Controllable synthesis of CeO2 nanoparticles with different sizes and shapes and their application in NO oxidation

Abstract

This study describes the synthesis of cobalt–ceria catalysts with octahedron and nanosphere shapes via a facile and surfactant-free hydrothermal method. The morphology of the products could be controlled by adjusting the proportion of solvent. The products evolved from nanospheres to octahedra with decreasing ethylene glycol/water volume fraction ratio in the reaction system. The formation process of the nanospheres involved dissolution–recrystallization-assembly and Ostwald ripening processes. Furthermore, the sizes of the obtained ceria–cobalt nanospheres were about 30 to 150 nm; these were composed of many crystallites with sizes of approximately 7 to 9 nm. The size of the ceria–cobalt nanospheres could be controlled by changing the cobalt doping amount in the mixed water–glycol system. These synthesized catalysts were applied for NO oxidation. The catalytic performance is closely related to the oxygen vacancy and the NO adsorption ability. In the low cobalt doping amount, NO adsorption and desorption played an important role in the oxidation process. However, the adsorption and activation O₂ was the key step when the NO adsorption and desorption ability was similar.