Gu, Junwen;
(2023)
Understanding the preparation of hierarchically structured zeolites and their modification for catalytic applications.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This program is aimed to investigate the mechanism of the hierarchical zeolite formation and its application in heterogeneous catalysis as a support shell. The train of thought starts from synthesising hierarchical zeolite using bottom-up and top-down approaches. In the top-down approach, Cetyl trimethyl ammonium bromide (CTAB) is used as the mesopores template, and different hydroxides are used as bases to open the microporous structure. Through various comparison studies, the mechanism of the different pore system formations is investigated under the characterization of in situ small angle x-ray scattering (in situ SAXS) in synchrotron light research institute (SLRI) Thailand. In bottom-up approach, steam-assisted method was employed to synthesize macroporous silicalite-1 with tetrapropylammonium hydroxide (TPAOH) as the structure-directing additive (SDA). At the same time, all the hierarchical zeolites will be characterized by x-ray diffraction (XRD), ex situ small angle x-ray scattering (ex situ SAXS) and scan electron microscope (SEM). The metal-supported gold nanoparticles will anchor into the larger pores in hierarchical zeolites. These modified catalysts are further characterized by x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and x-ray absorption near edge structure (XANES). Transmission electron microscope (TEM) showed a reasonable size of metallic or oxidated gold in modified catalysts, and the XPS and XAS results also convinced the correct oxidation state. During catalysis tests, the modified catalysts are performing well, and the gas chromatography (GC) results showed good conversion and selectivity. After the catalysis test, the XRD results showed great stability of this hierarchical zeolite outer shell. Other than the normally supported gold catalysts, this new shell-shaped catalyst will avoid aggregation of the catalyst during the reaction, get rid of the diffusion limitation and pore blockage problem that eliminates the diffusion limitation and pore blockage problem in conventional microporous material.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Understanding the preparation of hierarchically structured zeolites and their modification for catalytic applications |
| Language: | English |
| Additional information: | Copyright © The Author 2023. 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 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-pp.ucl.ac.uk/id/eprint/10178650 |
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