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1、JOURNALOFCATALYSIS95,501-511(1985)PreparationandCharacterizationofEquilibriumAdsorption-PreparedMolybdena-AluminaCatalystsC.V.CACERES,**’J.L.G.FIERRO,*-*A.LOPEZAOUDO,*M.N.BLANCO,?ANDH.J.THOMASt*InstitutedeCatalisisyPetroleoquimica.CSIC,Serrano119,28OMMadrid.Spain,a
2、ndtCentrodeInvestigationyDesarrollodeProcesosCataliticos(CINDECA),C47,W257,1900LaPlats,ArgentineReceivedFebruary12,1985;revisedMay1,1985Thepreparationofmolybdena-ahuninacatalystswasstudiedusinganequilibriumadsorptionmethodat50°Cinwhichthemolybdenumanionsfromsolutio
3、nwereadsorbedontheahuninasurfaceatpHvaluesbetween5.70and7.70neartoitsisoelectricpoint.Intheseexperimentalconditionsatwo-stepadsorptionisothermwasfound,indicatingthattheloadingofthecarrierwasverydependentonthesoluteconcentration.Bycombiningdifferentcharacterizationt
4、echniques,namely,temperature-programmedreductionandkineticsofreduction,reflectancespectroscopy,chemisorptionofNOandO2probe-molecules,infraredspectroscopyofNO,andextractionbyammonia,itisshownthatatlowsoluteconcentrationstheMOishighlydispersed,mostlyastetmhedmhycoord
5、inated(byoxygenions)MOspecies.However,poorerdispersionwasfoundatintermediateandhighsoluteconcentrations.Inthislattercase,thecombineduseofchemisorptionandextractiondataindicatedthatoncakiningat500°Cthesurfaceofthecarrierbecomespopu-latedwithbothtetrahedrahy(monolaye
6、r)andoctahedrahy(smallclusters)coordinatedMo-spe-ties.01985AcdemicPress.Inc.INTRODUCTIONwhenimpregnatedwithammoniumhep-tamolybdate(AHM)solutionsofpHlowerTheimportanceoftheconcentrationandorhigherthantheIEP,respectively.More-pHoftheimpregnatingsolutionintheprepover,
7、intheAHMsolutionsthefollowingarationofmolybdena-aluminacatalystsionicequilibriumoccurs,hasbeenrecognizedandusedtoexplainthe‘t&o+Mo,O&ti7MoO:-+gH+characteristicsandbehaviorofthesurfacespeciesofcatalysts(1-8).Apioneerworkwhichmeansthattheadsorptionofoctahe-aboutthege
8、nesisofmolybdena-aluminadrallycoordinatedpolymolybdate,Mo[O],catalystswasreportedbySonnemansandionsshouldbefavoredbylowpH,whereasMars(4).Theyfoun
