AVS 65th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Wednesday Sessions
       Session HC+SS-WeM

Paper HC+SS-WeM6
Adsorption, Thermal Stability, and Kinetics of Atomic Oxygen at Ag(111) and Ag(110) Surfaces

Wednesday, October 24, 2018, 9:40 am, Room 201A

Session: Mechanisms and Reaction Pathways of Heterogeneously Catalyzed Reactions
Presenter: Sara Isbill, University of Tennessee Knoxville
Authors: S. Isbill, University of Tennessee Knoxville
S. Roy, University of Tennessee Knoxville
Correspondent: Click to Email
Transition-metal surfaces are commonly used to catalyze transformations of small organic compounds, but the catalyst structures and catalytic mechanisms are not yet completely understood. Silver surfaces are important industrial catalysts for the partial oxidation of ethylene to ethylene oxide and methane to methanol. While significant strides have been taken towards revealing the complex chemical pathways of oxidation reactions on silver surfaces, the role of subsurface oxygen (oxygen adsorbed just beneath the surface) in surface reconstruction and oxidative catalysis by silver has yet to be elucidated. In the present study, density functional theory (DFT) was used to probe the interactions of atomic oxygen with the surface and subsurface of Ag(111) and Ag(110) surfaces. The goal was to investigate adsorption, thermal stability, and kinetics of surface and subsurface oxygen at different coverages on the metal surfaces and examine their effects on the structural and catalytic properties of silver. On Ag(111), it was found that both surface and subsurface adsorption energies decreased with oxygen coverage, but surface adsorption weakened more drastically than subsurface adsorption. In contrast, on Ag(110), surface adsorption remained more favorable than subsurface adsorption at all studied coverages. Our thermodynamic and kinetic models of O/Ag(111) based on DFT-computed equilibrium constants and activation energies show that the stability of subsurface oxygen is sensitive to coverage, thereby indicating that the participation of subsurface oxygen in catalysis would strongly depend on coverage. Overall, our results provide valuable qualitative insight into the formation and motion of subsurface oxygen on Ag(111) and Ag(110) surfaces, the importance of metal-adsorbate charge transfer in these systems, and the possible roles of subsurface oxygen in catalytic oxidation by silver.