Distribution of cations in lanthanum-exchanged NaY zeolites

Abstract

The locations of the exchangeable cations of partially La-exchanged NaY zeolites (Si/Al = 2.29) in dehydrated and rehydrated states have been determined using powder X-ray diffraction and 129Xe NMR and from the isotherm of adsorbed xenon.Most the La3+ ions in LaNaY tend to migrate irreversibly from supercages into sodalite cages or hexagonal prisms, while the Na+ ions prefer to stay in the supercages after sample dehydration treatment at 350 °C. Sites I and II are occupied by La3+ and Na+ ions, respectively, while both Na+ and La3+ ions are located at site I'. The amount of La3+ ions in sodalite cages increases with the increase of La content and the readsorption of water. The occupancy of Na+ ions at site II was found to decrease with increasing degree of La exchange from both X-ray diffraction studies and from the xenon adsorption isotherm. 129Xe NMR results indicate that the nature of intersupercage void space is similar for LaNaY and NaY.