Direct Observation of Site-Specific Molecular Chemisorption of O2 on TiO2(110).pdf

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1、pubs.acs.org/JPCLDirectObservationofSite-SpecificMolecularChemisorptionofO2onTiO2(110)††‡,†Zhi-TaoWang,YinggeDu,ZdenekDohnalek,andIgorLyubinetsky*†EnvironmentalMolecularSciencesLaboratory,InstituteforInterfacialCatalysis,andPacificNorthwestNationalLa

2、boratory,‡Richland,Washington99352,UnitedStates,andFundamentalandComputationalSciencesDirectorate,InstituteforInterfacialCatalysis,andPacificNorthwestNationalLaboratory,Richland,Washington99352,UnitedStatesABSTRACTMolecularlychemisorbedO2speciesweredi

3、rectlyimagedonre-ducedTiO2(110)at50Kwithhigh-resolutionscanningtunnelingmicroscopy(STM).TwodifferentO2adsorptionchannels,oneatbridgingoxygenvacancies(VO)andanotherat5-foldcoordinatedterminaltitaniumatoms(Ti5c),havebeenidentified.WhileO2speciesattheTi5

4、csiteappearsasasingleprotrusioncenteredontheTi5crow,theO2atVOmanifestsitselfbyadisappearanceoftheVOfeature.ItisfoundthattheSTMtipcaneasilydissociateO2species,unlessextremelylowmagnitudeofthetunnelingparametersareused.TheO2moleculeschemisorbedatlowtem-

5、peraturesatthesetwodistinctsitesarethemostlikelyprecursorsforthetwoO2dissociationchannels,observedattemperaturesabove150and230KattheVOandTi5csites,respectively.SECTIONSurfaces,Interfaces,CatalysishechemistryofoxygenonTiO2surfacesisanim-(DFT)resultshav

6、eindicatedthatchemisorbedanionicO2portantcomponentinmanycatalyticandphotocata-speciesbindratherstronglyatVO'swithadsorptionenergyTlyticprocesses,suchaswatersplittingandwasteontheorderof2eV.18-20Photostimulateddesorption1-34-6remediation,andhasbeenexte

7、nsivelystudied.Inpar-studieshavedemonstratedtheexistenceoftwotypesofticular,O2isconsideredasoneoftheoxidizingreagentsinchemisorbedOspecies,21-23whilethemaximumamount2photooxidationprocessesandalsoasanelectronscavengerofchemisorbedO2hasbeenexperimental

8、lydeterminedfacilitatingthesereactions,althoughtheexactroleofO2isstilltobeabouttwicetheVOcoverageattemperaturesbelow1,2,7unclear.Inaddition,surface-boundoxygenspeciesmay∼100K.10However,detailedinformationregardingtheO22,7considerablyaffectTiO2