Mechanistic Insights on the Hydrodeoxygenation of Benzyl Alcohol with a Pd-Terpyridine Catalyst

Abstract

Lignin is a readily available renewable carbon polymer consisting of aromatic monomers, which can be used in the generation of alternative fuels. However, many of these monomers contain oxygen, reducing their usability and overall value. Therefore, catalytic hydrodeoxygenation that allows for the removal of oxygen atoms while preserving the aromaticity of these monomers is desirable. The Vannucci group at the University of South Carolina has developed a catalyst for this purpose, chloro(2,2’:6’,2’’-terpyridine-4’-carboxylic acid) palladium(II) chloride. Their catalyst has shown high conversion and selectivity with model lignin monomers at low temperatures when attached to the surface of amorphous silica to generate a molecular/heterogeneous catalyst motif. The two mechanisms investigated include one where the Pd center is reduced and one where an intermediate Pd-hydride species appears. In this thesis, we use density functional theory to determine the structures for the intermediate and transition state species, and their corresponding energies. With these energies, we ascertain which of the proposed reaction mechanisms is energetically favored. Understanding this mechanism and determining what leads to the high conversion and selectivity of this catalyst will help in the future development of similar catalysts with increased efficiency, conversion, and selectivity, potentially leading to a wider availability of these fuels.