The electrochemical and 'in situ' FTIR techniques were employed to investigate the interaction of platinum with sulfonic acids and the carbon monoxide electro-oxidation on platinum based nanoparticles. In the first section, cyclic voltammetry (CV) and subtractively normalized interfacial fourier transform infrared reflection spectroscopy (SNIFTIRS) were combined to describe the characteristics of the adsorption and desorption processes of three sulfonic acids at a Pt surface. The 1-butanesulfonic acid, which is a hydrogenated sulfonic acid, adsorbed reversibly at the Pt (111) surface when its bulk concentration was lower than 10-2 M. The nonafluoro-l-butanesulfonic acid did not adsorb at the Pt (111) electrode surface in this concentration range. The trifluoromethane sulfonic acid irreversibly blocked the Pt (111) electrode surface. Furthermore, the cyclic voltammetry and SNIFTIRS studies demonstrated that adsorption of 1-butanesulfonic acid at a polycrystalline Pt electrode surface is much weaker than at a Pt (111) electrode. These results may indicate that Nafion® membrane which has a similar chemical composition to nonafluoro-l-butanesulfonic acid will interact weakly with a Pt catalyst surface. In the second section, infrared reflectance adsorption spectroscopy (IRRAS) was combined with stripping voltammetry to study the CO electro-oxidation on Pt based nanoparticles. This study demonstrated that CO adsorbed at the surface of Pt nanoparticles forms multiple surface states characterized by different bonding energies. These bonding states correspond to CO adsorption at different bonding sites present at the surface of Pt nanoparticles with variable sizes. The electrocatalytic properties of both a mixture of Pt and Ru nanoparticles and the Ru decorated Pt nanoparticles have also been investigated. A bifunctional mechanism for the CO electro-oxidation at these catalysts was observed. The Pt-Ru nanoparticle catalyst showed a better performance towards CO electro-oxidation as compared with the traditional Pt-Ru alloy catalysts.