To study the correlation between crystal facets and oxygen vacancies, three kinds of ceria samples with various crystal facets, cube , rod  and octahedron , were prepared. For further comparison, two kinds of ceria samples with  facets (20–30 nm rod and 5–8 nm filiform) were also constructed. The morphology, crystal structure, surface composition, reducibility and oxygen defects of the prepared samples were characterized by SEM, XRD, N2 adsorption–desorption, H2-TPR, XPS and EPR, respectively. The results showed that the surface oxygen defect contents of the samples followed the order: CeO2–F > CeO2–C > CeO2–R > CeO2–O, indicating that the content of oxygen vacancies is closely related on the crystal facets. The catalytic performance of the samples are all in line with that of the Oads/Olatt ratios, suggesting that crystal facets play a crucial role on surface oxygen vacancies and phenol oxidation of the ceria samples. Furthermore, although the CeO2–R sample (rods) and the CeO2–F sample (filiform) are mainly enclosed by  facets, the CeO2–F showed better catalytic performance than that of CeO2–R, revealing that the phenol oxidation not only depends on the crystal facets of CeO2 but also with its surface oxygen vacancy contents.
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This work is supported by National Nature Science Foundation of China (51572004, 21504001), Natural Science Foundation of the Higher Education Institutions of Anhui Province, China (KJ2016SD06), Natural Science Fund for Distinguished Young Scholars from Anhui Polytechnic University (2016JQ01), and Top-notch Talent Cultivation Plan from Anhui Polytechnic University (2016BJRC002).
R.P. Rocha, S.G.P. Soares, A.G. Gonçalves, J.J.M. Órfão, M.F.R. Pereira, J.L. Figueiredo, Appl. Catal. A Gen. 548, 62 (2017)CrossRefGoogle Scholar