Spreading and phase transformations in highly dispersed CeO{sub 2}/SiO{sub 2} and Pd/CeO{sub 2}/SiO{sub 2} systems
- 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, Vol. 131, Issue 1; Other Information: PBD: Jun 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
High-Temperature Thermodynamics of Cerium Silicates, A-Ce2Si2O7, and Ce4.67(SiO4)3O
Irradiation-induced reactions at the CeO2/SiO2/Si interface