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 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. 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 σ-alkyl metal bonded intermediate and the variation in products distribution among the various metals is rationalized taking into account electronic factors.

Figure optionsDownload high-quality image (54 K)Download as PowerPoint slideResearch highlights▶ Effect of Group VIII transition metals on the activity and selectivity on the cis-2-butene-1,4-diol hydrogenation. ▶ σ-Alkyl as key intermediate explaining the products selectivity in the mechanism of the reaction. ▶ Discrimination between Pt, Ir and Ni metals favouring the hydrogenation and Rh, Pd and Ru promoting the isomerization. ▶ Relation between electronic factors and selectivity of metals.