Performance of ion-exchanged zeolite and metallosilicate catalysts on nitric oxide decomposition

Abstract

In this study, the decomposition of NO over metal ion-exchanged zeolite and metallosilicate catalysts was investigated. NO in an atmosphere containing propane and large excess of O₂ was selectively reduced using ZSM-5, Cu-silicate and Fe-silicate catalysts. H-form, Cu/H-form, and Pt/H-forms of all the three catalysts were used in the experiments. Experimental results revealed that the catalytic activity for the decomposition of NO was in the following order: H-form > Cu/H-form > Pt/H-form. The results also indicated that the catalytic activity for the combustion of propane of Pt/H-form was the highest followed by H-form and Cu/H-form. For the ZSM-5 catalysts, the amount of Cu ion that can be exchanged was affected by time, temperature, and pH. It was observed that at the same pH value, the amount of Cu in Na-ZSM-5 and NH₄-ZSM-5 was approximately the same and higher than that of H-ZSM-5. The catalytic activity of Cu ion-exchanged ZSM-5 catalysts for the decomposition of NO was found to be dependent on the forms of ZSM-5 used in the copper ion exchange process. Maximum conversion of each catalyst was observed during the temperature of 300-450°C. It was demonstrated, using NH₄-ZSM-5, H-ZSM-5, Na-ZSM-5, and Cu ion-exchanged catalysts, that the absence of oxygen increased the temperature for the maximum conversion of NO. The activities for NO + C₃H₈ reaction on Cu ion-exchanged ZSM-5 catalysts were affected by remaining cations, i.e., Na+, NH₄+ , and H+ in absence of O₂. The Cu/NH4-ZSM-5 catalyst having NH₄+ ion exhibited the highest activity for this reaction condition. On the other hand, the activities for the NO + C₃H₈ + O₂ system on Cu ion-exchanged ZSM-5 catalysts depended on copper content of catalysts.