T. Kodaira, T. Ikeda
Jul 12, 2010
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Journal
Journal of Physical Chemistry C
Abstract
To elucidate the properties and roles of tetramethylammonium (TMA+) ions acting as a structure-directing agent (SDA) on the synthesis of ZK-4 zeolites having the LTA framework, as-synthesized ZK-4’s with Si-to-Al atomic ratios (Si/Al) between one and three were characterized with SEM, TG-DTA, CHN gas chromatography, 1H−13C CP/MAS NMR, powder XRD, and Raman spectroscopy. From the TG-DTA and the CHN gas chromatography measurements, the number of TMA+ ions per pseudounit cell (a ∼ 1.2 nm) increases up to two with the increased Si/Al ratio. After the selective occupation of the TMA+ ion in the β-cage at low Si/Al ratio, TMA+ ions start to occupy the α-cage at Si/Al ∼ 1.4. The actual structure of TMA+ ions in β-cages was directly determined by the Rietveld analysis of the obtained XRD data. The β-cage is stabilized and supported by bare TMA+ ions, i.e., no water molecules in β-cage. The electron density distribution images obtained with the MPF analysis of the XRD data revealed that electron density of TMA+ io...