Ceria-supported Au catalysts for selective oxidation of CO under simulated fuel processing conditions for polymer electrolyte membrane fuel cell (PEMFC) application were investigated. Fresh and used catalysts were characterized by X-ray diffraction, X-ray fluorescence and transmission electron microscopy (TEM). The influence of catalyst heat treatment, reaction temperature, gas composition and space velocity on CO conversion and CO2 selectivity has been evaluated. Air calcination at 500 degreesC resulted in the establishment of adequate interfacial metal oxide properties which are essential to promote the selective CO oxidation. CO conversion close to 100% was obtained at 120 degreesC, whereas CO2 selectivities not higher than 40% were obtained in the entire temperature range investigated (80-120 degreesC). The presence Of CO2 in the inlet stream negatively affected both CO conversion and CO2 selectivity. Both calcined and uncalcined Au/CeO2 catalysts resulted to be very stable, as demonstrated by 120h endurance tests. TEM investigation of the used catalysts revealed that a surface An particles reconstruction occurred during reaction. (C) 2004 Elsevier B.V. All rights reserved.