Dealumination of zeolites with silicon tetrachloride vapour. Part 6.—Zeolites Li, Na-X and Li, Na-Y

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Abstract
The reaction of zeolites Li, Na-X and Li, Na-Y with SiCl4 vapour has been examined by IR spectroscopy, 29Si and 27Al magic-angle-spinning NMR (MAS NMR), X-ray diffraction and atomic absorption spectrophotometry. The aim was to prepare a fully crystalline and highly siliceous polymorph of silica with the faujasite structure. This can be achieved in single step when the starting material is the lithium form of zeolite Y. However, zeolite Li, Na-X cannot be similarly dealuminated with SiCl4 vapour. The reason for this is not the ‘screening’ of the framework by the charge-balancing cations, as previously suggested, but the presence in the framework of zeolite X of six-membered rings containing three aluminium atoms.