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RESEARCH PRODUCT

Aluminum-27 double-rotation NMR investigations of SAPO-5 with variable silicon content

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Summary Double-rotation NMR (DOR) studies of 27 Al species in SAPO-5, a silicon aluminophosphate molecular sieve with a one dimensional channel system, have revealed a minimum of three aluminum sites resulting from the synthesis. The DOR technique was used specifically to increase the spectral resolution by removing the broadening influences from second-order quadrupolar interactions associated with the spin 5/2 27 Al nuclei. The DOR investigations of SAPO-5 crystals with variable Si/Al ratios resulted in the identification of three aluminum species, two consistent with the reported isotropic shift values for AlPO 4 -5; however, these two resonances are only observable when small quantities of silicon are added to the synthesis. Increased substitution of silicon into the AFI framework caused the two peaks in the NMR spectra to coalesce into one resolvable resonance. The third aluminum species, observable in syntheses with only small amounts of silicon, corresponds to a condensed aluminophosphate phase similar to cristobalite.