Effect of framework structure of ZSM-11 and ZSM-5 zeolites on their catalytic performance in the conversion of methanol to olefins

The catalytic performance of zeolites are closely related to their framework structure and a clear understanding of such a structure-performance relationship is of great significance in revealing catalytic reaction mechanism as well as in exploring efficient zeolite catalysts. Herein, ZSM-11 and ZSM-5 zeolites with similar morphology, crystal size, textural properties and acidity were hydrothermally synthesized; the effect of their difference in the 10-ring channels on the catalytic performance in the conversion of methanol to olefins (MTO) were investigated by using various characterization techniques. The results indicate that in comparison with the straight channel of ZSM-11, the sinusoidal channel of ZSM-5 has greater diffusion resistance, which promotes the hydrogen-transfer in higher olefins, conduces to forming more polymethylbenzene species and then raises the contribution of aromatic-based cycle. In contrast, ZSM-11 with straight channel can abate the formation of polymethylbenzene species and enhance the alkene-based cycle. As a result, compared with ZSM-5-60 of similar morphology and acidity, ZSM-11-60 as a catalyst in MTO exhibits longer lifetime (98.3 h vs. 65.4 h) and higher selectivity to propene (34.6% vs. 27.4%). The insight shown in this work helps to have a better understanding of the relation between zeolite structure and catalytic performance in MTO and is then beneficial to the development of better catalysts and processes for MTO.