Date of Award

December 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Jesse Q. Bond

Keywords

Heterogeneous catalysis, Levulinic acid, Maleic acid, Oxidation, Solid acid, Vanadium

Subject Categories

Engineering

Abstract

With continued depletion of fossil carbon, there is a need to utilize renewable sources of energy and consumer end products. In this context, we examine the aerobic oxidation of levulinic acid, a bio-based platform chemical derived from lignocellulosic biomass, to produce maleic anhydride, a valuable commodity chemical. This process is carried out over supported vanadium oxide catalysts. Yields as high as 71% of the theoretical maximum were achieved at 573 K over a vanadium oxide catalyst supported on SiO2. The exact mechanism underlying this transformation is complex, but our results suggest that maleic anhydride forms by the oxidative cleavage of the methyl carbon in α- and β-angelica lactones, which form as primary products by facile dehydration of LA. We have identified all major and minor/side products, and we propose plausible mechanisms leading to their formation. These mechanistic insights allow us to envision strategies for controlling product selectivity during oxidative cleavage reactions. To probe the extent to which vanadate structure dictates reactivity and selectivity, we consider the oxidative cleavage of 2-pentanone over a number of vanadium oxide catalysts that vary in both vanadium oxide structure and support. We observe that activity and selectivity on supported vanadium oxides is sensitive to both the choice of support and the vanadium loading. Rates scale inversely with the electronegativity of the heteroatom present in the solid oxide support. Finally, as vanadium oxide surfaces display both acid/base and redox functions, we have developed a set of reaction-based tools for characterizing acid site character and density in solid oxides. Specifically, we employ a series of amine titrants in FTIR, Temperature Programmed, and Steady State reaction studies to provide in situ titration of Brønsted acid site density under reaction conditions. In doing so, we observe that small pore zeolites screen amine molecules based on their kinetic diameter, while materials that vary in Brønsted:Lewis site distribution display contrasting Brønsted acid site densities that are dependent on the degree of substitution of the α-carbon in the alkylamine. Finally, we try to develop new techniques to better measure the intrinsic activity of a Brønsted catalyzed reaction.

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Open Access

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