Effect of the Presence of Ammonium Peroxodisulfate on the Direct Precipitation of Ceria and Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions

Direct precipitation of nanometer‐sized particles of ceria–zirconia (CeO 2 –ZrO 2 ) solid solutions with cubic and tetragonal structures was successfully attained from acidic aqueous solutions of cerium(III) nitrate (Ce(NO 3 ) 3 ) and zirconium oxychloride (ZrOCl 2 ) through the addition of ammonium peroxodisulfate ((NH 4 ) 2 S 2 O 8 ), because of promotion of the hydrolysis via the oxidation of Ce 3+ ions, together with the simultaneous hydrolysis of ZrOCl 2 under hydrothermal conditions. Ultrafine CeO 2 particles also could be formed from relatively concentrated aqueous solutions of the same trivalent cerium salt in the presence of (NH 4 ) 2 S 2 O 8 via hydrolysis. The crystallite size and lattice strain of as‐precipitated solid solutions varied, depending on the composition within the CeO 2 –ZrO 2 system. Creation of a solid solution of ZrO 2 into a fluorite‐type CeO 2 lattice clearly introduced lattice strain, as a consequence of the decreasing crystallite size. Both the direct precipitation process and the effectiveness of the presence of (NH 4 ) 2 S 2 O 8 for the synthesis of CeO 2 –ZrO 2 solid solutions were discussed.