Thermally Selective Formation of Subsurface Oxygen in Ag(111) and Consequent Surface Structure

Abstract

Derouin, Jonathan; Farber, Rachael G.; Turano, Marie E.; Iski, Erin V.; and Killelea, Daniel. Thermally Selective Formation of Subsurface Oxygen in Ag(111) Just Accepted "Just Accepted" manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides "Just Accepted" as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. "Just Accepted" manuscripts appear in full in PDF format accompanied by an HTML abstract. "Just Accepted" manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). "Just Accepted" is an optional service offered to authors. Therefore, the "Just Accepted" Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the "Just Accepted" Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these "Just Accepted" manuscripts. Thermally Selective Formation of Subsurface Oxygen inAg (111) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 AbstractA long-standing challenge in the study of heterogeneously catalyzed reactions on silver surfaces has been the determination of what oxygen species are of greatest chemical importance.This is due to the coexistence of several different surface phases on oxidized silver surfaces. A further complication is subsurface oxygen (O sub ). O sub are O atoms absorbed into the near surface of a metal, and are expected to alter the surface in terms of chemistry and structure, but these effects have yet to be well characterized. We studied oxidized Ag(111) surfaces after exposure to gas-phase O atoms to determine how O sub is formed and how its presence alters the resultant surface structure. Using a combination of surface science techniques to quantify O sub formation and the resultant surface structure, we observed that once 0.1 ML of O sub has formed, the surface dramatically, and uniformly, reconstructed to a striped phase at the expense of all other surface phases. Furthermore, O sub formation was hindered at temperatures above 500 K.The thermal dependence for O sub formation suggests that at industrial catalytic conditions of 475 -500 K for the epoxidation of ethylene-to-ethylene oxide, O sub would be present and is a factor in the subsequent reactivit...

Selective Catalytic Ammonia Oxidation to Nitrogen by Atomic Oxygen Species on Ag(111)

“…[25][26][27][28][29]32 Other methods were also utilized for atomic oxygen delivery onto the Ag(111) surface under UHV conditions, such as NO 2 decomposition 31,36,38,40,47,50 and thermal gas cracking. 41,42,45 Ozone decomposition is an extremely efficient method for dosing high concentrations of oxygen atoms on metal surfaces under UHV conditions (i.e., in the absence of elevated-pressure exposures). Efficient atomic oxygen delivery onto single-crystal model catalyst surfaces with ozone was successfully carried out for Al(111), 51 Pd(111), 52 Pt(111), 52,53 and Au(111).…”

“…It is worth mentioning that, in the current work, the (4×4)-O/Ag(111) structure was not observed in any of the investigated coverages, because this structure is not stable when oxygen is accumulated under UHV conditions. 44,45 Nevertheless, in the current work, the saturation exposure of 0.04 langmuir was attributed to 1 MLE and was used to calibrate and quantify other desorption signals. As can be seen in Figure 1b, for the ozone exposures above 0.08 langmuir, surface oxygen coverage starts to exceed the convergence coverage of 1 MLE.…”

Insight into subsurface adsorption derived from a lattice-gas model of atomic oxygen on Ag(111)

“…We propose that the strong O-O repulsion on the surface that leads to saturation of surface oxygen at ∼0.3 ML in our model promotes subsurface adsorption as well as surface reconstruction, as is suggested by the 0.375-0.5 ML coverages of surface oxygen in the common reconstructions of O/Ag(111). 29 Figure 4: Top views of oxygen atoms adsorbed to the (a) surface, (b) first subsurface, and (c) second subsurface of Ag(111) from an energetically favorable population distribution predicted by the model. The total oxygen coverage is 1 ML, occupying a p(4×6) supercell of Ag(111).…”

The nature of electrophilic oxygen: Insights from periodic density functional theory investigations

“…Ag-O interactions are surprisingly diverse in nature and highly dependent of temperature, pressure as well as Ag facets and concentration of oxygen. [20,26,27] Oxidation of Ag surface to form bulk oxide like Ag 2 O is a complicated process as observed in the recent studies. [28][29][30][31] It is worth noting here some industrial facts regarding epoxidation.…”