Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts
/ Nature, 461 (2009)
- Center for Functional Nanomaterials, Department of Chemistry, KAIST,
- Graduate School of Nanoscience and Technology (WCU), KAIST,
- KAIST Institute for the NanoCentury,
- Graduate School of EEWS (WCU), KAIST, Daejeon 305-701, Korea
- Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden
- Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai 599-8570, Japan
- These authors contributed equally to this work.
Correspondence to: Ryong Ryoo1,2,3 Correspondence and requests for materials should be addressed to R.R. (Email: http://nbst.kaist.ac.kr/%22mailto:email@example.com/%22/%22" TARGET="_blank">firstname.lastname@example.org).
Zeolites?microporous crystalline aluminosilicates?are widely used in petrochemistry and fine-chemical synthesis1, 2, 3 because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations3, 4, 5 that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion4, 5. This has been realized by synthesizing zeolite nanocrystals6, by exfoliating layered zeolites7, 8, 9, and by introducing mesopores in the microporous material through templating strategies10, 11, 12, 13, 14, 15, 16, 17 or demetallation processes18, 19, 20, 21, 22. But except for the exfoliation, none of these strategies has produced \\\'ultrathin\\\' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.