Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.787312
Title: The controlled hydro/solvothermal synthesis of ceria-based materials
Author: Dunn, Alexander James Aiken
ISNI:       0000 0004 7972 4326
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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Abstract:
This thesis reports on the one-pot hydro/solvothermal synthesis of a range of mixed metal cerium oxides with potential catalysis applications. The produced materials were characterised using a wide range of techniques to understand the synthesis-dependent variations in crystallite size, morphology, surface absorbed species and redox properties. The hydrothermal synthesis of bismuth-substituted cerium dioxide is reported. The choice of starting reagents in the hydrothermal reaction was found to affect the crystallite sizes of the resulting Ce0.5Bi0.5O2-δ samples. The Ce0.5Bi0.5O2-δ samples with the lower crystallite size and hence larger surface areas were derived from the use of Ce(NH4)2(NO3)6 as the cerium source. In situ X-ray diffraction and X-ray absorption experiments indicate that the cubic structure of Ce0.5Bi0.5O2-δ is formed via formation of poorly ordered CeO2 followed by the reduction of bismuth and/or to the crystallisation of α-Bi2O3 from the bismuth starting reagents prior to its inclusion into CeO2. The solvothermal reaction of CeCl3 with LnCl3 (Ln = La, Pr, Gd and Tb) in polyethylene glycol at 240 °C yields a range of previously unreported Ce1-xLnx(OH)2Cl samples with a unusual morphology. Barring lanthanum, up to approximately 50% lanthanide-substitution was achieved. Contrarily, the series of Ce1-xLnx(OH)CO3 materials prepared via the use of nitrate precursors achieved only 20% lanthanide-substitution. The thermal decomposition of the lanthanide-substituted cerium precursors produces materials that adopt the fluorite type unit cell and retain their unique crystal morphology. X-ray absorption near-edge structure spectra recorded at the Pr and Tb K-edges indicates the existence of both in two oxidation states, Tb3+/Tb4+ and Pr3+/Pr4+. The results deduced from XANES spectra of the mixed oxides agree with the calculated lattice parameters refined from the X-ray diffraction patterns. The incorporation of lanthanide cations improves the reducibility of ceria as measured by H2-temperature programmed reduction. Three methods using alkoxide starting reagents have successfully been able to synthesise the ordered k-Ce2Zr2O8 phase. Powder X-ray diffraction shows that the cationic ordering can be achieved at temperatures as low as 1000 °C without the use of reducing gases. A study of both the local environment and structure of the zirconium substituted ceria samples reveals that the solvothermal method of synthesis produces materials that contain a larger quantity of Ce3+.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.787312  DOI: Not available
Keywords: QD Chemistry
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