Low-Temperature Direct Synthesis of Nanoparticles of Fluorite-Type Ceria–Zirconia Solid Solutions by "Forced Cohydrolysis" at 100°C

Nanometer-sized particles ranging from 2 to 3 nm of CeO2 (ceria)–ZrO2 (zirconia) solid solutions with cubic and/or tetragonal fluorite-type structure in the wide composition range from 20 to 100 mol% CeO2, without a trace of monoclinic ZrO2 phase, could be directly synthesized at low temperature of 100°C from acidic aqueous solutions of ZrOCl2 and (NH4)2Ce(NO3)6 by forced simultaneous hydrolysis, i.e., "forced cohydrolysis." Analytical values of CeO2/ZrO2 ratio in the as-precipitated solid solutions showed fairly good agreement with starting compositions in the solutions. The proceeding of the hydrolysis and formation rate of fluorite-type solid solutions tended to slow down at near median composition. Any change in crystalline phase of as-precipitated solid solutions was not observed by powder X-ray diffractometry after heat treatment in air below 1000°C. Ceria–zirconia solid solutions with fluorite structures containing large amount of ZrO2 maintained high surface area after heat treatment at 1000°C.