Selective production of para-xylene and light olefins from methanol over the mesostructured Zn–Mg–P/ZSM-5 catalyst
The mesostructured Zn–Mg–P/ZSM-5 catalyst has been fabricated for direct conversion of methanol to p-xylene and light olefins (C2=–C4=). The Zn-modified ZSM-5 zeolites afford the main activity for methanol aromatization. The subsequent Mg–P co-modification improves the shape-selectivity towards p-xylene and promotes the production of light olefins, by partially blocking the pore-openings and strongly passivating the acidity. Inevitably, the catalyst activity is diminished during the modification process. To enhance the mass transfer and increase the overall reactivity, additional mesoporosity has been incorporated into the catalyst by desilication. The combination of mesoporous zeolite structure and Zn–Mg–P modification endows the catalyst with an efficient and stable catalytic performance, yielding ca. 19 wt% p-xylene (>90 wt% para-selectivity) and ca. 46 wt% light olefins with a nearly complete methanol conversion in a 50 h reaction. This work also provides a strategy to compensate for the reduced activity and deteriorated stability of the modified catalysts in shape-selective reactions.