对苯二酚氧化

DOI:10.1021/la101631m16349Langmuir2010,26(21),16349–16354PublishedonWeb07/15/2010pubs.acs.org/Langmuir©2010AmericanChemicalSocietyPerformanceofaBiomimeticOxidationCatalystImmobilizedonSiliconWafers:ComparisonwithItsGoldCongener†KristoferL.E.Eriksson,‡WinnieW.Y.Chow,‡CarlaPuglia,‡Jan-ErlingB€ackvall,§EmmanuelleG€othelid,*,‡andSvenOscarsson‡‡DepartmentofPhysicsandAstronomy,UppsalaUniversity,Box516,S-75120Uppsala,Sweden,and§DepartmentofOrganicChemistry,StockholmUniversity,ArrheniusLaboratory,S-10691Stockholm,SwedenReceivedApril23,2010.RevisedManuscriptReceivedJune24,2010Withtheaimofextendingtheusefulnessofanexistingbiomimeticcatalyticsystem,cobaltporphyrincatalyticunitswiththiollinkerswereheterogenizedviachemicalgraftingtosiliconwafersandutilizedforthecatalyticoxidationofhydroquinonetop-benzoquinone.Atomicforcemicroscopy(AFM)andX-rayphotoelectronspectroscopy(XPS)wereusedtoanalyzethemorphologyandcompositionoftheheterogeneouscatalyst.Theresultsofthecatalyticoxidationofhydroquinoneobtainedwithporphyrinsgraftedonsiliconwerecomparedwiththoseobtainedearlierwiththesamecatalystinhomogeneousphaseandimmobilizedongold.Itwasfoundthatthecatalysiscouldrunover400h,withoutshowinganysignofdeactivation.Themeasuredcatalyticactivityisatleast10timeshigherthanthatmeasuredunderhomogeneousconditions,butalso10timeslowerthanthatobservedwiththecatalyticunitimmobilizedongold.Thereasonsofthisdiscrepancyarediscussedintermofsubstrateinfluenceandoverlayerorganization.Thesilicon-immobilizedcatalysthaspotentialasanadvancedfunctionalmaterialwithapplicationsinoxidativeheterogeneouscatalysisoforganicreactions,asitcombineslong-termrelativelyhighactivitywithlowcost.IntroductionThereiscurrentlyalargeinterestinperformingchemistryina“green”way,thatis,inanatom-economic,energyefficient,andselectivewaywithoutproductionofharmfulbyproducts(“green”chemistry).1-5Withinthefieldofoxidativecatalysis,therearemanyexamplesofthis,concerningbothheterogeneous3,5-9andhomogeneouscatalysis.10-13Sincehomogeneouscatalystsaredissolvedinthereactionmedium,aproblemoftenencounteredinsuchprocessesistheneedtoseparatethecatalystfromtheproductsandreactants.Anotherwidespreadproblemisthatthecatalystcanexhibitlowstabilityunderhomogeneousconditions.Forinstance,metalporphyrinsandmetalphthalocyaninecata-lystsareknowntoeasilylosetheiractivityduetodimerizationorotherdegradationreactions.14-17Thisisevenmorepronouncedwhenmovingtoindustrialscaleprocesseswheretheincompat-ibilitywithflowreactorsandlackoflong-termcatalyticstabilityareseriousobstaclesfortheemploymentofhomogeneouscata-lysts.Onesolutiontothisproblemistoimmobilizethehomo-geneouscatalysttoasolidsupport,thusmakingaheterogeneouscatalystfromitshomogeneouscounterpart.17,18Todate,onlyfewsuchheterogeneouscatalystshavecometocommercialusemainlyduetoleakageofthecatalystintothereactionmediaaswellasitsstability.19,20Inpreviouswork,wehavestudiedabiomimeticoxidationcatalystunderhomogeneousandheterogeneousconditionswhenattachedtogold.21,22Itwasfoundthatthegoldsupportedcatalystoutperformeditshomogeneouscounterpartbyfar.Theprospectofutilizingsiliconinplaceofgoldassupportimpliesseveraladvantages,since,inadditiontobeingcheaper,italsooffersmuchgreaterflexibilitywhenitcomestothedesignandmanufacturingofthesupport.Inthepresentstudy,wehaveinvestigatedtheperformanceoftheabove-mentionedcatalyticunit,athiol-derivatizedcobaltporphyrin(CoTPP-L)(showninFigure1),whenimmobilizedontoasiliconwafer.Themoleculeswerechemicallygraftedontothenativesiliconoxidelayerofthesiliconwafersbyanewlydevelopedimmobilizationmethod,andthefindingswerecomparedtoourearlierresults.21Thecatalyticper-formancewasevaluatedbyfollowingtheoxidationofhydroquinone†PartoftheMolecularSurfaceChemistryandItsApplicationsspecialissue.*Correspondingauthor:[e-mail]:þ46184713616.Fax:þ46184713524.(1)See,forexample,ChemicalReviewsissueongreenchemistry:Chem.Rev.2007,107,2167-2820.(2)Somorjai,G.A.;Park,J.Y.Angew.Chem.,Int.Ed.2008,47,9212–9228.(3)Samorjai,G.A.;Frei,H.;Park,J.Y.J.Am.Chem.Soc.2009,131,16589–16605.(4)Zeng,T.;Chen,W.;Cirtiu,C.M.;Moores,A.;Song,G.;Li,C.GreenChem.2010,12,570–573.(5)Oliveira,R.L.;Kiyohara,P.K.;Rossi,L.M.GreenChem.2010,12,144–149.(6)Min,B.K.;Friend,C.M.Chem.Rev.2007,107,2709–2724.(7)Hutchings,G.J.Catal.Today2007,122,196–200.(8)Thomas,J.M.;Raja,R.Annu.Rev.Mater.Res.2005,35,315–350.(9)Thomas,J.M.;Raja,R.Catal.Today2006,117,22–31.(10)Backvall,J.E.;Chowdhury,R.L.;Karlsson,U.J.Chem.Soc.,Chem.Commun.1991,7,473–475.(11)(a)Wang,G.Z.;Andreasson,U.;Backvall,J.E.J.Chem.Soc.,Chem.Commun.1994,9,1037–1038.(b)Csjernyik,G.;Ell,A.H.;Fadini,L.;Pugin,B.;B€ackvall,J.E.J.Org.Chem.2002,67,1657–1662.(12)Sheldon,R.A.;Arends,I.W.C.E.;TenBrink,G.J.;Dijksman,A.Acc.Chem.Res.2002,35,774–781.(13)Piera,J.;B€ackvall,J.E.Angew.Chem.,Int.Ed.2008,47,3506–3523.(14)Balch,A.L.;Mazzanti,M.;StClaire,T.N.;Olmstead,M.M.Inorg.Chem.1995,34,2194–2200.(15)Basolo,F.;Hoffman,B.M.;Ibers,J.A.Acc.Chem.Res.1975,8,384–392.(16)Belal,R.;Meunier,B.J.Mol.Catal.1988,44,187–190.(17)Fu,B.;Yu,H.C.;Huang,J.W.;Z