Conversion of halon 1211 has been studied over γ-Al₂O₃ and supported 0.5% Pd catalysts (Pd/Al₂O₃, Pd/fluorinated Al₂O₃, Pd/AlF₃, Pd/Al₂O₃ pretreated with CH₄ and CHClF₂). The experiments were performed in the temperature range of 443–523 K, in a tubular alumina reactor. The temperature of the reactor was maintained uniformly by a three zone furnace. The reaction products were quantified with a micro gas chromatograph and identified with a gas chromatograph–mass spectrometer. The catalysts were characterised with XRD diffractometry and the content of halogen on the catalysts was determined with an ion chromatograph. The measurements were presented in terms of the conversion of halon 1211 and product selectivity, as functions of catalyst type, catalyst time on stream and composition of inlet gases. Transformation of Pd to Pd carbide is observed in the CH₄ treated Pd/Al₂O₃, but not in the CHClF₂ treated Pd/Al₂O₃ in which case Al₂O₃ was partially fluorinated. In the absence of hydrogen, the conversion of halon 1211 over Al₂O₃ and Pd/Al₂O₃ gives a similar product profile and the reactions follow a heterogeneous halogen exchange reaction pathway, which takes place on the positively charged aluminum ions. Introduction of hydrogen has no apparent effect on either halon 1211 conversion level or the product profile during the conversion of halon 1211 over Al₂O₃. Over supported Pd catalysts, major products are hydrogenated species which include CH₂F₂, CH₄, C₂H₆, C₃H₆, CH₃Br and CHF₃. The most striking feature of the hydrodehalogenation reactions is the increasing CH₂F₂ selectivity with time on stream, especially on Pd/Al₂O₃ and the CH₄ treated Pd/Al₂O₃. The changing selectivity during the catalytic hydrodehalogenation reactions is mainly ascribed to the interaction of support with Pd.