A method of treatment for decomposing fluorine compounds, comprising the step of contacting a gas flow containing said fluorine compounds, which comprises fluorine as a halogen element, and any of the elements carbon, nitrogen, and sulphur as a compound with said fluorine, with a fluorine compound-decomposition catalyst in the presence of steam at a temperature in the range of approximately 200 to 800°C to hydrolyse the fluorine compound in said gas flow, wherein said gas flow containing said fluorine compounds is contacted with a catalyst comprising Aℓ to convert said fluorine compounds to hydrogen fluoride.