Date of Award

Summer 8-22-2018

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Brian Frederick

Second Committee Member

William DeSisto

Third Committee Member

Rachel Austin

Additional Committee Members

Barbara Cole

Carl Tripp

Abstract

Interest in conversion of biomass into renewable fuels has motivated development of thermochemical methods for production of bio-oil and development of hydrodeoxygenation catalysts for upgrading the oil. Two types of catalysts were investigated. The catalytic activity of unsupported tungsten oxide bronze catalysts for the conversion of guaiacol was explored as a representative compound from bio-oil. The reactions were carried out in a trickle bed reactor at various concentrations of the reactant and hydrogen pressure, as well as varying catalyst activation and reaction temperatures. The reaction pathway from guaiacol to phenol by demethoxylation, followed by hydrogenation to cyclohexanol, and finally dehydration to cyclohexene was determined experimentally. Kinetic data revealed approximately first order dependence on hydrogen pressure and zeroth order dependence on guaiacol concentration. Langmuir- Hinshelwood-Hougan-Watson models were tested within a plug flow reactor model. The best fit was for a reaction mechanism in which the guaiacol methoxy C-O bond scission was the rate controlling step with guaiacol and some phenol blocking active sites. Catalytic activity and selectivity of supported Ni-based catalysts were also studied for the same model compound (guaiacol) in order to evaluate the role of metal hydrogenation sites and acid dehydration sites. The supports used were SiO2, Al2O3 and SiO2-Al2O3. All catalysts were prepared by the incipient wetness impregnation method and were characterized by different physico-chemical techniques. Conversion reactions were carried out in a batch reactor at 5 MPa of H2 pressure and 300 °C. The maximum catalytic activity among the Ni/Al2O3 catalysts was attributed to the formation of a greater number of active metal sites arising from an optimal nickel dispersion at a loading of 8 wt%. At higher Ni content, the formation of Ni aggregates was observed resulting in loss of active sites. The selectivity (at constant conversion and metal loading) toward deoxygenated products, cyclohexene and cyclohexane, was clearly related to the acid sites of the support, which were much greater on SiO2-Al2O3.

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