A 1% Pt/CeO2 catalyst prepared by the solution combustion method shows a higher catalytic activity for CO oxidation by O-2 compared to Pt metal particles. At least six hydrogen atoms are taken up per Pt at -25 degreesC. The structure of 1% Pt/CeO2 catalyst has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Rietveld refinement shows that Pt ions are incorporated into the CeO2 matrix in the form of Ce1-xPtxO2-delta solid solution. A decrease in oxygen content in 1% Pt/CeO2 is seen in relation to pure CeO2. TEM studies show that Pt is dispersed as atoms or ions and only a small amount as Pt metal particles. The Pt(4f) core level region in XPS shows that Pt is present mostly in the pt(2+) ionic state on CeO2 surface. FTIR of 1% Pt/CeO2 shows a strongly adsorbed CO peak at 2082 cm(-1) corresponding to oxidized Pt. These structural studies show that Pt ions in the catalyst are substituted for Cell ions in the form of Ce1-xPtxO2-delta, creating oxide ion vacancies leading to a strong pt(2+)-CeO2 interaction that is responsible for higher catalytic activity.