Selective Catalytic Reduction of no by Hydrocarbon in Oxidizing Atmosphere

Abstract

In the presence of O2, SO2, and H2O selective reduction of NO by hydrocarbon over various catalysts, especially, over copper ion-exchanged zeolite has been studied. Simultaneous presence of O2 and hydrocarbon such as ethene, propene, and propane with NO in the reactant gas resulted in the great enhancement of the catalytic activity for the removal of NO at low temperature (473–673 K). On the other hand, the addition of CO, H2, or CH4 to the NO+O2 system did not cause any selective reduction of NO. In the former selective reduction, the increment of concentration of hydrocarbon increased the conversion into N2 and expanded the active temperature region. Addition of oxygen to reactant stream is necessary to achieve the selective reduction of NO, and with Cu-MFI zeolite the maximum activity was observed in the range of oxygen concentration of 0.8–2.0%. No deterioration in the catalytic activity was observed at 573 K even after 30 h of continuous service. When SO2 or H2O was added to NO–O2+hydrocarbon gas stream, a certain decrement in the catalytic activity of Cu-MFI zeolites was observed. Within the present experiments, the activity was restored in its absence. Various metal ion-exchanged zeolites, metal loading alumina, and oxides have been screened as catalysts for the reaction and it was clarified that Cu-MFI zeolite catalysts are the most active at high SV region. The addition of copper to zeolites, alumina, and silica-alumina greatly enhanced the activities.