Effects of secondary mesoporosity and zeolite crystallinity on catalyst deactivation of ZSM-5 in propanal conversion

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Cooperative effects of secondary mesoporosity and zeolite crystallinity on the deactivation of ZSM-5 were investigated during propanal conversion. Varied secondary mesoporosities were introduced into a commercial ZSM-5 by alkaline desilication using solutions with different NaOH concentrations (0.1 -0.5 M). The results showed that the mesoporosity gradually increased with the concentration of NaOH, while the intrinsic zeolitic microporosity decreased. This indicated that the alkaline desilication for mesopore generation is a destructive technique that sacrifices the zeolite crystallinity. In propanal conversion, ZSM-5 showed a longer catalyst lifetime as the external surface area increased (or as the zeolite framework thickness decreased) in the mild desilication regime (NaOH concentration < 0.3 M). The enhanced catalyst lifetime could be attributed to the facilitated diffusion of coke precursors out of the zeolite structure. However, when the zeolite crystallinity or microporosity of ZSM-5 was decreased too much from excessively severe alkaline treatments (NaOH concentration > 0.3 M), deactivation of the catalyst became again faster. The result indicates that the crystallinity or the microporosity of ZSM-5 is also important in suppressing coke formation. This is in line with earlier reports showing that coke formation itself is a shape-selective reaction and significantly inhibited in the constrained space of the unique 10-membered micropore channels of ZSM-5. The present results imply that the generation of large mesoporosity (enhancing the diffusion of coke precursors) while keeping the zeolite crystallinity intact (suppressing coke formation by shape-selectivity) is highly desirable for designing a zeolite catalyst with an enhanced catalyst lifetime. (C) 2017 Elsevier Inc. All rights reserved.
Publisher
ELSEVIER SCIENCE BV
Issue Date
2017-06
Language
English
Article Type
Article
Citation

MICROPOROUS AND MESOPOROUS MATERIALS, v.245, pp.16 - 23

ISSN
1387-1811
DOI
10.1016/j.micromeso.2017.02.071
URI
http://hdl.handle.net/10203/224048
Appears in Collection
CBE-Journal Papers(저널논문)
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