Method for producing composite oxide and composite oxide catalyst

Abstract

Provided are a method for producing a composite oxide and the composite oxide. The method includes steps of: (a) preparing a Ce aqueous solution not less than 80 mol % of which Ce ions are tetravalent, and a Zr aqueous solution; (b1) mixing the Zr aqueous solution and a portion of the Ce aqueous solution to prepare a mixed aqueous solution (X1); (c1) hydrothermally processing the solution (X1); (b2) adding the remainder of the Ce aqueous solution of step (a) to a colloidal solution (Y1) of a composite salt obtained from step (c1) to prepare a colloidal solution (Y2) of a composite salt; (c2) hydrothermally processing the solution (Y2); (d) mixing a colloidal solution (Y3) of a composite salt obtained from step (c2) with an alkaline solution and a surfactant to prepare a precipitate; and (e) calcining the precipitate.

What is claimed is: 
     
         1 . A composite oxide obtained by a method comprising the steps of:
 (a) preparing at least a cerium aqueous solution 80 to 100 mol % of which cerium ions are tetravalent, and a zirconium aqueous solution containing zirconium ions;   (b1) mixing said zirconium aqueous solution and a portion of said cerium aqueous solution prepared in step (a) to prepare a mixed aqueous solution (X1);   (c1) hydrothermally processing said mixed aqueous solution (X1);   (b2) adding a remainder of said cerium aqueous solution prepared in step (a) to a colloidal solution (Y1) of a composite salt obtained by said hydrothermal processing in step (c1) to prepare a colloidal solution (Y2) of a composite salt;   (c2) hydrothermally processing said colloidal solution (Y2) of a composite salt obtained from step (b2) ;   (d) mixing a colloidal solution (Y3) of a composite salt obtained by said hydrothermal processing in step (c2) with an alkaline solution and a surfactant to prepare a precipitate; and   (e) calcining said precipitate,   wherein the composite oxide comprises Ce, Zr, Pr, and oxygen, and   wherein the content of Zr is not less than 20 mol% and not more than 50 mol %, and the content of Pr is not more than 5 mol %, with respect to the total of the elements other than oxygen being 100 mol %.   
     
     
         2 . A composite oxide catalyst comprising the composite oxide of  claim 1  and a catalytic metal Ni. 
     
     
         3 . The composite oxide catalyst according to  claim 2  for use as a catalyst for hydrocarbon steam reforming or purification of exhaust gas.