External surface modification of as-made ZSM-5 and their catalytic performance in the methanol to propylene reaction

Article abstract of DOI:10.1016/S1872-2067(18)63117-1

Post-synthetic treatment of high-silica as-made ZSM-5 with organic template in the micropores was explored to reduce/remove the external surface acid density of ZSM-5. It is found that Na₂H₂EDTA treatment can selectively remove the surface Al atoms, but generates new acid sites (likely silanol nests) on the external surface. H₃PO₄ treatment is unable to remove surface Al atoms, while small amount of P is left on the external surface, which effectively decreases the acid density. The catalytic performance of the resultant materials is evaluated in the methanol conversion reaction. H₃PO₄ treatment can effectively improve both the catalytic lifetime and the stability of propene selectivity. This occurs due to a combination of the increased tolerance to the external coke deposition and the depressed coking rate (reduced side reactions). Na₂H₂EDTA treatment only prolongs the catalytic lifetime, resulting from the improved tolerance to the external coke deposition. Under the optimized H₃PO₄ treatment condition, the resultant ZSM-5 gives a catalytic lifetime of about 1.5 times longer than the precursor. Moreover, the propene selectivity is improved, showing a slight increasing trend until the deactivation.

Full text of DOI:10.1016/S1872-2067(18)63117-1

ChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426
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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
Externalꢀsurfaceꢀmodificationꢀofꢀas‐madeꢀZSM‐5ꢀandꢀtheirꢀcatalyticꢀ
performanceꢀinꢀtheꢀmethanolꢀtoꢀpropyleneꢀreactionꢀ
a,b,c
b,c
b
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b,c
b,c
XuebinꢀZhaoꢀ ,ꢀYangꢀHongꢀ ,ꢀLinyingꢀWangꢀ ,ꢀDongꢀFanꢀ ,ꢀNanaꢀYanꢀ ,ꢀXiaonaꢀLiuꢀ ,ꢀ ꢀ
b,#
a,
b,$
PengꢀTianꢀ ,ꢀXinwenꢀGuoꢀ *,ꢀZhongminꢀLiuꢀ
ꢀ
aꢀStateꢀKeyꢀLaboratoryꢀofꢀFineꢀChemicals,ꢀPSU‐DUTꢀJointꢀCenterꢀforꢀEnergyꢀResearch,ꢀSchoolꢀofꢀChemicalꢀEngineering,ꢀDalianꢀUniversityꢀofꢀTechnology,ꢀ
Dalianꢀ116024,ꢀLiaoning,ꢀChinaꢀ
bꢀNationalꢀEngineeringꢀLaboratoryꢀforꢀMethanolꢀtoꢀOlefins,ꢀStateꢀEnergyꢀLowꢀCarbonꢀCatalysisꢀandꢀEngineeringꢀR&DꢀCenter,ꢀDalianꢀNationalꢀLaboratoryꢀ
forꢀCleanꢀEnergy,ꢀCollaborativeꢀInnovationꢀCenterꢀofꢀChemistryꢀforꢀEnergyꢀMaterials (iChEM),ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀ
Sciences,ꢀDalianꢀ116023,ꢀLiaoning,ꢀChinaꢀ
cꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences,ꢀBeijingꢀ100049,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Post‐syntheticꢀtreatmentꢀofꢀhigh‐silicaꢀas‐madeꢀZSM‐5ꢀwithꢀorganicꢀtemplateꢀinꢀtheꢀmicroporesꢀwasꢀ
Receivedꢀ31ꢀMayꢀ2018ꢀ
Acceptedꢀ6ꢀJuneꢀ2018ꢀ
Publishedꢀ5ꢀAugustꢀ2018ꢀ
exploredꢀtoꢀreduce/removeꢀtheꢀexternalꢀsurfaceꢀacidꢀdensityꢀofꢀZSM‐5.ꢀItꢀisꢀfoundꢀthatꢀNa
treatmentꢀcanꢀselectivelyꢀremoveꢀtheꢀsurfaceꢀAlꢀatoms,ꢀbutꢀgeneratesꢀnewꢀacidꢀsitesꢀ(likelyꢀsilanolꢀ
nests)ꢀonꢀtheꢀexternalꢀsurface.ꢀH PO ꢀtreatmentꢀisꢀunableꢀtoꢀremoveꢀsurfaceꢀAlꢀatoms,ꢀwhileꢀsmallꢀ
amountꢀofꢀPꢀisꢀleftꢀonꢀtheꢀexternalꢀsurface,ꢀwhichꢀeffectivelyꢀdecreasesꢀtheꢀacidꢀdensity.ꢀTheꢀcatalyticꢀ
performanceꢀ ofꢀ theꢀ resultantꢀ materialsꢀ isꢀ evaluatedꢀ inꢀ theꢀ methanolꢀ conversionꢀ reaction.ꢀ H PO
2
H EDTAꢀ
2
3
4
3
4
Keywords:ꢀ
Methanolꢀtoꢀpropeneꢀ
ZSM‐5ꢀzeoliteꢀ
Modificationꢀ
Phosphoricꢀacidꢀ
Ethylenediamineꢀtetraaceticꢀacid
treatmentꢀcanꢀeffectivelyꢀimproveꢀbothꢀtheꢀcatalyticꢀlifetimeꢀandꢀtheꢀstabilityꢀofꢀpropeneꢀselectivity.ꢀ
Thisꢀoccursꢀdueꢀtoꢀaꢀcombinationꢀofꢀtheꢀincreasedꢀtoleranceꢀtoꢀtheꢀexternalꢀcokeꢀdepositionꢀandꢀtheꢀ
depressedꢀcokingꢀrateꢀ(reducedꢀsideꢀreactions).ꢀNa
lifetime,ꢀresultingꢀfromꢀtheꢀimprovedꢀtoleranceꢀtoꢀtheꢀexternalꢀcokeꢀdeposition.ꢀUnderꢀtheꢀoptimizedꢀ
PO4ꢀtreatmentꢀcondition,ꢀtheꢀresultantꢀZSM‐5ꢀgivesꢀaꢀcatalyticꢀlifetimeꢀofꢀaboutꢀ1.5ꢀtimesꢀlongerꢀ
2 2
H EDTAꢀtreatmentꢀonlyꢀprolongsꢀtheꢀcatalyticꢀ
H
3
thanꢀtheꢀprecursor.ꢀMoreover,ꢀtheꢀpropeneꢀselectivityꢀisꢀimproved,ꢀshowingꢀaꢀslightꢀincreasingꢀtrendꢀ
untilꢀtheꢀdeactivation.ꢀ
©ꢀ2018,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
fieldsꢀsinceꢀitꢀwasꢀoriginallyꢀdevelopedꢀbyꢀLurgiꢀcompanyꢀ[1].ꢀItꢀ
hasꢀbeenꢀrecognizedꢀthatꢀtheꢀmethanolꢀconversionꢀoverꢀzeoliteꢀ
catalystsꢀisꢀaꢀtypicalꢀacidꢀcatalyzedꢀprocessꢀandꢀcokeꢀdepositionꢀ
isꢀtheꢀmainꢀcauseꢀofꢀtheꢀcatalystꢀdeactivationꢀ[5–8].ꢀZSM‐5ꢀzeo‐
lite,ꢀ withꢀ aꢀ 3Dꢀ interconnectedꢀ poreꢀ systemꢀ composedꢀ ofꢀ
10‐memberedꢀ rings,ꢀ isꢀ currentlyꢀ theꢀ mostꢀ effectiveꢀ catalyst,ꢀ
whichꢀ hasꢀ foundꢀ applicationꢀ inꢀ theꢀ industrialꢀ fixedꢀ bedꢀ MTPꢀ
Withꢀtheꢀdepletionꢀofꢀoilꢀresource,ꢀtheꢀmethanolꢀtoꢀpropeneꢀ
(MTP)ꢀ processꢀ providesꢀ anꢀ alternativeꢀ routeꢀ toꢀ produceꢀ pro‐
peneꢀbeyondꢀtheꢀconventionalꢀsteamꢀcrackingꢀofꢀnaphthaꢀandꢀ
fluidꢀ catalyticꢀ crackingꢀ processꢀ [1–4].ꢀ Theꢀ MTPꢀ reactionꢀ hasꢀ
arousedꢀsignificantꢀinterestꢀinꢀbothꢀtheꢀacademicꢀandꢀindustrialꢀ
*
ꢀ
$ꢀ
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐411‐84986133;ꢀFax:ꢀ+86‐411‐84986134;ꢀE‐mail:ꢀguoxw@dlut.edu.cnꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐411‐84379218;ꢀFax:ꢀ+86‐411‐84379289;ꢀE‐mail:ꢀtianpeng@dicp.ac.cnꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐411‐84379998;ꢀFax:ꢀ+86‐411‐84379289;ꢀE‐mail:ꢀliuzm@dicp.ac.cnꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21676262),ꢀandꢀtheꢀKeyꢀResearchꢀProgramꢀofꢀFrontierꢀSciences,ꢀCASꢀ
QYZDB‐SSW‐JSC040).ꢀ
DOI:ꢀ10.1016/S1872‐2067(18)63117‐1ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ39,ꢀNo.ꢀ8,ꢀAugustꢀ2018ꢀ ꢀ ꢀ
(

ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
1419ꢀ
process.ꢀ ꢀ
synthesizedꢀinꢀtheꢀabsenceꢀofꢀorganicꢀstructure‐directingꢀagentꢀ
canꢀselectivelyꢀremoveꢀframeworkꢀAlꢀonꢀtheꢀexternalꢀsurface,ꢀ
producingꢀ aꢀ uniqueꢀ ZSM‐5ꢀ zeoliteꢀ catalystꢀ thatꢀ hasꢀ veryꢀ fewꢀ
acidꢀ sitesꢀ onꢀ itsꢀ externalꢀ surface.ꢀ Theꢀ treatedꢀ ZSM‐5ꢀ showedꢀ
highꢀresistanceꢀtoꢀcokeꢀformationꢀduringꢀtheꢀcrackingꢀofꢀhexaneꢀ
orꢀotherꢀparaffinꢀmolecules.ꢀ
Inꢀthisꢀcontribution,ꢀaꢀfacileꢀpost‐syntheticꢀtreatmentꢀmeth‐
odꢀwasꢀdevelopedꢀtoꢀremove/modifyꢀtheꢀexternalꢀsurfaceꢀacid‐
ityꢀ ofꢀ ZSM‐5ꢀ byꢀ utilizingꢀ as‐madeꢀ ZSM‐5ꢀ containingꢀ organicꢀ
structureꢀ directingꢀ agentꢀ (OSDA)ꢀ asꢀ theꢀ precursor.ꢀ Theꢀ exist‐
enceꢀ ofꢀ OSDAꢀ inꢀ theꢀ as‐madeꢀ ZSM‐5ꢀ crystalsꢀ mayꢀ effectivelyꢀ
blockꢀtheꢀchannelsꢀandꢀconfineꢀtheꢀmodificationꢀonꢀtheꢀcrystalꢀ
exteriorꢀ withoutꢀ alteringꢀ theꢀ internalꢀ acidityꢀ andꢀ integrityꢀ ofꢀ
DueꢀtoꢀtheꢀspaceꢀlimitationꢀinꢀtheꢀmicroporesꢀofꢀZSM‐5ꢀ(0.51ꢀ
nmꢀ×ꢀ0.55ꢀnm,ꢀ0.53ꢀnmꢀ×ꢀ0.56ꢀnm),ꢀtheꢀcokeꢀdepositionꢀinꢀtheꢀ
crystalꢀinteriorꢀcanꢀbeꢀgreatlyꢀavoidedꢀduringꢀtheꢀMTPꢀreaction.ꢀ
AndꢀtheꢀdeactivationꢀonꢀZSM‐5ꢀisꢀcloselyꢀrelatedꢀtoꢀtheꢀexternalꢀ
surfaceꢀacidityꢀ[9].ꢀTherefore,ꢀattemptsꢀhaveꢀbeenꢀmadeꢀtoꢀre‐
duceꢀtheꢀexternalꢀsurfaceꢀacidityꢀofꢀZSM‐5,ꢀaimingꢀtoꢀretardꢀtheꢀ
cokeꢀ depositionꢀ rateꢀ andꢀ improveꢀ theꢀ catalyticꢀ stability.ꢀ Theꢀ
strategiesꢀdevelopedꢀtoꢀpassivateꢀtheꢀexternalꢀsurfaceꢀacidꢀsitesꢀ
ofꢀzeolitesꢀcanꢀbeꢀmainlyꢀclassifiedꢀasꢀmacromoleculeꢀdeposi‐
tionꢀ [10–19],ꢀ synthesisꢀ ofꢀ zeolitesꢀ withꢀ core‐shellꢀ structureꢀ
[20–23],ꢀmetalꢀorꢀnon‐metalꢀmodificationꢀ[24–28]ꢀandꢀsoꢀon.ꢀ
Theꢀ macromoleculesꢀ reportedꢀ forꢀ theꢀ pas‐
sivation/modificationꢀofꢀexternalꢀsurfaceꢀacidꢀsitesꢀofꢀzeolitesꢀ
includeꢀ bulkyꢀ organophosphorusꢀ compoundsꢀ [10,11],ꢀ bulkyꢀ
nitrogenꢀcompoundsꢀ[12]ꢀandꢀvariousꢀsiloxaneꢀ[14–19].ꢀLoschꢀ
etꢀal.ꢀ[29]ꢀonceꢀinvestigatedꢀtheꢀeffectꢀofꢀsurfaceꢀpassivationꢀofꢀ
nano‐sizedꢀ ZSM‐5ꢀ onꢀ theꢀ methanolꢀ conversionꢀ reactionꢀ byꢀ aꢀ
chemicalꢀliquidꢀdepositionꢀ(CLD)ꢀtechniqueꢀusingꢀtetraethylor‐
thosilicate.ꢀTheꢀresultantꢀcatalystꢀexhibitedꢀanꢀenhancedꢀselec‐
tivityꢀtoꢀlowerꢀolefins,ꢀbutꢀaꢀsignificantꢀdecreaseꢀinꢀtheꢀstability,ꢀ
whichꢀwasꢀdueꢀtoꢀtheꢀpartialꢀblockingꢀofꢀmicroporesꢀ(theꢀcokingꢀ
processꢀexclusivelyꢀoccurredꢀwithinꢀtheꢀporesꢀandꢀfastenedꢀtheꢀ
catalystꢀ deactivation).ꢀ Phosphorusꢀ modificationꢀ ofꢀ HZSM‐5ꢀ
zeoliteꢀbyꢀwetꢀimpregnationꢀhasꢀlongꢀbeenꢀknownꢀtoꢀdecreaseꢀ
aromaticꢀformationꢀandꢀimproveꢀcatalyticꢀstabilityꢀinꢀmethanolꢀ
conversionꢀchemistryꢀ[26,30,31].ꢀImpregnationꢀofꢀHZSM‐5ꢀwithꢀ
phosphoricꢀ acidꢀ leadsꢀ toꢀ theꢀ hydrolysisꢀ ofꢀ frameworkꢀ Alꢀ andꢀ
theꢀcondensationꢀofꢀBrønstedꢀacidꢀsitesꢀwithꢀPOHꢀgroups,ꢀre‐
sultingꢀ inꢀ higherꢀ frameworkꢀ Si/Alꢀ ratioꢀ andꢀ theꢀ decreaseꢀ ofꢀ
strongꢀacidꢀsitesꢀ[31,32].ꢀHowever,ꢀphosphoricꢀacidꢀcanꢀdepositꢀ
bothꢀinꢀtheꢀinnerꢀporeꢀandꢀexternalꢀsurfaceꢀofꢀZSM‐5ꢀdueꢀtoꢀitsꢀ
smallerꢀ size.ꢀ Recently,ꢀ Liuꢀ etꢀ al.ꢀ [24]ꢀ reportedꢀ anꢀ effectiveꢀ
methodꢀ toꢀ prepareꢀ P‐modifiedꢀ H‐ZSM‐5ꢀ withꢀ theꢀ preferentialꢀ
coveringꢀ ofꢀ theꢀ externalꢀ surfaceꢀ acidꢀ sitesꢀ byꢀ addingꢀ ethanolꢀ
duringꢀtheꢀimpregnation.ꢀThisꢀoccurredꢀbecauseꢀbulkyꢀorganicꢀ
phosphatesꢀwereꢀlikelyꢀformedꢀfromꢀtheꢀreactionꢀofꢀphosphoricꢀ
acidꢀ andꢀ ethanol,ꢀ whichꢀ depositedꢀ onꢀ theꢀ externalꢀ surfaceꢀ ofꢀ
HZSM‐5ꢀ crystals.ꢀ Theꢀ obtainedꢀ materialꢀ gaveꢀ highꢀ p‐xyleneꢀ
selectivityꢀalongꢀwithꢀaꢀrelativelyꢀhighꢀcatalyticꢀactivityꢀinꢀtolu‐
eneꢀdisproportionationꢀreaction.ꢀ
theꢀ crystals.ꢀ Twoꢀ commonꢀ reagents,ꢀ Na
2
H
2
EDTAꢀ andꢀ H
3
PO ,ꢀ
4
hereinꢀ wereꢀ exploredꢀ forꢀ theꢀ post‐syntheticꢀ treatment.ꢀ Itꢀ isꢀ
mentionedꢀthatꢀlargeꢀmoleculeꢀEDTA,ꢀasꢀaꢀpowerfulꢀchelatingꢀ
agent,ꢀhasꢀbeenꢀwidelyꢀusedꢀforꢀtheꢀdealuminationꢀofꢀYꢀzeoliteꢀ
[36].ꢀButꢀitsꢀuseꢀforꢀtheꢀdealuminationꢀofꢀZSM‐5ꢀisꢀquiteꢀrare.ꢀ
Theꢀvariationsꢀofꢀstructureꢀintegrity,ꢀsurfaceꢀacidꢀdensityꢀandꢀ
catalyticꢀperformanceꢀofꢀtheꢀmodifiedꢀZSM‐5ꢀwereꢀinvestigated.ꢀ
Moreover,ꢀ theꢀ H
3
PO ꢀ concentrationꢀ wasꢀ optimizedꢀ toꢀ furtherꢀ
4
prolongꢀtheꢀlifetimeꢀinꢀtheꢀMTPꢀreaction.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2.1.ꢀ ꢀ Materialsꢀ ꢀ
Theꢀchemicalꢀreagentsꢀusedꢀinꢀsynthesisꢀandꢀmodificationꢀofꢀ
ZSM‐5ꢀzeolitesꢀ include:ꢀtetraethylꢀorthosilicateꢀ(TEOS,ꢀTianjinꢀ
Kemiouꢀ Chemicalꢀ Reagentꢀ Co),ꢀ aluminiumꢀ iso‐propoxideꢀ
(Al(OPri)
3
,ꢀ
Sinopharmꢀ
Chemicalꢀ
Reagentꢀ
Co.),ꢀ
tetrapropylammoniumꢀ hydroxideꢀ (TPAOH,ꢀ 10ꢀ wt%ꢀ Tianjinꢀ
Jingrunꢀ Chemicalꢀ Co),ꢀ ureaꢀ (Tianjinꢀ Damaoꢀ Chemicalꢀ Co),ꢀ
ethylenediamineꢀ tetraaceticꢀ acidꢀ disodiumꢀ saltꢀ (Na
TiandaꢀChemicalꢀReagentꢀCo.ꢀLtd.),ꢀphosphoricꢀacidꢀ(85.0ꢀwt%,ꢀ
SichuanꢀXianfengꢀChemicalꢀCo.).ꢀ
2
H EDTA,ꢀ
2
2.2.ꢀ ꢀ SynthesisꢀandꢀmodificationꢀofꢀZSM‐5ꢀzeolitesꢀ
TheꢀsynthesisꢀofꢀZSM‐5ꢀzeoliteꢀwasꢀaccordingꢀtoꢀtheꢀreport‐
edꢀ literatureꢀ [37].ꢀ Theꢀ gelꢀ molarꢀ compositionꢀ wasꢀ
Zeolitesꢀwithꢀcore‐shellꢀstructureꢀareꢀgenerallyꢀsynthesizedꢀ
byꢀepitaxialꢀgrowthꢀofꢀinertꢀshellꢀoutsideꢀzeoliteꢀcore.ꢀInꢀprinci‐
ple,ꢀtheꢀdegreeꢀofꢀsurfaceꢀcoverageꢀandꢀshellꢀthicknessꢀareꢀtheꢀ
keyꢀfactorsꢀinfluencingꢀtheꢀcatalyticꢀperformance.ꢀLuoꢀetꢀal.ꢀ[33]ꢀ
successfullyꢀ synthesizedꢀ ZSM‐5@S‐1ꢀ material,ꢀ whichꢀ gaveꢀ
comparableꢀpropeneꢀselectivityꢀwithꢀtheꢀZSM‐5ꢀprecursorꢀandꢀ
aꢀprolongedꢀlifetimeꢀfromꢀ74ꢀtoꢀ139ꢀhꢀinꢀtheꢀMTPꢀreaction.ꢀTheꢀ
changeꢀinꢀlifetimeꢀ shouldꢀresultꢀfromꢀtheꢀ reducedꢀnumberꢀofꢀ
externalꢀacidꢀsitesꢀandꢀtheꢀattenuatedꢀoccurrenceꢀofꢀsideꢀreac‐
tions.ꢀ Yinꢀ etꢀ al.ꢀ [34]ꢀ alsoꢀ demonstratedꢀ thatꢀ theꢀ coverageꢀ ofꢀ
surfaceꢀ acidꢀ sitesꢀ asꢀ aꢀresultꢀofꢀcontiguousꢀ silicalite‐1ꢀcoatingꢀ
wasꢀtheꢀreasonꢀforꢀtheꢀhighꢀstabilityꢀandꢀselectivityꢀofꢀZSM‐5ꢀinꢀ
300SiO
2
:1Al
2
O
3
:90TPAOH:6000H O:450urea.ꢀDetainedꢀsynthe‐
2
sisꢀ procedureꢀ wasꢀ carriedꢀ outꢀ asꢀ follows:ꢀ 104.2ꢀ gꢀ TEOSꢀ wasꢀ
addedꢀ dropwiseꢀ intoꢀ 210.5ꢀ gꢀ TPAOHꢀ solutionꢀ underꢀ stirring.ꢀ
Afterꢀ12ꢀh,ꢀ0.681ꢀgꢀAl(OPri) ꢀwasꢀaddedꢀintoꢀtheꢀmixtureꢀandꢀ
stirredꢀforꢀ12h.ꢀAfterꢀfurtherꢀadditionꢀofꢀ45.0ꢀgꢀureaꢀandꢀstirredꢀ
forꢀ1ꢀh,ꢀtheꢀresultingꢀmixtureꢀwasꢀtransferredꢀintoꢀanꢀautoclave.ꢀ
Theꢀ crystallizationꢀ wasꢀ carriedꢀ outꢀ atꢀ 180ꢀ °Cꢀ forꢀ 48ꢀ hꢀ underꢀ
tumblingꢀ 60ꢀ r/min.ꢀ Theꢀ as‐madeꢀ sampleꢀ wasꢀ centrifuged,ꢀ
washedꢀwithꢀdistilledꢀwater,ꢀdriedꢀatꢀ120ꢀ°Cꢀovernight.ꢀ
3
Typicalꢀpost‐syntheticꢀmodificationꢀtreatmentꢀprocessꢀwithꢀ
H PO4ꢀsolutionꢀwasꢀasꢀfollows:ꢀ1.5ꢀgꢀas‐madeꢀsampleꢀwasꢀaddedꢀ
3
toꢀ20.0ꢀmLꢀsolutionꢀ(1ꢀmol/L)ꢀinꢀaꢀTeflon‐linedꢀstainlessꢀsteelꢀ
autoclave.ꢀAfterꢀtreatmentꢀatꢀ90ꢀ°Cꢀforꢀ12ꢀhꢀunderꢀtumblingꢀ60ꢀ
r/min,ꢀtheꢀslurryꢀwasꢀfiltered,ꢀwashedꢀwithꢀdistilledꢀwaterꢀforꢀ
threeꢀtimesꢀuntilꢀpH=7.ꢀAllꢀproductsꢀwereꢀdriedꢀatꢀ120ꢀ°Cꢀover‐
nightꢀandꢀcalcinedꢀatꢀ550ꢀ°Cꢀforꢀ8ꢀhꢀtoꢀremoveꢀtheꢀorganicꢀtem‐
CH
3
Brꢀconversionꢀreaction.ꢀ
Recently,ꢀselectiveꢀdealuminationꢀmethodsꢀwereꢀreportedꢀtoꢀ
removeꢀtheꢀexternalꢀsurfaceꢀacidꢀsitesꢀofꢀZSM‐5.ꢀInagakiꢀetꢀal.ꢀ
35]ꢀfoundꢀthatꢀpost‐syntheticꢀHNO ꢀtreatmentꢀofꢀZSM‐5ꢀzeoliteꢀ
[
3

1420ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
plate.ꢀInꢀtheꢀcaseꢀofꢀNa
toꢀ 1–2ꢀ byꢀ HClꢀ andꢀ theꢀ finalꢀ slurryꢀ wasꢀ filtrated,ꢀ followedꢀ byꢀ
washingꢀwithꢀlargeꢀamountꢀofꢀhotꢀwaterꢀdueꢀtoꢀtheꢀlowꢀsolubil‐
2
H
2
EDTA,ꢀtheꢀsolutionꢀpHꢀwasꢀadjustedꢀ
0.3ꢀgꢀcalcinedꢀcatalystꢀwasꢀpressed,ꢀsievedꢀtoꢀ40–60ꢀmeshꢀ
andꢀ loadedꢀ inꢀ aꢀ fixed‐bedꢀ quartzꢀ tubularꢀ reactorꢀ withꢀ innerꢀ
diameterꢀofꢀ8ꢀmm.ꢀPriorꢀtoꢀtheꢀreaction,ꢀtheꢀcatalystꢀwasꢀacti‐
vatedꢀatꢀ550ꢀ°Cꢀforꢀ60ꢀmin,ꢀandꢀthenꢀtheꢀtemperatureꢀwasꢀad‐
justedꢀ toꢀ reactionꢀ temperature.ꢀ Methanolꢀ wasꢀ fedꢀ byꢀ passingꢀ
theꢀcarrierꢀgasꢀ(40.0ꢀmL/min)ꢀthroughꢀaꢀsaturatorꢀcontainingꢀ
methanolꢀ atꢀ 35ꢀ °C,ꢀ whichꢀ gaveꢀ aꢀ WHSVꢀ ofꢀ 4.0ꢀ h .ꢀ Methanolꢀ
conversionꢀ wasꢀ performedꢀ underꢀ atmosphericꢀ pressure.ꢀ Theꢀ
effluentꢀ productsꢀ fromꢀ reactorꢀ wereꢀ keptꢀ atꢀ 200ꢀ °Cꢀ andꢀ ana‐
lyzedꢀ byꢀ anꢀ onlineꢀ Agilentꢀ 7890Aꢀ GCꢀ equippedꢀ withꢀ aꢀ PONAꢀ
capillaryꢀcolumnꢀ(100ꢀmꢀ×ꢀ0.25ꢀmmꢀ×ꢀ0.5ꢀm)ꢀandꢀaꢀFIDꢀdetec‐
ityꢀofꢀNa
wasꢀcarriedꢀoutꢀatꢀ80ꢀ°CꢀwithꢀNH
threeꢀtimesꢀtoꢀremoveꢀtheꢀpossibleꢀresidualꢀsodiumꢀduringꢀtheꢀ
Na EDTAꢀ treatment.ꢀ Theꢀ calcinedꢀ precursorꢀ andꢀ samplesꢀ
modifiedꢀ byꢀ Na EDTAꢀ andꢀ H PO ꢀ wereꢀ namedꢀ asꢀ ZSM‐5,ꢀ
2 2
H EDTA.ꢀTheꢀammoniumꢀexchangeꢀofꢀcalcinedꢀsampleꢀ
4
NO ꢀsolutionꢀ(1.0ꢀmol/L)ꢀforꢀ
3
–1
H
2 2
H
2 2
3
4
ZSM‐5‐E‐x,ꢀZSM‐5‐P‐xꢀrespectively,ꢀwhereꢀxꢀrepresentꢀtheꢀsolu‐
tionꢀconcentration.ꢀ ꢀ
2.3.ꢀ ꢀ Characterizationꢀ
tor.ꢀTheꢀconversionꢀandꢀselectivityꢀwereꢀcalculatedꢀonꢀCH ꢀba‐
2
sis.ꢀ Dimethylꢀ etherꢀ (DME)ꢀ wasꢀ consideredꢀ asꢀ reactantꢀ inꢀ theꢀ
calculation.ꢀForꢀtheꢀ1,3,5‐triisopropylbenzeneꢀ(TIPB)ꢀcrackingꢀ
reaction,ꢀsimilarꢀconditionꢀwasꢀemployedꢀexceptꢀthatꢀtheꢀreac‐
tionꢀtemperatureꢀwasꢀ360ꢀ°C.ꢀ
Theꢀ powderꢀ XRDꢀ patternꢀ wasꢀ recordedꢀ onꢀ aꢀ PANalyticalꢀ
α
X'Pertꢀ PROꢀ X‐rayꢀ diffractometerꢀ withꢀ Cu‐K ꢀ radiationꢀ (λꢀ =ꢀ
0
.15418ꢀ nm),ꢀ operatingꢀ atꢀ 40ꢀ kVꢀ andꢀ 40ꢀ mA.ꢀ Theꢀ chemicalꢀ
compositionꢀ ofꢀ solidꢀ samplesꢀ wasꢀ determinedꢀ withꢀ aꢀ Philips‐
Magix‐601ꢀX‐rayꢀfluorescenceꢀ(XRF)ꢀspectrometer.ꢀXPSꢀmeas‐
urementsꢀ wereꢀ performedꢀ usingꢀ aꢀ Thermoꢀ ESCALABꢀ 250Xiꢀ
2.5.ꢀ ꢀ Cokeꢀanalysisꢀ
spectrometerꢀwithꢀAlꢀK
surfaceꢀchargeꢀofꢀtheꢀsampleꢀwasꢀcalibratedꢀbyꢀreferencingꢀtoꢀ
theꢀAlꢀ2pꢀpeakꢀofꢀAl ꢀatꢀ74.7ꢀeV.ꢀTheꢀcrystalꢀmorphologyꢀwasꢀ
observedꢀ usingꢀ aꢀ scanningꢀ electronꢀ microscopyꢀ (Hitachiꢀ
SU8020).ꢀN ꢀadsorption‐desorptionꢀisothermsꢀatꢀ–196ꢀ°Cꢀwereꢀ
α
ꢀradiationꢀasꢀtheꢀexcitationꢀsource.ꢀTheꢀ
Theꢀcokeꢀpercentꢀofꢀdischargedꢀcatalystsꢀwasꢀcalculatedꢀbyꢀ
ꢀ
thermogravimetricꢀanalysisꢀ(TGA)ꢀandꢀtheꢀlossꢀbetweenꢀ300toꢀ
ꢀ
O
2 3
700°Cꢀwasꢀusedꢀtoꢀestimateꢀcokeꢀcontent.ꢀConsideringꢀthatꢀtheꢀ
differentꢀamountsꢀofꢀmethanolꢀprocessedꢀonꢀeachꢀcatalyst,ꢀtheꢀ
averageꢀcokeꢀdepositionꢀrateꢀareꢀdefinedꢀasꢀfollowed:ꢀ
2
determinedꢀonꢀaꢀMicromeriticsꢀASAP2020.ꢀPriorꢀtoꢀtheꢀmeas‐
urement,ꢀsamplesꢀwereꢀdegassedꢀatꢀ350ꢀ°Cꢀunderꢀvacuumꢀforꢀ4ꢀ
h.ꢀTheꢀtotalꢀsurfaceꢀareaꢀwasꢀcalculatedꢀbasedꢀonꢀtheꢀBETꢀequa‐
tion.ꢀTheꢀmicroporeꢀvolumeꢀandꢀmicroporeꢀsurfaceꢀareaꢀwereꢀ
evaluatedꢀusingꢀtheꢀt‐plotꢀmethod.ꢀ AlꢀsolidꢀstateꢀNMRꢀexper‐
imentsꢀwereꢀperformedꢀonꢀaꢀVarianꢀInfinityꢀplusꢀ600ꢀWBꢀspec‐
trometerꢀ withꢀ BBOꢀ MASꢀ probeꢀ operatingꢀ atꢀ magneticꢀ fieldꢀ
strengthꢀofꢀ14.1ꢀT.ꢀTheꢀresonanceꢀfrequenciesꢀwereꢀ104.2ꢀMHzꢀ
Rcokeꢀ=ꢀ10C/((1–C/100)ꢀ×ꢀTꢀ×ꢀM)ꢀ
where:ꢀRcokeꢀ(mg/(gcat·h)):ꢀtheꢀaverageꢀcokeꢀdepositionꢀrate,ꢀCꢀ
(%):ꢀ theꢀ cokeꢀ percentꢀ inꢀ dischargedꢀ catalystsꢀ determinedꢀ byꢀ
TGA,ꢀTꢀ(h):ꢀreactionꢀtime,ꢀMꢀ(g):ꢀtheꢀcatalystꢀamount.ꢀ
Theꢀcokeꢀformationꢀinsideꢀmicroporesꢀ(internalꢀcoke)ꢀwasꢀ
calculatedꢀ fromꢀ theꢀ decreaseꢀ inꢀ theꢀ microporeꢀ volumeꢀ deter‐
27
minedꢀbyꢀN
2
ꢀadsorptionꢀatꢀ–196ꢀ°C,ꢀassumingꢀtheꢀcokeꢀdensityꢀ
3
(dcoke)ꢀofꢀ1.22ꢀg/cm .ꢀTheꢀcokeꢀcontentꢀdepositedꢀonꢀtheꢀexter‐
nalꢀ surfaceꢀ wasꢀ calculatedꢀ byꢀ subtractingꢀ theꢀ internalꢀ cokeꢀ
contentꢀ fromꢀ theꢀ totalꢀ cokeꢀ contentꢀ determinedꢀ byꢀ TGA.ꢀ Theꢀ
amountsꢀofꢀinternalꢀcokeꢀandꢀexternalꢀcokeꢀwereꢀcalculatedꢀasꢀ
followsꢀ[39–41]:ꢀ
andꢀchemicalꢀshiftsꢀwereꢀreferencedꢀtoꢀ1.0ꢀmol/LꢀAl(NO
spinningꢀ rateꢀ ofꢀ theꢀ samplesꢀ atꢀ theꢀ magicꢀ angleꢀ wasꢀ 4ꢀ kHz.ꢀ
Temperature‐programmedꢀdesorptionꢀofꢀammoniaꢀ(NH ‐TPD)ꢀ
3 3
) .Theꢀ
3
wasꢀmeasuredꢀonꢀaꢀchemicalꢀadsorptionꢀinstrumentꢀofꢀMicro‐
metricꢀ 2920.ꢀ Eachꢀ sampleꢀ (40–60ꢀ mesh,ꢀ 0.20ꢀ g)ꢀ wasꢀ loadedꢀ
intoꢀaꢀquartzꢀU‐shapedꢀreactorꢀandꢀpretreatedꢀatꢀ600ꢀ°Cꢀforꢀ1ꢀhꢀ
inꢀflowingꢀHe.ꢀAfterꢀtheꢀpretreatment,ꢀtheꢀsampleꢀwasꢀcooledꢀ
W
internalꢀcokeꢀ=ꢀ(Vmicro,ꢀfreshꢀ–ꢀVmicro,ꢀafterꢀreactionꢀ×ꢀ ꢀ
(1ꢀ+ꢀWtotalꢀcoke))ꢀ×ꢀdcokeꢀ ꢀ
externalꢀcokeꢀ=ꢀWꢀtotalꢀcokeꢀ–ꢀWinternalꢀcokeꢀ
W
downꢀtoꢀ100ꢀ°CꢀandꢀsaturatedꢀwithꢀNH
3 3
ꢀgas.ꢀThenꢀNH ‐TPDꢀwasꢀ
whereꢀ Winternalꢀcoke,ꢀ Wexternalꢀcoke,ꢀ andꢀ Wtotalꢀcokeꢀ areꢀ theꢀ amountsꢀ
carriedꢀoutꢀinꢀaꢀconstantꢀflowꢀofꢀHeꢀ(20ꢀmL/min)ꢀfromꢀ100ꢀtoꢀ
(gcoke/gcat)ꢀ ofꢀ internal,ꢀ external,ꢀ andꢀ totalꢀ coke,ꢀ respectively.ꢀ
6
00ꢀ°Cꢀatꢀaꢀheatingꢀrateꢀofꢀ10ꢀ°C/min.ꢀ
Fourierꢀ transformꢀ infraredꢀ (FT‐IR)ꢀ spectraꢀ afterꢀ pyridineꢀ
V
micro,freshꢀ andꢀ Vmicro,ꢀ afterꢀ reactionꢀ areꢀ theꢀ microporeꢀ volumesꢀ
3
(cm /g)ꢀofꢀtheꢀcatalystsꢀbeforeꢀandꢀafterꢀtheꢀreaction.ꢀdcokeꢀisꢀtheꢀ
cokeꢀdensityꢀ(1.22ꢀg/cm ).ꢀ
3
adsorptionꢀ wereꢀobtainedꢀonꢀ aꢀBrukerꢀTensorꢀ27ꢀinstrumentꢀ
withꢀ aꢀ resolutionꢀ ofꢀ 4ꢀ cm .ꢀ Samplesꢀ wereꢀ pressedꢀ intoꢀ aꢀ
self‐supportingꢀwaferꢀ(Rꢀ=ꢀ13ꢀmm,ꢀ20ꢀmg)ꢀandꢀevacuatedꢀ(10 ꢀ
Pa)ꢀinꢀanꢀIRꢀcellꢀatꢀ723ꢀKꢀforꢀ30ꢀminꢀpriorꢀtoꢀeachꢀmeasurement.ꢀ
Adsorptionꢀofꢀpyridineꢀwasꢀconductedꢀatꢀroomꢀtemperatureꢀforꢀ
−1
−2
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ CharacterizationꢀofꢀZSM‐5ꢀzeolitesꢀafterꢀpost‐syntheticꢀ
treatmentꢀ ꢀ
1ꢀ minꢀ toꢀ ensureꢀ saturatedꢀ loadingꢀ andꢀ thenꢀ evacuationꢀ wasꢀ
carriedꢀ outꢀ atꢀ 350ꢀ °Cꢀ forꢀ 30ꢀ minꢀ andꢀ cooledꢀ downꢀ toꢀ roomꢀ
temperatureꢀpriorꢀtoꢀacquisitionꢀofꢀIRꢀspectra.ꢀTheꢀdensitiesꢀofꢀ
BrønstedꢀandꢀLewisꢀacidꢀsitesꢀwereꢀcalculatedꢀfromꢀtheꢀIAꢀval‐
uesꢀ ofꢀ theꢀ differenceꢀ spectraꢀ atꢀ 1540ꢀ andꢀ 1450ꢀ cm ,ꢀrespec‐
tively,ꢀusingꢀtheꢀextinctionꢀcoefficientsꢀreportedꢀbyꢀEmeisꢀ[38].ꢀ ꢀ
Theꢀ XRDꢀ patternsꢀ ofꢀ ZSM‐5ꢀ treatedꢀ byꢀ Na
2
H EDTAꢀ andꢀ
2
H
3
PO ꢀ solutionsꢀ areꢀ shownꢀ inꢀ Fig.ꢀ S1.ꢀ Itꢀ canꢀ beꢀ seenꢀ thatꢀ
4
−1
ZSM‐5‐E‐1ꢀandꢀZSM‐5‐P‐1ꢀhaveꢀaꢀtypicalꢀdiffractionꢀpatternꢀofꢀ
MFIꢀtopology,ꢀshowingꢀtheꢀhighꢀstabilityꢀofꢀas‐madeꢀZSM‐5ꢀtoꢀ
theꢀ post‐syntheticꢀ treatment.ꢀ Theꢀ relativeꢀ crystallinityꢀ calcu‐
o
2.4.ꢀ ꢀ Catalyticꢀreactionꢀ
latedꢀbasedꢀonꢀtheꢀintensityꢀofꢀtheꢀcharacteristicꢀpeaksꢀatꢀ7.8 ,ꢀ
o
o
8
.8 ꢀ andꢀ 22.4 ꢀ areꢀ listedꢀ inꢀ Tableꢀ S1.ꢀ Aꢀ decreaseꢀ inꢀ relativeꢀ

ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
1421ꢀ
crystallinityꢀwasꢀobservedꢀforꢀZSM‐5‐E‐1.ꢀTheꢀSEMꢀimagesꢀofꢀ
theꢀsamplesꢀareꢀdisplayedꢀinꢀFig.ꢀS2,ꢀshowingꢀaꢀthinꢀflakinessꢀ
morphologyꢀwithꢀthicknessꢀofꢀaboutꢀ100ꢀnm.ꢀNoꢀclearꢀdiffer‐
enceꢀinꢀtheꢀsurfaceꢀsmoothnessꢀandꢀmorphologyꢀcanꢀbeꢀdistin‐
guishedꢀforꢀtheꢀcrystalsꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreat‐
ZSM-5-P-1
ZSM-5-E-1
ZSM-5
ment.ꢀ Theꢀ N ꢀ adsorption‐desorptionꢀ isothermsꢀ andꢀ poreꢀ dis‐
2
tributionsꢀofꢀtheꢀsamplesꢀareꢀgivenꢀinꢀFig.ꢀS3.ꢀTheꢀcorrespond‐
ingꢀtexturalꢀpropertiesꢀareꢀlistedꢀinꢀTableꢀS1.ꢀItꢀcanꢀbeꢀseenꢀthatꢀ
theꢀ microporeꢀ surfaceꢀ areaꢀ andꢀ microporeꢀ volumeꢀ ofꢀ theꢀ
treatedꢀ samplesꢀ displayꢀ aꢀ littleꢀ increase,ꢀ whileꢀ theꢀ externalꢀ
surfaceꢀareaꢀandꢀmesoporeꢀvolumeꢀslightlyꢀdecrease.ꢀItꢀisꢀspec‐
ulatedꢀthatꢀthereꢀmayꢀexistꢀsmallꢀamountsꢀofꢀamorphousꢀmate‐
rialsꢀonꢀtheꢀshellꢀregionꢀofꢀtheꢀparentꢀcrystals,ꢀwhichꢀwasꢀre‐
movedꢀbyꢀtheꢀpost‐syntheticꢀtreatment.ꢀ ꢀ
27
Solid‐stateꢀ AlꢀMASꢀNMRꢀspectraꢀwereꢀmeasuredꢀtoꢀinves‐
tigateꢀtheꢀchangeꢀofꢀlocalꢀatomicꢀenvironmentsꢀinꢀtheꢀsamplesꢀ
andꢀareꢀdisplayedꢀinꢀFig.ꢀ1.ꢀOneꢀstrongꢀbroadꢀresonanceꢀcen‐
teredꢀaroundꢀ56ꢀppmꢀisꢀobservedꢀforꢀtheꢀcalcinedꢀZSM‐5,ꢀwhichꢀ
isꢀattributedꢀtoꢀtetrahedralꢀAlꢀspeciesꢀ[42].ꢀItꢀimpliesꢀthatꢀonlyꢀ
100
80
60
40
Chemical shift (ppm)
Fig.ꢀ1.ꢀ AlꢀMASꢀNMRꢀspectraꢀofꢀcalcinedꢀsamples.ꢀ
20
0
-20
-40
27
frameworkꢀAlꢀatomsꢀexistꢀinꢀtheꢀzeoliteꢀprecursor.ꢀNoꢀobviousꢀ
changeꢀ canꢀ beꢀ foundꢀ inꢀ theꢀ 27Alꢀ MASꢀ NMRꢀ spectraꢀ afterꢀ
post‐syntheticꢀ treatment,ꢀ indicatingꢀ thatꢀ theꢀ presentꢀ strategyꢀ
couldꢀeffectivelyꢀprotectꢀtheꢀframeworkꢀAlꢀatomsꢀfromꢀdealu‐
minationꢀbyꢀpreventingꢀaccessꢀofꢀtheꢀmodifierꢀintoꢀtheꢀcrystalꢀ
interior.ꢀ ꢀ
Tableꢀ1ꢀlistsꢀtheꢀbulkꢀandꢀsurfaceꢀSi/Alꢀratiosꢀofꢀtheꢀcalcinedꢀ
samples.ꢀ Itꢀ canꢀ beꢀ seenꢀ thatꢀ theꢀ bulkꢀ Si/Alꢀ ratioꢀ increasesꢀ
slightlyꢀforꢀZSM‐5‐E‐1ꢀandꢀZSM‐5‐P‐1.ꢀOnꢀtheꢀotherꢀhand,ꢀtheꢀ
ZSM‐5ꢀ precursorꢀ givesꢀ aꢀ surfaceꢀ Si/Alꢀ ratioꢀ ofꢀ 60,ꢀ whichꢀ isꢀ
obviouslyꢀ lowerꢀ thanꢀ theꢀ valueꢀ ofꢀ theꢀ bulk,ꢀ implyingꢀ anꢀ Alꢀ
enrichmentꢀ phenomenonꢀ onꢀ theꢀ crystalꢀ surface.ꢀ Theꢀ surfaceꢀ
Si/Alꢀratiosꢀofꢀtheꢀtreatedꢀsamplesꢀdifferꢀfromꢀeachꢀother;ꢀtheꢀ
valueꢀofꢀZSM‐5‐P‐1ꢀisꢀcloseꢀtoꢀtheꢀprecursor,ꢀwhereasꢀaꢀgreatꢀ
increaseꢀ isꢀ observedꢀ forꢀ ZSM‐5‐E‐1.ꢀ Itꢀ isꢀ speculatedꢀ thatꢀ theꢀ
as‐madeꢀZSM‐5ꢀhasꢀhighꢀresistanceꢀtoꢀtheꢀacidꢀtreatment,ꢀandꢀ
andꢀ peakꢀ height.ꢀ However,ꢀ theꢀ intensityꢀ ofꢀ high‐temperatureꢀ
desorptionꢀ peakꢀ ofꢀ ZSM‐5‐P‐1ꢀ dropsꢀ slightly,ꢀ indicatingꢀ theꢀ
decreaseꢀofꢀstrongꢀacidꢀsites.ꢀTheꢀacidꢀdensityꢀcalculatedꢀbasedꢀ
onꢀtheꢀhigh‐temperatureꢀdesorptionꢀpeakꢀisꢀlistedꢀinꢀTableꢀ1.ꢀ
Theꢀpyridine‐adsorbedꢀFT‐IRꢀspectraꢀareꢀdisplayedꢀinꢀFig.ꢀ2(b).ꢀ
–1
Theꢀ peaksꢀ atꢀ 1540ꢀ andꢀ 1455ꢀ cm ꢀ areꢀ attributedꢀ toꢀ theꢀ
vibrationsꢀ associatedꢀ withꢀ pyridineꢀ adsorptionꢀ onꢀ Brønstedꢀ
acidꢀ sitesꢀ andꢀ Lewisꢀ acidꢀ sites,ꢀ respectivelyꢀ [43].ꢀ Theꢀ
correspondingꢀquantitativeꢀresultsꢀareꢀgivenꢀinꢀTableꢀ1,ꢀwhichꢀ
indicateꢀ thatꢀ theꢀ treatedꢀ samplesꢀ possessꢀ aꢀ slightlyꢀ higherꢀ
Brønstedꢀ acidꢀ sitesꢀ andꢀ lowerꢀ Lewisꢀ acidꢀ sitesꢀ thanꢀ theꢀ
precursor.ꢀTheꢀvariationsꢀoccurꢀpossiblyꢀdueꢀtoꢀtheꢀremovalꢀofꢀ
theꢀ amorphousꢀ materialsꢀ onꢀ theꢀ externalꢀ surfaceꢀ andꢀ areꢀ
consistentꢀ withꢀ theꢀ resultsꢀ inꢀ theꢀ partꢀ ofꢀ texturalꢀ
characterization.ꢀ Theꢀ acidityꢀ characterizationꢀ resultsꢀ togetherꢀ
withꢀtheꢀaboveꢀparagraphsꢀimplyꢀthatꢀtheꢀstructuralꢀintegrityꢀinꢀ
theꢀ crystalꢀ interiorꢀ ofꢀ ZSM‐5ꢀ remainsꢀ intactꢀ afterꢀ theꢀ
post‐syntheticꢀtreatment.ꢀ
TIPBꢀ crackingꢀ reactionꢀ wasꢀ employedꢀ toꢀ investigateꢀ theꢀ
externalꢀsurfaceꢀacidityꢀofꢀtheꢀsamplesꢀ(Fig.ꢀ3).ꢀZSM‐5‐P‐1ꢀgivesꢀ
theꢀ lowestꢀ TIPBꢀ conversionꢀ amongꢀ theꢀ samples.ꢀ Thisꢀ isꢀ
reasonableꢀbecauseꢀtheꢀstrongꢀinteractionsꢀbetweenꢀPꢀandꢀAlꢀ
atomsꢀ onꢀ theꢀ P‐richꢀ surfaceꢀ canꢀ effectivelyꢀ decreaseꢀ theꢀ
numberꢀandꢀstrengthꢀofꢀacidꢀsitesꢀ[44].ꢀHowever,ꢀunexpectedly,ꢀ
ZSM‐5‐E‐1ꢀ showsꢀ theꢀ highestꢀ catalyticꢀ activity.ꢀ Theꢀ TIPBꢀ
conversionsꢀonꢀZSM‐5‐E‐1ꢀareꢀmoreꢀthanꢀtwiceꢀasꢀhighꢀasꢀthoseꢀ
ofꢀ theꢀ precursorꢀ (theꢀ TIPBꢀ crackingꢀ experimentꢀ hasꢀ beenꢀ
repeatedꢀ overꢀ repeatedlyꢀ preparedꢀ ZSM‐5‐E‐1ꢀ andꢀ almostꢀ
similarꢀ resultsꢀ areꢀ obtained).ꢀ Itꢀ seemsꢀ contraryꢀ toꢀ theꢀ highꢀ
Na
2
H EDTAꢀisꢀmoreꢀeffectiveꢀthanꢀacidsꢀforꢀtheꢀdealuminationꢀ
2
ofꢀhigh‐SiꢀZSM‐5.ꢀMoreover,ꢀthereꢀisꢀsmallꢀamountsꢀofꢀPꢀspeciesꢀ
leftꢀonꢀZSM‐5‐P‐1ꢀ(0.17ꢀwt%).ꢀTheꢀbulkꢀandꢀsurfaceꢀP/Alꢀratiosꢀ
ofꢀZSM‐5‐P‐1ꢀareꢀgivenꢀinꢀTableꢀ1.ꢀAnꢀobviouslyꢀhigherꢀsurfaceꢀ
P/Alꢀ ratioꢀ canꢀ beꢀ observed,ꢀ implyingꢀ thatꢀ theꢀ Pꢀ atomsꢀ areꢀ
mainlyꢀlocatedꢀonꢀtheꢀexteriorꢀofꢀZSM‐5ꢀcrystals.ꢀ ꢀ
Theꢀ acidꢀ propertiesꢀ ofꢀ theꢀ samplesꢀ wereꢀ examinedꢀ byꢀ
3
NH ‐TPDꢀ andꢀ pyridine‐adsorbedꢀ FT‐IR.ꢀ Theꢀ resultsꢀ areꢀ
summarizedꢀ inꢀ Fig.ꢀ 2ꢀ andꢀ Tableꢀ 1.ꢀ Thereꢀ existꢀ twoꢀ distinctꢀ
ꢀ
desorptionꢀ peaksꢀ centeredꢀ aroundꢀ 180 andꢀ 380ꢀ °Cꢀ inꢀ theꢀ
NH ‐TPDꢀcurvesꢀ(Fig.ꢀ2(a)),ꢀcorrespondingꢀtoꢀweakꢀandꢀstrongꢀ
3
acidꢀsitesꢀinꢀtheꢀsamples.ꢀInꢀcomparisonꢀwithꢀZSM‐5ꢀprecursor,ꢀ
ZSM‐5‐E‐1ꢀ showsꢀlittleꢀ changeꢀinꢀtheꢀdesorptionꢀtemperatureꢀ
Tableꢀ1ꢀ
TheꢀSi/AlꢀratioꢀandꢀacidꢀpropertiesꢀofꢀZSM‐5ꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreatment.ꢀ
Bulkꢀphaseꢀaꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Surfaceꢀphaseꢀbꢀ
AcidꢀdensityꢀbyꢀPy‐IRꢀ(μmol/g)ꢀ
AcidꢀdensityꢀbyꢀNH
(μmol/g)ꢀ
3
‐TPDꢀ
Catalystꢀ
Si/Alꢀ
124ꢀ
126ꢀ
P/Alꢀ
–ꢀ
–ꢀ
Si/Alꢀ
ꢀ 60ꢀ
220ꢀ
ꢀ 78ꢀ
P/Alꢀ
–ꢀ
–ꢀ
Bꢀ
Lꢀ
Bꢀ+ꢀLꢀ
ZSM‐5ꢀ
ZSM‐5‐E‐1ꢀ
ZSM‐5‐P‐1ꢀ
112.2ꢀ
122.3ꢀ
119.6ꢀ
15.5ꢀ
ꢀ 7.3ꢀ
ꢀ 5.8ꢀ
127.6ꢀ
129.6ꢀ
125.4ꢀ
112.6ꢀ
115.1ꢀ
104.3ꢀ
130ꢀ
0.44ꢀ
2.17ꢀ
aꢀDeterminedꢀbyꢀXRF.ꢀ ꢀDeterminedꢀbyꢀXPS.ꢀ
b

1422ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
(
a)
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
(b)
1545
1455
1600
1550
1500
Wavenumber (cm )
1450
1400
100
200
300
400
o
500
600
1
Temperature ( C)
Fig.ꢀ2.ꢀNH ‐TPDꢀcurvesꢀ(a)ꢀandꢀpyridine‐adsorbedꢀFT‐IRꢀspectraꢀ(b)ꢀofꢀZSM‐5ꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreatment.ꢀ
3
surfaceꢀ Si/Alꢀ ratioꢀ ofꢀ ZSM‐5‐E‐1ꢀ (Tableꢀ 1).ꢀ Possibly,ꢀ silanolꢀ
nestsꢀ [45]ꢀ areꢀ formedꢀ onꢀ theꢀ externalꢀ surfaceꢀ ofꢀ ZSM‐5‐E‐1ꢀ
crystalsꢀfollowingꢀtheꢀremovalꢀofꢀframeworkꢀAlꢀatomsꢀduringꢀ
theꢀ post‐syntheticꢀ treatment.ꢀ Theꢀ silanolꢀ groupsꢀ interactingꢀ
throughꢀ extendedꢀ hydrogenꢀ bondingꢀ haveꢀ moderateꢀ acidityꢀ
andꢀcontributeꢀtoꢀtheꢀenhancedꢀTIPBꢀcrackingꢀactivityꢀ[47].ꢀ
Theꢀcokeꢀcontentꢀofꢀdischargedꢀcatalystsꢀwasꢀdeterminedꢀbyꢀ
TGꢀanalysisꢀ(Fig.ꢀS4).ꢀTheꢀcokeꢀdistributionsꢀinꢀtheꢀmicroporesꢀ
andꢀ onꢀ theꢀ externalꢀ surfaceꢀ wereꢀ estimatedꢀ accordingꢀ toꢀ theꢀ
resultsꢀofꢀN
ꢀphysisorptionꢀandꢀTGꢀanalysis.ꢀAsꢀshownꢀinꢀFig.ꢀ4,ꢀ
2
theꢀcokeꢀisꢀmainlyꢀdistributedꢀonꢀtheꢀexternalꢀsurfaceꢀofꢀZSM‐5ꢀ
(atꢀ leastꢀ 75%ꢀ ofꢀ theꢀ totalꢀ cokeꢀ content),ꢀ whichꢀ isꢀ consistentꢀ
withꢀ theꢀ previousꢀ reportsꢀ [9,39–41].ꢀ Theꢀ treatedꢀ samplesꢀ
possessꢀmoreꢀexternalꢀcokeꢀthanꢀ theꢀ precursor,ꢀ indicatingꢀ anꢀ
increasedꢀ toleranceꢀ toꢀ theꢀ externalꢀ cokeꢀ deposition.ꢀ Theꢀ
correspondingꢀ cokeꢀ depositionꢀ rateꢀ isꢀ shownꢀ inꢀ Fig.ꢀ 4.ꢀ
ZSM‐5‐P‐1ꢀ possessesꢀ lowerꢀ externalꢀ cokeꢀ depositionꢀ rate,ꢀ
whereasꢀZSM‐5‐E‐1ꢀgivesꢀhigherꢀexternalꢀcokeꢀdepositionꢀrateꢀ
thanꢀtheꢀprecursor.ꢀTheꢀvariationsꢀofꢀexternalꢀcokeꢀdepositionꢀ
rateꢀ onꢀ theꢀ treatedꢀ samplesꢀ areꢀ consistentꢀ withꢀ theꢀ TIPBꢀ
crackingꢀ results.ꢀ Onꢀ theꢀ otherꢀ hand,ꢀ bothꢀ ZSM‐5‐E‐1ꢀ andꢀ
ZSM‐5‐P‐1ꢀgiveꢀlowerꢀinternalꢀcokeꢀcontentꢀandꢀdepositionꢀrateꢀ
thanꢀtheꢀprecursor,ꢀwhichꢀevidencesꢀanꢀenhancedꢀmassꢀtransferꢀ
inꢀ bothꢀ samplesꢀ (theꢀ microporesꢀ areꢀ moreꢀ openꢀ afterꢀ theꢀ
treatment).ꢀItꢀisꢀinferredꢀthatꢀtheꢀimprovedꢀcatalyticꢀlifetimeꢀofꢀ
ZSM‐5‐P‐1ꢀ isꢀ dueꢀ toꢀ aꢀ combinationꢀ ofꢀ theꢀ increasedꢀ externalꢀ
toleranceꢀ toꢀ theꢀ externalꢀ cokeꢀ depositionꢀ andꢀ theꢀ depressedꢀ
cokingꢀ rateꢀ (reducedꢀ sideꢀ reactions);ꢀ butꢀ forꢀ ZSM‐5‐E‐1,ꢀ theꢀ
increasedꢀtoleranceꢀtoꢀtheꢀexternalꢀcokeꢀshouldꢀbeꢀtheꢀmajorꢀ
reason.ꢀ Likely,ꢀ theꢀ post‐syntheticꢀ treatmentꢀ removesꢀ theꢀ
amorphousꢀ materialsꢀ aroundꢀ theꢀ poreꢀ openingsꢀ andꢀ helpsꢀ
improveꢀtheꢀtoleranceꢀtoꢀtheꢀexternalꢀcokeꢀdeposition.ꢀ
Theꢀ productsꢀ selectivitiesꢀ onꢀ theꢀ samplesꢀ asꢀ aꢀ functionꢀ ofꢀ
TOSꢀ areꢀ shownꢀ inꢀ Fig.ꢀ 5.ꢀ Moreover,ꢀ detailedꢀ productꢀ
distributionsꢀatꢀTOSꢀ=ꢀ60ꢀhꢀareꢀlistedꢀinꢀTableꢀ2.ꢀItꢀcanꢀbeꢀseenꢀ
thatꢀtheꢀZSM‐5ꢀprecursorꢀgivesꢀpropeneꢀasꢀtheꢀmostꢀabundantꢀ
product,ꢀfollowedꢀbyꢀbutene,ꢀC5+Nꢀandꢀethene.ꢀTheꢀselectivitiesꢀ
toꢀethene,ꢀpropeneꢀandꢀbuteneꢀdropꢀasꢀtheꢀreactionꢀproceeds,ꢀ
whileꢀ thoseꢀ ofꢀ C5+Nꢀ andꢀ aromaticsꢀ increase.ꢀ Itꢀ isꢀ generallyꢀ
acceptedꢀ thatꢀ theꢀ reactionꢀ onꢀ ZSM‐5ꢀ followsꢀ aꢀ dual‐cycleꢀ
mechanism:ꢀ etheneꢀ mainlyꢀ originsꢀ fromꢀ theꢀ aromatics‐basedꢀ
cycle,ꢀ whileꢀ propeneꢀ andꢀ higherꢀ alkenesꢀ areꢀ formedꢀ toꢀ aꢀ
considerableꢀextentꢀfromꢀtheꢀolefins‐basedꢀcycleꢀ[46–48].ꢀTheꢀ
3.2.ꢀ ꢀ CatalyticꢀperformanceꢀinꢀMTPꢀreactionꢀ
Catalyticꢀ testsꢀ ofꢀ methanolꢀ toꢀ olefinsꢀ reactionꢀ overꢀ theꢀ
ꢀ
samplesꢀwereꢀcarriedꢀoutꢀatꢀ480 °CꢀwithꢀaꢀmethanolꢀWHSVꢀofꢀ
–1
4
.0ꢀ h .ꢀ Theꢀ methanolꢀ conversionꢀ asꢀ aꢀ functionꢀ ofꢀ TOSꢀ isꢀ
presentedꢀ inꢀ Fig.ꢀ 4.ꢀ Bothꢀ ZSM‐5‐E‐1ꢀ andꢀ ZSM‐5‐P‐1ꢀ showꢀ anꢀ
improvedꢀ catalyticꢀ lifetimeꢀ asꢀ comparedꢀ withꢀ theꢀ ZSM‐5ꢀ
precursor.ꢀ Givenꢀ thatꢀ theꢀ crystalꢀ interiorsꢀ ofꢀ ZSM‐5‐E‐1ꢀ andꢀ
ZSM‐5‐P‐1ꢀ areꢀ littleꢀ influencedꢀ asꢀ revealedꢀ byꢀ theꢀ aboveꢀ
characterizations,ꢀtheꢀimprovementꢀofꢀcatalyticꢀlifetimeꢀshouldꢀ
beꢀcloselyꢀrelatedꢀtoꢀtheꢀchangeꢀofꢀtheꢀsurfaceꢀproperties.ꢀ ꢀ
80
60
40
20
0
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
0
20 40 60 80 100 120 140 160 180 200
TOS (min)
Fig.ꢀ3.ꢀTIPBꢀconversionꢀonꢀZSM‐5ꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreat‐
ment.ꢀ

ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
1423ꢀ
Internal
External
Internal
External
100
2.5
0
0
0
0
.25
.20
.15
.10
98
96
94
92
90
2
1
1
0
.0
.5
.0
.5
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
0.05
.00
0
20
40
60
TOS (h)
80
100
120
0
0.0
(a)
(b)
(c)
(a)
(b)
(c)
Fig.ꢀ4.ꢀTheꢀmethanolꢀconversionꢀasꢀaꢀfunctionꢀofꢀTOS,ꢀtheꢀcokeꢀcontent,ꢀcokeꢀdistributionꢀandꢀcokeꢀdepositionꢀrateꢀonꢀtheꢀdischargedꢀZSM‐5ꢀcatalysts.
ꢀ
–1
(
a)ꢀZSM‐5,ꢀ(b)ꢀZSM‐5‐E‐1,ꢀ(c)ꢀZSM‐5‐P‐1.ꢀReactionꢀconditions:ꢀ480°C,ꢀmethanolꢀWHSVꢀ=ꢀ4.0ꢀh .ꢀ
2
2
2
2
5
4
3
2
4
4
2
1
0
8
6
4
4
40
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
38
36
34
32
21
20
19
18
17
0
20
40
60
80
100
120
0
20
40
60
80
100
120
0
20
40
60
80
100
120
TOS (h)
TOS (h)
TOS (h)
3
6
2
8
4
0
6
2
8
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
3
2
2
2
1
1
4
3
2
1
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
6
4
ZSM-5
ZSM-5-E-1
ZSM-5-P-1
0
20
40
60
80
100
120
0
20
40
60
80
100
120
0
20
40
60
80
100
120
TOS (h)
TOS (h)
TOS (h)
Fig.ꢀ5.ꢀProductsꢀselectivityꢀasꢀaꢀfunctionꢀofꢀTOSꢀoverꢀZSM‐5ꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreatment.ꢀReactionꢀconditions:ꢀ480ꢀ°C,ꢀmethanolꢀWHSVꢀ=
–1
4
.0ꢀh .ꢀTheꢀdataꢀfluctuationꢀinꢀtheꢀselectivityꢀofꢀaromaticsꢀoverꢀZSM‐5‐P‐1ꢀisꢀdueꢀtoꢀtheꢀinterruptionꢀbyꢀaddingꢀmethanolꢀtoꢀtheꢀsaturator.ꢀ
depressionꢀ ofꢀ lowerꢀ olefinsꢀ asꢀ theꢀ increaseꢀ ofꢀ TOSꢀ impliesꢀ aꢀ
droppingꢀactivityꢀofꢀbothꢀcycles.ꢀTheꢀevolutionꢀtrendꢀofꢀproductꢀ
selectivityꢀ onꢀ ZSM‐5‐E‐1ꢀ resemblesꢀ thatꢀ onꢀ theꢀ ZSM‐5ꢀ
precursor,ꢀwhichꢀsuggestsꢀsimilarꢀsurfaceꢀpropertiesꢀofꢀtheꢀtwoꢀ
samplesꢀ despiteꢀ theirꢀ differentꢀ surfaceꢀ Si/Alꢀ ratios.ꢀ However,ꢀ
forꢀZSM‐5‐P‐1,ꢀtheꢀselectivityꢀofꢀpropeneꢀisꢀmaintainedꢀatꢀhighꢀ
levelꢀuntilꢀtheꢀdeactivation;ꢀtheꢀselectivitiesꢀofꢀbuteneꢀandꢀC5+Nꢀ
areꢀ relativelyꢀ stableꢀ atꢀ theꢀ firstꢀ dozensꢀ ofꢀ hours,ꢀ whileꢀ theꢀ
etheneꢀ selectivityꢀ displaysꢀ aꢀ continuousꢀ droppingꢀ trend.ꢀ Theꢀ
higherꢀpropeneꢀselectivityꢀonꢀZSM‐5‐P‐1ꢀshouldꢀbeꢀattributedꢀ
toꢀ theꢀ decreasedꢀ externalꢀ acidꢀ density,ꢀ whichꢀ abatesꢀ theꢀ
consecutiveꢀreactionꢀofꢀlightꢀolefinsꢀonꢀtheꢀexternalꢀsurfaceꢀandꢀ
consistsꢀwithꢀitsꢀlowerꢀselectivitiesꢀtoꢀC9+ꢀaromaticsꢀ(formedꢀonꢀ
canꢀ effectivelyꢀ improveꢀ bothꢀ theꢀ catalyticꢀ lifetimeꢀ andꢀ theꢀ
stabilityꢀofꢀpropeneꢀselectivity.ꢀ
3.3.ꢀ ꢀ Influenceꢀofꢀphosphoricꢀacidꢀconcentrationꢀ
Givenꢀ theꢀ higherꢀ propeneꢀ selectivityꢀ andꢀ longerꢀ lifetimeꢀ
observedꢀ onꢀ ZSM‐5‐P‐1,ꢀ theꢀ H
3
PO ꢀ concentrationꢀ inꢀ theꢀ
4
post‐syntheticꢀtreatmentꢀwasꢀfurtherꢀadjustedꢀtoꢀoptimizeꢀtheꢀ
catalyticꢀperformance.ꢀTheꢀproductꢀSi/AlꢀratiosꢀandꢀPꢀcontentsꢀ
ofꢀtheꢀsamplesꢀareꢀsummarizedꢀinꢀTableꢀ3.ꢀNoꢀregularꢀchangeꢀinꢀ
theꢀSi/AlꢀratioꢀcanꢀbeꢀobservedꢀfollowingꢀtheꢀincreaseꢀofꢀH
concentration,ꢀandꢀtheꢀsamplesꢀhaveꢀsimilarꢀbulkꢀandꢀsurfaceꢀPꢀ
contents.ꢀ Theꢀ insignificantꢀ effectꢀ ofꢀ H PO ꢀ solutionꢀ onꢀ theꢀ
3
PO ꢀ
4
3
4
theꢀ externalꢀ acidꢀ sites)ꢀ andꢀ alkanesꢀ (C
demonstrateꢀ thatꢀ theꢀ reductionꢀ ofꢀ externalꢀ surfaceꢀ acidꢀ sitesꢀ
2
‐
4
0).ꢀ Theseꢀ resultsꢀ
dealuminationꢀ ofꢀ high‐Siꢀ as‐madeꢀ ZSM‐5ꢀ isꢀ understandable,ꢀ
sinceꢀ high‐Siꢀ zeolitesꢀ areꢀ generallyꢀ acknowledgedꢀ toꢀ beꢀ

1424ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
Tableꢀ2ꢀ
a
ProductsꢀdistributionꢀofꢀtheꢀmethanolꢀconversionꢀoverꢀZSM‐5ꢀbeforeꢀandꢀafterꢀpost‐syntheticꢀtreatmentꢀ .ꢀ
bꢀ
Selectivityꢀ (wt%)ꢀ
Sampleꢀ
Lifetimeꢀ(h)ꢀ
CH
4
ꢀ
C
2‐40ꢀ
2 4
C H ꢀ
C
3
H
6
ꢀ
4 8
C H ꢀ
C
5+Nꢀ
BTEXꢀ
4.7ꢀ
4.5ꢀ
2.7ꢀ
2.9ꢀ
A
C9+
ꢀ
ZSM‐5ꢀ
ꢀ 80ꢀ
ꢀ 98ꢀ
100ꢀ
118ꢀ
ꢀ 92ꢀ
1.6ꢀ
1.3ꢀ
1.3ꢀ
1.0ꢀ
4.1ꢀ
4.1ꢀ
1.8ꢀ
1.9ꢀ
1.5ꢀ
7.9ꢀ
7.9ꢀ
7.9ꢀ
8.7ꢀ
7.0ꢀ
41.0ꢀ
41.0ꢀ
44.5ꢀ
44.1ꢀ
45.9ꢀ
21.3ꢀ
22.1ꢀ
24.5ꢀ
25.4ꢀ
24.9ꢀ
16.6ꢀ
16.7ꢀ
15.7ꢀ
14.6ꢀ
17.0ꢀ
2.8ꢀ
2.4ꢀ
1.6ꢀ
1.3ꢀ
1.0ꢀ
ZSM‐5‐E‐1ꢀ
ZSM‐5‐P‐1ꢀ
ZSM‐5‐P‐3ꢀ
ZSM‐5‐P‐5ꢀ
aꢀ
0.9ꢀ
–1
2.0ꢀ
b
N
Reactionꢀconditions:ꢀ480ꢀ°C,ꢀWSHVꢀ=ꢀ4.0ꢀh .ꢀTheꢀlifetimeꢀisꢀdefinedꢀasꢀmethanolꢀconversionꢀofꢀaboveꢀ99%.ꢀ ꢀTheꢀdataꢀareꢀcollectedꢀatꢀTOSꢀ=ꢀ60ꢀh.ꢀC5+
non‐aromaticꢀproductsꢀwithꢀcarbonꢀnumberꢀ>ꢀ4,ꢀBTEX:ꢀlightꢀaromaticsꢀwithꢀcarbonꢀnumberꢀ<ꢀ9,ꢀAC9+:ꢀheavyꢀaromaticsꢀwithꢀcarbonꢀnumberꢀ≥ꢀ9.ꢀ
ꢀ
resistantꢀ toꢀ theꢀ acidꢀ solution.ꢀ Indeed,ꢀ weꢀ haveꢀ carriedꢀ outꢀ
post‐syntheticꢀHClꢀtreatmentꢀofꢀtheꢀsameꢀprecursorꢀandꢀalmostꢀ
unchangedꢀSi/Alꢀratiosꢀareꢀobtainedꢀ(TableꢀS2).ꢀ ꢀ
consistentꢀwithꢀtheꢀlowerꢀexternalꢀacidꢀdensityꢀ(TIBPꢀcrackingꢀ
ability)ꢀandꢀlowerꢀtoleranceꢀtoꢀtheꢀexternalꢀcokeꢀdepositionꢀonꢀ
ZSM‐5‐P‐5.ꢀItꢀimpliesꢀthatꢀsuitableꢀH
3
PO ꢀconcentrationꢀinꢀtheꢀ
4
TheꢀTIPBꢀconversionsꢀofꢀtheꢀsamplesꢀareꢀalsoꢀlistedꢀinꢀTableꢀ
.ꢀ Aꢀ gradualꢀ dropꢀ ofꢀ theꢀ TIPBꢀ conversionꢀ canꢀ beꢀ observedꢀ
post‐syntheticꢀ treatmentꢀ ofꢀ as‐madeꢀ ZSM‐5ꢀ isꢀ importantꢀ toꢀ
maximizeꢀtheꢀcatalyticꢀlifetime.ꢀ ꢀ
3
followingꢀ theꢀ increaseꢀ ofꢀ H PO ꢀ concentration,ꢀ whichꢀ impliesꢀ
3
4
Theꢀ productꢀ selectivitiesꢀ asꢀ aꢀ functionꢀ ofꢀ TOSꢀ overꢀ theꢀ
samplesꢀ areꢀ shownꢀ inꢀ Fig.ꢀ S5.ꢀ Detailedꢀ productꢀ distributionsꢀ
(TOSꢀ=ꢀ60ꢀh)ꢀareꢀpresentedꢀinꢀTableꢀ2.ꢀSimilarꢀtoꢀZSM‐5‐P‐1,ꢀ
ZSM‐5‐P‐3ꢀ andꢀ ZSM‐5‐P‐5ꢀ displayꢀ similarꢀ evolutionꢀ trendꢀ ofꢀ
productꢀselectivityꢀasꢀtheꢀreactionꢀproceeds.ꢀTheꢀselectivitiesꢀofꢀ
propene,ꢀ buteneꢀ andꢀ C5+Nꢀ areꢀ relativelyꢀ stableꢀ atꢀ theꢀ firstꢀ
dozensꢀofꢀhours,ꢀwhileꢀtheꢀselectivityꢀtoꢀetheneꢀdropsꢀgradually.ꢀ
Fromꢀ Tableꢀ 2,ꢀ theꢀ selectivitiesꢀ towardsꢀ heavyꢀ aromaticꢀ andꢀ
alkanesꢀ decreaseꢀ graduallyꢀ fromꢀ ZSM‐5‐P‐1ꢀ toꢀ ZSM‐5‐P‐5,ꢀ
whichꢀ impliesꢀ theꢀ restrainedꢀ sideꢀ reactionsꢀ andꢀ consistꢀ withꢀ
theirꢀdroppingꢀexternalꢀacidꢀdensity.ꢀThisꢀalsoꢀexplainsꢀwellꢀtheꢀ
highestꢀpropeneꢀselectivityꢀobservedꢀoverꢀZSM‐5‐P‐5ꢀwithꢀtheꢀ
lowestꢀexternalꢀacidꢀdensity.ꢀ ꢀ
theꢀ reductionꢀ ofꢀ externalꢀ acidꢀ densityꢀ fromꢀ ZSM‐5‐P‐1ꢀ toꢀ
ZSM‐5‐P‐5.ꢀ Theꢀ TIPBꢀ crackingꢀ onꢀ pureꢀ Siꢀ silicalite‐1ꢀ isꢀ alsoꢀ
testedꢀunderꢀtheꢀsameꢀconditions,ꢀwhichꢀgivesꢀaꢀconversionꢀofꢀ
1
.8%ꢀandꢀconfirmsꢀtheꢀexistenceꢀofꢀsmallꢀamountꢀofꢀacidꢀsitesꢀ
onꢀ theꢀ H PO ‐treatedꢀ samples.ꢀ Theꢀ reductionꢀ inꢀ theꢀ externalꢀ
surfaceꢀacidꢀdensityꢀasꢀtheꢀincreasingꢀH PO ꢀconcentrationꢀmayꢀ
3
4
3
4
beꢀ causedꢀ byꢀ theꢀ slightꢀ degradationꢀ ofꢀ surfaceꢀ structuralꢀ
integrityꢀwhenꢀZSM‐5ꢀwasꢀtreatedꢀunderꢀhigherꢀconcentrationꢀ
acidꢀsolution.ꢀ
Fig.ꢀ 6ꢀ showsꢀ theꢀ methanolꢀ conversionꢀ resultsꢀ overꢀ theꢀ
H
3
PO ‐treatedꢀ samples.ꢀ Theꢀ catalyticꢀ lifetimeꢀ reachesꢀ aꢀ
4
maximumꢀ ofꢀ 118ꢀ hꢀ onꢀ ZSM‐5‐P‐3ꢀ andꢀ reducesꢀ toꢀ 92ꢀ hꢀ onꢀ
ZSM‐5‐P‐5.ꢀTheꢀimprovementꢀinꢀcatalyticꢀlifetimeꢀofꢀZSM‐5‐P‐3ꢀ
isꢀapparentlyꢀbiggerꢀthanꢀthatꢀofꢀhigh‐SiꢀZSM‐5ꢀwithꢀsimilarꢀPꢀ
4.ꢀ ꢀ Conclusionsꢀ
loadingꢀ(obtainedꢀbyꢀimpregnationꢀofꢀHZSM‐5ꢀwithꢀH
3
PO )ꢀinꢀ
4
theꢀ previousꢀ reportꢀ [49].ꢀ Theꢀ cokeꢀ contentꢀ inꢀ theꢀ dischargedꢀ
catalystsꢀwasꢀevaluatedꢀbyꢀTGꢀanalysisꢀ(Fig.ꢀS4)ꢀandꢀtheꢀcokeꢀ
distributionsꢀinꢀtheꢀcrystalꢀinteriorꢀandꢀonꢀtheꢀexternalꢀsurfaceꢀ
areꢀalsoꢀpresentedꢀinꢀFig.ꢀ6.ꢀClearly,ꢀZSM‐5‐P‐1ꢀandꢀZSM‐5‐P‐3ꢀ
haveꢀ similarꢀ externalꢀcokeꢀcontent,ꢀwhichꢀisꢀobviouslyꢀhigherꢀ
thanꢀ thatꢀ onꢀ ZSM‐5‐P‐5.ꢀ Theꢀ externalꢀ cokeꢀ depositionꢀ rateꢀ
showsꢀ aꢀ reducingꢀ trendꢀ fromꢀ ZSM‐5‐P‐1ꢀ toꢀ ZSM‐5‐P‐5,ꢀ inꢀ
accordanceꢀ withꢀ theꢀ externalꢀ acidꢀ densityꢀ ofꢀ theꢀ samplesꢀ
revealedꢀbyꢀTIPBꢀcracking.ꢀOnꢀtheꢀotherꢀhand,ꢀtheꢀinternalꢀcokeꢀ
contentꢀandꢀdepositionꢀrateꢀshowꢀaꢀsequenceꢀofꢀZSM‐5‐P‐3ꢀ<ꢀ
ZSM‐5‐P‐5ꢀ<ꢀZSM‐5‐P‐1ꢀ<ꢀZSM‐5.ꢀTheꢀabnormalꢀorderꢀbetweenꢀ
ZSM‐5‐P‐3ꢀandꢀZSM‐5‐P‐5ꢀsuggestsꢀaꢀreducedꢀmassꢀtransferꢀinꢀ
ZSM‐5‐P‐5,ꢀwhichꢀmayꢀbeꢀcausedꢀbyꢀtheꢀdegradationꢀofꢀsurfaceꢀ
structuralꢀ integrityꢀ ofꢀ ZSM‐5‐P‐5.ꢀ Thisꢀ speculationꢀ isꢀ alsoꢀ
Inꢀsummary,ꢀweꢀhaveꢀpresentedꢀaꢀfacileꢀstrategyꢀtoꢀreduceꢀ
theꢀexternalꢀsurfaceꢀacidityꢀofꢀhigh‐silicaꢀZSM‐5ꢀbyꢀutilizingꢀtheꢀ
as‐madeꢀ zeoliteꢀ asꢀ aꢀ precursor.ꢀ Theꢀ existenceꢀ ofꢀ OSDAꢀ inꢀ theꢀ
as‐madeꢀ ZSM‐5ꢀ crystalsꢀ effectivelyꢀ blocksꢀ theꢀ channelsꢀ andꢀ
confinesꢀtheꢀmodificationꢀonꢀtheꢀcrystalꢀexteriorꢀwithoutꢀalter‐
ingꢀ theꢀ internalꢀ acidityꢀ andꢀ integrityꢀ ofꢀ theꢀ crystals.ꢀ H
PO4ꢀ
3
Internal
External
Internal
External
0
0
0
0
.25
.20
.15
.10
a
2.0
a
b
b
1.5
1.0
0.5
c
c
Tableꢀ3ꢀ
Theꢀ productꢀ compositionsꢀ andꢀ TIPBꢀ conversionꢀ (TOSꢀ =ꢀ 5ꢀ min)ꢀ overꢀ
3
ZSM‐5ꢀmodifiedꢀbyꢀH PO4ꢀsolutionꢀwithꢀdifferentꢀconcentrations.ꢀ
0.05
Pꢀcontentꢀ(wt%)ꢀ TIPBꢀconversion
Catalystꢀ
Si/Alꢀaꢀ Si/Alꢀbꢀ
aꢀ
bꢀ
Bulkꢀ Surfaceꢀ
(%)ꢀ
6.5ꢀ
5.7ꢀ
4.5ꢀ
1.8ꢀ
0.00
0.0
ZSM‐5‐P‐1ꢀ
ZSM‐5‐P‐3ꢀ
ZSM‐5‐P‐5ꢀ
Silicalite‐1ꢀ
130ꢀ
132ꢀ
128ꢀ
78ꢀ
55ꢀ
79ꢀ
–ꢀ
0.17ꢀ
0.12ꢀ
0.13ꢀ
–ꢀ
1.38ꢀ
1.21ꢀ ꢀ
1.30ꢀ
–ꢀ
Fig.ꢀ6.ꢀTheꢀmethanolꢀconversionꢀasꢀaꢀfunctionꢀofꢀTOS,ꢀtheꢀcokeꢀcontent,ꢀ
cokeꢀdistributionꢀandꢀcokeꢀdepositionꢀrateꢀoverꢀZSM‐5ꢀbeforeꢀandꢀafterꢀ
theꢀ H PO ꢀ Treatment.ꢀ (a)ꢀ ZSM‐5‐P‐1,ꢀ (b)ꢀ ZSM‐5‐P‐3,ꢀ (c)ꢀ ZSM‐5‐P‐5.
–ꢀ
3
4
aꢀDeterminedꢀbyꢀXRF.ꢀ ꢀDeterminedꢀbyꢀXPS.ꢀ
b
–1
Reactionꢀconditions:ꢀ480ꢀ°C,ꢀmethanolꢀWHSV=4.0ꢀh .ꢀ
ꢀ

ꢀ
XuebinꢀZhaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ39ꢀ(2018)ꢀ1418–1426ꢀ
1425ꢀ
treatmentꢀ cannotꢀ removeꢀ surfaceꢀ Alꢀ atoms,ꢀ butꢀ theꢀ smallꢀ
amountꢀofꢀPꢀleftꢀonꢀtheꢀ externalꢀ surfaceꢀ effectivelyꢀdecreasesꢀ
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theꢀacidꢀdensity.ꢀNa
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areꢀgeneratedꢀonꢀtheꢀexternalꢀsurfaceꢀafterꢀNa EDTAꢀtreat‐
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2 2
H EDTAꢀtreatmentꢀselectivelyꢀremovesꢀtheꢀ
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2 2
H
2 2
3
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lowerꢀ externalꢀ cokeꢀ depositionꢀ rateꢀ (reducedꢀ sideꢀ reactions),ꢀ
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Chin.ꢀJ.ꢀCatal.,ꢀ2018,ꢀ39:ꢀ1418–1426ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(18)63117‐1
Externalꢀsurfaceꢀmodificationꢀofꢀas‐madeꢀZSM‐5ꢀandꢀtheirꢀcatalyticꢀperformanceꢀinꢀtheꢀmethanolꢀtoꢀpropyleneꢀreactionꢀ
ꢀ
XuebinꢀZhao,ꢀYangꢀHong,ꢀLinyingꢀWang,ꢀDongꢀFan,ꢀNanaꢀYan,ꢀXiaonaꢀLiu,ꢀPengꢀTian*,ꢀXinwenꢀGuoꢀ*,ꢀZhongminꢀLiuꢀ*ꢀ
DalianꢀUniversityꢀofꢀTechnology;ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences;ꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences
ꢀ
Post‐syntheticꢀtreatmentꢀofꢀas‐madeꢀZSM‐5ꢀwithꢀNa
PO ꢀmodificationꢀcanꢀfurtherꢀenhanceꢀtheꢀpropeneꢀselectivityꢀdueꢀtoꢀtheꢀdepressedꢀexternalꢀcokeꢀdepositionꢀrateꢀ(reducedꢀsideꢀreac‐
tions).ꢀ
2 2
H
EDTAꢀorꢀH
3
PO ꢀsolutionꢀcanꢀprolongꢀtheꢀMTPꢀreactionꢀlifetimeꢀofꢀZSM‐5.ꢀTheꢀ
4
H
3
4

1426ꢀ
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高硅ZSM-5原粉的外表面改性及其在甲醇制丙烯反应中的应用
a,b,c
b,c
b
b
b,c
b,c
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a,*
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赵学斌 , 洪 杨 , 王林英 , 樊 栋 , 闫娜娜 , 刘晓娜 , 田 鹏 , 郭新闻 , 刘中民
a
大连理工大学化工学院, 宾州州立大学-大连理工大学联合能源研究中心, 精细化工国家重点实验室, 辽宁大连116024
b
中国科学院大连化学物理研究所, 甲醇制烯烃国家工程实验室, 国家能源低碳催化与工程研发中心,
洁净能源国家实验室, 能源材料化学协同创新中心, 辽宁大连116023
c
中国科学院大学, 北京100049
摘要: 使用来源广泛的甲醇为原料制取丙烯, 是对石油路线生产丙烯的重要补充. 尽管以ZSM-5分子筛为催化剂的固定床
甲醇制丙烯(MTP)技术已经实现了工业应用, 但进一步提高催化剂的寿命和丙烯的选择性一直是学术界和工业界的研究热
点. MTP过程作为典型的酸催化反应, 积碳是催化剂失活的主要原因, 由于ZSM-5分子筛十元环孔道的空间限制作用, 积碳
主要分布在外表面. 因此, 消除外表面的酸性位点对延长催化剂的寿命至关重要, 但修饰外表面酸性位点的同时往往会改
2 2 3 4
变样品的其他性质, 如孔径、整体酸量等. 本文分别使用Na H EDTA和H PO 处理高硅ZSM-5分子筛原粉(微孔内含有机模
板剂)来选择性地减小或消除外表面的酸密度, 而不影响分子筛内部的性质, 并考察了处理后样品的MTP性能. 使用N 物理
2
2
7
吸附、SEM和 Al MAS NMR表征样品的织构性质、形貌和Al原子的化学环境, XPS和三异丙苯裂解实验表征外表面的硅
铝比和酸密度. 表征结果表明, Na EDTA处理虽然可以选择性的脱除表面Al原子, 但会在外表面产生新的酸点(可能是
硅巢). H PO 处理虽然不能脱除表面的Al原子, 但外表面残留的P物种能够有效的减小酸密度. MTP评价结果表明, H PO
4
2
H
2
3
4
3
处理能够有效的延长催化剂的寿命和维持丙烯的选择性, 这是因为H
3
PO
4
处理既提高了外表面的容碳能力, 也抑制了积碳
PO 后处理的条
沉积的速率. Na EDTA处理仅能增加外表面的容碳能力, 所以其只能延长催化寿命. 通过进一步优化H
2
H
2
3
4
件, 处理后的ZSM-5样品的催化寿命可以延长至前体的1.5倍, 同时, 丙烯的选择性也略有提高, 并且在失活前维持增加的趋
势.
关键词: 甲醇制丙烯; ZSM-5分子筛; 改性; 磷酸; 乙二胺四乙酸
收稿日期: 2018-05-31. 接受日期: 2018-06-06. 出版日期: 2018-08-05.
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基金来源: 国家自然科学基金(21676262); 中国科学院前沿科学重点研究计划(QYZDB-SSW-JSC040).
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).