Determination of Acid Site Location in Dealuminated MCM-68 by 27Al MQMAS NMR and FT-IR Spectroscopy with Probe Molecules

Ryoichi Otomo, Toshiki Nishitoba, Ryota Osuga, Yusuke Kunitake, Yuichi Kamiya, Takashi Tatsumi, Toshiyuki Yokoi

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

A series of MCM-68 zeolites with different Si/Al ratios were prepared by treatment with nitric acid and compared with beta zeolites. Speciation of aluminum and location of acid sites changed depending on the Si/Al ratio. The location of Brønsted acid sites in MCM-68 samples was able to be classified by FT-IR measurements with pyridine and 2,6-di-tert-butylpyridine as probe molecules, and the number of Brønsted acid sites was quantified according to the locations. For high-aluminum MCM-68, Brønsted acid sites were broadly distributed in both the 12-ring channel and 10-ring windows as well as inside the supercage. The Brønsted acid sites in the 12-ring channel were easily removed by the acid treatment, and consequently, high-silica MCM-68 had Brønsted acid sites predominantly in the 10-ring windows and inside the supercage. 27Al MQMAS NMR spectra of high-silica MCM-68 showed two specific peaks assignable to T6 and T7 sites, which did not face the 12-ring channel, forming the Brønsted acid sites highly tolerant to the acid treatment. MCM-68 catalysts showed better catalytic performance in dehydration of sorbitol than beta, mordenite, and ZSM-5. Large void spaces at the intersection of 12- and 10-ring channels and inside the supercage for MCM-68 made it easy to take bulky transition states in the dehydration of sorbitol, resulting in its high catalytic performance.

Original languageEnglish
Pages (from-to)1180-1191
Number of pages12
JournalJournal of Physical Chemistry C
Volume122
Issue number2
DOIs
Publication statusPublished - 2018 Jan 18
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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