Effect on remaining cations in copper ion-exchanged ZSM-5 zeolite for selective reduction of nitric oxide

Abstract

This research compared the performance between Cu/Na-ZSM-5 and Cu/H-ZSM-5 on the selective catalytic reduction of nitric oxide by propane and studied the effect of the residual cations in the catalysts. Characteristics and activities in various reactions of catalysts were investigated. From the characterization study, it was found that there is no different in structure, crytalline, surface area, acidity and coke formation between Cu/Na-ZSM-5 and Cu/H-ZSM-5. However, Cu/H-ZSM-5 has more Cu1+ than Cu/Na-ZSM-5 although the total amounts of copper in both catalysts are the same. This indicates the effect of remaining cations on the oxidation state of copper in ZSM-5 zeolites. Both steady state and unsteady state transient experiments were also tested. Since H-ZSM-5 is active for NO oxidation but is not for NO decomposition, it was suggested that oxygen prefer adsorb on H-ZSM-5 and then react with NO in gas phase to form NO2. Furthermore, NO was found to promote the hydrocarbon combustion for H-ZSM-5 catalyst. Cu/H-ZSM-5 is more active than Cu/Na-ZSM-5 for the NO decomposition. Also, NO2 was more formed and N2O was less produced in NO decomposition for the Cu/H-ZSM-5 system. The NO reduction in the presence of oxygen over Cu/Na-ZSM-5 gave more NO conversion to N2 than Cu/H-ZSM-5 system, particularly at high GHSV condition whereas Cu/H-ZSM-5 is more active than Cu/Na-ZSM-5 in the absence of oxygen reaction. Cu1+ might participate in NO decomposition and causes Cu/H-ZSM-5 is more active in the NO decomposition. Proton acid site might involve in NO2 production and causes the Cu/H-ZSM-5 system more produces NO2. Since NO2 is reduced easier than NO, the reduction with propane in the absence of oxygen would be more take place in the Cu/H-ZSM-5.