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

Silica supported Group VIII metal catalysts (Pd, Pt, Ru, Rh and Ir) have been tested at 303K 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: PdRh > Pt > Ru > Ir. Significant differences were observed in products distribution. Ir/SiO2 and Pt/SiO2 favour the hydrogenation reaction to butane-1,4-diol, whereas Rh/SiO2, Pd/SiO2 and Ru/SiO2 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.