Locating catalytically active oxygen on Ag(111)-A spectromicroscopy study

Sebastian Günther, Sebastian Böcklein, Joost Wintterlin, Miguel A. Niño, Tevfik O. Menteş, Andrea Locatelli

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

The loading of an Ag(111) sample with oxygen was monitored by insitu low-energy electron microscopy and X-ray photoemission electron microscopy during NO2 dosing at T≥480K. At first, adsorbed oxygen populates the Ag(111) surface, which initiates the (4×4) reconstruction leading to the characteristic O1s core level at 528.30eV. The formation of this phase proceeds on a mesoscopic length scale by traveling fronts separating reconstructed from non-reconstructed surface areas. Continued NO2 dosing leads to the accumulation of a new oxygen species mainly at steps and step bunches. Characterized by an O1s peak with two components at 530.20eV and 530.75eV, this species represents the active oxygen during the ethylene epoxidation reaction over Ag. The 530.20eV component is attributed to surface oxygen, the 530.75eV species to subsurface oxygen. This inhomogeneous accumulation of the active oxygen occurs at a very low rate. However, the preparation route can be changed, which strongly accelerates the population of the catalytically active oxygen species and leads to a homogeneous distribution of oxygen on the surface. This route involves the complete formation of the O(4×4) reconstruction by NO2 dosing, followed by a complete de-reconstruction of the surface by desorption of the oxygen adlayer. The faster population kinetics is related to the Ag adatom transport during such a reconstruction/de-reconstruction cycle.

Original languageEnglish
Pages (from-to)3342-3350
Number of pages9
JournalChemCatChem
Volume5
Issue number11
DOIs
StatePublished - Nov 2013

Keywords

  • Epoxidation
  • Oxygen
  • Photoelectron spectroscopy
  • Silver
  • Surface analysis

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