The understanding of the surface properties of supported metal and alloy nanoparticle catalysts is essential for exploiting their unique catalytic properties for fuel cell and hydrogen storage applications. This presentation discusses recent findings of an investigation of CO adsorption and oxidation on silica-supported metal nanoparticles, Au/SiO2, Pt/SiO2 and AuPt/SiO2 with controlled sizes (2-5 nm) and alloy compositions, which were prepared by molecular encapsulation and thermal treatment. The CO adsorption on the nanoparticles was characterized using an FTIR technique. The results are correlated to the electrocatalytic properties of the catalysts in fuel cell reactions. The results revealed important insights into the understanding of the relationship between the catalytic activity and the surface binding properties of the nanoparticles. The correlation between the surface composition and binding properties, along with their implications to the design of nanostructured catalysts for fuel cell and hydrogen storage applications, are also discussed.