Date of Completion

10-8-2018

Embargo Period

10-5-2018

Keywords

ceramic matrix composites, carbon fiber, boron nitride, hydrogen storage, ammonia borane, carbon dioxide hydrogenation, carbon dioxide XPS, OMS-2

Major Advisor

Steven L. Suib

Associate Advisor

Edward Neth

Associate Advisor

Raymond Joesten

Field of Study

Chemistry

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Four classes of materials with energy sector applications have been developed or characterized herein. Processing requirements that lead to a toughened carbon fiber reinforced silicon carbide ceramic matrix composite with a compliant and oxidation resistance boron nitride interface coating were developed. Preliminary experiments resulted in highly brittle composites when BN was applied by CVD to as-received fiber. This led to a requirement of heat treating the carbon fiber to favorably modify the fiber surface prior to BN deposition. The compound ammonia borane was investigated as a potential chemical hydrogen storage material for hydrogen fuel cell applications. Two known thermal decomposition steps which yield hydrogen gas, borazine impurities, and residual B-N inorganic polymers were corroborated by several techniques. A high temperature decomposition step leading to boron nitride, and an unreported gaseous impurity from the two known decomposition steps were identified. The reactivity of a γ-alumina supported, fcc cobalt (Co/Al2O3) catalyst was evaluated in a CO2/H2 feedstock for activity towards CO, methane, C2+ hydrocarbons and methanol. Comparable methane selectivites were obtained at low and high pressures. At low pressures the balance was composed mostly of CO while at high pressures the balance was composed mostly of C2+ hydrocarbons. This suggest CO2* is preferentially hydrogenated at higher pressures instead of dissociating to CO* and O*. The evolution of the catalyst composition and structure during fabrication was tracked by a several techniques. The acid/base character of CO2(g) specifically towards exterior framework surfaces (to the exclusion of tunnel sites) on the manganese oxide octahedral molecular sieve OMS-2, was measured using synchrotron based soft X-Ray photoelectron spectroscopy. In addition to fundamental interest, the adsorption of CO2 on OMS-2 has direct relevance to several energy sector applications. CO2 is often considered to be a Lewis acid probe for surface basicity, but may also exhibit basic character towards acidic surface sites. Measurements of surface acidity and basicity aid in the determination of how these properties dictate the activity and selectivity of a heterogenous catalyst towards any given reaction.

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