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. Ž . Nitrous oxide N O was decomposed over Rh supported on ceriarzirconia CerZr composite oxide, and the effects of 2 the composition of the oxide and of its calcination temperature on the catalytic performance of Rh were investigated. Ceria was fragile against high temperature calcination, while addition of Zr remarkably increased its thermal stability to retain high surface area even at the calcination temperature of 9008C. Rh was supported on these oxides and was calcined at 5508C. The Rh supported on the composite oxide with a CerZr molar ratio of 7r3 which had been calcined at 9008C exhibited the highest activity. TEM and ESCA analyses revealed that the Rh strongly interacted with the oxide, and there was a possibility that a part of Rh even dissolved into its bulk. The Rh exposed to the surface of the composite oxide in a highly dispersed Ž state exhibited the high catalytic activity. However, when the calcination temperature of the composite oxide CerZr molar . ratio of 7r3 was increased to 12008C, its surface area decreased remarkably and the supported Rh was present in an aggregated state. The Rh in this state had only low catalytic activity despite its high surface concentration.