Pt/CeO2 catalysts with different metal particle sizes were prepared by impregnation of chlorine-free precursor, Pt(NH3)(4)(NO3)(2), with different Pt loadings (1, 3, 5, 10 wt%), on a commercial ceria. These catalysts and a CePt5 powder, which was regarded as a reference catalyst, were tested in the hydrogenation of crotonaldehyde as a function of the reduction treatment (from 473-973 K). A dramatic difference in the influence of the reduction temperature on the reactivity was observed between the high and low loaded metal catalysts: after reduction at 973 K, high selectivity to crotyl alcohol (83%) was observed on the high loaded catalyst while on the 1% Pt/CeO2, crotyl alcohol selectivity was below 35%. Characterization by TEM, XPS and XRD showed differences in the particle size distributions and the presence of various nanostructural modifications during the increase of the reduction temperature. On the other hand, the reactivity of CePt5 powder indicates no ability of this compound for the carbonyl bond hydrogenation. The different SMSI states which could influence the reactivity are discussed: formation of epitaxial Pt (1 1 1) layer on CeO2 instead of Pt-CeOx interfacial sites or CePt5 sites, has been retained to be responsible for the increase in crotyl alcohol selectivity. (c) 2005 Elsevier B.V. All rights reserved.