MSE 298 Seminar (MDEA): Dynamical Evolution of Atomically Dispersed Catalysts

Abstract: A sustainable future necessitates the search for energy- and atom-efficient materials and processes in addition to a shift towards renewable sources of energy. Precious metals are widely used in industrial and automobile catalysts to facilitate transformations that meet our energy and material needs and emission standards. As these resources are becoming increasingly scarce, the catalysis community is focusing efforts on identifying more viable atom-efficient catalysts. One way to accomplish this is by making all atoms available for reaction by atomically dispersing a precious metal on a stable support such as an oxide. While microscopy and spectroscopy combined with computational studies yield critical insights into the location and coordination of these metal centers, the study of operando characteristics remains challenging as an undercoordinated metal atom is likely to be mobile under reaction conditions. Computational catalysis studies that traditionally rely on a zero-kelvin or static quantum chemistry methods do not provide an adequate description of the dynamically evolving site. We aim to develop a dynamical picture of the active site and reaction mechanisms by combining static quantum chemistry (specifically density functional theory or DFT) with ab initio molecular dynamics (AIMD). Our group uses the automobile exhaust reaction of CO oxidation as model chemistry and atomically dispersed Pt-group metals on rutile TiO2 as the representative catalyst. Our high-temperature AIMD studies uncover the formation of near-linear O-Pt-O configurations that are thermally stable but not identified previously with conventional DFT. The metal atom also exhibits varying degrees of stability or mobility in the presence of different adsorbates at reaction temperatures, with a diffusion coefficient that is qualitatively consistent with adsorbate binding energy. We are combining these insights with DFT-driven mechanistic studies to identify preferred CO oxidation mechanisms based on both turnover frequencies as well as the dynamical stability of the metal atom in the presence of reaction intermediates. Based on this analysis and its extension to a multitude of metal coordination sites on the support, we aim to develop a computational protocol for determining site-averaged and site-optimized kinetics for these complex catalytic systems to identify stable and active atom-efficient catalysts for automobile and industrial applications.

Bio: Shaama Mallikarjun Sharada is the WiSE Gabilan Assistant Professor in the Mork Family Department of Chemical Engineering and Materials Science and assistant professor in the Department of Chemistry at the University of Southern California. Her research interests span the development and application of quantum chemistry methods to design catalysts for sustainable chemistry transformations. Her group is developing efficient algorithms, inspired from signal processing, for advancing sophisticated rate theories in catalysis. The group is also establishing frameworks for catalyst design and discovery towards efficient natural gas conversion and light-assisted carbon dioxide utilization. Sharada received her bachelor's and master's degrees in chemical engineering from the Indian Institute of Technology, Bombay (India) where she was awarded the Institute Gold Medal. She received her Ph.D. in chemical engineering from UC Berkeley in 2015 for developing efficient reaction path search algorithms for catalysis. As a postdoctoral researcher at Stanford University, her work spanned the development of machine learning density functionals and surface chemistry benchmarking databases. She is a recipient of the 2020 ACS Petroleum Research Fund Doctoral New Investigator Award and is a 2020 Scialog Fellow for the Negative Emissions Science initiative.