Mehdi Zare

Date of Award

Summer 2021

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Andreas Heyden

Abstract

In recent years, the biorefining industry and biofuels have emerged as a major American energy sector. Biofuels are fuels produced from plant and animal material, also referred to as biomass. This includes wood products, manure, and corn, among other materials. Compared to fossil fuels, biofuels are significantly more environmentally friendly and thus pose less of a threat to environmental health. In 2019, the United States consumed around 14.54 billion gallons of ethanol and around 1.81 billion gallons of biodiesel. By 2030, the United States is expected to consume around 95 Mtoe of biofuels. In order to meet current demand and expected growth in demand, it is necessary to advance the efficiency of biomass processing. In this context, special characteristics of biomass feedstock (highly reactive and water soluble, aqueous, and thermally unstable) demands liquid-phase processing technologies for higher product selectivity and lower cost. As a result, to design an efficient liquid-phase process, it is critical to understand the root causes of solvent effects on surface properties and energetics. However, despite recent improvements in studying reactions at gas-solid interfaces, methods capable of investigating reactions occurring at solid-liquid interfaces are less developed; primarily due to the inherent intricacies of a reaction system comprised of both a complex heterogeneous catalyst and a condensed phase.

The objectives of this study are to develop and validate a hierarchy of multi-scale methods for computing reaction and activation free energies of elementary processes vi occurring at metal-solvent interfaces and to apply these methods to the rational design of novel heterogeneous catalysts with exceptional activity and selectivity for the liquid-phase conversion of lignocellulosic biomass into transportation fuels or commodity and specialty chemicals. To gain a fundamental understanding of the role of metal identity (catalyst) on the solvent effect, we studied the aqueous-phase effect on the initial C-H and O-H bond cleavages of ethylene glycol (being a commonly studied surrogate molecule of biomass-derived polyols) over the (111) facet of six transition metal surfaces (Ni, Pd, Pt, Cu, Ag, Au) using our explicit solvation method, eSMS. We found a significant metal dependence on aqueous solvation effects that can be traced back to a different amount of charge-transfer between the adsorbed species and metals in the reaction and transition states for the different metal surfaces. In addition, we developed a new hybrid QM/MM approach for computing solvent effects on the free energy of adsorption and desorption processes that enables us to compare our work with experimental findings quantitatively. Consequently, comparison of computational predictions to experimental data of phenol adsorption on the Pt(111) surface indicates that adsorption free energies in the aqueous phase can be determined accurately within an error less than 0.10 eV.

Rights

© 2021, Mehdi Zare

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