Solid-conversion synthesis of three-dimensionally ordered mesoporous ZSM-5 catalysts for the methanol-to-propylene reaction

A facile synthesis of hierarchical ZSM-5 with the three-dimensionally ordered mesoporosity (3DOm ZSM-5) was achieved by solid conversion (SC) of SiO₂ colloidal crystals to high-crystalline ZSM-5. The products of 3DZ5_S/C and 3DZ5_S, which were severally transformed from the carbon-padded SiO₂ colloidal crystals and the initial SiO₂ colloidal crystals, exhibited not only a similar ordered structure and acidity but also higher crystallinity and more balanced meso-/micropore combination in comparison with 3DZ5_C obtained by the conventional confined space crystallization approach. All three synthesized 3DZ5 catalysts showed improved methanol-to-propylene performance than the commercially microporous ZSM-5 (CZ5), embodied in five times longer lifetime, higher propylene selectivity and S_propylene/S_ethylene ratio (P/E), and superior coke toleration with lower formation rate of coke (R_coke). Moreover, the 3DZ5_S catalyst in situ converted from SiO₂ colloidal crystals presented the highest selectivities of propylene (42.51%) and light olefins (74.6%) among all three 3DZ5 catalysts. The high efficiency in synthesis and in situ utilization of SiO₂ colloidal crystals demonstrate the proposed SC strategy to be more efficiently and eco-friendly for the high-yield production of not only 3DOm ZSM-5 but also other types of hierarchical zeolites.