Abstract
The steaming of USY (ultrastable Y) zeolite at 500°C has been studied by both 27Al and 29Si n.m.r. The 29Si n.m.r. data show a progressive removal of aluminium from the zeolite framework as a function of steaming time, and XRD confirms this observation in that the unit cell size also contracts with steaming. The 27Al n.m.r. spectra of these samples contain peaks assigned to aluminium in tetrahedral (framework) and octahedral (non-framework) sites. In the first 0.5 h of steaming, the peak due to tetrahedrally bound aluminium decreased in intensity, and the peak due to octahedrally bound aluminium increased in intensity. Thereafter, the aluminium n.m.r. spectra showed no further change. This indicates that aluminium is removed from the framework but remains in a tetrahedrally bound state. Resonances due to tetrahedrally and octahedrally bound aluminium respond differently to sample treatment. Hydration is most effective in narrowing the tetrahedral resonance, while acetylacetone treatment is most effective in narrowing the octahedral resonance.
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