Generating Assembled MFI Nanocrystals with Reduced b‐Axis through Structure‐Directing Agent Exchange Induced Recrystallization

Controlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties. Herein, we report a single step, Na+‐ and porogen‐ free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b‐axis thicknes...

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Bibliographic Details
Published in:Angewandte Chemie 2021-06, Vol.133 (25), p.14078-14087
Main Authors: Zhao, Xiaoling, Zeng, Shu, Zhang, Xueliang, Deng, Quanzheng, Li, Xiujie, Yu, Wenguang, Zhu, Kake, Xu, Shutao, Liu, Jichang, Han, Lu
Format: Article
Language:English
Subjects:
Alkenes
Aluminum
Catalysts
Chemistry
Crystal structure
Crystallization
Crystals
Dimethyl ether
dimethylether-to-olefin
hierarchical architecture
Mass transport
MFI zeolite
Nanocrystals
Nucleation
Process control
Process controls
Recrystallization
reduced b-axis thickness
Selectivity
Silicon
Zeolites
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Summary:Controlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties. Herein, we report a single step, Na+‐ and porogen‐ free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b‐axis thickness (5–23 nm) and adjustable Si/Al ratios between 35 to 120, employing the commonly used tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) as structure‐directing agents (SDAs). Homogeneous nucleation driven by both SDAs and subsequent SDA‐exchange induced dissolution‐recrystallization are responsible for the formation of such structure. The enhanced textural and diffusion properties account for a notable exaggeration of propene selectivity and catalyst lifetime in dimethyl ether‐to‐olefins (DTO) conversion. This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control. Aligned plate‐shaped MFI crystals with reduced b‐axis thickness were synthesized through homogeneous nucleation followed by structure‐directing agent (SDA) exchange induced recrystallization, using tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH). The obtained materials markedly exaggerated propene selectivity and showed prolonged catalyst lifetime in the conversion of dimethyl ether‐to‐olefins.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.202017031