CHANGE IN BENZENE ADSORPTION WITH ACIDO-BASICITY OF (CS,NA)X ZEOLITES STUDIED BY IR SPECTROSCOPY

The existence of two benzene-adsorbed species has been shown by i. r. spectroscopy on (Cs,Na)X zeolites with various cesium loadings. They have been assigned to benzene molecules interacting either with cations (C species), within the supercage, or with the oxygen of the 12-R windows (W species). The change in the intensity of those bands with the benzene loading allowed the concentration on each site to be determined. As the cesium content of the (Cs,Na)X zeolites increases, the amount and the stability of W species compared to C species is increased, both at low and high loadings. This is related to the increase of the framework oxygen charge and to the simultaneous decrease of the cation acidity as the cesium content of the zeolite increases. In samples with high cesium content, new C-C bands at 1486 and 3015 cm** minus **1 originate from the strong CH-oxygen interaction with O//4 on both sides of the benzene plane.