Pt/C and Pt-Ir/C catalysts with different atomic ratios were synthesized in a closed PTFE vessel by a microwave-irradiated polyol method. The characterization results indicated that the average Pt-Ir particle size changed only slightly and the face-centered crystalline structure gradually became more amorphous with increasing iridium content. The particle size could be controlled by altering the pH of the synthesis solution and the microwave heating rate. The carbon-supported catalysts and polytetrafluoroethylene were then loaded together on a foamed nickel (FN) carrier to obtain hydrophobic catalysts. The reaction mechanisms were presented for liquid phase catalytic exchange reaction, which could explain that a hydrophobic catalyst with a Pt/Ir molar ratio of 411 exhibited the best catalytic activity. Furthermore, the effect of particle size on catalytic performance was investigated. The activity of the Pt(4)Ir(1)/C/FN catalyst was enhanced by decreasing the average particle size, in the range of 2.5-3.8 nm. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.