Preparation Of Multi-tubular CeO₂-based Catalysts And Its Catalytic Activity For Soot Combustion

Recently,the PM of diesel emissions becomes the primary cause of atmospheric pollution,which has attracted extensive attention from the society.The diesel particulate filter?DPF?is considered to be an effective mean of emission control for diesel vehicles.The process of soot oxidation is a three phases reaction of soot/catalyst/O₂.The intrinsic activity of catalyst depends on the generation and transfer of reactive oxygen species,but the contact degree between catalyst and soot could influent the reactivity of catalyst deeply.It has been proved that the contact degree between catalyst and soot can be improved by adjusting the morphology of catalyst,so that the intrinsic activity of catalyst can be fully released.A siries of multi-tubular Ce-based catalysts were prepared by using loofah as biotemplate.The catalyst activity was discussed by soot-TPO.The morphology and surface chemical environment of catalysts were characterized by XRD,BET,SEM,H₂-TPR,O₂-TPO,Raman and XPS.The mechanism of soot catalytic oxidation was studied with the generation of reactive oxygen species and the change of different valence states of transition metal ions.The structure and catalytic activity of CeO₂-Zr O₂?Ce/Zr=1:1,x Hc-@CZs,x=1,3,5,8?doped with different contents of Cu were studied.When the Cu content is1%-8%,the crystal phases of catalysts were Ce_0.75Zr_0.25O₂ and Ce_0.16Zr_0.84O₂.With the increase of Cu content,the phase separation phenomenon aggravated.The addition of Cu could increase oxygen vacancies and improve redox ability of catalysts,thus increasing the catalytic activity of the catalyst.1Hc@CZs catalyst has the best catalytic activity(T₅₀=396?)and good reusability.The presence of phase separation cracked the multistage tubular structure,leading to the decline of catalytic activity of catalysts with high Cu content.The structure and catalytic activity of CeO₂-Mn O_x catalysts?CM-x,x=0.1,0.3,0.5,1?were studied in this chapter.It was found that the introduction of Mn was beneficial to the generation of more oxygen defects,and the catalytic activity of cerium manganese solid solution catalyst was significantly higher than that of CeO₂catalyst.With the increase of manganese content,the activity of catalyst increased first and then decreased.The CM-0.3 had the best catalytic activity(T₅₀=416?),reusability and stability.By comparing the multi-tubular cerium-based oxides doped with Mⁿ⁺?M=Mn,Fe,Co,Ni,Cu,La?of different transition metal ions?doping amount is 40 at.%?,it was found that all samples except the Ce-Cu had homogeneous CeO₂ cubic fluorite structure.Compared with CeO₂ catalyst prepared by the same method,the transition metal doped ceria-based solid solution catalysts have smaller grain size and larger specific surface area,which can promote the migration of reactive oxygen species in the lattice and improve the redox capacity of the catalyst.The transition metal doped ceria-based catalysts could promote the generation of oxygen defects in the catalyst,and improve oxygen vacancy concentration.The sequence of catalyst activity under loose contact was Ce-Mn>Ce-Cu>Ce-Co>Ce-Ni>Ce-Fe>Ce-La.The Ce-La had the worst catalytic activity,while the Ce-Mn had the best,which was in direct proportion to the number of reactive oxygen species on the surface.