Chemical and Structural Consequences of High Oxygen Coverages and Subsurface Oxygen in Catalytically Active Metals

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Catalysis is essential to technological advances, especially in the chemical industry. Partial oxidation of organic chemicals on metal surfaces (catalysts) is an extensively used catalytic reaction. However, the atomic-level details of these seemingly straightforward oxidation reactions have remained elusive. Many aspects of the metal surface factor in to its reactivity. Among them, the arrangements of metal atoms, and the abundance of various oxygen-containing species, play key roles. In this project, Dr. Dan Killelea of Loyola University Chicago (LUC) and his research group are studying how the surface structures and reactivity of these metal catalysts change under reaction conditions. Significantly, this project also examines subsurface oxygen, which are oxygen atoms dissolved into the near-surface layers of the solid catalysts. Although subsurface oxygen atoms may not be reactants themselves, they may affect the reactivity and properties of the surface in important ways. While surface chemistry research is central to this proposal, this project broadens participation in science outreach efforts to the Chicago Public Schools (CPS). One goal of this project is to support students of under-represented socioeconomic status to develop their interest in scientific careers. Through this project, LUC students engage CPS students in several contexts: the high school lab, tours of LUC facilities, and a Summer Internship Program. Additional engagement and outreach efforts include hosting CPS student meetings with admissions counselors from local universities, and trips to Argonne National Laboratory. With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Dan Killelea of Loyola University Chicago is advancing the understanding of the behavior of subsurface oxygen in metals by investigating its formation, and physical and chemical effects in three catalytic metals: rhodium, palladium, and platinum. In each, subsurface oxygen is thought to contribute to the selectivity of catalytic processes, but the origins of their activity remain unclear. The reactivity of the metals with various oxygen abundances is measured and the formation of subsurface oxygen is quantified with a combination of surface science techniques. The changes in the surface structures of the oxidized metals are directly observed using Scanning Tunneling Microscopy (STM). In addition to the STM images, density functional theory (DFT) is used to identify stable structures of surface and subsurface oxygen atoms on these metals and their effects. The data obtained with STM is complemented with other surface science measurements. In concert, these provide a detailed picture of the ensemble-averaged physical and chemical properties of metal surfaces with subsurface oxygen. The results of this project advance surface catalysis by providing much needed fundamental information about subsurface oxygen and reveal the importance of it in industrially relevant heterogeneously catalyzed reactions. Additionally, support from the NSF strengthens active collaborations with researchers in The Netherlands, Tulsa, and Chicago, as well as outreach efforts to local Chicago Public High Schools.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.