Oxidative Studies in Decontamination and Water Oxidation Catalysis Open Access

Sullivan, Kevin Paul (Spring 2019)

Permanent URL: https://etd.library.emory.edu/concern/etds/vh53ww558?locale=en


Oxidation reactions are ubiquitous throughout our society. The development of oxidation catalysts has propelled the advancement of civilization and allowed for significant advancements in science and technology. However, the Earth is currently entering a period in which human activities are causing substantial damage both through chemical pollution and global warming resulting from production of greenhouse gasses. This work addresses issues related to both these concerns, by outlining efforts towards the development of oxidation catalysts in three systems relevant to mitigating the impacts of toxic or polluting chemicals. In the first, synthesis and characterization of a new class of organic/inorganic hybrid polymers composed of covalently-bound 1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate clusters with varying counter-cations is described. These materials form gels within seconds upon contact with polar aprotic organic liquids and catalyze the degradation of odorants and toxic molecules under mild conditions including aerobic oxidation of thiols, hydrogen peroxide-catalyzed oxidation of sulfides, and hydrolysis of organophosphate chemical warfare agent analogues. The second project describes efforts towards the development of rapid aerobic oxidation catalysts for sulfoxidation reactions. Systems involving tetrabutylammonium tribromide and tetrabutylammonium nitrate are studied and optimized for catalyzing the aerobic oxidation of the mustard gas analogue 2-chloroethyl ethyl sulfide. The addition of Cu(II) to this system results in significant rate enhancements, as well as provides a detection capability by changing color in the presence of sulfides, followed by recovery of the original color when the sulfoxidation is complete. Finally, the third project described in this work details stability studies conducted on the water oxidation catalyst Na10[Co4(H2O)2(VW9O34)2] • 26 H2O. This polyoxometalate has been the subject of an ongoing debate regarding its stability under water oxidation catalysis conditions. Solution studies are examined clarifying the stability limitations in this system through 51V NMR resonance experiments on the polyoxometalate. The study demonstrates that the observed catalytic activity cannot be explained simply by Co(II)aq, but arises from multiple active water oxidation catalyst species in solution.

Table of Contents

Chapter 1: Introduction. 1

Overview of Oxidation Catalysis. 1

1.1       Oxidation on Earth. 2

1.2       Chemistry and Global Stewardship. 4

1.3       Examples of Important Oxidation Reactions. 8

1.3.1 Decontamination of Toxic Compounds. 8

1.3.2 Water Oxidation. 12

1.4       Polyoxometalates in Oxidation Catalysis. 17

1.4.1 Overview of Polyoxometalates. 17

1.4.2 Polyoxometalates in Decontamination. 19

1.4.3 Polyoxometalates in Water Oxidation. 19

1.5       Scope of Current Work. 20

1.6       References. 23

Chapter 2: Polyoxometalate-Based Gelating Networks for Entrapment and Catalytic Decontamination 36

2.1       Introduction: Multifunctional Catalytic Polymers. 37

2.1.1 Discovery of Hexavanadate-Based Polymers. 37

2.1.2 Hybrid Organic/Inorganic POMs. 39

2.1.3 Overview of Gels. 40

2.2       Experimental 43

2.2.1 General Methods. 43

2.2.2 Synthesis of Hexavanadate Materials. 47

2.2.3 Conditions for Catalytic Reactions. 49

2.2.4 Gelation Studies. 52

2.3       Results and Discussion. 52

2.3.1 Characterization. 52

2.3.2 Gelation Capability. 64

2.3.3 Catalytic Activity. 70

2.4       Conclusions. 79

2.5       References. 80

Chapter 3: Selective Aerobic Sulfoxidation by Brx/NOx Systems. 88

3.1       Introduction: Oxidation of Sulfides. 89

3.1.1 Overview of Sulfoxidation Reactions. 89

3.1.2 Introduction to Brx/NOx systems. 93

3.2       Experimental 97

3.2.1 General Methods. 97

3.3       Results and Discussion. 98

3.3.1 Revisiting the Brx/NOx reaction. 98

3.3.2 Reaction Optimization. 99

3.3.3 Mechanistic Studies. 106

3.3.4 Metal-Catalyzed Reactions. 112

3.3.5 Solid formulation. 120

3.4       Conclusions. 122

3.5       References. 123

Chapter 4: Speciation and Dynamics in the Na10[Co4V2W18O68]/Co(II)aq/CoOx Catalytic Water Oxidation System.. 130

4.1       Earth-Abundant Catalysts for Water Oxidation. 131

4.1.1 Cobalt Polyoxometalate-Catalyzed Water Oxidation. 132

4.1.2 Stability of Polyoxometalate Water Oxidation Catalysts. 133

4.2       Experimental 136

4.2.1 General Methods. 136

4.2.2 Synthesis of POMs. 136

4.2.3 Experimental Methods. 138

4.3       Results and Discussion. 145

4.3.1 Synthesis of Co4V2. 145

4.3.2 51V NMR Studies. 145

4.3.3 Additional Speciation Characterization. 159

4.3.4 Kinetic Studies. 172

4.4       Conclusions. 175

4.5        References 176

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