Effects of Support Surface Composition on the Activity and Selectivity of Pd/C Catalysts in Aqueous-Phase Hydrodechlorination Reactions

Two different activated carbons were treated with nitric acid and were used as supports to prepare 0.5 wt % Pd/C catalysts. The supports were characterized by N2 adsorption, elemental analysis, X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD) in order to study the modifications in the porous structure and in the surface chemistry composition. Both XPS and transmission electron microscopy (TEM) were employed to study the dispersion of Pd on the catalysts. Oxidation of the activated carbon led to a substantial increase in oxygen surface groups, whereas the porous structure was not modified significantly. All the catalysts were tested in the hydrodechlorination of 4-chlorophenol in aqueous phase at mild conditions. It was observed that an increase in the CO2/(CO + CO2) ratio obtained from TPD of the carbon supports is accompanied by a better dispersion of Pd and an increase in the catalyst activity and the selectivity toward cyclohexanol, which is less toxic than the other products, cyclohexanone and phenol.