| 摘要 |
PURPOSE: To obtain the composite oxide having a specific crystal phase and an excellent oxygen-absorbing and releasing ability by adding cerium oxide, zirconium oxide and hafnium oxide in prescribed amounts, respectively. CONSTITUTION: A cerium nitrate aqueous solution, a hafnium-containing zirconium nitrate salt aqueous solution, if necessary, a solution containing other metal ions, an ammonia aqueous solution, and an ammonium bicarbonate aqueous solution or an oxalic acid aqueous solution are mixed with each other to obtain the composite salt precipitates containing cerium, zirconium and the hafnium. The composite salt precipitates are calcined at 300-1000 deg.C to obtain the primary composite oxide. The primary composite oxide is charged into a vacuum heating oven, heated for removing impurities, reduced with H2 , CO, etc., at a high temperature, and subsequently subjected to a heating oxidation treatment using an oxidizing gas to obtain the composite oxide containing 4.99-98.99wt.% of cerium oxide, 1-95wt.% of zirconium oxide, and 0.01-20 wt.% of hafnium oxide, having a ϕphase as the crystal phase and having an oxygen-absorbing and releasing ability of >=10μmol/g at 400-700 deg.C. |
