Enhancement of hydrothermal stability of Cu-ZSM5 catalyst for NO decomposition

Abstract

RECu-ZSM5 samples (RE = La, Sm or Ce) have been prepared by ion-exchange of H-ZSM5 with rare earth and copper ions in an aqueous solution both simultaneously and consecutively (RE before copper), and their physico-chemical and catalytic properties in NO decomposition have been compared with those of a Cu-ZSM5 with a similar copper content. The catalysts have been characterized by N2 adsorption at 77 K (BET) and XRD before and after aging cycles under wet (2–2.5 vol % H2O) conditions at 450–500°C. NO decomposition tests have been carried out in a fixed bed reactor at 450°C under dry or wet conditions on both fresh and aged catalysts. NO adsorption tests have been performed at 120°C on the same samples. The addition of RE does not affect the crystalline structure, surface area, and porosity but strongly enhances the catalytic activity and the hydrothermal stability of Cu-ZSM5, which, on the contrary, is completely deactivated under wet conditions. The two-step exchanged catalysts provide better performances likely due to the larger RE exchange level obtained with this method. A unique linear correlation between the amount of N2O produced in the NO adsorption tests, related to the reoxidation of prereduced Cu+ sites, and the TOF, estimated from the catalytic activity tests, has been found for both fresh and aged catalysts.