Date of Award

Winter 2018

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Gonghu Li

Second Advisor

Howard R Mayne

Third Advisor

Magaret E Greenslade

Abstract

Carbon dioxide’s (CO2) presence as a greenhouse gas has increased drastically as industry expands across the globe. The utilization of this waste product as a resource is crucial in completing its carbon cycle with fossil fuels. Unfortunately, CO2 is thermodynamically stable due favorable entropy as a gas and enthalpically stable linear carbonyls. Nature can convert this waste product to a resource via photosynthesis where CO2 is converted into sugars. Metal catalysts have been developed to mimic photosynthesis with promising results in CO2 to fuel conversion by using sunlight as an energy source. Homogeneous catalysts have been studied extensively, but they suffer from poor stability under photochemical conditions. Heterogeneous catalysts also have been previously studied due to their stability and low cost but they lack catalytic efficiency. Promising multi-functional catalysts have been developed recently, but there is a lack of understanding on the mechanism of CO2 reduction for these systems.

In Chapter I, an introduction to CO2 reduction is provided along with examples of catalysts that have been studied previously in the literature. Multiple types of catalysts are include homogeneous, heterogeneous and hybrid. Hybrid rhenium (Re) catalysts are discussed as well and further explained in Chapter II, where ligand derivatization and surface linkages are optimized for enhanced CO2 reduction. The effects of structural changes and surface attachment are investigated, and infrared studies demonstrate the importance of ligand derivatization on catalysis.

Chapter III investigates a different hybrid system where cobalt macrocycles are deposited onto mesoporous silica surfaces. The photocatalytic properties of different macrocyclic ligands are studied. A conjugated macrocycle is introduced for visible light absorption and steric effect. Additionally, each catalyst was heated to see how the changes in surface conformations affect the selectivity of CO2 reduction.

Heterogeneous catalysts are investigated in Chapter IV where cobalt is deposited as an oxide on silica and mesoporous silica surfaces. Macrocyclic ligands are added during photocatalysis to observe possible in situ formation of an active catalytic species. Loadings of cobalt are also varied to study the effect of larger or smaller cobalt sites on the surface. Chapter V expands upon heterogeneous catalysts with Cu and Sn deposited on a commercially available semiconductor, P25 TiO2. Surface CO adsorption is studied via infrared studies to help understand their role in CO2 reduction. Additionally, oxygen vacancies on TiO2 are studied for each sample for their role in the catalytic mechanism.

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