plasma. The 50% of NOx removal from the diesel exhaust gas was achieved by the plasma /catalyst system.