A Pt and Co-B bicomponent catalyst supported on TiO2 (Pt/Co-B/TiO2) is prepared by a two-step impregnation-reduction method. This Pt/Co-B/TiO2 catalyst exhibits a higher activity for CO oxidation in the absence of H-2 and for preferential CO oxidation in the presence of H-2, as compared to the Pt/Co bimetallic component catalyst (Pt/Co/TiO2) prepared by H-2 reduction. Based on the results of the X-ray photoelectron spectroscopy analysis, the CO adsorption over different catalysts and the density functional computation of Co-B, it is proposed that the electron transfer from B to Co atoms in Co-B with an amorphous structure may be responsible for the promoted oxidation of CO over Pt/Co-B/TiO2. This electron transfer can keep a high surface electron density of Pt in Pt/Co-B/TiO2 via inhibiting the electron transfer from Pt to Co atoms, which is favorable for the activation of CO species adsorbed at Pt surface. (c) 2010 Elsevier B.V. All rights reserved.