Nanocrystalline cerium−bismuth oxides: synthesis, structural characterization, and redox properties

DOI: 10.1021/cm1025848

Authors: Kripasindhu Sardar (University of Warwick) , Helen Playford (University of Warwick) , Richard Darton (University of Keele) , Emma Barney (ISIS Facility) , Alex Hannon (ISIS Facility) , David Tompsett (Johnson Matthey Technology Centre) , Janet Fisher (Johnson Matthey Technology Centre) , Reza J. Kashtiban (University of Warwick) , Jeremy Sloan (University of Warwick) , Silvia Ramos (Diamond Light Source) , Giannantonio Cibin (Diamond Light Source) , Richard Walton (University of Warwick)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Chemistry Of Materials , VOL 22 (22)

State: Published (Approved)
Published: October 2010

Abstract: The hydrothermal oxidation of Ce3+ in basic aqueous solution by NaBiVO3 at 240 °C produces fine powders of cerium−bismuth oxides with crystallite sizes of less than 10 nm, as observed by transmission electron microscopy (TEM). Analysis of X-ray absorption near-edge structure at the Bi LIII and Ce LIII edges confirms the reduction of Bi5+ to Bi3+ and the oxidation of Ce3+ to Ce4+, consistent with a general chemical composition CeIV1-xBiIIIxO2-(x/2) (x ≤ 0.6) for the mixed oxides. The refined cubic lattice parameters from powder neutron diffraction indicate a fluorite-like solid solution with volume that increases with Bi content. Pair distribution functions derived from total neutron scattering yield estimated values for refined particle diameters that agree with TEM, showing a decreasing crystallite diameter with increasing bismuth content, and a full analysis reveals that despite average long-range structure being described well as a fluorite solid-solution, the local structure is distorted. Thus, the short-range structure can be simulated as a mixture of symmetric eight-coordinate Ce sites, as seen in CeO2, and distorted Bi sites, as seen in β-Bi2O3. Temperature programmed reduction studies reveal a large hydrogen uptake in the mixed oxides, which is reproducible on a second subsequent cycle. In situ powder XRD under hydrogen flow, however, reveals that this is due to partial phase separation to give bismuth metal. After six cycles, a material of initial composition Ce0.5Bi0.5O1.75 is completely phase-separated and its hydrogen uptake is reduced with high-resolution TEM analysis confirming the permanent reduction of the sample.

Subject Areas: Chemistry, Materials


Instruments: B18-Core EXAFS

Other Facilities: GEM at ISIS

Added On: 02/11/2010 08:49

Discipline Tags:

Physical Chemistry Catalysis Chemistry Materials Science

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) X-ray Absorption Near Edge Structure (XANES)