The mechanism of decomposition of N2O on Fe-ZSM-5 prepared by chemical vapor deposition was studied by step and pulse response experiments and by isotope labeling. The results show that only a very small fraction of the iron sites is taking part in the catalytic cycle. N2O deposits its oxygen atoms on these sites, the deposited oxygen atoms migrate over the iron cluster, exchange with other oxygen atoms and then desorb by recombination to O-2. On strongly dehydroxylated iron sites also a direct recombination of two oxygen atoms, which were deposited from N2O, is possible. The concentration of these sites increases after treatment of the samples at high temperatures in inert gas. The relation between the sites involved in N2O decomposition and the alpha-sites, which were first described by the group of Panov, is discussed. We can conclude that the deposition of N2O on Fe-ZSM-5 CVD catalysts creates active oxygen species on the catalyst surface (in particular, after pretreatments at high temperature), but their properties are different from those of a-oxygen. (c) 2005 Elsevier B.V. All rights reserved.