1. Facilely adjusting acidity features of zeolites by steaming treatment for enhanced methanol conversion to aromatics: A mechanism study.
- Author
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Xu, Zhenjun, Fu, Tingjun, Han, Yating, Li, Zhong, and Zhan, Guowu
- Subjects
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ZEOLITES , *ACIDITY , *ZEOLITE catalysts , *BRONSTED acids , *ALUMINUM construction - Abstract
[Display omitted] • Stability of different acid sites on ZSM-5 by steaming treatment was investigated. • Change of BASs was related to the distributed frameworks of Al and EFAl species. • The presence of EFAl and metal species improve stability of zeolitic frameworks. • Effects of steaming treatment of ZSM-5 on their MTA performance were investigated. • Reduction of Al pairs sites may suppress the hydrogen transfer aromatization process. In this contribution, the effects of the steaming treatment on the acidity and aluminum structure of ZSM-5 were systematically investigated by using different types of zeolite catalysts. The relationships between the acid properties and the catalytic performance of the methanol-to-aromatics (MTA) reaction were also elucidated. The results revealed that different kinds of acid sites showed varied stability during the steaming treatment. Especially for Brønsted acid sites (BAS), the reduction of the acid site was highly related to the stability of different distributed framework Al sites (Al single > Al pairs) and the existence of non-framework species ("neutralization" by the EFAL and ZnO). Additionally, the presence of the extra-framework aluminum (EFAl) and metal compensation ions could enhance the stability of the zeolite framework Si-O(H)-Al. Besides, it was found that the reduction degree in the content of the Zn-LAS (LAS = Lewis acid sites) was less than the Al-LAS. The effects of steaming treatment on acid properties over zeolites with different particle sizes were also explored. Furthermore, the catalytic performance for the MTA reaction showed that the stability of the ZSM-5 catalyst was significantly enhanced after the steaming treatment. Moreover, the reduction in the proportion of the Al pairs sites may inhibit the hydrogen-transfer aromatization process of alkenes, while the increase of the Al single species enhanced the cracking process of higher olefins, leading to the reduction of aromatics selectivity and the increase of light olefins selectivity, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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