The selective catalytic reduction of the unsaturated campholenic aldehyde to the corresponding unsaturated alcohol, naturanol, was investigated over 2 wt.% Pd supported on different metal oxides (MeOx = SiO2, TiO2, ZnO, Fe2O3, NiO, Co3O4). Pd/MeOx catalysts have been prepared by impregnation (series I) and coprecipitation (series CP) and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and temperature programmed reduction (TPR). Results obtained in the hydrogenation of campholenic aldehyde have shown that the activity and products distribution depend both on the nature of the support and the preparation method. Regarding the catalysts of series I, palladium supported on SiO2 and TiO2 resulted totally unselective towards formation of naturanol, but, when Pd was supported on reducible metal oxides (ZnO, Fe2O3, NiO, and Co3O4), the selectivity to naturanol strongly increases. Higher selectivity values to naturanol have been obtained on catalysts of the CP series. Among these latter, the Pd/Co3O4 catalyst resulted the most selective, with a yield to the unsaturated alcohol > 85%. On the basis of characterization and kinetic data, the role of the support and of the preparation method in the catalytic behaviour of Pd catalysts for the selective reduction of the carbonyl group is discussed.
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