Cong, Peixi;
(2023)
The application of X-ray techniques to identify deactivation processes and active species in novel catalytic materials.
Doctoral thesis (Ph.D), UCL (University College London).
Preview |
Text
Cong_Thesis.pdf - Other Download (10MB) | Preview |
Abstract
In this work, the evolution, steady-state operation and deactivation of active species in catalytic materials are studied in situ and under operando conditions, primarily using a multitude of X-ray techniques. The first results chapter focuses on the characterisation of acid-leached HZSM-5 where the temperature of zeolite collapse (tc) was found to correlate with the extent of framework Al3+ removal. Mo-ion exchange, whilst also removing framework Al3+, has a negligible effect on the tc. A model Mo-SSZ-13 material revealed that within a single crystal, the Al-rich and Si-rich regions amorphised at different temperatures and with different modalities. A survey of Cu-containing zeolites revealed that increased Cu loading reduces tc. This instability is caused by Cu-promoted α-cristobalite formation. XAFS revealed that at tc Cu(II) reduced to Cu(I) in ZSM-5, while it remained as Cu(II) in SSZ-13, forming an isolated aluminate-like species. In chapter 4 an operando hydrothermal aging study of Cu-zeolite catalysts was performed. Here we observed that in Cu-SSZ-13 at 800 °C, the Cu(II) in the 8 ring undergoes irreversible reduction to Cu(I), whilst Cu(II) in the 6-rings are stable. At 900 °C it suffers total framework collapse caused by the physical size of growing α-cristobalite. The hydrothermal effect on the Cu-zeolite catalyst can be viewed as affecting the redox state of the Cu and the stability of the zeolite framework. We rationalised that the effort to improve on one factor will have an inverse impact on the properties of the other. Finally, we focused on characterising the active species in a novel Suzuki cross-coupling catalyst Y3Pd2. The
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | The application of X-ray techniques to identify deactivation processes and active species in novel catalytic materials |
| Open access status: | An open access version is available from UCL Discovery |
| 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.ucl.ac.uk/id/eprint/10168719 |
Archive Staff Only
 |
View Item |
