A self-supported SS-fiber@meso-HZSM-5 core–shell catalyst via caramel-assistant synthesis toward prolonged lifetime for the methanol-to-propylene reaction

Abstract

A self-supported SS-fiber@meso-HZSM-5 core–shell catalyst was essentially designed and engineered from micro- to macro-scale by caramel-assistant hydrothermal synthesis. The significant role of caramel during the crystallization process was revealed in detail. Caramel not only created the mesoporosity in the ZSM-5 crystals, but also released acid under hydrothermal synthesis conditions which lowered the zeolite crystallinity. By taking advantage of the mesopore development in a hierarchical micro–meso–macropore structure with favourably-tuned acidic properties, such a catalyst provided a dramatically prolonged lifetime of 845 h (>90% conv.) with high propylene selectivity (e.g., 48%) in the MTP reaction. The hierarchical pore structure development mainly increased the accommodation capacity of the zeolite shell for receiving formed coke thereby leading to a dramatically prolonged lifetime in the MTP reaction.