Water-gas shift activity of Cu surfaces and Cu nanoparticles supported on metal oxides

J. A. Rodriguez, P. Liu, X. Wang, W. Wen, J. Hanson, J. Hrbek, M. Pérez, J. Evans

Research output: Contribution to journalArticlepeer-review

96 Scopus citations

Abstract

Oxide supported Cu catalysts show significant activity for the water-gas shift reaction (WGS, CO + H2O → H2 + CO2) but their performance is not fully understood and is highly dependent on the synthesis conditions or the nature of the oxide support. This article describes a series of new studies examining the water-gas shift activity of Cu/MgO(1 0 0) surfaces and compares it to the activities found for pure copper systems, Cu nanoparticles in contact with well-defined surfaces of TiO2, ZnO, MoO2 and CeO2, and Cu cations present in mixed-metal oxides. Catalytic tests performed over CuFe2O4, Ce1-xCuxO2 or CuMoO4 show significant WGS activity only when the Cu cations in the mixed-metal oxide are reduced to metallic copper. Thus, Cu nanoparticles were deposited on different oxide surfaces and their WGS activity was measured in a batch reactor (PCO = 20 Torr; PH2 O = 10 Torr; T = 575-650 K). The WGS activity of the Cu nanoparticles supported on MgO(1 0 0) was 2-3 times larger than that of Cu(1 0 0). Even better WGS catalysts were obtained when Cu was deposited on CeO2(1 1 1) or TiO2(1 1 0). An apparent activation energy of 13.8 kcal/mol was found for the WGS on Cu/MgO(1 0 0). This is smaller than the value of 15.2 kcal/mol observed on Cu(1 0 0), and substantially larger than the values of 7-9 kcal/mol seen for the apparent activation energies of the Cu/CeO2(1 1 1) and Cu/TiO2(1 1 0) catalysts. Post-reaction surface characterization pointed to the lack of O vacancies in the Cu/MgO(1 0 0) catalysts. This is in contrast to results found for Cu/CeO2(1 1 1) and Cu/TiO2(1 1 0), where the oxide support exhibits a significant concentration of O vacancies as a consequence of the WGS reaction. The oxygen vacancies present in Cu/CeO2(1 1 1) and Cu/TiO2(1 1 0) help in the dissociation of the water molecule and reduce the apparent activation energy for the WGS process. Such a phenomenon cannot occur on the Cu/MgO(0 0 1) catalysts, and the main steps of the WGS probably take place on the Cu nanoparticles.

Original languageEnglish (US)
Pages (from-to)45-50
Number of pages6
JournalCatalysis Today
Volume143
Issue number1-2
DOIs
StatePublished - May 15 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

Keywords

  • CO oxidation
  • Carbon monoxide
  • Copper
  • Hydrogen production
  • Magnesium oxide
  • Metal oxides
  • Water
  • Water-gas shift

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