Press Releases
Nov. 7, 2007

Discovery of a new aspect in nanocrystalline mixed oxides:

The origin and dynamics of tremendous oxygen storage/release function
of a Pt/ordered CeO2-ZrO2 Catalyst studied by time-resolved XAFS technique
Presenters
  • Yasuhiro Iwasawa (Department of Chemistry, Graduate School of Science, the University of Tokyo)
  • Mizuki Tada (Department of Chemistry, Graduate School of Science, the University of Tokyo)
  • Takashi Yamamoto (Department of Chemistry, Graduate School of Science, the University of Tokyo)
Figure

Figure1: Energy-dispersive XAFS for OSC dynamics of CeO2-ZrO2 nanocrystal

Mixed oxides find a variety of applications to various catalyses due to cooperative or synergistic multi-functions by the components involved in the mixed oxides. Despite the success of the utilization of many mixed oxides, there is still few knowledge of the origin and dynamic mechanism of the multi-functions at different element sites under the working conditions. Cocatalysts with oxygen storage/release capacity (OSC) in automobile exhaust gas-cleaning three-way catalysts are typical mixed oxides. We have succeeded in characterizing electronic and structural dynamics of an industrially practical Pt/CeO2-ZrO2 catalyst with an ordered arrangement of Ce and Zr ions during the oxygen storage/release processes at 573-773 K by real-time energy-dispersive XAFS of 2ms time-resolution at Zr K-edge and 300ms time-resolution of Ce L3-edge, and found the key issues and roles of Ce and Zr ions in the tremendous dynamic functions of the mixed-oxide catalyst. We found that the electronic and structural transformations at Ce and Zr sites, respectively during the oxygen storage/release processes do not synchronize with each other in the CeO2-ZrO2 solid solution. The activation energy for the OSC functions at Ce sites was also much different from that at Zr sites. In the both oxygen storage and release processes, the valence of Ce sites changed firstly, then the structural transformation at Zr sites occurred to make or break Zr-O bonds. The fast valence change of Ce ions and the moderate structure change around Zr ions are responsible for the high OSC of the ordered CeO2-ZrO2 phases. The present DXAFS study demonstrated the dynamics and roles of each of Ce and Zr ions in the industrially practical Pt/CeO2-ZrO2 catalyst for the first time.