Low-Temperature Redox Properties of Nanocrystalline Cerium (IV) Oxides Revealed by in Situ XANES

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• 作者：Deena R. Modeshia ; Christopher S. Wright ; Julia L. Payne ; Gopinathan Sankar ; Steven G. Fiddy ; Richard I. Walton
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：September 27, 2007
• 年：2007
• 卷：111
• 期：38
• 页码：14035 - 14039
• 全文大小：370K
• 年卷期：v.111,no.38(September 27, 2007)
• ISSN：1932-7455

文摘

Time-resolved, in situ XANES studies of some cerium titanate pyrochlores and a fluorite-type bismuth-cerium oxide under reducing and oxidizing gas atmospheres reveal that reduction of cerium occurs attemperature below 500 C in each of the materials. Cerium oxidation state during these treatments is quantifiedby deconvolution of the Ce L_III-edge XANES signal using fitted Lorentzians and comparison to data fromreference materials of known average oxidation state. In the case of the cerium titanate pyrochlore,complementary XANES experiments at the Ti K-edge show that average titanium oxidation state is largelyunaffected on reduction of the sample, although small changes in titanium local environment are apparentthat are most likely due to thermal expansion effects as well as an expansion of the structure due to thereduction of cerium. Reoxidation of the pyrochlore is extremely facile, occurring even under hydrogen, whichmay be attributed to an increase in crystallite size and loss of oxide-rich surfaces, which is backed up byTEM observations.