Two different aluminium trifluorides (alpha-AlF3 and gamma-AlF3) of high-area have been prepared, characterised by XRPD, N-2 physisorption, IR, X-ray fluorescence, TPD and SEM techniques, and tested for the Cl/F exchange reaction of CCl2F2 (CFC-12) and CHClF2 (HCFC-22) in the gas phase. Catalyst alpha-AlF3 is more active than catalyst gamma-AlF3 for both reactions. This is due to both its higher amount of Lewis acid sites, as deduced from ammonia-TPD and pyridine FT-IR studies, and its higher TOF values, which favours the Cl/F exchange in CFC and HCFC compounds. The main products obtained are those which result from the exchange of one chlorine by one fluorine, CClF3 and CHF3 for the exchange reaction of CCl2F2 and CHClF2, respectively.