Electrochemical Oxidation of Low Molecular Weight Alkanes to Liquid Fuels at Molecular Interfaces

低分子烷烃在低温高压下部分氧化成相应的醇被认为是催化和能源领域的重大挑战之一。大规模开采甲烷涉及能源密集型处理，如蒸汽和二氧化碳重整，以及从开采现场运输的液化。考虑到包括英国在内的世界各地分布着大量的天然气，加上当地原料生产的甲烷，有一个令人信服的理由来开发低成本/低能量的甲烷催化转化为易于运输的液体燃料(而不是液化)。在这种背景下，电化学方法为甲烷部分氧化提供了一种极具吸引力的方法，不仅在可扩展性方面，而且由于这种技术固有的低碳足迹。原则上，界面过程所需的过电位可以通过(I)直接光激发催化剂或(Ii)将电化学反应器耦合到光伏器件来产生。然而，到目前为止，还没有设计出可行的烷烃氧化电化学方法。该项目不同于所有传统的催化方法，目的是将多相催化、光催化和纳米级电催化的元素结合起来。甲烷的复杂氧化是该项目的关键，它将在水和不相容的有机溶液之间的界面上被激活，在界面上可以外部调节Galvani电位差。这种方法背后的基本原理是最大化高效纳米结构电催化剂之间的反应截面，LMWA累积在有机相中，水作为OH自由基的来源。界面电位差不仅可以改变氧化的驱动力，而且可以在氧化物和碳基纳米结构上组装高活性的催化中心方面发挥重要作用。胶体氧化物载体如二氧化钛在这一过程中可以起到多种作用，包括：促进表面羟基和活性中心之间的相互作用，在紫外光照射下产生高活性的羟基自由基，避免金属活性中心的不可逆聚集/凝聚。在碳纳米管和石墨烯的情况下，这些载体还将增强电催化活性纳米中心的稳定性，并在甲烷氧化过程中提取积累在纳米结构中的电子。在液/液界面的恒电位控制下，界面过程的动力学将通过电化学和光电化学技术进行监测。此外，产品和中间体的生成将通过各种原位和非原位技术进行研究，例如拉曼光谱和层析方法。甲烷因其天然的丰度而成为关键目标，但由于其低反应性而被认为是一个特别的挑战。因此，该方法还将扩大到包括乙烷、丙烷和丁烷等其他低分子水杨酸的电氧化。该项目将集中于两个关键目标：i.建立甲烷和其他低分子水合物在极化液/液交界处电化学/光电化学氧化为相应醇的物理原理。与分子界面的能量部分相关的多电子转移反应的新方法和催化剂。

The partial oxidation of low molecular weight alkanes (LMWA), to their corresponding alcohols, at low temperature and pressure is considered to be one of the grand challenges in the area of catalysis and energy. Large scale exploitation of methane involves energy intensive processing, such as steam and carbon dioxide reforming, as well as liquefaction for transport from the extraction field. Considering the vast amount of natural gas distributed around the world, including the UK, in addition to local methane produced by feedstock, there is a compelling case to develop low cost/energy catalytic conversion of methane to easily transportable liquid fuels (rather than liquefaction). In this context, electrochemical methods provide an extremely attractive approach to the partial oxidation of methane, not only in terms of scalability, but also due to the inherent low carbon footprint of such technology. In principle, the required overpotential for the interfacial process can be generated by (i) direct photoexcitation of the catalyst or by (ii) coupling electrochemical reactors to photovoltaic devices. However, to date, no viable electrochemical method has been designed for alkane oxidation. This project departs from all conventional catalytic approaches, in order to combine elements of heterogeneous catalysis, photocatalysis and nanoscale electrocatalysis. The complex oxidation of methane, the key LMWA in this project, will be activated at the interface between an aqueous and an immiscible organic solution, at which the Galvani potential difference can be tuned externally. The rationale behind this approach is to maximise the reaction cross-section between high performing nanostructured electrocatalysts, LMWA accumulated in the organic phase and water as a source of OH radicals. The interfacial potential difference can play an important role, not only in changing the driving force for the oxidation, but also in the assembly of highly reactive catalytic centres supported on oxides and carbon based-nanostructures. Colloidal oxide supports such as TiO2 can play multiple roles in the process, including: promoting the interaction between surface OH groups and the active centres, generating highly active OH radicals upon UV-illumination and avoiding irreversible aggregation/coagulation of the metallic active centres. In the case of carbon nanotubes and graphene, these supports will also enhance the stability of the electrocatalytically active nanocentres, as well as extracting electrons accumulated at the nanostructures during methane oxidation. The dynamics of the interfacial processes will be monitored by electrochemical and photoelectrochemical techniques, under potentiostatic control of the liquid/liquid interface. Furthermore, the generation of products and intermediates will be investigated by a variety of in-situ and ex-situ techniques such as Raman spectroscopy and chromatographic methods. Methane is a key target due to its natural abundance, but is recognised to be a particular challenge due to its low reactivity. Consequently the approach will also be broadened to span the electro-oxidation of other LMWA such as ethane, propane and butane. The project will focus on two key goals:i. Establishing the physical principles underlying the electrochemical / photoelectrochemical oxidation of methane and other LMWA to the corresponding alcohols at polarisable liquid/liquid junctionsii. Novel approaches and catalysts for multi-electron transfer reactions of relevance to the energy sector at molecular interfaces.