Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde (2-butenal) have been performed at 333 K over Cl-free Pt/ZrO2 and Pt/CexZr1-xO2 catalysts (0.2 <= x <= 0.8) after reduction under H-2 at low (473 K) and high (773 K) temperatures. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, and X-ray photoelectron spectroscopy after each reduction treatment. An important effect of the support composition on the catalytic activity was observed for both reactions. The catalytic behavior of Pt in the two test reactions studied was strongly dependent on the support composition and on the reduction temperature. For toluene hydrogenation, after reduction at 473 K, catalytic activity was higher for catalysts with no or low ceria content. Furthermore, whereas the increase in the reduction temperature hardly modified the activity of Pt/ZrO2, it strongly deactivated the catalysts with high cerium content in the support. For crotonaldehyde hydrogenation, on the other hand, increased reduction temperature produced a general increase in activity (except for the catalyst with the highest cerium content), along with an increase in selectivity toward the hydrogenation of the carbonyl bond to yield crotyl alcohol. The results are explained on the basis of the effect of partial reduction of Ce(IV) in the support. (c) 2006 Elsevier Inc. All rights reserved.