The current research investigated N2O decompositions over the catalysts Ir/Fe-USY, Fe-USY and Ir-USY under various conditions, and found that a trace amount of iridium (0.1 wt%) incorporated into Fe-USY significantly enhanced N2O decomposition activity. The decomposition of N2O over this catalyst (Ir/Fe-USY-0.1%) was also partly assisted by NO present in the gas mixture, in contrast to the negative effect of NO over noble metal catalysts. Moreover, Ir/Fe-USY-0.1% can decompose more than 90% at 400 degrees C (i.e. the normal exhaust temperature) under simulated conditions of a typical nitric acid plant, e.g. 5000 ppm N2O, 5% O-2, 700 ppm NO and 2% H2O in balance He, and such an activity can be kept for over 110 h under these strict conditions. The excellent properties of bimetallic Ir/Fe-USY-0.1% catalyst are presumably related to the good dispersion of Fe and Iron the zeolite framework, the formation of framework Al-O-Fe species and the electronic synergy between the Ir and Fe sites. The reaction mechanism for N2O decomposition has been further discussed on the temperature-programmed desorption profiles of O-2, N-2 and NO2. (C) 2008 Elsevier B.V. All rights reserved.