Hydrodechlorination of carbon tetrachloride (CCl4) has been studied at various reaction temperatures, mole ratios (H-2/CCl4), and WHSVs over 1% Pt/MgO. The main factors determining conversion of CCl4 and deactivation of the catalyst were reaction temperature and H-2/CCl4 mole ratio. The optimum reaction conditions for obtaining stable and high conversions of CCl4 above 90% were the reaction temperature of 413 K, H-2/CCl4 mole ratio of 9, and WHSV of 9000 liters/kg/h. The surface area of catalyst decreased due to phase change of MgO to MgCl2 . xH(2)O during reaction. Relative to fresh catalyst, the amounts of carbon and chlorine increased and that of oxygen decreased in used catalyst, especially in deactivated catalyst. The catalyst used for the steady-state reaction did not chemisorb H-2 at room temperature, but chemisorbed nearly the same amounts of H-2 as those observed for the fresh catalyst at 373 K. From the XPS and XAFS measurements the active phase of Pt during hydrodechlorination appeared to be a surface PT(II) species with Cl ligands, While the bulk remained as Pt metal.