Structure Evolution of Nanocrystalline CeO2 Supported on Silica: Effect of Temperature and Atmosphere

Microstructure evolution of nanocrystalline CeO2 supported on amorphous SiO2 upon heat treatment in air or in hydrogen at 800-1100°C was studied by TEM, XRD, FTIR and Raman spectroscopy. Sintering of CeO2 and SiO2 with no interface reaction was observed up to 1100°C in air. In hydrogen, formation of various cerium silicates occurred depending on temperature and CeO2:SiO2 molar ratio. For CeO2 content below Ce2Si2O7 (disilicate) stoichiometry formation of a quasi-two-dimensional silicate was observed at 900 -1050°C. Proposed structural formula of the silicate Ce6[Si4O13][SiO4]2 and its lattice parameters: a=2.3422, b=0.7196, c=1.0082 nm in Pca21 space group, indicate its close similarity to a group of Ln3[BSiO6][SiO4] borosilicates (Ln=La, Ce, Nd, Sm, Eu) and to I-type La2Si2O7 disilicate. FTIR spectra of the silicate contain characteristic absorption band at 648 cm-1, probably representing vibration of Si-O-Si bridge in [Si4O13] group.