Hydrodechlorination reactions of 2-chloro-1,1,1,2-tetrafluoroethane and chloroethane in H2 and D2 on Pd catalysts Original Research Article

Deuterium isotope exchange was employed to investigate some of the reaction steps for the hydrodechlorination of CF3CFHCl and CH3CH2Cl on supported Pd catalysts. Hydrodechlorination rates for both compounds using D2 or H2 were identical. It is concluded that H or D species are not involved in the rate-determining step of the hydrodechlorination reaction. Experiments using a combined H2 and D2 feed for hydrodechlorination of CF3CFHCl showed that CF3CFH2 was preferentially formed over CF3CFHD. This experimental observation can be explained by isotope effects and is consistent with gas phase H2 in equilibrium with adsorbed H and a reaction step consisting of the combination of surface adsorbed CF3CFH species with adsorbed H. Deuterated product distributions of CF3CFHCl and CH3CH2Cl hydrodechlorination experiments with D2 were analyzed to explore the reaction steps beyond the kinetically relevant steps. The main product of CF3CFHCl hydrodechlorination was CF3CFHD, showing that the CCl bond is preferentially broken. In the case of CH3CH2Cl, substantial CH bond breaking accompanies the initial CCl scission. Deuterium exchange experiments with ethane on Pd/C and Pd/ZrO2 were also investigated and the results indicate that the CH3CH2Cl product distribution is not caused by re-adsorption and subsequent exchange reaction of ethane.