Methods to synthesize zeolites with different crystal habits and assemble zeolite crystals into specific structures are reviewed for the rational design of zeolite particle morphologies.

In this study, zinc species were introduced into HZSM-5 zeolite supports with coffin, rod, sphere and hollow capsule morphologies by wet impregnation. The regulation of the morphology of HZSM-5 zeolite supports on modification effect of zinc, as well as subsequent catalytic activities for the methanol-to-aromatics (MTA) process were investigated by multi-technologies. The results indicated that the catalytic activities of Zn/HZSM-5 zeolite catalysts were remarkably affected by the morphology of the supports. Among the different morphologies of Zn/HZSM-5 zeolite catalysts, Hollow-IM possessed superior selectivity for aromatics (48.59%), and their catalytic activities followed the order of Hollow-IM > Sphere-IM > Rod-IM > Coffin-IM. The superior catalytic performance of Hollow-IM was attributed to the hollow capsule structure and mesoporous shell, which not only achieved a good synergistic effect between active (ZnOH)⁺ and acid sites by facilitating the formation of the highest content and uniform dispersion of (ZnOH)⁺ sites, but also increased the contact time as the primary products escaped from the hollow cavity through the Zn/HZSM-5 shell. Furthermore, this special structure promoted the faster removal of precursors of carbon deposition, as well as facilitating the diffusion and mass transfer of the reactants and products, thereby endowing Hollow-IM with enhanced catalytic stability (156 h).

The Zn species in the Zn/ZSM-5 catalyst undergo reciprocal transformation of ZnO clusters and ZnOH⁺ during the ethylene aromatization process. They then migrate to form large-grain ZnO on the outer surface, and finally lost as Zn vapor.