SAPO-34 Nuclear Composite ZeoliteImporting the Heavy Aromatic-Based Route for Light Olefins Formation in the N‑Hexane–Methanol Combined Reaction

To effectively utilize the high light olefins’ selectivity of SAPO-34 and slow down its rapid deactivation, the S34S/Z5­(ST) capsule zeolite has been prepared by the steam-assisted crystallization (SAC) technique as a promising catalyst for boosting the coupling reaction of n-hexane–methanol. The SAC technique prevents the SAPO-34 crystal skeleton from collapsing in the harsh alkaline precursor of ZSM-5. In comparison with that of ZSM-5, the S34S/Z5­(ST) illustrated a 20.6 wt % increase of light olefins’ selectivity, 17.3 wt % increase of n-hexane conversion, and a 114.3 wt % improvement of catalyst lifetime under the identical reaction conditions. The higher tetra-methylbenzene, as the highly reactive intermediate, in the extracted species of spent S34S/Z5­(ST) than that in the other spent samples suggested that the pathway for producing propylene from aromatic-based route was improved. Meanwhile, reduced PAHs in the extracted species demonstrated that the coking was slowed down. The reduction in the velocity of methanol proliferation to SAPO-34 nucleus caused by the capsule architecture could be the reason for the step-down coking.