in order to supply pure hydrogen to proton exchange membrane (PEM) fuel cells and avoid CO poisoning, selective CO oxidation in H-2 was studied over Ce-Pt/gamma-Al2O3. Adding the Ce promoted the CO conversion and selectivity of Pt/gamma-Al2O3 with changing loading weights of Pt and Ce, oxygen concentration, residence time, and the composition of gases (H2O, CO2, and N-2). At 250 degrees C, adding H2O to the feed gas enhanced the CO, conversion due to the water-gas shift reaction. While, adding CO2 to the feed gas suppressed the CO conversion due to the reversible water-gas shift reaction. In situ BET and XRD tests showed that well-dispersed metallic Pt particles (-2 nm) existed on the Ce oxide over the alumina support, which helps to supply oxygen to the Pt for a high activity of CO oxidation and selectivity. (c) 2005 Elsevier B.V. All rights reserved.