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1、PublishedonWeb12/28/2007FormationofPd/AuNanostructuresfromPdNanowiresviaGalvanicReplacementReactionXiaoweiTeng,†QiWang,‡PingLiu,†,§WeiqiangHan,*,†AnatolyI.Frenkel,*,‡WenWen,§NebojsaMarinkovic,
2、JonathanC.Hanson,§andJoseA.Rodriguez§CenterforFunctionalNanomat
3、erials,BrookhaVenNationalLaboratory,Upton,NewYork11973,DepartmentofPhysics,YeshiVaUniVersity,NewYork,NewYork10016,DepartmentofChemistry,BrookhaVenNationalLaboratory,Upton,NewYork11973,andDepartmentofChemicalEngineering,UniVersityofDelaware,Newark,Delaware1
4、9716ReceivedSeptember26,2007;E-mail:whan@bnl.gov;anatoly.frenkel@yu.eduAbstract:Bimetallicnanostructureswithnon-randommetalatomsdistributionareveryimportantforvariousapplications.Tosynthesizesuchstructuresviabenignwetchemistryapproachremainschallenging.Thi
5、spaperreportsasynthesisofaAu/PdalloynanostructurethroughthegalvanicreplacementreactionbetweenPdultrathinnanowires(2.4(0.2nminwidth,over30nminlength)andAuCl3intoluene.Bothmorphologicalandstructuralchangesweremonitoredduringthereactionupto10h.Continuouschang
6、esofchemicalcompositionandcrystallinestructurefromPdnanowirestoPd68Au32andPd45Au55alloys,andtoAunanoparticleswereobserved.Moreinterestingly,byusingcombinedtechniquessuchashigh-resolutiontransmissionelectronmicroscopy(HRTEM),X-raydiffraction(XRD),energydisp
7、ersiveX-rayspectrometry(EDS),UV-visabsorption,andextendedX-rayabsorptionfinestructure(EXAFS)spectroscopy,wefoundtheformationofPd68Au32non-randomalloywithAu-richcoreandPd-richshell,andrandomPd45Au55alloywithuniformlymixedPdandAuatominsidethenanoparticles,re
8、spectively.Densityfunctionaltheory(DFT)calculationsindicatedthatalkylaminewillstronglystabilizePdtothesurface,resultingindiffusionofAuatomsintothecoreregiontoformanon-randomalloy.Webelievesuchbenignsynthetictechniquescanalsoenablethelargescalepreparationof
9、varioustypesofnon-randomalloysforseveraltechnicallyimportantcatalysisapplications.1.IntroductionRecently,nearsurfacealloy(NSA)hasshownpromiseasacatalystdesign.7,13-16Forexample,Ptcore-rich/Cushell-richNobleme
