Understanding the Role of Activated Oxygen Species in the Room Temperature Conversion of Methane to Methanol

在化石资源中，天然气——尤其是甲烷（其主要成分）——是生产多种烃基商品化学品最具吸引力的原料。作为世界领先的甲烷生产国，美国拥有巨大的页岩甲烷储层，以及未来可获得的大量沼气，美国处于引领世界甲烷转化为化学品革命的位置。不幸的是，现有的甲烷转化过程能量效率低下，导致大量的二氧化碳（CO2）排放。现有甲烷活化方法的一个很有前途的替代方法是在催化剂的促进下进行低温、水相电化学转化。当与风能和太阳能等可再生能源结合使用时，电催化过程理论上可以实现完全无二氧化碳的化学品和甲烷燃料生产。为此，该项目研究了各种电催化甲烷反应途径，最终目标是开发出廉价、高效、经济的燃料和化学品，如甲醇。具体来说，该项目将结合两个高水平的科学目标，研究五种已知的途径，以产生甲烷-甲醇反应所需的表面活性氧。第一个目的是确定活性氧的种类以及电化学电位对反应选择性和活性的影响。对于每个活性氧途径，第二个目标是通过结合反应过程中表面物质的原位表征和电化学数据来确定速率决定步骤。这两个目标将标准电化学技术与表面增强红外光谱、同位素标记和GC/MS产物表征相结合，以揭示每种途径的速率、选择性和反应顺序。为了实现这五种途径，只需要三种不同的催化剂：氧化多晶Pt， RuO2和NiO:ZrO2。催化剂的化学性质和形状因素的数量被故意限制，以促进深入的了解，可以为进一步开发具有更大活性的甲烷活化和甲醇形成选择性的其他催化剂提供信息。通过科学目标产生的基本理解将直接提供给两个本科生主导的工程活动，从而实现研究和教育的强大整合。以实验室为基础的本科生研究将侧重于将选定的催化剂整合到新的反应器方案中。此外，本科高级设计团队将专注于设计新反应堆周围的支持性电厂平衡，并对各种配置进行初步的技术经济评估。最后，该项目将通过几个面向代表性不足的高中生的实践推广项目来平衡。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Among fossil resources, natural gas - especially methane (its chief component) – is the most attractive feedstock for producing a wide range of hydrocarbon-based commodity chemicals. As the world’s leading methane producer, and with vast reservoirs of shale methane, as well as the future availability of a significant amount of biogas methane, the U.S. is in position to lead the world in a methane-to-chemicals revolution. Unfortunately, existing methane conversion processes are energetically inefficient, resulting in significant carbon dioxide (CO2) emissions. One promising alternative to existing processes for methane activation is low temperature, aqueous electrochemical conversion as promoted by catalysts. When paired with renewable energy sources, like wind and solar, electrocatalytic processes can theoretically achieve completely CO2-free production of chemicals and fuels from methane. To that end, the project investigates various electrocatalytic methane reaction pathways, with the eventual goal of enabling the development of inexpensive, efficient, and economical fuels and chemicals, such as methanol.Specifically, the project will combine two high-level scientific aims to investigate five known pathways to create the surface-active oxygen species needed to enable the methane-to-methanol reaction. The first aim focuses on identifying the types of activated oxygen species and the effects of electrochemical potential on reaction selectivity and activity. For each active oxygen pathway, the second aim focuses on identifying the rate determining step by combining in-situ characterization of the surface species during reaction with electrochemical data. Together the two aims combine standard electrochemical techniques with surface enhanced infrared spectroscopy, isotope labeling and GC/MS product characterization to uncover the rate, selectivity, and reaction order for each pathway. To enable the five pathways, only 3 different catalysts are needed: oxidized polycrystalline Pt, RuO2 and NiO:ZrO2. The number of catalyst chemistries and form factors are purposely limited, to promote a depth of understanding that can inform further development of additional catalysts that have even greater activity towards methane activation and selectivity for methanol formation. The fundamental understanding generated through the scientific aims will be fed directly to two undergraduate-led engineering activities, allowing for strong integration of research and education. Laboratory-based undergraduate research will focus on integrating down-selected catalysts into new reactor schemes. Additionally, undergraduate senior design teams will focus on designing the supporting balance-of-plant around the new reactors, and performing preliminary techno-economic assessments of various configurations. Finally, the project will be balanced by several hands-on outreach programs to under-represented high-school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.