In Situ X-ray Probes of Surface-Mediated Pollutant Formation

该项目旨在展示如何使用X射线光谱仪来探测燃烧源界面处污染物形成的详细微观方面。 由于燃烧过程，许多污染物被引入环境中，并且人们越来越认识到，与污染物的产生相关的重要途径涉及多相过程，即，表面反应，其中，没有反应途径或动力学的明确的机理图。 该项目将开发仪器，生成关于具有重大健康影响的污染物如何形成的基本信息，从而提供减少其产生所需的知识。 将开发一个用于同步加速器X射线光谱实验的终端站，以监测燃烧过程的微观方面。 终端站将是一个真空系统，带有一个温度可调的样品保持器，可以加入感兴趣的反应物。 该系统将被设计为使得荧光产率XAFS（s-射线吸收精细结构）光谱可以以各种方式进行。 将生成不同类型的X射线光谱。 扩展X射线吸收精细结构（EXAFS）光谱将用于确定结构信息，X射线吸收近边结构（XANES）光谱将用于化学指纹识别应用。 具体地，该终端站将被优化用于探测含氯芳族物质（例如，氯苯酚）吸附在金属氧化物表面，以及它们如何反应形成多氯二苯并对二恶英和二苯并呋喃（PCDD/Fs）。 EXAFS光谱将用于确定芳香族化合物（如2-氯苯酚）如何吸附在氧化的金属表面。 此外，EXAFS光谱将用于确定反应后，反应中间体的结构信息已被允许进行。 还可以通过探测更有限的光谱范围（XANES区域）来生成燃烧过程的动力学数据。%统一这些想法的关键点是，通过结合环境科学和x射线光谱学的技术，可以生成全新类型的数据，以阐明燃烧过程中产生污染物的化学途径。 在仪器开发和环境科学应用领域接受培训的学生，这也是美国工业的优先事项，将在这个就业市场上具有很强的竞争力。

This project aims to show how an X-ray spectroscopy apparatus can be used to probe detailed microscopic aspects of pollutant formation that occur at interfaces in combustion sources. Many pollutants are introduced into the environment as a result of combustion processes, and there is a growing realization that important pathways related to the production of the pollutants involve heterogeneous processes, i.e., surface reactions, for which, there is no clear mechanistic picture of the reaction pathways or kinetics. This project carries to develop instrumentation that generates essential information regarding how pollutants with significant health effects are formed, and thereby provide the knowledge required for reducing their production. An end-station for synchrotron-based x-ray spectroscopy experiments will be developed for monitoring microscopic aspects of combustion processes. The end-station will be a vacuum system with a temperature-regulated sample holder that can be dosed with reactants of interest. The system will be designed so that fluorescence yield XAFS(s-ray absorption fine structure) spectroscopy can be performed in a variety of ways. Different types of x-ray spectra will be generated. Extended x-ray absorption fine structure (EXAFS) spectroscopy will be used for determining structural information, and x-ray absorption near edge structure (XANES) spectroscopy will be used for chemical fingerprinting applications. Specifically, this end-station will be optimized for probing how chlorine-containing aromatic species (e.g., chlorophenols) are adsorbed on metal oxide surfaces, and how they react to form polychlorinated dibenzo-p-dioxins and dibensofurans (PCDD/Fs). EXAFS spectra will be used to determine how aromatic compounds (such as 2-chlorophenol) are adsorbed on oxidized metal surfaces. Also, EXAFS spectra will be used to determine structural information on reaction intermediates after the reaction has been allowed to progress. It will also be possible to generate kinetic data on combustion processes by probing a more limited spectral range, the XANES region.%%%The key point unifying these ideas is that by combining techniques from environmental science and x-ray spectroscopy, wholly new types of data can generated to elucidate chemical pathways that generate pollutants in combustion processes. Students trained in areas of instrumentation development and applications to environmental sciences, which are also priorities for U.S. industry, will be highly competitive in this job market.