COMPOSITION BASED ON CERIUM AND ZIRCONIUM OXIDES HAVING A SPECIFIC SURFACE WHICH IS STABLE BETWEEN 9

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Composition comprising cerium oxide and zirconium oxide in a weight ratio of 10/90 to 90/10 has a surface area which, after a first calcination at 900[deg]C for 4 hours and then a second calcination at 1000[deg]C for 10 hours, varies by no more than 20%. Independent claims are also included for : (1) composition comprising cerium oxide and zirconium oxide in a cerium oxide/zirconium oxide weight ratio of 0.24-4 and at least one other rare earth metal oxide in an amount of up to 30 wt.%, with a surface area which, after a first calcination at 900[deg]C for 4 hours and then a second calcination at 1000[deg]C for 10 hours, varies by no more than 15%; (2) a process for producing the composition; (3) a catalyst system comprising the composition; (4) internal combustion engine exhaust gas treatment using the composition as a catalyst.