The Interaction of Silver with Oxygen

Abstract

Oxygen overlayer / Dissolved oxygen / Fitting interstitial sites / Silver oxide decomposition Silver under ambient conditions is always covered at least with adsorbed atomic oxygen and coadsorbed C02, and at 300 the low susceptibility of the metal to oxidation may thus be assigned to the existence of this overlayer. At elevated temperatures surface species are desorbed without leading to a higher reactivity of Ag. Our experiments showed that under these conditions in the presence of 02 large amounts of dissolved oxygen are formed, and this species proved to be hard to remove either thermically or by heating the sample in hydrogen. According to the structural conditions of the silver lattice atomic oxygen fits perfectly into the octahedral holes so that dissolution is possible with hardly changing the atomic distances.Unter normalen Umgebungsbedingungen ist Silber stets bedeckt zumindest mit atomar adsorbiertem Sauerstoff und koadsorbiertem C02; die geringe Oxidationsneigung des Metalls bei 300 C kann dieser Obcrflächcnschicht zugeschrieben werden. Bei höheren Temperaturen desorbieren die Oberflächenspezics. doch nimmt dadurch die Reaktivität des Ag nicht zu. Wie unsere Untersuchungen zeigten, werden unter diesen Bedingungen in Gegenwart von 02 große Mengen von Sauerstoff gelöst, die thermisch oder durch Aufheizen unter Wasserstoff nur schwer zu entfernen sind. In der Gitterstruktur des Silbers paßt atomarer Sauerstoff präzise in die Oktaederlücken, so daß sich bei der Einlagerung die Atomabstände kaum zu ändern brauchen.

The silver–oxygen system in catalysis: new insights by near ambient pressure X-ray photoelectron spectroscopy

“…Here we use the label, Oa 1 in connection with our previous works and the traditional thermal desorption notation. [17][18][19][20][21][22][23][24][25]27 Dynamics of oxygen species at 150-230 8C 230 1C for 30 min, for spectra acquisition. Initially, fast scans were acquired and when changes were no longer observed in a time scale of 10 min, a set of core-levels for different elements was measured (carbon, oxygen, silver, chlorine, silicon), for which the O1s signals are displayed in Fig.…”

“…25 Finally, comparison of the experimentally determined O/Ag atomic concentration ratios for Ob with numerical calculations (presented in ESIw) suggests that the measured amounts of Ob are considerably higher than what is expected for an O overlayer with 1 ML coverage on atomically flat Ag(111), which corroborate the argument that this species might extend below the surface into the sub-surface and bulk regions. The dynamic nature of the interaction of oxygen with silver at elevated temperatures was established in the past in a series of papers [17][18][19][20][21][22][23][24][25][26][27] combining different experimental techniques. In this context, oxygen migration to the sub-surface/bulk by interstitial diffusion played a central role as a driving force for the solid state dynamics that results in the surface restructuring and also as a precursor for the formation of highly stable oxygen species.…”

“…16 Later, Schlo¨gl and co-workers devoted special attention to the interaction of oxygen with silver at high temperatures, which would be more representative of real catalysts under methanol oxidation conditions. [17][18][19][20][21][22][23][24][25][26][27] In contrast to the static description obtained by the classical surface science approach, a very dynamic picture emerged from this series of studies with a strong interplay between oxygen incorporation in the sub-surface and bulk with structural and morphological changes in the silver, which ultimately modifies the oxygen species present at the surface. Systematic theoretical studies based on density function theory calculations were performed by the group of Scheffler.…”

On the correlation between microstructural changes of Ag-H-ZSM-5 catalysts and their catalytic performances in the selective catalytic reduction of NOx by methane

“…The other is catalyzing the direct combustion of methane. As has been extensively studied in the reaction of epoxidation of ethylene and oxidative coupling of methane, surface adsorbed oxygen species (O ␣ ) on Ag catalyze the complete oxidation of hydrocarbons to CO 2 and H 2 O [26,29]. Thus at the beginning of the SCR reaction, due to the existence of large amount of active intermediates NO x (x ≥ 2), silver catalysts showed higher activity for the selective catalytic reduction of NO x by CH 4 .…”

The Role of Subsurface Oxygen in the Silver-Catalyzed, Oxidative Coupling of Methane

“…The first species is referred to as O α . This is chemisorbed atomic oxygen which is believed to catalyze the oxi-dehydrogenation of methanol to formaldehyde as well as the complete oxidation to CO 2 and water 22 . It is a highly-reactive oxygen species exhibiting a strongly nucleophilic character.…”