COMBINED MAS NMR AND X-RAY-POWDER DIFFRACTION STRUCTURAL CHARACTERIZATION OF HYDROFLUOROCARBON-134 ADSORBED ON ZEOLITE NAY - OBSERVATION OFCATION MIGRATION AND STRONG SORBATE-CATION INTERACTIONS

Na-23 MAS NMR and synchrotron X-ray powder diffraction methods have be en used to study the binding of hydrofluorocarbon-134 (HFC-154, CF2HCF 2H) in zeolite NaY. A contraction of the volume of the unit cell is ob served on gas adsorption, and the interaction of HFC-134 with the extr aframework sodium cations is so strong that extraframework sodium cati ons in the sodalite cages (site I') migrate into the supercages. These sodium cations are found on positions close to the site III' position s of zeolite NaX. Both ends of the HFC molecules are bound to sodium c ations, the HFC molecule bridging the site II and III' cations in the supercages. The strong cation-HFC interaction results in a considerabl e displacement of the sodium site II cation along the [111] direction into the supercage and an increase in the T-O-T bond angle for the thr ee oxygen atoms coordinated to this cation. A decrease in the Na-23 qu adrupole coupling constant on HFC adsorption from 4.4 to less than 2.8 MHz, for the sodium cations originally located in the sodalite cages (site I'), is consistent with the sodium cation migrations.