CATALYST COMPOSITIONS COMPRISING ZIRCONIUM, CERIUM AND YTTRIUM OXIDES HAVING A HIGH REDUCIBILITY

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Catalyst compositions useful for the conversion of vehicular exhaust gases contain zirconium, cerium and yttrium oxides with a cerium oxide proportion of from 3% to 15%, and yttrium oxide proportions corresponding to the following conditions : 6% at most if the cerium oxide proportion is from 12% excluded and 15% included; 10% at most if the cerium oxide proportion is from 7% excluded and 12% included; 30% at most if the cerium oxide proportion is from 3% to 7% included, the balance being zirconium oxide; such compositions may optionally include an oxide of a rare earth selected from among lanthanum, neodymium and praseodymium.