silica with 3d mesocellular pore structure used as … pe-sba-15 silica, which showed a 3d spherical...

2017Vol 2 No 3 11

1copy Under License of Creative Commons Attribution 30 License | This article is available in httpwwwimedpubcomsynthesis-and-catalysis-open-access

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Research Article

DOI 1041722574-0431100017

Synthesis and Catalysis Open AccessISSN 2574-0431

Pardo-Tarifa F12 Montes V2 Claure M3 Cabrera S3 Kusar H1 Marinas A2 and Boutonnet M1

1 KTH-RoyalInstituteofTechnologyChemicalTechnologyTeknikringen42SE-10044StockholmSweden

2 UMSA-UniversidadMayordeSanAndreacutesInstitutodelGasNaturalCampusUniversitarioLaPazBolivia

3 UCO-UniversidaddeCoacuterdobaDepartamentodeQuiacutemicaOrgaacutenicaCampusdeExcelenciaAgroalimentario(ceiA3)CampusdeRabanalesMarieCurieBuidingE-14014CoacuterdobaSpain

Corresponding author FatimaPardo-Tarifa

pardokthse

KTH-RoyalInstituteofTechnologyChemicalTechnologyTeknikringen42SE-10044StockholmSweden

Tel +46(0)87908251

Citation Pardo-TarifaFMontesVClaureMCabreraSKusarHetal(2017)Silicawith3DMesocellularPoreStructureUsedasSupportforCobaltFischer-TropschCatalystSynthCatalVol2No311Introduction

Ordered Mesoporous Silica (OMS) are considered of a greatinterest due to their unique properties such as highly orderedpore structures high specific surface area as well as tunableporesizeandvolumeOMSusedascatalystsupportsissuitablefor reactions involving bulky molecules and its structure isconvenient for avoiding the agglomeration and coalescenceof the deposited catalyst particles resulting in higher catalystdispersion[1-4]

SeveralmesoporousstructuresofsilicashavebeenusedascobaltcatalystsupportsinFischer-TrospchSynthesis(FTS)[56]FTSisanexothermicreactionbetweenH2andCOwhichproduceawidevarietyofhydrocarbons(gasliquidandwaxes)usedasfuelsandchemicals [78] The porosity of the catalysts support plays animportant role in this kindof reactionswherebulkymolecules

are involved If the pores become too narrow differences inreactantdiffusionratescanleadtosignificantchangesinproductselectivitythelonghydrocarbonchainselectivityandyieldcanbereducedtheproducedwatercanbemoreeasilyaccumulatedandoxidizethemetalliccobalt[9-14]Asaconsequenceseveralstudies have been performed on the support pore size effectoncobaltFischer-TropschcatalystsOutcomesonthosestudiesreported that wide pore catalysts supports are preferable forhigher CO conversion and higher selectivity to hydrocarbonswith longer than five carbon atoms (SC5+) in length [315-19]Subsequently newmesoporous structures are investigated tofindnewoutcomesnotonlyincobaltcatalystforFTSbutalsoforotherapplications

ReceivedApril222017 Accepted July292017Published August222017

Silica with 3D Mesocellular Pore Structure Used as Support for Cobalt

Fischer-Tropsch Catalyst

AbstractThe typicalMCM-41andSBA-15 silica typesweremodified inorder toexpandtheir pores by addition of a swelling agent at mild conditions The MCM-41SBA-15 and Pore-expanded (PE) mesoporous silicas ie PE-SBA-15 and PE-MCM-41 were synthesized by the atrane route and used as supports in thepreparationofcobaltFischerndashTropschcatalystsThesynthetizedsilicaspresentedahomogeneousmorphologywithnarrowporesizedistributionof1D2Dand3DporestructuresThemost interestingporestructureandsizewaspresentedbythePE-SBA-15silicawhichshoweda3Dsphericalcellstructureof30nmdiameterinterconnectedbysmallwindowporesof7nmofdiameterThesesupportswereusedincobaltcatalystpreparationThecharacterizationresultsshowedthatthepore structure andpore size affected the growthof cobalt oxideparticles andcobalt-silica interaction These factors played an important role on the cobaltdispersionandDegreeofReduction(DOR)CoSBA-15andCoPE-SBA-15catalystspresentedsimilarphysicochemicalpropertiesrelatedwiththeCo3O4buttheporesizeandstructureofthesupportwasdifferentAll thecatalystsweretested inFischer-TropschreactionatclosetoindustrialconditionsCoPE-SBA-15catalystshowed the best CO conversion and selectivity to long-chain hydrocarbonsresultsattributedtothehigherdegreeofreductionofcobaltbutmainlytotheopennetworkwith3Dstructureporesof the silica supportwhich reduced thediffusionlimitationsofthereactantsandproducts

Keywords Silica 3D pore structure SBA-15 MCM-41 Co3O4 Fischer-Tropschsynthesis

2

ARCHIVOS DE MEDICINAISSN 1698-9465

2017Vol 2 No 3 11

This article is available in httpwwwimedpubcomsynthesis-and-catalysis-open-access


OMSiscommonlypreparedusingasurfactant-templatesynthesisprocedurebasedonvarioustemplatingagentstoformdifferentstructurearraysThemostcommonstructuresare1DhexagonalarrayieMCM-41whichconsistsofparallelchannelsthatareonly accessible in one direction 2D arraywith interconnectedparallelandperpendicularchannelsieSBA-15andmorenewlyinvestigated3Dcage-likestructurewithacubicarrayformedbyasystemofinterconnectedporesieMCM-48[420]

The OMS is formed by a silicon oxide network throughpolycondensation reactions of a molecular precursor in liquidmedia this is the conventional sol-gel synthesis methodHowever a modified version of this technique is the atrane route methoddevelopedbyCabreraetal[2122]Thismethodis basedon theuseof a simple structural directingagent ieCetyltrimethylammonium Bromide (CTAB) and a complexingpolyalcoholTriethanolamine(TEAH3)ThisTEAH3formschelatedcomplexes called atranes ie complexes which include tri-ethanolamine-like ligandspecies (Figure 1)withawidevarietyofMetals(M)Theatranecomplexislessreactivethananormalorganometallic precursor in aqueous solution Therefore thehydrolysis and condensation reaction rate of the inorganiccomponents is slowed down when a metal-atrane complex isused[21-23]

To our knowledge onlyMCM-41 has been synthetized by theatranerouteandneverSBA-15andporeexpandedMCM-41andSBA-15TheadvantageofsynthetizingthesematerialstroughtheatranerouteisthattheexpansionoftheporesisperformedatmildconditionsWhileotherinvestigationsreportedtheobtainof the samematerials by exposing the materials for a periodof48hat100degC inanautoclave Ithasbeenexplainedbeforethe important role of porosity for cobalt catalyst support inthe performance of Fischer-Tropsch reaction For this reasonthe synthesis of the proposed silica seems very interesting Inadditionmanystudieson1D ieMCM-41and2D ieSBA-15channel structure andporesplaced in 3D structure ieMCM-48havebeenexploredbutalmostanyworkon silicawith3DmesocellularstructureporeshavebeeninvestigatedforthiskindofcatalystandreactionThereforethesynthesisofsilicawith3DmesocellularstructureporesisveryattractiveforcobaltFischerndashTropschsynthesis

Theaimofthisworkfirstistoextendthesynthesisofmesoporoussilica by the atrane route towards other structures especially3D mesocellular structure second explore the effect of porestructureandsizeofsilicaonthefinalcobaltcatalystandfinallytestthesecatalystsinFischer-Tropschsynthesis

Experimental PartSupports synthesisMCM-41 and PE-MCM-41 synthesis Mesoporous silica(MCM-41andPE-MCM-41)waspreparedbytheatraneroute[2124-27] TEOS (tetraethyl orthosilicate Si(OC2H5)4) wasadded to TEAH3 (triethanolamine N (CH2ndashCH2ndashOH)3) andheated at 140degC for 20 min under stirring in order to formsilatranecomplexesNaOH(1M)wasthenaddedtothesilatrane

complex solution and the resulting solution was cooled downto 80degC afterwards the surfactant CetyltrimethylammoniumBromide (CTAB) was added to the solution The final solutionwas kept under stirring for at least 30 min Thereafter thetemperaturewasloweredto50degCandwaterwasaddedtothesolution under stirring The productwas kept under the sameconditions for2handwas thenagedwithout stirringat roomtemperaturefor24hThepore-expandedMCM-41(PE-MCM-41)wassynthesizedinthesamemannerasMCM-41withtwomaindifferences First a swelling agent Triisopropylbenzene (TIPB)was added after the addition of the surfactant (CTAB) in theproceduredescribedpreviouslysecondthesystemwasagedat70degCfor24hinaclosesystemafterwateradditionThemolarratiosoftheusedreagentswere1Si4TEAH330H2O1NaOH01CTAB90H2O005TIPB

SBA-15 and pore-expanded PE-SBA-15 synthesis The SBA-15was synthetized by dissolving the surfactant P123 (Mav=5800EO20-PO70-EO20)in2MHClsolutionAhomogeneoussolutionwas obtained after stirring at 40degC for 3 h Afterwards thesilatranecomplex(similartotheoneusedpreviouslyforMCM-41synthesis)wasaddedtothesolutionundervigorousstirringandkeptfor12hatthesameconditionsThefinalproductwaskeptagingfor24hatroomtemperatureThepore-expandedSBA-15(PE-SBA-15)waspreparedinthesamewayastheSBA-15withthesingleexceptionthattheswellingagent135-trimethylbenzene(TMB)wasaddedtothesynthesissolutionpriortotheadditionofthesilatranecomplexwiththefunctionofworkingasamicelleexpander[28]Thefinalsolutionwaskeptagingat70degCfor24hTheemployedmolarratioswere0017P12300054TMB435HCl183H2O1TEOS

In all the cases theprecipitated solidwas separated from theliquidwastebyfiltrationandwashedrepeatedlywithwaterandethanolThematerialwasdriedfor12hat70degCandtheorganiccompoundswereremovedfromthesolidbycalcination(5hat120degCthen3hat350degCand5hat550degC)withatemperaturerampof5degCmin

Cobalt catalyst preparation The cobalt-based catalysts werepreparedbytheincipient-wetnessimpregnationtechniquePriorto the cobalt impregnationprocedure the supports (MCM-41PE-MCM-41SBA-15andPE-SBA-15)weredried inairat120degCfor5h Later12wtCo fromaCo(NO3)2middot6H2Oprecursorwasdissolved inpurifiedwater toavolumeequivalent to theporevolume of each support The impregnated powder was thendriedinairat120degCfor5handsubsequentlycalcinedinairat350degCfor10h(heatingrate1degCmin)Thefinalcobaltcontentinthecatalystswas120plusmn01wtthesevalueswerecalculatedusingthestoichiometrybetweenhydrogenandcobaltfromthetotalH2consumptioninthetemperature programmed reduction (TPR)experiment

Catalyst characterizationBrunauerndashEmmettndashTeller (BET) technique was used for thecalculationofsurfaceareatheporevolumeandporediameterwas calculated the Barrett-Joyner-Halenda (BJH) techniqueMeasurements were performed with a Micromeritics ASAP

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2000 unit Themorphology of the supports and final catalystswere studied by high resolution-scanning electronmicroscopyusing an XHR-SEM Magellan 400 instrument supplied by theFEI Company The samples were investigated using a lowaccelerating voltage and no conductive coating TransmissionElectronMicroscopy(TEM) imageswerecollectedusinga JEOLJEM1400microscopeAllsamplesweremountedon3mmholeycarboncoppergridsThespeciesidentificationwasperformedbyX-rayDiffraction(XRD)onaSiemensD5000X-raydiffractometerwith Cu Kα radiation (40 kV 30mA) Crystallite sizes of Co3O4 werecalculatedbyusingtheScherrerequationandbyassumingspherical particles [29] The Codeg crystallite size was estimatedfromCo3O4usingtheformulad(Codeg)=075d(Co3O4)[3031]ThecatalystreducibilitywasinvestigatedbyhydrogenTemperatureProgrammed Reduction (TPR) on a Micromeritics Autochem2910[32]TheDegreeofReduction(DOR)wascalculatedusingH2-TPRofthein-situ reducedcatalystsTheThermalConductivityDetector(TCD)wascalibratedwithAg2OasstandardTheDORwascalculatedassumingthatunreducedcobaltafterreductionwasintheformofCo2+[3334]

TheappliedformulausedtocalculateDORwas[35]

1

TCD

co co

A fDOR

X AW= minus

ATCD[aug]isthearearesultingfromtheintegrationoftheTCDsignalfortheCo-catalystnormalizedpermasscatalystf[molesofH2au]isacalibrationfactorcorrelatingtheareaoftheTCDsignalandtheH2consumedfortheAg2OstandardXCoisthemassfractionofcobaltinthecatalystsampleandAWCoistheatomicweightofCo(589gmol)

Thecobaltdispersion(D)andthecobaltcrystallitesize(d(Codeg)nm)were calculated byhydrogen static chemisorption on thereduced catalysts The measurements were performed on aMicromeriticsASAP202degCunitat35degCAcompletedescriptionof the sample preparation procedure and instrument analysisforthematerialscharacterizationcanbefoundinourpreviouswork[36]

Catalytic testingFischerndashTropsch experiments were performed in a stainless-steel fixed-bed reactor at process conditions 210degC 20 barmolarH2COratio=21Amixtureof1gofcatalystwithapelletsizebetween53ndash90μmwasdilutedandmixedwith5gofSiCinordertoachieveaneventemperatureprofileandwasthereafterplaced in the reactor [36] Prior to the reaction the catalystwasactivatedbyreducing it in situ withhydrogenat350degCfor16hatatmosphericpressureThecatalystsweretestedintwoperiodsfirsta syngasflowof100Ncm3min (NTP) for25hofTimeofStream(TOS)and thereafter in thesecondperiod thegasflowwaschangedinordertoobtainCOconversionof30[33353738] The heavy Hydrocarbons (HCs) andmost of thewater were condensed in two traps kept at 120degC and room-temperature respectively Theproductgases leaving the trapsweredepressurized andanalyzedon-linewith anAgilent 6890GasChromatograph(GC)equippedwithaThermalConductivityDetector(TCD)andaFlameIonizationDetector(FID)H2N2CO

CH4andCO2wereseparatedbyaCarbosieve II packed column andanalyzedontheTCDThepercentageofCOconversionwascalculatedby

( ) 100in outconv

in

CO COCO mol

COminus

= times

C1ndashC6productswereaccuratelyseparatedbyanalumina PLOT column andquantifiedon theFIDdetectorFromwhich itwaspossibletodeterminetheC5+selectivity(SC5+)which isawidelyusedmeasure for long-chainhydrocarbonsselectivityTheSC5+ifexcludingCO2fromtheC-atombalance isdefinedasfollows[3539]

25 1 2 3 4100 ( )C C C C C CO freeS S S S S+ = minus + + +

Results and DiscussionSynthesis approachThe silatrane formation Forthefirsttimeageneralizedsynthesisstrategy for thepreparationofmesoporousmaterialswith1D2Dand3Dstructuresusingtheatrane route ispresentedinthisstudyThesilatranecomplexwasobtainedbyfullydeprotonatedtriethanolamine-like species as ligands [2127] The (TEAH3)triethanolamine N(CH2-CH2ndashOH)3 reacts with tetraortosilicateSi(OC2H5)4)andreplacesthefouralcoholsfromtheTEOSforminga stable amine-trialkoxo-complexes by acting (tetradentate)tripodligand(Figure 1)[2140]

MCM-41 and PE-MCM-41 silica formation Once the silatranewere formed water addition promotes their consequenthydrolysisprocesses(thermodynamicallyfavored)Evenatbasicmediumthehydrolysisprocessisdelayduetotheformedmetal-complexiesilatraneDuethestericeffectoftheligandsinthesilatranecomplex(Figure 1)theOH-groupshavedifficultiestoreach themetal ldquoSirdquo Consequently the hydrolysis is slow andsubsequently the silica polymerization also slows down Thefinalformedoligomershasanegativechargedensityduetotheethanoleliminationfromtheatranecomplexatthesametimethecationicsurfactant(CTA+Br-)isformedinmicellaraggregatesofCTA+whichcanmatchwithnegativelychargedoligomersbystrongelectrostaticinteractionandformsilicacoatedsurfactantmicelles[23]

Self-assembly of surfactant micelles and swelling agent TheCTABhasapositivechargedpolarheadgroupandalargealkylchainasanon-polargroupTheCTABmicellestendtoformanellipsoid shape in aqueous solution with the hydrophilic headgroups and condensed counter ions being considered as anelectrondenseshellaroundthecoreformedbythehydrophobictails Depending on the CTAB concentration it might formhexagonalmesotructureswith 1D channel structure structurethatthesilicawilladoptaftersurfactantremovalieMCM-41InthecaseofPE-MCM-41theswellingagentTIPBself-organizeinside the array channels formed with CTA+ into concentriccylindersexpandinginthiswaythemicellediameter[4142]

SBA-15 and PE-SBA-15 silica formation The surfactant P123usedfortheSBA-15synthesisisamixtureofatriblockcopolymerPolyethylene oxidepolypropylene oxidepolyethylene oxide

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(EOPOEO) The EO block is hydrophilic and the PO block ishydrophobic [43] Themicellization of the triblock copolymersis driven by the hydrophobic Polyethylene Oxide (PO) blockwith a core consistingofPOblocks anda coronaof EOblocks[44-46] The hydrophilic part EO will attract the anionic oxo-hydroxo-Sioligomersforminginthiswaytheinorganicsiliceouscondensation on themicellesWhen the TMB is added to thesynthesis it prefers to self- assemble in the hydrophobic coreof PO causing the micelles to swell Finally the addition ofthe swelling agent (TMB) might affect the surfactant micellesequilibriumformationandproducedisorganizedmaterialsas itwasreportedsomewhereelse[4748]ForthisreasonwesuggesttouseasilatranecomplexasmetalprecursorsofSiInadditionthesynthesisofpore-expandedsilicasinourcasewasperformedatsoftconditionswhileothermethodsproposedtheuseofanautoclaveinapostsynthesisprocess

Materials characterizationChemical composition and particle size analysis (X-ray diffraction) X-ray diffraction patterns measured at angles(2θ=10ndash80deg) did not show any peak for the supports showingtheabsenceofcrystallinedomainsthereafterarenotpresentedin this work Table 2 and Figure 2 show the results for thecobaltcatalystsfromtheXRDdiffractogramsCo3O4speciesareidentifiedforallthecatalystsFromthe(311)Co3O4peaklocatedat2θ=369degtheaverageparticlesizeusingScherrersequationwascalculatedinTable 2ThecalculatedparticlesizevalueforCo3O4was converted toCodeg Results show thatCo3O4particlesincreasewiththesupportporediameterObtainingthesmallestCo3O4particlesizeforCoMCM-41CoPE-SBA-15andCoSBA-15showsalmostthesamecobaltoxideaverageparticlesize

Textural properties The textural properties of the supportsand cobalt catalysts are listed in Table 1 The N2 adsorption-desorption isothermsandporesizedistributionofall thesilica

supportsaccordingtotheBarrettndashJoynerndashHalenda(BJH)method[47]areshowninFigure 3AccordingtotheIUPACnomenclatureall the catalysts have type IV (a) isotherms corresponding tomesoporous adsorbents with a pore diameter in the range of2ndash50nm[4849]

BothMCM-41andSBA-15silicas(Figure 3)presentnarrowporesize distribution SBA-15 has almost twice the average porediametersizeofMCM-41silica(Table1)PE-MCM-41presentsaparticular physisorption isothermwith twohysteresis thefirstone for PPO=045ndash08 related to the N2 condensation insidethecylindricalporesofthematerialas inthecaseofMCM-41the second small hysteresis loopatPPO=090ndash095 is ascribedtoN2condensation in the inter-particle poreswith a pore sizedistribution at 30 nm Consequently it is assumed that thismaterialhasstructuralandtexturalporosity

Thehysteresis for PE-SBA-15 inFigure 3 presents a typeH2(b)loop associated with pore blocking this type of hysteresisloops describes a 3D cell structure with interconnected pores(windows)[49]Thecelldiameterandthewindowdiameterareobtained from the adsorption and desorption branches of theisothermsrespectively(Figure 3 and Table 1)

BoththeBETsurfaceareaandtotalporevolumeofthesupportsafter cobalt deposition decrease and the average pore sizeincrease(Table 2)Theexplanationgivenforthisfactisthatthesmaller pores plugging by cobalt oxide particles makes theminaccessibletoN2(adsorbate)moleculesandthusdecreasesthesurfaceareaandporevolumewhiletheporesizeresultsbigger[50]

Scanning and transmission electron microscopies RepresentativeSEM images of MCM-41 PE-MCM-41 SBA-15 and PE-SBA-15are illustrated inFigure 4MCM-41showsaperfecthexagonalstructure extrapolated from its nano-scale structure SBA-15presents fiber-like morphologies of different sizes and widths

NH2C

CH2

HO

H2C

CH2

OH

H2CCH2

OH

O

Si

O

O

O

CH2

CH3

H2C

H3C

H2C

H3C

CH2

CH3

+

a) b) c)

d) e)

O

N

OSi

O

N OH

HO

O

O

N OSi

O

N

HO

O

Si

N

O OO

O

O

N O

SiO

N

OSi

O

Si

NO

O

N

O

O

OO

O

Figure 1 Molecular structures for the silatrane oligomers a) Triethylortosilicate precursor(TEOS)b)TriethanolamineTEAcomplexingagentc)monomers[Si(TEA)2H2]d)dimer[Si2(TEA)3H] e) trimer [Si3(TEA)4] for a better understanding of the structures thehydrogenswereeliminated

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[51]ThemorphologyfromtheinitialMCM-41andSBA-15waschangedfromhexagonalandcylindricaltubestoagglomeratedsphericalparticlesThisresultwasproducedbytheadditionoftheswellingagentandsuggests that theswellingagent isnotonlyinsidetheCTABandP123micellesbutalsooutsidewhichcanpreventtheformationofbigandlongparticles

Themorphology of the supports did not changed after cobaltdepositionthereaftertheSEMpicturesarenotpresentedinthiswork

FurtherstudiesfromtheTEMimagesinFigure 5 showedthatCoMCM-41CoPE-MCM-41andCoSBA-15havechannelstructureswith different pore sizes Here it is evident that PE-MCM-41preservedthechannelsfromMCM-41silicabutchangedthe1Dchannelformationto2DchannelswithperpendiculardirectionPE-SBA-15 changed the mesostructure to a 3D mesocellularfoamshapeThisisinagreementwithN2adsorption-desorptionresultsCobaltparticleswerealsoidentifiedinFigure 5 (A1 and A2)DuetodifferencesinelectronicdensitytheareasofdarkercontrastwereassignedtocobaltoxidewhilsttheareasoflightercontrastwereduetothesilicasupportCoMCM-41presentedawell-organizedporestructureofthesupportwithagglomeratedcobalt oxide particlesmostly outside de pores (Figure 5) ThecobaltoxideseemstobemoredispersedinsidetheporesinCoPE-MCM-41 (Figure 5 (B2))On theothersideahomogeneousdispersionandparticlesizeofCo3O4areseeninCoSBA-15CoPE-SBA-15 shows the 3D mesocellular foam pore structure of

the silica The networkwas formed for pore cellswith amainporediameterof30nmandinterconnectedwindows(Figure 5 (D2)) Additionally thismaterial showed big agglomerations ofcobaltoxidebutalsoparticlesinsidethesphericalpores(Figure 5 (D1)) Inall thecasesCo3O4particlesseemstobeformedonboththeexternalandinternalsurfaceofthematerialswhicharecomparablewithotherresearches[52]

Physicochemical analysis H2-Temperature Programmed Reduction Acomparisonofthereductiontemperatureprofilesfor the final catalysts are shown in Figure 6 Unsupported aswell as supported cobalt oxide Co3O4 is reduced in two stepsone(Co3O4 + H2rarr3CoO+H2O)andthesecondstep(3CoO+3H2 rarr3CoO+3H2O)Thelastoneismoresensitivetothesupportparticle size particle-support interaction reductant flow (rateandcomposition)andheatingrateFigure 2showstwomainH2uptakesforallthecatalyststhefirstoneattemperaturesbelow500degC corresponding to the reduction of Co3O4 and CoO thesecondoneattemperatureshigherthan500degCcorrespondenttostrongmetalsupportinteraction[53-55]

Thenit isconcludedthatmoreCo3O4andlessCoOspeciesarepresent in CoMCM-41 than in CoPE-MCM-41 while the Co-silicates species are higher in CoMCM-41 From these resultsonecanexpectthatCoPE-MCM-41hasmorereduciblecobaltat350degCwhichisrequiredforFTSThesedifferencesareattributedtothehighersurfaceareaandsmallporediametersizewhichfavors the formation of very small particles that can easilyinteractwithndashOHspeciespresent inMCM-41silicaCoSBA-15shows more CoO species than Co3O4 and less cobalt-supportspeciescomparedwithCoPE-SBA-15Cobalt-supportinteractionin CoPE-SBA-15 is attributed to the more open network ofthe silica supportwhich favors the diffusion of Co ions duringimpregnationandcalcinationThereafterthesecobaltionsmightreachthewindowporesinthecellsphereswheretheprobabilityofinteractwiththesilanolgroupsishigherduethesmallwindowporesize

CoMCM-41 and CoSBA-15 catalysts showed very differentreductionpropertiesOneexplanationmightbetheporediameterofthesilicasupportItwasreportedthatsmallerporediameterinmesoporoussilicalikelyformsandstabilizessmallercobaltoxideparticleswithhigherdispersionNeverthelesstheporediameterofthesilicasupportmaterialisnottheonlypossibleexplanationfordiversereductionpropertiesSomeauthorstriedtoexplainthedifferencebetweenMCM-41andSBA-15andfoundthattheporesurfaceconsistsofregularlyarrangedisolatedsurfaceSiOHgroupsTheseOHspecies inparalleldirectiontothecylindricalpore axis are absent in MCM-41 On the contrary the innersurfaceofSBA-15containsisolatedandinteractingSiOHgroupsable to formhydrogenbondswithotherOHgroupsaswell asgeminalSi(OH)2groupswithallofthempointinginalldirectionsofspacePoremodelshaveshownthattheinnersurfaceofSBA-15 issubstantiallyldquorougherrdquothantheporesurfaceofMCM-41[56]Thereforeitisreasonabletothinkthatduetotherougherinner surfaceof theSBA-15 support the interactionsof cobaltparticleswith silica surface sites in the CoSBA-15 catalyst areweakerandasaresultlesscobalt-silicateisformed

Table 1 TexturalpropertiesofthesupportsandcatalystsbyN2-adsorption(aDeterminedfromasinglepointofadsorptionatPP0=0998

bEstimatedbyBJH formalism(desorptionbranch)Thetwovalues represent thecelldiameterandwindowdiameterofthecellfromBJHadsorptionanddesorption)

Sample BET Surface area (m2g)

Total pore volumea (cm3g)

Mesopore diameterb (nm)

MCM-41 1200 09 26PE-MCM-41 900 18 63

SBA-15 940 11 75PE-SBA-15 860 19 29350

CoMCM-41 990 08 31CoPE-

MCM-41 633 14 68

CoSBA-15 721 08 79CoPE-SBA-15 576 18 29071

Table 2 Physicochemical characteristics (aCalculated from ScherrerequationbAccordingwithd(Codeg)=075d(Co3O4)

CParticlesizecalculatedafterreductionat350degCfor16hinH2

dMetaldispersionafterreductionat 350degC for 16 h in H2

eDispersion corrected by DOR According tod(Codeg) 96 H DOR

D= fDegreeofreductionfromTPRofreducedcatalysts)

SampleXRD H2-Chemisorption

d(Co3O4)a d(Codeg)b d(Codeg)

cH (nm)

Dd()Decorr DORf

(nm) (nm) () ()CoMCM-41 70 53 47 72 71 35

CoPEMCM-41 94 70 61 68 56 43CoSBA-15 151 113 72 80 80 60

CoPESBA-15 147 111 75 74 74 58

6


2017Vol 2 No 3 11



20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15

Figure 2 X-Raypatternsforthestudiedcatalystscalcinedat550degC

PE-MCM-41

PE-SBA-15 SBA-15

Figure 3 TheN2sorptionisothermsandporesizedistributioncurvesforthemesoporoussilicasupports

The Codeg particle size and dispersion is calculated from H2-chemisorptionaftercatalystactivationandreportedin Table 2ThistechniqueshowedsimilarCodegparticlesizescomparedwithXRDanalysis CoSBA-15 showed thehighestdispersion Theseresult could be attributed to the weak Condashsilicate interactioncausedbythepresenceofinterconnected2Dporesandtheporesinnersurfacediscussedpreviously[56]ConsequentlytheDegree

ofReduction(DOR)ishigherforCoSBA-15ItisinterestingtonotethatthedegreeofreductionisalsohighforCoPE-SBA-15eventhough it has a high cobalt-silicate formation The explanationgiventothisfactistheporestructureandsizeofthesilicaItwasreportedthatwaterproducedduringreductionprocessoxidizestheCodegeffect that ismorepronounced incatalystswithsmallandlongporesduetowateraccumulationinsidethepores[11]

7


2017Vol 2 No 3 11



Figure 4 RepresentativeSEMimagensofa)MCM-41b)PE-MCM-41c)SBA-15andd)PE-SBA-15calcinedat550degCfor6h

howeverthisisnotthecaseforthePE-SBA-15whichhaslarge3Dsphericalporesandtheproducedwaterismoreeasytodiffusethroughthisnetworkandpossiblymightbe lessCodegoxidationwhichcanfavorthedegreeofreduction

Catalytic activityAs explained in the experimental part the tests consisted oftwoperiods In thefirst period the catalystswere tested at aGasHourlySpaceVelocity(GHSV)of6000mlh-gcatalyst (NTP)in order to compare the CO conversion In the second periodthe GHSV was adjusted in order to operate at CO conversionof 30 plusmn 4 The GHSV employed during each period and thecorrespondingaverageCOconversionsarepresentedin Table 3

AscanbededucedbycomparingCOconversionsduringthefirstperiod the catalyst activity decreases in the following orderCoPE-SBA-15gtCoSBA-15gtCoPE-MCM-41gtCoMCM-41 By thephysicochemicalcharacterizationitwasdeductedthatourbestcandidatesfortheFischer-TropschreactionwasCoSBA-15andCoPE-SBA-15 Both catalysts had similar cobalt particle sizedegreeofreductionanddispersionhoweverthecatalyticresultsshowedalmostdoubleCOconversion forCoPE-SBA-15 (Table 3)Hereafterthecatalyticresultisattributedmainlytothepore

structureandaverageporediameterThepresenceof3DporeswithsphericalshapeandporewindowsmightfavorthereactantsandproductsdiffusionWhileinthe1Dand2Dpores(CoMCM-41CoSBA-15andCoPE-MCM-41)aremorelimited

LowerCOconversionforCoMCM-41wasobservedasexpectedfromthephysicochemicalcharacterization ItcanberelatedtothelowavailabilityofactivecobaltonthecatalystsurfaceduetothehighformationofCo-silicateswhichareeasiertoformwhenahighsurfaceareaispresentduetothepresenceofmore-OHspeciesanddispositioninsidethepores

Furthermore Table 3 shows a comparison of the productselectivities during the second period at around 30 of COconversion In general the selectivity to hydrocarbons with acarbon chain longer than five carbon atoms (SC5+) increases athigherCOconversionThiseffectisusuallyascribedtoahigherextentofsecondaryreaction(α-olefinre-adsorption)andortheeffect of a higher partial pressure of thewater formed duringFT reaction [1757] As the selectivity of C5+ increaseswith COconversiontheselectivitytoCH4isthenreducedHowevertheselectivitytoC5+decreasesintheorderCoPE-SBA-15gtCoSBA-15gtCoPE-MCM-41gtCoMCM-41 This might be attributed to

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2017Vol 2 No 3 11



Figure 5 Representative TEM imagens of A) CoMCM-41 B) CoPE-MCM-41 C) CoSBA-15D)CoPE-SBA-15aftercobaltdepositioncalcinedat350degCfor10hTheletterswithnumber2showshigherresolutionofcatalysts

the small pore size of the supportswith channel structure ieMCM-41SBA-15andPE-MCM-41whereH2difusesfasterthanCOduetomolecularsizeThisleadstohigherH2COratioswithinthe catalyst channels and a higher H2CO ratio promotes theselectivitytomethaneandshorthydrocarbonchainsInthecase

ofCoPE-SBA-15thathascellspheresstructuresthisgradientofH2CO is limited and the intermediate hydrocarbon chains arenoteasilyhydrogenatedTheselectivitytoCO2islowforallthecatalystsanddecreasesathigherCOconversionsduetowatergasshiftreactionsduetothewaterproductionatFTS[24]

Table 3Conversionlevelsandselectivitydataforthedifferentcatalysts(aSelectivitiesareCO2-free)

GHSV Catalysts XCO () S4a () SC5+a () SCO2 ()

6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

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ConclusionMesoporous silicas with structure type MCM-41 SBA-15 andtheircorrespondentpore-expandedPE-MCM-41andPE-SBA-15weresynthetizedbytheatranerouteandusedassupportsforcobalt Fischer-Tropsch catalysts The atrane route allowed thesynthesisofhomogeneousmaterialswithtunableporediameterand narrow pore size distribution at soft conditions The finalsilicamaterialshad1D2Dand3DstructuresTheparticlesizeofthedepositedcobaltoxideonthesematerialswasinfluencedbythesupportporesizeHigherdegreeofreductionwasfoundfor largerCo0particlesonCoSBA-15andCoPE-SBA-15which

resulted inmore catalytic active sitesHowever CoPE-SBA-15catalystshowedbettercatalyticresultsintermsofCOconversionandselectivitytohydrocarbonswithchainslongerthan5carbonatoms Such a good results were attributed to the 3D porestructureandporesizeofthesilicawhichfavoredthereactantsandproductsdiffusion

AcknowledgmentsSwedishInternationalDevelopmentCooperationAgency(SIDA)NanoandesnetworkandEuropeanprojectCOSTactionCM0903are thanked for financial support Special thanks to GustavoGarciacutea(LulearingUniversity)forSEMpictures

0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI

Figure 6 H2TPRprofilesofthecobaltcatalystscalcinedat350degCfor10h(MSI=metal-supportinteraction)

References1 KrukMJaroniecMRyooRJooSH(2000)CharacterizationofMCM-

48silicaswith tailoredpore sizes synthesizedviaahighlyefficientprocedureChemMater121414-1421

2 Li ZWu J Yu JHanDWuL et al (2016)Effectof incorporationmanner of Zr on the CoSBA-15 catalyst for the FischerndashTropschsynthesisJMolCatalAChem424384-392

3 ShimizuTUshikiIOtaMSatoYKoizumiNetal(2015)Preparationofmesoporous silica supported cobalt catalystsusing supercriticalfluidsforFischerndashTropschsynthesisChemEngResDes9564-68

4 Tuumlysuumlz H Schuumlth F (2012) Ordered Mesoporous Materials asCatalystsAdvCatal55127-239

5 Vande Loosdrecht JBotesFGCiobica IMFerreiraACGibsonP

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7 DryME (2002) The FischerndashTropschprocess 1950ndash2000 CatalysisToday71227-241

8 SuaacuterezPariacutesR Lopez LBarrientos J PardoFBoutonnetMet al(2015) Catalytic conversion of biomass-derived synthesis gas tofuelsTheRoyalSocietyofChemistry2762-143

9 AzzamKJacobsGMaWDavisBH(2014)Effectofcobaltparticlesize on the catalyst intrinsic activity for fischer-tropsch synthesisCatalLetters144389-394

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10 BecharaRBalloyDDauphinJYGrimblotJ(1999)InfluenceoftheCharacteristicsofγ-AluminasontheDispersionandtheReducibilityofSupportedCobaltCatalystsChemMater111703-1711

11 Dalai AK Davis BH (2008) FischerndashTropsch synthesis A review ofwatereffectson theperformancesofunsupportedandsupportedCocatalystsApplCatalAGen3481-15

12 Iglesia E (1997) Fischer-tropsch synthesis on cobalt catalystsStructuralrequirementsandreactionpathwaysStudSurfSciCatal153-162

13 KhodakovAYBecharaRGriboval-ConstantA(2002)StructureandcatalyticperformanceofcobaltFischerTropschcatalystssupportedbyperiodicmesoporoussilicasStudSurfSciCatal1421133-1140

14 vanSteenEClaeysMDryMEvandeLoosdrechtJViljoenELetal (2005) Stability of nanocrystals Thermodynamic analysis ofoxidationandre-reductionofcobaltinwaterhydrogenmixturesJPhysChemB1093575-3577

15 WeiLZhaoYZhangYLiuCHongJetal(2016)FischerndashTropschsynthesisovera3DfoamedMCFsilicasupportTowardamoreopenporousnetworkofcobaltcatalystsJCatal340205-218

16 Jung JS Kim SWMoon DJ (2012) FischerndashTropsch Synthesis overcobaltbasedcatalystsupportedondifferentmesoporoussilicaCatalToday185168-174

17 Ghampson IT Newman C Kong L Pier E Hurley KD et al(2010)Effects of pore diameter on particle size phase and turnoverfrequency in mesoporous silica supported cobalt FischerndashTropschcatalystsApplCatalAGen38857-67

18 Saib AM Claeys M Van Steen E (2002) Silica supported cobaltFischerndashTropschcatalystseffectofporediameterofsupportCatalToday71395-402

19 XiongHZhangYLiewKLiJ(2008)FischerndashTropschsynthesisTheroleofporesizeforCoSBA-15catalystsJMolCatalBEnzym29568-76

20 SchuumlthFWingenASauerJ(2001)Oxideloadedorderedmesoporousoxides for catalytic applications Microporous Mesoporous Mater44ndash45465-476

21 CabreraSHaskouri JEAlamoJBeltraacutenABeltraacutenDetal (1999)Surfactant-assisted synthesis of mesoporous alumina showingcontinuouslyadjustableporesizesAdvMater11379-381

22 CabreraSHaskouriJEIGuillemCLatorreJBeltraacuten-PorterAetal(2000) Generalised syntheses of orderedmesoporous oxides theatranerouteSolidStateSci2405-420

23 de Zaacuterate DO Fernaacutendez L Beltraacuten A Guillem C Latorre J et al(2008) Expanding the atrane route Generalized surfactant-freesynthesisofmesoporousnanoparticulatedxerogelsSolidStateSci10587-601

24 RytterETsakoumisNEHolmenA(2016)Ontheselectivitytohigherhydrocarbons in Co-based FischerndashTropsch synthesis Catal Today2613-16

25 ElHaskouriJCabreraSGuillemCLatorreJBeltraacutenAetal(2002)Atrane precursors in the one-pot surfactant-assisted synthesis ofhighzirconiumcontentporoussilicasChemMater145015-5022

26 CabreraMS(1999)Quiacutemicaenmediosorganizadosparalaobtencioacutende nuevas aluacuteminas aluminosilicatos y ALPOs mesoporosos contamantildeodeporomodulableinstitutoUniversitariodeCienciadelosMaterialesUniversitatdeValenciaValenciaSpain

27 ElHaskouriJCabreraSCaldeacutesMAlamoJBeltran-PorterAetal(2001) Orderedmesoporousmaterials composition and topologycontrolthroughchemistryIntJInorganicMater31157-1163

28 GarciaPRAFBicevRNOliveiraCLPSantrsquoAnnaOAFantiniMCA(2016)ProteinencapsulationinSBA-15withexpandedporesMicroporousMesoporousMater23559-68

29 Sprague M J (1985) Characterization of heterogeneous catalystsChemieIngenieurTechnik57430-430

30 DelannayF(1984)CharacterizationofHeterogeneousCatalysts

31 SchankeDVadaSBlekkanEAHilmenAMHoffAetal(1995)StudyofPt-promotedcobaltCOhydrogenationcatalystsJCatal15685-95

32 BhatiaSBeltraminiJDoDD(1990)TemperatureprogrammedanalysisanditsapplicationsincatalyticsystemsCatalToday7309-438

33 BorgOslashEriSBlekkanEAStorsaeligterSWigumHetal(2007)FischerndashTropschsynthesisoverγ-alumina-supportedcobaltcatalystseffectofsupportvariablesJCatal24889-100

34 Tristantini D Loumlgdberg S Gevert B BorgOslashHolmenA (2007) TheeffectofsynthesisgascompositionontheFischerndashTropschsynthesisover Coγ-Al2O3 and CondashReγ-Al2O3 catalysts Fuel ProcessingTechnology88643-649

35 Lualdi M Loumlgdberg S Regali F Boutonnet M Jaumlrarings S (2011)Investigation of mixtures of a Co-based catalyst and a Cu-basedcatalyst for the FischerndashTropsch synthesis with bio-syngas theimportanceofindigenouswaterTopCatal54977-985

36 Pardo-TarifaF (2017)Ce-promotedCoAl2O3catalysts forFischerndashTropschsynthesisIntJHydrogenEnergy

37 Storsaeligter S Borg Oslash Blekkan EA Holmen A (2005) Study of theeffectofwateronFischerndashTropschsynthesisoversupportedcobaltcatalystsJCatal231405-419

38 LualdiM(2012)Fischer-TropschSynthesisoverCobalt-basedCatalystsforBTLApplicationsKTHRoyalInstituteofTechnologySweden

39 LoumlgdbergSLualdiMJaumlraringsSWalmsleyJCBlekkanEAetal(2010)Ontheselectivityofcobalt-basedFischerndashTropschcatalystsevidenceforacommonprecursorformethaneandlong-chainhydrocarbonsJCatal27484-98

40 KondratenkoYFundamenskyVIgnatyevIZolotarevAAKochinaTetal (2017)Synthesisandcrystal structureof twozinc-containingcomplexesoftriethanolaminePolyhedron

41 SayariAYangYKrukMJaroniecM(1999)ExpandingtheporesizeofMCM-41 silicas useof amines as expanders indirect synthesisandpostsynthesisproceduresJPhysChemB1033651-3658

42 Sayari A Shee D Al-Yassir N Yang Y (2010) Catalysis over pore-expandedMCM-41mesoporousmaterialsTopCatal53154-167

43 httpsace-notebookcombandgap-measurements-of-low-k-porous-organosilicate-free-related-pdfhtml

44 BartoliniMMolinaJAlvarezJGoldwasserM(2015)EffectoftheporousstructureofthesupportonhydrocarbondistributionintheFischerndashTropschreactionJPowerSources2851-11

45 SanzRCallejaGArencibiaASanz-PeacuterezES(2015)CO2capturewithpore-expandedMCM-41silicamodifiedwithaminogroupsbydoublefunctionalizationMicroporousMesoporousMater209165-171

46 SanzRCallejaGArencibiaASanz-PeacuterezES(2013)CO2uptakeandadsorptionkineticsofpore-expandedSBA-15double-functionalizedwithaminogroupsEnergyFuels277637-7644

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47 BarrettEPJoynerLGHalendaPP(1951)ThedeterminationofporevolumeandareadistributionsinporoussubstancesIComputationsfromnitrogenisothermsJAmChemSoc73373-380

48 BrunauerSDemingLSDemingWETellerE(1940)OnatheoryofthevanderWaalsadsorptionofgasesJAmChemSoc621723-1732

49 ThommesMKanekoKNeimarkAVOlivier JP Rodriguez-ReinosoFetal(2015)Physisorptionofgaseswithspecialreferencetotheevaluationofsurfaceareaandporesizedistribution(IUPACTechnicalReport)PureApplChem871051-1069

50 MartiacutenezAPrietoGRollaacutenJ(2009)Nanofibrousγ-Al2O3assupportforCo-basedFischerndashTropschcatalystsponderingtherelevanceofdiffusionalanddispersioneffectsoncatalyticperformance JCatal263292-305

51 LinHPTangCY LinCY (2002)Detailed structural characterizationsof sba-15 and mcm-41 mesoporous silicas on a high-resolutiontransmissionelectronmicroscopeJChineseChemSoc49981-988

52 Taghavimoghaddam J Knowles GP Chaffee AL (2013) Impact ofpreparation methods on SBA-15 supported low cobalt-content

compositesstructureandcatalyticactivityJMolCatalBEnzym377115-122

53 Topsoslashe NY Topsoslashe H (1982) Adsorption studies onhydrodesulfurization catalysts I Infrared and volumetric study ofNOadsorptiononalumina-supportedCoMoandCo-MocatalystsintheircalcinedstateJCatal75354-374

54 SimionatoMAssafEM(2003)Preparationandcharacterizationofalumina-supportedCoandAgCocatalystsMaterRes6535-539

55 VandeLoosdrechtJVanderHaarMVanderKraanAMVanDillenAJ Geus JW (1997) Preparation and properties of supported cobaltcatalystsforFischer-TropschsynthesisApplCatalAGen150365-376

56 Hukkamaumlki JSuvantoSSuvantoMPakkanenTT(2004) InfluenceoftheporestructureofMCM-41andSBA-15silicafibersonatomiclayer chemical vapor deposition of cobalt carbonyl Langmuir 2010288-10295

57 GonzaacutelezOPeacuterezHNavarroPAlmeidaLCPachecoJGetal(2009)UseofdifferentmesostructuredmaterialsbasedonsilicaascobaltsupportsfortheFischerndashTropschsynthesisCatalToday148140-147

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OMSiscommonlypreparedusingasurfactant-templatesynthesisprocedurebasedonvarioustemplatingagentstoformdifferentstructurearraysThemostcommonstructuresare1DhexagonalarrayieMCM-41whichconsistsofparallelchannelsthatareonly accessible in one direction 2D arraywith interconnectedparallelandperpendicularchannelsieSBA-15andmorenewlyinvestigated3Dcage-likestructurewithacubicarrayformedbyasystemofinterconnectedporesieMCM-48[420]

The OMS is formed by a silicon oxide network throughpolycondensation reactions of a molecular precursor in liquidmedia this is the conventional sol-gel synthesis methodHowever a modified version of this technique is the atrane route methoddevelopedbyCabreraetal[2122]Thismethodis basedon theuseof a simple structural directingagent ieCetyltrimethylammonium Bromide (CTAB) and a complexingpolyalcoholTriethanolamine(TEAH3)ThisTEAH3formschelatedcomplexes called atranes ie complexes which include tri-ethanolamine-like ligandspecies (Figure 1)withawidevarietyofMetals(M)Theatranecomplexislessreactivethananormalorganometallic precursor in aqueous solution Therefore thehydrolysis and condensation reaction rate of the inorganiccomponents is slowed down when a metal-atrane complex isused[21-23]

To our knowledge onlyMCM-41 has been synthetized by theatranerouteandneverSBA-15andporeexpandedMCM-41andSBA-15TheadvantageofsynthetizingthesematerialstroughtheatranerouteisthattheexpansionoftheporesisperformedatmildconditionsWhileotherinvestigationsreportedtheobtainof the samematerials by exposing the materials for a periodof48hat100degC inanautoclave Ithasbeenexplainedbeforethe important role of porosity for cobalt catalyst support inthe performance of Fischer-Tropsch reaction For this reasonthe synthesis of the proposed silica seems very interesting Inadditionmanystudieson1D ieMCM-41and2D ieSBA-15channel structure andporesplaced in 3D structure ieMCM-48havebeenexploredbutalmostanyworkon silicawith3DmesocellularstructureporeshavebeeninvestigatedforthiskindofcatalystandreactionThereforethesynthesisofsilicawith3DmesocellularstructureporesisveryattractiveforcobaltFischerndashTropschsynthesis

Theaimofthisworkfirstistoextendthesynthesisofmesoporoussilica by the atrane route towards other structures especially3D mesocellular structure second explore the effect of porestructureandsizeofsilicaonthefinalcobaltcatalystandfinallytestthesecatalystsinFischer-Tropschsynthesis

Experimental PartSupports synthesisMCM-41 and PE-MCM-41 synthesis Mesoporous silica(MCM-41andPE-MCM-41)waspreparedbytheatraneroute[2124-27] TEOS (tetraethyl orthosilicate Si(OC2H5)4) wasadded to TEAH3 (triethanolamine N (CH2ndashCH2ndashOH)3) andheated at 140degC for 20 min under stirring in order to formsilatranecomplexesNaOH(1M)wasthenaddedtothesilatrane

complex solution and the resulting solution was cooled downto 80degC afterwards the surfactant CetyltrimethylammoniumBromide (CTAB) was added to the solution The final solutionwas kept under stirring for at least 30 min Thereafter thetemperaturewasloweredto50degCandwaterwasaddedtothesolution under stirring The productwas kept under the sameconditions for2handwas thenagedwithout stirringat roomtemperaturefor24hThepore-expandedMCM-41(PE-MCM-41)wassynthesizedinthesamemannerasMCM-41withtwomaindifferences First a swelling agent Triisopropylbenzene (TIPB)was added after the addition of the surfactant (CTAB) in theproceduredescribedpreviouslysecondthesystemwasagedat70degCfor24hinaclosesystemafterwateradditionThemolarratiosoftheusedreagentswere1Si4TEAH330H2O1NaOH01CTAB90H2O005TIPB

SBA-15 and pore-expanded PE-SBA-15 synthesis The SBA-15was synthetized by dissolving the surfactant P123 (Mav=5800EO20-PO70-EO20)in2MHClsolutionAhomogeneoussolutionwas obtained after stirring at 40degC for 3 h Afterwards thesilatranecomplex(similartotheoneusedpreviouslyforMCM-41synthesis)wasaddedtothesolutionundervigorousstirringandkeptfor12hatthesameconditionsThefinalproductwaskeptagingfor24hatroomtemperatureThepore-expandedSBA-15(PE-SBA-15)waspreparedinthesamewayastheSBA-15withthesingleexceptionthattheswellingagent135-trimethylbenzene(TMB)wasaddedtothesynthesissolutionpriortotheadditionofthesilatranecomplexwiththefunctionofworkingasamicelleexpander[28]Thefinalsolutionwaskeptagingat70degCfor24hTheemployedmolarratioswere0017P12300054TMB435HCl183H2O1TEOS

In all the cases theprecipitated solidwas separated from theliquidwastebyfiltrationandwashedrepeatedlywithwaterandethanolThematerialwasdriedfor12hat70degCandtheorganiccompoundswereremovedfromthesolidbycalcination(5hat120degCthen3hat350degCand5hat550degC)withatemperaturerampof5degCmin

Cobalt catalyst preparation The cobalt-based catalysts werepreparedbytheincipient-wetnessimpregnationtechniquePriorto the cobalt impregnationprocedure the supports (MCM-41PE-MCM-41SBA-15andPE-SBA-15)weredried inairat120degCfor5h Later12wtCo fromaCo(NO3)2middot6H2Oprecursorwasdissolved inpurifiedwater toavolumeequivalent to theporevolume of each support The impregnated powder was thendriedinairat120degCfor5handsubsequentlycalcinedinairat350degCfor10h(heatingrate1degCmin)Thefinalcobaltcontentinthecatalystswas120plusmn01wtthesevalueswerecalculatedusingthestoichiometrybetweenhydrogenandcobaltfromthetotalH2consumptioninthetemperature programmed reduction (TPR)experiment

Catalyst characterizationBrunauerndashEmmettndashTeller (BET) technique was used for thecalculationofsurfaceareatheporevolumeandporediameterwas calculated the Barrett-Joyner-Halenda (BJH) techniqueMeasurements were performed with a Micromeritics ASAP

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1

TCD

co co

A fDOR

X AW= minus





( ) 100in outconv

in

CO COCO mol

COminus

= times







4


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NH2C

CH2

HO

H2C

CH2

OH

H2CCH2

OH

O

Si

O

O

O

CH2

CH3

H2C

H3C

H2C

H3C

CH2

CH3

+

a) b) c)

d) e)

O

N

OSi

O

N OH

HO

O

O

N OSi

O

N

HO

O

Si

N

O OO

O

O

N O

SiO

N

OSi

O

Si

NO

O

N

O

O

OO

O


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MCM-41 1200 09 26PE-MCM-41 900 18 63

SBA-15 940 11 75PE-SBA-15 860 19 29350

CoMCM-41 990 08 31CoPE-

MCM-41 633 14 68

CoSBA-15 721 08 79CoPE-SBA-15 576 18 29071








cH (nm)

Dd()Decorr DORf

(nm) (nm) () ()CoMCM-41 70 53 47 72 71 35

CoPEMCM-41 94 70 61 68 56 43CoSBA-15 151 113 72 80 80 60

CoPESBA-15 147 111 75 74 74 58

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20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15


PE-MCM-41

PE-SBA-15 SBA-15




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6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

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0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


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11


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3


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1

TCD

co co

A fDOR

X AW= minus





( ) 100in outconv

in

CO COCO mol

COminus

= times







4


2017Vol 2 No 3 11











NH2C

CH2

HO

H2C

CH2

OH

H2CCH2

OH

O

Si

O

O

O

CH2

CH3

H2C

H3C

H2C

H3C

CH2

CH3

+

a) b) c)

d) e)

O

N

OSi

O

N OH

HO

O

O

N OSi

O

N

HO

O

Si

N

O OO

O

O

N O

SiO

N

OSi

O

Si

NO

O

N

O

O

OO

O


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MCM-41 1200 09 26PE-MCM-41 900 18 63

SBA-15 940 11 75PE-SBA-15 860 19 29350

CoMCM-41 990 08 31CoPE-

MCM-41 633 14 68

CoSBA-15 721 08 79CoPE-SBA-15 576 18 29071








cH (nm)

Dd()Decorr DORf

(nm) (nm) () ()CoMCM-41 70 53 47 72 71 35

CoPEMCM-41 94 70 61 68 56 43CoSBA-15 151 113 72 80 80 60

CoPESBA-15 147 111 75 74 74 58

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20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15


PE-MCM-41

PE-SBA-15 SBA-15




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6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

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0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













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11


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4


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NH2C

CH2

HO

H2C

CH2

OH

H2CCH2

OH

O

Si

O

O

O

CH2

CH3

H2C

H3C

H2C

H3C

CH2

CH3

+

a) b) c)

d) e)

O

N

OSi

O

N OH

HO

O

O

N OSi

O

N

HO

O

Si

N

O OO

O

O

N O

SiO

N

OSi

O

Si

NO

O

N

O

O

OO

O


5


2017Vol 2 No 3 11















MCM-41 1200 09 26PE-MCM-41 900 18 63

SBA-15 940 11 75PE-SBA-15 860 19 29350

CoMCM-41 990 08 31CoPE-

MCM-41 633 14 68

CoSBA-15 721 08 79CoPE-SBA-15 576 18 29071








cH (nm)

Dd()Decorr DORf

(nm) (nm) () ()CoMCM-41 70 53 47 72 71 35

CoPEMCM-41 94 70 61 68 56 43CoSBA-15 151 113 72 80 80 60

CoPESBA-15 147 111 75 74 74 58

6


2017Vol 2 No 3 11



20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15


PE-MCM-41

PE-SBA-15 SBA-15




7


2017Vol 2 No 3 11










8


2017Vol 2 No 3 11








6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















5


2017Vol 2 No 3 11















MCM-41 1200 09 26PE-MCM-41 900 18 63

SBA-15 940 11 75PE-SBA-15 860 19 29350

CoMCM-41 990 08 31CoPE-

MCM-41 633 14 68

CoSBA-15 721 08 79CoPE-SBA-15 576 18 29071








cH (nm)

Dd()Decorr DORf

(nm) (nm) () ()CoMCM-41 70 53 47 72 71 35

CoPEMCM-41 94 70 61 68 56 43CoSBA-15 151 113 72 80 80 60

CoPESBA-15 147 111 75 74 74 58

6


2017Vol 2 No 3 11



20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15


PE-MCM-41

PE-SBA-15 SBA-15




7


2017Vol 2 No 3 11










8


2017Vol 2 No 3 11








6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















6


2017Vol 2 No 3 11



20 30 40 50 60 70

Co3O4lowast

lowast

lowast

lowast lowastlowast

CoMCM-4120 30 40 50 60 70

lowastCo3O4

lowast

lowast

lowastlowast lowast

CoSBA-15

20 30 40 50 60 70

lowastCo3O4

lowastlowastlowast

lowast

lowast

2θ (deg)

CoPE-MCM-41

Inte

nsity

(au

)

20 30 40 50 60 70

Co3O4lowast

lowastlowastlowast

lowast

lowast

CoPE-SBA-15


PE-MCM-41

PE-SBA-15 SBA-15




7


2017Vol 2 No 3 11










8


2017Vol 2 No 3 11








6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















7


2017Vol 2 No 3 11










8


2017Vol 2 No 3 11








6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















8


2017Vol 2 No 3 11








6000CoMCM-41

44 122 763 141500 270 86 835 106000

CoPE-MCM-4157 101 800 07

1600 291 87 846 046000

CoSBA-15100 181 623 22

2550 280 136 744 186000

CoPE-SBA-15185 111 736 12

4800 285 72 852 08

9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















9


2017Vol 2 No 3 11






0 200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoPE-SBA-15

200 400 600 800 1000

MSI

Co3O4 gt CoO gt Co0

CoSBA-15

CoMCM-41

0 200 400 600 800 1000

Co3O4 gt CoO gt Co0

MSI

CoPE-MCM-41

Inte

nsity

(au

)

Temperature [degC]

0 200 400 600 800 1000 1200

Co3O4 gt CoO gt Co0

MSI













10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















10


2017Vol 2 No 3 11








































11


2017Vol 2 No 3 11















11


2017Vol 2 No 3 11















silica with 3d mesocellular pore structure used as … pe-sba-15 silica, which showed a 3d spherical...

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