Effect of oxygen deficiency and dopant on the defect structure in CeO2 nanoaprticles
Eric Nestor Tseng1*, Shih-Yun Chen1, William Lee1, Nan-Hong Chen1, Sheng-Chiang Yang2, Bing-Joe Hwang2
1Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
2Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
* presenting author:曾瀚輝, email:d10204001@mail.ntust.edu.tw
In this study, defect structure of CeO₂ nanoparticles (NPs), in particular, concentration dependence of defect distribution was investigated. Un-doped, Cr-doped and Sm doped CeO₂ NPs were prepared by the co-precipitation method and then annealed in different atmospheres (O₂ and Ar+H₂) at 300℃ to control the amounts of defects. Crystal structure, particle size and valence state were characterized by using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Temperature programmed reduction (TPR) was utilized to study the reaction with hydrogen at different temperatures. According to the catalyst behavior, the distribution of defect after different annealing process as well as the doping was unraveled. In the un-doped CeO₂ NPs, defects mainly concentrated at the surface before annealing. Oxidation reaction promotes the segregation of defects at surface while reduction reaction facilitates the diffusion of defects into the bulk. Our results also demonstrated that the evolution of defect structure was strongly dopant dependent. Doping with Cr facilitates the aggregation of vacancies while doping with Sm results in the core shell structure. At last, ferromagnetism among CeO₂ NPs with different defect structures was compared and the preferred type of defect structure was then suggested in this study.

Keywords: CeO2 nanoaprticles defect structure