Highly dispersed ceria and ceria-zirconia nanocomposites over silica surface for catalytic applications

Silica-supported CeO2 and CeO2-ZrO2 nanocomposite oxides were synthesized by a novel deposition-precipitation method and Subjected to thermal treatments at 773-1073 K to study their sintering behavior and oxygen storage/release capacity (OSC). The prepared catalysts were characterized using thermogravimetry, BET Surface area, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and other techniques. BET measurements indicate that CeO2-ZrO2/SiO2 (CZS) samples possess more specific surface area and substantial resistance towards thermal sintering relative to CeO2/SiO2 (CS) samples. XRD profiles reveal only the broad diffraction lines due to CeO2 in the case of CS while CZS discloses Ce0.75Zr0.25O2, Ce0.6Zr0.4O2 and Ce0.5Zr0.5O2 phases depending on the treatment temperature. Raman measurements of both series of samples indicate the presence of oxygen vacancies, lattice defects and displacement of oxygen ions from their ideal lattice positions. XPS studies indicate the presence of cerium at the surface in both 4+ and 3+ oxidation states. The HREM results reveal well dispersed CeO2 (similar to 3-4 nm) and Ce-Zr oxide particles (similar to 5 nm) over the amorphous SiO2 matrix in the case of CS and CZS samples. respectively. There was no significant increase in the size of the dispersed nano-oxides even after calcination at 1073 K. Both the samples exhibit reasonably high OSC values. (c) 2008 Elsevier B.V. All rights reserved.