| 總結: | Alkene epoxidation is a crucial chemical functionalization reaction that produces key chemical intermediates for the synthesis of various commercial end products. The current methods of producing epoxides are associated with a number of challenges, including the use of energy-intensive and hazardous oxidants such as chlorine or peroxides. Alternative processes that use molecular oxygen as a reagent are available, but they often require elevated temperatures and pressures, which pose significant safety concerns. To improve the safety and efficiency of epoxide production, there is a need for new methods that can overcome these limitations and enable the production of epoxides in a more sustainable and safe manner. From this perspective, this thesis work explores electrochemical alkene epoxidation using water as the oxygen source, delving into both fundamental and practical aspects of chlorine-mediated and direct approaches.
First, we discuss the mechanism of chlorine-mediated ethylene oxidation in saline water. We demonstrated that electrochemically generated chlorine selectively oxidizes ethylene to chloroethanol, which converts to ethylene oxide in alkaline aqueous electrolyte. Through detailed electrochemical kinetic studies, we reveal that the chlorine-mediated ethylene oxidation mechanism changes significantly in the presence and absence of ethylene, indicating that it is not a simple merging of the chlorine evolution and chemical chlorohydrin processes.
Next, we focus on understanding the effects of tuning single-atom dopants on manganese oxide for electrochemical direct epoxidation, employing operando X-ray absorption spectroscopy to probe oxidation state and structural changes under cyclooctene epoxidation conditions.
Finally, we present a sustainable and selective method for propylene epoxidation using an oxidized palladium-platinum alloy catalyst. This catalyst demonstrates remarkable Faradaic efficiency and rate toward epoxidation under ambient temperature and pressures, outperforming previously reported electrocatalysts for direct epoxidation. The reaction mechanism is investigated using a multi-faceted approach, including kinetic rate measurements, probe substrate analysis, and substrate-based descriptor assessment. This work advances sustainable epoxide synthesis, which currently has significant energy and environmental footprint.
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