Phase transition upon K{sup +} ion exchange into Na-low silica X: Combined NMR and synchrotron X-ray powder diffraction study
- State Univ. of New York, Stony Brook, NY (United States)
- ANSTO, Menai (Australia)
The mechanism by which K{sup +} ions exchange into zeolite Na-low silica X (LSX) (Na{sub 96}Al{sub 96}Si{sub 96}O{sub 384}{center_dot}nH{sub 2}O) has ben determined by studying structures of the Na-LSX and K-LSX end members in the Na-K LSX solid solution series as well as samples exchanged at the 20%, 42% and 80% K{sup +} levels. A preliminary investigation using {sup 29}Si MAS NMR spectroscopy revealed a two-phase region in the solid solution near 80% K{sup +} exchange. Rietveld analysis of the powder diffraction data collected from hydrated samples showed that, up to 42% of K{sup +} exchange, K{sup +} ions were located preferentially at site I{prime}, just outside the double 6-ring (D6R) in the sodalite age, and at site II, above the single 6-ring (S6R) in the supercage. Introduction of K{sup +} ions into site I{prime} repositioned Na{sup +} ions into site I, at the center of the D6R. An abrupt change in the cubic lattice parameter from 25.0389(5) to 25.2086(5) {angstrom} marked the formation of a second phase at the 80% K{sup +}-exchange level as K{sup +} ions began to occupy site I. No coexistence of phases was observed for the fully K{sup +}-exchanged sample (a = 25.2486(2) {angstrom}), where sites I and II were fully occupied by K{sup +} ions.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
- OSTI ID:
- 669768
- Journal Information:
- Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 9 Vol. 10; ISSN CMATEX; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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