Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Chemical and Biomolecular Engineering

First Advisor

John M. Vohs

Abstract

There has been a growing interest in converting biomass to value added fuels and chemicals due to the increasing concerns about global warming and sustainable energy. Selective hydrodeoxygenation is an essential step in such conversion. Previous studies have reported that bimetallic catalysts consisting a group 10 metal and a more oxyphilic metal (such as PdFe and PtZn) have efficacy in such upgrading, while fundamental understanding of such reactions is sorely lacking. In this work, a Zn-Pt model catalyst system was used to study the reaction molecules for biomass-derived oxygenates (furfural, benzaldehyde, anisole and guaiacol). Surface science techniques were used provide fundamental insight into the reaction mechanisms as well as the active sites on the catalyst. Overall, it was determined that Zn addition provides a specific binding site for the oxygen atom in the reactant molecule, which helps facilitate the selective C-O bond cleavage reaction. In addition, the interaction between the aromatic ring and catalytic surface is greatly limited by Zn addition, helping to avoid undesired ring saturation. In contrast, the aromatic oxygenates interacts with the Pt(111) surface via the π-orbitals of the ring in a parallel geometry, facilitating ring hydrogenation and unselective decomposition. Such observations were compared with anisole reaction on high surface area supported Pt and PtZn catalysts and consistent results were obtained. To understand how general the effect observed for Zn-Pt system are, reaction of anisole on Co/Pt(111) was also studied. Similar to the Zn addition, Co modifier also interacts closely with the oxygen atom and facilitate selective C-O bond cleavage in anisole. However, a much weaker electronic effect was observed for Co modifier. Similar to the Pt(111) surface, parallel geometry and strong interaction between the ring and Co/Pt(111) was observed.

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