In this work, well-defined silica-supported Pt and PtSn catalysts were prepared by surface organometallic reactions and were characterized by EXAFS-XANES at the Pt L-2,L-3 edge and XPS of the Pt 4f and Sn 3d levels. These catalysts were tested in the catalytic hydrogenation of cinnamaldehyde in the liquid phase. XPS results showed that in PtSn-OM* (not having butyl groups anchored on the surface), tin was present as Sn(0) adatoms "decorating" the metallic surface, isolating Pt atoms; in the PtSn-OM catalyst (Bu groups remain grafted on the surface), tin was found in the form of Sn(0) and Sn(II, IV) in similar proportions. EXAFS experiments do not provide evidence of the existence of PtSn alloys in any of these systems. In the bimetallic PtSn-BM systems, it was possible to observe by XPS that tin was found in the form of Sn(0) and Sn(II, IV). EXAFS experiments, in this case, allowed us to demonstrate the existence of a PtSn alloy diluting metallic Pt atoms. In tin-modified systems, when a fraction of ionic tin is present, the activation of the C=O group of the cinnamaldehyde is favored, increasing the selectivity to UOL. An increase in the number of Pt 5d holes measured by Pt-L-2,L-3 XANES could be indicating as a d --> s, p rehybridization process in the PtSn 3D small nanoclusters present in PtSn-BM catalysts.