| Among the various investigated metallic oxide supports,Ceria(CeO2),an important rare-earth product,have performed as good catalysts for CO oxidation under low temperature,because of their high oxygen storage capacity and the rich oxygen vacancies.However,as the supports,CeO2 also has some defects,such as the poor strength of the material and the relatively small surface area,which is the primary reason to limit its practical application.To overcome these problems,fabricating CeO2 material,especially those with a hollow ball or core-shell structure,can effectively expose different crystal planes,improve carrier surface area and mechanical strength,therefore to increase its supporting capacity.In this paper,prepared by the hydrothermal,better dispersion and nice morphology of CeO2 nano-bouquet,nano-spheres and hollow nano-spheres were obtained.And systematic study the various factors that affect the growth of the morphology,then made possible formation mechanism.Meanwhile,we also prepared Pd-only cerium oxide catalyst,and applied to the CO oxidation to evaluate their performance.The main contents include:(1)Two kinds of morphological structure of CeO2 crystallites were prepared through hydrothermal with different templates.Flower-like CeO2 were prepared by assisting with triblock copolymer(Pluronic P123).PVP(poly(vinylpyrrolidone))was applied as surfactant to facilitate the small CeO2 nanoparticles into sphere-like CeO2.The formation mechanism of CeO2 with two morphologies was discussed.Evidenced by analysis of the results,the catalytic activity on CO conversion of these materials at low temperatures followed in the order sphere-like Pd/CeO2<flower-like Pd/CeO2.Compounding characterization,the Pd/F-CeO2 catalyst with higher degree of defect sites connected with the mobility of activated oxygen shows better catalytic performance.What's more,from in situ-DRIFTS and CO2-TPD,it shows that there are more alkalescent positions on Pd/F-CeO2 catalyst,thus greater electronic density of the surface oxygen on the carrier than Pd/S-CeO2 catalyst.(2)we demonstrate a promising Ce-Al2O3 with hollow and self-encapsulated structures prepared by a facile one-pot hydrothermal method using aluminium potassium sulfate and cerium nitrate as precursors and urea as precipitating.The method has significant advantages over traditional template approaches to the large-scale production of hollow inorganic materials.It is interesting to discover that the condensed cores could be self-encapsulated into the hollow shells,and that the hollow shells were constructed with Ce-Al2O3 nano-flakelets and showed urchin-like morphologies.These microspheres were characterized by powder X-ray diffraction,scanning electron microscopy,and nitrogen adsorption.The reported experiments allowed us to propose the mechanism of formation of hollow microspheres.Formation of the hollow Ce-Al2O3 structures was strongly dependent on the reaction temperature and time.The surface area of Ce-Al2O3 hollow microspheres was calculated to be 126.2 m2 g-1,T50 =141?.(3)A simple solvothermal method has been used to synthesize novel CeO2 hollow spheres by controlled solvothermal reaction of cerium nitrate in a mixed solvent of PEG-400/H2O.The time-dependent CeO2 hierarchical structure was studied in detail,and we found that time exerts a crucial influence on the final morphologies of the products.A possible Ostwald ripening mechanism was discussed based on the nucleation and growth processes.In the process,PEG-400 molecules acted as solvent,capping agent and soft template.(4)CeO2 nano-spheres have been synthesized by a simple solvothermal method in a mixed solvent of ethylene glycol and cerium nitrate in an autoclave.Using the CeO2 ano-spheres as template,when adding aluminum nitrate,cerium oxide can be wrapped in aluminum;while adding CTAB and sodium aluminate would form Al2O3-CeO2 hollow spheres with ordered mesoporous structure. |
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