Selectivity to Olefins in the Hydrodechlorination of Chloroform with Activated Carbon-Supported Palladium Catalysts

This study analyzes the selectivity of Pd (1 wt %) catalysts supported on different activated carbons to produce olefins from hydrodechlorination of chloroform. It was found that selectivity to olefins was favored by a higher zerovalent to electrodeficient Pd ratio (Pd0/Pdn+) and by a lower amount of oxygen-containing surface functional groups on the activated carbon supports. Thus, the highest selectivity to olefins was obtained by catalysts supported on FeCl3- and ZnCl2-activated carbons. Conversely, the catalysts supported on KOH-, NaOH-, and H3PO4-activated carbons gave the lowest selectivity to olefins. These catalysts showed higher surface concentrations of electro-deficient Pd as well as high concentrations of oxygen functional groups that enhance the adsorption of reactants and intermediates. This leads to complete hydrogenation of reaction intermediates and poisoning of active sites by the adsorption of chlorocarbon compounds. ZnCl2-derived catalysts with the highest selectivity to olefins also showed an outstanding stability, most likely due to redispersion into very small and well-distributed Pd particles during the reaction. However, FeCl3-derived catalysts gave rise to sintering of Pd particles, resulting in a marked loss of activity.