Porous composite oxide and production method thereof

A method of producing a porous composite metal oxide, the method comprising:

• mixing a first aqueous solution comprising cerium and a second aqueous solution comprising zirconium to obtain a third solution comprising cerium and zirconium, a total concentration of ceria and zirconium in the third solution being 0.3 mol/L or less;
• adding a precipitating agent to the third solution to precipitate cerium and zirconium such that a precipitate is formed in the third solution;
• hydrolyzing the precipitate to form primary particles of a precursor of the composite metal oxide by polycondensation;
• aggregating the primary particles to form secondary particles in the third solution;
• aggregating the secondary particles by concentrating the third solution through solvent removal;
• and
• producing the porous composite metal oxide, the porous composite metal oxide having mesopores between the secondary particles,
• wherein the primary particles have a particle diameter of 3-15 nm, the secondary particles have a particle diameter of 30-100 nm, the mesopores have a pore diameter of 2-100 nm, and a percentage of mesopores having a pore diameter of 10 nm or more is 10% or more of a total mesopore volume.