Heptamethylbenzenium cation formation and the correlated reaction pathway during methanol-to-olefins conversion over DNL-6

Methanol conversion over SAPO molecular sieve DNL-6 was investigated from the view point of the reaction mechanism. The organic materials confined in the cavities of DNL-6 were mostly polymethylbenezenes. By combination of in situ NMR study with ex situ GC-MS measurements, the structure of heptamethylbenzenium ion (heptaMB(+)) formed during MTO reaction was definitely confirmed. Further evidences from the mass spectra and C-13 solid-state NMR spectra in the isotopic switch experiments showed that the side chain methylation mechanism was the main reaction route for olefin formation from hydrocarbon pool species. (C) 2013 Elsevier B.V. All rights reserved.