The Preparation Of Ceria-Based Core-shell Nanomaterials And Their Catalytic Performance

Due to rapid industrialization with excessive reliance on coal power and rapid growth in car ownership,air pollution,especially CO pollution,has become a serious problem in China,even in the world.Therefore,removing CO is urgent.As a simple and energy-efficient method of removing CO,CO oxidation turns out to be a hot topic in scientific research.Cerium oxide（CeO₂）,which is an excellent candidate for CO oxidation agent,attracts widespread attention because it can improve the CO oxidation reaction rate owing to its rich oxygen vacancy defects,high oxygen storage capacity and the special redox property,which derives from the reversible transformation between Ce3+ and Ce4+.The catalytic activity of cCria-based nanomaterials can be tuned by their morphologies,amount of oxygen vacancies,interfacial structures and the type of exposed crystal surfaces,as well as the synergistic effect exhibited by nanocomposites.The study of this project is to prepare well controlled core-shell nanospheres via solvothermal method with chitosan as soft template.Then we load noble metal gold on the core-shell nanospheres by the deposition-precipitation method to modify the support surface properties and improve the catalytic activity for CO oxidation.The main research contents and results of this paper are as follows:1.The synthesis of CeO₂ core-shell nanospheres and their CO oxidation propertiesA facile solvothermal method with the assistance of chitosan（CS）has been developed to prepare well-dispersed CeO₂ core-shell nanospheres.The obtained CeO₂ core-shell nanospheres were uniform with good dispersity.To further investigate the formation mechanism of core-shell structure and the role of chitosan in the reaction,we carried out a series of experiments by varying the reaction time and the amount of chitosan solution.It was found that the formation of ceria core-shell nanospheres includes the formation of ceria nanocrystals,non-directed self-assembly into solid nanospheres and the dissolution of part ceria nanocrystals.Compared with cube-like ceria obtained without the assistance of chitosan,it shows chitosan changes the morphology and exposed crystal surface of ceria,giving rise to further increase of oxygen vacancy and the improvement catalytic property of ceria.2.The preparation and CO catalytic performance of Au/CeO₂ core-shell nanospheresTo further improve catalytic performance of ceria,we modified the surface properties of ceria core-shell nanospheres by loading precious metal gold nanoparticles.We prepared a series of samples by loading different amounts of Au through deposition-precipitation method.The products obtained were characterized by SEM-EDS mapping,H2-TPR,CO oxidation etc.The results indicate that Au nanoparticles were load uniformly on the supports successfully.Moreover,loading Au increased oxygen vacancy as well as enhanced the reducibility and oxygen storage capacity,finally improved catalytic property of CO oxidation.In addition,the supports are mesoporous structures,anchoring gold nanoparticles to prevent them sintering.The XPS results show that the gold species on ceria core-shell nanospheres composed of Au0 and Au3+ before the test of oxidation of CO,then only as Au0 exists after CO test oxidation.nowever,Uhe gold species on cube-like ceria exist as Au0 either before or after CO test oxidation.Combined with the catalytic results,it is inferred that the co-existence of Au0 and Au3+ was benef1cial to improvement of the catalytic performance for CO oxidation.