CO adsorption was studied on Pt and Pt-x-Mo (x = 1, 4) catalysts supported on TiO2 by means of temperature-programmed desorption (TPD) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), and significant information on the structure, arrangement, and chemical state of Pt and Mo on the TiO2 Support was obtained by a combination of XPS, H-2 chemisorption, and DRIFTS. It was concluded that the Mo oxide species forms a solid solution with Pt, while a significant part of the Pt surface atoms are screened by two-dimensional Mo oxide nanoclusters. This structural arrangement results in the modification of the chemisorptive properties of Pt, and XPS measurements show that it is partially oxidized; this oxidation state is closely related to the concentration of hydroxyl species on the catalyst's surface. TPD experiments carried out under He flow had shown that the linearly adsorbed COL species on the Pt-x-Mo/TiO2 samples desorbs at temperatures below 375 K, which is almost 100 K below the COL species desorption from Pt/TiO2. This low desorption temperature of CO was attributed to its chemical oxidation at the boundaries of the Mo oxide nanoclusters by the OH species supplied by MoO(OH)(3), which was detected by XPS as the most abundant oxidation state. In addition, the execution of TPD experiments under H2 flow resulted in the desorption of the COL species for all three samples at significantly higher temperatures, 460, 425, and 390 K, for Pt/TiO2, Pt-Mo/TiO2, and Pt-4-Mo/TiO2, respectively. © 2005 Elsevier Inc. All rights reserved.