Catalytic oxidation of styrene to benzaldehyde over a copper Schiff-base/SBA-15 catalyst

Article abstract of DOI:10.1016/S1872-2067(14)60131-5

The amino-modified mesoporous material SBA-15 (NH₂-SBA-15) was prepared via co-condensation of tetraethylorthosilicate with 3-aminopropyltriethoxysilane in the presence of an amphiphilic triblock copolymer as a pore-directing agent under acidic

Full text of DOI:10.1016/S1872-2067(14)60131-5

ChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726
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ꢀ ꢀ ꢀ
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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
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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
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Article
Catalyticꢀoxidationꢀofꢀstyreneꢀtoꢀbenzaldehydeꢀoverꢀaꢀcopperꢀ
Schiff‐base/SBA‐15ꢀcatalystꢀ
XuechengꢀZhu,ꢀRuweiꢀShen,ꢀLixiongꢀZhangꢀ*ꢀ
StateꢀKeyꢀLaboratoryꢀofꢀMaterials‐OrientedꢀChemicalꢀEngineering,ꢀCollegeꢀofꢀChemistryꢀandꢀChemicalꢀEngineering,ꢀNanjingꢀTechꢀUniversity,ꢀNanjingꢀ
210009,ꢀJiangsu,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Theꢀamino‐modifiedꢀmesoporousꢀmaterialꢀSBA‐15ꢀ(NH ‐SBA‐15)ꢀwasꢀpreparedꢀviaꢀco‐condensationꢀ
2
Receivedꢀ1ꢀMarchꢀ2014ꢀ
Acceptedꢀ28ꢀAprilꢀ2014ꢀ
Publishedꢀ20ꢀOctoberꢀ2014ꢀ
ofꢀ tetraethylorthosilicateꢀ withꢀ 3‐aminopropyltriethoxysilaneꢀ inꢀ theꢀ presenceꢀ ofꢀ anꢀ amphiphilicꢀ
triblockꢀ copolymerꢀ asꢀ aꢀ pore‐directingꢀ agentꢀ underꢀ acidicꢀ conditions.ꢀ Theꢀ SBA‐15‐supportedꢀ Cu
Schiff‐baseꢀ complexꢀ (Cu‐SBA‐15)ꢀ wasꢀ thenꢀ synthesizedꢀ byꢀ condensationꢀ ofꢀ salicylaldehydeꢀ withꢀ
NH
2
‐SBA‐15,ꢀfollowedꢀbyꢀtheꢀadditionꢀofꢀaꢀsolutionꢀofꢀCu(NO
3
) .ꢀTheꢀsupportedꢀcomplexꢀwasꢀsys‐
2
tematicallyꢀcharacterizedꢀbyꢀelementalꢀanalysis,ꢀinductiveꢀcoupledꢀhighꢀfrequencyꢀplasmaꢀatomicꢀ
emissionꢀspectrometry,ꢀpowderꢀX‐rayꢀdiffraction,ꢀFourierꢀtransformꢀinfraredꢀspectroscopy,ꢀultravi‐
Keywords:ꢀ
Copper(II)ꢀSchiffꢀbaseꢀ
SBA‐15ꢀ
Styreneꢀoxidationꢀ
Benzaldehydeꢀ
Heterogeneousꢀcatalysis
olet‐visibleꢀspectroscopy,ꢀfieldꢀscanningꢀelectronꢀmicroscopy,ꢀtransmissionꢀelectronꢀmicroscopy,ꢀN
2
absorption‐desorption,ꢀandꢀthermoꢀgravimetricꢀanalysis,ꢀandꢀwasꢀusedꢀasꢀtheꢀcatalystꢀforꢀtheꢀselec‐
tiveꢀoxidationꢀofꢀstyreneꢀtoꢀbenzaldehyde.ꢀTheꢀinfluenceꢀofꢀtheꢀreactionꢀparametersꢀwasꢀassessed.ꢀ
Theꢀmaximumꢀconversionꢀofꢀstyreneꢀwasꢀ84.4%ꢀandꢀtheꢀselectivityꢀforꢀbenzaldehydeꢀwasꢀ83.9%,ꢀ
whenꢀtheꢀreactionꢀwasꢀconductedꢀwithꢀaꢀ2:1ꢀmolarꢀratioꢀofꢀH
2
O :styreneꢀinꢀtheꢀpresenceꢀofꢀ3.8ꢀwt%ꢀ
2
–1
catalystꢀatꢀ100ꢀ°Cꢀforꢀ8ꢀh.ꢀTheꢀTOFꢀwasꢀ261.1ꢀh ,ꢀandꢀtheꢀcatalystꢀcouldꢀbeꢀusedꢀthreeꢀtimesꢀwithoutꢀ
significantꢀ lossꢀ ofꢀ activity.ꢀ Theꢀ uniformlyꢀ sizedꢀ poreꢀ channels,ꢀ highꢀ specificꢀ surfaceꢀ area,ꢀ andꢀ
well‐distributedꢀactiveꢀcentersꢀofꢀtheꢀcatalystꢀmayꢀcontributeꢀtoꢀtheꢀhighꢀactivity.ꢀ
©ꢀ2014,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1.ꢀ ꢀ Introductionꢀ
catalyst.ꢀNevertheless,ꢀtheꢀlackꢀofꢀanꢀefficientꢀcatalystꢀhasꢀcur‐
tailedꢀtheꢀadoptionꢀofꢀthisꢀmethodꢀ[3].ꢀ
Benzaldehydeꢀ isꢀ anꢀ importantꢀ andꢀ valuableꢀ fineꢀ chemicalꢀ
Recently,ꢀ theꢀ synthesisꢀ ofꢀ benzaldehydeꢀ byꢀ styreneꢀ oxida‐
tionꢀ hasꢀ drawnꢀ muchꢀ attentionꢀ asꢀ theꢀ processꢀ isꢀ simpleꢀ andꢀ
environmentallyꢀfriendlyꢀ[4,5].ꢀTheꢀkeyꢀtoꢀtheꢀsuccessfulꢀuseꢀofꢀ
thisꢀ transformationꢀ isꢀ theꢀ designꢀ ofꢀ anꢀ active,ꢀ selective,ꢀ andꢀ
recyclableꢀ catalyst.ꢀ Variousꢀ catalysts,ꢀ suchꢀ asꢀ metalꢀ oxidesꢀ
[6–10],ꢀmetalsꢀ[11,12],ꢀmetalꢀdopedꢀzeolitesꢀ[13,14],ꢀsolidꢀacidsꢀ
[15,16],ꢀandꢀmetalꢀSchiffꢀbasesꢀorꢀsalenꢀcomplexesꢀ[17,18],ꢀhaveꢀ
beenꢀdiscussed.ꢀAmongꢀthese,ꢀtheꢀmetalꢀSchiff‐baseꢀcomplexesꢀ
demonstrateꢀhighꢀcatalyticꢀreactivity.ꢀHowever,ꢀtheseꢀhomoge‐
nousꢀcatalystsꢀareꢀusuallyꢀdifficultꢀtoꢀseparateꢀfromꢀtheꢀreactionꢀ
mixture,ꢀ makingꢀ theꢀ entireꢀ catalyticꢀ processꢀ unattractiveꢀ forꢀ
thatꢀhasꢀbeenꢀwidelyꢀusedꢀinꢀtheꢀsynthesisꢀofꢀseveralꢀsubstanc‐
es,ꢀincludingꢀ perfumes,ꢀ dyes,ꢀandꢀ pharmaceuticalsꢀ[1].ꢀGener‐
allyꢀ speaking,ꢀ itꢀ canꢀ beꢀ obtainedꢀ viaꢀ severalꢀ routesꢀ includingꢀ
benzylꢀalcoholꢀoxidation,ꢀindirectꢀelectrochemicalꢀoxidationꢀofꢀ
toluene,ꢀ benzoicꢀ acidꢀ hydrogenation,ꢀ andꢀ benzylꢀ chlorideꢀ hy‐
drolysisꢀ[2].ꢀHowever,ꢀtheseꢀmethodsꢀsufferꢀfromꢀlengthyꢀpro‐
cedures,ꢀ expensiveꢀ startingꢀ materials,ꢀ andꢀ theꢀ generationꢀ ofꢀ
copiousꢀandꢀtoxicꢀwaste,ꢀwhichꢀisꢀenvironmentallyꢀundesirable.ꢀ
Theꢀmostꢀidealꢀ preparationꢀmethodꢀisꢀtheꢀdirectꢀoxidationꢀofꢀ
tolueneꢀwithꢀairꢀorꢀoxygenꢀasꢀtheꢀoxidantꢀinꢀtheꢀpresenceꢀofꢀaꢀ
*ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐25‐83172265;ꢀFax:ꢀ+86‐25‐83172263;ꢀE‐mail:ꢀlixzhang@njtech.edu.cnꢀ ꢀ ꢀ
DOI:ꢀ10.1016/S1872‐2067(14)60131‐5ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ35,ꢀNo.ꢀ10,ꢀOctoberꢀ2014ꢀ ꢀ ꢀ

ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
1717ꢀ
industrialꢀapplication.ꢀConsequently,ꢀmuchꢀattentionꢀhasꢀbeenꢀ
focusedꢀonꢀimmobilizingꢀtheꢀcomplexesꢀonꢀsolidꢀsupportsꢀsuchꢀ
asꢀ zeolitesꢀ [19–22],ꢀ orderedꢀ mesoporousꢀ silicatesꢀ [23–28]ꢀ orꢀ
polymersꢀ[29–31]ꢀtoꢀaffordꢀheterogeneousꢀcatalysts.ꢀForꢀexam‐
ple,ꢀ Islamꢀ etꢀ al.ꢀ [29]ꢀ reportedꢀ aꢀ reusableꢀ polymer‐anchoredꢀ
Cu(II)ꢀ complexꢀ forꢀ theꢀ oxidationꢀ ofꢀ styreneꢀ toꢀ benzaldehydeꢀ
withꢀTBHPꢀasꢀoxidant.ꢀHowever,ꢀtheꢀconversionꢀofꢀstyreneꢀandꢀ
theꢀselectivityꢀforꢀbenzaldehydeꢀwereꢀonlyꢀ53%ꢀandꢀ52%,ꢀre‐
spectively.ꢀYangꢀetꢀal.ꢀ[24]ꢀpreparedꢀaꢀseriesꢀofꢀSBA‐15‐supp‐
ortedꢀCu(II)ꢀandꢀV(IV)ꢀSchiff‐baseꢀcomplexesꢀtoꢀstudyꢀtheꢀoxi‐
dationꢀofꢀstyrene.ꢀTheyꢀfoundꢀthatꢀtheꢀsupportedꢀoxovanadiumꢀ
NH
2
‐SBA‐15ꢀ(2.35ꢀg)ꢀwasꢀdispersedꢀinꢀ80ꢀmLꢀmethanol,ꢀandꢀ
20ꢀmLꢀsalicylaldehyde/methanolꢀsolutionꢀ(0.2ꢀmol/L,ꢀ0.488ꢀgꢀ
salicylaldehyde)ꢀ wasꢀ addedꢀ toꢀ formꢀ aꢀ light‐yellowꢀ solution.ꢀ
Afterꢀstirringꢀatꢀ30ꢀ°Cꢀforꢀ6ꢀh,ꢀtheꢀmixtureꢀwasꢀheatedꢀtoꢀ50ꢀ°Cꢀ
andꢀ10ꢀmLꢀCu(NO
3
) /methanolꢀsolutionꢀ(0.1ꢀmol/L)ꢀwasꢀaddedꢀ
2
dropwiseꢀtoꢀformꢀaꢀgreenꢀsolution.ꢀTheꢀreactionꢀmixtureꢀwasꢀ
stirredꢀforꢀaꢀfurtherꢀ12ꢀh.ꢀTheꢀsolidꢀwasꢀthenꢀcollectedꢀbyꢀsuc‐
tionꢀ filtration,ꢀ washedꢀ withꢀ methanolꢀ andꢀ water,ꢀ andꢀ finallyꢀ
driedꢀatꢀ80ꢀ°Cꢀovernight.ꢀTheꢀcontentꢀofꢀCuꢀwasꢀ0.101ꢀmmol/gꢀ
(ICP‐AES).ꢀ
catalystꢀshowedꢀgoodꢀselectivityꢀforꢀbenzaldehydeꢀusingꢀH
2 2
O ꢀ
2.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ
asꢀtheꢀoxidant.ꢀTheꢀconversionꢀofꢀstyreneꢀreachedꢀ84.1%ꢀandꢀ
theꢀselectivityꢀforꢀbenzaldehydeꢀwasꢀupꢀtoꢀ83.3%.ꢀHowever,ꢀanꢀ
organicꢀsolventꢀwasꢀused.ꢀInꢀaddition,ꢀaꢀpost‐synthesisꢀgraftingꢀ
methodꢀ wasꢀ employedꢀ forꢀ theꢀ surfaceꢀ modification.ꢀ Inꢀ sum‐
mary,ꢀ althoughꢀ theꢀ modifiedꢀ solidꢀ supportꢀ generallyꢀ main‐
tainedꢀtheꢀorderedꢀ structureꢀofꢀtheꢀ parentꢀmaterials,ꢀ theꢀ dis‐
tributionꢀ ofꢀ aminoꢀ groupsꢀ varied,ꢀ largelyꢀ dependingꢀ onꢀ theꢀ
reactivityꢀandꢀconcentrationꢀofꢀtheꢀprecursorsꢀusedꢀasꢀwellꢀasꢀ
theꢀreactionꢀconditions.ꢀTheꢀresultꢀwasꢀinferiorꢀcatalyticꢀactivi‐
tyꢀandꢀrecoverabilityꢀ[32–35].ꢀ
Low‐angleꢀX‐rayꢀdiffractionꢀ(XRD)ꢀpatternsꢀwereꢀrecordedꢀ
withꢀ aꢀ Rigakuꢀ X‐rayꢀ diffractometerꢀ withꢀ nickel‐filteredꢀ Cuꢀ K ꢀ
α
radiationꢀatꢀ40ꢀkVꢀandꢀ30ꢀmA.ꢀTheꢀsamplesꢀwereꢀscannedꢀinꢀtheꢀ
rangeꢀ 2θꢀ =ꢀ 0.7°–5.0°.ꢀ Theꢀ Fourierꢀ transformꢀ infraredꢀ (FT‐IR)ꢀ
spectraꢀwereꢀ collectedꢀonꢀaꢀNicoletꢀIS10ꢀ spectrometerꢀ (Ther‐
mo).ꢀ Fieldꢀ emissionꢀ scanningꢀ electronꢀ microscopeꢀ (FESEM)ꢀ
imagesꢀofꢀtheꢀ samplesꢀwereꢀobtainedꢀ withꢀ anꢀHITACHIS4800ꢀ
FSEMꢀandꢀtheꢀparticleꢀsizesꢀwereꢀmeasuredꢀusingꢀAdobeꢀPho‐
toshopꢀ software.ꢀ Theꢀ channelꢀ structuresꢀ wereꢀ observedꢀ onꢀ aꢀ
JEM‐2010‐UHRꢀ transmissionꢀ electronꢀ microscopeꢀ (TEM)ꢀ andꢀ
ultraviolet‐visibleꢀ(UV‐Vis)ꢀspectraꢀwereꢀrecordedꢀonꢀaꢀPerkinꢀ
ElmerꢀUV‐Visꢀspectrophotometer,ꢀLambdaꢀ950,ꢀinꢀtheꢀregionꢀofꢀ
200–800ꢀnm.ꢀAꢀBELSORPꢀIIꢀadsorptionꢀinstrumentꢀwasꢀusedꢀtoꢀ
determineꢀtheꢀspecificꢀsurfaceꢀarea,ꢀporeꢀvolume,ꢀandꢀporeꢀsize.ꢀ
Theꢀ specificꢀ surfaceꢀ areaꢀ (ABET)ꢀ wasꢀ calculatedꢀ byꢀ theꢀ BETꢀ
method,ꢀtheꢀporeꢀvolumeꢀ(Vtotal)ꢀwasꢀcalculatedꢀatꢀtheꢀrelativeꢀ
pressureꢀofꢀ0.99ꢀandꢀtheꢀporeꢀsizeꢀdistributionsꢀandꢀDpeakꢀwereꢀ
measuredꢀbyꢀtheꢀBJHꢀmethodꢀfromꢀtheꢀadsorptionꢀbranchꢀofꢀtheꢀ
isotherms.ꢀThermoꢀgravimetricꢀanalysisꢀ(TGA)ꢀwasꢀcarriedꢀoutꢀ
onꢀ aꢀ Netzschꢀ STA409ꢀ instrument.ꢀ CHNꢀ elementꢀ analysisꢀ wasꢀ
carriedꢀoutꢀusingꢀaꢀPerkin‐Elmerꢀ2400ꢀinstrument.ꢀTheꢀcontentꢀ
ofꢀCuꢀwasꢀmeasuredꢀbyꢀinductiveꢀcoupledꢀhighꢀfrequencyꢀplas‐
maꢀatomicꢀemissionꢀspectrometryꢀ(ICP‐AES)ꢀanalysis.ꢀ
Inꢀ thisꢀ paper,ꢀ weꢀ reportꢀ theꢀ directꢀ synthesisꢀ ofꢀ aꢀ uniformꢀ
amino‐modifiedꢀ SBA‐15ꢀ (NH
2
‐SBA‐15)ꢀ basedꢀ onꢀ aꢀ single‐stepꢀ
co‐condensationꢀ ofꢀ tetraethylorthosilicateꢀ (TEOS)ꢀ withꢀ 3‐
ꢀ
ami‐
nopropyltriethoxysilaneꢀ (APTES).ꢀ Theꢀ condensationꢀ reactionꢀ
tookꢀ placeꢀ inꢀ theꢀ presenceꢀ ofꢀ anꢀ amphiphilicꢀ PEO‐PPO‐PEOꢀ
triblockꢀcopolymerꢀ(P123)ꢀasꢀaꢀpore‐directingꢀagent.ꢀTreatmentꢀ
ofꢀ theꢀ preparedꢀ NH
densationꢀconditionsꢀfollowedꢀbyꢀtheꢀadditionꢀofꢀaꢀsolutionꢀofꢀ
Cu(NO ꢀ formedꢀ theꢀ SBA‐15‐supportedꢀ Cu(II)ꢀ Schiff‐baseꢀ
2
‐SBA‐15ꢀ withꢀ salicylaldehydeꢀ underꢀ con‐
)
3 2
complexꢀ(Cu‐SBA‐15).ꢀTheꢀimmobilizedꢀcomplexꢀwasꢀsuccess‐
fullyꢀusedꢀasꢀaꢀcatalystꢀforꢀtheꢀselectiveꢀoxidationꢀofꢀstyreneꢀtoꢀ
benzaldehydeꢀinꢀanꢀaqueousꢀmedium.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2
2
.1.ꢀ ꢀ Catalystꢀpreparationꢀ
2.3.ꢀ ꢀ Catalyticꢀactivityꢀtestꢀ
2
.1.1.ꢀ ꢀ PreparationꢀofꢀNH ‐SBA‐15ꢀ ꢀ
Theꢀoxidationꢀofꢀstyreneꢀwasꢀconductedꢀinꢀaꢀ100‐mLꢀstain‐
less‐steelꢀ high‐pressureꢀ autoclaveꢀ (Parr,ꢀ USA).ꢀ Theꢀ catalyst,ꢀ
NH ‐SBA‐15ꢀwasꢀpreparedꢀviaꢀtheꢀco‐condensationꢀmethodꢀ
2
describedꢀ inꢀ theꢀ literatureꢀ [36].ꢀ P123ꢀ (4.0ꢀ g,ꢀ Sigma‐Aldrich)ꢀ
wasꢀdissolvedꢀinꢀ125.0ꢀgꢀaqueousꢀHClꢀ(2ꢀmol/L).ꢀAfterꢀvigorousꢀ
stirringꢀatꢀ40ꢀ°Cꢀforꢀ4ꢀh,ꢀ7.9ꢀmLꢀTEOSꢀwasꢀaddedꢀdropwise.ꢀTheꢀ
resultantꢀsolutionꢀwasꢀpre‐hydrolyzedꢀforꢀ1ꢀhꢀbeforeꢀ0.92ꢀmLꢀ
APTESꢀ(YaohuaꢀChemicalꢀIndustry,ꢀShanghai,ꢀChina)ꢀwasꢀadd‐
ed.ꢀAfterꢀstirringꢀforꢀ20ꢀh,ꢀtheꢀwhiteꢀsolutionꢀwasꢀtransferredꢀ
intoꢀ aꢀ polypropyleneꢀ bottle,ꢀ andꢀ agedꢀ atꢀ 90ꢀ °Cꢀ forꢀ 24ꢀ h.ꢀ Theꢀ
solidꢀ wasꢀ collectedꢀ byꢀ suctionꢀ filtrationꢀ andꢀ driedꢀ atꢀ 50ꢀ °Cꢀ
overnight.ꢀTheꢀresidualꢀP123ꢀwasꢀremovedꢀbyꢀextractionꢀwithꢀ
boiledꢀethanolꢀ(1.0ꢀgꢀofꢀas‐synthesizedꢀmaterialꢀperꢀ200ꢀmLꢀofꢀ
ethanolꢀandꢀ10ꢀmLꢀofꢀconcentratedꢀHCl)ꢀforꢀ24ꢀh.ꢀTheꢀsolidꢀwasꢀ
collectedꢀbyꢀsuctionꢀfiltration,ꢀwashedꢀwithꢀwaterꢀandꢀethanol,ꢀ
andꢀdriedꢀatꢀ50ꢀ°Cꢀovernight.ꢀElementalꢀanalysisꢀgaveꢀCꢀ8.00%,ꢀ
Hꢀ3.27%,ꢀNꢀ1.53%.ꢀTheꢀcalculatedꢀNꢀcontentꢀwasꢀ1.09ꢀmmol/g.ꢀ
water,ꢀH
2
O ꢀ(30ꢀwt%),ꢀandꢀstyreneꢀ(5.200ꢀg)ꢀwereꢀaddedꢀintoꢀ
2
theꢀ vesselꢀ andꢀ itꢀ wasꢀ thenꢀ heatedꢀ toꢀ 100ꢀ °Cꢀ withꢀ aꢀ stirringꢀ
speedꢀofꢀ800ꢀr/min.ꢀAfterꢀtheꢀreactionꢀwasꢀcomplete,ꢀtheꢀmix‐
tureꢀ wasꢀ centrifugedꢀ (8000ꢀ r/min,ꢀ 2ꢀ min)ꢀ andꢀ theꢀ solidꢀ wasꢀ
washedꢀwithꢀEtOAc.ꢀTheꢀcombinedꢀorganicꢀphasesꢀwereꢀdriedꢀ
overꢀanhydrousꢀMgSO ,ꢀandꢀanalyzedꢀonꢀaꢀgas‐chromatographꢀ
4
(GC2014,ꢀ Shimadzuꢀ Instruments,ꢀ Japan)ꢀ equippedꢀ withꢀ DB‐5ꢀ
capillaryꢀcolumnꢀ(30ꢀmꢀꢀ0.25ꢀmmꢀꢀ0.25ꢀμm).ꢀTheꢀrecoveredꢀ
catalystꢀ wasꢀ washedꢀ withꢀ acetone,ꢀ alcohol,ꢀ andꢀ water,ꢀ andꢀ
driedꢀatꢀ100ꢀ°Cꢀovernightꢀbeforeꢀreuse.ꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ Catalystꢀcharacterizationꢀ
2.1.2.ꢀ ꢀ PreparationꢀofꢀCu‐SBA‐15ꢀ ꢀ
Theꢀlow‐angleꢀXRDꢀpatternsꢀofꢀNH ‐SBA‐15ꢀandꢀCu‐SBA‐15ꢀ
2

1718ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
–
1
areꢀdepictedꢀinꢀFig.ꢀ1(a).ꢀTheꢀpatternꢀofꢀNH
2
‐SBA‐15ꢀshowsꢀanꢀ
atꢀaboutꢀ1510ꢀcm ꢀcanꢀbeꢀobservedꢀinꢀbothꢀSchiff‐base‐SBA‐15ꢀ
andꢀ Cu‐SBA‐15ꢀ butꢀ hasꢀ aꢀ lowꢀ intensity,ꢀ indicatingꢀ theꢀ occur‐
renceꢀ ofꢀ theꢀ condensationꢀ ofꢀ salicylaldehydeꢀ withꢀ theꢀ aminoꢀ
intenseꢀdiffractionꢀindexedꢀtoꢀtheꢀ(100)ꢀplane,ꢀwhichꢀindicatesꢀ
theꢀ typicalꢀ mesoporousꢀ structureꢀ ofꢀ SBA‐15.ꢀ Theꢀ otherꢀ twoꢀ
smallꢀ characteristicꢀ peaksꢀ areꢀ notꢀ clearlyꢀ observed,ꢀ probablyꢀ
becauseꢀtheꢀuseꢀofꢀtheꢀsilaneꢀcouplingꢀagentꢀnegativelyꢀaffectedꢀ
theꢀformationꢀofꢀmicellesꢀandꢀresultedꢀinꢀanꢀirregularityꢀofꢀtheꢀ
groupsꢀ onꢀ theꢀ surfaceꢀ ofꢀ NH
sorptionꢀ peakꢀ ofꢀ C=Nꢀ stretchingꢀ vibrationꢀ shouldꢀ occurꢀ aroundꢀ
1640–1650ꢀcm ꢀforꢀtheꢀSchiff‐base‐SBA‐15.ꢀHowever,ꢀthisꢀpeakꢀ
isꢀ overlappedꢀ byꢀ theꢀ stretchingꢀ vibrationꢀ absorptionꢀ ofꢀ H O.ꢀ
2
‐SBA‐15.ꢀ Generally,ꢀ aꢀ weakꢀ ab‐
–1
2
pores.ꢀ FT‐IRꢀ spectraꢀ ofꢀ SBA‐15,ꢀ NH ‐SBA‐15,ꢀ Schiff‐base‐ꢀ
2
SBA‐15,ꢀ andꢀ Cu‐SBA‐15ꢀ areꢀ shownꢀ inꢀ Fig.ꢀ 1(b).ꢀ Theꢀ peaksꢀ atꢀ
Notably,ꢀ comparisonꢀ ofꢀ theꢀ IRꢀ spectraꢀ ofꢀ Cu‐SBA‐15ꢀ andꢀ
Schiff‐base‐SBA‐15ꢀindicatesꢀtheꢀpresenceꢀofꢀaꢀnewꢀadsorptionꢀ
peakꢀaroundꢀ1387ꢀcm ꢀinꢀCu‐SBA‐15.ꢀThisꢀnewꢀpeakꢀmayꢀre‐
sultꢀfromꢀtheꢀredꢀshiftꢀofꢀtheꢀC=Nꢀstretchingꢀvibrationꢀabsorp‐
tionꢀdueꢀtoꢀcoordinationꢀtoꢀcopperꢀions.ꢀ
–1
4
67,ꢀ799,ꢀ1081,ꢀandꢀ1230ꢀcm ꢀindicateꢀtheꢀcharacteristicꢀab‐
–1
–1
sorptionꢀofꢀO–Si–Oꢀbondsꢀandꢀtheꢀpeakꢀatꢀ946ꢀcm ꢀindicatesꢀ
–1
theꢀexistenceꢀofꢀSi–OH.ꢀTheꢀstrongꢀpeakꢀaroundꢀ1632ꢀcm ꢀinꢀallꢀ
theꢀsamplesꢀresultsꢀlargelyꢀfromꢀtheꢀbendingꢀvibrationꢀofꢀad‐
sorbedꢀwater,ꢀandꢀtheꢀbroadꢀbandꢀobservedꢀbetweenꢀ3700ꢀ
andꢀ2800ꢀcm ꢀisꢀattributedꢀtoꢀtheꢀ–OHꢀstretchingꢀvibrationꢀofꢀ
waterꢀadsorbedꢀonꢀtheꢀsurfaceꢀofꢀtheꢀcatalyst.ꢀTheꢀpresenceꢀofꢀ
Theꢀ FESEMꢀ imageꢀ ofꢀ NH ‐SBA‐15ꢀ isꢀ presentedꢀ inꢀ Fig.ꢀ
2
–1
2(a).ꢀ Theꢀ sampleꢀ showsꢀ aꢀ typicalꢀ rod‐likeꢀ morphologyꢀ ofꢀ
SBA‐15.ꢀAsꢀshownꢀinꢀFig.ꢀ2(b),ꢀtheꢀdiametersꢀofꢀmostꢀparti‐
clesꢀareꢀtypicallyꢀinꢀtheꢀrangeꢀofꢀ600–700ꢀnmꢀandꢀtheꢀaver‐
–1
theꢀ‐NH ꢀstretchingꢀvibrationꢀatꢀ3250ꢀcm ,ꢀtheꢀbendingꢀvibra‐
2
–1
–1
tionꢀatꢀ1510ꢀcm ꢀandꢀtheꢀN–Hꢀbendingꢀvibrationꢀatꢀ668ꢀcm ꢀ
confirmꢀtheꢀincorporationꢀofꢀtheꢀaminoꢀgroups.ꢀTheꢀabsorptionꢀ
ageꢀparticleꢀsizeꢀisꢀ740ꢀnm.ꢀTheꢀTEMꢀimagesꢀofꢀNH
2
‐SBA‐15ꢀ
andꢀCu‐SBA‐15ꢀareꢀshownꢀinꢀFig.ꢀ2(c)ꢀandꢀ(d),ꢀrespectively,ꢀ
SBA-15
(b)
(a)
NH
2
-SBA-15
Schiff-base-SBA-15
Cu-SBA-15
2
NH -SBA-15
Cu-SBA-15
1
2
3
4
5
4000 3500 3000 2500 2000 1500 1000 500
o
1
2
/( )
Wavenumbers (cm )
ꢀ
2 2
Fig.ꢀ1.ꢀ(a)ꢀXRDꢀpatternsꢀofꢀNH ‐SBA‐15ꢀandꢀCu‐SBA‐15.ꢀ(b)ꢀFT‐IRꢀspectraꢀofꢀSBA‐15,ꢀNH ‐SBA‐15,ꢀSchiff‐base‐SBA‐15,ꢀandꢀCu‐SBA‐15.ꢀ
0
0
0
0
0
0
.25
.20
.15
.10
.05
(a)
(
b)
.00
4
00
600
800 1000 1200 1400
Size (nm)
2
μm
(c)
(d)
1
00 nm
100 nm
ꢀ
2 2
Fig.ꢀ2.ꢀ(a)ꢀFESEMꢀimageꢀofꢀNH ‐SBA‐15;ꢀ(b)ꢀParticleꢀsizeꢀdistributionꢀofꢀtheꢀsample;ꢀ(c)ꢀTEMꢀimageꢀofꢀNH ‐SBA‐15;ꢀ(d)ꢀTEMꢀimageꢀofꢀCu‐SBA‐15.ꢀ

ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
Tableꢀ1ꢀ
1719ꢀ
1
0
0
0
0
0
.0
.8
.6
.4
.2
TexturalꢀpropertiesꢀofꢀNH ‐SBA‐15ꢀandꢀCu‐SBA‐15.ꢀ
2
2
3
Sampleꢀ
NH ‐SBA‐15ꢀ
A
BET/(m /g)ꢀ
V
total/(cm /g)ꢀ
Dpeak/nmꢀ
2
443ꢀ
0.54ꢀ
0.34ꢀ
5.41ꢀ
5.41ꢀ
Cu‐SBA‐15ꢀ
423ꢀ
100
Cu-SBA-15
NH -SBA-15
700 800
95
90
85
80
2
.0
2
00
300
400
Wavelength (nm)
Fig.ꢀ3.ꢀUV‐VisꢀspectraꢀofꢀNH ‐SBA‐15andꢀCu‐SBA‐15.ꢀ
500
600
2
Cu-SBA-15
andꢀprovideꢀaꢀdirectꢀvisualizationꢀofꢀwell‐orderedꢀhexagonalꢀ
arraysꢀofꢀ1Dꢀmesoporousꢀchannelsꢀforꢀbothꢀtypesꢀofꢀsample.ꢀ
Someꢀ poreꢀ wallsꢀ inꢀ theꢀ sampleꢀ haveꢀ collapsed,ꢀ whichꢀ ac‐
countsꢀforꢀtheꢀabsenceꢀofꢀtheꢀtwoꢀlow‐intensityꢀcharacteris‐
ticꢀpeaksꢀinꢀtheꢀXRDꢀpatterns.ꢀ
NH
2
-SBA-15
0
100
200
300
400
500 600
o
Temperature ( C)
Fig.ꢀ5.ꢀTGꢀcurvesꢀofꢀNH ‐SBA‐15ꢀandꢀCu‐SBA‐15.ꢀ
ꢀ
2
2
Figureꢀ 3ꢀ showsꢀ theꢀ UV‐Visꢀ spectraꢀ ofꢀ NH ‐SBA‐15ꢀ andꢀ
Cu‐SBA‐15.ꢀInꢀcontrastꢀtoꢀtheꢀspectrumꢀofꢀNH ‐SBA‐15,ꢀaꢀtypi‐
2
isꢀdueꢀtoꢀtheꢀdecompositionꢀofꢀtheꢀaminoꢀgroupsꢀandꢀtheꢀSchiffꢀ
bases.ꢀTheꢀweightꢀlossꢀofꢀCu‐SBA‐15ꢀoccursꢀatꢀlowerꢀtempera‐
calꢀ metal‐ligandꢀ bandꢀ aroundꢀ 390ꢀ nmꢀ isꢀ observedꢀ forꢀ
Cu‐SBA‐15ꢀ [24],ꢀ indicatingꢀ theꢀ successfulꢀ anchoringꢀ ofꢀ theꢀ
Cu(II)ꢀSchiff‐baseꢀcomplexꢀtoꢀtheꢀSBA‐15ꢀmatrix.ꢀ
tures,ꢀrelativeꢀtoꢀNH ‐SBA‐15,ꢀbecauseꢀofꢀtheꢀhigherꢀmolecularꢀ
2
massꢀ ofꢀ theꢀ Schiff‐basesꢀ comparedꢀ withꢀ thatꢀ ofꢀ theꢀ aminoꢀ
groups.ꢀFinally,ꢀtheꢀdecompositionꢀofꢀtheꢀaminopropylꢀgroupsꢀ
causedꢀtheꢀweightꢀlossꢀatꢀtemperaturesꢀaboveꢀ350ꢀ°C.ꢀ
2
AsꢀshownꢀinꢀFig.ꢀ4,ꢀtheꢀN ꢀadsorption‐desorptionꢀisothermꢀ
forꢀNH ‐SBA‐15ꢀisꢀtypeꢀIVꢀwithꢀanꢀH1‐typeꢀhysteresisꢀloop,ꢀtyp‐
2
icalꢀforꢀmesoporousꢀmaterialsꢀwithꢀcylindricalꢀporousꢀchannels.ꢀ
TheꢀCu‐SBA‐15ꢀsampleꢀmaintainsꢀtheꢀcharacteristicsꢀofꢀtypeꢀIVꢀ
yetꢀ withꢀ anꢀH2ꢀhysteresisꢀloop,ꢀprobablyꢀbecauseꢀofꢀaꢀpartialꢀ
blockingꢀofꢀtheꢀpores.ꢀTheꢀsizeꢀdistributionꢀcurvesꢀshowꢀsimilarꢀ
peaksꢀ atꢀ 5.41ꢀ nmꢀ whileꢀ theꢀ peakꢀ forꢀ Cu‐SBA‐15ꢀ hasꢀ aꢀ lowerꢀ
3.2.ꢀ ꢀ Optimizationꢀofꢀreactionꢀconditionsꢀ
3.2.1.ꢀ ꢀ Effectꢀofꢀtheꢀreactionꢀtimeꢀ
Figureꢀ6(a)ꢀshowsꢀtheꢀeffectꢀofꢀreactionꢀtimeꢀonꢀstyreneꢀox‐
idationꢀatꢀ100ꢀ°Cꢀusingꢀ0.300ꢀgꢀCu‐SBA‐15ꢀasꢀtheꢀcatalystꢀandꢀ
intensityꢀandꢀisꢀbroader.ꢀTheꢀtexturalꢀpropertiesꢀofꢀNH ‐SBA‐15ꢀ
2
andꢀCu‐SBA‐15ꢀareꢀsummarizedꢀinꢀTableꢀ1.ꢀTheꢀABETꢀandꢀporeꢀ
1.5ꢀequiv.ꢀH
2
O ꢀ(10ꢀwt%ꢀaqueous)ꢀasꢀtheꢀoxidant.ꢀTheꢀstyreneꢀ
2
volumesꢀ ofꢀ Cu‐SBA‐15ꢀ areꢀ slightlyꢀ lowerꢀ thanꢀ thoseꢀ ofꢀ
conversionꢀincreasedꢀwithꢀreactionꢀdurationꢀwhileꢀtheꢀselectiv‐
ityꢀforꢀbenzaldehydeꢀdeclinedꢀslowly.ꢀTheꢀconversionꢀreachedꢀ
55.4%ꢀandꢀtheꢀselectivityꢀwasꢀ80%ꢀafterꢀ8ꢀh.ꢀTheꢀconversionꢀofꢀ
styreneꢀfurtherꢀincreasedꢀafterꢀ9ꢀh,ꢀbutꢀstyreneꢀthenꢀunderwentꢀ
polymerization,ꢀ resultingꢀ inꢀ aꢀ considerableꢀ decreaseꢀ inꢀ selec‐
NH ‐SBA‐15.ꢀ Weꢀ considerꢀ thatꢀ theseꢀ resultsꢀ reflectꢀ theꢀ intro‐
2
ductionꢀofꢀtheꢀSchiff‐base‐coordinatedꢀcopperꢀcomplexꢀonꢀtheꢀ
material,ꢀleadingꢀtoꢀtheꢀblockageꢀofꢀsomeꢀpores.ꢀ
2
Theꢀ TGAꢀ resultsꢀ forꢀ NH ‐SBA‐15ꢀ andꢀ Cu‐SBA‐15ꢀ areꢀ illus‐
2
tratedꢀ inꢀ Fig.ꢀ 5.ꢀ Forꢀ bothꢀ NH ‐SBA‐15ꢀ andꢀ Cu‐SBA‐15,ꢀ theꢀ
tivity.ꢀThisꢀbehaviorꢀisꢀbecauseꢀtheꢀH
2
O ꢀwasꢀcompletelyꢀcon‐
2
weightꢀ lossꢀ belowꢀ 100ꢀ °Cꢀ isꢀ mainlyꢀ attributedꢀ toꢀ theꢀ lossꢀ ofꢀ
adsorbedꢀwater.ꢀTheꢀsubsequentꢀweightꢀlossꢀfromꢀ200–350ꢀ°Cꢀ
sumedꢀafterꢀ9ꢀh,ꢀandꢀtheꢀresidualꢀstyreneꢀunderwentꢀpolymer‐
izationꢀunderꢀtheseꢀconditions.ꢀ
4
3
2
1
00
00
00
00
0
(b)
(a)
2
NH -SBA-15
0.20
0.15
0.10
0.05
0.00
Cu-SBA-15
NH
Cu-SBA-15
30 35
2
-SBA-15
0.0
0.2
0.4
0.6
0.8
1.0
0
5
10
15
Pore diameter (nm)
ꢀadsorption‐desorptionꢀisothermsꢀ(a)ꢀandꢀcorrespondingꢀmesoporeꢀsizeꢀdistributionꢀcurvesꢀ(b)ꢀofꢀNH ‐SBA‐15ꢀandꢀCu‐SBA‐15.ꢀ
20
25
40
Relative pressure (p/p
0
)
ꢀ
Fig.ꢀ4.ꢀN
2
2

1720ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
3
.2.2.ꢀ ꢀ Effectꢀofꢀtheꢀreactionꢀtemperatureꢀ
Figureꢀ 6(b)ꢀ showsꢀ theꢀ effectꢀ ofꢀ reactionꢀ temperatureꢀ onꢀ
ofꢀH
tion.ꢀWeꢀinvestigatedꢀtheꢀeffectꢀofꢀH
tionsꢀ atꢀ 100ꢀ °Cꢀ forꢀ 8ꢀ hꢀ withꢀ variousꢀ amountsꢀ ofꢀ H
presenceꢀofꢀ0.300ꢀgꢀCu‐SBA‐15ꢀandꢀ2ꢀequiv.ꢀH .ꢀTheꢀresultsꢀ
areꢀshownꢀinꢀFig.ꢀ6(d).ꢀItꢀisꢀobviousꢀthatꢀtheꢀconversionꢀofꢀsty‐
reneꢀ isꢀ theꢀ highestꢀ withꢀ noꢀ extraꢀ H Oꢀadded.ꢀTheꢀadditionꢀofꢀ
Oꢀslowedꢀtheꢀoxidationꢀprocessꢀandꢀledꢀtoꢀaꢀlowꢀconversion.ꢀ ꢀ
2
OꢀaddedꢀinꢀtheꢀreactionꢀdeterminesꢀtheꢀH
Oꢀbyꢀconductingꢀtheꢀreac‐
Oꢀ inꢀ theꢀ
2
O
2
ꢀconcentra‐
2
styreneꢀoxidationꢀusingꢀ0.300ꢀgꢀCu‐SBA‐15ꢀasꢀtheꢀcatalystꢀandꢀ
.5ꢀequiv.ꢀH ꢀ(10ꢀwt%ꢀaqueous)ꢀasꢀtheꢀoxidantꢀforꢀ8ꢀh.ꢀItꢀisꢀ
2
1
O
2 2
O
2 2
clearꢀthatꢀtheꢀconversionꢀofꢀstyreneꢀrapidlyꢀdecreasedꢀwithꢀaꢀ
decreaseꢀinꢀtheꢀreactionꢀtemperature.ꢀWhenꢀtheꢀreactionꢀwasꢀ
performedꢀatꢀ80ꢀ°C,ꢀtheꢀconversionꢀofꢀstyreneꢀwasꢀonlyꢀ6.8%.ꢀ
However,ꢀtheꢀselectivityꢀwasꢀmuchꢀhigherꢀatꢀaꢀlowerꢀreactionꢀ
temperatureꢀ becauseꢀ theꢀ rateꢀ ofꢀ benzaldehydeꢀ oxidationꢀ toꢀ
benzoicꢀacidꢀisꢀalsoꢀlower.ꢀWhenꢀtheꢀreactionꢀwasꢀconductedꢀatꢀ
2
H
2
3.2.5.ꢀ ꢀ Effectꢀofꢀcatalystꢀloadingꢀ
Figureꢀ6(e)ꢀshowsꢀtheꢀinfluenceꢀofꢀcatalystꢀloading.ꢀTheꢀ
conversionꢀ ofꢀ styreneꢀ andꢀ theꢀ selectivityꢀ forꢀ benzaldehydeꢀ
wereꢀ 84.4%ꢀ andꢀ 83.9%,ꢀ respectively,ꢀ whenꢀ theꢀ reactionꢀ wasꢀ
1
00ꢀ°Cꢀforꢀ8ꢀh,ꢀtheꢀconversionꢀofꢀstyreneꢀreachedꢀ55.4%ꢀandꢀtheꢀ
selectivityꢀforꢀbenzaldehydeꢀwasꢀupꢀtoꢀ79.3%.ꢀ
conductedꢀ atꢀ 100ꢀ °Cꢀ forꢀ 8ꢀ hꢀ withꢀ 2ꢀ equiv.ꢀ H
2
O ꢀ andꢀ 0.200ꢀ gꢀ
2
3
.2.3.ꢀ ꢀ EffectꢀofꢀtheꢀamountꢀofꢀH
TheꢀeffectꢀofꢀtheꢀamountꢀofꢀH
conductingꢀ theꢀ reactionsꢀ atꢀ 100ꢀ °Cꢀ forꢀ 8ꢀ h.ꢀ H
aqueous)ꢀwasꢀusedꢀinꢀtheꢀpresenceꢀofꢀ0.300ꢀgꢀCu‐SBA‐15ꢀandꢀ
7.167ꢀgꢀH O.ꢀAsꢀshownꢀinꢀFig.ꢀ6(c),ꢀtheꢀconversionꢀofꢀstyreneꢀ
graduallyꢀ increasesꢀ withꢀ anꢀ increaseꢀ inꢀ theꢀ amountꢀ ofꢀ H
used.ꢀWhenꢀ2ꢀequiv.ꢀH ꢀwasꢀused,ꢀtheꢀconversionꢀofꢀstyreneꢀ
wasꢀ 70.6%ꢀ andꢀ theꢀ selectivityꢀ forꢀ benzaldehydeꢀ wasꢀ 79.6%.ꢀ
Whenꢀ 2.5ꢀ equiv.ꢀ H ꢀ wasꢀ used,ꢀ theꢀ conversionꢀ increasedꢀ toꢀ
4.5%,ꢀbutꢀtheꢀselectivityꢀdroppedꢀsharplyꢀtoꢀ65.4%.ꢀAꢀfurtherꢀ
increaseꢀ inꢀ theꢀ amountꢀ ofꢀ H ꢀ employedꢀ resultedꢀ inꢀ noꢀ in‐
creaseꢀinꢀstyreneꢀconversion,ꢀandꢀaꢀmuchꢀlowerꢀselectivity.ꢀThisꢀ
canꢀbeꢀascribedꢀtoꢀtheꢀremainingꢀH ꢀpromotingꢀtheꢀfurtherꢀ
oxidationꢀofꢀbenzaldehydeꢀtoꢀbenzoicꢀacid.ꢀOverall,ꢀtheꢀuseꢀofꢀ2ꢀ
equiv.ꢀH ꢀforꢀtheꢀcatalyticꢀoxidationꢀofꢀstyreneꢀisꢀsuitable.ꢀ
2
O
2
ꢀ
O
Cu‐SBA‐15.ꢀAnꢀincreaseꢀinꢀtheꢀamountꢀofꢀcatalystꢀusedꢀhasꢀlittleꢀ
effectꢀonꢀtheꢀreaction.ꢀHowever,ꢀwhenꢀtheꢀamountꢀofꢀtheꢀcata‐
lystꢀwasꢀreducedꢀtoꢀ0.150ꢀorꢀ0.100ꢀg,ꢀtheꢀreactionꢀmixtureꢀbe‐
cameꢀviscousꢀafterꢀ8ꢀh,ꢀprobablyꢀbecauseꢀofꢀtheꢀformationꢀofꢀ
styreneꢀoligomers.ꢀAꢀhighꢀloadingꢀofꢀtheꢀcatalystꢀisꢀrequiredꢀtoꢀ
accelerateꢀtheꢀrateꢀofꢀtheꢀoxidationꢀprocessꢀandꢀpreventꢀstyreneꢀ
polymerization.ꢀ
2
2
ꢀusedꢀwasꢀinvestigatedꢀbyꢀ
2 2
O ꢀ (10ꢀ wt%ꢀ
1
2
O
2 2ꢀ
O
2 2
Basedꢀonꢀtheꢀaboveꢀresults,ꢀweꢀobtainedꢀtheꢀoptimumꢀcon‐
ditionsꢀasꢀfollows:ꢀtheꢀreactionꢀshouldꢀbeꢀcarriedꢀoutꢀatꢀ100ꢀ°Cꢀ
O
2 2
8
forꢀ8ꢀhꢀusingꢀ2.0ꢀequivꢀH
2
O ꢀ(30ꢀwt%ꢀaqueous)ꢀandꢀ3.8ꢀwt%ꢀ
2
2
O
2
Cu‐SBA‐15ꢀcatalyst.ꢀTheꢀconversionꢀofꢀstyreneꢀobtainedꢀwasꢀ
upꢀtoꢀ84.4%,ꢀandꢀtheꢀselectivityꢀforꢀbenzaldehydeꢀwasꢀ83.9%.ꢀ
–
1
O
2 2
TheꢀTOFꢀofꢀtheꢀcatalystꢀwasꢀ261.1ꢀh .ꢀBenzoicꢀacidꢀwasꢀtheꢀ
onlyꢀby‐productꢀandꢀtheꢀformationꢀofꢀstyreneꢀoxideꢀwasꢀnotꢀ
observed.ꢀAtꢀtheꢀoptimumꢀconditions,ꢀweꢀfoundꢀthatꢀthisꢀhet‐
erogeneousꢀcatalystꢀgaveꢀcompetitiveꢀresultsꢀcomparedꢀwithꢀ
otherꢀreportedꢀcatalystsꢀinꢀtermsꢀofꢀconversionꢀandꢀselectivityꢀ
and,ꢀ inꢀ addition,ꢀ aꢀ highꢀ TOFꢀ wasꢀ obtainedꢀ (Tableꢀ 2).ꢀ Whenꢀ
2 2
O
3.2.4.ꢀ ꢀ EffectꢀofꢀtheꢀamountꢀofꢀH
2
Oꢀ
Sinceꢀthereꢀisꢀnoꢀco‐solventꢀusedꢀinꢀtheꢀreaction,ꢀtheꢀamountꢀ
60
50
40
30
20
90
80
70
60
50
60
90
80
70
60
50
90
80
70
60
50
(
a)
(b)
(
c)
1
00
5
9
4
0
0
0
90
2
8
5
0
8
4
5
6
7
8
80
85
90
95 100
1.5
2.0
n(H
2.5
):n(styrene)
3.0
Reaction time (h)
o
O
2
Reaction temperature ( C)
2
90
80
70
60
90
80
70
60
90
90
80
70
60
50
(
d)
(e)
80
70
60
50
0
5
10
15
20
25
0.2
0.3
0.4
Weight of water (g)
Amount of catalyst (g)
ꢀ
Fig.ꢀ6.ꢀEffectꢀofꢀreactionꢀtimeꢀ(a),ꢀtemperatureꢀ(b),ꢀamountꢀofꢀH
benzaldehyde.ꢀOtherꢀreactionꢀconditions:ꢀ(a)ꢀ100ꢀ°C,ꢀn(styrene):n(H
:1.5,ꢀ10ꢀwt%ꢀH ,ꢀ0.3ꢀgꢀcatalyst,ꢀ800ꢀr/min;ꢀ(c)ꢀ100ꢀ°C,ꢀ8ꢀh,ꢀ10ꢀwt%ꢀH
catalyst,ꢀ800ꢀr/min;ꢀ(e)ꢀ100ꢀ°C,ꢀ8ꢀh,ꢀn(styrene):n(H )ꢀ=ꢀ1:2,ꢀ30ꢀwt%ꢀH
2
O
2
ꢀ(c),ꢀweightꢀofꢀH
)ꢀ=ꢀ1:1.5,ꢀ10ꢀwt%ꢀH
,ꢀ0.3ꢀgꢀcatalyst,ꢀ800ꢀr/min;ꢀ(d)ꢀ100ꢀ°C,ꢀ8ꢀh,ꢀn(styrene):n(H
,ꢀ800ꢀr/min.ꢀ
2
Oꢀ(d),ꢀandꢀtheꢀamountꢀofꢀcatalystꢀ(e)ꢀonꢀtheꢀoxidationꢀofꢀstyreneꢀtoꢀ
,ꢀ0.3ꢀgꢀcatalyst,ꢀ800ꢀr/min;ꢀ(b)ꢀ8ꢀh,ꢀn(styrene):n(H )ꢀ=ꢀ
)ꢀ=ꢀ1:2,ꢀ0.3ꢀgꢀ
2
O
2
O
2 2
O
2 2
1
O
2 2
2
O
2
2
O
2 2
O
2 2
2
O

ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
1721ꢀ
Tableꢀ2ꢀ
Activityꢀofꢀtheꢀsupportedꢀmetalꢀcomplexꢀcatalysts.ꢀ
Selectivityꢀ(%)ꢀ
Conversionꢀ
Catalystꢀ
–
1
TOFꢀ(h )
Oxidantꢀ
Solventꢀ
Refrenceꢀ
(
%)ꢀ
Benzaldehydeꢀ
Styreneoxideꢀ
Cu‐SBA‐15ꢀ
VO‐Salen‐SBAꢀ
Cu‐Salen‐SBAꢀ
84.4ꢀ
84.1ꢀ
96.9ꢀ
78.5ꢀ
45.0ꢀ
84.0ꢀ
53.0ꢀ
83.9ꢀ
83.3ꢀ
45.2ꢀ
43.6ꢀ
99.0ꢀ
96.0ꢀ
52.0ꢀ
89.0ꢀ
0ꢀ
261.1ꢀ
ꢀ 67.4ꢀ
134.6ꢀ
196.0ꢀ
ꢀ ꢀ ꢀ 0.24ꢀ
ꢀ ꢀ 9.5ꢀ
H
2
O
O
O
2ꢀ
H
2
Oꢀ
thisꢀworkꢀ
25ꢀ
11.9ꢀ
13.5ꢀ
54.1ꢀ
0ꢀ
0ꢀ
48.0ꢀ
11.0ꢀ
H
2
2
ꢀ
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CNꢀ
CNꢀ
CNꢀ
CNꢀ
CNꢀ
CNꢀ
H
2
Airꢀ
H
2
H
2
TBHPꢀ
H
2
2
ꢀ
25ꢀ
28ꢀ
26ꢀ
27ꢀ
29ꢀ
30ꢀ
4
Co‐[H ]Salen‐SBAꢀ
SBA‐Fe(acac:salen)ꢀ
SBA‐VO(acac)ꢀ
O
O
2
ꢀ
ꢀ
2
2
PS‐NH ‐Cu‐Salꢀ
ꢀ 12.6ꢀ
ꢀ 50.0ꢀ
Polymerꢀsupportedꢀcobaltꢀcomplexꢀ
100ꢀ
O
2
ꢀ
H
2
Oꢀ
ꢀ
acetonitrileꢀwasꢀusedꢀasꢀaꢀsolventꢀunderꢀtheseꢀconditions,ꢀtheꢀ
conversionꢀofꢀstyreneꢀreachedꢀupꢀtoꢀ96.7%,ꢀwhileꢀtheꢀselec‐
tivityꢀ forꢀ benzaldehydeꢀ wasꢀ onlyꢀ 58.3%ꢀ becauseꢀ ofꢀ theꢀ for‐
mationꢀofꢀseveralꢀby‐productsꢀincludingꢀbenzoicꢀacidꢀ(16.7%),ꢀ
phenylacetaldehydeꢀ (15.8%)ꢀ andꢀ phenylethyleneꢀ glycolꢀ
O
OH
(
9.2%).ꢀ
ꢀ
HO
H
·
OH
·OH
O
H
O
O
3
.3.ꢀ ꢀ Catalystꢀrecyclingꢀ
·OH
+
H
H
Recyclabilityꢀisꢀoneꢀofꢀtheꢀmostꢀimportantꢀbenefitsꢀofꢀsup‐
HO
O
H O
portedꢀ catalystsꢀ andꢀ makesꢀ themꢀ attractiveꢀ forꢀ commercialꢀ
applications.ꢀWeꢀthereforeꢀinvestigatedꢀtheꢀrecoveryꢀandꢀre‐
cyclabilityꢀ ofꢀ theꢀ supportedꢀ catalystꢀ used.ꢀ Theꢀ resultsꢀ areꢀ
summarizedꢀinꢀTableꢀ3ꢀandꢀshowꢀthatꢀtheꢀCu‐SAB‐15ꢀcatalystꢀ
couldꢀbeꢀsuccessfullyꢀusedꢀthreeꢀtimesꢀwithoutꢀsignificantꢀlossꢀ
ofꢀtheꢀactivity.ꢀTheꢀmainꢀproductꢀandꢀby‐productꢀwereꢀben‐
zaldehydeꢀandꢀbenzoicꢀacid,ꢀrespectively,ꢀandꢀnoꢀstyreneꢀox‐
ideꢀwasꢀdetectedꢀinꢀanyꢀofꢀtheꢀcases.ꢀTheꢀ slightꢀdecreaseꢀinꢀ
selectivityꢀ forꢀ theꢀ recoveredꢀ catalystꢀ isꢀ probablyꢀ dueꢀ toꢀ re‐
sidualꢀ organicsꢀ onꢀ theꢀ catalystꢀ impedingꢀ theꢀ desorptionꢀ ofꢀ
benzaldehydeꢀfromꢀtheꢀcatalyticꢀcenters,ꢀleadingꢀtoꢀover‐oxid‐
ationꢀtoꢀbenzoicꢀacid.ꢀ
2
2
O
HO
2 2
H O
Schemeꢀ1.ꢀPlausibleꢀreactionꢀmechanismꢀofꢀstyreneꢀoxidation.ꢀ ꢀ
toꢀ aꢀ hydroxyl‐hydroxylperoxistyreneꢀ intermediateꢀ uponꢀ nu‐
cleophilicꢀ attackꢀ byꢀ anotherꢀ moleculeꢀ ofꢀ H
2
O .ꢀ Carbonꢀ bondꢀ
2
cleavageꢀ ofꢀ thisꢀ unstableꢀ intermediateꢀ thenꢀ producesꢀ benzal‐
dehydeꢀandꢀformaldehyde.ꢀSinceꢀtheꢀintermediateꢀstyreneꢀox‐
ideꢀwasꢀnotꢀdetectedꢀduringꢀtheꢀcourseꢀofꢀtheꢀreaction,ꢀweꢀcon‐
cludedꢀthatꢀtheꢀcatalyticꢀoxidationꢀofꢀstyreneꢀ withꢀ Cu‐SBA‐15ꢀ
followsꢀtheꢀfirstꢀpathway.ꢀInꢀaddition,ꢀasꢀcanꢀbeꢀseenꢀfromꢀtheꢀ
3.4.ꢀ ꢀ Mechanismꢀofꢀstyreneꢀoxidationꢀ
reactionꢀmechanism,ꢀ2ꢀequiv.ꢀH
2
O ꢀisꢀrequiredꢀforꢀstyreneꢀoxi‐
2
dationꢀ toꢀ benzaldehyde.ꢀ Thisꢀ isꢀ inꢀ goodꢀ agreementꢀ withꢀ ourꢀ
experimentalꢀ results,ꢀ whichꢀ showedꢀ thatꢀ theꢀ conversionꢀ wasꢀ
Styreneꢀcanꢀgenerallyꢀbeꢀoxidizedꢀtoꢀbenzaldehydeꢀviaꢀtwoꢀ
distinctꢀ pathwaysꢀusingꢀaꢀ copper(II)ꢀ Schiff‐baseꢀcomplexꢀasꢀ aꢀ
catalystꢀ (Schemeꢀ 1)ꢀ [27].ꢀ Theꢀ firstꢀ pathꢀ involvesꢀ aꢀ radicalꢀ
generallyꢀlowꢀwhenꢀlessꢀthanꢀ2ꢀequiv.ꢀofꢀH
highꢀconversionꢀofꢀstyreneꢀwasꢀobserved,ꢀwithꢀdecreasedꢀselec‐
tivityꢀifꢀmoreꢀH 2ꢀwasꢀemployed.ꢀ
2
O ꢀwasꢀused,ꢀwhileꢀaꢀ
2
mechanism.ꢀOneꢀmoleculeꢀofꢀH
2 2
O ꢀadsorbedꢀonꢀtheꢀcatalystꢀfirstꢀ
2
O
decomposesꢀtoꢀtwoꢀhydroxylꢀradicals.ꢀTheseꢀradicalsꢀthenꢀaddꢀ
toꢀ theꢀ C=Cꢀ bondꢀ ofꢀ styreneꢀ toꢀ formꢀ phenylethyleneꢀ glycol,ꢀ
whichꢀthenꢀundergoesꢀoxidativeꢀcleavageꢀtoꢀformꢀbenzaldehydeꢀ
andꢀformaldehyde.ꢀBenzaldehydeꢀisꢀreadilyꢀoxidizedꢀtoꢀbenzoicꢀ
4.ꢀ ꢀ Conclusionsꢀ
WeꢀpreparedꢀNH
2
‐SBA‐15ꢀusingꢀaꢀone‐potꢀco‐condensationꢀ
acid.ꢀ Alternatively,ꢀ styreneꢀ firstꢀ reactsꢀ withꢀ theꢀ activeꢀ H
moleculeꢀtoꢀformꢀstyreneꢀoxide,ꢀwhichꢀmayꢀfurtherꢀtransformꢀ
2
O
2
ꢀ
method,ꢀ andꢀ anchoredꢀ theꢀ copper(II)ꢀ Schiff‐baseꢀ complexꢀ toꢀ
affordꢀaꢀsolidꢀcatalyst,ꢀCu‐SBA‐15,ꢀforꢀtheꢀselectiveꢀoxidationꢀofꢀ
styreneꢀ toꢀ benzaldehyde.ꢀ Theꢀ highestꢀ conversionꢀ ofꢀ styreneꢀ
Tableꢀ3ꢀ
reachedꢀ 84.4%,ꢀ theꢀ selectivityꢀ forꢀ benzaldehydeꢀ wasꢀ upꢀ toꢀ
ExperimentalꢀresultsꢀonꢀtheꢀrecyclingꢀofꢀCu‐SBA‐15.ꢀ
–1
83.9%,ꢀandꢀtheꢀTOFꢀofꢀtheꢀcatalystꢀwasꢀ261.1ꢀh .ꢀTheꢀcatalystꢀ
ꢀb
ꢀ
Styreneꢀ
Selectivity ꢀ(%)
couldꢀ beꢀ usedꢀ threeꢀ timesꢀ withoutꢀ significantꢀ lossꢀ ofꢀ activity.ꢀ
Theꢀdistributionꢀofꢀaminoꢀgroupsꢀonꢀtheꢀmaterialꢀpreparedꢀbyꢀ
theꢀone‐potꢀco‐condensationꢀmethodꢀmayꢀbeꢀbetterꢀthanꢀisꢀtheꢀ
caseꢀwithꢀaꢀpost‐synthesisꢀgraftingꢀmethod.ꢀTherefore,ꢀtheꢀac‐
tiveꢀspeciesꢀcouldꢀbeꢀwellꢀdistributedꢀonꢀtheꢀsurfaceꢀofꢀtheꢀpre‐
paredꢀCu‐SBA‐15ꢀcatalyst,ꢀleadingꢀtoꢀaꢀhigherꢀcatalyticꢀactivity.ꢀ
Cycleꢀ
ꢀa
ꢀ
Conversion ꢀ(%) Benzaldehyde BenzoicꢀAcidꢀ Styreneꢀoxide
1
ꢀ
84.4ꢀ
86.9ꢀ
85.7ꢀ
83.9ꢀ
81.6ꢀ
81.2ꢀ
16.1ꢀ
18.4ꢀ
18.8ꢀ
0ꢀ
0ꢀ
0ꢀ
2
ꢀ
3
ꢀ
aꢀ
StyreneꢀconversionꢀcalculatedꢀviaꢀGCꢀanalysis.ꢀ
bꢀ
ProductꢀselectivityꢀcalculatedꢀviaꢀGCꢀanalysis.ꢀ

1722ꢀ
XuechengꢀZhuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1716–1726ꢀ
GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2014,ꢀ35:ꢀ1716–1726ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872-2067(14)60131-5
CatalyticꢀoxidationꢀofꢀstyreneꢀtoꢀbenzaldehydeꢀoverꢀaꢀcopperꢀSchiff‐base/SBA‐15ꢀcatalystꢀ
ꢀ
XuechengꢀZhu,ꢀRuweiꢀShen,ꢀLixiongꢀZhang*ꢀ
NanjingꢀTechꢀUniversityꢀ
ꢀ
AꢀCu‐SBA‐15ꢀcatalystꢀwasꢀpreparedꢀbyꢀimmobilizingꢀaꢀcopperꢀSchiff‐baseꢀcomplexꢀontoꢀanꢀamino‐modifiedꢀmesoporousꢀmaterialꢀSBA‐15,ꢀ
synthesizedꢀviaꢀaꢀone‐potꢀco‐condensationꢀmethod.ꢀTheꢀcatalystꢀwasꢀusedꢀforꢀtheꢀoxidationꢀofꢀstyreneꢀtoꢀbenzaldehydeꢀinꢀanꢀaqueousꢀ
medium.ꢀ
FonsecaꢀAꢀM.ꢀApplꢀOrganometꢀChem,ꢀ2012,ꢀ26:ꢀ44ꢀ
21] MauryaꢀMꢀR,ꢀSainiꢀP,ꢀKumarꢀA,ꢀCostaꢀPessoaꢀJ.ꢀEurꢀJꢀInorgꢀChem,ꢀ
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