The deactivation behavior of Pd catalysts on different supports in the hydrodechlorination of chloropentafluoroethane (CF3CF2Cl) was investigated. Changes of the BET surface area and the metal percentage exposed, measured by a multipurpose in situ catalyst characterization system during the reaction, gave some information about the deactivation mechanism of the Pd catalysts. The deactivation of the Pd catalysts was mainly caused by sintering of Pd particles rather than by coking. The sintering of Pd particles on the catalyst surface was promoted by the reaction of hydrogen fluoride with the support of the catalysts.