This paper reports a study of PtSn/TiO 2 catalysts reduced at two different temperatures (473 and 773 K) by infrared spectroscopy of CO adsorbed at 298 K and XPS, as well as their behaviour in the vapour phase selective hydrogenation of crotonaldehyde at 333 K. Catalysts with 2 wt% Pt and different Pt:Sn atomic ratios were prepared by co-impregnation of a commercial TiO 2 (P25, from Degussa) with aqueous solutions of H 2 PtCl 6 and SnCl 2 Á2H 2 O. XPS results show that tin is in oxidized state when the catalysts are reduced at 473 K, whereas a proportion is in the metallic state after reduction at 773 K. The amount of surface platinum decreases when the tin loading and the reduction temperature increase. The presence of Pt-Sn alloy in the catalysts after reduction at high temperature has been assessed by in situ IR spectroscopy of adsorbed CO, although a proportion of platinum remains in a non-alloyed state. The catalytic activity in the vapour-phase hydrogenation of crotonaldehyde increases after high temperature reduction, and the same behaviour is obtained with selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol, the best selectivity being obtained for the catalyst with the lowest Pt/Sn ratio.