Schmidt, Alexis Oliver;
(2021)
Synthesis and characterisation of nanoporous and core-shell zeotype materials.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The main objective of the PhD thesis project is to explore the synthetic aspects and gel chemistry of small pore zeolitic materials, both silicoaluminophosphate and aluminosilicate zeolites. Herein, variations of SAPO-34 and shell@core type synthesis methods involving SAPO-34, SSZ-13, and silicalite-1 were studied. Correlations between structural properties and stability of shell@core type nanoporous systems were established via laboratory-based characterisation techniques, with X-ray diffraction (XRD) being the primary analysis tool. First, SAPO-34 synthesis methods and its gel chemistry were investigated to improve directed incorporation of silicon into the zeolite framework and enhance its stability. Following calcination runs on processingdependent as-synthesised SAPO-34 samples derived from precipitated SiO2 with 10 mol% Si in the reactant gel via a successive order of addition, it was discovered these experienced the least deterioration on their CHA framework. Next, shell@core synthesis variations for silicalite-1@SAPO-34 compositions were explored to understand the gel chemistry behind these structure formations and increase in their stability. The aim was to modify the surface structure of SAPO-34 by growing a continuous hydrophobic silicalite-1 shell over SAPO-34 core crystals that can shield the core from water and maintain its desired stability. Because the CHA framework topology in specific products appears undamaged after condensation of TEOS with acetic acid, it appears to be that amorphous SiO2 has accumulated on the surface of SAPO34 crystals and preserved these in the very alkaline synthesis medium of the reactant gel. Finally, shell@core synthesis alternatives for compositions with SSZ-13, an aluminosilicate which is isostructural to SAPO-34, were studied to unravel their gel chemistry. In the case of silicalite-1@SSZ-13 materials, the CHA phase of SSZ-13 appears to be slowly superseded by the MFI phase of silicalite-1 with protracted crystallization times. This may point to recrystallization of the CHA framework topology of SSZ-13 to the MFI type of ZSM-5.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Synthesis and characterisation of nanoporous and core-shell zeotype materials |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10130545 |
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