Nanoceria synthesis in molten KOH-NaOH mixture: Characterization and oxygen vacancy formation

Nanoceria was synthesized by treating cerium carbonate hydrate in a molten KOH-NaOH mixture at 200 degrees C. The nanoceria thus synthesized under a hydrogen atmosphere had a crystal size of 21.6 nm measured by XRD, consistent with the particle size of 23 nm measured by TEM. Raman spectra results indicated that the nanoceria produced under hydrogen had a downshift of 0.9 cm(-1) from the sample synthesized in air. XPS spectra showed that the Ce3+ fraction of the nanoceria synthesized in hydrogen was greater than that produced in air. The oxygen vacancies were formed by partial oxidization of the precursor in molten KOH-NaOH mixture. The UV visible absorption properties of ceria synthesized under hydrogen showed a 34 nm red-shift compared with that synthesized in air. The nanoceria prepared in this work had a better catalytic property for CO oxidization than the commercial nanoceria. Results indicated that the increased Ce3+ fraction or oxygen vacancies formed by this partial oxidization process extended the absorption edge of ceria resulting in a narrower band gap, and enhanced the catalytic activity of nanoceria. This method has proven to provide a simple and scalable method for the synthesis of high quality nanoceria.