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Author ORCID Identifier
Open Access Dissertation
Doctor of Engineering (DEng)
Year Degree Awarded
Month Degree Awarded
Friederike C Jentoft
Catalysis and Reaction Engineering | Chemical Engineering
The use of biomass-derived ligno-cellulose as a possible alternative source of fuels and chemicals to fossil-based hydrocarbons, however, biomass offers many challenges based on processing and its high oxygen content. One promising upgrading route is deoxydehydration, a reaction which combines a deoxygenation by a sacrificial reductant and dehydration in a single step to selectively convert vicinal diols into an olefin. This reaction is highly selective when using homogeneous oxo-rhenium catalysts, which can easily undergo the necessary changes in coordination and oxidation state, however the high cost of rhenium and difficulty of homogeneous catalyst recovery make these catalysts untenable for large scale biomass upgrading.
This thesis details work in developing more robust and economical solid catalysts for deoxydehydration. A series of oxide-supported oxo-rhenium catalysts using silica, titania, alumina, iron oxide, and zirconia supports were synthesized and tested which demonstrated high activity and up to 95% selectivity. However, due to the liquid phase chemistry of the reaction, these catalysts demonstrated various propensities to deactivate over multiple runs through leaching of the active rhenium species. We observed that leaching was promoted by the presence of the diol. The severity of the leaching was dependent on not only the support, but the choice of reactant and solvent and after complete diol conversion, the leached rhenium would precipitate out of the reaction mixture, enabling a release and catch leaching mitigation strategy. In preliminary work using microporous zeolites as a support to inhibit leaching, it was found that the acid site of the zeolite provided an anchoring site for the oxo-rhenium species which reduced leaching, but also lowered selectivity due to side reactions catalyzed by the acid site.
Vanadium, tungsten, molybdenum, and manganese catalysts were screened for deoxydehydration activity as low-cost alternatives to rhenium. The molybdenum catalysts were found to be the most promising, with the homogeneous ammonium heptamolybdate catalyst achieving 50% alkene yield and the oxide-supported molybdenum catalysts achieving 22% alkene yield using triphenylphosphine as the reductant. It was also found that the ammonium counterion in ammonium heptamolybdate promoted activity for molybdenum-catalyzed deoxydehydration.
Sharkey, Bryan E., "Development and Characterization of Robust and Cost-Effective Catalysts for Selective Biomass Upgrading to Fuels and Chemicals by Deoxydehydration" (2020). Doctoral Dissertations. 1921.
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