Infrared spectroscopy coupled with adsorption of probe molecules such as CO and NO was used to investigate the surface adsorption properties of reduced Ru and Ru-Pt/NaY catalysts. CO adsorption at room temperature on the monometallic catalyst yielded three main bands at 2145, 2088, and 2031 cm(-1), which were assigned to CO bonded on Ru-oxidized species in close interaction with the support, a carbonyl cluster compound with Ru atoms highly coordinated with CO molecules, and CO linearly bonded on Ru-0 particles, respectively. They were not thermally stable and moved around between 1843 and 1881 cm(-1) as the temperature was increased. This new band was attributed to CO bonded in a bridge form on two Ru-0 atoms, the metal being in a different dispersion state when compared to the just-reduced catalyst. The same three bands were observed for CO adsorption on the bimetallic catalyst, in addition to the 2074 cm(-1) band, which was attributed to CO linearly bonded to Pt-0. As the temperature was raised, no CO was bonded to the bridge form on two Ru-0 atoms, probably due to the geometric effect of the presence of the second metal. NO can partially replace the CO preadsorbed species on RuNaY and Ru-PtNaY catalysts. Bands at 1943 and 1889 cm(-1) were observed and were attributed to the NO chemisorb ed on Run+ and Ru-0, respectively. Meanwhile, CO cannot displace the strongly adsorbed NO species preadsorbed on the two catalysts.