The irreversible adsorption of Sn on the three Pt basal planes (Sn/Pt(111), Sn/Pt(100) and Sn/Pt(110)) and the oxidation of adsorbed carbon monoxide have been studied by cyclic and stripping voltammetry. The presence of Sn adatoms blocks the adsorption of hydrogen on platinum, and leads to the observation of a new oxidation peak ascribed to the four-electron oxidation of the Sn adatom at potentials above 0.5 V. The oxidation of adsorbed carbon monoxide is enhanced by the presence of Sn on all three Pt single crystals. On Sn/Pt(111) and Sn/Pt(110), oxidation of adsorbed CO occurs in two distinct potential regions: a pre-peak region at potentials below 0.50 V and the main peak at higher potentials. In the pre-peak, the oxidation of adsorbed CO is suggested to take place at the direct interface between Pt and Sn through the formation of an activated water species on Sn that is not observable in the blank voltammetry. In the main peak, the COad oxidation reaction is suggested to occur through the classical bifunctional mechanism of OH adsorbed on Sn with CO adsorbed on Pt atoms no adjacent to Sn atoms. On Sn/Pt(100), the "pre-peak mechanism" is not observed. (C) 2016 Elsevier B.V. All rights reserved.