Thermal stability and siting of aluminum in isostructural ZSM-22 and Theta-1 zeolites

Conventional Si-29 and Al-27 MAS NMR techniques and Al-27 two-dimensional Multiple Quantum Magic Angle Spinning (2D MQMAS) NMR technique were used to characterize two isostructural TON type zeolites (Theta-1, ZSM-22). Nonuniform distribution of framework aluminum and the preferential population of T3 and T4 sites by the aluminum atoms in the TON material were established. The aluminum sites of Theta-1 sample showed higher thermal stability compared to ZSM-22 sample, despite of the higher aluminum content and higher calcination temperature. It was shown that Al-27 2D MQMAS NMR technique can be used for monitoring the minute differences in the surrounding of aluminum T sites, caused by the different templates and the post-synthesis treatments. (c) 2006 Elsevier B.V. All rights reserved.