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Indexed by:Journal Papers

Date of Publication:2016-01-01

Journal:CATALYSIS SCIENCE & TECHNOLOGY

Included Journals:SCIE、EI

Volume:6

Issue:3

Page Number:713-721

ISSN No.:2044-4753

Abstract:Zeolites synthesized without any organic structure-directing agent (OSDA) have several advantages over conventional zeolites synthesized with OSDAs. Their Al-rich compositions, however, are sometimes not suitable for applications as catalysts. In the present study, post-synthetic modification was performed using an Al-rich Beta zeolite synthesized without any OSDAs (designated as "Beta.OF)") to obtain high-silica Beta zeolites. We have successfully developed a facile post-synthetic method for tuning the Al content of Beta(OF) with the *BEA-type structure retained by calcination at >750 degrees C followed by acid treatment. Solid-state Si-29 and Al-27 MAS NMR analyses revealed that during calcination, framework Al atoms were isomorphously substituted with Si atoms to form high-silica frameworks and concomitant extra-framework Al species. The stability of the obtained frameworks against acid treatment was evaluated in terms of the framework Al content, finding that the framework with the Si/Al ratio higher than 12 is well stabilized enough for acid treatment. Thus, dealuminated Beta(OF) zeolites with high-silica compositions were found to be effective catalysts for the methanol-to-olefin (MTO) reaction; particularly, the Beta zeolite with the Si/Al ratio of 112 maintained the conversion of methanol over 90% with selectivity to C-2-C-4 olefins over 70% even at 40 hours on stream at WHSV = 3.2 h(-1).