Spreading and phase transformations in highly dispersed CeO{sub 2}/SiO{sub 2} and Pd/CeO{sub 2}/SiO{sub 2} systems

Journal Article · Sun Jun 01 04:00:00 EDT 1997 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1997.7364· OSTI ID:589036

Kepinski, L; Wolcyrz, M ^[1]

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1. Institute of Low Temperature and Structure Research, Wroclaw (Poland)

The effect of Pd on spreading and reaction of CeO{sub 2} nanocrystallites with silica support on high temperature reduction in hydrogen was studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Without Pd, CeO{sub 2} nanocrystallites (size ca. 5 nm) began to spread onto the silica at 870 K, producing at 970 K uniform nearly amorphous overlayer. With Pd, the spreading occurred at 100 K lower temperature and moreover at 970 K the raft-like Ce{sub 4.67}(SiO{sub 4}){sub 3}O silicate crystals were formed in contact with the Pd particles. Chlorine from the PdCl{sub 2} precursor reacted with ceria at 770 and 870 K to form the ribbon-like CeOCl crystals, which at 970 K became unstable, probably undergoing transformation into Ce silicate. Formation of Ce silicate and CeOCl during the high temperature reduction is a possible mechanism of the deactivation of the ceria-promoted Pd/SiO{sub 2} catalysts (irreversible Ce{sup 4+} to Ce{sup 3+} reduction).

• OSTI ID: 589036
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 131; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERIUM OXIDES
CRYSTALS
DEACTIVATION
ELECTRON DIFFRACTION
PALLADIUM OXIDES
PHASE TRANSFORMATIONS
SILICA
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION