Journal of Molecular Catalysis A: Chemical 169 (2001) 235–246 Crotonaldehyde hydrogenation over clay-supported platinum catalysts István Kun a,b , György Szöllösi a , Mihály Bartók a,b,∗ a Organic Catalysis Research Group of the Hungarian Academy of Sciences, H-6720 Szeged, Dóm tér 8, Hungary b Department of Organic Chemistry, University of Szeged, H-6720 Szeged, Dóm tér 8, Hungary Received 2 March 2000; received in revised form 13 April 2000; accepted 5 December 2000 Abstract Two clay-supported platinum catalysts were prepared by impregnation and tested in the liquid phase hydrogenation of crotonaldehyde. Over both catalysts, the unsaturated alcohol selectivity was increased (to 49%) compared to that obtained over platinum on conventional supports (maximum 20%). The effect of the solvent, the subtrate initial concentration, the hydrogen pressure and the reaction time was studied. The benefic effect of the support was observed only if an alcohol was used as solvent. A deuterium tracer study revealed the coaction of the Lewis acid sites of the clay supports in adsorption of the substrate leading to an increase in the crotyl alcohol selectivity. The self poisoning of the metal over the clay-supported catalysts was supposed to inhibit the C=C group hydrogenation. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Hydrogenation; Crotonaldehyde; Crotyl alcohol; Clay-supported platinum; Lewis acid sites; Self-poisoning; Deuterium distribution 1. Introduction The hydrogenations of unsaturated carbonyl com- pounds belong to the most important reactions in the synthesis of fine chemicals used in the production of pharmaceuticals, flavorings and perfumes [1]. This is confirmed by the increasing efforts devoted to find new systems able to produce one of the products in high yields [2,3]. As shown in Scheme 1, the hydrogenation of these substrates (A) gives two semi-hydrogenated products: the saturated carbonyl compound (B) and the unsaturated alcohol (C) which can be further hy- drogenated to the saturated alcohol (D). Depending on the reaction conditions side products may form by de- hydration of the alcohol, condensation of the carbonyl compounds or reaction with an alcoholic solvent lead- ∗ Corresponding author. E-mail address: bartok@chem.u-szeged.hu (M. Bart´ ok). ing to acetals. From these products the most difficult to obtain, especially in the case of ,-unsaturated carbonyl compounds, is the unsaturated alcohol. Over supported noble metal catalysts, the C=C bond is hydrogenated more easily than the C=O bond. Several attempts have been made to develop suitable heterogeneous catalytic systems able to hydrogenate selectively the carbonyl group. The studies on selec- tive hydrogenation of ,-unsaturated aldehydes have been recently reviewed by Gallezot and Richard [4]. As these studies revealed, forcing the substrate molecule to a preferential adsorption through the C=O group or hindering the adsorption through the C=C group will increase the selectivity of the unsaturated alcohol. Accordingly, high ,-unsaturated alcohol selectivities were obtained by using: (i) catalysts with low metal dispersion, (ii) bimetallic catalysts or al- loys, (iii) metal salts or organometallic compounds as Lewis acid additives, (iv) alkali metal ion promoters, 1381-1169/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S1381-1169(00)00566-5