Platinum surfaces alloyed with an electropositive metal (e.g., Fe, Sn) are known to largely improve the selectivity in the hydrogenation of alpha, beta-unsaturated aldehydes toward unsaturated alcohols. We have investigated various adsorption modes for acrolein and prenal on the Pt80Fe20 (1 1 1) surface applying spin-polarized density-functional theory, following a similar recent study on a pure Pt (1 1 1) surface (F. Delbecq, P. Sautet, J. Catal. 211 (2002) 398). It turns out that only the existence of iron atoms in the surface layer bears the potential to influence the hydrogenation selectivity in favor of unsaturated alcohols. On the clean alloy surface there is a strong segregation of Pt atoms toward the surface layer, but a significantly higher aldehyde-adsorption energy upon the formation of O-Fe bonds can change the surface segregation profile, increasing the Fe content in the surface layer. The electronic structure changes due to O-Fe instead of O-Pt interactions will be discussed. Eventually, calculated vibrational spectra are presented as a link to experiments. (C) 2003 Elsevier Science (USA). All rights reserved.