Silica and Alumina Pd-Sn Catalysts : Correlations Between Structure and Surface Properties of the Catalysts and Their Catalytic Performances in Citral Hydrogenation

The catalytic performances of two series of silica and alumina supported PdSn were studied for the selective hydrogenation of citral. Contrary to the literature dealing with Pd-based catalysts, these bimetallic systems showed high selectivity towards the unsaturated alcohols (nerol and geraniol). Hence, this study was aimed at establishing correlations between the structure and surface properties of these materials and their catalytic performance for the hydrogenation of citral. The different characterization methods (TEM coupled with EDX, TPR and cyclohexane dehydrogenation) prove that tin is in intimate contact with palladium. Moreover, the results of FTIR studies of CO adsorption and XPS measurements indicate that the structure and surface properties of Pd are strongly affected by Sn addition. In fact, it appears that the role of the modifier on the metallic Pd surface and/or in its close vicinity is to act as Lewis acid sites (i.e. partially oxidized species) to activate the carbonyl group by interaction with a lone electron pair of oxygen (Fig. 1). The high selectivity obtained in this study could then be attributed to the formation of “Pd-Snⁿ⁺”.