Not only was the surface site density in a 0.78% Pt/SiO2 catalyst determined by using selective chemisorption techniques, but the surface chemistry related to decompositive N2O adsorption on the Pt surface was also described by in situ DRIFTS techniques. The “O” coverage established by N2O decomposition at 363 K on a clean Pt surface was equal to that via hydrogen adsorption at 300 K; however, both the coverage of chemisorbed oxygen via O2 chemisorption at 300 K and the COirr coverage were somewhat lower than the “O” monolayer coverage. Surface titration of the “O”-covered Pt crystallites after N2O decomposition at 363 K gave a consistent Pts density with the hydrogen chemisorption. In situ DRIFTS spectra of CO adsorbed at 300 K on both clean and H-covered Pt surfaces exhibited a strong peak at 2,076 cm(-1) for linearly adsorbed CO with a small extent of multi-coordinated CO near 1,803 cm(-1). The adsorption of CO at 300 K on an “O”-covered Pt surface via dissociative N2O adsorption at 363 K appeared subsequently a band at 2,186 cm(-1) due to a tiny amount of PtsO crystallites, which could be completely reduced to H-covered ones, when titrated with H2 at 300 K. The adequate description for these CO adsorption behaviors on different surfaces is PtsO+2CO(g)→PtsCO+CO2(g), although to very small extent, the addition onto PtsO occurs. Spectra of CO adsorbed on the oxidized Pts via N2O decomposition gave consistent surface chemistry with in situ gravimetric measurements. The surface reactions acquired by DRIFTS spectra potentially offer an approach to remove N2O from emission sources by combining its catalytic dissociation with titration of the chemisorbed “O” atoms using either H2 or CO, particularly H2 because of complete recovery to a clean Pts.