NSF-DFG Confine: Plasma-Catalysis in Confined Spaces for Cold Start NOx Abatement in Automotive Exhaust

该项目旨在改变传统的化学加工方式，以确保可持续发展的未来。催化作用促进所需的化学反应，它在定义减少污染、高能量密度燃料以及高效安全的燃料和肥料的现代标准方面发挥了关键作用。本项目旨在通过非平衡等离子体与表面催化反应的耦合，发展对化学催化实践中新概念的理解。在毛细管微反应器中减少氮氧化物，模仿现代催化转化器中的“蜂窝状单体”，在接近环境温度下作为测试平台系统。交通运输尾气排放占危害人类健康和环境的氮氧化物污染的大部分。最先进的汽车尾气后处理系统可以有效地修复超过阈值点燃温度473 K（200摄氏度）的氮氧化物，足以克服催化过程中固有的动力学限制。该项目利用等离子体化学和热催化过程之间的相互作用，在有限的几何形状中，使汽车在接近环境温度的情况下减少氮氧化物。这解决了发动机预热期间的“冷启动”汽车排放，这占氮氧化物车辆污染的80%。该项目进一步促进了美国和德国在STEM领域的科学合作和培训。等离子体化学以体积为单位发生，涉及到短寿命的反应中间体——离子、自由基、电子和振动激发的物质——当它们撞击到选择性的催化表面时，可能会影响化学转化和传统催化无法达到的途径。等离子体反应时间尺度的差异（-10^-6到10秒）和催化化学反应时间尺度的差异（10^-1到10秒），以及等离子体（体积）和催化（表面）化学反应的不同长度尺度意味着，只有当表面体积比很大，才能实现等离子体和表面催化化学之间的有效耦合，从而使短寿命等离子体衍生的中间体高通量到达催化剂表面。因此，能够实现非常高的表面体积比的约束，是将体积和快速等离子体化学与选择性、较慢的表面催化过程结合起来的关键。该项目结合了反应器设计、先进的光谱和光谱诊断以及多尺度建模，以研究在受限反应环境中影响等离子体催化化学耦合的反应和输运现象。这包括(1)在毛细管微反应器内等离子体和热催化过程的联合操作中探测反应物质的特征扩散时间尺度和寿命；(2)开发光谱和光谱测量工具，以识别和枚举气相和催化剂表面上的短寿命反应中间体；(3)开发描述这些受限反应环境中基础过程的多尺度模型。这将有助于阐明反应和输运现象如何影响等离子体-催化耦合，并描述新的催化物种和氮氧化物还原途径。该项目是通过“密闭空间中的化学和传输（NSF-DFG）”机会获得的，这是一项由美国国家科学基金会和德国科学研究协会（DFG）参与的合作征集。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。

This project seeks to transform traditional chemical processing to ensure a sustainable future. Catalysis, which facilitates desired chemical reactions, has played a key role in defining the modern standard of pollution abatement, high-energy density fuels, and proficient and safe fuels and fertilizers. This project aims to develop an understanding of new concepts in the practice of chemical catalysis enabled by coupling of non-equilibrium plasma with surface catalyzed reactions. NOx abatement in capillary microreactors, mimicking “honeycomb monoliths” in modern-day catalytic converters, at near ambient temperatures serve as a testbed system. Tailpipe emissions in transportation account for a majority of NOx pollution harming human health and the environment. State-of-the-art automobile exhaust after-treatment systems remediate NOx efficiently above a threshold light-off temperature 473 K (200 degrees C), sufficient to overcome kinetic limitations inherent in catalytic processes. The project harnesses interactions among plasma chemistry and thermocatalytic processes in confined geometries to enable NOx reduction in automobiles at near ambient temperatures. This addresses “cold start” automotive emissions during engine warm up, which account for 80% of NOx vehicular pollution. This project furthers US-German scientific collaboration and training in STEM.Plasma chemistry occurs volumetrically and involves short-lived reactive intermediates—ions, radicals, electronically- and vibrationally-excited species—which when impinged on a selective catalytic surface could effect chemical transformations and pathways inaccessible to conventional catalysis. The disparity in reaction timescales of plasma (sub-10^-6 to 10 s) and catalytic chemistry (10^-1 to 10 s) and the different length scales for plasma (volume) and catalytic (surface) chemistry implies that effective coupling between plasma and surface catalytic chemistry can only be achieved if surface-to-volume ratios are large to enable a high flux of short-lived plasma-derived intermediates to the catalyst surface. Hence, confinement, enabling very high surface-to-volume ratios, is key to coupling volumetric and fast plasma chemistry with selective, slower surface-based catalytic processes. The project combines reactor design, advanced spectroscopic and spectrometric diagnostics, and multiscale modeling to examine reaction and transport phenomena impacting plasma-catalytic chemistry coupling in confined reaction environments. This includes (1) probing characteristic diffusion time scales and lifetimes of reactive species in combined operation of plasma- and thermocatalytic processes within capillary microreactors, (2) developing spectroscopic and spectrometric tools to identify and enumerate short-lived reactive intermediates in the gas phase and on catalyst surfaces and (3) developing multiscale models describing the underpinning processes in these confined reaction environments. This will allow to elucidate how reaction and transport phenomena impact plasma-catalytical coupling and describe new catalytic species and pathways for NOx reduction. This project was awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).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.