Preparation And Properties Study Of Ceria Hollow Composite Structures

Ceria?CeO₂?, as a key component in the formulation of catalysts and catalyst supports, has been extensively investigated in various catalytic reactions owing to its excellent redox property and high oxygen storage capacity. To enhance CeO₂ catalytic activity, generally, one may either optimize its morphologies/structures or combine it with secondary species, e.g. noble metal nanoparticles?NPs? or other metal oxides, to form composites. So far, various kinds of morphologies/structures of CeO₂ have been designed and realized and its structure-dependent properties have been well studied as well. Especially, the structure with high surface area, for example, a mesoporous structure, is highly desired since this kind of structure not only facilitates the dispersion of secondary components, but also favors the transportation of reactant molecules to the active sites more effectively.Various cerium-containing precursors are used to construct CeO₂ or CeO₂-based composites. However, very little attention is paid to Ce2?SO4?3 as a precursor, possibly due to its high decomposition temperature?up to 850 °C for transformation into CeO₂? and water-soluble characteristic. Considering Ce2?SO4?3 is insoluble in ethanol and its morphologies can be easily controlled, in this thesis, we choose Ce2?SO4?3 as the precursor to synthesize mesoporous CeO₂ and CeO₂-based composites.After an interfacial reaction between water-soluble cerium sulfate?Ce2?SO4?3? precursor and NaOH in ethanol at room temperature, the Ce2?SO4?3 successfully converts into CeO₂ without calcination or acid/base etching process. The obtained CeO₂ not only inherits initial hollow hierarchical morphology of Ce2?SO4?3 precursor but also possesses mesoporous structure, which enables it to be an ideal support for Au NPs in CO oxidation. In contrast, the CeO₂ derived from direct calcination of Ce2?SO4?3 precursor displays severe sintering and exhibits worse catalytic performance toward CO oxidation.Using the similar method, CeO₂-CuO nanorods with mesoporous structure were synthesized by a facile and mild strategy, which involves an interfacial reaction between Ce2?SO4?3 precursor and NaOH in ethanol at room temperature, followed by a solvothermal treatment of as-prepared CeO₂ and Cu?CH3COO?2. Upon solvothermal treatment, CuO species is highly dispersed onto CeO₂ nanorod surface to form CeO₂-CuO composites, which still maintain mesoporous feature. Raman spectroscopy, X-ray photoelectron spectroscopy?XPS? and hydrogen temperature-programmed reduction?H2-TPR? analysis revealed that there is a strong interaction between CeO₂ and CuO, which is possibly responsible for high catalytic activity toward CO oxidation of the mesoporous CeO₂-CuO nanorods.This work represents a good demonstration of an interfacial reaction-engaged process capable of generating hollow nanostructures from water-soluble precursors. When other suitable water-soluble precursors are chosen, this method is expected to be implemented to the fabrication of other hollow metal oxide materials.