Characterization of clay-based K catalysts and their application in Friedel-Crafts alkylation of aromatics

Toluene was alkylated with benzyl chloride and benzyl alcohol using a series of clays (KSF, KSF/0, K0, KP10, K10, KS from Süd Chemie) obtained by treating a bavarian bentonite by different acids and a Hungarian bentonite (Mád) as catalysts in a batch reactor. The catalysts were characterized by chemical analysis, thermal analysis, nitrogen adsorption, solid state nuclear magnetic resonance, X-ray diffraction. The acidity of these solids was determined by infrared spectroscopy using pyridine as molecular probe. The structure, specific surface area, and distribution of Lewis/Brønsted acidity of these clays can be changed to a great extent by acidic or thermal treatment. The rate of alkylation is related to Brønsted acidity when the substrate is benzy alcohol. When benzyl chloride is used as alkylating agent, the Fe 3+ content of the clay controls the activity, and iron containing clays show high activities in spite of their low Lewis acidities.