Oscillatory behaviour in nitrous oxide decomposition on over-exchanged Cu-ZSM-5 zeolite

N 2 O decomposition on over-exchanged Cu-ZSM-5 zeolite was investigated in the range of temperatures from 323 to 400°C. When only N 2 O in helium was fed, regular periodic oscillations of the outlet concentration of N 2 O were observed. Catalyst pretreatment affected the pattern of the oscillations, but not their periods or amplitudes. Also the average conversion of N 2 O to N 2 and O 2 was dependent on the initial oxidation state of the catalytic active sites, being lower when the catalyst was pretreated in oxygen. The addition of NO, O 2 or both in the feed resulted in disappearance of the oscillations and decrease of N 2 O conversion. The experimental observations are in agreement with a scheme of reactions in which N 2 O acts either as oxidizing or as reducing agent for the catalytic sites.