XE-129 NMR-STUDY OF ZSM-5 TYPE ZEOLITES - EFFECT OF CATIONIC SITES

A comprehensive Xe-129 NMR spectroscopy study on H-ZSM-5 zeolites havi ng different aluminum contents and on cation-exchanged ZSM-5 zeolites is reported. The parent H-ZSM-5 zeolites were ion-exchanged with Group I-III metal ions (K, Ca, Sr, Ba, Al, La) to varying degrees. The chem ical shift of adsorbed Xe-129 is seen to be a function of the pentasil structure of ZSM-5, of the number of free Bronsted acid sites and of the number of metal cations in the framework. Differences in the chemi cal shift of Xe-129 are seen between cations due to their different po larizing forces against xenon. The amount of cations has also an effec t on the delta(Xe-Xe) term in Fraissard's equation that may be caused by changes in the diffusional characteristics of Xe atoms in the ZSM-5 framework.