Ceriumoxideiswidelyusedinautomotivecatalysts.Ceriaisthoughttopromotethewatergasshiftreaction,stabilizethealuminasupport,andstabilizethenoblemetaldispersion;however,itsmostimportantroleistoactasanoxygenstoragecomponent.Thispropertyenablesthecatalysttooperatemoreef®cientlybymakingitlesssensitivetoconcentrationvariationsthatoccurintheexhauststreamduringnormaldrivingconditions.Typically,asacatalystages,itsconversionef®ciencyundertransientconditionsdecreasesinpartbecausetheceriaparticleslosetheirabilitytoreversiblystoreandrelease(asCO2orH2O)oxygen.Oneexplanationforthislossinactivity,ishightemperaturesinteringoftheceriaparticleswhichrendersthebulkoftheceriainactivefortheCe4toCe3redoxreaction.Anotherexplanationforthislossinactivityisthatcontactbetweenceriaandthenoblemetals,whichareknowntopromotethereleasereaction,islostduetonoblemetalsintering.Duetothetendencytodeactivateathightemperaturethereisaneedformorethermallystableoxygenstoragematerialswhichcanwithstandtemperaturesatorabove9008Cforlongperiodsoftime.
OneapproachpreviouslyusedtostabilizeceriaagainstsinteringwastodopeitwithotherrareearthelementssuchasLa2O3andGa2O3;however,thesematerialsdidnotprovetobesigni®cantlybetterinfullyformulatedautomotivecatalysts.Morerecently,ithasbeenreportedthattheadditionofZrO2tocerialeadstoimprovementsinceria'soxygenstoragecapacity.Thesampleswereusuallycharacterizedbytemperatureprogrammedreduction(TPR)andXraydiffraction(XRD)anditwasobservedthatthereductionofceriawasfacilitatedastheamountofZrincorporatedincreased.XRDanalysisshowedthatZrwasincorporatedintothecerialatticetherebyformingaceria±zirconiasolidsolution.Inthisearliestwork,thepreparationproceduresusednvolvedhightemperatures(900±15008C),resultinginhighlysintered,andthuslowsurfaceareamaterials,makingthemundesirableaspracticalcatalystmaterials.Mostrecently,deLeitenburgetal.havereportedthathighersurfaceareamaterialscanbeformedbyco-precipitationfromceriumandzirconiumnitratesfollowedbycalcinationinatemperaturerangebetween827and11278C.Nunanetal.recentlyreporteddataonfullyformulatedPt±Rh=CeZr=Al2O3catalysts.Thesampleswereevaluatedusingenginebenchagingandtesting.TheauthorscorrelatedtheimprovedperformanceoftheZrcontainingcatalystswiththepresenceofaCeO2=ZrO2solidsolution;however,mostofthedetailsofcatalystformulationwereproprietary,makingitdif®culttoisolateandunderstandhowthesolidsolutiongivesrisetobetterperformance
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