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

Abstract

Direct precipitation of nanometer-sized particles of ceria–zirconia (CeO2–ZrO2) solid solutions with cubic and tetragonal structures was successfully attained from acidic aqueous solutions of cerium(III) nitrate (Ce(NO3)3) and zirconium oxychloride (ZrOCl2) through the addition of ammonium peroxodisulfate ((NH4)2S2O8), because of promotion of the hydrolysis via the oxidation of Ce3+ ions, together with the simultaneous hydrolysis of ZrOCl2 under hydrothermal conditions. Ultrafine CeO2 particles also could be formed from relatively concentrated aqueous solutions of the same trivalent cerium salt in the presence of (NH4)2S2O8 via hydrolysis. The crystallite size and lattice strain of as-precipitated solid solutions varied, depending on the composition within the CeO2–ZrO2 system. Creation of a solid solution of ZrO2 into a fluorite-type CeO2 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 (NH4)2S2O8 for the synthesis of CeO2–ZrO2 solid solutions were discussed.