RECu-ZSM5 samples (RE = La, Sm or Ce) have been prepared by ion-exchange of H-ZSM5 with rare earth and copper ions in 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 chracterized by N2 adsorption at 77K (BET) and XRD before and after ageing 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 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 deactived under wet conditions. The two steps 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 re-oxidation of pre-reduced Cu+ sites, and the TOF, estimated from the catalytic activity tests, has been found for both fresh and aged catalysts. * corresponding author; E-mail: pirone@irc.na.cnr.it Tel. [+39] 0817682235 – Fax [+39] 0815936936 PUBBLICATO A5055451 (PAD – 735851)