Preparation Of The Double-Layered Carrier Of CeO₂/3DOM TiO₂-Supported Transition Metal Oxide Catalysts And Their Catalytic Performances For Diesel Soot Combustion

Diesel vehicles have the characteristics of high thermal efficiency,good economy,low CO₂ emission and excellent dynamic performance.They have the advantages of alleviating energy shortage and conforming to low carbon emission,making the diesel engine of motor vehicles become the trend of the times.However,in recent years there have been various kinds of air pollution,such as fog and haze.Among them,the diesel exhaust particulate matter（PM）is one of the important factors for causing air pollution.Soot particles not only pollute the air environment,but also have small particle size and easy to float.They adsorb a lot of carcinogenic substances on the surface and cause harm to human health.At present,post-processing technology is one of the most effective ways to eliminate soot particles.Therefore,the study and development of new and efficient catalysts to eliminate PM have important scientific research significance and environmental protection significance.In this thesis,a new type of catalysts was designed and prepared based on the two ideas and aspects.One is to design three-dimensional ordered macroporous catalysts,which allows the soot particles to pass through,diffusion mass transfer inside the catalyst,contact with more active sites,and effectively increase the contact surface of the catalyst and the reactant.The other is to design the double-layered carrier of CeO₂/3DOM TiO₂.The synergistic action of cerium and titanium improves the structural stability and oxygen storage-relase capacity of the carrier.The active components of the transition metal oxide were loaded on the double-layered carrier,and were highly dispersed on the pore frameworks with nanometer sizes.Thus it enhances the redoxy properties of the catalysts and further improves the activity of catalysts.The as-prepared double-layered support and the catalysts were characterized by means of SEM,TEM,HTEM,XRD,UV-Vis,Raman,H₂-TPR and TPO.The main contents and conclusions are as follows.1.Polymethyl methacrylate（PMMA）microspheres with average diameter of 380nm were prepared by emulsion polymerization.The obtained PMMA microspheres were monodispersed and their size distribution was very narrorow.PMMA colloidal crystal templates were prepared by centrifugal deposition.The base carrier 3DOM TiO₂ was prepared by using titanium butoxide,hydrochloric acid,water and ethanol as precursor solution.Their structures are regular and the walls of macrous pores are uniform and solid.2.The three-dimensional ordered macroporous CeO₂/3DOM TiO₂ carrier was successfully prepared by the dropping-precipitation method.The macroporous structures are still intact and the pore channels are permeable,which increases the effective contact between the carbon particles and the catalyst.The obtained carrier has a certain catalytic activity.CeO₂ which produces low vanlence cerium and oxygen defects can provide"oxygen pool".When TiO₂ coexists with CeO₂,cerium dioxide has synergistic catalysis with TiO₂ which makes the catalyst carrier have some activity.Not only do double-layered carrierr enhance the activity of the catalyst,and improve the selectivity of CO₂,but also it enhances the stability of the catalyst.Therefore,the double-layered carrier of CeO₂/3DOM TiO₂ is a very excellent carrier.3.Three series of catalysts y-Co₃O₄/CeO₂/3DOM TiO₂,m-MnO_x/CeO₂/3DOM TiO₂,n-CuO/CeO₂/3DOM TiO₂ were prepared by loading transition metal Co,Mn and Cu oxides on the three dimensional ordered macroporous double-layered carrier CeO₂/3DOM TiO₂.The transition metal elements have variable valences,and their oxide crystals are generally irregular.There are a large number of lattice defects and oxygen vacancies in the crystals,which has a good effect on the catalysis of soot oxidation.The catalytic activity for soot combustion can be tuned by changing the type and amount of transition metal oxides.The catalytic evaluation results showed that catalytic activity follows the order of MnO_x/CeO₂/3DOM TiO₂>Co₃O₄/CeO₂/3DOM TiO₂>CuO/CeO₂/3DOM TiO₂.Compared with the corresponding the double-layered carriers,their soot combustion catalysis has been greatly improved.