Operando Electron Microscopy of Nanoparticle Surfaces and Interfaces During Catalysis

该项目推进了电子显微镜作为一种工具，阐明反应条件下的负载型金属催化剂的结构。由氧化物载体上的金属纳米颗粒组成的催化剂在反应气体环境中经常会发生结构和组成的变化，而这些变化很难用间接方法来推断，从而使催化剂设计陷入了反复试验的方法。该项目将利用原位像差校正的透射电子显微镜领域的新发展，使催化转化率与催化剂结构的原子分辨率观察同时进行，从而为为广泛的商业重要催化过程设计更有效的催化剂打开大门。已开发出一种催化剂样品架，使高分辨率电子显微镜能够在商业上重要的反应，特别是与低温氢燃料电池相关的流动气体混合物的存在下进行。在反应和非反应条件下，同时测量气体组成(通过显微镜中的残余气体分析仪和电子能量损失测量)和催化剂结构的相关成像，将允许建立与催化剂活性相关的催化剂图像数据库。重点介绍了二氧化铈负载的铜或铂纳米粒子上的CO氧化、水-气变换和CO优先氧化等反应。这些系统被认为涉及纳米颗粒-载体界面上的协同反应；因此，将特别注意获得与界面区域相关的结构模体的图像。为了进行比较，将在非相互作用的载体上加载相同的金属颗粒进行相应的实验。预计图像数据库将提供有价值的信息，以指导开发在催化剂工作条件下更准确的催化剂结构模型，改进催化位置和相关反应机理的计算模型，以及预测更活跃的金属-载体组合所需的信息。该项目还将涉及一套全面的教育和推广努力，旨在激发各级学生对与电子显微镜有关的科学机会的兴趣。

The project advances transmission electron microscopy as a tool for elucidating the structure of supported metal catalysts under reaction conditions. Catalysts consisting of metal nanoparticles on oxide supports often undergo changes in structure and composition in reactive gas environments that are difficult to infer using indirect methods, thus relegating catalyst design to trial-and-error approaches. The project will exploit new developments in the field of in situ aberration corrected transmission electron microscopy, which allows catalytic conversions to be measured simultaneously with atomic resolution observations of catalyst structure, thereby opening the door to the design of more efficient catalysts for a broad range of commercially important catalytic processes.A catalyst sample holder has been developed that allows high-resolution electron microscopy to be conducted in the presence of flowing gas mixtures of the types used in commercially important reactions, especially those relevant to low-temperature hydrogen fuel cells. The simultaneous measurement of gas composition (via both a residual gas analyzer and electron energy loss measurements in the microscope) and associated imaging of catalyst structures, under both reactive and non-reactive conditions, will allow the construction of a database of catalyst images that can be related to catalyst activity. Emphasis will be placed on reactions such as CO oxidation, water-gas shift, and CO preferential oxidation on Cu or Pt nanoparticles supported on cerium dioxide. Those systems are believed to involve concerted reactions at the nanoparticle-support interface; hence, special attention will be directed to obtaining images of the structural motifs associated with the interfacial regions. For comparison, corresponding experiments will be run on the same metal particles loaded on non-interactive supports. It is anticipated that the database of images will provide valuable information to guide the development of more accurate models of catalyst structures under working catalyst conditions, improved computational models of catalytic sites and associated reaction mechanisms, and information needed to predict more active metal-support combinations. The project will also involve a comprehensive set of educational and outreach efforts designed to excite students at all levels in scientific opportunities associated with electron microscopy.