Hydrogenation of acrolein, as a model molecule representing the alpha,beta-unsaturated aldehydes, has been studied with SiO2- and Al2O3-supported Pt and Cu catalysts. These catalysts were used to study the effects of various surface modifications. In addition to sulfurization by thiophene, the Pt/SiO2 catalysts were modified by acetylene, by inactive metal (Sn, Cu) admixture, and by gas modifiers (CO). Furthermore, the effect of modification of the surface by the reaction mixture in the initial stages of the reaction was followed. It appeared that the selectivity in the hydrogenation of the alpha,beta-unsaturated aldehydes is influenced mainly by the presence of sites on the catalysts, which activate the aldehydic oxygen and allow an easy supply of hydrogen atoms. Effect of the ensemble size is much less important. Sulfurization as performed in this paper causes only a marginal effect on selectivity. Small selectivity effects can be also caused by gas modifiers like carbon monoxide.