Platinum/H-BEA zeolite and Pt/A1(2)O(3) were studied as catalysts in the vapour-phase hydrodehalogenation of chlorobenzene. Both catalysts show high activity in the hydrogenolysis of the carbon-halogen bond. Deactivation of platinum-H-BEA is ascribed to acid catalyzed oligomerization reactions and coke formation. This is supported by quantitative DSC analyses and by extraction/GC-MS experiments. Replacement of Bronsted acid sites in platinum/H-BEA by sodium ions results in a diminished coke formation and an improved stability.