The sharp peak at 469 cm−1 in Fig. 3a was ascribed to the F2g vibration band of CeO2. It continuously moved toward the lower Raman shifts and broadened for the 0.1CeO2/SnO2, Sn0.3Ce0.7O2 and Sn0.5Ce0.5O2 catalysts (Fig. 3b–d). The Raman shift of this R547 peak is strongly related to the decrease of the ceria crystallite size  and . Additionally, the widening of the peak is sensitive to the symmetry of the crystal lattice . The lower the symmetry of the crystal lattice is, the broader the peak is. Therefore, the lowered and broadened F2g vibration bands of CeO2 over the Ce-rich catalysts suggest photosystems the incorporation of the Sn cations into the CeO2 lattice inhibits the crystal growth and perturbs the structural symmetry of the Ce-rich catalysts. Herein, the F2g band of the Sn0.7Ce0.3O2 catalyst (465 cm−1) located at the similar Raman shift as that of the 0.1CeO2/SnO2 (464 cm−1), although the former had a smaller ceria crystallite size (Table 1). This abnormal phenomenon might be due to the overlap of F2g (CeO2) and Eg (SnO2) vibration bands.