ADSORPTION OF CHCLF2 ONTO ION-EXCHANGED Z SM-5 ZEOLITES

Adsorption of CHClF2 on a series of alkali metal (Li+, Na+, K+, Rb+, C s+) ion-exchanged ZSM-5 zeolites have been studied by the analysis of adsorption isotherms and IR spectroscopy. At low temperature (273 K), physisorbed CHClF2 molecules filled up the pore of ZSM-5 zeolites wher eas the isosteric heats of adsorption were much larger than the heat o f condensation of CHClF2 irrespective of the cation incorporated in th e zeolite. It was indicated, therefore, the adsorption in these system s was governed by the dispersion force of pore wall. The microscopic c haracter of admolecules was, however, strongly affected by the electri c field of the cation. IR spectra of adsorbed CHClF2 indicated that th e C-H bond of the admolecule was oriented in the parallel direction wi th the electric field exerted by cation site, and these orientation re sulted in a decrease in the intensity of nu(C-H) band and the low freq uency shifts of nu(C-Cl) band. At high adsorption temperature (469 K), surface analysis showed that a part of adsorbed CHClF2 reacted with A l in the zeolite framework In a manner to form a surface compound cont aining F and Al atoms.