Spray Freeze Drying as a Smart Method in Preparation of Ultra-Fine CeO2-MOX Materials

Abstract

Cerium-oxide based nano-materials attract increasing interest for their use in multiple applications. In particular, the substitution of Ce atoms by other elements with lower or higher oxidation state is used to control oxygen vacancies within the oxide structures, which can greatly enhance the material properties for catalysis applications. Among the synthesis approaches, spray freeze drying method has been proved to be an extremely efficient method for the preparation of uniform nano-partical for different application. In this method, the pure solution or mixed solutions were directly sprayed into liquid nitrogen and immediately frozen to form a suspension, then, the iced droplets were dried in the freeze-dryer to reach the final product. However, in this work we deal with, the preparation of ultra-fine materials based on CeO₂ fluorite structures and the substitution in its lattice with La and/or Co metal. The effect of Ce/La ratio on the properties of the final product was also investigated. During the experiment, the advantage of spray-freeze-drying process was successfully achieved. The characterization of the powder product was analyzed by means of EDX, TGA, XRD, DLS, and TEM which confirm the formation of nano-particles in the fluorite structure. For Ce:Co and when the Ce: La ratio is 0.2, 0.5, only cubic phase of CeO₂-MO₂ solid solution with ?uorite structure is observed with hig oxygen storage capacity, while Ce-La₁ show the hcp structure of lanthanum.

Keywords: nano-materials, Ceria, Lanthanium, metal loading spray freeze drying