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The impact of zeolite pore structure on the catalytic behavior of CuZnAl/zeolite hybrid catalysts for the direct DME synthesis

Paper ID Volume ID Publish Year Pages File Format Full-Text
40242 45848 2013 10 PDF Available
Title
The impact of zeolite pore structure on the catalytic behavior of CuZnAl/zeolite hybrid catalysts for the direct DME synthesis
Abstract

•Six 10-ring pore zeolites (ZSM-5, FER, IM-5, TNU-9, MCM-22, ITQ-2) studied.•Zeolite pore structure influences performance of hybrids in syngas-to-DME.•Extent of deactivation increases with amount of surface aluminum and external area.•Deactivation of hybrids related to CuZnAl-zeolite interactions.

In this work, the influence of the pore structure of 10-ring zeolites used as the methanol dehydration function in CuZnAl(CZA)/zeolite hybrid catalysts was studied for the direct dimethyl ether (DME) synthesis. To this purpose, six different 10-ring H-zeolites (ZSM-5, FER, IM-5, TNU-9, MCM-22, ITQ-2) with alike bulk Si/Al ratios (in the 9–14 range) were employed. Additionally, the effect of crystallite size (for ZSM-5) and selective surface dealumination by treatment with oxalic acid (for MCM-22) was also investigated. While the initial activity of the zeolites for methanol dehydration was driven by the concentration of strong Brønsted acid sites, the extent of decay was dictated by the pore structure, which determined the amount and nature of the formed carbon species. When evaluated for direct DME synthesis under methanol synthesis-controlled conditions, all CZA/zeolite hybrid catalysts (prepared by grinding, CZA:zeolite mass ratio of 2:1) experienced a decline of CO conversion (and DME yield) with time-on-stream (TOS) due to a gradual loss of the methanol synthesis activity of the Cu-based component. Interestingly, the stability with TOS was the lowest for the hybrid catalysts comprising zeolites with large external surface areas (Sext) such as ITQ-2 and MCM-22. Moreover, for zeolites with similar Sext, the deactivation extent of the hybrid catalysts increased with the concentration of surface Al species (from XPS) in the zeolite. Thus, the delaminated ITQ-2 zeolite (Si/Alsurf = 10.6, Sext = 324 m2/g) produced the less stable hybrid while that comprising zeolite TNU-9 (Si/Alsurf = 17.9, Sext = 12 m2/g) displayed the highest stability during the syngas-to-DME experiments. These results suggest that the deterioration of the methanol synthesis activity of the CZA catalyst in the hybrid catalysts prepared by grinding is produced by detrimental interactions between zeolitic Al species and Cu sites at the surface-contact between zeolite and CZA particles.

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Keywords
Methanol dehydration; Synthesis gas; Direct DME synthesis; CuZnAl methanol synthesis catalyst; 10-ring zeolite; Pore structure; Hybrid catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 468, 5 November 2013, Pages 102–111
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us