Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part I: Oxidation state and surface species on Pt/CeO2 under reaction conditions

O. Pozdnyakova, D. Teschner, A. Wootsch, J. Kröhnert, B. Steinhauer, H. Sauer, L. Tóth, F. C. Jentoft, A. Knop-Gericke, Z. Paál, R. Schlögl

Research output: Contribution to journalArticle

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Abstract

The CO content of hydrogen feed to proton-exchange membrane fuel cells (PEMFCs) must be kept under 1-100 ppm for their proper operation. This can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen (PROX). The present study reports on the mechanism of the PROX reaction on Pt/CeO2 catalyst, using catalytic tests, in situ DRIFTS, high-pressure XPS, HRTEM, and TDS techniques. Bulk metallic, pronounced adsorbate-induced surface Pt, and a small amount of oxidized Pt sites were detected by in situ high-pressure XPS under PROX conditions. The preoxidized ceria surface was strongly reduced in pure H2 but significantly reoxidized under PROX conditions (i.e., O2 + CO in excess hydrogen) at T=358 K. The remaining small amount of Ce3+ decreased with increasing temperature. HRTEM found well-crystallized CeO2 particles (8-10 nm) in the case of activated (pre-oxidized) sample that transformed in a large extent to an oxygen deficient ceria supercell structure after PROX reaction. Metallic Pt particles (2-3 nm) and small (0.5-0.6 nm) Pt clusters were found by HRTEM. These findings were in accordance with the variations in relative intensity of the corresponding PtCO bands (DRIFTS). Different types of carbonate and formate species were detected (XPS and DRIFTS). Their possible role in the reaction mechanism is discussed. Resolved OH bands could not be found by DRIFTS in the PROX reaction mixture indicating significant amount of adsorbed water in a hydrogen-bonded structure. Its presence seems to suppress hydrogen oxidation while CO oxidation still takes place, as the metallic particles are covered by CO (DRIFTS). The direct contribution of surface water in a low-temperature water-gas shift-type reaction in the PROX mixture is proposed.

Original languageEnglish
Pages (from-to)1-16
Number of pages16
JournalJournal of Catalysis
Volume237
Issue number1
DOIs
Publication statusPublished - Jan 1 2006

Fingerprint

Cerium compounds
Carbon Monoxide
Catalyst supports
Hydrogen
catalysts
Oxidation
oxidation
hydrogen
formic acid
X ray photoelectron spectroscopy
Catalysts
Water gas shift
Carbonates
formates
Proton exchange membrane fuel cells (PEMFC)
Adsorbates
surface water
Surface waters
water
fuel cells

Keywords

  • Ceria
  • Fuel cell
  • High pressure XPS
  • HRTEM
  • Hydrogen purification
  • In situ DRIFTS
  • Platinum
  • Preferential CO oxidation
  • PROX
  • Pt/Ce O
  • TDS

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part I : Oxidation state and surface species on Pt/CeO2 under reaction conditions. / Pozdnyakova, O.; Teschner, D.; Wootsch, A.; Kröhnert, J.; Steinhauer, B.; Sauer, H.; Tóth, L.; Jentoft, F. C.; Knop-Gericke, A.; Paál, Z.; Schlögl, R.

In: Journal of Catalysis, Vol. 237, No. 1, 01.01.2006, p. 1-16.

Research output: Contribution to journalArticle

Pozdnyakova, O. ; Teschner, D. ; Wootsch, A. ; Kröhnert, J. ; Steinhauer, B. ; Sauer, H. ; Tóth, L. ; Jentoft, F. C. ; Knop-Gericke, A. ; Paál, Z. ; Schlögl, R. / Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part I : Oxidation state and surface species on Pt/CeO2 under reaction conditions. In: Journal of Catalysis. 2006 ; Vol. 237, No. 1. pp. 1-16.
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AU - Teschner, D.

AU - Wootsch, A.

AU - Kröhnert, J.

AU - Steinhauer, B.

AU - Sauer, H.

AU - Tóth, L.

AU - Jentoft, F. C.

AU - Knop-Gericke, A.

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