Study of Ion-Exchanged Microporous Lithosilicate Na–RUB-29 Using Synchrotron X-Ray Single-Crystal Diffraction and 6Li MAS NMR Spectroscopy
✍ Scribed by So-Hyun Park; Martin Kleinsorge; Clare P. Grey; John B. Parise
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 385 KB
- Volume
- 167
- Category
- Article
- ISSN
- 0022-4596
No coin nor oath required. For personal study only.
✦ Synopsis
Synchrotron X-ray single-crystal diffraction analyses revealed that as-synthesized and Na-exchanged RUB-29 (Cs 1Àx , Na x ) 14 Li 24 [Si 72 Li 18 O 172 ] . yH 2 O ðx ¼ 0; 0:9Þ displays the lattice symmetry I222. With increasing ion-exchange time, the Na cations preferentially replace Cs in the larger sites located at the intersections of the 10MR/10MR/8MR channels. The smaller Cs sites are then replaced. While Na cations are easily incorporated on the Cs sites, most of non-framework Li cations remain in the channel system. Relocation of Li cations onto new sites within the channels was observed only after 13 days of ion exchange. Using high-field (14.1 T) NMR spectroscopy, at least six separate 6 Li resonances could be resolved for the first time by solid-state 6 Li MAS NMR spectroscopy and assigned to Li in the framework and non-framework sites of the microporous lithosilicate materials. The fate of Li in both framework and extra-framework sites during exchange was also followed by 6 Li MAS NMR spectroscopy with an Na-exchanged RUB-29 powder sample.