The effect of Sn addition to Pd on the selective liquid-phase hydrogenation of citral to alpha,beta-unsaturated alcohols (VA: nerol and geraniol) was examined. Pd-Sn/SiO2 bimetallic catalysts were prepared by successive impregnation method and were characterized by transmission electronic microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX), temperature-programmed reduction (TPR), Fourier transform infrared (FFIR) spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS). Sn addition to Pd/SiO2 catalysts significantly modifies their properties for citral hydrogenation performed at 130 degrees C, under 7 MPa and in isopropanol solvent, inducing a promoting effect on the VA selectivity. This promoting effect is related to the existence of a Pd-Sn interaction highlighted by EDX analysis, TPR under hydrogen and FTIR of adsorbed CO. The latter technique suggested the presence of a geometric effect on catalytic activity. Maximum VA selectivities (>75% at 30% citral conversion) were obtained when an alloy of the Pd3Sn type is formed in the bimetallic particles, as confirmed by TPR and XPS. Moreover, FTIR measurements of the adsorbed CO singleton frequency as well as XPS binding energy shifts strongly imply an electron transfer from Sn to Pd, which is proposed to be responsible for enhanced adsorption of citral C=O bond on the surface of Pd-Sn/SiO2 bimetallic catalysts. To our knowledge, it is the first time that modified Pd catalysts lead to such important UA selectivity values during alpha,beta-unsaturated aldehyde hydrogenation. (C) 2011 Elsevier Inc. All rights reserved.