Hydrolysis Reaction and Amorphization of Ce-Ti Oxide Catalysts During Synthesis.

The change in the crystallinity of Ce-Ti oxide nanocatalysts with different water contents was investigated in terms of the local atomic structure and the surface atomic concentration. The crystallization of TiO₂, which was induced by the hydrolysis of the Ti precursor, was observed in the catalyst synthesized via a liquid phase reaction employing a mixture of ethanol and distilled water as the solvent. The hydrolysis reaction of the Ti precursor was impeded in the solvent mixture of ethanol and anhydrous ethanol. CeO₂ nanocrystallization occurred due to the suppression of the TiO₂ crystal growth. Low crystallinity of the catalyst synthesized in a single anhydrous ethanol solvent was observed through the broadened X-ray diffraction (XRD) peak and the diffused ring pattern in transmission electron microscopic (TEM) images. In addition, the Ce-O and Ce-Ce bond lengths of the catalyst synthesized using the single solvent decreased beyond those of the catalysts synthesized in the mixed solvent, indicating the amorphization of the catalyst. It was also verified that the inhibition of the precursor crystallization during the synthesis led to the enhanced dispersion of the nanocatalyst, compared to the stoichiometry of the surface atomic concentration.