Date of Award

2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Chemical and Biomolecular Engineering

First Advisor

John M. Vohs

Abstract

The negative social and environmental impacts from burning of fossil fuels motivated the development of renewable and sustainable sources for the production of electricity such as wind and solar. Lignocellulosic biomass has emerged as a promising feedstock for carbon-based fuels and chemicals and much research effort has recently been directed at developing efficient catalytic pathways for the upgrading of lignin-derived oxygenate into useful products. This dissertation aimed to study the viability of utilizing bifunctional catalysts consisting of a transition metal either supported on or modified by a reducible metal oxide to promote the direct C-O bond cleavage in aromatic oxygenates (m-cresol). Surface science techniques such as HREELS, XPS and TPD were used to provide insights into the reaction pathway and mechanism of this reaction. In all studies featured in this thesis, transition metals such as Pt and Ni, exhibit moderate selectivity to desired product, toluene. It was found that the strong interaction between aromatic rings and metal surfaces facilitates the ring hydrogenation which forms an intermediate pool. While metal catalysts promoted by WOx and NbOx are extremely active and selective for the direct deoxygenation reaction. The interaction at the metal-metal oxide interfaces helps keep the metal oxide partially reduced and provide the active bonding sites for the adsorption of hydroxyl groups. It was also found that the m-cresol tends to adsorb on oxygen vacancies while the aromatic rings are tilted away from the surface. This bonding configuration would promote the direct deoxygenation of hydroxyl group.

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