Surface acidity and catalytic activity of mixed Fe-Al and Cr-Al pillared montmorillonites

Abstract

The incorporation of transition metal oxide pillars such as those of iron and chromium along with Al₂O₃ pillars within the interlayers of a montmorillonite clay is investigated. The surface acidity of these catalysts has been evaluated for the first time employing the equilibrium adsorption of an electron donor, perylene, and the results are compared with those obtained by temperature programmed desorption of ammonia. The principle is based on the ability of a catalyst surface site to accept a single electron from an electron donor like perylene to form charge transfer complexes and the amount of adsorbed species

is measured quantitatively by UV-vis spectroscopy. Finally, an attempt has been made to correlate the acidity determined by the two independent methods and the catalytic activity of present systems in the benzoylation of toluene with benzoyl chloride. Incorporation of Fe and Cr has changed the properties of Al pillared montmorillonite. Fe pillared systems have been found to be very good catalysts for benzoylation reaction.