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Carbon monoxide oxidation on nanostructured CuOx/CeO2 composite particles characterized by HREM, XPS, XAS, and high-energy diffraction

Skårman, Björn LU ; Grandjean, D; Benfield, RE; Hinz, A; Andersson, Arne LU and Wallenberg, Reine LU (2002) In Journal of Catalysis 211(1). p.119-133
Abstract
Nonstoichiometric CuOx/CeO2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and... (More)
Nonstoichiometric CuOx/CeO2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu2O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO2 sur ace. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces Of CeO2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen. (C) 2002 Elsevier Science (USA). (Less)
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organization
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Contribution to journal
publication status
published
subject
keywords
HREM, inert gas condensation, activation, thermal, carbon monoxide oxidation, morphology, dispersion, amorphous, crystallinity, nonstoichiometry, nanocomposite, ceria, copper oxide, XPS, high-energy diffraction, XANES, EXAFS
in
Journal of Catalysis
volume
211
issue
1
pages
119 - 133
publisher
Elsevier
external identifiers
  • wos:000178377800012
  • scopus:0036795211
ISSN
1090-2694
DOI
10.1006/jcat.2002.3735
language
English
LU publication?
yes
id
3561fd29-fa21-4bab-a5f0-88f3f2b1e4ea (old id 326413)
date added to LUP
2007-11-07 18:08:06
date last changed
2017-11-19 03:33:29
@article{3561fd29-fa21-4bab-a5f0-88f3f2b1e4ea,
  abstract     = {Nonstoichiometric CuOx/CeO2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu2O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO2 sur ace. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces Of CeO2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen. (C) 2002 Elsevier Science (USA).},
  author       = {Skårman, Björn and Grandjean, D and Benfield, RE and Hinz, A and Andersson, Arne and Wallenberg, Reine},
  issn         = {1090-2694},
  keyword      = {HREM,inert gas condensation,activation,thermal,carbon monoxide oxidation,morphology,dispersion,amorphous,crystallinity,nonstoichiometry,nanocomposite,ceria,copper oxide,XPS,high-energy diffraction,XANES,EXAFS},
  language     = {eng},
  number       = {1},
  pages        = {119--133},
  publisher    = {Elsevier},
  series       = {Journal of Catalysis},
  title        = {Carbon monoxide oxidation on nanostructured CuOx/CeO2 composite particles characterized by HREM, XPS, XAS, and high-energy diffraction},
  url          = {http://dx.doi.org/10.1006/jcat.2002.3735},
  volume       = {211},
  year         = {2002},
}