Solid solubility and oxygen storage capability of In³⁺-doped CeO₂

CeO₂ is an important rare earth oxide and can be used in automotive exhaust three-way catalysts on the basis of its oxygen storage capability. Ion doping is an effective method to enhance the oxygen storage capability of CeO₂. And when doping a cation whose size is smaller than Ce⁴⁺ and valence is lower than +4, it tends to evolve more defects. It is known that defects play important roles in enhancing the oxygen storage capability of CeO₂. Therefore, In ion was selected as a dopant cation which matches above two factors of size and valence. In this work, a series of CeO₂ with different content of In³⁺ were synthesized via a two-step process. The precursor was synthesized by a solvothermal method at 200℃ using a mixture solvent of (CH₂OH)₂ and H₂O, as well as Ce(NO₃)₃·6H₂O and In(NO₃)₃·4.5H₂O as Ce and In sources, respectively. CeO₂ was obtained after the precursor was calcined at 500℃ for 2 h in air. It was found that the solid solubility of In³⁺ in CeO₂ was 1% (molar fraction). The doping of 1%In³⁺ in CeO₂ almost had no impact on the morphology of multilayered structure. However, a second phase of small particles appeared and there were some changes of the morphology of multilayered structure when the concentration of In³⁺ increased further. The specific surface area of the 1%In³⁺ solid solution was 100 m²/g, which was th highest among all the samples, and undoped CeO₂ (92 m²/g) ranked second. When the content of In³⁺ was above the solid solubility,i.e., 1%In³⁺, the specific surface area decreased. The low temperature oxygen storage capability could be improved from 3.6×10^-4 mol/g for undoped CeO₂ to 4.4×10^-4 mol/g for 1%In³⁺-doped CeO₂. When the In³⁺ content was greater than or equal to 3%, the low temperature oxygen storage capability decreased at the beginning, and then almost no change. Lattice parameter decreased and the concentration of Ce³⁺ and oxygen vacancy increased by the doping of In³⁺. Moreover, lattice parameter, the specific surface area, concentration of oxygen vacancy and low temperature oxygen storage capacity could mark a turning point for 1%In³⁺. It could be found that the low temperature oxygen storage capability was in relation to both the specific surface area and the concentration of oxygen vacancy of CeO₂. In addition, the low temperature reduction peaks shifted towards lower temperatures with the addition of In³⁺.