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1、StrategiestobreaklinearscalingrelationshipsJavierPerez-RamirezGInstituteforChemicalandBioengineering,ETHZurich,Zurich,Switzerland,instituteofChemicalResearchofCatalonia,TheBarcelonaInstituteofScienceJavierPerez-RamirezGInstituteforChemicalandBioengineering,ETHZurich,Zurich,Switzerland,instituteofChe
2、micalResearchofCatalonia,TheBarcelonaInstituteofScienceandNuriaLopezandTechnology,Tarragona,Spain,e-mail:jprchem.ethz.ch;nlopeziciq.esThesearchfornewcatalyticmaterialshasreliedonhighlytime-andhuman-resource-consumingprocedures.Theappearanceoftheoreticalmethodsthatemploydensityfunctionaltheorycoupled
3、tokineticmodelshasallowedtherationalunderstandingofactivityvolcanoplotsandselectivityabruptprofilesthatresemblecliffs.However,thesemethodologiespresentseveraldrawbacksastheoptimizationisconfinedtoafamilyofmaterials,typicallymetals,andnotappliedtotheoverallphaseandcompositionalspace,thereforethemaxim
4、umactivitymightnotbesufficientforpracticalapplications.Volcanosemergefromthesymmetrybetweentheadsorptionenergiesofdifferentintermediatesonthecatalyst,andthuscircumventingthesedependenciesiscrucialtoidentifybettercatalyticmaterials.Herewepresentarevisionoftheadvancesinthefieldthatindicatethatcomplexi
5、tyinthematerialsiskeytoidentifyingalternativepathsandthusovercomethedrawbacksofscalingrelationships.Thenot-too-strong,not-too-weakbondingofkeyintermediatesmarksthesweetspotfingerprintofoptimalcatalyticmaterials.ThisprinciplewasintroducedfirstbySabatier,whoshowedthatthelight-offtemperatureofcatalysed
6、reactionsdisplayedavolcanoshapeasafunctionofformationenergiesI；.Sincethen,theoreticalapproachestorationalcatalyticdesignhavebeenbasedonidentifyingtheactivityofvolcanoesandhowlheydependonafew,descriptors,typicallythebindingenergiesof(oneortwo)intermediatcs5-4.Withlheappearanceof(hedensityfunctionalth
7、eory(DFT)andwide-spreadaccesstocomputers,simulationshavebeenestablishedasoneofthepillarsinunderstandingandpredictingcatalysis.Nowadays,itispossible(oimplementrobustDFTtechniquesincomputationalcodes,providingdetailedelectronicstructure,thermodynamicandkineticparametersofincreasinglycomplexreactionnet
8、works.Therefore,computationallyderivedvolcanoplotshavebecomethegoldstandardincatalystdesign6.Volcanosprovideasystematicwayforcatalyticoptimizationbyfinelytuningtheadsorptionenergiesorthroughdynamicoperation7,andhaveproventobeapowerfultoolforassessingalloycomposition,size,metal/oxideinterfaces10,pHde
9、pendenceandhaveevenbeenreportedinhomogeneouscatalysts12.ThesameprinciplescanbeusedinelectrocatalysisoncethepotentialandpHtermsarcintroduced,andi(islikelytoappearinphotochemistry,althoughthishasnotbeendemonstratedyet.However,thereisanincreasingpressuretogobeyondthetopofthesevolcanoesThereareseveralre
10、asonsbehindthisneed.Itiswellknownthatthemaximumoftheobservedrateprovidesthelimitfortheactivity,andthismightbeinsufficientforthepracticalapplicationofcatalytictechnologies16.Inaddition,descriptorsaretypicallyenergies,andthermodynamicsforintermediatescumbersometoobtainexperimentally.Moreover,addressin
11、gselectiveprocessesthroughvolcanoesisnotstraightforwardasseveralpathsneed(obeinvestigatedwithsimilaraccuracy,andlherespectivevolcanoesneedtobesuperimposed17.Asforthepracticalaspects,theidentifiedmaximumdocsnotprovideasyntheticroute1*towardsthedesiredcomposition.Finally,somefalsenegatives(outliers)mi
12、ghtappearastherealphasespaceismuchbiggerthanasinglecatalystfamily.Insummary,theconceptofvolcanoispracticaltoractivityalthoughaddressesselectivityandstabilityaspectspoorly.Thelatterhavebeensolvedbyapplyingfilters,forinstancetoassessthattheactivephasecanexistunderreactionconditions.Volcanosarenotsouse
13、fulforfull-phasespacediscoveryintheirpresentformulation,buttheyareveryconvenientforcatalystoptimizationwithinafamilyofcompounds,forexample,alloysandbimetallics.Inthefollowing,weaddresslhedifferentapproximationsthathavebeenemployedintheliterature(oalleviatethelimitationsofthevolcanoesbyincreasingthec
14、omplexityofmaterialsandthechemicalvariability.Tothisend,wefirstdescribetheappearanceofthelinearscalingrelationships(LSRs)andhowthesearetransfenedintothevolcanoandcliffshapesoncemicrokineticbalancesareconsideredandthenprovideaperspectiveonthestrategiesinlheliteraturetoalterLSRsbyincreasingcomplexity.
15、TheoriginofvolcanosandcliffsToimprovecatalyticperformancebeyondthevolcanositisnecessarytounderstandwhytheyappear.TheprocedureisexemplifiedinFig.1,wheretheparticularmodelemployedcomprisesaselectiveprocess(A+1/2BP)andasidepath(A*Q),themodelsforwhichcanbeaccessedfromref.也Thestandardprocedureisasfollows
16、:thedetailedreactionnetworkismappedcarefullyfbratleastonecatalyticcompoundandthecorrespondingenergiesarecalculatedbyDFT,thenamicrokineticmodelthatwrapsalltheelementarystepsisdeveloped.Inacomplexreactionwithmultipleintermediates,itturnsoutthatthebondorderconservationtheoiyandtheelectroncountingrulesimplythattheenergiesofintermediatesarelinkedonetoanotherinalinearmanner(tLSRs20,Fig.la).Thisisparticularlyapplicabletometalsforwhichthesmoothnessoftheelectroncloudhelpsaddre
