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Novel in Situ Techniques for Studies of Model Catalysts

Lundgren, Edvin LU ; Zhang, Chu LU ; Merte, Lindsay R. LU ; Shipilin, Mikhail LU ; Blomberg, Sara LU ; Hejral, Uta LU ; Zhou, Jianfeng LU ; Zetterberg, Johan LU and Gustafson, Johan LU (2017) In Accounts of Chemical Research 50(9). p.2326-2333
Abstract

ConspectusMotivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most of these studies have been performed in well-controlled environments and have been instrumental for the present day understanding of catalysis, providing information on surface structures, adsorption sites, and adsorption and desorption energies relevant for catalysis. However, the approach has been criticized for being too far from a catalyst operating under industrial conditions at high temperatures and pressures. To this end, a significant amount of effort over the years has been used to develop methods to investigate catalysts at more realistic conditions under operating conditions. One... (More)

ConspectusMotivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most of these studies have been performed in well-controlled environments and have been instrumental for the present day understanding of catalysis, providing information on surface structures, adsorption sites, and adsorption and desorption energies relevant for catalysis. However, the approach has been criticized for being too far from a catalyst operating under industrial conditions at high temperatures and pressures. To this end, a significant amount of effort over the years has been used to develop methods to investigate catalysts at more realistic conditions under operating conditions. One result from this effort is a vivid and sometimes heated discussion concerning the active phase for the seemingly simple CO oxidation reaction over the Pt-group metals in the literature.In recent years, we have explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures and temperatures. In this contribution, results from catalytic CO oxidation over a Pd(100) single crystal surface using Near Ambient Pressure X-ray Photo emission Spectroscopy (NAPXPS), Planar Laser-Induced Fluorescence (PLIF), and High Energy Surface X-ray Diffraction (HESXRD) are presented, and the strengths and weaknesses of the experimental techniques are discussed. Armed with structural knowledge from ultrahigh vacuum experiments, the presence of adsorbed molecules and gas-phase induced surface structures can be identified and related to changes in the reactivity or to reaction induced gas-flow limitations. In particular, the application of PLIF to catalysis allows one to visualize how the catalyst itself changes the gas composition close to the model catalyst surface upon ignition, and relate this to the observed surface structures. The effect obscures a straightforward relation between the active phase and the activity, since in the case of CO oxidation, the gas-phase close to the model catalyst surface is shown to be significantly more oxidizing than far away from the catalyst. We show that surface structural knowledge from UHV experiments and the composition of the gas phase close to the catalyst surface are crucial to understand structure-function relationships at semirealistic conditions. In the particular case of Pd, we argue that the surface structure of the PdO(101) has a significant influence on the activity, due to the presence of Coordinatively Unsaturated Sites (CUS) Pd atoms, similar to undercoordinated Ru and Ir atoms found for RuO2(110) and IrO2(110), respectively.

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organization
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Contribution to journal
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published
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in
Accounts of Chemical Research
volume
50
issue
9
pages
8 pages
publisher
The American Chemical Society
external identifiers
  • scopus:85029686818
  • wos:000411548800028
ISSN
0001-4842
DOI
language
English
LU publication?
yes
id
e1da10d6-212f-4d13-aef7-98c26d00378a
date added to LUP
2017-10-05 14:05:21
date last changed
2018-05-29 09:38:20
@article{e1da10d6-212f-4d13-aef7-98c26d00378a,
  abstract     = {<p>ConspectusMotivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most of these studies have been performed in well-controlled environments and have been instrumental for the present day understanding of catalysis, providing information on surface structures, adsorption sites, and adsorption and desorption energies relevant for catalysis. However, the approach has been criticized for being too far from a catalyst operating under industrial conditions at high temperatures and pressures. To this end, a significant amount of effort over the years has been used to develop methods to investigate catalysts at more realistic conditions under operating conditions. One result from this effort is a vivid and sometimes heated discussion concerning the active phase for the seemingly simple CO oxidation reaction over the Pt-group metals in the literature.In recent years, we have explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures and temperatures. In this contribution, results from catalytic CO oxidation over a Pd(100) single crystal surface using Near Ambient Pressure X-ray Photo emission Spectroscopy (NAPXPS), Planar Laser-Induced Fluorescence (PLIF), and High Energy Surface X-ray Diffraction (HESXRD) are presented, and the strengths and weaknesses of the experimental techniques are discussed. Armed with structural knowledge from ultrahigh vacuum experiments, the presence of adsorbed molecules and gas-phase induced surface structures can be identified and related to changes in the reactivity or to reaction induced gas-flow limitations. In particular, the application of PLIF to catalysis allows one to visualize how the catalyst itself changes the gas composition close to the model catalyst surface upon ignition, and relate this to the observed surface structures. The effect obscures a straightforward relation between the active phase and the activity, since in the case of CO oxidation, the gas-phase close to the model catalyst surface is shown to be significantly more oxidizing than far away from the catalyst. We show that surface structural knowledge from UHV experiments and the composition of the gas phase close to the catalyst surface are crucial to understand structure-function relationships at semirealistic conditions. In the particular case of Pd, we argue that the surface structure of the PdO(101) has a significant influence on the activity, due to the presence of Coordinatively Unsaturated Sites (CUS) Pd atoms, similar to undercoordinated Ru and Ir atoms found for RuO<sub>2</sub>(110) and IrO<sub>2</sub>(110), respectively.</p>},
  author       = {Lundgren, Edvin and Zhang, Chu and Merte, Lindsay R. and Shipilin, Mikhail and Blomberg, Sara and Hejral, Uta and Zhou, Jianfeng and Zetterberg, Johan and Gustafson, Johan},
  issn         = {0001-4842},
  language     = {eng},
  month        = {09},
  number       = {9},
  pages        = {2326--2333},
  publisher    = {The American Chemical Society},
  series       = {Accounts of Chemical Research},
  title        = {Novel in Situ Techniques for Studies of Model Catalysts},
  url          = {http://dx.doi.org/},
  volume       = {50},
  year         = {2017},
}