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Characterisation of order/disorder in mixed metal oxide catalyst materials by reverse Monte Carlo modelling of X-ray and neutron total scattering
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Summer, Aron (2023) Characterisation of order/disorder in mixed metal oxide catalyst materials by reverse Monte Carlo modelling of X-ray and neutron total scattering. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3980008
Abstract
A deep dive into structural disorder of cerium zirconium oxides relevant for catalysis is undertaken focusing on a reverse Monte Carlo approach driven by total scattering X-ray and neutron data collected at synchrotron facilities. Cation nano-domains and interstitial oxygen are discovered after a atomic scale solid solution Ce0.75Zr0.25O2 material is is heated to 1050 °C under H2 paired with a subsequent reoxidation via heating under air at 400 °C. An overall loss of oxygen storage capacity is observed and rationalised as consequence of the nanoscale cation segregation clearly outweighs the beneficial properties of the inclusion of interstitial oxygen.
In another reverse Monte Carlo study relating to stoichiometric ceria zirconia it is shown that synthesis route dramatically impacts the presence and types of local cation structures observed as shown by Clapp configuration analysis. A statistical approach to characterising local structures within face centred cubic atomic arrangements. For the first time a κ-CeZrO4 phase, prepared by reduction at 1050 °C followed by oxidation at 400 °C, is modelled via a large box reverse Monte Carlo approach revealing significant cation and oxide disorder. The disorder relating to the cation sites are characterised and shown to be a heavily defected pyrochlore-like cation ordering. The oxide lattice disorder is shown to be myriad with significant concentrations of interstitial sites occupied, split sites and more generalised anisotropy within the oxide lattice present, shining light on the origins of the high oxygen storage capacity associated to κ-CeZrO4 materials prepared at relatively low reduction temperatures.
The Ce0.5Zr0.5O2 transition to pyrochlore ordering at ~1000+ °C is observed in an in-situ X-ray pair distribution study and shows a distinct mis-alignment between changes in the local structure and the average cation ordered structure that is determined form the super lattice Bragg reflections.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Zirconium oxide, Neutrons -- Scattering, Cerium oxide crystals, X-rays -- Scattering, Monte Carlo method, Oxidation, Order-disorder models, Lattice dynamics | ||||
Official Date: | March 2023 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Walton, Richard I. ; Playford, Helen Y. | ||||
Format of File: | |||||
Extent: | x unnumbered, 195 pages : illustrations | ||||
Language: | eng |
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