Preparation Of Hierarchical Structure Cerium-based Catalyst And Its Performance In Purifying Soot

Due to its excellent performance,diesel engine is widely used in a variety of mechanical equipment.However,particles?PM?and nitrogen oxides?NOx?formed in the process of exhaust emissions pose a great threat to the atmosphere and human health.The main components of the particles are soot and some sulfate,while the main components of NOx are?NO and NO₂?.At present,it is an effective and widely used technology for automobile exhaust post-treatment,and the research and development of purification catalyst is very important.The special electronic structure of rare earth oxides and their catalytic implications,At present,it is an effective and widely used technology for automobile exhaust post-treatment,and the research and development of purification catalyst is very important.The special electronic structure of rare earth oxides and their catalytic effects have attracted researchers'attention,and cerium oxide has good oxygen storage and release capacity.In this paper,the catalytic activity of cerium oxide in soot reaction was studied by using mesoporous nanocrystal as the carrier and loading the composite oxides of copper oxide and manganese oxide respectively.The main studies are as follows:1.CeO₂ nanosheets was prepared by hydrothermal method,and then CuO/CeO₂mesoporous nanosheets was synthesized by wet impregnation.The physical and chemical properties of the catalyst were characterized by XRD,FESEM,TEM,BET,XPS,H₂-TPR,O₂-TPD and NO+O₂-TPSR,The activity of the catalyst was evaluated by TPO.Through a series of catalyst activity tests,it was found that CuCe7.2 had the best catalytic activity,with a Tm of 494?and a near 100%selectivity of CO₂.The good catalytic activity of CuCeX catalyst is due to the lamellar morphology and high surface area,which increase the contact surface between soot and catalyst,providing a large number of active sites.The mesoporous channels of the nanosheet increase the adsorption and diffusion of the gas?NO and O₂?and enlarge the contact surface between the catalyst and the reaction gas?NO and O₂?.The enhancement of redox performance and the increase of defect sites promote the adsorption and activation of surface reactive oxygen species,which is conducive to the oxidation of NO and the generation of more NO₂ to participate in the reaction.The results of different reaction atmospheres showed that both NO and water vapor promoted the catalytic combustion of soot.Finally,the stability test found that CuCe7.2 has good stability.2.CeO₂ nanosheet was prepared by hydrothermal method,and Mn_xCe_1-xO₂ mesoporous nanosheet was prepared by dipping method.The physical and chemical properties of the catalyst were characterized by XRD,FESEM,BET,XPS,H₂-TPR,O₂-TPD,NO-TPDand NO+O₂-TPSR,The activity of the catalyst was evaluated by TPO.Through the activity comparison,it was found that Mn_0.09Ce_0.91O₂ catalyst had the best catalytic activity,its T_m was 481?,and the selectivity of carbon dioxide was close to 100%.Mn_0.09Ce_0.91O₂ catalyst has good catalytic activity mainly because:First,the high surface area of the nanocrystalline sheet expands the contact interface and contact point between the catalyst and the soot,increasing the active site of the soot combustion.Secondly,the mesoporous channels in the nanometer tablets can reduce the blockage of mass transfer of gas reactants?NO and O₂?,which is conducive to the adsorption and diffusion of gas.The contact interface between catalyst and gas reactant is enlarged.Third,the increase of oxygen vacancy is conducive to adsorption and activation of more surface oxygen species,producing more reactive oxygen species.More high valence state manganese cations(such as Mn⁴⁺and Mn³⁺)are conducive to oxidation reaction and increase the adsorption and activation of surface oxygen species.At the same time,reactive oxygen species are beneficial to the oxidation of NO to form NO₂,which oxidation capacity is much higher than that of NO,thus improving the combustion activity of soot.In addition,due to the strong synergy between Mn and Ce,the storage capacity and oxidation capacity of NO were enhanced.