Photooxidation of Methane over Au/SiO₂ catalysts under Mild Conditions
- 주제(키워드) interband transition , charge transfer , partial oxidation , gold , nanoparticle
- 주제(DDC) 621.042
- 발행기관 아주대학교 일반대학원
- 지도교수 Eun Duck Park
- 발행년도 2024
- 학위수여년월 2024. 2
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000033318
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Accounting for 34 percent of natural gas, methane is a considerable component to address worldwide energy consumption. Methane conversion to functionalized-valuable products catalyzed by photocatalytic systems is promisingly hypothesized as the alternative under simultaneously harvesting solar energy. Unlike the traditional thermo-catalysis, photocatalysis can generate high energetic charge carriers under mild conditions which can activate and cleavage C-H bond of methane molecules. The spatial redox reactions within photocatalyst can prevent unnecessary radical collisions, thus further enhancing thermodynamics equilibrium aspect and suppressing the carbon dioxide generation caused by the overoxidation. As an extension of photocatalysis in the use of plasmon resonance nanoparticles (NPs), the plasmonic catalysis emerges at the interface of chemistry, plasmonic, and quantum electrodynamics in opening a brightening future to control the rates and selectivity of photocatalysis. Due to the unique optical properties, a variety of noble and non-noble metals can functionally behave as plasmonic nanomaterials (e.g. nanostructured Au, Ag, Cu). The localized surface plasmonic resonance (LSPR) effect is importantly controllable on the activity of plasmonic materials. This study presents a partial oxidation approach for the selective conversion of gaseous methane to liquid formic acid (HCOOH) while suppressing carbon dioxide production. This photoreaction capitalizes on the chemical potential inherent in charge carriers generated via interband transitions of gold nanoparticles. These energetic electron and hole carriers interact profoundly with adsorbed oxygen molecules (O₂), yielding reactive singlet oxygen (¹O₂) species. The investigation shows spin-forbidden transitions facilitated by a dexter-type electron exchange process. Remarkably, the resultant ¹O₂ species effectively reduce the energy barrier associated with C–H bond activation to 21.1 kJ mol¯¹. This process initiates the catalytic cascade following the Eley-Rideal model at ambient conditions. Consequently, it drives the preferential production of the oxygenated liquid product, HCOOH, demonstrating an impressive selectivity of > 97%.
more목차
CHAPTER 1. INTRODUCTION 1
1.1. Background 1
1.2. Noble metals induced photocatalysis systems. 9
1.3. Reactive oxygen species (ROS) 26
CHAPTER 2. EXPERIMENTS 29
2.1. Materials 29
2.2. Catalyst preparation procedure 29
2.3. Catalyst characterization 30
2.4. Photoreaction procedure 31
2.5. Kinetic evaluation 32
2.6. Singlet oxygen (¹O₂) detection 33
CHAPTER 3. RESUTLS AND DISCUSSION 35
3.1 Photocatalytic oxidation of CH₄ by Au NPs. 36
3.2. Plasmonic modulation of catalytic activity. 48
3.3. Determination of the time-dependent concentrations for the oxygenated products in CH₄OR 49
3.4. Dependence of CH₄OR kinetics on reactant concentrations. 51
3.5. Singlet oxygen generation induced by photoirradiation of Au NPs. 55
3.6. Metal contents dependence 62
3.7. Support dependence 71
CHAPTER 4. CONCLUSIONS 82
REFERENCES 84
