Determination of Ce valence in Rh-Ce/Al2O3 catalysts by X-ray absorption

✍ Scribed by D.D. Beck; T.W. Capehart; R.W. Hoffman

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 664 KB
• Volume: 159
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(89)87411-1

✦ Synopsis

Measurements of the cerium L,,, absorption edges of Rh-Ce/Alz03 catalysts were made lo determine changes in the cerium valence produced by high temperature treatments in oxygen or hydrogen. The valences of cerium in the catalyst treated in oxygen at 900°C and CeO, are nearly identical. However, approximately 50% of the cerium is trivalent in the catalyst treated in hydrogen at 900°C. Several local environments consistent with the reduced catalyst valence, namely, cerium alloyed with rhodium, nonstoichiometric cerium oxides, and heterogeneous mixtures of cerium oxides, are examined. We conclude that on Rh-Ce/Alz03 treated in hydrogen at 9OO"C, Ce exists as a mixture of CezOl and CeAIO,. Air exposure at 25°C converts the Cez03 portion to C&.