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Controlled Hydrothermal Synthesis of Complex Mixed Oxides Using Solution Redox Chemistry

Published online by Cambridge University Press:  10 February 2011

Richard I. Walton ,
Kripasindhu Sardar ,
Helen Y. Playford ,
Deena R. Modeshia ,
Richard J. Darton ,
Janet Fisher  and
David Thompsett
Richard I. Walton*
Affiliation:
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
Kripasindhu Sardar
Affiliation:
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
Helen Y. Playford
Affiliation:
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
Deena R. Modeshia
Affiliation:
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
Richard J. Darton
Affiliation:
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
Janet Fisher
Affiliation:
Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading, RG4 9NH United Kingdom.
David Thompsett
Affiliation:
Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading, RG4 9NH United Kingdom.
*
*Email: [email protected]
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Abstract

We present the results of a study of the solvothermal synthesis of mixed-metal cerium-containing oxides all prepared from CeCl3.7H2O at less than 250 ºC in single step reactions. The use of NaBiO3 in the presence of aqueous NaOH yields fluorite solid solutions Ce1-xBixO2-x/2 (x ≤ 0.6), whereas the use of either H2O2 or NaBrO3 as oxidant in the presence of TiF3 yields a Ce(IV) pyrochlore (Na0.33Ce0.67)2Ti2O7. With replacement of a fraction of the Ti reagent by Sn(IV) acetate, tin doping is possible in the pyrochlore. The materials have all been assessed for their use in catalysis by performing temperature programmed reduction (TPR) experiments under dilute hydrogen flow. The cerium-bismuth oxides show large and apparently reversible hydrogen uptake, but in situ powder X-ray diffraction shows that this is accompanied by phase separation into bismuth metal and CeO2 that occurs over 5 or more TPR cycles. In contrast, the cerium (IV) titanate pyrochlore shows reversible reduction at low temperature (150 ºC, after an activation step), which gives the material potential use as a precious metal support for catalysis: such as in the water-gas-shift reaction. Although Sn doping lowers the onset of reduction of the pyrochlore, consistent with an expanded lattice, the materials suffer from collapse to give SnO.

Keywords

hydrothermalcrystal growthcatalytic
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1309: Symposium EE – Solid-State Chemistry of Inorganic Materials VIII , 2011 , mrsf10-1309-ee01-06
Copyright
Copyright © Materials Research Society 2011

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References

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