Date of Award

Spring 2019

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Aaron K. Vannucci

Abstract

Lignin is one component of lignocellulosic biomass and is the only renewable, naturally-occurring source of aromatics in the world. However, lignin also provides a highly-oxygenated, complex, heterogeneous structure making the procurement of isolated aromatic molecules quite difficult. There has been extensive research in recent years to develop approaches to catalytically breakdown the lignin polymer into monomeric units. This works aims to develop a number of catalytic techniques for the upgrading of these monomeric units of lignin to produce means for producing chemical building blocks as well as suitable fuels from biomass sources.

A method for the silanolysis of alcohols has been developed using a non-corrosive base catalyst, K2CO3. Chapter 2 details the reactions between a variety of alcohols and hydrosilanes to generate silyl ethers under mild conditions. These mild conditions allow for a wide substrate scope of alcohols to be explored due to a high functional group tolerance. Many of the alcohols that have successfully been silylated in this work are aromatic units. In total, 25 silylated alcohols were prepared through use of 5 different hydrosilanes. This silylation process is successful in the presence of reactive C–H bonds. The silylated alcohols prepared in this work have the potential to be used in polymer synthesis as well as to be used in hydrodeoxygenation reactions that would otherwise be difficult to perform.

The aim of Chapter 3 is to explore the hydrodeoxygenation capabilities of the homogeneous transition metal catalysts, (2,2′:6′,2′′-terpyridine)nickel(II) hexafluorophosphate and chloro(2,2′:6′,2′′-terpyridine)palladium(II) chloride. The latter exhibited excellent activity and performed completely selective hydrodeoxygenation of benzylic oxygenates under very mild conditions. This catalysis was also observed at room temperature. The results of this work indicate a single-site molecular catalyst, which leads to the complete selectivity and lack of side product formation.

In Chapter 4, the development of heterogeneous single-site molecular complexes is explored for the selective hydrodeoxygenation of benzylic oxygenates. The catalysts prepared are direct modifications to the successful catalyst in Chapter 3. Chloro(2,2′:6′,2′′- terpyridine-4′-carboxylic acid)palladium(II) chloride and chloro(-([2,2′:6′,2′′-terpyridin]- 4′-yl) benzoic acid)palladium(II) chloride, were synthesized and used to modify the surface of amorphous silicon dioxide to generate a hybrid molecular/heterogeneous catalyst. The hybrid catalytic system exhibited excellent activities and selectivities for hydrodeoxygenation while displaying the ability to recycle through multiple catalytic reactions. Spectroscopic techniques indicate that the molecular catalyst is present on the surface of SiO2 and the formation of unwanted metallic Pd nanoparticles can be avoided. Post reaction analysis of the surface-modified oxide catalysts confirmed prolonged molecular integrity of the catalysts and sustained binding of the catalysts to the oxide surface when nonpolar solvents were employed for reactions.

Available for download on Monday, May 11, 2020

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