Cu-Ce/gamma-Al2O3 catalysts promoted with Co were tested for the low temperature selective oxidation of CO in excess hydrogen. The effects of Cu-Ce composition, Co as a dopant, stoichiometric ratio (lambda = 2O(2)/CO), water vapor and CO2 on the selective oxidation of CO to CO2, O-2 consumption and selectivity of O-2 to CO oxidation as a function of temperature are presented. Also, the catalytic properties of the catalysts were investigated by using X-ray diffraction, CO-/H-2-temperature programmed reduction, temperature programmed oxidation, CO-/CO2-/H2O-temperature programmed desorption (TPD). Small addition (0.2 wt) of Co onto the Cu-Ce/gamma-Al2O3 brought large increase in selective CO oxidation activity. In the presence of either CO2 (13 vol%) or H2O (10 Vol%) in the reformed gas feed, both Cu-Ce/gamma-Al2O3 and Cu-Ce-Co/gamma-Al2O3 showed decreased activity in CO oxidation at low temperatures, especially, under 200 degreesC. Compared with the Cu-Ce/gamma-Al2O3, however, the Cu -Ce-Co/gamma-Al2O3 gives higher resistivity for the CO2 and H2O. From the CO2/H2O-TPD results, it could be explained that the main cause for the decrease in catalytic activity with CO2 and H2O in the feed may be attributed to the competitive adsorption of CO and CO, as well as the blockage of the active sites by water vapor at low reaction temperatures. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.