TY - JOUR
T1 - Ceria-based catalysts for the production of H2 through the water-gas-shift reaction
T2 - Time-resolved XRD and XAFS studies
AU - Wang, Xianqin
AU - Rodriguez, José A.
AU - Hanson, Jonathan C.
AU - Gamarra, Daniel
AU - Martínez-Arias, Arturo
AU - Fernández-García, Marcos
N1 - Funding Information:
Acknowledgements The research carried out at the Chemistry Department of Brookhaven National Laboratory was financed through Contract No. DE-AC02-98CH10086 with the US Department of Energy, Division of Chemical Sciences. The NSLS is supported by the Divisions of Materials and Chemical Sciences of DOE. Work at the ‘‘Instituto de Catálisis (CSIC)’’ was done with financial support from CICYT (Contracts No. CTQ2004-03409/BQU and MAT2003-03925); D. G. thanks the FPI program of the Ministerio de Educación y Ciencia for a PhD grant. Thanks are due to Syed Khalid and Wolfgang Caliebe for their help and facilities given in the operation of beamlines X18B and X19A. The authors are grateful to M. Stephanopoulos for many useful conversations about the behavior of ceria-based catalysts during the water-gas shift.
PY - 2008/7
Y1 - 2008/7
N2 - Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H2 production from the water-gas-shift (WGS) reaction over Ce1-xCuxO2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuOx/CeO2 and AuOx/CeO 2 catalysts obtained through impregnation of ceria. For the fresh Ce1-xCuxO2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce 1-xCuxO2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO2-x. Time-resolved XRD and XAFS results also indicate that Cuδ+ and Auδ+ species present in fresh CuOx/CeO2 and AuOx/CeO2 catalysts do not survive above 200 °C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H2O, indicating that CO reduced ceria while H2O oxidized it. Our data suggest that H2O dissociation occurred on the Ovacancy sites or the Cu-Ovacancy and Au-Ovacancy interfaces. The rate of H2 generation by a Ce0.95Cu0.05O 2 catalyst was comparable to that of a 5 wt% CuOx/CeO 2 catalyst and much bigger than those of pure ceria or CuO.
AB - Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H2 production from the water-gas-shift (WGS) reaction over Ce1-xCuxO2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuOx/CeO2 and AuOx/CeO 2 catalysts obtained through impregnation of ceria. For the fresh Ce1-xCuxO2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce 1-xCuxO2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO2-x. Time-resolved XRD and XAFS results also indicate that Cuδ+ and Auδ+ species present in fresh CuOx/CeO2 and AuOx/CeO2 catalysts do not survive above 200 °C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H2O, indicating that CO reduced ceria while H2O oxidized it. Our data suggest that H2O dissociation occurred on the Ovacancy sites or the Cu-Ovacancy and Au-Ovacancy interfaces. The rate of H2 generation by a Ce0.95Cu0.05O 2 catalyst was comparable to that of a 5 wt% CuOx/CeO 2 catalyst and much bigger than those of pure ceria or CuO.
KW - Ceria catalysts
KW - Copper catalysts
KW - Gold catalysts
KW - Hydrogen
KW - In situ characterization
KW - Water-gas shift reaction
KW - X-ray absorption fine structure
KW - X-ray diffraction
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U2 - 10.1007/s11244-008-9071-6
DO - 10.1007/s11244-008-9071-6
M3 - Article
AN - SCOPUS:47549115848
SN - 1022-5528
VL - 49
SP - 81
EP - 88
JO - Topics in Catalysis
JF - Topics in Catalysis
IS - 1-2
ER -