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Modification of zeolites and synthesis of SAPO-templated carbon
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons.

In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications.

The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons.

Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail.

In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University , 2017. , p. 71
Keywords [en]
microporous material, zeolite, SAPO templated carbon, hydrothermal synthesis, CVD, post modification, direct modification, snowflake
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-141834ISBN: 978-91-7649-831-6 (print)ISBN: 978-91-7649-832-3 (electronic)OAI: oai:DiVA.org:su-141834DiVA, id: diva2:1089294
Public defence
2017-06-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-05-19 Created: 2017-04-19 Last updated: 2017-05-22Bibliographically approved
List of papers
1. De-agglomeration of IZM-2 zeolite crystals by post-synthetic treatment
Open this publication in new window or tab >>De-agglomeration of IZM-2 zeolite crystals by post-synthetic treatment
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2016 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 225, p. 185-191Article in journal (Refereed) Published
Abstract [en]

Highly intergrown nanocrystals are commonly observed in zeolite samples, and the densely packed agglomerates may result in small secondary porosity, which restricts the advantage of hierarchical structures. In this work we take IZM-2 zeolite as an example to demonstrate a post-treatment method with diluted hydrofluoric acid solution, which de-agglomerates intergrown zeolite nanocrystals and improves the secondary porosity. The treated samples preserve high crystallinity, similar framework composition and distinctively higher external surface area compared to the agglomerated ones. The results show that this treatment is an effective method for de-agglomeration of intergrown nanocrystals without affecting the original framework.

Keywords
Zeolite, Nanocrystals, De-agglomeration, Post treatment, Hierarchical porosity
National Category
Chemical Sciences Nano Technology Materials Engineering
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-130161 (URN)10.1016/j.micromeso.2015.12.021 (DOI)000373421700020 ()
Available from: 2016-05-12 Created: 2016-05-09 Last updated: 2017-05-11Bibliographically approved
2. Microporous pure-silica IZM-2
Open this publication in new window or tab >>Microporous pure-silica IZM-2
2017 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 237, p. 222-227Article in journal (Refereed) Published
Abstract [en]

Pure-silica IZM-2 was synthesized for the first time, and the concentration of sodium hydroxide used during synthesis affected the phase purity and size of crystals. Most of the micropores in calcined pure silica IZM-2 that was synthesized in the presence of high concentrations of sodium hydroxide were inaccessible to N-2 adsorption; however, the micropores could be rendered accessible by applying either of two different post-synthetic treatments. Pure-silica IZM-2 could also be synthesized without sodium ions using the hydroxide version of the template. In this case, the micropores were accessible to N-2 directly after calcination. The size of pure-silica IZM-2 crystals obtained increased with the concentration of sodium hydroxide, with the highest concentrations giving spherical and micrometer-sized aggregates of pure-silica IZM-2 that consisted of intergrown particles (60-500 nm). The nature of the defects in pure-silica IZM-2 was studied with a combination of H-1, and Si-29 solid-state NMR spectroscopy. As expected, direct-polarization Si-29 NMR spectroscopy showed that the number of non-condensed silica groups decreased upon calcination. Calcined samples also showed broader Si-29 NMR bands for the fully condensed silica moieties, which indicated a broader distribution of bond angles and/or bond lengths. The siloxy and silanol groups in calcined pure-silica IZM-2 were accessible to protonation as determined by H-1 NMR spectroscopy. We could not determine the structure of pure-silica IZM-2 in its aggregated form; however, further studies of the synthetic conditions could yield larger, non-aggregated crystals that would facilitate structural determination.

Keywords
Pure silica, IZM-2, Zeolite, Synthesis, Defects, Post treatment
National Category
Chemical Sciences Nano Technology Materials Engineering
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-136718 (URN)10.1016/j.micromeso.2016.09.033 (DOI)000387836100024 ()
Available from: 2016-12-19 Created: 2016-12-14 Last updated: 2017-05-11Bibliographically approved
3. Nanocrystalline TON-type zeolites synthesized under static conditions
Open this publication in new window or tab >>Nanocrystalline TON-type zeolites synthesized under static conditions
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-141831 (URN)
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-05-11Bibliographically approved
4. SAPO-templated carbon
Open this publication in new window or tab >>SAPO-templated carbon
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-141833 (URN)
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-05-11Bibliographically approved

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