Ce2/3Cr1/3O2+y: a new oxygen storage material based on the fluorite structure

Singh, Preetam ; Hegde, M. S. ; Gopalakrishnan, J. (2008) Ce2/3Cr1/3O2+y: a new oxygen storage material based on the fluorite structure Chemistry of Materials, 20 (23). pp. 7268-7273. ISSN 0897-4756

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Official URL: http://pubs.acs.org/doi/abs/10.1021/cm802207a

Related URL: http://dx.doi.org/10.1021/cm802207a


In an exploratory search for new oxygen storage materials (OSMs), we have identified a fluorite-type solid solution series, Ce1-xCrxO2+y (0 < x ≤ 1/3), of which the x = 1/3 member, Ce2/3Cr1/3O2.11 (oxide I), exhibits excellent reversible oxygen release/storage properties at relatively low temperatures (~350 °C). Oxide I prepared by a hydrothermal route crystallizes in a metastable nanocrystalline (~4 nm) fluorite type structure (α = 5.352 Å) where the cerium and chromium are randomly distributed. Characterization of oxide I by electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetry for the composition, crystal structure, oxidation states of metal atoms, and oxygen stoichiometry yields the formula CeIV2/3CrVI1/9CrIV2/9O2.10 ± 0.02 for oxide I. Investigation of oxygen release/intake by temperature programmed hydrogen reduction and thermogravimetric studies has revealed that oxide I possesses a high oxygen storage capacity of 0.175 moles of O2/mole up to 550°C; this value is better than or comparable to the best OSMs based on CeO2-ZrO2. The temperature (~350°C) at which facile oxygen release/intake occurs with oxide I is also lower than that of CeO2-ZrO2 based oxides. Formation of oxide I with a cation-disordered fluorite structure, unlike other lanthanide analogs, and its oxygen release/storage properties are discussed in terms of the redox chemistry of CeIV/III and CrVI/IVin the solid state.

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