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1、AppliedCatalysisA:General215(2001)271278Acomparativestudyofwater-gas-shiftreactionoverceriasupportedmetalliccatalystsS.Hilairea,X.Wanga,T.Luoa,R.J.Gortea,∗,J.WagnerbaDepartmentofChemicalEngineering,UniversityofPennsylvania,Philadelphia,PA19104,USAbSüd-ChemieInc.,P
2、.O.Box32370,Louisville,KY40232,USAReceived5December2000;receivedinrevisedform16February2001;accepted16February2001AbstractWater-gas-shift(WGS)reactionrateshavebeenmeasuredonPd/ceria,Ni/ceria,Fe/ceria,Co/ceria,ceria,andPd/silica.Pd/ceriaexhibitedmuchhigheractivitie
3、sthaneitherceriaaloneorPd/silica,demonstratingacooperativeeffectbetweenPdandceria.Pd/ceriaandNi/ceriashowedessentiallythesameactivitiesandweremuchmoreactivethaneitherCo/ceriaorFe/ceria.ReactionordersonPd/ceriawereapproximatelyzeroth-orderinCO,half-orderinH2O,inver
4、se-half-orderinCO2andinverse-first-orderinH2.Diffusereflectance,FTIRmeasurementsonPd/ceriaindicatetheceriaexistsinareducedstateunderWGSconditionsandiscoveredbycarbonatespeciesthatareremovedonlybyreoxidationofceria.TheimplicationsoftheseresultsforimprovedWGScatalysis
5、arediscussed.©2001ElsevierScienceB.V.Allrightsreserved.Keywords:Watergasshiftreaction;Ceria;Ceriumcarbonates;Pd;Ni;Fe;Co1.IntroductionTherearetwopicturesthathaveemergedregardingthemechanismfortheWGSreactiononceria-basedCeriaisacrucialcomponentofautomotive,three-ca
6、talysts.ShidoandIwasawausedinfraredspec-way,emissions-controlcatalysts,inpartbecauseittroscopyandtemperature-programmeddesorptionpromotesprecious-metalcatalystsforthewater-gas-(TPD)toexamineceria-supportedRh[11].Theyshift(WGS)reaction[18].While,thishasbeenconclude
7、dthattheintermediateforthereactionisaknownformanyyears,theneedforactiveWGScata-bidentateformate,producedbythereactionofCOlystsfornontraditionalapplications,suchasfuelpro-withterminalhydroxylgroupsontheceria,andthatcessingforfuelcells,hasleadtorenewedinterestinther
8、atedeterminingstepisthedecompositionoftheexaminingceria-supportedmetalsforthisapplication.bidentateformatetoH2andaunidentatecarbonate.Because,theactivit
