The Correlation of Subsurface Oxygen Diffusion with Variations of Silver Morphology in the Silver–Oxygen System

Nagy, Anton J.; Mestl, Gerhard; Herein, Daniel; Weinberg, Gisela; Kitzelmann, Edith; Schlögl, Robert

doi:10.1006/jcat.1998.2388

Cited by 126 publications

(154 citation statements)

References 20 publications

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“…In the precision SEM images, irregular hill-and-valley structures can be discerned. Such morphology is similar to that reported in the literature for a clean polycrystalline metal surface [43][44][45]. In contrast, after a treatment in the reactant mixture, the surface becomes very rough (Fig.…”

Section: Ex Situ Surface Morphology and Effective Surface Area Measursupporting

confidence: 89%

“…Surface reorganizes into lower energy configurations via the localized surface diffusion most likely without volatilization or any loss of mass. Of course, the dissolution of small atoms such as H, C, and O into the subsurface layers might induce the faceting as well [43][44][45]. Such structural transformations are associated with changes in the oxygen sticking coefficient and, hence, in the reactivity.…”

Section: Discussionmentioning

confidence: 99%

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Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Каичев

Teschner

Saraev

et al. 2016

Journal of Catalysis

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The evolution of self-sustained reaction-rate oscillations in the catalytic oxidation of propane over a nickel foil has been studied in situ using X-ray photoelectron spectroscopy coupled with on line mass spectrometry and gas chromatography. Changes in the effective surface area and in the catalyst morphology under reaction conditions have been examined by scanning electron microscopy and a krypton adsorption technique. It is shown that the regular kinetic oscillations arise under oxygen-lean conditions. CO, CO 2 , H 2 , H 2 O, and propylene are detected as products.The conversion of propane oscillates in a range from 1% to 23%. During the half-periods with high activity, the main reaction pathway is the partial oxidation of propane: selectivity toward CO achieves 98%. In contrast, during the half-periods with low activity, the reaction proceeds through three competitive pathways: the partial oxidation of propane, the total oxidation of propane, and the dehydrogenation of propane to propylene. The driving force for the selfsustained kinetic oscillations is the periodic reoxidation of nickel. According to the Ni2p and O1s core-level spectra measured in situ, the high-active catalyst surface is represented by metallic nickel, whereas during the inactive half-periods the catalyst surface is covered with a thick layer of NiO. The intensity of O1s spectra follows the oscillations of O 2 in the gas phase during the oxidation of propane. It is found that during the induction period before the regular oscillations appear, a rough and porous structure develops because of strong reconstruction of the catalyst surface. The thickness of the reconstructed layer is approximately 10-20 µm. This process is accompanied with at least an 80-fold increase in the effective surface area compared with a clean, non-treated nickel foil, which undoubtedly leads to a drastic increase in the number of active sites. We believe that it is the main reason for the induction period always being  Corresponding author.E-mail address: vvk@catalysis.ru (V.V. Kaichev) 2 observed before the appearance of self-sustained oscillations in the catalytic oxidation of light hydrocarbons over catalysts with a low specific surface area (single crystals, foils, or wires).Moreover, without such reconstruction, the oscillations cannot arise due to low activity of such catalysts.

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Section: Ex Situ Surface Morphology and Effective Surface Area Measursupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Каичев

Teschner

Saraev

et al. 2016

Journal of Catalysis

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“…Treatment of silver in O 2 at elevated temperatures can lead to the formation of surface, bulk, and subsurface oxygen species [50,51], which influence the state of adjacent silver atoms. According to theoretical calculations [24][25][26]71], the dissociation of dihydrogen on clean, oxygenfree silver surfaces is an endothermic process.…”

Section: Effect Of a Pre-treatment In Omentioning

confidence: 99%

“…The affinity of silver toward oxygen is well known [50,51], and a variety of oxygen species dissolved in the bulk, in the subsurface region, and on the surface of silver have been described [51][52]. Exposure of silver to O 2 at temperatures between 8001023 K induces massive changes in the surface morphology [51,52]; and the use of silver in oxidation reactions (of methane or methanol) can lead to similar effects [9,11].…”

Section: Introductionmentioning

confidence: 99%

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Activation of dihydrogen on supported and unsupported silver catalysts

Hohmeyer

Kondratenko

Bron

et al. 2010

Journal of Catalysis

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The activation of dihydrogen on silica, silver, and silica-supported silver (9 wt% Ag) was investigated. Both, silica and silver are individually able to dissociate dihydrogen. Silanol groups on silica undergo H→D exchange at 393 K in D2 as detected by IR spectroscopy. HD is observed in temporal analysis of products (TAP) experiments when H2 and D2 are sequentially pulsed on silver at 673 K; even when the time delay between the isotopes is 4 s, HD is formed, indicating that long-lived surface hydrogen species are present. Differential scanning calorimetry (DSC) shows that the activation of dihydrogen is an activated process: heat signals evoked through H2 pulses on Ag/SiO2 grow with increasing temperature (373523 K). Nonetheless, the presence of silver on the silica surface accelerates the Si-OH→Si-OD exchange. Investigation of the exchange kinetics on Ag/SiO2 shows that diffusion processes of activated hydrogen species are rate-determining at higher temperatures ( 373 K), when activation of D2 on silver becomes facile. Indications of diffusion limitation are observed already at 313 K on Pt/SiO2. TAP and DSC measurements show that H2 is more readily activated on silver that has been treated in O2 at 673 K followed by reduction in H2 at 673 K. Morphological changes induced to the silver surfaces or (sub)surface oxygen species are presumed responsible for this effect

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Oxidation of Alcohols with Molecular Oxygen

Mallát

Baiker

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Oxidation in the Gas Phase Metals Oxides Phosphates Zeolites Oxidation in the Liquid Phase Platinum‐Group Metals Gold Oxides Molecular Sieves Hydrotalcites Phosphates and Apatites Heterogenized Metal Complexes Summary

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The Correlation of Subsurface Oxygen Diffusion with Variations of Silver Morphology in the Silver–Oxygen System

Cited by 126 publications

References 20 publications

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Activation of dihydrogen on supported and unsupported silver catalysts

Oxidation of Alcohols with Molecular Oxygen

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