Abstract: A catalyst suitable for the treatment of automotive engine exhaust exhibiting enhanced oxygen storage capacity. The catalyst composition contains, in addition to a catalytic material such as one or more of platinum, rhodium and palladium dispersed on an activated alumina support, an oxygen storage component ("OSC") which is an intimately mixed oxide of ceria and praseodymia having a Pr:Ce atomic ratio in the range of about 2:100 to 100:100 and optionally containing one or more other rare earth metal oxides. The OSC is segregated from the catalytic material and may optionally have dispersed thereon a limited amount of a second catalytic metal component, such as platinum, rhodium and/or palladium. The intimately mixed oxide may be formed by co-precipitation by impregnation of bulk ceria particles with a praseodymium precursor, or any other method to form an intimately mixed oxide. The OSC may comprise at least about 5% by weight of the combined weight of the OSC and the catalytic component.

Abstract: A catalytic material effective for the reduction of NO.sub.x and the oxidation of at least carbon monoxide includes an oxygen storage component that provides superior oxygen storage function. The oxygen storage component includes an intimately combined mixed oxides including cerium, neodymium and zirconium. Typically, the ceria constitutes more than about 30 percent by weight of the ceria plus zirconia in the intimately combined mixed oxide, e.g., from about 32 to 44 weight percent. Preferably, the intimately combined mixed oxide also includes up to about 26 percent neodymia by weight of the ceria, e.g., from 18.6 to 23.5 percent. The intimately combined mixed oxide may be a co-formed material that may be prepared by, e.g., co-precipitating compounds of zirconium and the rare earth metal and calcining the co-precipitate.