The catalytic activities of low-temperature CO oxidation and preferential CO oxidation (PROX) in rich-H-2 stream over the Pt/SiO2 and rare earth oxides modified Pt/SiO2 catalysts have been investigated. The addition ofrare earth oxide additives to the Pt/SiO2 catalyst can promote the catalytic performance remarkably. The catalytic activities for PROX are dependent on the basicities of these oxides. The higher basic strength leads to higher activity. For Pt-CeO2/SiO2, the catalytic activity depends strongly on the content of CeO2 and on the mole ratio of CO/O-2. XRD and H-2-temperature-programmed reduction (TPR) results show that the additives not only improve the dispersion of metallic Pt on the support surface, but also increase the reducibility of PtOx in Pt-CeO2/SiO2. The formation of the Pt-Ce alloy decreases the electron back-donation from the Pt 5d orbital to the 2 sigma* orbital of CO, and consequently suppresses CO-Pt bonding, resulting in the lowered CO coverage. (C) 2008 Elsevier B.V. All rights reserved.