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A study on catalytic reactions over TiO2- and WO3-based catalysts prepared by surface modifications with V- and N-dopants and plasma processes

초록/요약

Metal oxides are frequently used in various forms of catalysts. Among them, TiO2 is a representative oxide system which is widely used as a photocatalyst as well as a thermal catalyst. In addition, WO3 is also a widely studied material in various applications as catalysts and sensors due to its facile redox properties associated with its color changes. Based on this motivation, we fabricated TiO2–or WO3–based oxide systems through hydrothermal and plasma-assisted methods and studied catalytic reactivity in relation to its surface properties. In addition, to extend our study toward an understanding on how to enhance catalytic properties of these functional materials, we also studied the characteristics of N2 plasma and employed the afterglows of the N2 plasma for surface modification of TiO2 films. Finally, we have applied our present understanding on the role of oxide catalysts and plasma into the development of a new one-step catalytic process for the catalytic conversion of methane into methanol, which is at the heart of C1 chemistry.

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목차

Chapter 1. Thermal transformation of anatase TiO2 nanocrystals and their photocatalytic activity 1
1.1. Introduction 1
1.2. Experimental details 4
1.2.1. Preparation and modification of anatase TiO2 nanocrystals 4
1.2.2. Characterization methods and techniques 5
1.2.3. Photoactivity evolution 6
1.3. Results and Discussion 7
1.3.1. Analysis of as-synthesized anatase TiO2. 7
1.3.2. Analysis of temperature-controlled anatase TiO2. 11
1.3.3. Photoactivity of anatase TiO2 at 300 and 600 19
1.4. Conclusion 23
Chapter 2. V-doping of anatase TiO2 nanocrystals for the control of its thermal and photocatalytic reactivities 24
2.1. Introduction 25
2.2. Experimental details 27
2.2.1. Synthesis of V-doped anatase TiO2 nanocrystals 27
2.2.2. Synthesis of VOx on TiO2 nanocrystals 28
2.2.3. Characterization and analysis of V-TiO2 experiment 29
2.3. Results and Discussion 30
2.3.1. Effect on anatase TiO2 nanocrystals by V-dopants 30
2.3.2. Impact on catalytic reaction of TiO2 by vanadia loading 45
2.4. Conclusion 57
Chapter 3. N-doping of anatase TiO2 nanocrystals with N2 plasmas and their characterization 59
3.1. Introduction 59
3.2. Experimental details 61
3.2.1. Preparation anatase TiO2 nanocrystals film 61
3.2.2. Analysis system of N2 plasma emission spectrum 62
3.2.3. The plasma condition of N-doping on anatase TiO2 nanocrystals 63
3.2.4. Analysis of N2 plasma spectrum and prepared N-doped TiO2 63
3.3. Results and Discussion 65
3.3.1. Analysis of various changes in afterglow of N2 plasma generated 65
3.3.2. A study on selective surface nitridation of TiO2 nanocrystals in the N2-O2 afterglows of UHF plasmas 72
3.4. Conclusion 86
Chapter 4. Synergistic roles of Pd and WO3 in CO oxidation over Pd/WO3 films produced on a glass substrate 88
4.1. Introduction 88
4.2. Experimental details 90
4.2.1. Pd/WO3 film synthesis 90
4.2.2. Characterization 90
4.2.3. Measurements of CO oxidation reactivity 91
4.3. Results and Discussion 91
4.3.1. Structural characterization of the film 91
4.3.2. CO oxidation reaction kinetics over the film 93
4.3.3. XPS study of the sample 99
4.4. Conclusion 105
Chapter 5. A direct methane-to-methanol conversion (C1 chemistry) process employing RF plasma and oxide-based catalysts 106
5.1. Introduction 106
5.2. Experimental details 108
5.2.1. Preparations of various catalysts 108
5.2.2. Setting of RF plasma reactor 109
5.2.3. Experimental products analysis 110
5.3. Results and Discussion 111
5.3.1. Various experiment conditions of RF plasma 111
5.3.2. Changes in methanol production by direct or indirect excitation conditions in PPC systems 115
5.3.3. Change in methanol yield of IPC system using a capillary doped with TiO2 catalyst 118
5.4. Conclusion 121
REFERENCES 123

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