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Abstract
This thesis deals with a very specific class of functional nanomaterials known as
mesoporous zeolites. Zeolites are a class of crystalline aluminosilicate minerals
characterized by featuring pores or cavities of molecular dimensions as part of their
crystal structure. Mesoporous zeolites are zeolites which in addition to these channels
and cavities, i.e. the micropores (less than 2 nm), also feature porosity in the mesopore
size region (2-50 nm). The presence and ordered structure of the micropores is of
profound influence for different applications of zeolites since they effectively make
zeolites behave like molecular sieves capable of separating molecules by their size. This
property in combination with acidic properties resulting from hydroxyl groups bridging
silicon and aluminum ions in the zeolite framework make zeolites interesting as shapeselective
solid acid catalysts. Unfortunately, diffusion in the micropores is inherently
slow resulting in poor effective usage of zeolites in catalysis. To the end of improving
diffusion in zeolites, several strategies have been pursued including developing widerpore
zeolite structures, preparing zeolites in nanocrystalline form, supporting zeolites on
carriers, and introducing auxiliary pore systems in each individual zeolite crystal
resulting in mesoporous zeolite single crystals. With the exception of the wide-pore
zeolites, these materials are termed hierarchically porous zeolites since they feature two
(or more) distinct pore systems; the micropores and the meso-/macropores. The main
methods for preparing mesoporous zeolite single crystals are by crystallization of the
zeolite in the presence of carbon which is subsequently removed by combustion or by
subjecting normal purely microporous zeolites to alkaline treatments resulting in
mesopore formation by selective extraction of silicon from the framework. It is
described how various carbon templates allow for tuning the porosity of mesoporous
zeolites and that cheap mesopore templates may be prepared by carbonization of
sucrose. It is also described how the two main methods for preparing mesoporous
zeolites can be combined so that the porosity of a mesoporous zeolite may be enhanced
by subjecting it to alkaline treatment. Finally, it is described how crystallization of
synthesis gels containing fluoride lead to new mesoporous zeolite-like materials,
namely mesoporous aluminophosphate zeotypes.
Original language | English |
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Place of Publication | Kgs. Lyngby, Denmark |
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Publisher | Technical University of Denmark |
Number of pages | 198 |
Publication status | Published - Nov 2008 |
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Dive into the research topics of 'Chemical Design of Functional Nanomaterials'. Together they form a unique fingerprint.Projects
- 1 Finished
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Chemical Design of Functional Nanotube Materials
Egeblad, K. (PhD Student), Christensen, C. H. (Supervisor), Ståhl, K. (Examiner), Chandler, B. (Examiner), Iversen, B. B. (Examiner) & Fehrmann, R. (Main Supervisor)
01/06/2005 → 25/02/2009
Project: PhD