Direct decomposition of nitrous oxide (N2O) on noble metal catalysts supported on alumina was examined in the presence of oxygen. The iridium catalysts supported on alumina showed higher activities than the other noble metal catalysts. Although the catalyst activity was affected by oxygen formed by N2O decomposition at lower temperatures, desorption of oxygen proceeded promptly at the temperature > 350 degrees C, and the catalytic activity was recovered by increasing the reaction temperature from 350 to 400 degrees C. Therefore, the Ir/Al2O3 catalyst can be used for N2O decomposition in the presence of oxygen at relatively higher temperatures. (C) 2007 Elsevier Ltd. All rights reserved.