The hydrodehalogenation of halon 1211 over Ni, Pd and Pt supported on γ-alumina was studied. The effect of reaction temperature and hydrogen/halon 1211 input ratio was examined. Steady state catalytic activities of Pd and Pt are very similar, and much higher than that of Ni. Hydrodehalogenation over Pd favours the formation of CH₂F₂, while Pt and Ni produce primarily CH₄ and CH₃F, respectively. Product profiles suggest that the hydrodehalogenation of halon 1211 over Pd and Pt follows a reaction mechanism which is similar to hydrodehalogenation of CFC-12. Over Ni catalysts, the primary hydrodehalogenation reactions are those which first remove one halogen (Cl or Br) and then remove two halogens (one F and either Br or Cl). The higher mobility of hydrogen atom on the surface of Pt is consistent with the observation that only trace amounts of C₂₊ hydrocarbons were detected when Pt was used compared with Pd and Ni. Increasing selectivity to CH₂F₂ with time on stream over Pd and Pt is mainly ascribed to the transformation of support alumina to partially fluorinated alumina.