Oxygen atoms on transition metal surfaces are highly mobile under the demanding pressures and temperatures typically employed for heterogeneously catalyzed oxidation reactions. This mobility allows for rapid surface diffusion of oxygen atoms, as well as absorption into the subsurface and reemergence to the surface, resulting in variable reactivity. Subsurface oxygen atoms play a unique role in the chemistry of oxidized metal catalysts, yet little is known about how subsurface oxygen is formed or returns to the surface. Furthermore, if oxygen diffusion between the surface and subsurface is mediated by defects, there will be localized changes in the surface chemistry due to the elevated oxygen concentration near the emergence sites. We observed that oxygen atoms emerge preferentially along the boundary between surface phases and that subsurface oxygen is depleted before the surface oxide decomposes.

Surface structure and oxidation are key to silver-based heterogeneous catalysis. Prevention of surface reconstruction may favor electrophilic oxygen, which is believed to be the active species in silver-catalyzed oxidation. To determine whether terrace width or step geometry enables control of oxidation and concomitant reconstruction, we investigated oxidation of the topmost layer of a curved Ag(111) crystal. This crystal contains a range of terrace widths having either A- or B-type step geometries. Atomic oxygen was used to facilitate oxidation, temperature-programmed desorption quantified the extent of oxygen adsorption, and scanning tunneling microscopy characterized the formation of reconstructed areas. While A-type steps prove to have little influence, B-type steps hinder reconstruction. We attribute the difference to geometric-dependent growth mechanisms of silver oxide surface reconstructions.

In recent years, the use of silver-based materials for selective and highly active ethanol reactivity in single atom catalysis and the ethanol oxidation reaction in direct fuel cells highlights the importance of silver (Ag) in an ethanol economy. Understanding the interaction of ethanol with Ag(111) and the natural defects found on extended Ag(111) is critical to the overall understanding of more complex catalytic processes including ethanol activation over Ag-based catalysts. The research herein aims to characterize the interaction of ethanol molecules on undercoordinated defect sites of Ag(111) to mimic active sites found on Ag nanoparticle catalysts. The interaction between ethanol and Ag(111) was studied using temperature programed desorption (TPD), x-ray photoelectron spectroscopy, and density functional theory (DFT). Molecular ethanol adsorption and desorption from Ag(111) and the distinction between undercoordinated Ag(111) adsorption sites were determined using TPD in correlation with DFT. Complete analysis of TPD data for ethanol adsorbed to terrace sites was used to calculate a kinetic prefactor (3.4 × 1015) and desorption energy (0.54 eV). A better understanding of defect-dependent behavior for ethanol on silver can lead to a greater insight into high surface area nanoparticle catalysts used in industries, catalytic converters, and photo-, electro-, and heterogeneous catalysis. The results suggest that ethanol preferentially adsorbs to undercoordinated sites on Ag(111), resulting in higher binding energies for these molecules (Redhead first order approximation for desorption energies is terrace, 0.54 eV; step edge, 0.57 eV; and kink sites, 0.61 eV). Furthermore, alteration of the silver surface can lead to a redistribution of these sites.

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