Zeolites synthesized in nonalkaline fluoride media are characterised by129Xe and27Al n.m.r. spectroscopy. In gallium MFI, the element is present in the framework. As in the case of aluminum, the xenon chemical shift at zero concentration depends only on the Si/Ga ratio. For samples with less than 4 Ga/u.c. overall, the distribution is heterogeneous (the crystallite core is Ga-rich). The presence of highly positively charged nonframework AlNFinteracting strongly with the xenon is demonstrated in a Beta zeolite. This has also been observed in MFI-type zeolites. In this latter case, the charge on the AlNFdecreases with the AlNFconcentration as a result of the formation of probably more polymerized species. © 1991 Butterworth-Heinemann.
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