Doping Modification Of Cerium Oxide Catalyst And Its Catalytic Oxidation Of Soot Particles

The exhaust from diesel engines contains a large amount of carbon soot particles,and the particulate emissions into the atmosphere can cause serious air pollution.Diesel particulate trap（DPF）is one of the effective means to solve this problem.In this paper,a series of cerium-based monolithic catalysts with efficient catalysis of carbon soot particles are designed by surface modification of cordierite and using the excellent oxygen storage capacity of Ce O₂ to achieve passive regeneration of catalyzed diesel particulate filter（c DPF）.The details are as follows:（1）The surface of cordierite was modified by sol-gel method+impregnation method and loaded with cerium-samarium solid-solution catalyst,and the surface was impregnated and roasted using low concentration of KNO₃ to prepare cerium-samarium solid-solution monolithic catalyst containing K species.The amorphous K salts were homogeneously present on the surface of the cerium-samarium solid-solution catalyst by FT-IR,XRD,SEM and EDS characterization,and the SEM results showed that different concentrations of K⁺caused different degrees of microcracks on the surface of the cerium-samarium solid-solution,and the XRD results showed that the main chemical composition of the cerium-samarium solid-solution was Ce_0.6Sm_0.4O_1.8 crystalline phase.XPS combined with H₂-TPR analysis showed that K salts could increase the mobility of surface oxygen species,causing an increase in Ce³⁺content to33.6%,increasing the surface active oxygen content and preparing monolithic catalysts with high catalytic activity（2）In this paper,a series of monolithic catalysts with different Cu/Ce atomic molar ratios,Z-Cu-x（x=0,0.05,0.1,0.15,0.2,where x is the Cu/Ce atomic molar ratio）,were prepared using sol-gel+impregnation method by growing aluminum borate whisker clusters on cordierite surface using molten salt method and cordierite/aluminum borate whisker as substrate.The length and width of the whiskers were counted using the software Nano measure 1.2 in combination with SEM images,and it was found that the aluminum borate whiskers with good toughness and large aspect ratio grew densely and were uniformly distributed on the surface of cordierite,and the catalyst particles were coated on the surface of cordierite/aluminum borate whiskers,which did not affect the morphology of aluminum borate whiskers.The XRD and XPS results showed that the doped element Cu was highly dispersed on the surface of Ce O₂ as Cu O and did not enter the Ce O₂ lattice,and the synergistic effect of Cu²⁺and Ce³⁺accelerated the conversion of reactive oxygen species on the surface.The catalytic performance and cycling performance tests showed that the catalytic activity of its monolithic catalyst for carbon soot particles was best when the Cu/Ce atomic molar ratio was 0.15,and the lowest values were reached at T₁₀（455°C）and T₅₀（514°C）.（3）A series of monolithic catalysts Z-Ce_xMn_1-xO_y（x=0.9,0.8,0.6,0.4,where x is the atomic molar ratio of Mn/（Mn+Ce））were prepared by doping Ce O₂ with the transition metal element Mn,and the effect of the atomic molar ratio Mn/（Mn+Ce）on the catalytic performance was investigated.SEM showed that the surface of aluminum borate whisker was successfully loaded with catalyst particles and the high specific area of cordierite/aluminum borate whisker interface provided many sites for catalyst particle attachment.XRD and XPS analysis showed that Mn ions entered into the lattice of Ce O₂ to generate Mn-Ce-O solid solution,which promoted the generation of surface active oxygen and caused the conversion and migration of oxygen species,and the addition of Mn element could cause the contraction of Ce O₂ lattice and the reduction of catalyst grain size,which exposed more active sites and had better low-temperature oxidation activity.When the atomic ratio Mn/（Mn+Ce）exceeds a certain threshold,Mn ions will break away from the cubic fluorite structural lattice to achieve phase separation and generate Mn₂O₃,which affects the catalytic activity of the monolithic catalyst.The oxidation catalytic performance and cycling tests proved that when the atomic molar ratio of Mn/（Mn+Ce）was 0.4,Z-Ce_0.6Mn_0.4O_yhad the lowest T₁₀（459℃）and T₅₀（531℃）,and the cycling effect was excellent with only 6℃change in T₅₀ after 4 times cycling test.