A process which comprises providing a porous matrix, mixing said porous matrix with a precursor solution containing manganese and cerium ions dissolved therein, triggering the formation of a non-fluid phase which contains manganese and cerium in the interior of said porous matrix, separating said porous matrix from a liquid phase containing soluble metals, completing the formation of said non-fluid phase which contains manganese and cerium in the interior of said porous matrix, heat treating said porous matrix to convert said non-fluid phase containing manganese and cerium placed therein into a manganese oxide-cerium oxide composite, and isolating said composite from said porous matrix. The resulting composite, and its use as a catalyst, are also provided.