Understanding the restructuring of model metal catalysts in reactant gases

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Transition metals play key roles as catalysts in applications ranging from chemical and energy production to environmental remediation. Ample evidence indicates that catalyst structures do not remain unchanged during use. Instead, substantial and important restructuring occurs due to rearrangement of the metal atoms to make new structures. This restructuring has major consequences on catalytic properties, sometimes beneficial and sometimes not. Currently, scientists do not understand how the restructuring occurs at the atomic scale or under conditions similar to those used during catalysis. With funding from the NSF Chemical Catalysis Program, this research is providing a fundamental understanding of this chemistry under relevant gas pressures and reaction temperatures. It is being performed with a combination of cutting edge experiments by Dr. Franklin Tao from University of Kansas and computational modeling by Dr. Philippe Sautet from University of California Los Angeles. Drs. Tao and Sautet are incorporating this theoretical modeling and experimental work into the education and training of high school, undergraduate, and graduate students. Summer research internships for public high school students in their laboratories are also being provided. With funding from the Chemical Catalysis Program of the Division of Chemistry, Dr. Tao of the University of Kansas and Dr. Sautet from UCLA are combining advanced in situ/operando characterization and first principle based modelling to develop a fundamental understanding of the metal catalyst restructuring process. The research compares several metals (Pt, Pd, Ni, Co, Cu) under a pressure of carbon monoxide and other reactants. The experimental methods include high pressure scanning tunneling microscopy (HP-STM) and operando Ambient Pressure X-ray Photoelectron Spectroscopy. These surface-sensitive surface techniques allow for uncovering surface chemistry and structure of metals under a pressure of gas and provide an initial global view of the mechanism and determine global kinetic rates. Theoretical modelling brings an understanding of the atomistic elementary steps and of their energies. It also provides kinetic results that are compared with experimental measurement, hence validating the approach. Since large systems are required for the calculation, energies are obtained by using an accurate high dimensional neural network potential, previously trained from a density functional theory database. The influence of restructuring on catalytic reaction is being explored with the example of the water-gas shift reaction on Pt and Cu surfaces. Drs. Tao and Sautet are developing an outreach program focused on introducing high-school students to model catalysis research and on undergraduate student training.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.