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Activation of dihydrogen on supported and unsupported silver catalysts

Hohmeyer, Jens and Kondratenko, Evgenii and Bron, Michael and Kröhnert, Jutta and Jentoft, Friederike C. and Schlögl, Robert and Claus, Peter (2010):
Activation of dihydrogen on supported and unsupported silver catalysts.
In: Journal of Catalysis, pp. 5-14, 269, (1), [Online-Edition: http://dx.doi.org/10.1016/j.jcat.2009.10.008],
[Article]

Abstract

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 the activated hydrogen species are rate determining at higher temperatures (greater-or-equal, ≥ 373 K), when the 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.

Item Type: Article
Erschienen: 2010
Creators: Hohmeyer, Jens and Kondratenko, Evgenii and Bron, Michael and Kröhnert, Jutta and Jentoft, Friederike C. and Schlögl, Robert and Claus, Peter
Title: Activation of dihydrogen on supported and unsupported silver catalysts
Language: English
Abstract:

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 the activated hydrogen species are rate determining at higher temperatures (greater-or-equal, ≥ 373 K), when the 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.

Journal or Publication Title: Journal of Catalysis
Volume: 269
Number: 1
Uncontrolled Keywords: Silver catalysts; Silica; Dissociative adsorption; Isotopic exchange; Temporal analysis of products (TAP); Differential scanning calorimetry (DSC); Infrared spectroscopy (FTIR)
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Fachgebiet Technische Chemie > Technische Chemie II
07 Department of Chemistry > Fachgebiet Technische Chemie
Date Deposited: 12 Oct 2009 07:23
Official URL: http://dx.doi.org/10.1016/j.jcat.2009.10.008
Additional Information:

Available online 14. November 2009

Identification Number: doi:10.1016/j.jcat.2009.10.008
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