Mechanistic study of the preferential CO oxidation was carried out over a Pt(1.0 wt.%)/NaY zeolite catalyst from 300 to 523 K by combination of kinetics and spectroscopy. The mechanism of CO oxidation at 300 K was proposed on the basis of spectroscopic study, and the activity at low temperatures was assumed to originate from small Pt clusters. The analysis of XPS and TEM revealed that metallic state of Pt was rather stable after the reaction. The kinetics suggests a Langmuir-Hinshelwood mechanism in the oxygen-limited low-rate branch (O-2 adsorption/dissociation is strongly depressed by adsorbed CO), being responsible for CO oxidation in H-2-rich gas in the temperature range of 423-523 K. In situ DRIFT spectra show that the Pt surface is dominated by linearly bound CO species, and the presence of H-2 leads to a significant red-shift of the C-O stretch frequency, which indicates a H-ad-induced modification of the Pt CO bond, not just a coverage-dependent frequency shift. Consequently. CO oxidation was significantly enhanced in H-2-rich gas. (C) 2011 Elsevier Inc. All rights reserved.