Exhaust gas purifying catalyst, metal oxide particle and production process thereof

A process for producing a metal oxide particle having a core where the total molar number of alumina and silica is larger than the molar number of ceria, and a surface layer where the molar number of ceria is larger than the total molar number of alumina and silica, said process comprising:

• preparing a solution containing a ceria sol and a sol of at least either one of alumina and silica, wherein the isoelectric point of the ceria sol differs more than 3.5 from that of said at least one of alumina and silica sol,
• adjusting the pH of said solution to be closer to the isoelectric point of the sol of at least either one of alumina and silica than to the isoelectric point of the ceria sol, and to fall within and ±2.0 of the isoelectric point of alumina and/or silica sol, and
• aggregating the sol from said solution to produce an aggregate.