Fluorinated alumina catalysts have been prepared with different fluorine content and studied by combining textural and structural characterizations (BET, Porosity, DRX), surface composition (XPS), acidity (potentiometric titration) and catalytic properties in alkylation of benzene by propylene. Impregnation by NH4F solution modifies the surface of the alumina phase, with the formation of fluoride surface species at low fluorine content and the formation of AlF3 and aluminium hydroxyfluoride as the isolated crystallites at high fluorine content. Increase of the activity with the fluorine content up to 14.5 wt % also suggests the participation of these compounds in the catalytic sites. As far as the alkylation of benzene over these catalysts are concerned the reaction was found to be highly selective toward cumene, which avoid the formation of undesirable heavy products.