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Dissertation
Fundamental Catalytic Properties of Faceted Anatase Nanoparticles and Their Influence on Supported Molybdena
Washington State University
Doctor of Philosophy (PhD), Washington State University
2023
DOI:
https://doi.org/10.7273/000005053
Abstract
To better investigate the fundamental catalytic properties of metal oxide surfaces, faceted nanoparticles are commonly used to complement surface science perspectives. However, surface complexities such as intrinsic defect sites (i.e. steps, corners, kinks) and surface OH groups on macroscopic powders limit the efficacy of faceted nanoparticles to study fundamental structure-functionality. Furthermore, the influence of anchoring facets on the catalytic properties of supported secondary oxide catalysts is poorly understood. This dissertation sought to address these gaps in knowledge by investigating faceted {101} and {001} dominant anatase TiO2 nanoparticles. Controlling the proportion of exposed {001} interfaces revealed elevated thermal stability, density, and variable speciation of {001} bound surface OH that promoted alkanol dissociation, thus affecting its catalytic behavior during methanol-TPSR. Intentional hydroxylation of {101} by alkaline hydrogen peroxide treatments narrowed the differences in methanol-TPSR with {001}, implying surface OH contribute to observed facet-dependent behaviors. Because of its sensitivity to supporting interfaces and bifunctional properties, supported molybdena (MoOx) was used as a model oxide to study facet-dependent structure-functionality. The elevated hydroxylation of {001} was shown to induce greater MoOx dispersion compared to aggregated clusters on {101}. Greater dispersion on {001} led to more prevalent redox-active Mo-O-Ti interfaces while Brönsted acidity unique to Mo-O-Mo moieties formed on {101}, imparting facet-dependent structure-functionality during methanol conversion. Finally, the ensemble of surface active sites making up faceted anatase nanoparticles was further refined by investigating the naturally defective curvature of the studied {001} nanoplates. Redox-inert SiO2 was selectively anchored to step edge sites on the curved {001} plane via chemical grafting. By blocking step edge sites, a more representative assessment of {101} vs {001} activity in methanol oxidation was determined, illustrating the anomalous and significant impact structural heterogeneity imparts on macroscopic powders. This work highlights the commonly overlooked, yet consequential nature of surface OH groups, facet supporting interfaces, and intrinsic defects of high surface area catalysts. The knowledge acquired in this dissertation betters our understanding of faceted surfaces to further narrow the materials gap and to improve future catalyst design.
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Details
- Title
- Fundamental Catalytic Properties of Faceted Anatase Nanoparticles and Their Influence on Supported Molybdena
- Creators
- Anthony William Savoy
- Contributors
- Yong Wang (Advisor)Jean-Sabin McEwen (Committee Member)Zdenek Dohnalek (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Voiland College of Engineering and Architecture
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 217
- Identifiers
- 99901019536001842
- Language
- English
- Resource Type
- Dissertation