Dissertation
Elucidating the role of water in reaction intermediates and catalytic mechanisms on titanium oxide and zeolites
Washington State University
Doctor of Philosophy (PhD), Washington State University
2023
DOI:
https://doi.org/10.7273/000005048
Abstract
Because of the omnipresent nature of water in biomass conversions, unraveling its impact on various biomass upgrading reactions is imperative. However, a molecular level understanding on water effect on Lewis and Brønsted sites is still lacking. In this dissertation, a combination of in situ nuclear magnetic resonance (NMR), in situ diffuse reflection infrared Fourier transform spectroscopy-temperature programmed desorption DRIFTS-TPD, kinetic investigations, and DFT simulations is applied to provide insight into water effect on alkanol dehydration and carboxylic acid ketonization. On Lewis acid catalysts, introducing H2O vapor in gaseous feed decreases the carboxylic acid ketonization reaction rate by increasing the intrinsic activation barrier. H2O associates with the adsorbed acetate or acetic acid intermediates leading to less reactive bridging bidentate carboxylates. Furthermore, it is discovered that water inhibition on alkanol dehydration displays a clear facet-dependence. Inhibition on TiO2(001) is about 3 times more severe than that on TiO2(101). On TiO2(001), water inhibits isopropoxide dehydration via formation of a stable isopropoxide-H2O complex with lower reactivity while water only forms weak hydrogen bond with molecular IPA adsorbed on TiO2(101) surfaces. On Brønsted acid catalysts ZSM-5, adding cyclohexanol does not change the interaction of water with Brønsted acid sites (BAS) due to formation of hydronium ions evidencing that cyclohexanol occupies the space between the hydronium ions in the micropores while decalin is displaced from micropores due to weak interaction with BAS. The current study provides a foundation for a deeper comprehension of water's impact on Lewis and Brønsted acid catalysts in alkanol dehydration and carboxylic acid ketonization in scientific applications. Additionally, it shed lights on the design of catalysts for practical applications that take into account the presence of water, with the aim of improving catalytic systems.
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Details
- Title
- Elucidating the role of water in reaction intermediates and catalytic mechanisms on titanium oxide and zeolites
- Creators
- Wenda Hu
- Contributors
- Yong Wang (Advisor)Su Ha (Committee Member)Di Wu (Committee Member)NORBERT KRUSE (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
- 273
- Identifiers
- 99901019535801842
- Language
- English
- Resource Type
- Dissertation