Date of Award

Spring 2023

Project Type

Thesis

Program or Major

Chemistry

Degree Name

Master of Science

First Advisor

Gonghu Li

Second Advisor

Margaret E Greenslade

Third Advisor

Roy Planalp

Abstract

Ever-increasing fossil-fuel combustion along with massive CO2 emissions has aroused a global energy crisis and climate change. The most straightforward way of tackling this problem is to reduce emissions, but this might not be enough or even possible in all instances, where the use of fossil fuels cannot be simply avoided. A more proactive approach is to capture and convert CO2 into value-added products. Unfortunately, CO2 is thermodynamically stable and its thermocatalytic conversion requires high temperatures and pressures. Alternatively, CO2 reduction could be carried out using light (photocatalysis) or electricity (electrocatalysis) as the energy input.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 briefly discussed, including homogeneous, heterogeneous, hybrid, and single atom catalysts. Heterogeneous catalysts are investigated in Chapter II where cobalt oxide is deposited on silica surfaces. Macrocyclic ligands are added during photocatalysis to allow the possible in situ formation of an active catalytic species. Ligand coordination during the reaction is possible when small cobalt oxide atomic sites are present, leading to the formation of active catalysts. A simple microwave deposition of Co(III) can eliminate multiple synthetic steps during ligand coordination and purification. Chapter III expands upon heterogeneous catalysts by depositing nickel, copper or iron oxide on SiO2 surfaces with or without cobalt oxide. For catalysts consisting of mixed metal oxides, the following trend was observed in CO2 reduction: High-CoOx-CuOx/SiO2 (synthesized with CuCl) > High-CoOx-FeOx/SiO2 > High-CoOx-CuOx/SiO2 (synthesized with CuCl2)> High-CoOx-NiOx/SiO2. The CO2-reduction activity of different single atom catalysts (SACs) is studied in chapter IV. Under high-temperature calcination, different types of functionalized carbon nitride were obtained and used as support for Co SACs. Studies using X-ray absorption spectroscopy confirmed the presence of single cobalt sites. By comparing the amount of CO production in CO2 reduction, a CoSAC@bCN sample is about 5 times more active than a sample with higher cobalt loading, indicating that only a small amount of cobalt precursors can exist in the single-atom state, and the single-atom catalyst exhibits better photocatalytic activity.

Download

Share

COinS