Kinetics for the Hydrodechlorination of Chlorofluorocarbons over Model Palladium Catalysts

The kinetics for the hydrodechlorination reaction of 2-chloro-1,1,1,2-tetrafluoroethane (CF3-CFClH), 1,1-dichlorotetrafluoroethane (CF3-CFCl2), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF3-CCl3) are reported on three model catalysts: a palladium foil and two Pd single crystals of (111) and (100) orientation. The turnover rates for the hydrodechlorination of 1,1-dichlorotetrafluoroethane were similar for the three model catalysts tested, suggesting that the reaction is not sensitive to the structure of the catalyst. However, the turnover rates for hydrodechlorination of the three compounds tested are very dependent on the structure of the reactant, spanning a range of seven orders of magnitude. The experimentally determined reaction orders for the main products are about 1 in the reactant, 0.5 in H2 and -1 in HCl. The derived reaction steps based on these orders consist of the adsorption of the chlorofluorocarbon (rate determining step) and equilibrated steps between gas phase H2, gas phase HCl and adsorbed hydrogen and chlorine atoms. This chemistry is important in the manufacture of many new compounds that use hydrodechlorination as an intermediate step.