Selective production of propylene from methanol: Mesoporosity development in high silica HZSM-5

The mesoporosity development in high silica HZSM-5 was carried out by alkaline desilication treatment and soft template method, and its relationship with the catalytic performance of the modified catalysts in methanol-to-propylene reaction was studied. High propylene selectivity (42.2%) and propylene/ethylene ratio (10.1) were observed on the high silica HZSM-5 catalyst modified by alkaline desilication. The enhanced catalytic performance can be attributed to the newly created open mesopores on the surface of the zeolite crystals together with the low Brønsted acidity. A greater amount of mesoporosity could be readily formed in HZSM-5 crystals via the soft template route. However, the mesopores formed in this method are randomly distributed in the zeolite crystals and play a minor role in the molecular transport of the reaction, so the improvement in propylene selectivity and propylene/ethylene ratio of the catalyst is less evident. The higher propylene selectivity and propylene/ethylene ratio on modified HZSM-5 (especially by alkaline treatment) than unmodified HZSM-5 could be also related to different contributions of the methylaromatics route and olefins methylation/cracking route in MTP reaction.