Mixed domain models for the distribution of aluminum in high silica zeolite SSZ-13

High silica zeolite SSZ-13 with Si/Al ratios varying from 11 to 17 was characterized by aluminum-27 and silicon-29 NMR spectroscopy. Aluminum-27 MAS and MQMAS NMR data indicated that in addition to tetrahedral aluminum sites, a fraction of aluminum sites are present in distorted tetrahedral environments. Although in samples of SSZ-13 having high Si/Al ratios all aluminum atoms are expected to be isolated, silicon-29 NMR spectra revealed that in addition to isolated aluminum atoms (Si(1Al)), non-isolated aluminum atoms (Si(2Al)) exist in the crystals. To model these contributions of the various aluminum atoms, a mixed-domain distribution was developed, using double-six membered rings (D6R) as the basic building units of SSZ-13. A combination of different ideal domains, one containing isolated and the other with non-isolated aluminum sites, has been found to describe the experimental silicon-29 NMR data.