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Comparison of mesoporous SSZ-13 and SAPO-34 zeolite catalysts for the methanol-to-olefins reaction

Paper ID Volume ID Publish Year Pages File Format Full-Text
54688 47020 2014 9 PDF Available
Title
Comparison of mesoporous SSZ-13 and SAPO-34 zeolite catalysts for the methanol-to-olefins reaction
Abstract

•Methods to improve stability SSZ-13 and SAPO-34 in MTO explored.•Silylation improves methanol conversion capacity of mesoporous SSZ-13.•Not possible to prepare mesoporous SAPO-34 with mesoporogen C22-4-4Br2, successfully employed to obtain mesoporous SSZ-13.•Mesoporous (organosilane-derived) SAPO-34 has similar methanol conversion capacity as microporous SAPO-34.•Coke formation in SAPO-34 slower than in SSZ-13 due to weaker Brønsted acid sites.

Several approaches to improve the catalytic performance of SSZ-13 and SAPO-34 for application as acid catalysts in the methanol-to-olefins (MTO) reaction were explored. Silylation of mesoporous SSZ-13 with a Si/Al ratio of 20 zeolite resulted in increased lifetime in the MTO reaction. Lowering the acidity of SSZ-13 by increasing the Si/Al ratio to 50 also increased the lifetime. The generation of additional mesoporosity in SSZ-13 with a Si/Al ratio of 50 by use of the organosilane octadecyl-(3-trimethoxysilylpropyl)-ammonium chloride (TPOAC) only resulted in a minor improvement of the lifetime. Attempts to synthesize mesoporous SSZ-13 at high Si/Al ratios by use of (C22H45N+(CH3)2C4H8N+(CH3)2C4H9)Br2 (C22-4-4Br2) were unsuccessful, and instead ZSM-5 zeolite was obtained. Similarly, SAPO-34 could not be made hierarchical by using C22-4-4Br2 as a mesoporogen. In this case, other AlPO-phases were obtained. Mesoporous SAPO-34 was synthesized by using TPOAC in the synthesis gel. The additional intracrystalline mesoporosity did not lower the deactivation rate of SAPO-34 as was earlier observed for SSZ-13. The total methanol conversion capacity per acid site for microporous and mesoporous SAPO-34 were however comparable. The lower acidity of the acid sites in SAPO-34 led to the complete utilization of the micropore space. This is to be contrasted to SSZ-13 zeolite, for which the increased rate of coke formation results in more extensive coking deactivation and underutilization of the micropore space.

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Keywords
SAPO-34; SSZ-13; Methanol-to-olefins; Stability; Hierarchical zeolites
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Comparison of mesoporous SSZ-13 and SAPO-34 zeolite catalysts for the methanol-to-olefins reaction
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 235, 15 October 2014, Pages 160–168
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
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Price was $35.95
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Price after discount Only $4.95
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