Supported Pd catalysts for the hydrogenation of campholenic aldehyde: influence of the support and preparation method

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.