Nov 2023
Abstract
Supported noble metal catalysts are extensively used in industry and their catalytic performance is strongly affected by particle size and shape. In the last decade, supported single atoms and subnanometer clusters have attracted a lot of interest since they maximize the metal utilization and have shown extraordinary catalytic properties for many reactions. However, to tailor the catalyst properties for specific reactions and determine possible limitations, there is a need to understand, on the atomic scale, the origin of their reactivity. In this talk, I will present my group’s efforts in understanding the dynamics, both structural and ligand, of supported metal single atoms and clusters and the consequences on reaction mechanisms. This is achieved through detailed kinetics measurements coupled with in-situ and in-operando infrared and x-ray absorption spectroscopies to follow the structure and coordination of the metal. An important finding is that the ability of isolated metal atoms and subnanometer clusters to bind with multiple adsorbates and dynamically restructure during the reaction cycle results in complex mechanisms. For example, Eley-Rideal mechanism, which is rarely seen on extended metal surfaces, becomes a major reaction pathway for CO oxidation on isolated Pt and Ir atoms. The effect of the reaction environment on the structural dynamics and the consequences on activity for CO oxidation and activity/selectivity for semi-hydrogenation of acetylene to ethylene will be presented. Finally, I will discuss the differences between supported single atoms, small clusters and extended metal surfaces as well as their potential advantages and limitations.
Bio
Dr. Karim is a Full Professor in the Department of Chemical Engineering at Virginia Tech. Prior to Virginia Tech in 2014, he worked as a senior research scientist (2008-2014) at the Pacific Northwest National Laboratory (PNNL). Dr. Karim earned his BSc in Biomedical Engineering from Cairo University in Egypt (2000) then moved to the U.S. and received his PhD in Chemical Engineering from the University of New Mexico working with Prof. Abhaya Datye (2001-2006) followed by a postdoctoral fellowship at the University of Delaware in the Chemical Engineering Department with Prof. Dionisios Vlachos (2007-2008). His research is focused on the synthesis and characterization of nanomaterials, and the design of heterogeneous catalysts for energy and environmental applications using controlled synthesis, detailed kinetics and a combination of advanced in-situ and in-operando characterization techniques (electron microscopy, microcalorimetry, SAXS, XAFS, FTIR).
Dr. Karim has received the 3M Non-Tenured Faculty Award (2015), Virginia Tech Institute for Critical Technology and Applied Science (ICTAS) Junior Faculty Award (2015), 2021 Industrial & Engineering Chemistry Research Class of Influential Researchers, Virginia Tech College of Engineering Dean’s award for Excellence in Research (2022). He is a co-principal investigator for the Synchrotron Catalysis Consortium (SCC) and is a member of the Young Editorial board for Journal of Energy Chemistry. Dr. Karim has co-authored 70 peer reviewed publications, one patent and delivered over 40 invited lectures and presentations.