The electro-oxidation of ethanol was studied on Pt and PtSn catalysts using electrochemical, in situ reflectance spectroscopy and chromatography techniques. First, the beneficial effect of tin for ethanol electro-oxidation was established by cyclic voltammetry; the PtSn catalyst activity was ahnost double that on Pt. Then, the identification of intermediates and reaction products formed was performed. The following species were detected: adsorbed CO, adsorbed CH3CO, CH3CHO, CH3COOH and CO2. Finally, a comparison of the electrocatalytic behaviour of Pt and PtSn catalysts based on data from in situ reflectance spectroscopy (SNIFTIRS and SPAIRS techniques), electrolysis and CO stripping measurements was made. It appeared that, as in methanol oxidation on a PtRu catalyst, two effects are involved in ethanol electro-oxidation on PtSn: the bifunctional mechanism and the ligand effect. The presence of tin allows ethanol to adsorb dissociatively, then to break the C-C bond, at lower potentials and with a higher selectivity than on pure Pt. It allows the formation of acetic acid at lower potentials than on Pt alone. From these results, a mechanism of ethanol electro-oxidation on Pt and PtSn catalysts was proposed. (C) 2003 Elsevier B.V. All rights reserved.