In this project, Au dosed electrochemical deposited (ED) CeO2 samples of different thicknesses and on different substrates are prepared as model catalysts for various characterisation techniques. The surface chemistry structures of prepared model catalysts are studied utilising X-ray photoelectron spectroscopy (XPS), hard X-ray photoelectron spectroscopy (HAXPES) and near-ambient XPS (NAP-XPS), and the results are compared for various types of CeO2 samples including CeO2 single crystal, commercial CeO2 powder with different diameters and chemical vapour deposited CeO2 film on Cu and Si. These data are used to design a robust fitting procedure and interpretation of the satellite structures of Ce 3d core levels. The effect of temperature on Au clusters deposited on the ceria surfaces is examined, both in UHV and NAP-XPS. The morphologies and crystal structures of the model catalysts are characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) ex situ and in situ to support the surface chemistry characterisation results. It is found that heating to high temperatures under vacuum that CeO2 can be reduced and then transform to stoichiometry Ce2O3. Aggregation and reduction of Au nanoparticles occurs, even at relatively low temperatures both in UHV and in NAP-XPS conditions. Probe reaction CO oxidation is used to confirm the catalysis ability of Au dosed ED CeO2 model catalysts in NAP-XPS, the results are used as reference to compare with Water Gas Shift (WGS) reaction. Reduction and oxidation of the CeO2 surface, gas adsorption and formation of intermediate C=O/O-C=O species are found to occur during the WGS reaction, using NAP-XPS. In addition, Ce-OH species are observed experimentally for the first time from peaks appearing in Ce 3d spectra, the possible peak positions and full width at half maximum (FWHM) are proposed.
Date of Award | 31 Dec 2024 |
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Original language | English |
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Awarding Institution | - The University of Manchester
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Supervisor | Andrew Thomas (Supervisor) & Alex Walton (Supervisor) |
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- Au/CeO2
- NAP-XPS
- HAXPES
- TEM
- Model Catalysts
Investigation of surface chemistry and crystal structure of Au supported CeO2 model catalysts
Liu, X. (Author). 31 Dec 2024
Student thesis: Phd