Phase constitution and oxygen storage capacity of Bi³⁺ doped CeO₂ nanopowders

Bi³⁺ doped CeO₂ nanoparticles with various Bi³⁺ contents were synthesized by hydrothermal mothed. The samples were characterized by XRD, HRTEM, XPS and Raman spectroscopy. Based on the results of XRD, it is found that all the diffraction peaks could be identified as CeO₂ when the content of Bi³⁺ was less than 20at%. A second phase Bi₂O₃ emerged if the content of Bi³⁺ was higher than 40at%. Temperature programmed reduction (H₂-TPR) shows that the oxygen storage capacity (OSC) of the samples was significantly improved by the introduction of Bi³⁺ and was closely related with the phase constitution. In the case of without second phsase of Bi₂O₃, the enhancement of OSC should be attributed to the the doping of Bi³⁺. After Bi₂O₃ was evolved, the OSC of mixed oxides further increased. However, the reduction peaks of H₂-TPR curves split obviously at low temperature. This means that the consumption of hydrogen contained two reduction reactions of CeO₂ and Bi₂O₃, therefore, the results of H₂-TPR curves are a sum of both reactions.