The behavior of rhodium(Rh) in Rh/alumina catalysts under high-temperature oxidization and reduction condition was investigated by X-ray Diffraction(XRD), X-ray photoelectron spectroscopy(XPS), and transmission electron microscope(TEM). g, q, a-phase alumina were used for the catalyst supports. The 1wt% Rh was impregnated with Rh(NO₃)₃, dried at 110°C in air and calcined in 10%H₂ in N₂at 500°C for 2h. The samples were oxidized in air at 600°C, 900°C, and 1200°C for 10h. The reductive treatment of the oxidizedvsamples was after achieved in the infrared-furnace connected to XPS chamber in 0.1 atm of 10%H₂ in N₂ at 800°C.

XRD measurements of Rh/ g -alumina oxidized in air at 1200°C for 10h, showed that the alumina was transformed to alpha phase, and that Rh was completely dissolved into alumina. In the XPS measurement the Rh3d _5/2 peak was observed at about 310.2eV in the binding energy which is 1.8eV higher than the value of rhodium oxide. Therefore we are able to distinguish between the chemical states of the Rh dissolved into alumina and the Rh oxidized on alumina. XPS revealed that a part of Rh was dissolved into the alumina in any phase alumina by oxidization at 600°C. After 900°C aging, almost all Rh were dissolved into g and q -alumina, and about 80% of detected Rh was dissolved into a-alumina.

The XPS results from reduced samples followed by oxidization at 1200°C, showed that a part of Rh was reduced and the Rh3d_5/2 peak was appeared at about 3eV lower binding energy than the dissolved state. Small clusters less than 2nm in diameter were found on the support by TEM observation. It is considered that reduced Rh was reduced to the metal and clustered on the alumina.

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