Zn-P Co-Modified Hierarchical ZSM-5 Zeolites Directly Synthesized via Dry Gel Conversion for Enhanced Methanol to Aromatics Reaction

Abstract

A unique method to prepare Zn-P co-modified hierarchical ZSM-5 zeolites was developed. The ZSM-5 zeolite was directly synthesized by a dry gel conversion without adding any templates or seeds. Afterwards, the hierarchical structure was endowed to the ZSM-5 zeolite by the sequential desilication-dealumination. Zn and P species were then introduced into the hierarchical ZSM-5 zeolites by the impregnation method and their activity in methanol to aromatics process was investigated. It was found that the Zn-P co-modified hierarchical ZSM-5 zeolites possessed more Zn-related Lewis acid sites, and the ratio of Zn(OH)+/ZnO was increased. The catalytic evaluation results revealed that the benzene, toluene and xylene (BTX) and aromatics selectivity were significantly improved from 20.59% and 29.41% of pristine ZSM-5 zeolite to 28.12% and 41.88% of Zn-P co-modified hierarchical counterpart (1.5Zn0.3P/HZSM-5), respectively. Owing to the introduced highly stable Zn-P co-modified hierarchical structures, the lifetime (conversion not less than 99%) of ZSM-5 zeolite during methanol to aromatics reaction was increased from 6 h to 18 h.

Conversion of Methanol to Para-Xylene over ZSM-5 Zeolites Modified by Zinc and Phosphorus

“…In the present work, when doping P for modification, the introduced P species may cover or interact with B acids and L acids, resulting in a significant reduction in the density of B acids and L acids [ 42 , 53 ]. The addition of P had a passivating effect on the acidity of the catalyst, especially on B acids, resulting in the decrease in methanol conversion and aromatics selectivity [ 54 ]. The advantage was that, with the decrease in the concentration of strong acid sites in the HZSM-5 zeolite, the formation rate of internal coke decreased, thus enhancing the catalytic stability.…”

Novel-ordered hierarchical ZSM-5 zeolite with interconnected macro–meso–microporosity for the enhanced methanol to aromatics reaction

“…24 Therefore, the Zn species is considered to be the most suitable one due to its superior dehydrogenation, low cost, and low toxicity. 25 Inspired by the previous work, we rationally designed an ordered hierarchical ZSM-5 zeolite with interconnected macro-meso-microporosity by bottom-up confined steamassisted crystallization, in which a three-dimensional ordered macro-mesoporous carbon material (3DOMmC) with a network structure was first prepared by droppingsuction filtration. Then the obtained 3DOMmC was utilized as a hard template to synthesize the ordered hierarchical ZSM-5 zeolite.…”

“…24 Therefore, the Zn species is considered to be the most suitable one due to its superior dehydrogenation, low cost, and low toxicity. 25…”