Chromium oxide has been fluorided to several monolayers depth by interaction with HF at 625 K. The interaction of CCl3F and CCl2F2 with these surface chromium fluoride layers has been studied by temperature-programmed reaction. In the case of the reaction of CCl3F, mono- and bi-exchange occurs with, the surface monolayer fluoride, forming CCl2F2 and CClF3 simultaneously at a peak maximum temperature of 520 K. Exchange with the subsurface fluoride layers occurs at a peak maximum temperature of 680 K, as the fluoride ions from the bulk migrate to the surface and chloride ions on the surface migrate inward. In both temperature regions, mono-exchange predominates by a factor of about 10(2). Line-shape analysis of the temperature dependence of the rates of production of CCl2F2 and CClF3 gave activation energies of 53 and 54 kJ mol(-1) for exchange with the surface fluoride, so the difference in rates must be the need for special dimer-type surface, sites for the bi-exchange. The activation energy for exchange of F ions evolving from the bulk calculated by line-shape analysis is 83 kJ mol(-1) for mono-exchange and 100 kJ mol(-1) for bi-exchange. These higher values than those obtained by reaction with the surface fluoride ion derive from the added activation energy for migration of the fluoride ion from the bulk to the surface.