Upon treatment of Sn-Pt/SiO2 catalysts with crotonaldehyde (CA) at 80 degrees C formation of Sn4+ species was evidenced by Mossbauer spectroscopy. These results have confirmed the earlier suggestion that the "reaction induced selectivity improvement" observed in the hydrogenation of CA to crotylalcohol over Sn-Pt/SiO2 catalysts is related to the formation and stabilization of ionic forms of tin in the atomic closeness to the platinum. It is suggested that in our Sn-Pt/SiO2 catalysts the formed Sn4+ species are responsible for the activation of the carbonyl group, while further hydrogenation of crotylalcohol to n-butanol is prevented by the presence of a tin enriched Sn-Pt alloy phase on which the readsorption of crotylalcohol is strongly hindered.