Water-Gas Shift Activity of Cu Surfaces and Cu Nanoparticles Supported on Metal Oxides
Oxide supported Cu catalysts show significant activity for the water-gas shift reaction (WGS, CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) 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 TiO{sub 2}, ZnO, MoO{sub 2} and CeO{sub 2}, and Cu cations present in mixed-metal oxides. Catalytic tests performed over CuFe{sub 2}O{sub 4}, Ce{sub 1-x}Cu{sub x}O{sub 2} or CuMoO{sub 4} 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 (P{sub CO} = 20 Torr; P{sub H{sub 2}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 CeO{sub 2}(1 1 1) or TiO{sub 2}(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/CeO{sub 2}(1 1 1) and Cu/TiO{sub 2}(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/CeO{sub 2}(1 1 1) and Cu/TiO{sub 2}(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.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 980677
- Report Number(s):
- BNL-93595-2010-JA; CATTEA; TRN: US201015%%2062
- Journal Information:
- Catalysis Today, Vol. 143, Issue 1-2; ISSN 0920-5861
- Country of Publication:
- United States
- Language:
- English
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