Local structure change of Rh on alumina after treatments in high‐temperature oxidizing and reducing environments

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Abstract
The effects of high‐temperature oxidization and reduction on the local structures of Rh in Rh/Al 2 O 3 catalysts were investigated. After oxidization at 1200 °C, XPS measurements indicated that the Rh was in a highly oxidized state. Extended x‐ray absorption fine structure (EXAFS) analysis for the highly oxidized Rh showed a shorter distance between the Rh atom and the next cation than that in Rh 2 O 3 . The shortened distance agrees with the Rh substitution model, in which Rh substituted for the inner Al site of the α‐Al 2 O 3 lattice. Stepwise reductions with XPS measurements after oxidization at 1200 °C revealed that the Rh that diffused into γ‐Al 2 O 3 was more resistant to reduction than that diffused into α‐Al 2 O 3 . The Rh aged at 600 °C was oxidized but had no specific local structure. Copyright © 2005 John Wiley & Sons, Ltd.

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