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1、JOURNALOFCATALYSIS168,16–25(1997)ARTICLENO.CA971573ReducibilityofCobaltSpeciesinSilica-SupportedFischer–TropschCatalystsA.Yu.Khodakov,¤J.Lynch,¤,1D.Bazin,yB.Rebours,¤N.Zanier,¤B.Moisson,¤andP.Chaumette¤¤InstitutFranc¸aisduPetrole,B.P.311,92506Rueil-Malmaiso
2、nCedex,France;´yLaboratoirepourl’UtilisationdeRayonnementElectromagnetique,´UniversiteParis-Sud,91405Orsay,France´ReceivedJuly12,1996;revisedOctober24,1996;acceptedDecember9,1996temperature-programmedreduction(TPR),X-rayphoto-ReducibilityofCospeciesinsilica
3、supportedFischer–Tropschelectronspectroscopy(XPS),FouriertransforminfraredcatalystswasstudiedusinginsituXRD,insituEXAFS,andFTIRspectroscopy(FTIR),andextendedX-rayabsorptionfinespectroscopywithcarbonmonoxideasamolecularprobe.Crys-structure(EXAFS),etc.X-raydif
4、fractionwhichpermitstallineCophasesintheoxidisedcatalystswerecharacterisedusingthesizeandconcentrationofoxideandmetalcrystallitesXRD.Intheoxidisedsampleswithalargeconcentrationofamor-tobemeasuredisoneofthemostcommon.DifferentCophousphase,EXAFSshowedtheprese
5、nceofsmalloxideclustersspecieswerereportedtobefoundintheoxideprecursorsincludingseveralCoatoms.Itwasfound(insituXRD,EXAFS)thatofFischer–TropschcatalystsusingXRD:(1)Co3O4oxidecalcinationofoxidisedCocatalystsunderinertatmosphereresulted3Ccrystallinephase;(2)C
6、oOcrystallinephase;(3)CoionsinaselectivetransformationofCo3O4toCoOat623–673K.FTIRor/andCo2ClocatedinAl3CorSi4CoxidiccrystallitesorspectroscopywithCOasamolecularproberevealedthepresenceofdifferentsitesassociatedwithCoafterthereductionofthecatalystsinwelldisp
7、ersedsurfacespecies;(4)CoAlO4orCo2SiO4withhydrogenat723K:Cometalsites(ºCOD2025cm¡1),Co2Cionscrystallineor/andamorphousphase.inthecrystallinephaseofCoO(º¡1nCFTIRhasbeenusedtoidentifythenatureofactiveCOD2143cm),andCospeciesintheamorphousphase(º¡1COD2181cm).Th
8、eresults(XRD,sitesinCo3O4,Co/Al2O3modifiedwithdifferentpromotersEXAFS,FTIR)showedthatthehydrogenreductionpropertiesofandCo/SiO2catalystsaswell(12,13,25–27).ReducedCoparticlesofcobaltoxideonsilicadepende
