ORIGINAL PAPER Ceria-based Catalysts for the Production of H 2 Through the Water-gas-shift Reaction: Time-resolved XRD and XAFS Studies Xianqin Wang Æ Jose ´ A. Rodriguez Æ Jonathan C. Hanson Æ Daniel Gamarra Æ Arturo Martı ´nez-Arias Æ Marcos Ferna ´ndez-Garcı ´a Published online: 28 May 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H 2 production from the water-gas-shift (WGS) reaction over Ce 1-x Cu x O 2 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 CuO x /CeO 2 and AuO x /CeO 2 catalysts obtained through impregnation of ceria. For the fresh Ce 1-x Cu x O 2 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-x Cu x O 2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO 2-x . Time-resolved XRD and XAFS results also indicate that Cu d+ and Au d+ species present in fresh CuO x /CeO 2 and AuO x /CeO 2 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 H 2 O, indicating that CO reduced ceria while H 2 O oxidized it. Our data suggest that H 2 O dissociation occurred on the O vacancy sites or the Cu–O vacancy and Au–O vacancy inter- faces. The rate of H 2 generation by a Ce 0.95 Cu 0.05 O 2 catalyst was comparable to that of a 5 wt% CuO x /CeO 2 catalyst and much bigger than those of pure ceria or CuO. Keywords Hydrogen  Water-gas shift reaction  Ceria catalysts  Copper catalysts  Gold catalysts  In situ characterization  X-ray diffraction  X-ray absorption fine structure 1 Introduction The world demand for energy and the need for protecting our environment can be achieved by increasing energy efficiency and by developing ‘‘clean’’ energy sources. Hydrogen is a potential answer to satisfying many of our energy needs while reducing (and eventually eliminating) carbon dioxide and other greenhouse gas emissions [1–3]. The water-gas shift (WGS) reaction CO þ H 2 O ! CO 2 þ H 2 ð Þ is used in industrial hydrogen production as well as in fuel processing for fuel cell applications [4]. CeO 2 -based catalysts have been reported to be very promising for the WGS reaction. Among these materials, the two most studied systems currently are Cu- and Pt-based catalysts [5–8]. It is anticipated that, with proper development, metal promoted ceria catalysts should realize much higher CO conversions than even commercial CuZnO catalysts [9]. However, the roles played by ceria and the metal in the WGS reaction are still a matter of debate. The redox properties and oxygen storage capacity of ceria are usually considered important, while the metal plays a direct role in the mechanism of the WGS reaction [9]. In order to clarify the debate, in situ time-resolved characterization of the catalysts under operational condi- tions is critical. In this article, we illustrate how two synchrotron-based techniques, time-resolved X-ray dif- fraction (XRD) and X-ray absorption fine structure (XAFS), can be useful for examining the behavior of ceria-contain- ing catalysts under the WGS reaction. To the best of our knowledge, no systematic studies have been reported X. Wang  J. A. Rodriguez (&)  J. C. Hanson Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA e-mail: rodrigez@bnl.gov D. Gamarra  A. Martı ´nez-Arias  M. Ferna ´ndez-Garcı ´a Instituto de Cata ´lisis y Petroleoquı ´mica, CSIC, Campus Cantoblanco, 28049 Madrid, Spain 123 Top Catal (2008) 49:81–88 DOI 10.1007/s11244-008-9071-6