Dissertation
SURFACE ENGINEERING OF FE-BASED CATALYSTS FOR SELECTIVE HYDRODEOXYGENATION OF PHENOLICS: FROM REACTION MECHANISM TO CATALYST DESIGN
Doctor of Philosophy (PhD), Washington State University
01/2020
Handle:
https://hdl.handle.net/2376/110945
Abstract
While hydrodeoxygenation (HDO) plays pivotal roles in biomass valorization, development of inexpensive sulfur-free catalysts for selective hydrogenolysis of the C-O bond in phenolics (i.e., selective removal of oxygen without aromatic ring saturation) under liquid-phase conditions is highly challenging in terms of both thermodynamics and kinetics. Due to the moderate oxophilicity, the earth-abundant and inexpensive Fe is selected as a catalyst and we first performed a mechanistic study and demonstrated that despite of the highly selective C-O bond cleavage of phenolics on Fe-based catalyst in vapor-phase reaction conditions, the facile tautomerization reaction pathway was opened up in liquid-phase reaction, leading to the dominant aromatic ring saturation. To inhibit the tautomerization, we performed surface engineering to Fe-based catalyst with graphene overlayer and alkali metal (i.e., Cs). The graphene prevents the Fe surface from oxidation by hydroxyls or water produced during HDO reaction. More importantly, further tailoring the surface electronic properties of graphene-covered Fe with the addition of Cs to inhibit the tautomerization of catalyst surface. This catalyst produces arenes with 100% selectivity from liquid-phase HDO of phenol with high durability. We then investigated the active site by comparing the surface evolution of two distinct catalysts promoted by alkali metals (i.e. Fe covered by discontinuous carbon layer containing 0% carbide and Cs/Fe3C containing 100% carbide). The results suggest that, though carbide may be active in HDO reaction, its surface rapidly evolved to the more stable structure, i.e. the defective graphene on Fe, to catalyze the HDO of phenols. After preliminarily understanding the active site, we enhanced its oxygen elimination property by adding Co to facilitate the redox cycle during HDO. The carbon coating to the alloy surface mitigates aggregation in H2 atmosphere at high temperature. Spectroscopic study showed further doping Cs species on surface inhibited the tautomerization of phenol, consequently achieving high selectivity to direct hydrogenolysis. In an optimized reacting condition, the Cs-G@CoFe converted 88% phenol with 90% benzene selectivity in liquid phase, which has been rarely reported among sulfur-free and inexpensive catalysts.
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Details
- Title
- SURFACE ENGINEERING OF FE-BASED CATALYSTS FOR SELECTIVE HYDRODEOXYGENATION OF PHENOLICS: FROM REACTION MECHANISM TO CATALYST DESIGN
- Creators
- Jianghao Zhang
- Contributors
- Yong Wang (Advisor)Su Ha (Committee Member)Jean-Sabin McEwen (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 272
- Identifiers
- 99900581497601842
- Language
- English
- Resource Type
- Dissertation