Oxide Ionic Conductive Catalysts For Soot Combustion And NO_x Storage And Reduction

Ca2Fe2O5, Ca2AlFeO5, Ca3Co2O6, DyBaCo4O7and DyBa(Co0.9Al0.1)4O7were chosen ascatalysts in this work. All these materials exhibit excellent ionic conductivity. Additionally,transition metals (Co or Fe) with variable valence states were present in these materials,which are generally considered to have superior redox properties. Moreover, alkaline earthmetals (Ca or Ba) were also introduced in these materials which are capable of storing NO_x.Therefore, these materials are good candidates as catalysts for soot combustion, NO_xstorageand reduction (NSR).In this work, different methods were tried to prepare oxide ionic conductive catalysts.Ca2Fe2O5and Ca2AlFeO5were succesfully obtained by solution combustion method.Ca3Co2O6can be sythesised using complex method and the effects of complexing agents(Citric Acid, ETDA and Citric Acid+EDTA) were studied on the structure and activities ofcatalysts. DyBaCo4O7and DyBa(Co0.9Al0.1)4O7were prepared with complex method usingEDTA as complexing agent. These as-prepared catalysts are then characterized with BET,XRD and H2-TPR. Moreover, their catalytic activities were also evaluated for soot combustionunder the atmosphere of both O2and NO+O2, together with the performance of NSR. Majorconclusions are drawn as follows:The soot combustion activity of Ca2AlFeO5is much better than that of Ca2Fe2O5both inthe atmosphere of O2and NO+O2. No big differences in CO2selectivities were discovered.The soot oxidation activity of Ca2Fe2O5in NO+O2is better than that in O2. Similar sootcombustion activity of Ca2AlFeO5in NO+O2was observed with that in O2.No matter which complexing agent was used (Citric Acid, ETDA or Citric Acid+EDTA), Ca3Co2O6can be successfully synthesized. Almost the same results were found in theBET and the soot combustion activities in O2with Tmat around460℃. Considering theconvenience of the preparation process, citric acid was chosen as the complexing agent tosyntheseize Ca3Co2O6(Citric Acid), which are used fot further research. Almost the sameresults in Tmvalues were observed for the soot combustion both in NO+O2and O2. CO2selectivities can be reached above97％in these two different atmosphere. Under lean/richtransient operating conditions,51.7μmol/g of NO_xcan be stored on Ca3Co2O6and7.2％of NO_xcan be reduced to N2.In O2, slight better soot combustion activity was obtained on DyBa(Co0.9Al0.1)4O7thanthat on DyBaCo4O7, both under loose and tight contact conditions. In NO+O2,DyBa(Co0.9Al0.1)4O7displayed more superior catalytic soot oxidation activity thanDyBaCo4O7under both contact conditions. Under lean/rich transient operating conditions,The amount of stored NO_x storage on DyBa(Co0.9Al0.1)4O7were tested to be69.0μmol/g and8.0％of NO_xcan be reduced to N2in the process.