Supported iridium catalyst was found to be highly active for NO reduction with C3H6 in a stoichiometric condition. Among the supported iridium catalysts tested here. Ir/CeO2 showed the highest activity. In order to examine the influence of CeO2 support on the catalytic performance of supported iridium, we prepared CeO2 by precipitation method using different cerium precursors. Iridium catalyst supported on CeO2 prepared by using Ce(IV) precursor (Ce(NH4)(2)(NO3)(6)) showed higher activity for NO reduction with C3H6 than that by using Ce(III) precursor (Ce(NO3)(3)center dot 6H(2)O), although the former catalyst has low BET surface area and low iridium dispersion. The activity of iridium catalyst supported on CeO2, which was prepared by using Ce(III) precursor, calcined at different temperature was also found to increase with increasing the calcination temperature of CeO2 support. The low activity of iridium catalyst supported on CeO2 calcined at 600 degrees C was considered to be due to a strong metal support interaction (SMSI) effect by the reaction gas treatment at 600 degrees C, resulting in the formation of less active Ir-CeO2 interacting species. On the other hand, the use of CeO2 calcined at higher temperatures was found to be important to obtain a catalytically active iridium species under the stoichiometric reaction condition. (C) 2011 Elsevier B.V. All rights reserved.