Operando Transmission Electron Microscopy - A New Tool for Catalysis Research

多年来，原位环境透射电镜技术被用于研究反应气体条件下高比表面积非均相催化剂的结构和组成。然而，在多相催化研究中，我们希望将催化剂中发生的结构和化学变化与同时测量反应产物或所谓的操作数方法联系起来。原子分辨率分析与气相催化产物同时检测的结合尚未在电子显微镜下得到证实。亚利桑那州立大学的研究员Peter Crozier愿意用一些创造性的想法、设备和方法设计来解决这个挑战。本提案的主要目标是发展原子分辨率的透射电子显微镜（TEM），并将这种方法应用于高比表面积非均相催化剂的基本问题。为了实现这一目标，将开发样品制备方法，大幅增加电子显微镜反应池中催化剂的体积，从而产生更大量的产物气体。还将开发基于电子能量损失谱和质谱的产品气体定量检测方法。电子能量损失光谱的气体分析特别适合于提出的operando目标，因为它与原子分辨率成像兼容。operando技术将用于研究纳米颗粒在催化一些重要的能量相关反应过程中发生的变化。本文将研究多种负载金属和负载氧化物催化剂在中温条件下的CO氧化反应。在显微镜反应细胞中同时检测气体产物，将有可能确定在催化开始时纳米颗粒中发生的独特结构和行为变化。实验还将进行与甲烷部分氧化有关的反应，探索其在高温条件下的操作性。这一提议具有革命性意义，因为operando TEM的成功开发将为催化研究人员提供一种强大的新原子分辨率工具，用于研究高表面积材料的结构和催化作用。利用高空间分辨率的电子能量损失光谱，还将开发一种检测单个纳米颗粒表面的气体吸附物和中间体的方法。即使在这一领域取得部分成功，也将为纳米颗粒上的气体表面相互作用提供全新的见解。operando显微技术将广泛应用于催化中的许多问题，并允许在高表面积材料上探索结构-性能关系。这项工作的长期目标是开发高空间分辨率的原位技术，使动态纳米结构材料的变化与催化性能相关联。该研究项目将培养研究生和本科生对能源相关的多相催化剂、纳米材料合成方法和先进的原位纳米表征的发展做出贡献和学习。PI教授一门关于纳米材料用于能源生产和储存的课程，并将广泛利用这项研究来教授催化纳米颗粒的基本功能。能源和催化纳米材料的教育模块将使用华硕面向中学生的Best Program和华硕面向K-12的Science is Fun Program来开发和定位。这两个拓展项目都专门针对女性和少数族裔学生，鼓励他们考虑从事科学和工程方面的职业。

ABSTRACTIn situ environmental transmission electron microscopy has been employed for many years to investigate the structure and composition of high surface area heterogeneous catalysts under reactive gas conditions. However in heterogeneous catalysis research, we want to correlate the structural and chemical changes taking place in a catalyst with simultaneous measurement of reaction products, or so-called operand methods. The combination of atomic resolution analysis coupled with simultaneous detection of gas phase catalysis products has not yet been demonstrated within the electron microscope. Investigator Peter Crozier of Arizona State University is willing to tackle this challenge with some creative thought and equipment and methodology design.The main goal of this proposal is to develop atomic resolution operando transmission electron microscopy (TEM) and apply this approach to fundamental problems in high surface area heterogeneous catalysts. To accomplish this goal, sample preparation methods will be developed that substantially increase the volume of catalyst in the reaction cell of the electron microscope so that larger quantities of product gas are generated. Quantitative methods for detecting product gases based on electron energy-loss spectroscopy and mass spectrometry will also be developed. Gas analysis with electron energy-loss spectroscopy is particularly well suited to the proposed operando goal because it is compatible with atomic resolution imaging. The operando technique will be employed to investigate the changes taking place on nanoparticles during catalysis for a number of important energy related reactions. CO oxidation at intermediate temperatures will be studied on a variety of supported metal and supported oxide catalysts. With simultaneous detection of gas products in the microscope reaction cell, it will be possible to determine the unique structural and behavioral changes that take place in the nanoparticles at the onset of catalysis. Experiments will also be performed on reactions relevant to partial oxidation of methane to explore the operando capability under high temperature conditions. This proposal is transformative because successful development of operando TEM will provide researchers in catalysis with a powerful new atomic resolution tool for correlating structure and catalysis on high surface area materials. An approach for detecting gas adsorbates and intermediates on the surfaces of individual nanoparticles will also be developed using high spatial resolution electron energy-loss spectroscopy. Even partial success in this area would provide completely new insights into gas-surface interactions on nanoparticles. The technique of operando microscopy will have wide application to many problems in catalysis and allow structure-property relations to be explored on high surface area materials. A long-term goal of this work is to develop high spatial resolution in situ techniques that allow dynamic nanostructural materials changes to be correlated with catalytic properties. This research program will train graduate and undergraduate students to contribute and learn about the developments in energy-related heterogeneous catalysts, methods of nanomaterials synthesis and advanced in situ nanocharacterization. The PI teaches a course on nanomaterials for energy production and storage and will draw extensively on this research to teach fundamental functionalities in catalytic nanoparticles. Educational modules on energy and catalytic nanomaterials will be developed and targeted using ASUs Best Program for middle school students and ASUs Science is Fun program which targets K-12. Both outreach programs specifically target female and minority student to encourage them to consider careers in science and engineering.