Preparation Of Mesoporous CeO₂ And Its Application In Gold-Catalyzed CO Oxidation Reaction

There are plenty of rare earth materials in our country.Among them,CeO₂ has been widely used because of its unique crystal structure and high oxygen storage capability. Mesoporous CeO₂ is active in the field of catalyzed reactions.Nowadays,researches are focus on preparing high BET surface area,ordered mesoporous structured and pore-size controll-able mesoporous CeO₂ materials to make it more powerful in the catalyzed reactions.In this paper,mesoporous CeO₂ materials or composites are prepared using CMK-3 and carbon aerogels with incipient impregnation method.The influences of impregnation method, impregnation sequence,pretreatment of the template,structure of the template,templateremoved temperature and CeO₂ contents on the CeO₂ were investigated.The material is used as support of the Au catalyst to catalyze CO oxidation reaction and the activity is studied.The microstructure and appearance of the materials were characterized by N₂ adsorptiondesorption, XRD and TEM methods.The characterization results were studied correspond to the CO oxidation reaction results.The results indicate that CeO₂ prepared from the CMK-3 template show two-dimensional hexagonal ordered structure,narrow??e-size distribution and the particle size is below 10nm. CeO₂ prepared with multiple impregnation method show long distance ordered structure while that prepared with one step impregnation method show short distance ordered structure. When the template-removal temperature is increased,the ordered structure of CeO₂ will be destroied,particle size and pore size increase,BET surface area decrease and pore size distribution narrowed.CeO₂ prepared with multiple impregnation method and with templated-removal temperature of 350℃shows best catalytic activity for CO oxidation when used as the support of Au catalyst(T_50%=21.2℃).CeO₂ was prepared from the carbon aerogel template.The yield increases after the template is treated with ammonia.When the template-removal temperature is decreased,the BET surface area of CeO₂ increase and particle size decreased.The particle size effect of the CeO₂ as support is obvious in the CO oxidation.The activity of catalyst decrease as the particle size of the support increase.CeO₂/MgAl₂O₄ composites were prepared using CMK-3 as the template with multiple impregnation method.The appearance and the lowest templated-removal temperature of the CeO₂/MgAl₂O₄ composites were correspond to the impregnation sequence.The activity of catalyst increase as the CeO₂ amount of the support increase when the CeO₂/MgAl2O₄ composites are used as the Au catalyst support for the CO oxidation reaction.CeO₂/SBA-15 composites were prepared with multiple impregnation method.When the CeO₂ amount of the composites increase,the BET surface area and the total pore size decrease while the particle size of the CeO₂ in the channel of SBA-15 grows bigger.. CeO₂/SBA-15 composites with different CeO₂ amount were used as the support of the Ag catalyst for CO oxidation reaction.Ag catalyst with the CeO₂ amount of 9.6wt%show best catalytic activity in CO oxidation(T_50%=74.9℃).