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1、NanoStructuredMaterials,Vol.11,No.8,pp.995±1007,1999ElsevierScienceLtdPergamonCopyright©2000ActaMetallurgicaInc.PrintedintheUSA.Allrightsreserved.0965-9773/99/$±seefrontmatterPIIS0965-9773(00)00431-1SURFACESOFDOPEDNANOPHASECERIUMOXIDECATALYSTS1,221A.E.C.Palmqvist²,M.Wirde,U.GeliusandM.Muhammed1Dep
2、artmentofMaterialsChemistry,RoyalInstituteofTechnology-KTH,10044Stockholm,2SwedenDepartmentofPhysics,UppsalaUniversity,75121Uppsala,Sweden(ReceivedJanuary3,2000)(AcceptedJanuary4,2000)AbstractÐSolidsolutionsofnanophaseceriumoxideshavebeenpreparedandtherelationshipbetweentheirbulkcrystalstructurean
3、dsurfacecharacteristicshasbeenstudiedatroomtemperaturewithX-raydiffraction(XRD)and213121X-rayphotoelectronspectroscopy(XPS).Dopantswithavalencelowerthan14,suchasCa,Nd,andPb,introducestructuraldefects(oxygenvacancies)intheceriumoxidelattice,whichhasbeenfoundtoaffecttheredoxcatalyticactivityofthemat
4、erials.TheintroductionofoxygenvacanciesleadstotheappearanceofanO1scorelevelpeakwithashiftof2.0±2.5eVtohigherbindingenergiesascomparedtothecorelevelpeakofthelatticeoxygeninCeO2.TheintensityofthishighbindingenergyO1speakvarieswiththeexpectedconcentrationofoxygenvacanciesinthesurface,thetypeofdopantc
5、ationanditsconcentrationinthesolidsolution.ItwasfoundthatcarbonateandhydroxidespeciesareresponsiblefortheappearanceofthisO1speak,presumablyasaresultofcappingofoxygenvacanciesatthesurface.Theimplicationsofthesesurfacegroupsonthecatalyticactivityofthematerialsarediscussed.©2000ActaMetallurgicaInc.1.
6、IntroductionTheimportanceofX-rayphotoelectronspectroscopy(XPS)forstudyingcatalyticmaterialshaslongbeenwellrecognized.Incatalysis,itisoftenmoreimportanttoperformacarefulcharacterizationofelementalcomposition,oxidationstates,coordinationnumbers,anddiffusivitiesofthecatalystsurfacethanofthebulk.Furth
7、ermore,itisoftenadvantageoustousematerialshavinghighsurfaceareas,e.g.materialswithverysmallparticlesizes.SolidsolutionsofnanophaseCeO2powdershavebeenpreparedforalargenumberofdifferentdopants(1).Thecatalyticoxidat
