Applied Catalysis A: General 390 (2010) 141–147 Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata Hydrogenation versus isomerization in the reaction of cis-2-butene-1, 4-diol over supported catalysts: The role of Group VIII transition metals in driving the products selectivity Maria Grazia Musolino ∗ , Cinzia V. Caia, Francesco Mauriello, Rosario Pietropaolo Dipartimento Mecmat, Facoltà di Ingegneria, Università Mediterranea di Reggio Calabria, Loc. Feo di Vito, I-89122 Reggio Calabria, Italy article info Article history: Received 14 July 2010 Received in revised form 4 October 2010 Accepted 4 October 2010 Available online 12 October 2010 Keywords: Supported Group VIII metal catalysts Cis-2-butene-1,4-diol hydrogenation Isomerization -Alkyl intermediate Electronic parameters abstract Silica supported Group VIII metal catalysts (Pd, Pt, Ru, Rh and Ir) have been tested at 303 K in liquid- phase reaction of cis-2-butene-1,4-diol with hydrogen at atmospheric pressure. The catalysts have been characterized by TPR, XRD and TEM. The catalytic activity changes in the order: Pd ≫ Rh > Pt > Ru > Ir. Sig- nificant differences were observed in products distribution. Ir/SiO 2 and Pt/SiO 2 favour the hydrogenation reaction to butane-1,4-diol, whereas Rh/SiO 2 , Pd/SiO 2 and Ru/SiO 2 significantly promote double bond and geometric isomerization processes, leading to 2-hydroxytetrahydrofuran and trans-2-butene-1,4- diol, respectively. Formation of products, deriving from isomerization and hydrogenation reactions, is explained on the basis of a mechanism involving a common -alkyl metal bonded intermediate and the variation in products distribution among the various metals is rationalized taking into account electronic factors. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The catalytic hydrogenation of unsaturated alcohols is of indus- trial and fundamental interest, since the reaction is generally accompanied by side processes, such as double bond migration, geometric isomerization (when a cis substrate is considered) and often C–OH hydrogenolysis [1–3]. Therefore, the achievement of a high selectivity towards a desired product is a very important chemical target. Cis-2-butene-1,4-diol was chosen as a probe molecule to study liquid-phase hydrogenation of unsaturated alcohols, due to its ver- satility to give different final products [4–6]. Our investigation has focused, so far, on understanding the effect of some reaction param- eters, such as the metal particle size, the chemical nature of the support [7], and the addition of alkali and alkali earth promoters [8]. Furthermore, a kinetic study on the reaction of cis-2-butene- 1,4-diol with hydrogen in the presence of supported palladium and platinum catalysts has been also carried out, clarifying the reaction network and determining the relative kinetic parameters [9,10]. Scheme 1 displays the complex reaction mechanism of the hydrogenation of cis-2-butene-1,4-diol over supported metal catalysts, involving the formation of butane-1,4-diol, trans-2- ∗ Corresponding author. Tel.: +39 0965 875312; fax: +39 0965 875248. E-mail address: mariagrazia.musolino@unirc.it (M.G. Musolino). butene-1,4-diol, 2-hydroxytetrahydrofuran, crotyl alcohols iso- mers, deriving, respectively, from double bond hydrogenation, geometric and double bond isomerization and C–OH hydrogenoly- sis. However, a comparison of the behaviour of different supported metals towards the selectivity to the observed products shown in Scheme 1 was, so far, never investigated. On the other hand, by altering the supported metal different electronic and geometric parameters are introduced that affect adsorption and reaction; thus a wide variation in reaction rate and products distribution can occur. In this work the cis-2-butene-1,4-diol hydrogenation is exam- ined over SiO 2 supported Group VIII metal catalysts (Pd, Pt, Ru, Rh, Ir) at 303 K and atmospheric pressure, in order to highlight the role of the metal specificity towards the selectivity to different reac- tion products (hydrogenation, isomerization and hydrogenolysis derived) and that of their electronic and/or geometric peculiar- ities in driving the reaction. Complementary characterization of the catalysts by temperature-programmed reduction (TPR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) was also performed. 2. Experimental 2.1. Materials and catalysts preparation Cis-2-butene-1,4-diol (Aldrich, impurity of the trans isomer 5%), ethanol (Fluka, 99.8% analytical grade) and ultra high purity 0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.10.006