The hydrodechlorination of CCl2F-CClF2 (CFC-113) was studied using silica- and activated carbon-supported Ru, Rh, Pd, and Pt catalysts. The activity of the catalysts changed with time-on-stream. Ru was most stable among the four noble metals and gave a simple product distribution yielding CClF=CF2 (CFC-1113) and CHClF-CClF2 (HCFC-123a) as main products. Over silica- supported Ru, CFC-1113 yield decreased gradually with time-on-stream but HCFC-123a yield did not change throughout the reaction, suggesting that these products were formed on different sites of Ru. XRD studies and temperature-programmed reduction of the spent catalyst revealed that the deactivation was caused by halogen-containing carbonaceous species accumulated on the Ru surface during the reaction. The carbonaceous species seemed to be formed on the active site for CFC-1113 formation. Because CFC-1113 selectivity was higher over the catalyst having higher Ru dispersion, it was assumed that the hydrodechlorination of CFC-113 is structure-sensitive and CFC-1113 formation is promoted by Ru having highly unsaturated coordination sphere. (C) 2003 Elsevier B.V. All rights reserved.