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 effect of coke distribution (external versus internal coke) on the deactivation behavior was investigated in methane dehydroaromatization (MDA) using benchmark metal-modified HZSM-5 catalysts. A hollow HZSM-5 capsule zeolite (HC) was facilely prepared by a one-step hydrothermal strategy with the assistance of Na₂EDTA and n-butylamine, and a commercial HZSM-5 (CZ) with a similar Si/Al molar ratio was used as a reference support. Four catalysts (Mo/HC, W/HC, Mo/CZ, and W/CZ) were synthesized via an incipient wetness impregnation method, and tested in the MDA reaction. The properties of coke species were characterized by means of the TG, TPO, HRTEM, and UV-Raman techniques, and different locations of coking over the spent catalysts were obtained. The results showed that external coke can give rise to a more severe deactivation than internal coke owing to the blockage of the pore mouths with external coke that decreased the diffusion length of feed gas in the zeolite channels. This phenomenon could be explained by the excellent catalytic stability over the hollow Mo/HZSM-5 capsule catalyst during the MDA reaction, which is associated with the lower external coke formation rate. Finally, the evolution of Mo species and coke species over the coked Mo/HC catalyst was determined by in situ UV-Raman spectroscopy during the TPO process, and the regeneration by O₂ was conducted for the hollow Mo/HZSM-5 capsule catalyst.

A facile route was developed to one-step synthesize ZSM-5 hollow microspheres. It was found that their crystallization occurred at near neutral pH with the assistance of EDTA²⁻ ions via a “crystallization in a confined space” mechanism, and the resultant sample gave an exceptional yield of aromatics with a long catalytic lifetime in the methanol-to-aromatics process.

Phosphorous modified ZSM-5 zeolites were synthesized by incipient wetness impregnation. Their performances for the methanol to aromatics conversion (MTA) were subsequently evaluated and the relationship between the catalyst structure and performance was focused on. The obtained results indicated that the introduction of phosphorous resulted in the modification of the catalyst structure characteristics and acidic properties, i.e., the reduction in the external surface area and micropore volume, the narrowing of the pore size, and the decrease in the quantity and strength of acid sites. As a result, the P/HZSM-5 catalyst exhibited the enhanced selectivity for the para-xylene (PX) in xylene isomers and xylene in aromatics, and their increase degrees were intensified with the increasing P content. The selectivity of PX in X increased from 23.8% to nearly 90% when P content was 5 wt.%. Meanwhile, the selectivity of xylene in aromatics was enhanced from 41.3% to 60.2%.