Solid-state nuclear magnetic resonance investigation of cation siting in LiNaLSX zeolites

• Published in: Microporous and mesoporous materials Vol. 26; no. 1; pp. 27 - 35
• Main Authors: Feuerstein, M., Engelhardt, G., McDaniel, P.L., MacDougall, J.E., Gaffney, T.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 16.12.1998; Elsevier
• Subjects: 23Na MAS NMR; 7Li MAS NMR; Cation location; Chemistry; Exact sciences and technology; Gas sorption; General and physical chemistry; Ion-exchange; Low-silica LiNaX; Surface physical chemistry; Zeolites: preparations and properties; Gas sorption; Cation location; 23Na MAS NMR; 7Li MAS NMR; Low-silica LiNaX; Sorption; Atomic position; Faujasite; Sodium ion; Nuclear magnetic resonance; Zeolite; Ion exchange; Experimental study; Lithium ion; Molecular sieve; Modified material
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(98)00211-X

The location of Li + and Na + cations in a series of dehydrated low-silica LiNaX zeolites (LiNaLSX, framework Si/Al ratio=1.0) were characterized by 7Li and 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Depending on the Li + content, up to three lines were observed in the 7Li MAS NMR spectra attributed to Li + cations on SI′, SII and SIII sites. The 23Na MAS NMR spectra of the pure sodium form NaLSX and of LiNaLSX samples with low Li + contents contain up to five lines belong to Na + cations located on SI, SI′, SII, and two different SIII′ sites. LiNaLSX zeolites containing more than 40% of Li + show only a single narrow line in the 23Na MAS NMR spectra attributed to mobile sodium cations. The populations of the different cation sites were determined from the relative line intensities of the MAS NMR spectra. Below about 70% Li + exchange, lithium cations are located only on sites SI′ and SII. Between 70% and 100% Li + content these sites are fully occupied by Li +, and the population of site SIII by Li + increases. It was found that the nitrogen-adsorption capacity correlates well with the occupation of Li + at site SIII.