Operando Transmission Electron Microscopy - A New Tool for Catalysis Research

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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.