Pt and Ir catalysts (3% w/w) supported on Ce0.97Ru0.03O2 were synthesized and successfully tested in a low-temperature CO oxidation process. The CO oxidation was followed in-operation, by FTIR spectroscopy. The catalysts were characterized by SEM-EDS, HTEM, XRD, DRS UV–vis, XPS techniques and BET isotherms. It was found that Pt and Ir nanoparticles on Ce0.97Ru0.03O2 drastically improved the CO oxidation in comparison to CeO2, showing the best performance the Pt/ Ce0.97Ru0.03O2 system. From the FTIR studies, a route for CO oxidation was proposed. The CO oxidation pathway in Ce0.97Ru0.03O2 considers that CO was adsorbed at the Ce and Ru sites, while O2 is adsorbed on the surface oxygen vacancies, being activated by nearby Ru species. Subsequently, the activated oxygen reacts with CO linked to Ce and Ru to produce CO2. Also, Pt and Ir promotes oxygen vacancies, increasing the activation-adsorption of O2 and, consequently, the activity of the catalyst was improved.