Preparation, Characterization, OSC And NSC Of Ceria Zirconia Solid Solutions

It is imperative to innovate in the catalyst for purification of vehicle exhaust gasbecause air pollution resulting from the increase of vehicles is even serious. Thisdissertation is devoted to the research on preparation of ceria-zirconia solid solutionwith larger specific surface area, high thermal stability and oxygen storage capacity assupport for such purifying catalysts. The work will be benefit for developing novelhigh-efficient catalysts for exhaust gas treatment.In this dissertation, a series of Ce_xZr_1-xO₂ solid solutions, which have smallerparticle size, larger surface area and better capability of oxygen storage and releasethan those prepared by traditional co-precipitation method, were prepared byUltrasound-assisted Membrane Reaction (UAMR) method. The oxygen storagecapacities (OSC) of the Ce(0.8)Zr_0.2O₂, Ce_0.6Zr_0.4O₂ and Ce₍0.4Zr0.6O₂ solid solutionsprepared by UAMR method were 21%, 14% and 41%, respectively, which werehigher than those fabricated by traditional method. The research results indicated thatCe(0.8)Zr_0.2O₂ solid solutions exhibited lowest temperature of oxygen release. The peaktemperature of oxygen release decreased from 582 to 457℃when x value increasedfrom 0.4 to 0.8 for Ce_xZr_1-xO₂ samples prepared by traditional co-precipitation. Forcomparison, the peak temperature of oxygen release decreased from 560 to 447℃when x value increased from 0.4 to 0.8 for Ce_xZr_1-xO₂ samples prepared by UAMRmethod. The OSCs of Ce₍0.4Zr0.6O₂ solid solutions prepared by co-precipitation andUAMR method were 201 and 284μmol/g, respectively.The Ce_0.5Zr_0.5O₂·xBaO solid solutions have been prepared by UAMR method toimprove the thermal stability. The samples were characterized by BET, XRD, OSC,NSC and NO-TPD techniques. The results indicated that the Ba content hold anoptimum value of x=0.16. The OSC and thermal stability of CeO₂-ZrO₂ solid solutioncould be improved by the adulteration of a small quantity of Ba. However, the thermalstability would be deteriorated by more Ba load. The Ce_0.5Zr_0.5O₂·xBaO (x=0.16)material has the maximum amount of OSC of 745μmol/g for the fresh sample and346μmol/g for the ageing sample. The NO storage capacity of Ce_0.5Zr_0.5O₂·xBaOincreased with x value lineally. Furthermore, the introduction of Ba⁽2+ restrained thegrowth of particles by reducing the crystal interphase energy of CeO₂-ZrO₂ solid Vsolutionand thus to improve the thermal stability of Ce_0.5Zr_0.5O₂·xBaO solid solution.To sum up, the Ce_0.5Zr_0.5O₂·xBaO solid solution was a novel material withsimultaneous oxygen and NO storage capacity and high thermal stability.The CeAl₁₂O₂0 samples have been prepared by UAMR method. Thecharacterization results of BET, TPR, OSC and O₂-TPD indicated that the samplesusing ammonium acid carbonate as precipitator have higher thermal stability thanthose using ammonia. The surface area of sample using ammonium acid carbonate asprecipitator was 172 m²/g for fresh sample and 90 m²/g for ageing sample. Thesamples precipitated by ammonium acid carbonate had better capability of oxygenstorage and release at low temperature. The OSC was higher than that of samplesprecipitated by ammonia for 87%. The samples prepared by UAMR method exhibitedhigher thermal stability than the samples prepared by traditional method when usingthe same precipitator. The surface area of fresh sample was 218 m²/g and droped to120 m²/g for ageing sample.A kind of novel Si₃N₄-Ce_0.6Zr_0.35Y_0.05O₂ oxides composite powders has beenprepared by UAMR method. The microstructure and characterization of the Si₃N₄-Ce_0.6Zr_0.35Y_0.05O₂ powders were investigated by BET and TEM. The analysis resultshowed that a Si₃N₄-Ce_0.6Zr_0.35Y_0.05O₂ core-shell structure was not obtained. The OSCand thermal stability needs further investigation.