Mesoporous polyoxometalate-based ionic hybrid as a highly effective heterogeneous catalyst for direct hydroxylation of benzene to phenol

Article abstract of DOI:10.1016/S1872-2067(17)62991-7

Self-assembled mesoporous polyoxometalate-based ionic hybrid catalyst, [PxyDim]_2.5PMoV₂, was prepared by combining p-xylene-tethered diimidazole ionic liquid [PxyDim]Cl₂ with Keggin-structured V-substituted polyoxometalate

Full text of DOI:10.1016/S1872-2067(17)62991-7

ChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
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
ꢀ
ꢀ
Article
Mesoporousꢀpolyoxometalate‐basedꢀionicꢀhybridꢀasꢀaꢀhighlyꢀ ꢀ
effectiveꢀheterogeneousꢀcatalystꢀforꢀdirectꢀhydroxylationꢀofꢀbenzeneꢀ
toꢀphenolꢀ
#
PingpingꢀZhaoꢀ*,ꢀYunyunꢀZhang,ꢀDaokuanꢀLi,ꢀHongyouꢀCuiꢀ ,ꢀLipengꢀZhang
ꢀ
SchoolꢀofꢀChemicalꢀEngineering,ꢀShandongꢀUniversityꢀofꢀTechnology,ꢀZiboꢀ255049,ꢀShandong,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Self‐assembledꢀ mesoporousꢀ polyoxometalate‐basedꢀ ionicꢀ hybridꢀ catalyst,ꢀ [PxyDim]2.5PMoV
preparedꢀ byꢀ combiningꢀ p‐xylene‐tetheredꢀ diimidazoleꢀ ionicꢀ liquidꢀ [PxyDim]Cl ꢀ withꢀ Keg‐
gin‐structuredꢀV‐substitutedꢀpolyoxometalateꢀH 40.ꢀTheꢀobtainedꢀhybridꢀwasꢀshownꢀtoꢀbeꢀ
aꢀmesostructuredꢀandꢀhydrophobicꢀmaterialꢀwithꢀgoodꢀthermalꢀstability.ꢀInꢀtheꢀH ‐basedꢀhydrox‐
2
,ꢀ wasꢀ
Receivedꢀ15ꢀOctoberꢀ2017ꢀ
Acceptedꢀ28ꢀNovemberꢀ2017ꢀ
Publishedꢀ5ꢀFebruaryꢀ2018ꢀ
2
5
PMo10V O
2
O
2 2
ylationꢀofꢀbenzeneꢀtoꢀphenol,ꢀtheꢀhybridꢀshowedꢀextraordinaryꢀcatalyticꢀactivityꢀandꢀrate,ꢀandꢀquiteꢀ
stableꢀreusability.ꢀTheꢀuniqueꢀhydrophobicꢀpropertiesꢀandꢀmesoporousꢀstructureꢀofꢀtheꢀhybridꢀwereꢀ
responsibleꢀforꢀitsꢀexcellentꢀcatalyticꢀperformance.ꢀ
Keywords:ꢀ
Polyoxometalateꢀ
Mesoporousꢀ
Benzeneꢀhydroxylationꢀ
Heterogeneousꢀcatalystꢀ
Phenol
©ꢀ2018,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1.ꢀ ꢀ Introductionꢀ
friendlyꢀ H
2
O ‐basedꢀ hydroxylationꢀ ofꢀ benzene.ꢀ Amongꢀ them,ꢀ
2
V‐containingꢀ POMꢀ catalystsꢀ haveꢀ provenꢀ toꢀ beꢀ effectiveꢀ cata‐
lystsꢀbecauseꢀofꢀtheꢀrelativelyꢀmildꢀreactionꢀconditionsꢀrequiredꢀ
forꢀ directꢀhydroxylationꢀofꢀbenzeneꢀtoꢀphenolꢀ[17,18].ꢀUnfor‐
tunately,ꢀisolatingꢀandꢀrecyclingꢀtheseꢀcatalystsꢀisꢀdifficultꢀ be‐
causeꢀ POMsꢀ readilyꢀ dissolveꢀ inꢀ theꢀ polarꢀ reactionꢀ system.ꢀ
Therefore,ꢀtheꢀpreparationꢀofꢀheterogeneousꢀPOMsꢀforꢀtheꢀdi‐
rectꢀhydroxylationꢀofꢀbenzeneꢀ hasꢀ becomeꢀ anꢀ interestingꢀandꢀ
challengingꢀtask.ꢀ
Phenolꢀisꢀamongꢀtheꢀmainꢀrawꢀmaterialsꢀusedꢀinꢀtheꢀchemi‐
calꢀ industry,ꢀ includingꢀ inꢀ theꢀ synthesisꢀ ofꢀ resins,ꢀ fungicides,ꢀ
preservatives,ꢀ andꢀ pharmaceuticals.ꢀ Industrially,ꢀ phenolꢀ isꢀ
producedꢀ byꢀ theꢀ three‐stepꢀ cumeneꢀ process,ꢀ whichꢀ hasꢀ highꢀ
energyꢀconsumptionꢀandꢀproducesꢀmuchꢀenvironmentalꢀpollu‐
tionꢀ[1].ꢀTherefore,ꢀmanyꢀattemptsꢀhaveꢀbeenꢀmadeꢀtoꢀdevelopꢀ
aꢀone‐stepꢀhydroxylationꢀofꢀbenzeneꢀtoꢀphenolꢀusingꢀdifferentꢀ
oxidants,ꢀsuchꢀasꢀO
systemsꢀ withꢀ Pd‐basedꢀ compositeꢀ membraneꢀ reactorsꢀ [5].ꢀ
Schiffꢀ basesꢀ [6],ꢀ vanadium‐containingꢀ mesoporousꢀ carbonꢀ
2
ꢀ[2],ꢀH
2
O
2
ꢀ[3],ꢀandꢀN
2
Oꢀ[4],ꢀasꢀwellꢀasꢀH
2
‐O
2
ꢀ
Theꢀ immobilizationꢀ ofꢀ POMsꢀ ontoꢀ porousꢀ supportsꢀ isꢀ aꢀ
commonlyꢀ usedꢀ strategyꢀ toꢀ heterogenizeꢀ POMsꢀ catalystꢀ [19].ꢀ
However,ꢀ thisꢀ approachꢀ inevitablyꢀ suffersꢀ fromꢀ slowꢀ reactionꢀ
ratesꢀand/orꢀleachingꢀofꢀactiveꢀsites.ꢀRecently,ꢀtheꢀmodificationꢀ
ofꢀPOMsꢀwithꢀorganicꢀunits,ꢀsuchꢀasꢀionicꢀliquidsꢀ(ILs),ꢀorgano‐
metallicꢀcomplexes,ꢀorganicꢀpolymers,ꢀandꢀsilicaꢀmatrices,ꢀhasꢀ
[7–11],ꢀ TS‐1ꢀ molecularꢀ sievesꢀ [12],ꢀ Fe‐basedꢀ metal‐organicꢀ
frameworksꢀ (MOFs)ꢀ [13],ꢀ andꢀ polyoxometalatesꢀ (POMs)ꢀ
[14–16]ꢀhaveꢀbeenꢀappliedꢀasꢀcatalystsꢀinꢀtheꢀenvironmentallyꢀ
*
ꢀ
ꢀCorrespondingꢀauthor.ꢀFax:ꢀ+86‐533‐2781213;ꢀE‐mail:ꢀzhaopingping@sdut.edu.cnꢀ
Correspondingꢀauthor.ꢀFax:ꢀ+86‐533‐2781213;ꢀE‐mail:ꢀcuihy@sdut.edu.cnꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21506118,ꢀ21476132,ꢀ51574160)ꢀandꢀShandongꢀProvinceꢀFounda‐
tionꢀforꢀOutstandingꢀYoungꢀScientistꢀ(BS2014CL030).ꢀ
DOI:ꢀ10.1016/S1872‐2067(17)62991‐7ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ39,ꢀNo.ꢀ2,ꢀFebruaryꢀ2018ꢀ ꢀ ꢀ

ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
335ꢀ
beenꢀ developedꢀ toꢀ prepareꢀ POM‐basedꢀ organic‐inorganicꢀ hy‐
bridꢀ heterogeneousꢀ catalystsꢀ [20–24].ꢀ Inꢀ thisꢀ context,ꢀ theꢀ as‐
semblyꢀofꢀPOMsꢀwithꢀtask‐specificꢀionicꢀliquidꢀcationsꢀisꢀaꢀsuc‐
cessfulꢀ exampleꢀ thatꢀ isꢀ beneficialꢀ forꢀ adjustingꢀ theꢀ solubility,ꢀ
redoxꢀproperties,ꢀandꢀsurfaceꢀmicroenvironmentꢀofꢀPOMs.ꢀPre‐
viously,ꢀweꢀhaveꢀreportedꢀaꢀseriesꢀofꢀPOM‐basedꢀionicꢀhybridꢀ
catalystsꢀpreparedꢀbyꢀcombiningꢀionicꢀliquidꢀcationsꢀwithꢀhet‐
eropolyanions,ꢀwithꢀtheꢀresultingꢀionicꢀsolidsꢀshownꢀtoꢀbeꢀef‐
fectiveꢀ catalystsꢀ forꢀ theꢀ oxidationꢀ ofꢀ sulfidesꢀ andꢀ benzeneꢀ
Fourierꢀ transformꢀ infraredꢀ (FT‐IR)ꢀ spectraꢀ wereꢀ recordedꢀ
onꢀ aꢀ Nicoletꢀ 360ꢀ FT‐IRꢀ instrumentꢀ (usingꢀ KBrꢀ discs)ꢀ inꢀ theꢀ
–1
wavenumberꢀ regionꢀ 4000–400ꢀ cm .ꢀ Elementalꢀ analysisꢀ wasꢀ
performedꢀusingꢀaꢀCHNꢀelementalꢀanalyzerꢀ(VarioꢀELꢀcube)ꢀandꢀ
inductivelyꢀ couplingꢀ plasmaꢀ spectrometerꢀ (ICP,ꢀ Jarrell‐Ashꢀ
1100).ꢀ X‐rayꢀ diffractionꢀ (XRD)ꢀ patternsꢀ wereꢀ recordedꢀ onꢀ aꢀ
BrukerꢀD8ꢀAdvanceꢀpowderꢀdiffractometerꢀusingꢀaꢀNi‐filteredꢀ
CuꢀK ꢀradiationꢀsourceꢀatꢀ40ꢀkVꢀandꢀ200ꢀmA,ꢀinꢀtheꢀ2ꢀrangeꢀofꢀ
α
5o–50ꢀatꢀaꢀscanꢀrateꢀofꢀ2/min.ꢀBrunauer‐Emmett‐Tellerꢀ(BET)ꢀ
surfaceꢀareasꢀwereꢀmeasuredꢀatꢀtheꢀtemperatureꢀofꢀliquidꢀni‐
trogenꢀ usingꢀ aꢀ Micromeriticsꢀ ASAP2010ꢀ analyzer.ꢀ Samplesꢀ
[25–27].ꢀ Nevertheless,ꢀ self‐assembledꢀ ionicꢀ hybridsꢀ areꢀ non‐
porousꢀ andꢀ haveꢀ lowꢀ specificꢀ surfaceꢀ areas,ꢀ whichꢀ limitꢀ theꢀ
heterogeneousꢀ catalyticꢀ activityꢀ inꢀ mass‐transfer‐controlledꢀ
systemsꢀ [28].ꢀ Theꢀ directꢀ hydroxylationꢀ ofꢀ benzeneꢀ usingꢀ
POM‐basedꢀpolymericꢀionicꢀhybridꢀheterogeneousꢀcatalystsꢀhasꢀ
alsoꢀbeenꢀstudiedꢀ[29].ꢀDespiteꢀtheꢀhighꢀspecificꢀsurfaceꢀareasꢀ
andꢀexcellentꢀ performanceꢀobtained,ꢀcomplexꢀ stepsꢀandꢀlargeꢀ
amountsꢀofꢀorganicꢀsolventꢀareꢀrequiredꢀforꢀcatalystꢀprepara‐
tion.ꢀTherefore,ꢀaꢀsimpleꢀapproachꢀtoꢀprepareꢀaꢀhighlyꢀefficientꢀ
heterogeneousꢀPOM‐basedꢀcatalystꢀwithꢀmesoporousꢀstructureꢀ
andꢀhighꢀspecificꢀsurfaceꢀareaꢀisꢀrequired.ꢀ
–3
wereꢀdegassedꢀatꢀ150ꢀCꢀtoꢀaꢀpressureꢀofꢀ10 ꢀTorrꢀbeforeꢀanal‐
ysis.ꢀ Scanningꢀ electronꢀ microscopyꢀ (SEM)ꢀ imagesꢀ wereꢀ rec‐
ordedꢀusingꢀaꢀHitachiꢀS‐4800ꢀfield‐emissionꢀscanningꢀelectronꢀ
microscope.ꢀ Thermogravimetricꢀ (TG)ꢀ analysisꢀ wasꢀ conductedꢀ
usingꢀ aꢀ STA409ꢀ instrumentꢀ inꢀ dryꢀ airꢀ atꢀ aꢀ heatingꢀ rateꢀ ofꢀ 10ꢀ
C/min.ꢀ
2.2.ꢀ ꢀ Catalystꢀpreparationꢀ
Inꢀcontrast,ꢀitꢀshouldꢀbeꢀnotedꢀthatꢀhighlyꢀhydrophobicꢀor‐
ganicꢀframeworksꢀinꢀhybridꢀcatalystsꢀactꢀasꢀdynamicꢀtrapsꢀthatꢀ
canꢀadsorbꢀrelativelyꢀnonpolarꢀsubstrateꢀmoleculesꢀandꢀeasilyꢀ
desorbꢀ relativelyꢀ polarꢀ productꢀ moleculesꢀ [30,31].ꢀ Therefore,ꢀ
hydrophobicꢀorganicꢀsegmentsꢀinꢀhybridꢀcatalystsꢀcanꢀenhanceꢀ
theꢀprobabilityꢀofꢀinteractionsꢀbetweenꢀtheꢀsubstrateꢀandꢀcata‐
lyticꢀ center,ꢀ whichꢀ wouldꢀ improveꢀ theꢀ catalyticꢀ activityꢀ andꢀ
selectivity.ꢀ ꢀ
Accordingly,ꢀweꢀhereinꢀreportꢀaꢀhighlyꢀhydrophobicꢀmeso‐
porousꢀ POM‐basedꢀ hybridꢀ catalystꢀ preparedꢀ byꢀ pairingꢀ
V‐containingꢀ POMꢀ anionsꢀ withꢀ p‐xylene‐tetheredꢀ diimidazoleꢀ
ionicꢀliquidꢀcationsꢀ(Fig.ꢀ1).ꢀTheꢀcatalystsꢀnotꢀonlyꢀexhibitꢀen‐
hancedꢀcatalyticꢀactivitiesꢀforꢀtheꢀdirectꢀhydroxylationꢀofꢀben‐
2.2.1.ꢀ ꢀ PreparationꢀofꢀH
40,ꢀhereinꢀabbreviatedꢀasꢀPMoV
accordingꢀtoꢀourꢀpreviousꢀworkꢀ[29].ꢀInꢀdetail,ꢀMoO
0.115ꢀmol)ꢀandꢀV ꢀ(2.1ꢀg,ꢀ0.0115ꢀmol)ꢀwereꢀaddedꢀtoꢀdeion‐
izedꢀwaterꢀ(250ꢀmL),ꢀandꢀheatedꢀtoꢀrefluxꢀunderꢀvigorousꢀstir‐
ring,ꢀ usingꢀ aꢀ water‐cooledꢀ condenser.ꢀ Anꢀ aqueousꢀ solutionꢀ ofꢀ
5
PMo10
V
2
O
40
ꢀ
5 2
H PMo10V O
2
,ꢀwasꢀpreparedꢀ
3
ꢀ(16.59ꢀg,ꢀ
O
2 5
H
3
PO
toꢀtheꢀmixture.ꢀWhenꢀtheꢀmixtureꢀbecameꢀaꢀclearꢀorange‐redꢀ
solution,ꢀitꢀwasꢀcooledꢀtoꢀroomꢀtemperature.ꢀH 40ꢀwasꢀ
4
ꢀ(1.33ꢀg,ꢀ0.0115ꢀmol,ꢀ85ꢀwt%)ꢀwasꢀthenꢀaddedꢀdropwiseꢀ
5
PMo10
V O
2
obtainedꢀasꢀanꢀorange‐redꢀpowderꢀafterꢀevaporatingꢀtheꢀsolu‐
tionꢀtoꢀdrynessꢀandꢀpurificationꢀbyꢀrecrystallization.ꢀ
2.2.2.ꢀ ꢀ Preparationꢀofꢀionicꢀliquidꢀprecursorsꢀ
zeneꢀ withꢀ H
2 2
O ,ꢀ butꢀ alsoꢀ facilitateꢀ catalystꢀ recoveryꢀ fromꢀ theꢀ
2
Dicationicꢀionicꢀliquidꢀprecursorꢀ[PxyDim]Cl ꢀwasꢀpreparedꢀ
reactionꢀsystem.ꢀTheꢀexcellentꢀcatalyticꢀperformancesꢀofꢀtheseꢀ
catalystsꢀ areꢀ mostlyꢀ attributedꢀ toꢀ theꢀ contributionsꢀ ofꢀ theirꢀ
porousꢀstructuresꢀandꢀhydrophobicꢀmicroenvironments.ꢀ
asꢀ follows.ꢀ Methylimidazoleꢀ (0.21ꢀ
mol)ꢀ andꢀ
,'‐dichloro‐p‐xyleneꢀ (0.10ꢀ mol)ꢀ wereꢀ dissolvedꢀ inꢀ dichloro‐
methaneꢀ (50ꢀ mL)ꢀ atꢀ 35ꢀ Cꢀ underꢀ aꢀ nitrogenꢀ atmosphereꢀ andꢀ
stirredꢀforꢀ48ꢀh.ꢀTheꢀsolventꢀwasꢀthenꢀremovedꢀbyꢀdistillationꢀ
andꢀtheꢀresidueꢀwasꢀwashedꢀwithꢀTHFꢀ(3ꢀ×ꢀ30ꢀmL).ꢀAfterꢀdryingꢀ
2.ꢀ ꢀ Experimentalꢀ ꢀ
2
underꢀ aꢀ highꢀ vacuum,ꢀ [PxyDim]Cl ꢀ wasꢀ obtainedꢀ asꢀ aꢀ whiteꢀ
2.1.ꢀ ꢀ Materialsꢀandꢀanalyticꢀmethodsꢀ
solidꢀinꢀ95%ꢀyield.ꢀ ꢀ
2
Analogousꢀionicꢀliquidꢀ[EthDim]Cl ꢀwasꢀpreparedꢀaccordingꢀ
Allꢀ chemicals,ꢀ includingꢀ benzeneꢀ (99.5%),ꢀ acetonitrileꢀ
99.9%),ꢀ aceticꢀ acidꢀ (99.8%),ꢀ andꢀ dichloromethaneꢀ (99.9%),ꢀ
wereꢀ purchasedꢀ fromꢀ Sinopharmꢀ Chemicalꢀ Reagentꢀ Co.,ꢀ Ltd.ꢀ
andꢀusedꢀwithoutꢀfurtherꢀpurification.ꢀ ꢀ
toꢀaꢀliteratureꢀprocedureꢀ[20].ꢀMethylimidazoleꢀ(0.21ꢀmol)ꢀandꢀ
1,2‐dichloroethaneꢀ (0.10ꢀ mol)ꢀ wereꢀ dissolvedꢀ inꢀ isopropanolꢀ
(50ꢀmL)ꢀatꢀ80ꢀCꢀunderꢀaꢀnitrogenꢀatmosphereꢀandꢀstirredꢀforꢀ
48ꢀh.ꢀOnꢀreactionꢀcompletion,ꢀtheꢀsolventꢀwasꢀremovedꢀbyꢀdis‐
tillation,ꢀandꢀtheꢀproductꢀwasꢀdriedꢀunderꢀhighꢀvacuumꢀtoꢀaf‐
(
fordꢀ[EthDim]Cl
2
ꢀasꢀaꢀcolorlessꢀliquidꢀinꢀ83%ꢀyield.ꢀIonicꢀliquidꢀ
ꢀ wasꢀ synthesizedꢀ usingꢀ theꢀ sameꢀ method.ꢀ
ꢀwasꢀsynthesizedꢀaccordingꢀtoꢀaꢀliteratureꢀprocedureꢀ
[
[
[
ButDim]Cl
2
BMim]Cl
2
29].ꢀ
2
.2.3.ꢀ ꢀ Preparationꢀofꢀpolyoxometalate‐basedꢀionicꢀhybridsꢀ
Polyoxometalateꢀ(POM)‐basedꢀionicꢀhybridsꢀwereꢀpreparedꢀ
byꢀreactingꢀtheꢀionicꢀliquidꢀprecursorsꢀwithꢀPMoV .ꢀInꢀaꢀtypicalꢀ
procedure,ꢀ [PxyDim]Cl ꢀ (5.0ꢀ mmol)ꢀ andꢀ PMoV ꢀ (2.0ꢀ mmol)ꢀ
wereꢀseparatelyꢀdissolvedꢀinꢀdeionizedꢀwaterꢀ(2.0ꢀmmol).ꢀTheꢀ
2
2
2
Fig.ꢀ1.ꢀSchematicꢀpreparationꢀofꢀionicꢀhybridꢀcatalysts.ꢀ

336ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
aqueousꢀ PMoV
2
ꢀ solutionꢀ wasꢀ addedꢀ toꢀ theꢀ [PxyDim]Cl
2
ꢀ solu‐
withꢀtheꢀcalculatedꢀresults.ꢀTGꢀanalysisꢀ(Fig.ꢀ2)ꢀshowedꢀthatꢀtheꢀ
startingꢀdecompositionꢀtemperatureꢀofꢀ[DiPxyim]2.5PMoV ꢀwasꢀ
tion,ꢀ followedꢀ byꢀ stirringꢀ atꢀ roomꢀ temperatureꢀ forꢀ 6ꢀ h.ꢀ Theꢀ
formedꢀyellowꢀprecipitateꢀwasꢀthenꢀfiltered,ꢀwashedꢀwithꢀwaterꢀ
2
aboutꢀ270ꢀCꢀ(curveꢀ(1)),ꢀwhichꢀwasꢀmarkedlyꢀhigherꢀthanꢀ200ꢀ
Cꢀ forꢀ theꢀ ionicꢀ liquidꢀ (curveꢀ (2)).ꢀ Theꢀ drasticꢀ massꢀ lossꢀ ofꢀ
nearlyꢀ25%ꢀinꢀtheꢀtemperatureꢀrangeꢀ270–530ꢀCꢀcorrespond‐
(
3ꢀ×ꢀ10ꢀmL)ꢀandꢀethanolꢀ(3ꢀ×ꢀ10ꢀmL),ꢀandꢀdriedꢀunderꢀvacuum,ꢀ
affordingꢀ [PxyDim]2.5PMoV .ꢀ Usingꢀ theꢀ aboveꢀ procedure,ꢀ
PxyDim] HPMoV ꢀandꢀ[PxyDim]H PMoV ꢀwereꢀalsoꢀpreparedꢀ
usingꢀ theꢀ correspondingꢀ molarꢀ ratiosꢀ ofꢀ theꢀ respectiveꢀ reac‐
tants.ꢀ Analogousꢀ hybridsꢀ [EthDim]2.5PMoV andꢀ
ButDim]2.5PMoV ꢀwereꢀalsoꢀpreparedꢀaccordingly.ꢀ
2
2+
[
2
2
3
2
edꢀ toꢀ thermalꢀ decompositionꢀ ofꢀ organicꢀ cationꢀ [PxyDim] ꢀ inꢀ
theꢀhybrid.ꢀThisꢀphenomenonꢀdemonstratedꢀtheꢀhighꢀthermalꢀ
2
ꢀ
2
stabilityꢀofꢀ[PxyDim]2.5PMoV ꢀdueꢀtoꢀformationꢀofꢀtheꢀionicꢀhy‐
[
2
bridꢀ[25,26].ꢀ
Fig.ꢀ3ꢀshowsꢀtheꢀFT‐IRꢀspectraꢀofꢀILꢀ[PxyDim]Cl
[PxyDim]2.5PMoV .ꢀTheꢀFT‐IRꢀspectrumꢀofꢀ[PxyDim]Cl
showsꢀcharacteristicꢀbandsꢀatꢀ1170–1630ꢀcm ꢀandꢀ3010–3140ꢀ
2
ꢀandꢀhybridꢀ
2
.3.ꢀ ꢀ Catalystꢀevaluationꢀ
2
2
ꢀclearlyꢀ
–1
–1
Benzeneꢀ (0.78ꢀ g,ꢀ 10ꢀ mmol),ꢀ aꢀ mixtureꢀ ofꢀ acetonitrileꢀ andꢀ
aceticꢀacidꢀ(volumeꢀratioꢀ1:1,ꢀ8ꢀmL),ꢀandꢀcatalystꢀ(0.1ꢀg)ꢀwereꢀ
addedꢀ toꢀ aꢀ 25‐mLꢀ flaskꢀ reactor.ꢀ Aqueousꢀ H ꢀ (30ꢀ wt%,ꢀ 30ꢀ
mmol)ꢀwasꢀthenꢀaddedꢀdropwiseꢀtoꢀtheꢀstirredꢀmixtureꢀinꢀtheꢀ
reactorꢀ withinꢀ 20ꢀ min.ꢀ Theꢀ reactionꢀ timeꢀ wasꢀ recordedꢀ fromꢀ
cm ꢀassignedꢀtoꢀorganicꢀgroups,ꢀindicatingꢀtheꢀcoexistenceꢀofꢀ
imidazoleꢀ andꢀ p‐xyleneꢀ units.ꢀ Afterꢀ combiningꢀ [PxyDim]Cl
2
ꢀ
O
2 2
withꢀH
5
PMo10
V
2
O
40,ꢀtheꢀ characteristicꢀvibrationꢀbandsꢀ forꢀtheꢀ
5–
[PMo10
V
2
O40] ꢀspeciesꢀwereꢀobservedꢀatꢀ1054,ꢀ947,ꢀ868,ꢀandꢀ
–1
796ꢀ cm ,ꢀ attributedꢀ toꢀ P–O
Mo–O –Moꢀ vibrations,ꢀ respectively.ꢀ Moreover,ꢀ theꢀ peaksꢀ as‐
signedꢀ toꢀ theꢀ organicꢀ moietyꢀ inꢀ [PxyDim]2.5PMoV ꢀ wereꢀ onlyꢀ
slightlyꢀ shifted,ꢀ indicatingꢀ formationꢀ ofꢀ hybridꢀ
[PxyDim]2.5PMoV ꢀ viaꢀ strongꢀ ionicꢀ bondꢀ interactionsꢀ andꢀ hy‐
a
,ꢀ Mo=O
d
,ꢀ Mo–O –Mo,ꢀ andꢀ
b
whenꢀ H
2 2
O ꢀ additionꢀ wasꢀ complete.ꢀ Theꢀ typicalꢀ reactionꢀ tem‐
c
peratureꢀandꢀtimeꢀwereꢀ70ꢀCꢀandꢀ1ꢀh,ꢀrespectively.ꢀAfterꢀtheꢀ
reaction,ꢀtheꢀmixtureꢀwasꢀcentrifugedꢀtoꢀremoveꢀtheꢀsolidꢀcata‐
lyst,ꢀandꢀtheꢀsupernatantꢀwasꢀanalyzedꢀbyꢀgasꢀchromatographyꢀ
2
2
(
GC)ꢀusingꢀanꢀAgilentꢀ7890Bꢀchromatographꢀequippedꢀwithꢀaꢀ
drogen‐bondingꢀnetworksꢀ[32].ꢀ
SEMꢀimagesꢀofꢀ[PxyDim]2.5PMoV ꢀ(Fig.ꢀ4(a)ꢀandꢀ(b))ꢀshowedꢀ
irregularꢀ honeycomb‐shapedꢀ morphologiesꢀ causedꢀ byꢀ theꢀ ac‐
FIDꢀdetectorꢀandꢀcapillaryꢀcolumnꢀ(SE‐54ꢀ30ꢀmꢀ×ꢀ0.32ꢀmmꢀ×ꢀ0.3ꢀ
μm).ꢀTheꢀGCꢀovenꢀtemperatureꢀwasꢀheldꢀatꢀ80ꢀCꢀandꢀthenꢀin‐
creasedꢀatꢀ10ꢀC/min,ꢀholdingꢀatꢀ100ꢀCꢀforꢀ2ꢀminꢀandꢀ220ꢀCꢀ
forꢀ 4ꢀ min.ꢀ Underꢀ theꢀ conditionsꢀ employed,ꢀ onlyꢀ phenolꢀ wasꢀ
detectedꢀasꢀaꢀproduct,ꢀwithꢀnoꢀGCꢀsignalsꢀforꢀcatechol,ꢀhydro‐
quinone,ꢀorꢀbenzoquinoneꢀwereꢀobserved.ꢀHowever,ꢀtheꢀreac‐
tionꢀmixtureꢀchangedꢀtoꢀaꢀdarkꢀcolor,ꢀprobablyꢀdueꢀtoꢀtheꢀfor‐
mationꢀofꢀheavyꢀcompoundsꢀ(coke)ꢀthatꢀcannotꢀbeꢀdetectedꢀbyꢀ
GC.ꢀ1,4‐Dioxaneꢀwasꢀusedꢀasꢀanꢀinternalꢀstandardꢀtoꢀcalculateꢀ
benzeneꢀ conversionꢀ (benzeneꢀ conversionꢀ =ꢀ (initialꢀ benzeneꢀ
2
100
80
60
40
(1)
(
(
mmol)ꢀ –ꢀ unconvertedꢀ benzeneꢀ (mmol))ꢀ /ꢀ initialꢀ benzeneꢀ
mmol)),ꢀ phenolꢀ yieldꢀ (phenolꢀ yieldꢀ (basedꢀ onꢀ benzene)ꢀ =ꢀ
phenolꢀ (mmol)/initialꢀ benzeneꢀ (mmol)),ꢀ andꢀ theꢀ turnoverꢀ
numberꢀ(TONꢀ=ꢀphenolꢀ(mmol)/V
ꢀinꢀcatalystꢀ(mmol)).ꢀToꢀtestꢀ
catalyticꢀrecyclingꢀofꢀ[PxyDim]2.5PMoV ,ꢀtheꢀcatalystꢀwasꢀsepa‐
ratedꢀbyꢀfiltrationꢀafterꢀreaction,ꢀwashedꢀwithꢀacetonitrileꢀ(3ꢀ×ꢀ
0ꢀmL),ꢀandꢀdriedꢀunderꢀvacuumꢀatꢀ80ꢀCꢀforꢀ6ꢀh.ꢀTheꢀrecov‐
eredꢀcatalystꢀwasꢀreusedꢀinꢀtheꢀnextꢀrun.ꢀ
20
0
2
(
2)
2
100 200 300 400 500 600 700
2
Temperature (C)
Fig.ꢀ2.ꢀTGꢀcurvesꢀofꢀ(1)ꢀ[PxyDim]2.5PMoV
2
ꢀandꢀ(2)ꢀ[PxyDim]Cl .ꢀ
2
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
(1)
3.1.ꢀ ꢀ Catalystꢀcharacterizationꢀ
3010
1630
(2)
x 2
Elementalꢀ analysisꢀ resultsꢀ forꢀ [PxyDim] H5–2xPMoV ꢀ areꢀ
1170
3140
shownꢀinꢀTableꢀ1.ꢀTheꢀC,ꢀH,ꢀandꢀNꢀcontentsꢀcorrespondedꢀwellꢀ
Tableꢀ1ꢀ
1054
Elementalꢀanalysisꢀofꢀ[PxyDim]
x
H
5–2xPMoV
2
.ꢀ
8
68
947
Experimentalꢀresultsꢀ(calculatedꢀvalues)/wt%
Catalystꢀ
7
96
Cꢀ
Nꢀ
Hꢀ
[
[
[
PxyDim]2.5PMoV
PxyDim] HPMoV
PxyDim]H PMoV2ꢀ
2
ꢀ
2
ꢀ
19.1ꢀ(19.9)ꢀ
16.7ꢀ(16.9)ꢀ
10.3ꢀ(9.6)ꢀ
19.0ꢀ
5.4ꢀ(5.8) 2.0ꢀ(2.3)
4.2ꢀ(4.9) 1.9ꢀ(1.9)
2.7ꢀ(2.8) 1.3ꢀ(1.1)
3
500 3000
1500
Wavenumber
1000
500
2

1
(
cm
)
3
Recycledꢀ
5.6ꢀ
1.9ꢀ
Fig.ꢀ3.ꢀFT‐IRꢀspectraꢀofꢀ(1)ꢀ[PxyDim]Cl
2
ꢀandꢀ(2)ꢀ[PxyDim]2.5PMoV .ꢀ
2

ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
337ꢀ
2
pearedꢀforꢀ[PxyDim]2.5PMoV .ꢀForꢀtheꢀlatter,ꢀaꢀnewꢀbroadꢀBraggꢀ
(
a)
(b)
peakꢀwasꢀdetectedꢀatꢀ2θꢀ=ꢀ8.1,ꢀclearlyꢀshowingꢀthatꢀtheꢀhybridꢀ
hadꢀ aꢀ noncrystalꢀ structure.ꢀ Thisꢀ amorphousꢀ structureꢀ wasꢀ inꢀ
agreementꢀ withꢀ theꢀ SEMꢀ imageꢀ (Fig.ꢀ 4(b)).ꢀ Therefore,ꢀ itꢀ wasꢀ
concludedꢀthatꢀhybridꢀ[PxyDim]2.5PMoV
talꢀstructureꢀcontainingꢀaꢀcertainꢀregularꢀion‐pairꢀarray.ꢀ
TheꢀBETꢀsurfaceꢀareasꢀofꢀ[PxyDim]2.5PMoV ꢀandꢀtheꢀIL–POMꢀ
analoguesꢀwereꢀcharacterizedꢀusingꢀnitrogenꢀsorptionꢀexperi‐
ments.ꢀAsꢀshownꢀinꢀFig.ꢀ6,ꢀtheꢀisothermsꢀofꢀ[PxyDim]2.5PMoV
wereꢀtypeꢀIVꢀwithꢀaꢀclearꢀH1‐typeꢀhysteresisꢀloopꢀinꢀtheꢀrelativeꢀ
pressureꢀ p/p ꢀrangeꢀofꢀ0.8ꢀtoꢀ 1.0,ꢀindicatingꢀtheꢀ formationꢀofꢀ
mesoporousꢀ materials.ꢀ Theꢀ BETꢀ surfaceꢀ areaꢀ andꢀ totalꢀ poreꢀ
2
ꢀpossessedꢀaꢀnoncrys‐
2
2
ꢀ
(
(
c)
e)
(d)
(f)
o
2
3
volumeꢀwereꢀ58.5ꢀm /gꢀandꢀ0.44ꢀcm /g,ꢀrespectivelyꢀ(Tableꢀ2,ꢀ
Entryꢀ 1).ꢀ Theꢀ mostꢀ probableꢀ distributionꢀ ofꢀ mesoporesꢀ ap‐
pearedꢀ atꢀ 29.9ꢀ nm.ꢀ However,ꢀ controlꢀ catalystꢀ
[
EthDim]2.5PMoV ,ꢀ containingꢀ anꢀ alkylꢀ groupꢀ insteadꢀ ofꢀ
2
p‐xylene,ꢀwasꢀaꢀnonporousꢀmaterialꢀwithꢀaꢀsurfaceꢀareaꢀofꢀonlyꢀ
2
2
.3ꢀ m /gꢀ(Tableꢀ2,ꢀEntryꢀ4).ꢀTheseꢀresultsꢀdemonstratedꢀthatꢀ
theꢀp‐xyleneꢀgroupsꢀplayedꢀimportantꢀrolesꢀinꢀtheꢀformationꢀofꢀ
mesoporousꢀstructuresꢀandꢀencouragedꢀusꢀtoꢀprepareꢀandꢀtestꢀ
aꢀseriesꢀofꢀcatalystsꢀ[PxyDim]
x
H
5–2xPMoV
2
ꢀwithꢀdifferentꢀmolarꢀ
ratiosꢀofꢀ[PxyDim] ꢀtoꢀPOM.ꢀTheꢀnitrogenꢀsorptionꢀisothermsꢀ
ofꢀtheꢀresultantꢀsamplesꢀareꢀshownꢀinꢀFig.ꢀ6.ꢀ[PxyDim] HPMoV
2+
2
2
ꢀ
showedꢀaꢀtypicalꢀtype‐IVꢀisothermꢀinꢀaꢀpressureꢀrangeꢀofꢀ0.8ꢀ<ꢀ
Fig.ꢀ4.ꢀ(a,ꢀb)ꢀSEMꢀimagesꢀandꢀ(c,ꢀd)ꢀTEMꢀimagesꢀofꢀ[PxyDim]2.5PMoV
SEMꢀimagesꢀofꢀ(e)ꢀ[PxyDim]H PMoV ꢀandꢀ(f)ꢀ[EthDim]2.5PMoV .ꢀ
2
;ꢀ
2
p/p ꢀ<ꢀ0.1,ꢀaꢀlowerꢀBETꢀsurfaceꢀareaꢀ(49.3ꢀm /g)ꢀwithꢀaꢀlargerꢀ
3
2
2
0
averageꢀmesoporeꢀsizeꢀofꢀ35.6ꢀnm,ꢀandꢀaꢀtotalꢀporeꢀvolumeꢀofꢀ
3
0
.44ꢀ cm /gꢀ (Tableꢀ 2,ꢀ Entryꢀ 2).ꢀ However,ꢀ theꢀ lowerꢀ p‐xyleneꢀ
cumulationꢀofꢀtheꢀnanometerꢀballꢀandꢀnanoscaleꢀhollowꢀstruc‐
tures,ꢀwhichꢀmightꢀreflectꢀtheꢀinterconnectedꢀIL‐POMꢀsecond‐
contentꢀ gaveꢀ nonporousꢀ hybridꢀ materialꢀ [PxyDim]H
3
PMoV ,ꢀ
2
2
whichꢀwasꢀconsistentꢀwithꢀtheꢀlowꢀsurfaceꢀareaꢀ(<10ꢀm /g)ꢀforꢀ
commonꢀ organicꢀ POMꢀ salts.ꢀ Inꢀ conclusion,ꢀ twoꢀ mesoporousꢀ
IL‐POMꢀhybridꢀcatalystsꢀwithꢀmoderateꢀBETꢀsurfaceꢀareasꢀwereꢀ
2
aryꢀstructure.ꢀTEMꢀimagesꢀofꢀ[PxyDim]2.5PMoV ꢀ(Fig.ꢀ4(c)ꢀandꢀ
(d))ꢀ showedꢀ theꢀ existenceꢀ ofꢀ randomꢀ mesoporesꢀ amongꢀ theꢀ
intertwinedꢀ particlesꢀ andꢀ microporesꢀ ofꢀ IL‐cationsꢀ andꢀ
POM‐anions.ꢀ Inꢀ theꢀ caseꢀ ofꢀ analogousꢀ hybridsꢀ
(1)
[
PxyDim]H
3
PMoV
2
ꢀ andꢀ [EthDim]2.5PMoV ꢀ (Fig.ꢀ 4(e)ꢀ andꢀ (f)),ꢀ
2
theꢀ morphologiesꢀ changedꢀ toꢀ anꢀ irregularꢀ micrometer‐sizedꢀ
honeycomb‐shapedꢀ morphologyꢀ andꢀ angularꢀ blocksꢀ withꢀ aꢀ
roughꢀ surface,ꢀ respectively,ꢀ dueꢀ toꢀ packingꢀ ofꢀ theꢀ nanoscaleꢀ
primaryꢀparticles.ꢀ
(2)
XRDꢀ patternsꢀ ofꢀ pureꢀ
PxyDim]2.5PMoV ꢀ areꢀ shownꢀ inꢀ Fig.ꢀ 5.ꢀ Characteristicꢀ sharpꢀ
Braggꢀ peaksꢀ observedꢀ forꢀ Keggin‐typeꢀ H
5 2 40
H PMo10V O ꢀ andꢀ hybridꢀ
[
2
5
PMo10
V O40ꢀ disap‐
2
(3)
(4)
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
(1)
Fig.ꢀ6.ꢀN
2
ꢀadsorption‐desorptionꢀisothermsꢀofꢀ(1)ꢀ[PxyDim]2.5PMoV
2
,ꢀ(2)ꢀ
[
PxyDim]
2
HPMoV
2
,ꢀ(3)ꢀ[PxyDim]H
3
PMoV
2
,ꢀandꢀ(4)ꢀ[EthDim]2.5PMoV .ꢀ
2
Tableꢀ2ꢀ
Texturalꢀparametersꢀofꢀvariousꢀsamples.ꢀ
(2)
a
2
bꢀ
3
avꢀcꢀ/nm
29.9ꢀ
35.6ꢀ
21.7ꢀ
27.7ꢀ
Entry
Sampleꢀ
S
BETꢀ /ꢀ(m /g)ꢀ
V
pꢀ /(m /g)
D
1ꢀ
2
[PxyDim]2.5PMoV ꢀ
58.5ꢀ
0.44ꢀ
0.44ꢀ
0.03ꢀ
0.02ꢀ
1
0
20
30
40
50
2ꢀ
[PxyDim]
[PxyDim]H
[EthDim]2.5PMoV
ꢀBETꢀsurfaceꢀarea.ꢀ
2
HPMoV
2
ꢀ
49.3ꢀ
ꢀ 6.2ꢀ
3
ꢀ
3
PMoV2ꢀ
2
PMo10

4
ꢀ
2
ꢀ
ꢀ 2.3ꢀ
Fig.ꢀ5.ꢀXRDꢀpatternsꢀofꢀ(1)ꢀH
5
V
2
O40ꢀandꢀ(2)ꢀ[PxyDim]2.5PMoV
2
.ꢀ
a
b
ꢀTotalꢀporeꢀvolume.ꢀ ꢀAverageꢀporeꢀsize.ꢀ
c

338ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
obtainedꢀbyꢀadjustingꢀtheꢀp‐xyleneꢀcontent.ꢀ ꢀ
Tableꢀ3ꢀ
Catalyticꢀ performancesꢀ ofꢀ variousꢀ catalystsꢀ forꢀ theꢀ hydroxylationꢀ ofꢀ
a
3.2.ꢀ ꢀ Catalyticꢀactivityꢀ
benzeneꢀwithꢀH
2
O
2
ꢀ .ꢀ
Tableꢀ3ꢀcomparesꢀtheꢀperformancesꢀofꢀvariousꢀcatalystsꢀinꢀ
theꢀ hydroxylationꢀ ofꢀ benzeneꢀ withꢀ H
tectedꢀ withoutꢀ catalystꢀ orꢀ inꢀ theꢀ presenceꢀ ILꢀ precursorꢀ
PxyDim]Cl ꢀ orꢀ V‐freeꢀ H 40ꢀ (Entriesꢀ 1–3).ꢀ Whenꢀ
40ꢀwasꢀusedꢀasꢀtheꢀcatalyst,ꢀaꢀhighꢀphenolꢀyieldꢀofꢀ
9.7%ꢀwasꢀachieved,ꢀwithꢀ30.2%ꢀconversionꢀandꢀaꢀTONꢀofꢀ51.7ꢀ
Entryꢀ 4),ꢀ consistentꢀ withꢀ theꢀ proposalꢀ thatꢀ Vꢀ ionsꢀ inꢀ
2
O
2
.ꢀ Noꢀ phenolꢀ wasꢀ de‐
ꢀ
b
ꢀc
d
Entry
Catalystꢀ
noneꢀ
[PxyDim]Cl
Solubilityꢀinꢀreactionꢀ C /% Y /% TONꢀ
1
ꢀ
–ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
0ꢀ
[
H
2
(
2
3
PMo12O
2
ꢀ
2
ꢀ
solubleꢀ
solubleꢀ
solubleꢀ
5
PMo10V O
2
3ꢀ
H PMo O ꢀ
3
12 40
4
ꢀ
H
5
2
PMo10V O
40
ꢀ
30.2 29.7 51.7
28.0 27.4 57.1
29.4 28.9 69.5
24.6 24.5 55.7
19.5 18.9 37.8
15.5 14.6 32.4
20.7 20.7 47.0
5
ꢀ
[BMim]2.5PMoV2ꢀ
[PxyDim]2.5PMoV2
solubleꢀ
POM‐anionsꢀareꢀcatalyticallyꢀactiveꢀcentersꢀforꢀtheꢀhydroxyla‐
tionꢀ ofꢀ benzeneꢀ toꢀ phenolꢀ [19,20,23].ꢀ However,ꢀ pureꢀ
6ꢀ
7ꢀ
8ꢀ
9ꢀ
insolubleꢀ
insolubleꢀ
insolubleꢀ
insolubleꢀ
insolubleꢀ
[PxyDim]
[PxyDim]H
[EthDim]2.5PMoV
[ButDim]2.5PMoV
2
2
HPMoV2
5 2
H PMo10V O40ꢀ isꢀ aꢀ homogeneousꢀ catalystꢀ thatꢀ isꢀ difficultꢀ toꢀ
3
PMoV
2
isolateꢀ andꢀ reuse.ꢀ Aꢀ phenolꢀ yieldꢀ ofꢀ 27.4%ꢀ andꢀ TONꢀ ofꢀ 57.1ꢀ
wereꢀ obtainedꢀ usingꢀ theꢀ knownꢀ singleꢀ cationꢀ ionicꢀ hybridꢀ
2
10ꢀ
aꢀReactionꢀconditions:ꢀcatalystꢀ0.1ꢀg,ꢀbenzeneꢀ10ꢀmmol,ꢀmixedꢀsolventꢀ
,ꢀ30ꢀmmol,ꢀ70ꢀC;ꢀ
ꢀh.ꢀ ꢀBenzeneꢀconversion.ꢀ ꢀPhenolꢀyield.ꢀ ꢀTurnoverꢀnumber.ꢀ
[
BMim]2.5PMoV
insolubleꢀ duringꢀ theꢀ earlyꢀ reactionꢀ stage,ꢀ butꢀ graduallyꢀ dis‐
solvedꢀ withꢀ H ꢀ addition,ꢀ resultingꢀ inꢀ aꢀ homogeneousꢀ reac‐
2
ꢀ (Entryꢀ 5).ꢀ Noticeably,ꢀ [BMim]2.5PMoV ꢀ wasꢀ
2
(
1
ꢀ
acetonitrile/aceticꢀacid)ꢀ8ꢀmL,ꢀ1:1ꢀ(v/v);ꢀ30ꢀwt%ꢀH
2
O
2
b
c
d
O
2 2
tion.ꢀ Theꢀ resultsꢀ indicatedꢀ thatꢀ achievingꢀ anꢀ insolubleꢀ andꢀ
highlyꢀactiveꢀPOMꢀcatalystꢀforꢀheterogeneousꢀhydroxylationꢀofꢀ
dium,ꢀbutꢀalsoꢀaffordedꢀaꢀratherꢀhighꢀconversionꢀ(29.4%)ꢀandꢀ
phenolꢀyieldꢀ(28.9%),ꢀwithꢀtheꢀhighestꢀTONꢀofꢀ69.5ꢀ(Entryꢀ6).ꢀ
Thisꢀresultꢀwasꢀobtainedꢀunderꢀoptimizedꢀconditionsꢀafterꢀsys‐
tematicꢀinvestigationꢀofꢀvariousꢀreactionꢀparameters,ꢀincludingꢀ
amountꢀ ofꢀ catalyst,ꢀ reactionꢀ time,ꢀ reactionꢀ temperature,ꢀ andꢀ
benzeneꢀ withꢀ H
HPAꢀ catalystsꢀ areꢀ labile,ꢀ degradable,ꢀ andꢀ solubleꢀ inꢀ theꢀ pres‐
enceꢀofꢀH ꢀ[33].ꢀ
Interestingly,ꢀ newlyꢀ synthesizedꢀ mesoporousꢀ catalystꢀ
PxyDim]2.5PMoV ꢀwasꢀnotꢀonlyꢀinsolubleꢀinꢀtheꢀreactionꢀme‐
2
O ꢀ wasꢀ difficultꢀ becauseꢀ Keggin‐structuredꢀ
2
O
2 2
molarꢀratioꢀofꢀH
2
O ꢀtoꢀbenzene,ꢀasꢀshownꢀinꢀFig.ꢀ7.ꢀThisꢀcatalyticꢀ
2
[
2
3
2
2
1
0
5
0
5
30
25
20
15
10
5
(a)
(
b)
0
.04 0.06 0.08 0.10 0.12 0.14 0.16
1.0
1.5
2.0
2.5
3.0
3.5
Amount of catalyst (g)
H O / benzene ratio
2
2
3
2
2
0
5
0
3
0
(d)
(
c)
25
20
15
10
5
0
15
10
0
20
40
60
80
100
40
50
60
70
80
90
Reaction temperature (C)
Reaction time (min)
Fig.ꢀ7.ꢀInfluenceꢀofꢀreactionꢀconditionsꢀonꢀtheꢀhydroxylationꢀofꢀbenzeneꢀwithꢀH
2
O
2
ꢀoverꢀ[PxyDim]2.5PMoV
2
:ꢀ(a)ꢀCatalystꢀamount;ꢀ(b)ꢀMolarꢀratioꢀofꢀH
O
2 2
toꢀbenzene;ꢀ(c)ꢀReactionꢀtemperature;ꢀ(d)ꢀReactionꢀtime.ꢀGeneralꢀreactionꢀconditions:ꢀcatalystꢀ0.1ꢀg,ꢀbenzeneꢀ10ꢀmmol,ꢀ30ꢀwt%ꢀH
2
O ꢀ30ꢀmmol,ꢀace‐
2
tonitrile/aceticꢀacidꢀ8ꢀmL,ꢀ1:1ꢀ(v/v);ꢀ70ꢀC,ꢀ1ꢀh.ꢀ

ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
339ꢀ
performanceꢀ wasꢀ comparableꢀ toꢀ thatꢀ ofꢀ homogeneousꢀ
40,ꢀsuggestingꢀnoꢀsignificantꢀdeclineꢀinꢀtheꢀactivityꢀ
ofꢀtheꢀVꢀspeciesꢀafterꢀheterogenization.ꢀ
Mesoporousꢀ sampleꢀ [PxyDim] HPMoV
molarꢀ ratioꢀ ofꢀ [PxyDim] ꢀ toꢀ POM,ꢀ wasꢀ alsoꢀ aꢀ heterogeneousꢀ
catalystꢀandꢀgaveꢀanꢀexcellentꢀphenolꢀyieldꢀ(24.5%)ꢀandꢀTONꢀofꢀ
3
2
2
0
5
0
H
5
PMo10V O
2
(
1)
(2)
2
2
,ꢀ containingꢀ aꢀ 2:1ꢀ
(
3)
2+
(5)
(4)
5
5.7ꢀ(Entryꢀ7).ꢀNevertheless,ꢀ[PxyDim]2.5PMoV
2
ꢀshowedꢀhigherꢀ
15
10
5
2
BETꢀsurfaceꢀareaꢀ(58.5ꢀm /g)ꢀwithꢀaꢀsmallerꢀaverageꢀmesoporeꢀ
sizeꢀofꢀ29.9ꢀnmꢀ(Tableꢀ2,ꢀEntriesꢀ1,2).ꢀThisꢀcatalystꢀwasꢀmoreꢀ
conduciveꢀtoꢀtheꢀreactionꢀbecauseꢀmoreꢀactiveꢀsitedꢀwereꢀex‐
posed.ꢀ Therefore,ꢀ theꢀ phenolꢀ yieldꢀ ofꢀ [PxyDim]
slightlyꢀlowerꢀthanꢀthatꢀofꢀ[PxyDim]2.5PMoV .ꢀInꢀcontrast,ꢀnon‐
porousꢀ sampleꢀ [PxyDim]H PMoV ꢀ withꢀ aꢀ 1:1ꢀ molarꢀ ratioꢀ ofꢀ
PxyDim] ꢀtoꢀPOMꢀgaveꢀaꢀphenolꢀyieldꢀofꢀonlyꢀ18.9%ꢀandꢀTONꢀ
ofꢀ 37.8ꢀ (Entryꢀ 8),ꢀ whichꢀ mightꢀ dueꢀ toꢀ theꢀ lowerꢀ BETꢀ surfaceꢀ
2 2
HPMoV ꢀ wasꢀ
2
0
3
2
0
20 40 60 80 100 120 140
Reaction time (min)
2+
[
2
3
Fig.ꢀ8.ꢀCatalyticꢀkineticsꢀofꢀ(1)ꢀ[PxyDim]2.5PMoV
3)ꢀ [PxyDim]H PMoV ,ꢀ (4)ꢀ [EthDim]2.5PMoV
ButDim]2.5PMoV .ꢀ
2
,ꢀ(2)ꢀ[PxyDim]
2
HPMoV
2
areaꢀ (6.2ꢀ m /g)ꢀ andꢀ smallerꢀ totalꢀ poreꢀ volumeꢀ ofꢀ 0.03ꢀ cm /gꢀ
Tableꢀ 2,ꢀ Entryꢀ 3).ꢀ Asꢀ aꢀ result,ꢀ theꢀ mesoporousꢀ structureꢀ
seemedꢀ toꢀ playꢀ aꢀ keyꢀ roleꢀ inꢀ theꢀ excellentꢀ performanceꢀ ofꢀ
PxyDim]2.5PMoV .ꢀ
Toꢀclearlyꢀdetermineꢀtheꢀroleꢀofꢀtheꢀorganicꢀcation,ꢀtwoꢀcon‐
trolꢀ samples,ꢀ [EthDim]2.5PMoV ꢀ andꢀ [ButDim]2.5PMoV ,ꢀ wereꢀ
preparedꢀusingꢀdifferentꢀalkylꢀgroupsꢀinꢀplaceꢀofꢀp‐xyleneꢀinꢀtheꢀ
cation.ꢀ Catalystꢀ [EthDim]2.5PMoV ꢀ affordedꢀ aꢀ phenolꢀ yieldꢀ ofꢀ
onlyꢀ14.6%ꢀandꢀTONꢀofꢀ32.4ꢀ(Entryꢀ9),ꢀwhichꢀwereꢀbothꢀmuchꢀ
lowerꢀthanꢀthoseꢀofꢀ[PxyDim]H PMoV .ꢀ[ButDim]2.5PMoV ,ꢀwithꢀ
aꢀ longerꢀ alkylꢀ group,ꢀ affordedꢀ aꢀ slightlyꢀ betterꢀ phenolꢀ yieldꢀ
20.7%)ꢀ andꢀ TONꢀ ofꢀ 47ꢀ (Entryꢀ 10).ꢀ Furthermore,ꢀ itꢀ hasꢀ beenꢀ
(
[
3
2
2
,ꢀ andꢀ
(5)ꢀ
(
2
[
2
Catalystꢀreusabilityꢀisꢀespeciallyꢀimportantꢀforꢀpracticalꢀap‐
plications.ꢀTheꢀcatalyticꢀrecyclabilityꢀofꢀ[PxyDim]2.5PMoV ꢀwasꢀ
measuredꢀusingꢀfour‐runꢀsuccessiveꢀexperiments,ꢀasꢀshownꢀinꢀ
Fig.ꢀ9(a).ꢀIfꢀnoꢀfreshꢀcatalystꢀwasꢀaddedꢀtoꢀtheꢀrecoveredꢀcata‐
lyst,ꢀ theꢀ yieldꢀ decreasedꢀ slowly,ꢀ affordingꢀ 25.2%,ꢀ 23.7%,ꢀ andꢀ
2
2
2
2
2
3%ꢀyieldsꢀonꢀtheꢀsecond,ꢀthird,ꢀandꢀfourthꢀruns,ꢀrespectively.ꢀ
3
2
2
TheꢀIRꢀspectrumꢀofꢀtheꢀrecoveredꢀcatalystꢀwasꢀalmostꢀidenticalꢀ
toꢀthatꢀofꢀtheꢀfreshꢀcatalystꢀ(Fig.ꢀ9(b)).ꢀElementalꢀanalysisꢀofꢀtheꢀ
recoveredꢀcatalystꢀshowedꢀC,ꢀH,ꢀandꢀNꢀcontentsꢀofꢀ19.0%,ꢀ1.9%,ꢀ
andꢀ5.6%ꢀ(Tableꢀ1),ꢀwhichꢀwereꢀveryꢀcloseꢀtoꢀthoseꢀofꢀtheꢀfreshꢀ
catalyst,ꢀwithꢀnoꢀsignificantlyꢀenhancedꢀCꢀcontentꢀobservedꢀinꢀ
theꢀrecycledꢀcatalyst.ꢀFurthermore,ꢀVꢀwasꢀnotꢀobservedꢀinꢀtheꢀ
heatꢀrecyclableꢀfiltrateꢀbyꢀICP‐AESꢀanalysis.ꢀTheseꢀresultsꢀindi‐
catedꢀ thatꢀ theꢀ slowꢀ decreaseꢀ inꢀ yieldꢀ wasꢀ dueꢀ toꢀ theꢀ slightꢀ
physicalꢀ lossꢀ ofꢀ catalyticꢀ activeꢀ sitesꢀ duringꢀ theꢀ reactionꢀ andꢀ
recoveryꢀratherꢀthanꢀcokeꢀformationꢀonꢀtheꢀcatalystꢀsurfaceꢀorꢀ
structuralꢀdistortion.ꢀ ꢀ
(
reportedꢀthatꢀhydrophobicꢀorganicꢀsegmentsꢀinꢀaꢀhybridꢀcata‐
lystꢀareꢀbeneficialꢀforꢀtheꢀhydroxylationꢀofꢀbenzeneꢀdueꢀtoꢀtheꢀ
enhancedꢀencapsulabilityꢀwithꢀnonpolarꢀbenzeneꢀandꢀpromot‐
edꢀ releaseꢀ ofꢀ slightlyꢀ polarꢀ phenolꢀ [30,31].ꢀ Inꢀ summary,ꢀ theꢀ
aboveꢀ comparisonsꢀ furtherꢀ indicatedꢀ thatꢀ theꢀ hydrophobicꢀ
p‐xyleneꢀunitsꢀwereꢀindispensableꢀforꢀobtainingꢀhighꢀPOMꢀcat‐
alystꢀactivitiesꢀforꢀtheꢀhydroxylationꢀofꢀbenzeneꢀtoꢀphenolꢀusingꢀ
H
2
O .ꢀ Furthermore,ꢀ thisꢀ groupꢀ mightꢀ alsoꢀ supplyꢀ aꢀ differentꢀ
2
microenvironmentꢀwithinꢀtheꢀinternalꢀholesꢀofꢀtheꢀcatalystꢀforꢀ
reactionsꢀandꢀstronglyꢀaffectꢀtheꢀcatalyticꢀactivity.ꢀ ꢀ
Whenꢀaꢀsmallꢀamountꢀofꢀfreshꢀcatalystꢀwasꢀaddedꢀtoꢀtheꢀre‐
coveredꢀ catalystꢀ toꢀ compensateꢀ forꢀ catalystꢀ lossꢀ duringꢀ recy‐
clingꢀafterꢀeachꢀrun,ꢀtheꢀdeclineꢀinꢀphenolꢀyieldꢀwasꢀnegligible.ꢀ
Thisꢀphenomenonꢀnotꢀonlyꢀsuggestedꢀthatꢀheterogeneousꢀcata‐
Furthermore,ꢀcatalyticꢀkineticsꢀtestsꢀwereꢀperformedꢀforꢀse‐
lectedꢀ samplesꢀ [PxyDim]2.5PMoV
2
,ꢀ [PxyDim]
2
HPMoV
2
,ꢀ
[
PxyDim]H PMoV ,ꢀ [EthDim]2.5PMoV ,ꢀ andꢀ [ButDim]2.5PMoV
3
2
2
2
,ꢀ
lystꢀ [PxyDim]2.5PMoV
ꢀ wasꢀ reusableꢀ afterꢀ aꢀ simpleꢀ filtration,ꢀ
2
whichꢀhadꢀsignificantlyꢀdifferentꢀmorphologiesꢀandꢀporeꢀstruc‐
turesꢀ(Fig.ꢀ8).ꢀInꢀadditionꢀtoꢀaꢀphenolꢀyieldꢀofꢀnearlyꢀ25%ꢀafterꢀaꢀ
butꢀalsoꢀthatꢀtheꢀdecreaseꢀinꢀactivityꢀofꢀtheꢀrecoveredꢀcatalystꢀ
wasꢀdueꢀtoꢀphysicalꢀleachingꢀofꢀcatalyticꢀactiveꢀcenters,ꢀinꢀcon‐
trastꢀ toꢀ conventionalꢀ supportedꢀ catalysts,ꢀ whichꢀ areꢀ mostlyꢀ
deactivatedꢀdueꢀtoꢀcokingꢀ[34].ꢀ
reactionꢀtimeꢀofꢀ40ꢀmin,ꢀmesoporousꢀ[PxyDim]2.5PMoV ,ꢀwithꢀ
2
anꢀirregularꢀhoneycomb‐shapedꢀmorphologyꢀdueꢀtoꢀtheꢀaccu‐
mulationꢀofꢀnanometerꢀballs,ꢀexhibitedꢀtheꢀfastestꢀreactionꢀrate,ꢀ
whichꢀ wasꢀ muchꢀ higherꢀ thanꢀ thatꢀ ofꢀ mesoporousꢀ
4
.ꢀ ꢀ Conclusionsꢀ
[
PxyDim]
phologyꢀ causedꢀ byꢀ theꢀ accumulationꢀ ofꢀ largerꢀ particles.ꢀ Non‐
porousꢀ [PxyDim]H PMoV ꢀ andꢀ [ButDim]2.5PMoV ꢀ showedꢀ al‐
mostꢀ uniformꢀ reactionꢀ rates,ꢀ whichꢀ wereꢀ higherꢀ thanꢀ thatꢀ ofꢀ
EthDim]2.5PMoV .ꢀ Suchꢀ differencesꢀ inꢀ theꢀ reactionꢀ ratesꢀ fur‐
2
HPMoV
2
ꢀ withꢀ aꢀ similarꢀ honeycomb‐shapedꢀ mor‐
Aꢀnewꢀmesoporousꢀpolyoxometalate‐basedꢀionicꢀhybridꢀcat‐
alyst,ꢀ[PxyDim]2.5PMoV
theꢀ heterogeneousꢀ hydroxylationꢀ ofꢀ benzeneꢀ usingꢀ H
3
2
2
2
,ꢀhasꢀbeenꢀsuccessfullyꢀsynthesizedꢀforꢀ
O
2 2
,ꢀ
[
2
showingꢀ anꢀ enhancedꢀ phenolꢀ yieldꢀ andꢀ robustꢀ recyclability.ꢀ
Thisꢀhighlyꢀefficientꢀcatalyticꢀperformanceꢀwasꢀattributedꢀtoꢀtheꢀ
hydrophobicꢀmicroenvironmentꢀprovidedꢀbyꢀtheꢀnonpolarꢀor‐
ganicꢀ moietyꢀ inꢀ theꢀ hybrid,ꢀ andꢀ theꢀ mesoporousꢀ structure,ꢀ
therꢀdemonstratedꢀthatꢀtheꢀmesoporousꢀstructureꢀandꢀhydro‐
philic‐hydrophobicꢀpropertiesꢀofꢀtheꢀorganicꢀcationꢀinꢀtheꢀcata‐
lystꢀwereꢀrelatedꢀtoꢀtheirꢀcatalyticꢀactivityꢀinꢀtheꢀheterogeneousꢀ
hydroxylationꢀofꢀbenzeneꢀtoꢀphenolꢀusingꢀH
O .ꢀ
2 2
whichꢀenhancedꢀtheꢀdiffusionꢀofꢀbenzeneꢀintoꢀreactiveꢀV
2
ꢀcen‐
tersꢀ andꢀ desorptionꢀ ofꢀ theꢀ phenolꢀ product.ꢀ Theseꢀ promisingꢀ
3.3.ꢀ ꢀ Catalyticꢀreusabilityꢀ

340ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
40
35
30
25
20
15
10
5
0
(
1)
without fresh catalyst
adding fresh catalyst
(a)
(b)
(
2)
1
2
3
4
4000 3500 3000
1500 11000
500

Reaction run
Wavenumber (cm )
Fig.ꢀ9.ꢀ(a)ꢀCatalyticꢀreusabilityꢀofꢀ[PxyDim]2.5PMoV
acetonitrile/aceticꢀacidꢀ8ꢀmL,ꢀ1:1ꢀ(v/v);ꢀ70ꢀC;ꢀ1ꢀh.ꢀ(b)ꢀFT‐IRꢀspectraꢀofꢀ(1)ꢀ[PxyDim]2.5PMoV
2
ꢀinꢀtheꢀhydroxylationꢀofꢀbenzeneꢀusingꢀH
ꢀandꢀ(2)ꢀrecycledꢀ[PxyDim]2.5PMoV
2
O
2
.ꢀReactionꢀconditions:ꢀH
2
O
2
/benzeneꢀmolarꢀratioꢀ3:1;ꢀ
2
2
.ꢀ
resultsꢀhaveꢀencouragedꢀusꢀtoꢀextendꢀourꢀresearchꢀtoꢀdevelopꢀ
mesoporousꢀPOM‐basedꢀionicꢀhybridꢀcatalystsꢀforꢀotherꢀheter‐
[6] P.ꢀK.ꢀKhatri,ꢀB.ꢀSingh,ꢀS.ꢀL.ꢀJain,ꢀB.ꢀSain,ꢀA.ꢀK.ꢀSinha,ꢀChem.ꢀCommun.,ꢀ
011,ꢀ47,ꢀ1610–1612.ꢀ
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[
[
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GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2018,ꢀ39:ꢀ334–341ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(17)62991‐7
Mesoporousꢀpolyoxometalate‐basedꢀionicꢀhybridꢀasꢀaꢀhighlyꢀeffectiveꢀheterogeneousꢀcatalystꢀforꢀdirectꢀhydroxylationꢀofꢀ ꢀ
benzeneꢀtoꢀphenolꢀ
PingpingꢀZhaoꢀ*,ꢀYunyunꢀZhang,ꢀDaokuanꢀLi,ꢀHongyouꢀCuiꢀ*,ꢀLipengꢀZhangꢀ
ShandongꢀUniversityꢀofꢀTechnologyꢀ
ꢀ
Aꢀmesoporousꢀpolyoxometalate‐basedꢀionicꢀhybridꢀwasꢀdevelopedꢀasꢀaꢀheterogeneousꢀcatalystꢀforꢀH
2
O ‐basedꢀhydroxylationꢀofꢀbenzeneꢀ
2
toꢀphenol.ꢀTheꢀhydrophobicꢀmicroenvironmentꢀandꢀmesoporousꢀstructureꢀwereꢀresponsibleꢀforꢀitsꢀefficientꢀcatalyticꢀperformance.ꢀ

ꢀ
PingpingꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ334–341ꢀ
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基于多金属氧酸盐的介孔离子催化剂催化苯一步氧化制苯酚
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赵萍萍*, 张云云, 李道宽, 崔洪友 , 张丽鹏
山东理工大学化工学院, 山东淄博255049
摘要: 苯酚是一种重要的有机化工原料, 工业上主要采用合成路线长、原子利用率低、能耗高、环境污染严重的异丙苯法
生产. 当前, 随着绿色化学的普及, H 催化苯一步氧化制苯酚受到越来越多的关注. 在研究的众多催化剂中, 钒取代杂多
酸被认为是该反应最有效的催化剂之一. 然而, 纯杂多酸易溶于H O 催化的苯羟基化反应体系, 导致污染严重、后处理和
2
O
2
2
2
分离困难. 为了获得可回收的固体杂多酸催化剂, 通常将其负载于多孔载体上, 但这种方法常伴随着活性组分易溶脱, 反
应速率慢等缺点. 因此, 在H
战.
2 2
O 催化苯一步氧化制苯酚体系中获得高效、可重复使用的杂多酸基固体催化剂仍然是一个挑
采用有机单元修饰杂多酸是制备杂多酸基固体催化剂的有效方法. 研究表明, 有机基团的引入可以有效调控杂多酸
的溶解性和氧化还原性. 另一方面, 催化剂中的疏水微环境也能有效促进非极性底物与催化活性中心的相互作用, 提高反
应速率, 改善催化活性. 因此, 我们通过离子交换法将对二甲苯型双核咪唑离子液体阳离子与含钒杂多阴离子结合, 研究
制备了一种具有疏水微环境的介孔杂多酸基离子固体催化剂. 采用傅里叶变换红外光谱、X射线衍射、扫描电镜、N
2
吸附
-
脱附和CHN元素分析等表征手段对催化剂进行全面分析. 结果表明, 该催化剂是一种具有较高比表面积的半无定形疏水
o
2 2
有机杂多酸盐. 在H O 催化的苯一步氧化制苯酚反应中引导了液-固两相催化体系, 在反应时间1 h, 反应温度70 C, 苯酚产
率可达到28.9%, 与均相纯杂多酸的催化活性基本相当, 且催化剂重复使用性能良好. 催化剂构效关系和反应动力学研究
表明, 高比表面积和疏水微环境的构建加快了苯与催化活性中心的相互作用, 提高了催化反应速率和产物选择性. 同时,
咪唑基离子液体阳离子通过分子内的电子相互作用改善了杂多阴离子的氧化还原能力, 也赋予固体催化剂更高的催化活
2 2
性. 该研究为H O 催化苯一步氧化制苯酚反应提供了一种制备简单, 经济高效, 可重复使用的杂多酸基固体催化剂.
关键词: 多金属氧酸盐; 介孔; 苯羟基化; 多相催化; 苯酚
收稿日期: 2017-10-15. 接受日期: 2017-11-28. 出版日期: 2018-02-05.
*
通讯联系人. 传真: (0533)2781213; 电子信箱: zhaopingping@sdut.edu.cn
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通讯联系人. 传真: (0533)2781213; 电子信箱: cuihy@sdut.edu.cn
基金来源: 国家自然科学基金(21506118, 21476132, 51574160); 山东省中青年科学家奖励基金(BS2014CL030).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).