The low-temperature synthesis of cation-ordered Ce–Zr-based oxide via an intermediate phase between Ce and Fe†
Ce0.5Zr0.5O2 is a well-known oxygen storage material used in automobiles to maintain the air–fuel ratio during operation. It has been reported that the cation ordering of Ce and Zr ions and doping with transition metals improves the oxygen storage capacity (OSC) of the Ce–Zr-based oxides. In this study, Ce–Zr-based oxides were co-doped with Co and Fe to determine their effect on the oxygen storage capacity at low temperatures. Using the Pechini method, samples of (CeZrO4)100−x–(CoFe2O4)x (xCFO; x = 1 to 5) are prepared and their solubility limit, oxygen storage capacity, and stability are clarified. The solubility limit of xCFO was found to be 5CFO. A high OSC of 440.0 μmol O2 g−1 at 400 °C was found for 5CFO, which is 13.5 times higher than the 32.5 μmol O2 g−1 found for Ce0.5Zr0.5O2 without doping. This was attributed to the low formation enthalpy of oxygen vacancy and faster surface exchange kinetics. This solid solution is stable at 400 °C and decomposes at 900 °C. The results indicate that Fe induces phase transition to a cation-ordered phase, a pyrochlore-type Ce2Zr2O7, and lowers its transition temperature to 800 °C. The acceleration of the reduction of Ce and cation diffusion due to the formation of the intermediate phase of CeFeO3 resulted in these changes. From the results of this study, it can be concluded that Fe is a key element in improving the OSC properties of the Ce–Zr-based oxide and expands the possibilities for a cation-ordered κ-Ce2Zr2O8 catalyst.