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A novel methodology for synthesizing crystalline metallosilicates with expanded pore windows through molecular alkoxysilylation of zeolitic lamellar precursor
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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2008 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 26, 8178-8187 p.Article in journal (Refereed) Published
Abstract [en]

Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline structures with expanded pore apertures between the layers. The silylation process and the crystalline and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, 13C and 29Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N2 adsorption. In contrast to forming known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images. After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites. The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks, indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW topology.

Place, publisher, year, edition, pages
American Chemical Society , 2008. Vol. 130, no 26, 8178-8187 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-24775DOI: 10.1021/ja0758739ISI: 000257152800033OAI: oai:DiVA.org:su-24775DiVA: diva2:198286
Note
Part of urn:nbn:se:su:diva-7439Available from: 2008-04-03 Created: 2008-03-28 Last updated: 2010-12-01Bibliographically approved
In thesis
1. Development of electron microscopy towards nano-structured porous materials: Focus on novel zeolites from layered silicates and chiral mesoporous nanotubes
Open this publication in new window or tab >>Development of electron microscopy towards nano-structured porous materials: Focus on novel zeolites from layered silicates and chiral mesoporous nanotubes
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Three novel zeolites (M-IEZ-MWW, IEZ-FER and IEZ-CDO) have been successfully synthesised from the corresponding precursors. Structure characterisation of those materials was conducted by TEM. Our studies show that the structure of the new zeolites keeps identical layer to the corresponding known 3D zeolite, except for the distinct expansion of the layer spacing. Combining with results from XRD, N2 adsorption, IR and NMR, the expansion can be explained by the pillaring of T sites between the layers. Meanwhile, the intergrowth of 3D MWW and IEZ-MWW was observed in the Al-IEZ-MWW and Si-IEZ-MWW crystals, IEZ-CDO structure was found in the IEZ-FER crystals, and the intergrowth of CDO and new polymorph was observed in the CDS-1 crystal. Moreover, two new zeolites IM-5 and SSZ-57 were also studied by TEM. We found that the space group of IM-5 is non-centrosymmetrical, and in SSZ-57 the new structure with slightly larger c parameter was observed compared to MEL.

Chiral mesoporous silica nanotube and chiral mesoporous carbon nanotube were aslo investigated by TEM. We found that the former was synthesised by hollowing out process and it possesses chiral mesopores in the wall, the latter was synthesised by templating and seeding method. Electron tomography was first applied to study the handedness of the chiral mesoporous nanotube. Furthermore, TEM studies verified that bifunctional mesoporous silica has a Fm-3m structure, and mesoporous carbon FDU-16 has a Im-3m structure.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2008. 125 p.
Keyword
Transmission electron microscopy, Layered silicates, Chiral mesoporous nanotubes
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-7439 (URN)978-91-7155-602-8 (ISBN)
Public defence
2008-04-25, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:30 (English)
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Available from: 2008-04-03 Created: 2008-03-28 Last updated: 2010-04-14Bibliographically approved

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