The Department of Chemical and Biological Engineering presents its fall seminar series featuring guest speaker Cong Liu, chemist at Argonne National Laboratory, who will give a presentation on “Understanding the Heterogeneity and Dynamic Evolution of Heterogeneous Catalysts via Combined XANES Simulations and First-Principle Mechanistic Studies.” This seminar will take place on Wednesday, November 12, from 3:15–4:30 p.m. in room 131 of Perlstein Hall.

Abstract

Single-site heterogeneous catalysts (e.g., single-atom catalysts, supported organometallics and metal hydrides, etc.) have gained increasing attention in both industry and academia, integrating crucial aspects of homogeneous catalysis (high activity and selectivity) with the stability of heterogeneous catalysts. Because high-surface-area supports are usually preferred in synthesizing these catalysts, a lot of these catalysts often present high heterogeneity in the catalytic sites, resulting in a distribution of active-site structures and site-specific activities. Meanwhile, some of these catalysts may not be stable under reaction condition and can experience dynamic evolution during catalysis. In situ spectroscopic characterization (e.g., X-ray absorption spectroscopy (XAS)) is an effective technique to characterize supported catalysts under reaction conditions. In XAS, X-ray Absorption Near Edge Spectroscopy (XANES) spectra contains key information on the local coordination environment of the metal atom(s), and thus the analysis of which is more challenging. Some key characteristics of the metal centers and their coordination environment can be directly extracted from the experimental XAS, such as average oxidation state and coordination number. However, certain bonding interactions that are key to catalysis, such as metal-hydride, often present only subtle features in XANES spectra, and these are challenging to interpret directly from experimental spectra. In addition, interpreting XANES spectra of supported catalysts with high site heterogeneity is particularly difficult. This is because XAS measures all the catalytic sites, and the response from this technique is dominated by the sites with the highest volumetric density. However, the overall activity is dominated by the sites with the highest turnover frequencies, not necessarily those with the highest density. Computational XANES simulations offer a powerful technique for interpreting experimental spectra, providing a one-to-one correspondence between the molecular structure and spectral features. In this talk, we will discuss about our recent work on supported organometallic catalysts, a supported single-atom Cu catalyst, and the Fe-N-C catalyst to demonstrate that when integrated in situ and computational XANES analyses are combined with systematic mechanistic simulations, the most active catalytic site in dynamic and disordered catalytic systems can be identified.

Biography

Cong Liu is a chemist in the Chemical Sciences and Engineering (CSE) Division at Argonne National Laboratory. She received her Ph.D. degree in physical chemistry at University of North Texas in 2013. She was then awarded the Argonne Director’s Fellowship in Materials Science Division (MSD) at Argonne. She became assistant chemist of CSE in 2016, and chemist in 2021. She is also a Consortium for Advanced Science and Engineering (CASE) Fellow at University of Chicago. Her interests cover multi-scale modeling of catalytic C-H and C-C activation, atomic layer deposition, fuel cell reactions, CO2 reduction, and advanced battery materials, as well as development of machine learning approaches for catalysis. She is leading the computational efforts in multiple DOE BES and EERE funded programs, including Catalysis Science Program, Selective Interface Reaction Program, Computational Chemical Science (CCS) Program, Clean Energy Technologies and Low-Carbon Manufacturing Program, and the Electrocat Fuel Cell consortium. Her research has resulted in more than 90 publications with more than 7,500 citations, including some of the most prestigious journals such as Science and Nature, etc.