Halogen adsorbates on polymer-stabilized gold clusters: Mass spectrometric detection and effects on catalysis

Article abstract of DOI:10.1016/S1872-2067(16)62501-9

The mass spectrometry of gold clusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) revealed the presence of Cl adsorbates derived from synthetic precursors, mainly on the Au₃₄ and Au₄₃ clusters. Changes in the amount of Cl ads

Full text of DOI:10.1016/S1872-2067(16)62501-9

ChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1656–1661
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
ꢀ
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
ꢀ
ꢀ
Communication (Special Issue on Gold Catalysis)
Halogenꢀadsorbatesꢀonꢀpolymer‐stabilizedꢀgoldꢀclusters:ꢀMassꢀ ꢀ
spectrometricꢀdetectionꢀandꢀeffectsꢀonꢀcatalysisꢀ
a
a
b
ꢀa,c
a,c
RyoꢀIshidaꢀ ,ꢀSetsukaꢀAriiꢀ ,ꢀWataruꢀKurashigeꢀ ,ꢀSeijiꢀYamazoe ,ꢀKiichirouꢀKoyasuꢀ ,ꢀ ꢀ
b
a,c,
YuichiꢀNegishiꢀ ,ꢀTatsuyaꢀTsukudaꢀ *
ꢀ
aꢀDepartmentꢀofꢀChemistry,ꢀSchoolꢀofꢀScience,ꢀTheꢀUniversityꢀofꢀTokyo,ꢀ7‐3‐1ꢀHongo,ꢀBunkyoku,ꢀTokyoꢀ113‐0033,ꢀJapanꢀ
bꢀDepartmentꢀofꢀAppliedꢀChemistry,ꢀFacultyꢀofꢀScience,ꢀTokyoꢀUniversityꢀofꢀScience,ꢀ1‐3ꢀKagurazaka,ꢀShinjuku‐ku,ꢀTokyoꢀ162‐8601,ꢀJapanꢀ
cꢀElementsꢀStrategyꢀInitiativeꢀforꢀCatalystsꢀandꢀBatteriesꢀ(ESICB),ꢀKyotoꢀUniversity,ꢀKatsura,ꢀKyotoꢀ615‐8520,ꢀJapanꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Theꢀ massꢀ spectrometryꢀ ofꢀ goldꢀ clustersꢀ stabilizedꢀ byꢀ poly(N‐vinyl‐2‐pyrrolidone)ꢀ (Au:PVP)ꢀ re‐
vealedꢀtheꢀpresenceꢀofꢀClꢀadsorbatesꢀderivedꢀfromꢀsyntheticꢀprecursors,ꢀmainlyꢀonꢀtheꢀAu34ꢀandꢀAu43
clusters.ꢀChangesꢀinꢀtheꢀamountꢀofꢀClꢀadsorbatesꢀonꢀtheꢀAuꢀclustersꢀdidꢀnotꢀaffectꢀtheꢀcatalyticꢀprop‐
ertiesꢀforꢀtheꢀaerobicꢀoxidationꢀofꢀbenzylꢀalcohol,ꢀsuggestingꢀthatꢀtheꢀClꢀatomsꢀwereꢀonlyꢀweaklyꢀ
boundꢀtoꢀtheꢀAuꢀclusters.ꢀInꢀcontrast,ꢀtheꢀreplacementꢀofꢀClꢀwithꢀBrꢀonꢀtheꢀAu34ꢀandꢀAu43ꢀclustersꢀ
significantlyꢀsuppressedꢀactivity,ꢀwithoutꢀanyꢀinfluenceꢀonꢀtheꢀelectronicꢀstructure.ꢀThisꢀresultꢀindi‐
catedꢀthatꢀtheꢀBrꢀatomsꢀwereꢀstronglyꢀboundꢀtoꢀtheꢀAuꢀclustersꢀandꢀstericallyꢀblockedꢀtheirꢀactiveꢀ
sites.ꢀTheꢀsubstantialꢀreductionꢀofꢀtheꢀcatalyticꢀactivityꢀbyꢀtheꢀBrꢀadsorbatesꢀsuggestedꢀthatꢀtheꢀAu34
andꢀAu43ꢀclustersꢀmadeꢀaꢀmajorꢀcontributionꢀtoꢀtheꢀcatalyticꢀactivityꢀofꢀtheꢀAu:PVP.ꢀ
Receivedꢀ6ꢀMayꢀ2016ꢀ
Acceptedꢀ15ꢀJuneꢀ2016ꢀ
Publishedꢀ5ꢀOctoberꢀ2016ꢀ
Keywords:ꢀ
Goldꢀclusterꢀ
Poly(N‐vinyl‐2‐pyrrolidone)ꢀ
Halogenꢀadsorbatesꢀ
Aerobicꢀalcoholꢀoxidationꢀ
Massꢀspectrometry
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
Theꢀ catalysisꢀ ofꢀ nano‐sizedꢀ goldꢀ hasꢀ attractedꢀ growingꢀ in‐
terest,ꢀbothꢀinꢀacademiaꢀandꢀindustry,ꢀsinceꢀtheꢀdiscoveryꢀofꢀtheꢀ
catalysisꢀofꢀCOꢀoxidationꢀbyꢀheterogeneousꢀAuꢀcatalystsꢀ[1].ꢀItꢀisꢀ
widelyꢀ acceptedꢀ thatꢀ theꢀ diameterꢀ ofꢀ theꢀ Auꢀ catalystsꢀ isꢀ theꢀ
mostꢀ importantꢀ structuralꢀ parameterꢀ governingꢀ theꢀ catalyticꢀ
performanceꢀ [2–4].ꢀ Weꢀ reportedꢀ previouslyꢀ thatꢀ theꢀ catalyticꢀ
weꢀdemonstratedꢀthatꢀPVPꢀplayedꢀanꢀessentialꢀroleꢀinꢀactivatingꢀ
theꢀAuꢀclustersꢀbyꢀdonatingꢀelectronicꢀchargeꢀwhenꢀitꢀisꢀusedꢀasꢀ
aꢀstabilizerꢀ[8].ꢀRecently,ꢀweꢀalsoꢀshowedꢀthatꢀtheꢀresidualꢀthi‐
olatesꢀ onꢀ Auꢀ clustersꢀ supportedꢀ onꢀ porousꢀ carbonꢀ enhancedꢀ
theꢀ selectivityꢀinꢀtheꢀaerobicꢀoxidationꢀofꢀalcoholsꢀwithꢀsomeꢀ
reductionꢀinꢀtheꢀactivityꢀ[9].ꢀThisꢀphenomenonꢀwasꢀexplainedꢀ
inꢀ termsꢀ ofꢀ theꢀ stericꢀ hindranceꢀ andꢀ modulationꢀ ofꢀ theꢀ elec‐
tronicꢀstructuresꢀbyꢀtheꢀthiolateꢀligands.ꢀAsꢀopposedꢀtoꢀpoison‐
ing,ꢀtheꢀcatalyticꢀactivityꢀofꢀmetalꢀclustersꢀcanꢀbeꢀenhancedꢀbyꢀ
ligation,ꢀ asꢀ recentlyꢀ reportedꢀ forꢀ theꢀ hydrolyticꢀ oxidationꢀ ofꢀ
organosilanesꢀ byꢀ alkyne‐protectedꢀ AuAgꢀ alloyꢀ clustersꢀ [10].ꢀ
Duringꢀtheꢀmass‐spectrometricꢀcharacterizationꢀofꢀAu:PVP,ꢀweꢀ
activityꢀ ofꢀ Auꢀ nanoparticlesꢀ stabilizedꢀ byꢀ poly(N‐vinyl‐2‐pyr‐
ꢀ
rolidone)ꢀ(PVP)ꢀemergedꢀwhenꢀtheꢀparticleꢀdiameterꢀwasꢀbe‐
lowꢀ~4ꢀnm;ꢀtheꢀcatalyticꢀactivityꢀdramaticallyꢀincreasedꢀasꢀtheꢀ
diameterꢀdecreasedꢀ[5,6].ꢀThisꢀsize‐specificꢀcatalysisꢀindicatedꢀ
thatꢀAuꢀclustersꢀsmallerꢀthanꢀ2ꢀnmꢀmightꢀbeꢀpromisingꢀcandi‐
datesꢀ forꢀ activeꢀ catalystsꢀ [6,7].ꢀ Anotherꢀ importantꢀ factorꢀ forꢀ
catalysisꢀ isꢀ theꢀ interactionꢀ betweenꢀ theꢀ Auꢀ clustersꢀ andꢀ theꢀ
solidꢀsupportsꢀorꢀpolymersꢀusedꢀforꢀstabilization.ꢀForꢀexample,ꢀ
unexpectedlyꢀfoundꢀthatꢀClꢀatomsꢀderivedꢀfromꢀaꢀgoldꢀprecur‐
–
sorꢀ (AuCl
4
)ꢀ wereꢀ adsorbedꢀ onꢀ theꢀ Auꢀ clusters.ꢀ Motivatedꢀ byꢀ
*
ꢀCorrespondingꢀauthor.ꢀTel/Fax:ꢀ+81‐3‐5841‐4363;ꢀE‐mail:ꢀtsukuda@chem.s.u–tokyo.ac.jpꢀ ꢀ
Thisꢀ workꢀ wasꢀ supportedꢀ byꢀ theꢀ Elementsꢀ Strategyꢀ Initiativeꢀ forꢀ Catalystsꢀ andꢀ Batteriesꢀ (ESICB)ꢀ andꢀ aꢀ Grant‐in‐Aidꢀ forꢀ Scientificꢀ Researchꢀ
26248003,ꢀ15H01042)ꢀfromꢀtheꢀMinistryꢀofꢀEducation,ꢀCulture,ꢀSports,ꢀScienceꢀandꢀTechnologyꢀ(MEXT)ꢀofꢀJapan.ꢀ
DOI:ꢀ10.1016/S1872‐2067(16)62501‐9ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ37,ꢀNo.ꢀ10,ꢀOctoberꢀ2016ꢀ ꢀ ꢀ
(

ꢀ
RyoꢀIshidaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1656–1661ꢀ
1657ꢀ
thisꢀfinding,ꢀweꢀstudiedꢀtheꢀeffectꢀofꢀtheꢀpreviouslyꢀoverlookedꢀ
halogensꢀonꢀtheꢀcatalysisꢀofꢀAuꢀclusters.ꢀ
Au:PVPꢀ clustersꢀ wereꢀ preparedꢀ usingꢀ aꢀ microfluidicꢀ mixerꢀ
asꢀfollowsꢀ[11].ꢀFirst,ꢀtwoꢀsolutionsꢀ(AꢀandꢀB)ꢀwereꢀpreparedꢀbyꢀ
mixingꢀtwoꢀ aqueousꢀ solutionsꢀ atꢀ 273ꢀ K:ꢀaqueousꢀsolutionsꢀofꢀ
pleteꢀhigh‐resolutionꢀmassꢀspectraꢀareꢀshownꢀinꢀFig.ꢀ2(a).ꢀIn‐
terestingly,ꢀ theꢀ Clꢀ adsorbatesꢀ wereꢀ observedꢀ mainlyꢀ onꢀ Auꢀ
clustersꢀwithꢀsizesꢀofꢀnꢀ=ꢀ34ꢀandꢀ43.ꢀFig.ꢀ3(a)ꢀandꢀ(e)ꢀrepresentsꢀ
theꢀnumberꢀdistributionꢀofꢀClꢀadsorbatesꢀonꢀtheꢀAu34ꢀandꢀAu43,ꢀ
respectively.ꢀOnꢀaverage,ꢀ7–9ꢀClꢀatomsꢀwereꢀadsorbedꢀonꢀtheꢀ
Au34ꢀandꢀAu43.ꢀWeakꢀeven–oddꢀoscillationsꢀwereꢀfoundꢀinꢀtheꢀ
distributions.ꢀTheꢀClꢀadductsꢀdidꢀnotꢀdisappear,ꢀevenꢀafterꢀre‐
peatedꢀ deionizationsꢀ performedꢀ usingꢀ centrifugation.ꢀ Theseꢀ
resultsꢀdemonstratedꢀforꢀtheꢀfirstꢀtimeꢀthatꢀClꢀatomsꢀwereꢀad‐
sorbedꢀ onꢀ theꢀ exposedꢀ surfaceꢀ ofꢀ PVP‐stabilizedꢀ Auꢀ clusters.ꢀ
TheꢀadsorptionꢀofꢀClꢀonꢀAu:PVPꢀmayꢀnotꢀbeꢀsurprising,ꢀgivenꢀ
thatꢀ Clꢀ atomsꢀ fromꢀ syntheticꢀ precursorsꢀ areꢀ commonlyꢀ ob‐
servedꢀ inꢀ phosphine‐protectedꢀ Auꢀ clustersꢀ suchꢀ asꢀ
PVPꢀ(666.6ꢀmgꢀinꢀ20ꢀmL)ꢀandꢀHAuCl
mixedꢀ toꢀ produceꢀ solutionꢀ A,ꢀ andꢀ aqueousꢀ solutionsꢀ ofꢀ PVPꢀ
666.6ꢀmgꢀinꢀ25ꢀmL)ꢀandꢀNaBH ꢀ(56.7ꢀmg,ꢀ5ꢀmL)ꢀwereꢀmixedꢀtoꢀ
4
ꢀ(30ꢀmmol/L,ꢀ10ꢀmL)ꢀwereꢀ
(
4
produceꢀsolutionꢀB.ꢀSolutionsꢀ AꢀandꢀBꢀwereꢀthenꢀloadedꢀintoꢀ
twoꢀsyringesꢀandꢀinjectedꢀintoꢀtheꢀmicromixerꢀ(SIMM‐V2,ꢀInsti‐
tutꢀfürꢀMikrotechnikꢀMainzꢀGmbH)ꢀplacedꢀinꢀanꢀiceꢀbath,ꢀusingꢀ
automaticallyꢀ actuatedꢀ syringeꢀ pumps.ꢀ Bothꢀ syringeꢀ pumpsꢀ
wereꢀ activatedꢀ simultaneously,ꢀ usingꢀ aꢀ constantꢀ flowꢀ rateꢀ ofꢀ
2
00ꢀmL/h.ꢀTheꢀelutedꢀsolutionꢀwasꢀcollected,ꢀandꢀthenꢀstirredꢀ
[Au11(PPh
3
)
8
Cl
2
]Cl,ꢀAu11(PPh
3
)
7
Cl
3
,ꢀandꢀAu55(PPh
3
)
12Cl ꢀ[14–16].ꢀ
6
−
−
−
atꢀ273ꢀKꢀforꢀ1ꢀh.ꢀSubsequentꢀdeionizationꢀofꢀtheꢀobtainedꢀhy‐
drosolꢀviaꢀultrafiltrationꢀyieldedꢀAu:PVP.ꢀFig.ꢀ1ꢀshowsꢀportionsꢀ
ofꢀ theꢀ matrix‐assistedꢀ laserꢀ desorption/ionizationꢀ (MALDI)ꢀ
massꢀspectraꢀofꢀtheꢀAu:PVP,ꢀrecordedꢀusingꢀdifferentꢀapparat‐
uses.ꢀ Fig.ꢀ 1(a)ꢀ showsꢀ aꢀ negative‐ionꢀ MALDIꢀ massꢀ spectrumꢀ
measuredꢀusingꢀaꢀlinearꢀtime‐of‐flightꢀ(TOF)ꢀmassꢀspectrome‐
terꢀ(AXIMA‐CFR,ꢀShimadzu)ꢀatꢀrelativelyꢀhighꢀlaserꢀfluence.ꢀWeꢀ
observedꢀ aꢀ seriesꢀ ofꢀ Au
fromꢀ theꢀ polymerꢀ stabilization,ꢀ inꢀ agreementꢀ withꢀ previousꢀ
resultsꢀ[12].ꢀFig.ꢀ1(b)ꢀshowsꢀaꢀmassꢀspectrumꢀrecordedꢀusingꢀaꢀ
TOFꢀ massꢀ spectrometerꢀ withꢀ aꢀ nominalꢀ flightꢀ pathꢀ ofꢀ >17ꢀ mꢀ
usingꢀ aꢀ spiralꢀ ionꢀ trajectoryꢀ (JMS‐S3000,ꢀ JEOL)ꢀ andꢀ minimalꢀ
Additionally,ꢀhalideꢀionsꢀsuchꢀasꢀCl ,ꢀBr ,ꢀorꢀI ꢀcanꢀbeꢀstronglyꢀ
adsorbedꢀonꢀmetalꢀsurfacesꢀ[17–19],ꢀandꢀtheirꢀadsorptionꢀontoꢀ
specificꢀ facetsꢀ hasꢀ beenꢀ usedꢀ toꢀ fabricateꢀ anisotropicꢀ
nanostructuresꢀsuchꢀasꢀrods,ꢀwires,ꢀandꢀplatesꢀ[20,21].ꢀHalidesꢀ
mayꢀ modulateꢀ theꢀ electronicꢀ structureꢀ ofꢀ theꢀ Auꢀ clustersꢀ byꢀ
removingꢀelectronicꢀchargesꢀ[22].ꢀHence,ꢀtheꢀobservationsꢀre‐
portedꢀhereꢀraisedꢀaꢀconcernꢀthatꢀtheseꢀoverlookedꢀClꢀadsorb‐
atesꢀstericallyꢀand/orꢀelectronicallyꢀaffectedꢀtheꢀcatalysisꢀofꢀtheꢀ
Auꢀclusters.ꢀ
Theꢀ effectsꢀ ofꢀ theꢀ halogenꢀ adsorbatesꢀ onꢀ theꢀ catalysisꢀ ofꢀ
Au:PVPꢀwereꢀstudiedꢀusingꢀtheꢀaerobicꢀoxidationꢀofꢀbenzylꢀal‐
coholꢀasꢀaꢀmodelꢀreaction.ꢀTheꢀamountꢀandꢀvarietyꢀofꢀhalogenꢀ
adsorbatesꢀwereꢀchangedꢀbyꢀmixingꢀanꢀaqueousꢀsolutionꢀofꢀKXꢀ
(Xꢀ =ꢀ Cl,ꢀ Br,ꢀ I)ꢀ withꢀ theꢀ hydrosolꢀ ofꢀ Au:PVPꢀ preparedꢀ fromꢀ
−
n
ꢀ clustersꢀ producedꢀ viaꢀ desorptionꢀ
laserꢀ fluenceꢀ forꢀ theꢀ measurements.ꢀ Someꢀ massꢀ peaksꢀ wereꢀ
observedꢀ inꢀ additionꢀ toꢀ thoseꢀ attributedꢀ toꢀ theꢀ Au
Theseꢀ interdigitatedꢀ massꢀ peaksꢀ wereꢀ assignedꢀ toꢀ Au
−
n
ꢀ clusters.ꢀ
−
Cl
n m
ꢀ
basedꢀonꢀtheꢀisotopeꢀpatternꢀanalysisꢀ(insetꢀofꢀFig.ꢀ1(b)),ꢀalt‐
houghꢀ Clꢀ wasꢀ notꢀ detectedꢀ inꢀ previousꢀ X‐rayꢀ photoelectronꢀ
spectroscopyꢀ (XPS)ꢀ measurementsꢀ ofꢀ Au:PVPꢀ [13].ꢀ Theꢀ com‐
Fig.ꢀ 1. Representativeꢀ negative‐ionꢀ MALDIꢀ massꢀ spectraꢀ forꢀ Au:PVP,
recordedꢀusingꢀaꢀlower‐resolutionꢀapparatusꢀatꢀaꢀrelativelyꢀhighꢀlaserꢀ
fluenceꢀ(a),ꢀandꢀaꢀhigher‐resolutionꢀapparatusꢀatꢀaꢀlowꢀlaserꢀfluenceꢀ(b).
Theꢀinsetꢀshowsꢀtheꢀexperimentalꢀ(bottom)ꢀandꢀsimulatedꢀ(top)ꢀisotop‐
Fig.ꢀ2.ꢀRepresentativeꢀnegative‐ionꢀMALDIꢀmassꢀspectraꢀforꢀsixꢀsamplesꢀ
ofꢀ Au:PVP.ꢀ (a)ꢀ Au:PVP(X‐0);ꢀ (b)ꢀ Au:PVP(Cl‐10),ꢀ (c)ꢀ Au:PVP(Br‐5),ꢀ (d)ꢀ
Au:PVP(Br‐10),ꢀ(e)ꢀAu:PVP(I‐5);ꢀ(f)ꢀAu:PVP(I‐10).ꢀ
icallyꢀresolvedꢀmassꢀpeaksꢀforꢀAu34Cl .ꢀ
7

1658ꢀ
RyoꢀIshidaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1656–1661ꢀ
andꢀ(f)).ꢀTheꢀpopulationsꢀofꢀsmallerꢀAuꢀclustersꢀwereꢀenhancedꢀ
byꢀtheꢀreactionꢀwithꢀKI,ꢀsuggestingꢀthatꢀtheꢀAuꢀclustersꢀwereꢀ
−
convertedꢀtoꢀsmallerꢀclustersꢀbyꢀetchingꢀwithꢀI ꢀ[23,24].ꢀTheseꢀ
reactivityꢀ trendsꢀ wereꢀ consistentꢀ withꢀ theꢀ orderꢀ ofꢀ theꢀ bondꢀ
−
−
−
strengthꢀwithꢀtheꢀAuꢀsurface:ꢀI ꢀ>ꢀBr ꢀ>ꢀCl ꢀ[19,25].ꢀTheꢀMALDIꢀ
massꢀanalysisꢀindicatedꢀthatꢀtheꢀAuꢀclusterꢀsizeꢀforꢀAu:PVPꢀdidꢀ
notꢀ changeꢀ appreciablyꢀ afterꢀ treatmentꢀ withꢀ aqueousꢀ KClꢀ orꢀ
KBrꢀ solutionsꢀ (Fig.ꢀ 2(a)–(d)).ꢀ Theꢀ sizeꢀ ofꢀ theꢀ Au:PVPꢀ clustersꢀ
beforeꢀandꢀafterꢀtheꢀtreatmentꢀwithꢀaqueousꢀKClꢀorꢀKBrꢀsolu‐
tionsꢀ wasꢀ alsoꢀ examinedꢀ usingꢀ transmissionꢀ electronꢀ micros‐
copyꢀ(TEM)ꢀandꢀultraviolet‐visibleꢀ(UV‐vis)ꢀspectroscopy.ꢀTheꢀ
TEMꢀ imagesꢀ andꢀ sizeꢀ distributionsꢀ forꢀ Au:PVP(Cl‐10)ꢀ andꢀ
Au:PVP(Br‐10)ꢀ(Fig.ꢀ4(a))ꢀindicatedꢀthatꢀtheꢀAu:PVP(X‐0)ꢀsizeꢀ
(1.2ꢀ±ꢀ0.3ꢀnm)ꢀwasꢀretainedꢀduringꢀtheꢀreactionꢀwithꢀKXꢀ(Xꢀ=ꢀCl,ꢀ
Br).ꢀTheꢀUV‐visꢀspectraꢀ(Fig.ꢀ4(b))ꢀalsoꢀconfirmedꢀtheꢀretentionꢀ
ofꢀtheꢀAuꢀclusterꢀsize.ꢀ
Theꢀnumberꢀdistributionsꢀofꢀhalogensꢀwereꢀexaminedꢀbasedꢀ
onꢀ theꢀ MALDIꢀ massꢀ spectra,ꢀ withꢀ aꢀ focusꢀ onꢀ Au:PVP(X‐0),ꢀ
Au:PVP(Cl‐10),ꢀ Au:PVP(Br‐5),ꢀ andꢀ Au:PVP(Br‐10).ꢀ Itꢀ isꢀ inter‐
estingꢀtoꢀnoteꢀthatꢀClꢀandꢀBrꢀwereꢀadsorbedꢀpreferentiallyꢀonꢀ
Au34ꢀ andꢀ Au43,ꢀ asꢀ inꢀ theꢀ caseꢀ ofꢀ Au:PVP(X‐0).ꢀ Theꢀ populationꢀ
(I
n,N)ꢀofꢀtheꢀAu ꢀ(nꢀ=ꢀ34ꢀorꢀ43)ꢀclustersꢀcontainingꢀhalogensꢀwithꢀ
n
theꢀtotalꢀnumberꢀNꢀwasꢀcalculatedꢀaccordingꢀtoꢀtheꢀfollowingꢀ
equation:ꢀ
m,l0
mlN
ml0
–
–
In,N

I Au Cl Br
n
m
l
I Au Cl Br
n
m
l






m,l
m,l
ꢀ
whereꢀmꢀandꢀlꢀrepresentꢀtheꢀnumberꢀofꢀClꢀandꢀBr,ꢀrespectively,ꢀ
−
−
andꢀI(Au
n
Cl
m
Br
l
)ꢀindicatesꢀtheꢀintensityꢀofꢀtheꢀAu
n
Cl
m
Br ꢀmassꢀ
l
peak.ꢀForꢀexample,ꢀI34,2ꢀwasꢀcalculatedꢀbyꢀdividingꢀtheꢀtotalꢀionꢀ
−
−
intensitiesꢀ ofꢀ Au34Cl
2
−,ꢀ Au34ClBr ,ꢀ andꢀ Au34Br
ꢀ byꢀ thoseꢀ ofꢀ
2
−
Au34Cl
m
Br
l
ꢀwithꢀm,ꢀlꢀ≥ꢀ0ꢀandꢀmꢀ+ꢀlꢀ≠ꢀ0.ꢀTheꢀpopulationsꢀofꢀI34,N
ꢀ
andꢀI43,NꢀareꢀplottedꢀasꢀaꢀfunctionꢀNꢀinꢀFig.ꢀ3.ꢀTheꢀreactionꢀwithꢀ
KClꢀincreasedꢀtheꢀnumberꢀofꢀClꢀadsorbatesꢀ(Fig.ꢀ3(b)ꢀandꢀ(f)).ꢀ
Fig.ꢀ3.ꢀNumberꢀdistributionsꢀofꢀClꢀ(redꢀbars)ꢀandꢀBrꢀ(blueꢀbars)ꢀadsorb‐
ates.ꢀ (a)ꢀ Au:PVP(X‐0),ꢀ (b)ꢀ Au:PVP(Cl‐10),ꢀ (c)ꢀ Au:PVP(Br‐5),ꢀ andꢀ (d)ꢀ
Au:PVP(Br‐10)ꢀ forꢀ Au34;ꢀ (e)ꢀ Au:PVP(X‐0),ꢀ (f)ꢀ Au:PVP(Cl‐10),ꢀ (g)ꢀ
Au:PVP(Br‐5),ꢀandꢀ(h)ꢀAu:PVP(Br‐10)ꢀforꢀAu43.ꢀ
HAuCl .ꢀTheꢀmolarꢀratioꢀ(x)ꢀofꢀKXꢀwithꢀrespectꢀtoꢀtheꢀAuꢀclus‐
4
ters,ꢀcalculatedꢀassumingꢀaꢀclusterꢀsizeꢀofꢀ40,ꢀwasꢀvariedꢀfromꢀ5ꢀ
toꢀ 20.ꢀ Theꢀ clusterꢀ samplesꢀ obtainedꢀ afterꢀ deionizationꢀ
(achievedꢀ viaꢀ centrifugalꢀ ultrafiltrationꢀ withꢀ water)ꢀ areꢀ re‐
ferredꢀtoꢀasꢀAu:PVP(X‐x)ꢀ(Xꢀ=ꢀCl,ꢀBr,ꢀI)ꢀhereafter.ꢀAccordingꢀtoꢀ
thisꢀnotation,ꢀtheꢀas‐preparedꢀAu:PVPꢀclustersꢀcanꢀbeꢀdescribedꢀ
asꢀAu:PVP(X‐0).ꢀTheꢀamountꢀofꢀhalogenꢀatomsꢀadsorbedꢀonꢀtheꢀ
Au:PVP(X‐x)ꢀ wasꢀ probedꢀ usingꢀ MALDIꢀ massꢀ analysis.ꢀ Fig.ꢀ 2ꢀ
showsꢀ theꢀ negative‐ionꢀ MALDIꢀ massꢀ spectraꢀ forꢀ theꢀ
−
−
Au:PVP(X‐x).ꢀ Inꢀ additionꢀ toꢀ Au
n
,ꢀ Au
n
Cl ꢀ clustersꢀ wereꢀ ob‐
m
servedꢀforꢀAu:PVP(X‐0)ꢀandꢀAu:PVP(Cl‐10)ꢀ(Fig.ꢀ2(a)ꢀandꢀ(b)),ꢀ
−
andꢀ Cl‐ꢀ andꢀ Br‐containingꢀ Au
n
Cl
m
Br
l
ꢀ wereꢀ observedꢀ inꢀ theꢀ
−
massꢀspectraꢀofꢀAu:PVP(Br‐x)ꢀ(Fig.ꢀ2(c)ꢀandꢀ(d)).ꢀTheꢀAu
n
ꢀsizeꢀ
distributionsꢀdidꢀnotꢀchangeꢀappreciablyꢀafterꢀtheꢀreactionꢀwithꢀ
KClꢀorꢀKBr.ꢀAꢀcloseꢀinspectionꢀofꢀFig.ꢀ2(a)–(d)ꢀrevealedꢀthatꢀClꢀ
andꢀBrꢀwereꢀadsorbedꢀpreferentiallyꢀonꢀtheꢀAu34ꢀandꢀAu43ꢀclus‐
ters.ꢀ Inꢀ contrast,ꢀ theꢀ massꢀ spectraꢀ ofꢀ Au:PVP(I‐5)ꢀ andꢀ
Au:PVP(I‐10)ꢀshowedꢀsignificantlyꢀdifferentꢀpatternsꢀ(Fig.ꢀ2(e)ꢀ
Fig.ꢀ 4.ꢀ (a)ꢀ Representativeꢀ TEMꢀ imagesꢀ andꢀ sizeꢀ distributionsꢀ forꢀ
Au:PVP(Cl‐10)ꢀ andꢀ Au:PVP(Br‐10).ꢀ (b)ꢀ UV‐visꢀ absorptionꢀ spectraꢀ forꢀ
Au:PVP(Cl‐x)ꢀandꢀAu:PVP(Br‐x).ꢀ

ꢀ
RyoꢀIshidaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1656–1661ꢀ
1659ꢀ
Theꢀadditionꢀofꢀ5ꢀeq.ꢀofꢀKBrꢀtoꢀAu:PVPꢀcausedꢀnearlyꢀhalfꢀofꢀClꢀ
adsorbatesꢀ toꢀ beꢀ replacedꢀ withꢀ Brꢀ (Fig.ꢀ 3(c)ꢀ andꢀ (g)).ꢀ Inꢀ
Au:PVP(Br‐10),ꢀtheꢀoriginallyꢀadsorbedꢀClꢀatomsꢀwereꢀreplacedꢀ
almostꢀ completelyꢀ withꢀ Brꢀ (Fig.ꢀ 3(d)ꢀ andꢀ (h)).ꢀ Theseꢀ resultsꢀ
demonstrateꢀthatꢀBrꢀwasꢀboundꢀmoreꢀstronglyꢀtoꢀtheꢀAuꢀclus‐
tersꢀthanꢀCl,ꢀasꢀpreviouslyꢀreportedꢀforꢀtheꢀAuꢀsurfaceꢀ[19,25].ꢀ
Theꢀ electronicꢀ structureꢀ ofꢀ Au:PVP(X‐0)ꢀ andꢀ
Au:PVP(Br‐160)ꢀwasꢀanalyzedꢀusingꢀXPSꢀ(Fig.ꢀ5).ꢀTheꢀbindingꢀ
energiesꢀofꢀAuꢀ4f7/2ꢀforꢀAu:PVP(X‐0)ꢀandꢀAu:PVP(Br‐160)ꢀwereꢀ
determinedꢀtoꢀbeꢀ82.6ꢀandꢀ82.7ꢀeV,ꢀrespectively.ꢀTheseꢀvaluesꢀ
wereꢀslightlyꢀsmallerꢀthanꢀthatꢀofꢀbulkꢀgoldꢀ(84.0ꢀeV)ꢀdueꢀtoꢀtheꢀ
electronꢀ donationꢀ fromꢀ PVPꢀ [8,26],ꢀ butꢀ wereꢀ similarꢀ toꢀ eachꢀ
Tableꢀ1ꢀ
CatalyticꢀpropertiesꢀofꢀAu:PVP(X‐x)ꢀforꢀtheꢀaerobicꢀoxidationꢀofꢀbenzylꢀ
alcohol.ꢀ
2 atom% Au:PVP
300 mol% K CO3
2
H O, air, 300 K, 1 h
2
1
2
3
4
Selectivityꢀa,cꢀ(%)ꢀ
Catalystꢀ
xꢀ
Conversionꢀa,bꢀ(%)ꢀ
2
ꢀ
3ꢀ
4ꢀ
11ꢀ
14ꢀ
14ꢀ
12ꢀ
Au:PVP(X‐0)ꢀ
Au:PVP(Cl‐x)ꢀ
ꢀ 0ꢀ
10ꢀ
20ꢀ
ꢀ 5ꢀ
64ꢀ
66ꢀ
65ꢀ
42ꢀ
19ꢀ
13ꢀ
16ꢀ
22ꢀ
21ꢀ
51ꢀ
46ꢀ
50ꢀ
73ꢀ
64ꢀ
65ꢀ
37ꢀ
51ꢀ
48ꢀ
Au:PVP(Br‐x)ꢀ
1
2
0ꢀ
0ꢀ
ꢀ 3ꢀ
ꢀ 2ꢀ
other.ꢀTheꢀelectronꢀaffinitiesꢀofꢀtheꢀbareꢀAu
0–40ꢀwereꢀdeterminedꢀtoꢀbeꢀinꢀtheꢀrangeꢀofꢀ3.3–4.2ꢀeV,ꢀusingꢀ
photoelectronꢀspectroscopyꢀ[27,28].ꢀTheseꢀelectronꢀaffinitiesꢀofꢀ
theꢀAu ꢀclustersꢀ(nꢀ≈ꢀ30–40)ꢀwereꢀcomparableꢀtoꢀthoseꢀofꢀtheꢀ
halogensꢀ(3.61,ꢀ3.36,ꢀandꢀ3.06ꢀeVꢀforꢀCl,ꢀBr,ꢀandꢀI,ꢀrespectively).ꢀ
ThisꢀsuggestedꢀthatꢀtheꢀelectronicꢀstatesꢀofꢀtheꢀAu ꢀclustersꢀ(nꢀ≈ꢀ
0–40)ꢀwereꢀnotꢀsignificantlyꢀaffectedꢀbyꢀtheꢀhalogenꢀadsorb‐
n
ꢀclustersꢀwithꢀnꢀ≈ꢀ
3
Reactionꢀconditions:ꢀPhCH
2
OHꢀ(25.9ꢀµL,ꢀ0.25ꢀmmol),ꢀK
2
CO
2
3
ꢀ(103.7ꢀmg,ꢀ
Oꢀ (5ꢀmL),ꢀairꢀ
0.75ꢀmmol),ꢀ Au:PVPꢀ (0.5ꢀmmol/L,ꢀ 10ꢀmL,ꢀ2ꢀatom%),ꢀ H
n
pressureꢀ1ꢀatm,ꢀtemperatureꢀ300ꢀK,ꢀreactionꢀtimeꢀ1ꢀh.ꢀ
a
ꢀDeterminedꢀbyꢀgasꢀchromatography.ꢀ
bꢀDefinedꢀasꢀtheꢀ ratioꢀofꢀ theꢀamountꢀofꢀ 1ꢀconsumedꢀinꢀtheꢀoxidationꢀ
reactionꢀtoꢀtheꢀamountꢀofꢀ1ꢀatꢀtheꢀinitialꢀtime.ꢀ
n
3
cꢀ
Definedꢀasꢀtheꢀratioꢀofꢀ1ꢀconvertedꢀtoꢀtheꢀcorrespondingꢀproducts.ꢀ
ates;ꢀ thisꢀ wasꢀ inꢀ sharpꢀ contrastꢀ toꢀ theꢀ smallerꢀ Auꢀ clusters,ꢀ
whereꢀtheꢀhalogensꢀactedꢀasꢀelectronꢀacceptorsꢀ[14–16,22].ꢀ
TheꢀcatalyticꢀpropertiesꢀofꢀAu:PVP(X‐x)ꢀ(Xꢀ=ꢀClꢀandꢀBr)ꢀwereꢀ
evaluatedꢀusingꢀtheꢀaerobicꢀoxidationꢀofꢀbenzylꢀalcoholꢀinꢀairꢀasꢀ
aꢀ testꢀ reactionꢀ (Tableꢀ 1)ꢀ toꢀ revealꢀ theꢀ effectꢀ ofꢀ theꢀ Clꢀ andꢀ Brꢀ
adsorbatesꢀ onꢀ theꢀ catalysisꢀ ofꢀ theꢀ Auꢀ clusters.ꢀ Theꢀ effectꢀ ofꢀ Iꢀ
adsorbatesꢀ wasꢀ notꢀ evaluated,ꢀ becauseꢀ theꢀ clusterꢀ sizesꢀ ofꢀ
Au:PVP(I‐x)ꢀ wereꢀ significantlyꢀ differentꢀ fromꢀ thatꢀ ofꢀ
Au:PVP(X‐0)ꢀ (Fig.ꢀ 2(e)ꢀ andꢀ (f)).ꢀ Benzylꢀ alcoholꢀ (25.9ꢀ µL,ꢀ 0.25ꢀ
ꢀ
Au:PVP(Cl‐x)ꢀdidꢀnotꢀchangeꢀwithꢀrespectꢀtoꢀx.ꢀThisꢀresultꢀre‐
flectedꢀtheꢀdifferentꢀadsorptionꢀstrengthsꢀofꢀClꢀandꢀBr.ꢀAlthoughꢀ
theꢀClꢀadsorbatesꢀcouldꢀnotꢀbeꢀremoved,ꢀevenꢀusingꢀrepeatedꢀ
centrifugalꢀultrafiltration,ꢀtheyꢀwereꢀdesorbedꢀduringꢀtheꢀcata‐
lyticꢀreaction;ꢀelementalꢀanalysisꢀshowedꢀthatꢀtheꢀamountꢀofꢀClꢀ
forꢀ Au:PVP(X‐0)ꢀ wasꢀ reducedꢀ fromꢀ 0.32ꢀ toꢀ <0.01ꢀ wt%ꢀ afterꢀ
catalyticꢀ usageꢀ underꢀ theꢀ conditionsꢀ shownꢀ inꢀ Tableꢀ 1.ꢀ Thisꢀ
resultꢀ suggestedꢀ thatꢀ benzylꢀ alkoxideꢀ producedꢀ underꢀ basicꢀ
conditionsꢀreplacedꢀtheꢀClꢀadsorbateꢀforꢀtheꢀsubsequentꢀoxida‐
tionꢀreaction.ꢀTherefore,ꢀtheꢀcatalyticꢀactivityꢀwasꢀretainedꢀevenꢀ
whenꢀtheꢀamountꢀofꢀClꢀadsorbatesꢀisꢀincreased.ꢀInꢀcontrast,ꢀtheꢀ
reactionꢀwasꢀretardedꢀsignificantlyꢀbyꢀtheꢀBrꢀadsorbates,ꢀsug‐
gestingꢀ thatꢀ theyꢀ wereꢀ notꢀ removedꢀ efficientlyꢀ byꢀ theꢀ benzylꢀ
alkoxide.ꢀBecauseꢀtheꢀelectronicꢀstateꢀofꢀtheꢀAuꢀclustersꢀwasꢀnotꢀ
alteredꢀ appreciablyꢀ (Fig.ꢀ 5)ꢀ byꢀ theꢀ adsorptionꢀ ofꢀ Br,ꢀ theꢀ de‐
creasedꢀconversionꢀatꢀlargerꢀamountsꢀofꢀBrꢀadsorbatesꢀcouldꢀbeꢀ
explainedꢀbyꢀtheꢀstericꢀblockingꢀofꢀtheꢀactiveꢀsites.ꢀ
mmol),ꢀ K
mixedꢀinꢀaꢀtestꢀtube.ꢀTheꢀhydrosolꢀofꢀAu:PVP(X‐x)ꢀ(0.5ꢀmmol/L,ꢀ
0ꢀmL,ꢀ2ꢀatom%)ꢀwasꢀthenꢀaddedꢀtoꢀtheꢀmixedꢀsolution.ꢀTheꢀ
2 3 2
CO ꢀ (103.7ꢀ mg,ꢀ 0.75ꢀ mmol),ꢀ andꢀ H Oꢀ (5ꢀ mL)ꢀ wereꢀ
1
reactionꢀmixtureꢀwasꢀstirredꢀvigorouslyꢀatꢀ300ꢀKꢀforꢀ1ꢀh,ꢀandꢀ
thenꢀquenchedꢀwithꢀ1ꢀmol/LꢀHCl.ꢀTheꢀproductsꢀwereꢀextractedꢀ
withꢀethylꢀacetate,ꢀandꢀanalyzedꢀbyꢀgasꢀchromatography.ꢀTheꢀ
catalysisꢀ resultsꢀ forꢀ Au:PVP(X‐x)ꢀ areꢀ summarizedꢀ inꢀ Tableꢀ 1,ꢀ
andꢀtheꢀconversionsꢀareꢀshownꢀasꢀbarꢀgraphsꢀinꢀFig.ꢀ6.ꢀTheseꢀ
resultsꢀdemonstratedꢀthatꢀtheꢀeffectsꢀofꢀClꢀandꢀBrꢀonꢀtheꢀcataly‐
sisꢀ wereꢀveryꢀdifferent.ꢀTheꢀcatalyticꢀactivityꢀ ofꢀ Au:PVP(Br‐x)ꢀ
graduallyꢀ decreasedꢀ withꢀ increasingꢀ x,ꢀ whileꢀ thatꢀ ofꢀ
Fig.ꢀ 6.ꢀ Catalyticꢀ activityꢀ ofꢀ Au:PVP(X‐0)ꢀ (a),ꢀ Au:PVP(Cl‐10)ꢀ (b),ꢀ
Au:PVP(Cl‐20)ꢀ (c),ꢀ Au:PVP(Br‐5)ꢀ (d),ꢀ Au:PVP(Br‐10)ꢀ (e),ꢀ andꢀ
Au:PVP(Br‐20)ꢀ(f).ꢀ
Fig.ꢀ5.ꢀPhotoelectronꢀspectraꢀforꢀAu:PVP(X‐0)ꢀ(a)ꢀandꢀAu:PVP(Br‐160)ꢀ
(b).ꢀ

1660ꢀ
RyoꢀIshidaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1656–1661ꢀ
Theꢀ determinationꢀ ofꢀ theꢀ distributionꢀ ofꢀ clusterꢀ composi‐
301–309.ꢀ
[
2] M.ꢀHaruta,ꢀChem.ꢀRec.,ꢀ2003,ꢀ3,ꢀ75–87.ꢀ
3] A.ꢀStephen,ꢀK.ꢀHashmi,ꢀG.ꢀJ.ꢀHutchings,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.,ꢀ2006,ꢀ
tionsꢀinꢀtheꢀoriginalꢀAu:PVP(X‐0)ꢀsampleꢀbasedꢀonꢀtheꢀMALDIꢀ
massꢀspectraꢀ(Figs.ꢀ1(b)ꢀandꢀ2(a))ꢀwasꢀaꢀformidableꢀtask.ꢀThisꢀ
wasꢀbecauseꢀMALDIꢀmassꢀspectraꢀareꢀtypicallyꢀaffectedꢀbyꢀtheꢀ
distributionꢀofꢀtheꢀclusterꢀcompositionsꢀinꢀtheꢀsample,ꢀandꢀbyꢀ
theirꢀ ionizationꢀ efficiencyꢀ andꢀ fragmentationꢀ process,ꢀ whichꢀ
dependꢀ onꢀ theꢀ compositionꢀ ofꢀ theꢀ clusters.ꢀ Nevertheless,ꢀ theꢀ
[
4
5,ꢀ7896–7936.ꢀ
4] Y.ꢀLiu,ꢀH.ꢀTsunoyama,ꢀT.ꢀAkita,ꢀS.ꢀXie,ꢀT.ꢀTsukuda,ꢀACSꢀCatal.,ꢀ2011,ꢀ
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[
[
[
[
1
4
−
−
preferentialꢀ observationꢀ ofꢀ Au34Cl
thatꢀ theꢀ Au34Cl ꢀ andꢀ Au43Cl ꢀ clustersꢀ inꢀ theirꢀ neutralꢀ formꢀ
dominatedꢀinꢀtheꢀAu:PVP(X‐0)ꢀsample.ꢀTheꢀspecialꢀstabilityꢀofꢀ
ꢀcouldꢀbeꢀexplainedꢀbyꢀtheꢀclosureꢀofꢀtheꢀelectronicꢀshellꢀ
m
ꢀ andꢀ Au43Cl
m
ꢀ suggestedꢀ
m
m
8
Au34X
m
[8] H.ꢀ Tsunoyama,ꢀ N.ꢀ Ichikuni,ꢀ H.ꢀ Sakurai,ꢀ T.ꢀ Tsukuda,ꢀ J.ꢀ Am.ꢀ Chem.ꢀ
Soc.,ꢀ2009,ꢀ131,ꢀ7086–7093.ꢀ
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vasasith,ꢀJ.ꢀLimtrakul,ꢀT.ꢀTsukuda,ꢀACSꢀCatal.,ꢀ2014,ꢀ4,ꢀ3696–3700.ꢀ
10] Y.ꢀWang,ꢀX.ꢀK.ꢀWan,ꢀL.ꢀT.ꢀRen,ꢀH.ꢀF.ꢀSu,ꢀG.ꢀLi,ꢀS.ꢀMalola,ꢀS.ꢀC.ꢀLin,ꢀZ.ꢀC.ꢀ
withꢀ34ꢀvalenceꢀelectronsꢀ[27,28]ꢀifꢀweꢀassumedꢀthatꢀtheꢀelec‐
tronꢀtransferꢀfromꢀAu34ꢀtoꢀClꢀwasꢀnegligiblyꢀsmall.ꢀHowever,ꢀtheꢀ
originꢀofꢀtheꢀefficientꢀformationꢀofꢀAu43
questionꢀ[12].ꢀTheꢀsignificantꢀreductionꢀinꢀtheꢀcatalyticꢀactivityꢀ
whenꢀ Clꢀ wasꢀ replacedꢀ withꢀ Brꢀ indicatedꢀ thatꢀ magicꢀ Au Cl
clustersꢀ(nꢀ=ꢀ34,ꢀ43)ꢀinꢀAu:PVP(X‐0)ꢀmadeꢀanꢀessentialꢀcontri‐
X ꢀisꢀcurrentlyꢀanꢀopenꢀ
m
[
Tang,ꢀH.ꢀHäkkinen,ꢀB.ꢀK.ꢀTeo,ꢀQ.ꢀM.ꢀWang,ꢀN.ꢀF.ꢀZheng,ꢀJ.ꢀAm.ꢀChem.ꢀ
Soc.,ꢀ2016,ꢀ138,ꢀ3278–3281.ꢀ
n
m
ꢀ
[
[
[
11] H.ꢀ Tsunoyama,ꢀ N.ꢀ Ichikuni,ꢀ T.ꢀ Tsukuda,ꢀ Langmuir,ꢀ 2008,ꢀ 24,ꢀ
butionꢀtoꢀtheꢀcatalyticꢀactivity.ꢀFurtherꢀinvestigationꢀisꢀneededꢀ
toꢀdetermineꢀwhyꢀtheꢀmagic‐sizedꢀAuꢀclustersꢀwereꢀcatalytical‐
lyꢀreactive.ꢀ
1
1327–11330.ꢀ
12] H.ꢀ Tsunoyama,ꢀ T.ꢀ Tsukuda,ꢀ J.ꢀ Am.ꢀ Chem.ꢀ Soc.,ꢀ 2009,ꢀ 131,ꢀ
8216–18217.ꢀ
13] H.ꢀ Tsunoyama,ꢀ H.ꢀ Sakurai,ꢀ N.ꢀ Ichikuni,ꢀ Y.ꢀ Negishi,ꢀ T.ꢀ Tsukuda,ꢀ
Langmuir,ꢀ2004,ꢀ20,ꢀ11293–11296.ꢀ
[14] G.ꢀSchmid,ꢀChem.ꢀRev.,ꢀ1992,ꢀ92,ꢀ1709–1727.ꢀ
[15] L.ꢀ C.ꢀ McKenzie,ꢀ T.ꢀ O.ꢀ Zaikova,ꢀ J.ꢀ E.ꢀ Hutchison,ꢀ J.ꢀ Am.ꢀ Chem.ꢀ Soc.,ꢀ
2014,ꢀ136,ꢀ13426–13435.ꢀ
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17] J.ꢀ Lipkowski,ꢀ Z.ꢀ Shi,ꢀ A.ꢀ Chen,ꢀ B.ꢀ Pettinger,ꢀ C.ꢀ Bilger,ꢀ Electrochim.ꢀ
Acta.,ꢀ1998,ꢀ43,ꢀ2875–2888.ꢀ
18] A.ꢀChen,ꢀZ.ꢀShi,ꢀD.ꢀBizzotto,ꢀJ.ꢀLipkowski,ꢀB.ꢀPettinger,ꢀC.ꢀBilger,ꢀJ.ꢀ
Electroanal.ꢀChem.,ꢀ1999,ꢀ467,ꢀ342–353.ꢀ
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Soc.,ꢀ2012,ꢀ134,ꢀ14542–14554.ꢀ
1
Inꢀ summary,ꢀ weꢀ demonstratedꢀ theꢀ adsorptionꢀ ofꢀ Clꢀ atomsꢀ
onꢀAuꢀclustersꢀstabilizedꢀbyꢀPVPꢀusingꢀmassꢀspectrometry,ꢀandꢀ
investigatedꢀtheirꢀeffectꢀonꢀtheꢀcatalyticꢀproperties.ꢀTheꢀ cata‐
lyticꢀactivityꢀofꢀAu:PVPꢀwasꢀnotꢀaffectedꢀbyꢀtheꢀpresenceꢀofꢀCl,ꢀ
butꢀitꢀwasꢀsignificantlyꢀsuppressedꢀbyꢀtheꢀBrꢀadsorbates.ꢀThisꢀ
differenceꢀwasꢀattributedꢀtoꢀtheꢀdifferentꢀbindingꢀstrengthsꢀtoꢀ
gold.ꢀ Aꢀ substantialꢀ reductionꢀ inꢀ theꢀ catalysisꢀ wasꢀ observedꢀ
whenꢀtheꢀClꢀwasꢀreplacedꢀwithꢀBrꢀonꢀtheꢀAuꢀclusters,ꢀsuggestingꢀ
[
[
thatꢀmagic‐sizedꢀAu
n
ꢀclustersꢀ(nꢀ=ꢀ34,ꢀ43)ꢀdominantlyꢀactedꢀasꢀ
catalysts.ꢀ
[
[
Acknowledgmentsꢀ
[
21] S.ꢀ E.ꢀ Lohse,ꢀ N.ꢀ D.ꢀ Burrows,ꢀ L.ꢀ Scarabelli,ꢀ L.ꢀ M.ꢀ Liz‐Marzan,ꢀ C.ꢀ J.ꢀ
Murphy,ꢀChem.ꢀMater.,ꢀ2014,ꢀ26,ꢀ34–43.ꢀ
WeꢀthankꢀProf.ꢀHiroshiꢀNishiharaꢀ(TheꢀUniversityꢀofꢀTokyo)ꢀ
forꢀprovidingꢀusꢀwithꢀaccessꢀtoꢀtheꢀTEMꢀapparatus.ꢀ
[22] M.ꢀWalter,ꢀJ.ꢀAkola,ꢀO.ꢀLopez‐Acevedo,ꢀP.ꢀD.ꢀJadzinsky,ꢀG.ꢀCalero,ꢀC.ꢀ
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