Pt-based intermetallic compounds (IMCs) supported on silica were studied as a catalyst for the preferential oxidation (PROX) of CO in excess hydrogen to obtain the active catalyst at low temperatures. Pt3CO/SiO2 and PtCU/SiO2 were more active than Pt/SiO2 and Pt/Al2O3 in the temperature range of 373-453 K. Both IMC catalysts were stable during the reaction at 473 K without the irreversible segregation at surface. Infrared (IR). X-ray photoelectron spectroscopy (XPS), and adsorption measurements revealed a significant electron transfer from Pt atoms to Co or Cu atoms. The electron-deficient Pt atoms adsorbed CO weakly compared with Pt metal, accelerating the adsorption of oxygen on the IMC surface. Kinetic studies indicated that Co and Cu atoms in IMCs also adsorb oxygen. This improved oxygen adsorption likely resulted in the high PROX activity at low temperatures. The effects of hydrogen and water on the rate of CO2 formation also were studied. (C) 2008 Elsevier Inc. All rights reserved.