Structure evolution of nanocrystalline CeO2 supported on silica:: Effect of temperature and atmosphere

Microstructure evolution of nanocrystalline CeO(2) supported on amorphous SiO(2) upon heat treatment in air or in hydrogen at 800-1100 degreesC was studied by TEM, XRD, FTIR and Raman spectroscopy. Sintering of CeO(2) and SiO(2) with no interface reaction was observed up to 1100degreesC in air. In hydrogen, formation of various cerium silicates occurred depending on temperature and CeO(2):SiO(2) molar ratio. For CeO(2) content below Ce(2)Si(2)O(7) (disilicate) stoichiometry formation of a quasi-two-dimensional silicate was observed at 900-1050 degreesC. Proposed structural formula of the silicate Ce(6)[Si(4)O(13)][SiO(4)](2) and its lattice parameters: a = 2.3422, b = 0.7196, c = 1.0082 nm in Pca2(1) space group, indicate its close similarity to a group of Ln(3)[BSiO(6)][SiO(4)] borosilicates (Ln = La, Ce, Nd, Sm, Eu) and to I-type La(2)Si(2)O(7) disilicate. FTIR spectra of the silicate contain characteristic absorption band at 648 cm(-1), probably representing vibration of Si-O-Si bridge in [Si(4)O(13)] group. (C) 2002 Elsevier Science (USA).