Alumina-supported Pd, Ag and Pd–Ag catalysts: preparation through the polyol process, characterization and reactivity in hexa-1,5-diene hydrogenation

Abstract

Palladium and palladium–silver catalysts, supported on γ-alumina, were prepared by precipitation in a liquid polyol and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalysts were tested in the hydrogenation of hexa-1,5-diene in liquid phase, at 313 K. The addition of silver improved the hex-1-ene fractional selectivity in all cases, but lowered the catalyst activity when the Pd/Ag ratio was about unity. On the other hand a palladium-rich (Pd/Ag=4) bimetallic catalyst exhibited a very good activity and a good selectivity to hex-1-ene as well. The effects of silver addition are ascribed to the dilution of palladium atoms by silver atoms, which prevents the isomerisation of hexa-1,5-diene. Hence, the polyol method, which has been used up to now to prepare metal powders with controlled morphology, appears of interest in the elaboration of supported metal catalysts.