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

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Conventional 29Si and 27Al MAS NMR techniques and 27Al 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 27Al 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.