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Insights into the unexpected formation of hexamethylbenzene during steam reforming of dimethyl ether over zeolite-based bifunctional catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
54954 47033 2013 6 PDF Available
Title
Insights into the unexpected formation of hexamethylbenzene during steam reforming of dimethyl ether over zeolite-based bifunctional catalysts
Abstract

The effect of the acidity and topological structure of zeolites on the performance of the steam reforming of dimethyl ether (SRD) was comparatively investigated over the bifunctional catalyst composed of zeolite and Cu/ZnO/Al2O3 under the conditions of DME/H2O/N2 = 1/4/5, catalyst loading of 0.9 g, GHSV = 4000 mL g−1 h−1. The bifunctional catalyst was prepared by physically mixing Cu/ZnO/Al2O3 with H-ZSM-5 (Si/Al2O3 = 25), H-USY, and H-beta (Si/Al2O3 = 20), respectively. The acidic properties of the zeolite were characterized by NH3-TPD technique. Over all the bifunctional catalysts with a Cu/ZnO/Al2O3 to zeolite weight ratio of 1, SRD was dominantly occurred, and H-ZSM-5 based bifunctional catalyst showed the highest SRD performance, i.e., DME conversion of over 95% and H2 yield of about 80%. Moreover, light hydrocarbons were formed under SRD conditions as a result of DME (methanol) to hydrocarbons reactions (DTH, MTH). The results were well explained based on the two-step mechanism of SRD and the acidic properties of the zeolite. Unexpectedly, a white powdery product, which is determined to be hexamethyl benzene (HMB) by FT-IR, 1H and 13C NMR, GC/MS, and elemental analysis, was condensed at the outlet of the reactor when H-USY or H-beta based bifunctional catalysts were applied for SRD. Furthermore, the formation of HMB was more pronounced over the bifunctional catalyst by using H-beta as an acidic component. To the best of our knowledge, this is the first report on the formation of HMB under SRD conditions. Based on the results by changing the weight ratio of Cu/ZnO/Al2O3 to H-beta, the SRD mechanism, and the topological and acidic properties of H-beta, the formation of HMB was well explained as the side reactions of MTH and DTH and the larger channel sizes of zeolites Y and beta than that of the HMB molecules. Importantly, on the one hand, our findings can shed some lights on screening suitable solid acids for SRD. On the other hand, clear evidence is provided for the hydrocarbon pool mechanism of MTH reaction, and HMB is revealed to be the very possible species of hydrocarbon pool.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (203 K)Download as PowerPoint slideHighlights► Effect of zeolite structure and acidity on SRD was comparatively investigated. ► The acidity and structure of different zeolites play a key role for SRD. ► H-ZSM-5 based bifunctional catalyst is active and selective for SRD. ► First report on the formation of hexamethylbenzene under SRD conditions. ► Hexamethylbenzene is a possible hydrocarbon pool species for MTH reaction.

Keywords
Dimethyl ether; Steam reforming; Hydrogen; Hexamethylbenzene; Zeolite
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Insights into the unexpected formation of hexamethylbenzene during steam reforming of dimethyl ether over zeolite-based bifunctional catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 210, 1 July 2013, Pages 75–80
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
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Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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Any Questions? feel free to contact us