Hydrothermal Synthesis And CO Catalytic Performance Of Ceria Nanostructures

China possesses abundant rare earth resources, where Ce is the highest abundance of the whole rare earth. Because of its unique electronic structure of 4f, cerium oxide has many applications such as UV absorption, three-way catalyst, automobile exhaust purification catalyst, polishing agent, glass of decolorant, radiation resistant glass, electronic ceramics, etc. Cerium oxide nanomaterials, the particle size of which is relatively small, have surface effect, high quantum size effect, small size effect and macroscopic quantum tunneling effect and other characteristics. Therefore they have possessed many special properties different from traditional materials, and become a research hotspot in recent years in materials science. The size distribution and the morphology of cerium oxide nanomaterials have significant influences on properties. Therefore controllable synthesis of cerium oxide nanostructures need to be investigated. This paper focuses on the controllable synthesis of cerium oxide nanostructures via the hydrothermal process, meanwhile the structure, morphology and the catalytic performance of the as-prepared cerium oxide have been studied. The main contents and results of experiments are as follows:1. Templated-free hydrothermal synthesis of core-shell ceriaCore-shell ceria was synthesized through a one-pot hydrothermal process at 120℃ for 24 h. During the reaction, we used Ce(NO3)3-6H2O as Ce resources, CO(NH)2 as precipitating agents, H2O2 as oxidant, citric acid as directing agents, n-butyl alcohol as co-solvent. The morphology of the as-prepared sample and the intermediate products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) etc., according to the obvious results, the growth mechanism was nucleation-aggregation followed by Ostwald ripening. The test result of CO conversion indicated the core-shell nanostructured ceria possessed the good catalytic activity.2. Hydrothermal synthesis of flower-like ceria nanostructuresWe used CeCl3-7H2O as Ce resources, N,N-dimethylformamide as precipitating agents, KClO3 as oxidant, H2O as solvent to fabricate flower-like nanostructured ceria. Without template assisted, flower-like nanoparticles with the size ranging from 200 to 500 nm was successfully synthesized at 180℃ for 4 h. The morphology of the as-prepared sample and the intermediate products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) etc., in the reaction, two phases were formed and finally only one phase was obtained. According to the results, the growth mechanism was proposed including nucleation, self-assembly and oxidation. The as-prepared ceria showed good catalytic performance for CO conversion.3. Hydrothermal synthesis of ceria nanoparticles with (200)-dominant exposureClean-edged ceria nanoparticles with size ranging from 13 to 17 nm were synthesized via a rapid one-step hydrothermal process at 180℃ for 100 min, using Ce(NO3)3-6H2O as Ce resources, urotropine as precipitating agents, polyvinylpyrrolidone as surfactant, H2O as solvent. The morphology of the as-prepared sample and the products at different reaction conditions were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) etc., according to the results, the optimized reaction conditions such as reaction time, the added amount of urotropine and polyvinylpyrrolidone were determined. The test result of CO conversion indicated the ceria nanoparticles possessed the good catalytic activity.