The nature of acid sites on fluorinated $gamma;-Al2O3

A study has been made of the effect of fluorination on the surface of γ-Al2O3, with reference to the influence of the amount of fluorine on the type of acid sites, their strength, and their number. The acidity has been measured by adsorption-desorption of pyridine, 2,6-dimethylpyridine, and ammonia, and by butylamine titration. It has been found that fluorinated γ-Al2O3 presents both Brønsted and Lewis sites. The total number of Lewis acid sites decreases when the fluorine content increases, whereas the number of sites with strong acidity exhibits a maximum for samples with 2–4% of fluorine content. Also the number of Brønsted acid sites presents a maximum for the same fluorine content, despite the fact that only a small fraction of the sites created by fluorination exhibit strong acidity.