Support and solvent effects on the liquid-phase chemoselective hydrogenation of crotonaldehyde over Pt catalysts Original Research Article

A study of the selective reduction of crotonaldehyde to crotyl alcohol over Pt catalysts supported on various partially reducible solids including Fe2O3, Fe3O4, ZrO2, ZnO, TiO2 and SnO2 was conducted. The catalysts were characterized by thermal programmed reduction (TPR) and reduced at temperatures that were selected as a function of the presence of specific reduction peaks for Pt in the TPR profiles. The reduced catalysts were studied by XRD spectroscopy and TEM, and used for the liquid-phase hydrogenation of crotonaldehyde. As a rule, low reduction temperatures led to catalysts providing high yields in the unsaturated alcohol (2-butenol). Such yields were substantially increased by the addition of water in mixtures with dioxane to the medium, whether the medium was acid, neutral or basic. The highest selectivity towards crotyl alcohol was obtained with the solid Pt/ZnO reduced at 175 °C. This may have resulted from the presence of ZnOxCly species forming around Pt particles, which were detected by XPS and might have acted as Lewis acid sites facilitating anchoring of crotonaldehyde via its carbonyl double bond. The optimum working conditions, which included a reaction temperature of 30 °C and an initial hydrogen pressure of 0.414 MPa, afforded a selectivity higher than 90% for crotyl alcohol at conversions in the region of 40%.