Operando Electron Microscopy of Nanoparticle Surfaces and Interfaces During Catalysis

Arizona State University, Scottsdale AZ

Investigators

Abstract

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.