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          Institute: Fritz-Haber-Institut     Collection: Inorganic Chemistry     Display Documents



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ID: 434423.0, Fritz-Haber-Institut / Inorganic Chemistry
Activation of dihydrogen on supported and unsupported silver catalysts
Authors:Hohmeyer, Jens; Kondratenko, Evguenii; Bron, Michael; Kröhnert, Jutta; Jentoft, Friederike C.; Schlögl, Robert; Claus, Peter
Language:English
Research Context:Ag as hydrogenation catalyst
Date of Publication (YYYY-MM-DD):2010
Title of Journal:Journal of Catalysis
Journal Abbrev.:J. Catal.
Volume:269
Issue / Number:1
Start Page:5
End Page:14
Copyright:© 2009 Elsevier Inc. All rights reserved.
Review Status:Peer-review
Audience:Experts Only
Abstract / Description: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.
Free Keywords:Silver catalysts; Silica; Dissociative adsorption; Isotopic exchange; Temporal analysis of products (TAP); Differential scanning calorimetry (DSC); Infrared spectroscopy (FTIR)
External Publication Status:published
Document Type:Article
Communicated by:Robert Schlögl
Affiliations:Fritz-Haber-Institut/Inorganic Chemistry/Functional Characterization
Fritz-Haber-Institut/Inorganic Chemistry/Reactivity / Oxides
External Affiliations:Chemical, Biological & Materials Engineering, University of Oklahoma, Norman, OK 73019, USA
Ernst-Berl-Institut / TC II, TU Darmstadt, Petersenstr. 20, 64287 Darmstadt
Leibniz-Institut für Katalyse e.V., Richard-Willstätter-Str. 12, 12489 Berlin
Identifiers:URL:http://dx.doi.org/10.1016/j.jcat.2009.10.008 [only for subscriber]
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