Feng Zhang, - Unknown - Unknown - Unknown

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SupportingInformationBreakingSimpleScalingRelationsThroughMetal-OxideInteractions:UnderstandingRoomTemperatureActivationofMethaneonM-CeO2(M=Pt,NiorCo)InterfacesPabloG.Lustemberg,[a,b],+FengZhang,[c],+RamónA.Gutiérrez,[d]PedroJ.Ramírez,[d,e]SanjayaD.Senanayake,*[f]JoséA.Rodriguez*[c,f]andM.VerónicaGanduglia-Pirovano*[b]aInstitutodeFisicaRosario(IFIR),CONICET-UNR,Bv.27deFebrero210bis,S2000EZPRosario,SantaFe,ArgentinabInstitutodeCatálisisyPetroleoquímica,CSIC,C/MarieCurie2,28049Madrid,SpaincDepartmentofMaterialsScienceandChemicalEnginnering,SUNYatStonyBrook,StonyBrook,NewYork11794,UnitedStatesdFacultaddeCiencias,UniversidadCentraldeVenezuela,Caracas1020-A,VenezuelaeZoneca-CENEX,R&DLaboratories,AltaVista,64770Monterrey,MéxicofChemistryDivision,BrookhavenNationalLaboratory,Upton,NewYork11973,UnitedStates+P.G.LustembergandF.Zhangcontributedequallytothisworkandshouldberegardedasco-firstauthors.*Correspondingauthors:M.VerónicaGanduglia-Pirovano(vgp@icp.csic.es);SanjayaD.Senanayake(ssenanay@bnl.gov);JoséA.Rodriguez(rodriguez@bnl.gov)S1

1METHODSExperimentalMethods.Pt/CeO2(111).TheexperimentsexaminingtheactivationofCH4onPt/CeO2(111)surfaceswereperformedinaset-upthatcombinedanultra-highvacuum(UHV)chamberforsurfacecharacterizationandamicro-reactorforcatalytictests.1-3TheUHVchamberwasequippedwithinstrumentationforX-rayphotoelectronspectroscopy(XPS),low-energyelectrondiffraction(LEED),ion-scatteringspectroscopy(ISS),andthermal-desorptionmassspectroscopy(TDS).1-3InthepreparationofthePt/CeO2(111)modelcatalyst,followingthemethodologydescribedindetailinref.,3CemetalwasfirstevaporatedontoaRusinglecrystal(0001)at427°Cinthepresenceof5×10−7torrO2,andthenannealedto527°Cfor10minsatthesameO2pressure.Theceriafilmswereestimatedtobeca.4nmthick(≈10layersofO-Ce-O)basedontheattenuationoftheRu3dXPSsignal.Ptwasvapor-depositedontheas-preparedceriafilmat427°Cunder5×10−7torrO2,andthecoverageofPtwas~0.15ML(monolayer),estimatedbytheattenuationoftheCe3dXPSsignal.ForPt/CeO2(111)surfaces,singleatomsandsmallPtclustershavebeenobservedatlowcoveragesusingscanningtunnelingmicroscopy.4Inthestudiesofmethaneactivation,thesamplewastransferredinvacuotothereactorat25°C,thenthereactantgas,1Torrofpressure,wasintroduced.TheAP-XPSmeasurementswerecarriedoutonacommercialSPECSAP-XPSchamberequippedwithaPHOIBOS150EPMCD-9analyserattheChemistryDivisionofBrookhavenNationalLaboratory(BNL).IntheexperimentsexaminingtheactivationofCH4onPt/CeO2(111)modelcatalyst,50mTorrofCH4wasintroducedintotheanalysischamberandCe3d,Pt4fspectrawerecollectedunderthisgasatmosphereat25,127,227,327,427°C.TheCe3dphotoemissionlinewiththestrongestCe4+featureat916.9eVwasusedfortheenergycalibrationoftheAP-XPSsignals.Pt/CeO2Powder.ThepowdercatalystwaspressedontoanaluminiumplateandloadedintotheAP-XPSchamber.A10mTorrofO2wasintroducedandthesamplewasheatedto400°Ctoremoveanysurface-boundedcarbonspeciesbeforethetest.IntheexperimentsexaminingCH4activationonPt/CeO2powdercatalyst,a50mTorrofCH4wasusedandCe3d,Pt4fspectrawerecollectedat25,127,227,327,427°C.Thein-situtime-resolvedXRDanalyseswerecarriedoutat17BM(λ=0.24108Å)oftheAdvancedPhotonSource(APS),atArgonneNationalLaboratory(ANL).AS2

2Clausencellflowreactorwasusedforthemeasurement.5Thereactionconditionswerekeptthesameasthein-situXAFSmeasurementsandanamorphousSiflatpanel(PerkinElmer)detectorwasusedtocollecttwo-dimensionalXRDimagesthroughoutthereactionprocesses.TheimagesweresubsequentlyprocessedwithGSAS-IItoobtaindiagramsofIntensityversus2θ.ThelatticeparameterevolutionofceriawascalculatedbyRietveldrefinementalsousingGSAS-II.6PtparticlesoraggregateswerenotseeninXRDandTEMforthe0.5wt%Pt/CeO2powdercatalyst.Theuseoflowloadingiscrucialforthecomparisonofmodelsystemswithhighsurfaceareacatalystsandfordefiningstructure-functionrelationships.7TheoreticalModelsandComputationalMethods.Allelectronicstructurecalculationswerecarriedoutusingthespin-polarizedDFTapproachasimplementedintheViennaabinitiosimulationpackage(VASP)(vaspsite,http://www.vasp.at;versionvasp.5.3.5)8-9Ce(4f,5s,5p,5d,6s),O(2s,2p),Ni(3p,3d,4s),Co(3p,3d,4s)andPt(4f,5d,6s)electronswereexplicitlytreatedasvalencestateswithintheprojectoraugmentedwave(PAW)method10withaplane-wavecutoffenergyof415eV,whereastheremainingelectronswereconsideredaspartoftheatomiccore.Totalenergiesandforceswerecalculatedwithaprecisionof10-6eVand10-2eV/Åforelectronicandforceconvergence,respectively,withintheDFT+UapproachbyDudarevetal.11(Ueff=U−J=4.5eVfortheCe4felectrons)withthegeneralizedgradientapproximation(GGA)proposedbyPerdew,Burke,andErnzerhof(PBE).12Long-rangedispersioncorrectionswereconsideredwithDFTlatticeconstants,employingtheso-calledDFT-D3approach.13-14IntheXRDandTEMexperimentsforthePt/CeO2powdercatalyst,PtparticlesoraggregateswerenotseenandinthecaseofPt/CeO2(111),singleatomsandsmallPtclustershavebeenobservedatlowcoveragessuchastheoneusedhere(0.15ML).4Moreover,previousstudieshavehighlightedthespecialpropertiesofsinglePtatomsonceriasurfaces.15-19Forthesereasons,wehavemodeledtheinteractionofCH4withsinglePtatomsandsmallPt4clustersinclosecontactwiththestoichiometricCeO2(111)andfullyreducedCe2O3(0001)surfaces,aimingtoelucidatetheeffectsofthetwosupportsinthePtelectronicstructureandchemicalpropertiestowardsCH4adsorptionanddissociationascomparedtotheextendedPt(111)surfaceaswellastosimilarlydispersedceria-supportedNiandConanoparticles.ThePtn/CeO2(111)andPtn/Ce2O3(0001)(n=1and4)modelcatalystsweremodeledby22and33surfaceunitcellsforone-andS3

3flatfour-atommetalnanoparticles,respectively,withcalculatedceriabulkequilibriumlatticeconstant(CeO2:5.485Å;hexagonal(ferromagnetic)Ce2O3:a0/c0=3.917/6.182ÅandinternalparametersuCe/uO=0.2471/0.6448).InthecaseoftheCeO2(111)andCe2O3(0001)surfaceswith22periodicity,slabsoffifteenatomicslayers,i.e.,fiveCeO2(OCeO)tri-layersandthreeCe2O3(OCeOCeO)quintuple-layers,respectively,wereconsidered.FortheCeO2andCe2O3surfaceswith33periodicity,thinnerslabswiththreeCeO2tri-layersandoneCe2O3quintuple-layer,respectively,wereemployed.Correspondingmodelsofceria-supportedNiandConanoparticleswerecreatedandemployedhereforcomparison.ThestructuresoftheNi1-,Co1-and(flat)Ni4-ceriasystemscorrespondtotheonespreviouslyreported.1-2,20-21FortheextendedcleanPt(111)surface,slabsoffivemetallayersand33periodicitywithPBEoptimizedlatticeconstant(fccPt:3.975Å,showingthetypicaloverestimationof1-2%withrespecttoexperiment,3.912Å);22theNi(111)andCo(0001)surfacesweremodeledaspreviouslyreportedbyLiuetal.2Inallsurfacemodels,consecutiveslabswereseparatedbyatleasta12Å-thickvacuumlayertoavoidinteractionbetweentheslabsandtheirperiodicimages.Allmetal/ceriamodelsusedinthisworkareshowninFiguresS4andS5.Monkhorst-Packgridswitha3×3×1(2×2×1)and5×5×1k-pointsamplingwereusedforthe2×2(3×3)ceria-basedsystemsandtheextendedmetalsurfaces,respectively.Allatomsinthethree(one)bottomCeO2(Ce2O3)layersoftheceria-basedslabswith2×2periodicitywerekeptfixedattheiroptimizedbulk-truncatedpositionsduringgeometryoptimization,whereastherestoftheatomswereallowedtofullyrelax;fortheCeO2-andCe2O3-basedslabswith3×3periodicity,thebottomOCeOtri-layerandthebottomtwoatomiclayers(CeO),respectively,werekeptfixed,andfortheextendedmetalsurfaces,alsothebottomtwolayerswerenotallowedtorelax.Thenon-zero-point-correctedadsorptionenergyofmethanewascalculatedaccordingtothefollowingequationfortheexampleofthedissociativeadsorptiononthePtn/CeO2(111)system:Eads=E[(CH3+H)/Ptn-CeO2(111).]–E[Ptn-CeO2(111)]–E[CH4gas],whereE[(CH3+H)/Ptn-CeO2(111)]isthetotalenergyofthemethylandhydrogenspeciesco-adsorbedonthesurface,E[Ptn-CeO2(111)]isthetotalenergyofthesurfacewithouttheadsorbate,E[CH4gas]istheenergyofthemethanemoleculeingasphase.S4

4Tolocatetransitionstate(TS)structures,weemployedtheclimbingimagenudgedelasticbandmethod(CI-NEB)23withnineimagesforeachreactionpathway.ForalltheTSreportedinthiswork,wehavefoundonlyoneimaginaryfrequency,andthefullgeometryoptimizationsstartingfromitsbackandforwardnearestconfigurations(alongthereactionpath)endedinanon-dissociatedanddissociatedstate,respectively.Inthecalculatedpotentialenergyprofiles,theenergybarrier,EBarrier=ETSEIS,equalsthedifferencebetweentheenergyofthetransitionstate,ETS,andtheinitial(molecularlychemisorbed)state,EIS,whereastheeffectiveorapparentenergybarrierisgivenbytheenergyofthetransitionstate,ETS,referencedtogas-phaseCH4andthecleansurface.Theseenergieshavetobezero-pointcorrectedwhencomparedtothecorrespondingGibbsfreeenergyprofiles(G=E+E୞୔୉−TS)atagiventemperatureandpressure.ThechangeintheGibbsfreeenergyoftheinitial,transitionandfinalstatesoftheCH4CH3+Hreaction,referencedtogas-phaseCH4andthecleansurfaceofthemodelcatalyst,havebeencalculatedat300Kand1atmCH4,accordingtothefollowingequationfortheexampleoftheinitialstate:୕౗ౚ౩౬౟ౘ,ిౄరG(T)≈Eୟୱ+E୞୔୉−Tk୆ln(),୕౬౟ౘ,ౙ౛౗౤∗୕౬౟ౘ,ిౄౝ౗౩రwhereQ౗ౚ౩,Q୴୧ୠ,ୡ୪ୟ୬,andQ୴୧ୠ,େୌౝ౗౩arethevibrationalpartitionfunctionsofCH4୴୧ୠ,େୌరరchemisorbedonthesurface,thesurfacewithouttheadsorbate,andtheCH4moleculeingasphase,respectively.ΔEZPEisthezero-pointenergy(E୞୔୉)correctiontotheadsorptionenergycalculatedwithintheharmonicapproximation.Fortheentropyofthetransitionstatestructureonlytherealmodeshavebeenconsidered.S5

5FigureS1.CurvefittingofthePt4fX-rayphotoelectronspectraforthe(a)PtCeO2(111)and(b)0.5wt%Pt/CeO2,beforeCH4activationreactionandundertheCH4atmosphereat427ºC.TableS1.FittingparametersandresultsofthePt4fspectrainFigureS1.ThefittingresultsshowthatafterthedepositionofPtonCeO2(111),mostofthePt(~59%)adoptsa+1oxidationstate,withsomePt2+andPt0presentonthesurface.ThepeakpositionsofdifferentPtoxidationstatesinthespectraagreewellwiththeliteraturereportedresults.24S6

6FigureS2.SpectraofCe3dAP-XPSfor0.5wt%Pt/CeO2andPt/CeO2(111)intheCH4atmosphereatelevatedtemperatures.Thepowdercatalystwaspre-treatedin10mTorrO2at400°Ctoremovethesurface-boundedcarbonspecies,andthesampleswereexposedtoa50mTorrCH4duringthereactionprocess.FigureS3.(a)Timeresolvedin-situXRDprofileofPt/CeO2and(b)cerialatticeparameterevolutioninaCH4atmosphereasafunctionoftemperature.Reactionconditions:5cc/minCH4+5cc/minHe,rampingto700°Cwitha5°Crampingrate.Thein-situXRDprofileof0.5wt%Pt/CeO2andthecerialatticeparameterevolutionintheCH4atmosphereasafunctionoftemperatureareshowninFigureS3.OnlyceriapeakswereidentifiedduetothelowloadingandthesmallparticlesizeofPt.S7

7UponinteractionwithCH4,cerialatticegraduallyexpandedwithincreasingtemperature.Thediscrepancybetweentheactualcerialatticeexpansionandthecalculatedonefromthethermaleffectmanifeststhereductionofceriasupport,thatis,whenceriaisreducedthereisanincreaseintheionicradiiwhengoingfromCe4+toCe3+andtherepulsionbetweentheoxygenvacancieswiththeirsurroundingcationsresultinanabruptexpansionofthecerialattice.FromFigureS3b,onecanseethattheceriareductionalreadystartsatatemperatureof~300°C,whichagreeswithourAP-XPSresults,andasthetemperaturefurtherincreasesupto700°C,theceriareductionbecomessubstantial.ThetotalexpansionoftheceriasupportuponitsinteractionwithCH4until700°Cwas0.11Å.S8

8FigureS4.AdsorbedPt1+,Co2+andNi2+atomsonCeO0002(111)andPt,CoandNionCe2O3(0001).Pt,CoandNiatomsaredepictedingreen,violetandblue,respectively,whilesurface/subsurfaceoxygenatomsareinred/green,Ce4+inwhite,andCe3+ingray.Selectedinteratomicdistances(inpm)areindicated.Pt2+speciesonCeO2(111)areby0.27eVlessstablebut,basedontheevidencereportedintheliterature,25-26Pt2+canexistonthepartiallyreducedsurfaceandtheavailabilityofexcessoxygenatsurfacestepsontheoxidizedandreducedsurfacesisnecessaryforthestabilityofPt2+speciesinaPtO4configuration.S9

9FigureS5.AdsorbedPt4,Co4andNi4rhombohedralclustersontheCeO2(111)andCe2O3(0001)surfaces.Pt,CoandNiatomsaredepictedingreen,violetandblue,respectively,whilesurface/subsurfaceoxygenatomsareinred/green,Ce4+inwhite,andCe3+ingray.Selectedinteratomicdistances(inpm)areindicated.TheintegralheatofadsorptionofPtgasatomsformingPtnclustersontheCeO2(111)supportcanbecalculatedat0KaEheat=1/n[E(Ptn/CeO2)–E(CeO2)–n*E(Ptatom)]whereE(Ptn/CeO2)andE(CeO2)arethetotalenergiesofthePtn/CeO2(111)andCeO014912(111)surfaces,andE(Ptatom)isthatofagas-phasePtatominthe[Xe]4fdsconfiguration,calculatedwitha(121116)Å3periodiccellandtheΓ-point.AnisolatedPt1specieswasfoundtoadsorbonahollowsitecoordinatedtothreesurfaceoxygenatomswithEheat=3.46eV.AsforPt4,bothbi-dimensionalflatrhombohedral-shaped(Pt4.flat)andthreedimensionalclusterswithpyramidalshape(Pt4.pyr)clusterswereconsidered(seeFigureS6).Thestabilityoftheseclustersiscomparable,namely,Eheat=4.34and4.42eVforS10

10Pt4.flatandPt4.pyr,respectively.ThesePt4speciesalsoreducetheceriasupportuponadsorption.InthePt4.pyrcase,oneelectronistransferredfromthethreePtatomsformingthepyramidbase,whicharepartiallyoxidized,3×Pt0.33+,whereasthetopPtatomremainsasPt0.InthePt4.flat,twoelectronsaretransferredandallfourPtatomsindirectcontactwiththesupportareoxidized,4×Pt0.5+.Incomparisonwithceria-supportedsinglePtatomsandsmallPt4clusters,theanchoringofNiandCoatomsonthestoichiometricCeO2+2(111)surfaceyieldsNiandCo2+speciesandtwoCe3+ions,1-2respectively(FigureS4).IntheplanarNi4andCo4onCeO2(111),theaverageoxidationstateoftheNiandCoatomsare+0.5and+0.75,respectively(FigureS5),andonthefullyreducedCe2O3(0001)surface,theisolatedNiandCoatomsandthoseofthenanoparticlesaremetallic(FiguresS4andS5).FigureS6.ActivationbarrierforthedehydrogenationofmethaneonPt4-CeO2wherethestructureofthenanoparticleisapyramidwithaPt0atomatthevertexofthepyramidandnotincontactwiththesurfaceofCeO2(noZPEcorrection).Ascanbeseeninthefigure,theenergyprofileofthereactionpathissimilartothatofPt(111),withanactivationbarrierof0.67eVthatishigherthanthe0.15eVcorrespondingtoaplanarrhombohedralPt04nanoparticle.Consequently,despitethecoordination,Ptspeciesnotincontactwithceriaarenotactiveformethaneactivation.S11

11FigureS7.DifferentscenariosofcooperativedissociationbetweenpartiallyoxidizedPtandaceriaoxygen,wherehydrogenbindstooxygenandmethylisadsorbedontheplanarrhombohedralorpyramidalPt4nanoparticle.Ascanbeseeninthefigure,wefoundahighbarrierof1.00eVand1.31eVintherhombohedralandpyramidalcases,respectively(noZPEcorrection).Thus,itcanbeconcludedthat,onthesesystems,methaneisactivatedonthePtatomsoftheinterfacebutthedissociationisnon-cooperative.S12

12FigureS8.Totaldensityofstatesforthe(a)cleanPt(111)surfaceandthe(b)Pt1and(c)Pt4/CeO2(111)systemsTheredfilledcurvesaretheprojecteddensityofstates(PDOS)ontothePtstates.ForthePt(111)surface,onlythefirstPtatomiclayerisconsidered.TheenergyzeroistheFermilevel(EF).(e)Totaldanddz2projecteddensityofstatesonthePtatomoverwhichCH4dissociatesforthePt4/CeO2(111)system(cf.FiguresS5andS9),and(f)showsthesameresultbutforafree-standingPt4clusterresultingfromtheremovaloftheCeO2(111)supportfromPt4/CeO2(111),withoutfurthergeometryoptimization.(f)Isosurfaceofthechargewithinthe0.160.50eVenergyintervalin(e).Thefigureaboveshowsthetotaldensityofstatesforthe(a)cleanPt(111)surfaceandthe(b)Pt1and(c)Pt4/CeO2(111)systems.ThePt(111)andPt4/CeO2(111)systemswerecalculatedemployingsupercellswith(33)periodicityandthePt4/CeO2(111)systemwith(22).Theredfilledcurvesaretheprojecteddensityofstates(PDOS)ontothePtstates.ForthePt(111)surface,onlytheatomsinthesurfacelayerareconsidered.TheenergyzeroistheFermilevel(EF).(d)showsthetotaldanddz2projecteddensityofstatesonthePtatomoverwhichCH4dissociatesforthePt4/CeO2(111)system,and(e)showsthesameresultbutforafree-standingPt4clusterresultingfromtheremovaloftheCeO2(111)supportfromPt4/CeO2(111),withoutfurthergeometryoptimization.Thereisacleardifferencebetweenthedz2projecteddensityofstatesbetweenthetwosystems.Forthefree-standingclusterthestatesareoccupied,butforthesupportedone,forwhichPtatomsareinterfacialandoxidized,apartofthedz2statesappearabovetheFermilevel.(f)showstheisosurfaceofthechargewithinthe0.160.50eVenergyintervalin(e),wherethedz2orbitalshapecanbeappreciated.Thesestates,ifoccupied,willcauseaS13

13repulsiontothefrontiermethaneorbital,asaconsequenceofwhich,themoleculewillnotbeabletoapproachthesurfaceascloseasitdoesforthePt4/CeO2(111)system(cf.FigureS14below).ThisisthecaseforthePt(111)surface.TheelectronicperturbationinducedbythatthebindingofPtatomstooxygenatomsoftheceriasupportisimportantforreactivitytowardsthefirsthydrogenabstractionfromCH4inthePt/CeO2systems.E(eV)MetalISFSTSEBarrierEReactionNi(111)0.260.350.640.900.09Co(0001)0.210.420.750.960.21Pt(111)0.270.460.550.820.19E+ZPE(eV)Ni(111)0.230.430.530.760.20Co(0001)0.200.490.660.860.29Pt(111)0.240.540.440.680.30ΔG(eV)(300K)Ni(111)-0.15-0.180.700.85-0.03Co(0001)-0.12-0.240.770.89-0.12Pt(111)-0.20-0.410.580.78-0.21TableS2.Energyvaluesoftheinitialstate(IS:adsorbedCH4),finalstate(FS:adsorbedCH3+H)andtransitionstate(TS)ofthereactionpathwayforthefirstdehydrogenationofCH4onNi(111),Co(0001)andPt(111)surfaces.Theactivationbarrier(EBarrier)andthereactionenergy(EReaction)arealsolisted.FigureS9.ReactionenergyprofilefortheCH4→CH3+HreactiononPt(111).Thestructuresshownontheleftandrightofthereactionpathwaycorrespondtothesideviewsoftheoptimizedinitial(molecularlyadsorbed)andfinal(dissociated)statesusedinthesearchofthetransitionstatestructure.AllZPE-correctedenergiesarerelativetoCH4inthegasphaseandthecorrespondingcleansystems.TheGibbsfreeenergyprofilecorrespondsto300Kand1atmofCH4.S14

14EFS-ETSEBarrierΔETS=EISEFSEFS[Metal]PredictedCalculatedPredictedCalculatedΔEBarrierPt(111)-0.27-0.460.000.730.551.000.82-0.18Pt1/CeO2-0.66-0.76-0.300.53-0.061.190.60-0.59Pt4/CeO2-0.73-1,10-0.640.30-0.581.030.15-0.88Pt1/Ce2O3-0.16-1.45-0.990.07-0.010.230.15-0.08Pt4/Ce2O3-0.11-0.50-0.040.710.140.820.25-0.57Co(0001)-0.21-0.410.000.770.750.980.96-0.02Co1/CeO2-0.24-0.380.030.790.671.030.91-0.12Co4/CeO2-0.13-0.75-0.340.54-0.100.670.03-0.64Co1/Ce2O3-0.51-0.56-0.150.66-0.431.170.08-1.09Co4/Ce2O3-0.14-0.98-0.570.380.410.520.55+0.03Ni(111)-0.26-0.350.000.810.641.070.90-0.17Ni1/CeO2-0.41-0.43-0.080.750.461.160.87-0.29Ni4/CeO2-0.24-1.04-0.690.34-0.100.580.14-0.44Ni1/Ce2O3-0.87-0.52-0.170.69-0.151.560.72-0.84Ni4/Ce2O3-0.22-0.71-0.360.560.180.780.40-0.38TableS3.Calculated(noZPEcorrection)energies(ineV)fortheinitial,EIS,final,EFS,andtransitionstates,ETS,fortheCH4→CH3+HreactionontheMn/CeO2(111)andMn/Ce2O3(0001)(M:Pt,Co,Niandn=1,4)aswellasthePt(111),Co(0001),andNi(111)surfaces.AllenergiesarerelativetoCH4inthegasphaseandthecorrespondingcleansystems.ThepredictedETSvaluescorrespondtothevaluesobtainedusingthelinearscalingrelationshownETS=(0.67EFS+1.04)fortheactualcalculatedfinalstate,EFS.ThepredictedEBarriervaluescorrespondtotheactivationenergybarriercalculatedastheenergydifferencebetweenthepredictedenergyofthetransitionstateandthecalculatedenergyoftheinitialstate.ThemodelcatalystswhoseETSenergyislessthanzeroisrelatedtothefactthatonthemCH4bindsrelativelystrongly(0.4eV),sothatifthebarrierforthefirstHabstractionfromthechemisorbedCH4moleculeissufficientlylow,ETSwillbenegativewhenreferencedtogas-phaseCH4andthecleansurface.S15

15FigureS10.Topandsideviewsoftheinitialstate(IS),transitionstate(TS),andfinalstate(FS)fortheCH4CH3+HreactiononthePt1/CeO2,Co1/CeO2andNi1/CeO2modelcatalysts.Selectedinteratomicdistances(inpm)areindicated.S16

16FigureS11.Topandsideviewsoftheinitialstate(IS),transitionstate(TS),andfinalstate(FS)fortheCH4CH3+HreactiononthePt4/CeO2,Co4/CeO2andNi4/CeO2modelcatalysts.Selectedinteratomicdistances(inpm)areindicated.S17

17FigureS12.Topandsideviewsoftheinitialstate(IS),transitionstate(TS),andfinalstate(FS)fortheCH4CH3+HreactiononthePt1/Ce2O3,Co1/Ce2O3andNi1/Ce2O3modelcatalysts.Selectedinteratomicdistances(inpm)areindicated.S18

18FigureS13.Topandsideviewsoftheinitialstate(IS),transitionstate(TS),andfinalstate(FS)fortheCH4CH3+HreactiononthePt4/Ce2O3,Co4/Ce2O3andNi4/Ce2O3modelcatalysts.Selectedinteratomicdistances(inpm)areindicated.S19

19FigureS14.Comparisonoftopandsideviewsoftheinitialstate(IS),transitionstate(TS),andfinalstate(FS)fortheCH4CH3+Hreactiononthe(leftpanel)Pt(111),(middlepanel)Pt4/CeO2,and(rightpanel)Pt4/Ce2O3modelcatalysts.Selectedinteratomicdistances(inpm)areindicated.S20

20FigureS15.ReactionenergyprofilesfortheCH4→CH3+Hreactionon:a)Ptn/CeO2,b)Ptn/Ce2O3,c)Con/CeO2,d)Con/Ce2O3,e)Nin/CeO2andf)Nin/Ce2O3(n=1,4).Thestructuresshownontheleftandrightofthereactionpathwayscorrespondtothesideviewsoftheoptimizedinitial(molecularlyadsorbed)andfinal(dissociated)statesusedinthesearchofthetransitionstatestructure.AllZPE-correctedenergiesarerelativetoCH4inthegasphaseandthecorrespondingcleansystems.TheGibbsfreeenergyprofilecorrespondsto300Kand1atmofCH4.S21

21M1-CeO2M4-CeO2E(eV)E(eV)MetalISFSTSEBarrierEReactionMetalISFSTSEBarrierEReactionNi1(2+)0.410.430.460.870.02Ni40.241.040.100.140.80Co1(2+)0.240.380.670.910.14Co40.130.750.100.030.75Pt1(1+)0.660.760.060.600.14Pt40.731.100.580.150.37E+ZPE(eV)E+ZPE(eV)Ni1(2+)0.630.530.120.75+0.10Ni40.171.260.080.091.09Co1(2+)0.240.400.540.780.16Co40.100.880.080.020.88Pt1(1+)0.770.830.250.520.13Pt40.691.130.620.070.44ΔG(eV)(300K)ΔG(eV)(300K)Ni1(2+)0.220.060.540.76+0.16Ni40.101.070.000.101.17Co1(2+)0.110.080.660.77+0.03Co40.070.840.100.030.84Pt1(1+)0.530.660.020.550.13Pt40.541.050.450.090.51M1-Ce2O3M4-Ce2O3E(eV)E(eV)MetalISFSTSEBarrierEReactionMetalISFSTSEBarrierEReactionNi10.870.520.150.720.35Ni40.220.710.180.400.49Co10.510.560.430.080.05Co40.140.980.410.55084Pt10.161.450.010.151.30Pt40.110.500.140.250.39E+ZPE(eV)E+ZPE(eV)Ni10.870.490.280.590.38Ni40.211.010.050.160.79Co10.520.55------0.03Co40.111.020.280.390.91Pt10.121.380.000.121.26Pt40.110.560.060.170.45TableS4.Energyvaluesoftheinitialstate(IS:adsorbedCH4),finalstate(FS:CH3+H)andtransitionstate(TS)ofthereactionpathwayforthefirstdehydrogenationofCH4onMn/CeO2andMn/Ce2O3(M:Pt,Co,Niandn=1,4)surfaces.Theactivationbarrier(EBarrier)andthereactionenergy(EReaction)arealsolisted.S22

22Δq(C)StatePt(111)Co(0001)Ni(111)IS0.020.030.05FS0.450.470.41Pt1/CeO2Pt1/Ce2O3Co1/CeO2Co1/Ce2O3Ni1/CeO2Ni1/Ce2O3IS0.160.010.050.150.090.15FS0.080.160.200.230.160.34Pt4/CeO2Pt4/Ce2O3Co4/CeO2Co4/Ce2O3Ni4/CeO2Ni4/Ce2O3IS0.140.080.030.020.160.04FS0.120.200.510.400.500.23TableS5.Baderchargedifference(Δq=q–qgas)foraCatomintheCH4moleculeinthemolecularlyadsorbed(IS)anddissociated(FS)statesontheMn/CeO2,Mn/Ce2O3(M:Pt,Co,Niandn=1,4),Pt(111),Co(0001)andNi(111)surfaces.FigureS16.a)Scalingrelationforthesurface-stabilizedpathway(ETS=0.67EFS+1.04),accordingtoLatimeretal.27Includedarethe(non-ZPE-corrected)ETSandEFSvaluesforM1atomsandM4clusters(M=Pt,Co,Ni)ontheCeO2(111)andCe2O3(0001)surfaces,aswellasontheextendedPt(111),Co(0001)andNi(111)surfaces.b)Activationenergybarriers(non-ZPE-corrected)forCeO2(111)-andCe2O3(0001)-supportedM1andM4(M=Pt,Co,Ni)clustersaswellasfortheextendedM(111)(M=Pt,Ni)andCo(1000)surfaces.S23

23FigureS16areproducesthelinearscalingrelationbetweentheenergyofthetransitionstatestructureformethaneactivationviaasurface-stabilizedactivationpathway,ETS(referencedtogas-phaseCH4andthecleansurface),andthatofthefinalstate,E=E,asproposedbyLatimeretal.,27whichhasbeenobtainedusingawideFSCH3+HrangeofmaterialssuchasCaO,MgO,PdO,dopedMoS2,rutileoxidesinadditiontocleanaswellO-andOH-promotedmetals(blackdotsinFigureS16a).Atroomtemperature,low-loadedM/CeOδ+2(111)systems(M=Pt,Co,Ni)consistsofMnanoparticlesonthesupport,whereasuponinteractionwithCH4atelevatedtemperatures,morethanamonolayerofmethanereactswiththesystemsproducingM0andCeO2-x(111)(seeFigure2inthemaintext,S2andS3forPt-ceriaandRefs.2and1,20forCoandNi.ThelatterhavebeenmodeledusingtheCe2O3(0001)surfaceassupport(FiguresS4andS5).Todeterminetheapplicabilityofthelinearscalingrelationtocatalystsconsistingoflow-loadedmetalclustersonceriasurfaces,thepointscorrespondingtotheETSandEFSvaluesforthecleavageofthefirstCHbondinCH4onM1atomsandM4clusters(M=Pt,Co,Ni)onthestoichiometricCeO2(111)andfullyreducedCe2O3(0001)surfaces,aswellasontheextendedPt(111),Co(0001)andNi(111)surfaces(TableS3),havebeenaddedinFigureS16a.Inthemaintext,theparticularlylargedeviationsofthecalculatedETSvaluesfromthosepredictedbythelinearscalingrelationforthelow-loadedPt/CeO2(111)systemsofupto~1eV,havebeendiscussedandcomparedtothosefortheCo/CeO2andNi/CeO2systems,aswellastothatfortheextendedPt(111)surface.IthasbeenstatedthatontheelectronicallymodifiedinterfacialPtδ+atomsontheCeO2support,thebindingofCH4moleculesisparticularlyenhancedcomparedtothatonPt(111),thoughalsocomparedtothatonotherlow-loadedMδ+/CeO2systemswithM=CoorNi.IthasbeenarguedthatthebindingconfigurationsonthePt/CeO2systemsaresuchthattheCHbondthatwillfinallybecleavediselongated,facilitatingitscleavagewithamuchloweractivationenergybarrierthantheonepredictedbythelinearscalingrelation.InspectionofFigureS16brevealsthatactivationbarriersarealsosmallerfortheM0/Ce2O3(0001)systems(M=Pt,Co,Ni)ascomparedtothecorrespondingextendedmetallicsurfaces.ThisisinlinewiththestrongerbindingofthefinalstateontheM0/Ce2O3(0001)systems,sincestrongerCH3+HbindingenergiescorrespondtolowerETSenergies.Thecalculatedfinalstateenergies,EFS(inabsolutevalues),generallyfollowtheM4/Ce2O3>M1/Ce2O3>M-surfacetrend(TableS3).TheseresultsrevealthatevenS24

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