Imaging of Element-Specific 3D Distribution Dynamics in Working Bimetallic Catalysts by in-situ Anomalous Small-Angle X-Ray Scattering

有了这个奖项，化学系的化学测量和成像（CMI）计划将支持天普大学的孙玉刚博士将联合收割机计算和X射线方法结合起来，开发出一种快速化学成像工具，可以绘制出单个金属的位置。 利用这个工具，他和他的团队试图在原子的基础上收集纳米级金属催化剂颗粒中金属的实时三维“图片”。许多替代燃料来源来自基于这种金属纳米颗粒的催化过程。 新的测量方法揭示了催化剂中金属原子的排列和位置以及原子位置和排列在化学转化过程中如何变化的信息，这些方法具有很大的潜力，可以增强我们对这些系统中催化作用的基本理解。 这种针对长期挑战的新解决方案很可能为原子级结构如何影响纳米级催化剂的行为提供新的见解，同时也有可能了解其他纳米颗粒的化学行为如何随着时间的推移而受到其环境的影响。预计这些新的测量方法将对工业中使用的化学反应产生重大影响，从生产化学或药物构件的化学反应到生产替代燃料的化学反应。在国家实验室使用最先进的大型同步加速器X射线设施，培养学生成为典型化学家技能中代表性不足的重要领域的专家。更广泛地说，这项研究教育了一个高度多样化的学生群体，让他们了解如何使用尖端的化学测量工具来解决重要的科学问题，重点是替代燃料领域的劳动力发展。孙博士和他的团队还将研究成果融入费城社区，并通过一系列教育和外展计划，向当地城市/高需求学校和社区学院的学生和教师，以及参加国家科学基金会本科研究计划和天普大学TUteach计划的学生提供服务。在这个项目中，Sun博士和他的研究团队将小角X射线散射（SAXS）测量与从头算建模和计算结果相结合，以构建具有明确化学成分的均匀纳米颗粒的三维（3D）几何结构模型。该项目正在开发这种成像协议，以研究在工作条件下纳米颗粒催化剂中3D原子分布的元素特定演变。这种努力需要两个连续的步骤。首先，元素特定的SAXS图案从高度卷积的反常小角X射线散射（ASAXS）的纳米粒子的基础上惩罚回归方法去卷积。第二，正在开发一种成像协议，通过对去卷积的元素特异性SAXS图案进行从头算建模，来确定纳米颗粒中成分分布的元素特异性3D图像。ASAXS成像协议可以通过其与工作反应堆的使用而适用于原位ASAXS成像，从而允许研究操作中的催化剂中金属的元素特定3D分布的时间分辨演化。该奖项反映了NSF的法定使命，并被认为值得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来支持。

With this award, the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry is supporting Dr. Yugang Sun at Temple University to combine computation and X-ray methods to develop a rapid chemical imaging tool that maps out the location of individual metals. Utilizing this tool, he and his team seek to glean a real-time, three-dimensional "picture" of metals in nanoscale metal catalyst particles on an atom-by-atom basis. Many alternative fuel sources are derived from catalytic processes based on such metal nanoparticles. New measurement methods that reveal information about the arrangement and location of metal atoms in the catalyst and how atom location and arrangement change during the chemical conversion process have great potential to enhance our fundamental understanding of catalysis in these systems. This novel solution to a long-standing challenge may well provide new insights into the how atomic-level structure affects behavior of nanometer-sized catalysts, while also holding potential to understand how the chemical behavior of other nanoparticles is influenced by their environment over time. These new measurement methods are anticipated to lead to significant impacts on chemical reactions used in industry, ranging from those that produce chemical or pharmaceutical building blocks to those that produce alternative fuels. The use of the state-of-the-art large-scale synchrotron X-ray facilities at national laboratories trains the students to become specialists in a significant area that is underrepresented in the typical chemist's skill set. More broadly, the research educates a highly diverse group of students about the use of cutting-edge chemical measurement tools to address important scientific problems, with an emphasis on workforce development in the field of alternative fuels. Dr. Sun and his team also integrate research outcomes into the Philadelphia community and beyond through a range of education and outreach programs to students and teachers at local urban/high-need schools and Community Colleges, as well as students participating in a National Science Foundation undergraduate research program and the Temple University TUteach initiative.In this project, Dr. Sun and his research team integrate small-angle X-ray scattering (SAXS) measurements with ab initio modeling and calculation results to construct models of the three-dimensional (3D) geometry of uniform nanoparticles of well-defined chemical composition. This project is developing this imaging protocol to enable the study of the element-specific evolution of 3D atom distributions in bimetallic nanoparticle catalysts under working conditions. Such endeavors require two consecutive steps. First, the element-specific SAXS patterns are deconvoluted from the highly convoluted anomalous small-angle X-ray scattering (ASAXS) of bimetallic nanoparticles based on penalized regression methods. Second, an imaging protocol is being developed to determine element-specific 3D images of the composition distribution in bimetallic nanoparticles through ab initio modeling of the deconvoluted element-specific SAXS patterns. The ASAXS imaging protocol may then be applicable to in-situ ASAXS imaging through its use with working reactors, allowing for the study of the time-resolved evolution of element-specific 3D distributions of metals in bimetallic catalysts in operando.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.