CO2 Reduction Catalyzed by Mercaptopteridine Open Access
Xiang, Dongmei (2016)
Abstract
The catalytic reduction of CO2 is of great interest since it plays a significant role in climate change and the global energy cycle. Inspired by the role of pterin in biological systems as a redox mediator and C1 carrier, we studied 6,7-dimethyl-4-hydroxy-2-mercaptopter 6,7-dimethyl-4-hydroxy-2-mercaptopteridine (PTE) to catalyze CO2 reduction on the glassy carbon electrode. In bulk electrolysis of a saturated CO2 solution in the presence of the PTE catalyst, Fourier transform infrared data show the progression of carbarmate intermediate and reduced products, including formate, formaldehyde and methanol. 13C NMR spectroscopy and gas chromatography data prove the production of methanol with a Faradaic efficiency of 10-23%. A multiple hydride transfer mechanism is proposed for the progressive multi-electron reduction of CO2. PTE is proved to catalyze the reduction of CO2 at low overpotential and without the involvement of any metal.
Photochemical CO2 reduction was studied by using CdSe quantum dots as a photosensitizer. Transient absorbance spectroscopy in the ultraviolet spectral region proves the electron transfer from quantum dots to PTE catalyst. The photo-generated 1 e- reduced PTE is formed. However, the active form of catalysis should be the 2 e- reduced PTE, which calls for future work.
Table of Contents
Chapter 1. Introduction 1
1.1. The significance and challenge of CO2 reduction 1
1.2. Brief review of current CO2 reduction catalysis 7
1.2.1. Electrochemical CO2 reduction 8
1.2.1.1. Electrodes 8
1.2.1.2. Molecular electrocatalysts 10
1.2.2. Photochemical CO2 reduction 13
1.3. Discussion and debate of Bocarsly work 14
1.4. The role of pterin in biologic catalysis as C1 carrier 18
Reference 21
Chapter 2. CO2 Reduction Catalyzed by Mercaptopyridine and its Derivatives Attached on Gold Film 33
2.1. Introduction 33
2.2. Experiment section 34
2.2.1. Chemical and material 34
2.2.2. Electrochemistry set-up 34
2.2.3. FTIR set-up 35
2.2.4. Sample preparation and experimental process 36
2.2.5. Gas chromatography 37
2.3. Results and discussion 37
2.3.1. Comparison of redox chemistry on different electrodes 38
2.3.2. Studies of mercaptopyridine as a catalyst attached on gold films 40
2.3.3. Studies of mercaptopteridine as a catalyst attached on gold films 43
2.4. Conclusion 45
References 46
Chapter 3. CO2 Reduction Catalyzed by Mercaptopteridine on Glassy Carbon 48
3.1. Introduction 48
3.2. Experiment section 49
3.2.1. Chemical and material 49
3.2.2. Electrochemistry set-up 49
3.2.3. FTIR set-up 50
3.2.4. NMR 51
3.2.5. Gas chromatography 51
3.3. Results and discussion 52
3.3.1. Cyclic Voltammetry of PTE 52
3.3.1.1. Redox of PTE 52
3.3.1.2. PTE electrocatalysis 53
3.3.1.3. pH dependence 57
3.3.1.4. Salt concentration dependence 59
3.3.2. FTIR spectroelectrochemistry 60
3.3.3. Product analysis: GC and NMR 62
3.3.4. Proposed mechanism 65
3.3.5. Kinetic isotope effect (KIE) 65
3.3.6. Pte(II) and folic acid 70
3.4. Conclusion 70
References 72
Appendix 1 74
Chapter 4. Light-Driven CO2 Reduction 76
4.1. Introduction 76
4.2. Experiment 77
4.2.1. CdSe quantum dots synthesis 77
4.2.2. Transient absorbance spectroscopy 78
4.2.2.1. Transient absorbance spectroscopy-Visible region 78
4.2.2.2. Transient absorbance spectroscopy-UV region 78
4.2.3. Spectroelectrochemistry 79
4.3. Results and dicusssion 79
4.3.1. UV-Vis spectroelectrochemistry 79
4.3.2. PTE-quantum dots 82
4.3.3. Other photosensitizer (NADH, Ru(bpy)32+) 87
4.4. Conclusion 89
References 90
Chapter 5. Summary 92
Reference 93
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