ChBE Seminar Series: Structural Dynamics of Supported Metal Nano-Clusters
Speaker: Judith C. Yang, Professor of Chemical & Petroleum Engineering, University of Pittsburgh
Title: Structural Dynamics of Supported Metal Nano-Clusters
Heterogeneous catalysis, which impacts the worldwide economy and sustainability due to its ubiquitous role in energy production, depends sensitively on the nano-sized 3-dimensional structural habits of nanoparticles (NPs) and their physicochemical structural sensitivity to the environment. Our focus is on the development of integrated characterization and modeling tools and their applications appropriate for carrying out detailed studies on metallic nanoscale clusters comprised of a few to as many as 100 metal atoms. Two state-of-the-art methodologies, synchrotron X-ray absorption fine-structure (XAFS) and quantitative scanning transmission electron microscopy (STEM) methodologies are used and specially designed for determining the 3D structure and structural habits, both individually and as an ensemble, critical for understanding metallic nanoclusters. For example, we have shown that the structures of Pt NPs may be both ordered and disordered, depending on its size, support and adsorbates. While bulk amorphous Pt is unstable, its existence in NPs is a manifestation of their mesoscopic nature. As another example, the complex structures of Rh/Au bimetallic hydrogenation catalysts as synthesized via microwave heating were characterized using synchrotron XAFS and STEM. The XAFS spectra for these structures were simulated and compared against the experimental XAFS and STEM data to iteratively refine the models, revealing a distribution of atomic structures that were consistent with all experimental data. This work demonstrates that correlating the local characterization of TEM with the many-particle information from XAFS is essential to accurately describing the distribution of nanostructures as needed for theoretical modeling and understanding structure-catalytic property relationships.
Judith C. Yang is the William Kepler Whiteford Professor in Chemical and Petroleum Engineering, with a secondary appointment in Physics, at the University of Pittsburgh. She received her Bachelor’s at the University of California, Berkeley, in Physics and her PhD in Physics from Cornell University in 1993. She then went to the Max-Planck-Institute of Metallforschung, Stuttgart, Germany as a National Science Foundation (NSF) international post-doctoral fellow. In 1995, she returned to the US as a post-doc and visiting lecturer to the Frederick Seitz Materials Research Laboratory, U. Illinois at Urbana-Champaign. In 1999, she joined the faculty in Materials Science and Engineering at U. Pittsburgh. She is the 2002 recipient of the NSF career award, 2004 B.P. America Faculty fellowship, and the 2005 Chancellor’s Distinguished Research Award. She is a guest professor at Center for Advancing Materials Performance at the Nanoscale (CAMP-Nano) at the Xi’an Jiaotong University in Xi’an, China. She had been a visiting scholar in the Materials Science Department at Cambridge University and Oxford University in 2006, as well as a visiting scientist at the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory in 2012 to date. She is a 2017 American Physical Society (APS) fellow and 2018 Microscopy Society of America (MSA) fellow. Her research interests include oxidation, catalysis, surface reactions, gas-metal reactions, nanoparticles, nanostructures, and the development and use of advanced transmission electron microscopy, especially in situ and quantitative.