The acid-base properties of pure and fluorinated alumina (0.6-22 wt.%) were determined by temperature-programmed desorption of NH3 and by infrared spectroscopy (IR) of adsorbed pyridine and 2,6-dimethylpyridine. No direct correlation between total acidity of materials and catalytic activity in the alkylation of n-butene by isobutane was observed. However, a good correlation between Bronsted acidity and the catalytic activity was obtained. Indeed, the higher the overall Bronsted acidity is the higher their activity in the alkylation reaction increases. Moreover, inactive catalysts in alkylation were obtained by neutralizing selectively the Bronsted sites created by F-addition with sodium ions. From physical characterizations such as FTIR, it was proposed that the active Bronsted sites are associated to aluminium hydroxyfluorides formed during the catalysts preparation on low F-containing catalysts. (C) 2003 Elsevier B.V. All rights reserved.