Abstract
The hydrothermal dealumination of zeolite Y was followed by 29 Si and 27 Al MAS NMR. From deconvoluted MAS NMR spectra the amount of the different silicon and aluminium species, formed during steaming, could be determined. Next to well documented 27 Al signals at 60 ppm of tetrahedral framework Al and at 0 ppm of octahedral Al, lines at 50 ppm, 30 ppm and in the region of 4–0 ppm are observed, the chemical nature of which is discussed. Zeolite Y with framework Si/Al ratio from 3.5 to 17 contains non-negligible amounts of extra-framework silicon and aluminium species, which complicate the determination of the framework Si/Al and non-framework:framework Al ratios. A considerable amount of extra-framework aluminium is missing in the 27 Al MAS spectra. This ‘NMR-invisible’ aluminium, assigned to oligomeric alumina species, can be made ‘NMR-visible’ by complexation with acetylacetone under specific conditions.
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