Cerium LIII-edge EXAFS Investigation of the Structure of Crystalline and Amorphous Cerium Oxides


Cerium oxides have attracted considerable research interest due to a diversity of applications. For instance, the basicity function of cerium oxide when combined with the hydrogenation property of a metal such as Pt or Pd denotes CeO2 as a promising coversion catalyst. Thus, CeO2 can lead to selective hydrogenation catalysis of unsaturated compounds. The synthesis of CeO2 using different precipitation conditions was studied. The valence state of cerium ions and covalence with oxide ligands was also studied by varying the reaction conditions. Different H2O2 concentrations were employed during the precipitations of CeO2. XANES analysis showed a significant change in the intensity of the white line peaks of precipitated CeO2 revealing a smaller particle size as compared to anhydrous CeO2. However, no significant change in cerium spectroscopic valence for precipitated cerium oxides was observed, regardless of peroxide concentration, in comparison to the anhydrous CeO2. Precipitation of CeO2 utilizing H2O2 resulted in an increased bond distance, RCe-O/, as well as coordination number of the first coordination shell Ce-O. The degree of disorder increased with increasing H2O2 concentration during precipitation of CeO2, consequently increasing the potential for CeO2 precipitate to function as oxygen traps. Decreasing the particle size of CeO2 precipitates, with probable increase in oxygen trapping capability offered additional insight into the enhancement of the fuel cells performance using CeO2 precipitates.



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© 2004 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Sep 2004

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