Amphiphilic niobium oxyhydroxide as a hybrid catalyst for sulfurremoval from fuel in a biphasic system.

ContentslistsavailableatScienceDirect

Applied

Catalysis

B:

Environmental

j ou rn a l h om epa g e : w w w . e l s e v i e r . c o m / l o c a t e / a p c a t b

Amphiphilic

niobium

oxyhydroxide

as

a

hybrid

catalyst

for

sulfur

removal

from

fuel

in

a

biphasic

system

Luiz

C.A.

de

Oliveira

_,

_Nathália

_T.

_Costa

_,

_Josefredo

_R.

_Pliego

_Jr

_,

_Adilson

_C.

_Silva

_,

Patterson

P.

de

Souza

_,

_Patrícia

_S.

_de

_O.

_Patrício

a_{DepartmentofChemistry,UniversidadeFederaldeMinasGerais,Av.AntônioCarlos6627,CampusPampulha,31270-901,BeloHorizonte,MG,Brazil} b_{DepartmentofNaturalSciences,UniversidadeFederaldeSãoJoãodel-Rey,36301-160,SãoJoaodel-Rei,MG,Brazil}

c_{DepartmentofChemistry,CentroFederaldeEducac¸ãoTecnológicadeMinasGerais,CEFET-MG,Av.Amazonas5253,30421-169,BeloHorizonte,MG,Brazil}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received5February2013

Receivedinrevisedform26July2013 Accepted6August2013

Available online 18 August 2013 Keywords: Modifiedniobia Biphasicreaction Heterogeneouscatalysis Oxidationprocess

a

b

s

t

r

a

c

t

Here,weshowthatanewniobiumoxyhydroxide,NbO2OH,canbesynthesizedandmodifiedwitha

surfactanttobeusedasaheterogeneouscatalystforoxidativedesulphurization.Thematerialwastreated withhydrogenperoxidetogenerateoxidizinggroups(peroxospecies)onthesurface.Furthermore,this materialwasconvertedtoafamilyofsolidcatalyststhatcanstabilizewater/oilemulsionsandcatalyze reactionsattheliquid/liquidinterfacebyanchoringasurfactanttothecatalyst.Thematerialwasthen abletoefficientlyremoveasulfurouscompoundundermildconditions.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Desulphurizationoffueloilshasbecomeanenvironmentally urgentsubjectworldwide.Environmentalregulationshavelimited thesulfurlevelsindieselfuelstolessthan15ppmsince2006in theUnitedStates[1].However,itisverydifficultwithcurrent tech-nologytodecreasethesulfurcontentfromseveralhundredmg/L toonlyafewmg/L[2,3].Intheconventional hydrodesulphuriza-tionprocess(HDS),theuseofhightemperaturesandpressures, largeamountsofveryactivecatalysts,longresidencetimes,and largevolumereactorsareneededtoeffectivelyreducethesulfur contenttotheselowlevels.Selectivecatalyticoxidationcombined withextraction is one of the mostpromising desulphurization methods.Liquid/liquidextractionhasbeeneffectivelyutilizedto removesulfurand/ornitrogenmoleculesfrompetroleum distil-latesandsynfuels[4].However,thisprocessisrelativelyinefficient duetothesimilarchemicalcharacteristicsofbothsulfurousand nonsulfurouscompounds.Themorepolarsulphonescanbebetter extractedbypolarsolventsthansulphides;therefore,theefficiency ofdesulphurizationviaextractioncanbesignificantlyincreased byoxidizingsulphidestosulphones[5,6].Manyoxidativesystems

∗ Correspondingauthor.Tel.:+553134097550;fax:+553134095700. E-mailaddress:luizoliveira@qui.ufmg.br(L.C.A.deOliveira).

havebeencreated,however,thesesystemshavenotbeen selec-tiveenoughtooxidizeonlysulphidespresentinthefuelmixture. Furthermore,a largequantityofoxidantis required, increasing operatingcosts[7].Theamphiphiliccatalyst(Nb-amp)reported inthisworkcanselectivelyoxidizedibenzothiophenetothe cor-respondingsulphonewithstoichiometricamountsofH2O2under mildconditions.Furthermore,thesulphoneisremovedinsitufrom hexanebyacetonitrileduringthereaction,andthecatalystcanbe recycled.

Thesolidstructurethatwasobtainedinthisworkpermitted thegenerationofhighlyoxidizingsurfacegroupsbyH2O2 treat-ment (Nb-hyd). These groups,peroxo-species, which have only beenreportedbeforeinhomogenoussystems,canactasan effec-tiveoxygendonorinoxidationreactions[8–10].However,some importantreactionsneedmorethananactivecatalyst.Asreported inSciencerecentlybyCole-Hamilton[11]andCrossleyetal.[12], acatalystthatcansimultaneouslystabilizeemulsionsduringthe reactionwouldbehighlyadvantageousinstreamliningprocesses suchas biomass refining. Both of theseworks and others [13]

haveusednoblemetalsastheactivecatalyst.Here,wereporta newfamilyofsolidcatalystsbasedonthemorecommonmetal niobiumthatcanstabilizewater–oilemulsionsbyincorporating a hydrophobicsurfactantonthecatalystandcancatalyze reac-tionsattheliquid/liquidinterfacein oxidativedesulphurization processes.

0926-3373/$–seefrontmatter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.08.003

44 L.C.A.deOliveiraetal./AppliedCatalysisB:Environmental147 (2014) 43–48

2. Experimental

2.1. Synthesisandcharacterization

The catalyst was prepared by first treating 0.26M NH4[NbO(C2O4)2(H2O)]·(H2O)n with 1M NH4OH (14.0mL), followedbyheatingat70◦Cfor72h.Thismaterialwasusedasa precursorfor thepreparation ofhydrophilic NbO2OH (Nb-hyd), obtained by treating pure niobia (300mg) with 30% aqueous H2O2 (4mL) in H2O (80mL) for 30min. The yellowsolid was thenfiltered,washedwithdistilledwater,anddriedat60◦Cfor 12h. Then, the surfactant compound cetyltrimethylammonium bromide(CTAB,4.47mmol,Vetec)wasaddedtoasuspensionof NbO2OH(Nb-hyd)inH2O,andthemixturewasrefluxedfor4hto preparetheamphiphilichybridmaterial(Nb-amp).Theresulting catalyst (yellow powder) was filtered,washed with water and driedat60◦C.Thematerialswerecharacterizedbytransmission electron microscopy (TEM) with a JEOL transmission electron microscope(modelJEM2000EXII).

ADIGIDROP-DIgoniometer(GBXInstruments)wasusedto per-formcontactanglemeasurements.Thissystemisequippedwitha CCDcameraandanautomatedliquiddispenser.Thecontactangle wasdeterminedbyplacingH2Odroplets(10␮L)onthesurfaceof thesamplesusingasyringe.Thepurespecimenswerepressedto obtaindisks.Animagewastakenandthenanalyzedtogivean aver-ageanglebetweenthedropletandthesurface.Threeconsecutive measurementsweremadeatroomtemperatureusingtheSurface Energymodeofthesoftware,whichallowsdirectmeasurementof contactangle(indegrees).

Fouriertransforminfraredspectroscopy(FTIR)measurements ofthecatalystwerecarriedoutwithaShimadzuPrestige21 spec-trophotometerequippedwithanattenuatedtotalreflectance(ATR) accessory.Thespectraofthesampleswereobtainedintheregion from4000to240cm−1 usinga CsIcrystal witha resolution of 1cm−1and100signal-averagedscans.

Thermogravimetricanalysis(TG/DTG)wasperformedusinga DTG60SHIMADZU.Thesampleswereheatedfromroom tempera-tureto800◦Cusingaheatingrampof100◦Cmin−1underairflow (150mLmin−1).

2.2. Catalytictests

Theextraction–oxidationdesulphurizationexperimentswere conductedina20mLround-bottomflask.Forthecatalytic stud-ies500mLofasolutioncontaining1000mg/Lofdibenzothiophene dissolvedinn-hexane(modelcompoundofafuel)wasprepared.Of thissolution,10mLwasusedtopreparethemixturewith acetoni-trile(extractionliquid)andthecatalyst.Themixture,1mLH2O2 (30%,v/v)and2mLofacetonitrilewasstirredvigorouslyat25◦Cin thepresenceof10mgofcatalyst.Afterthereaction,theresulting mixturewasplacedinastaticstatetoformtwolayers.Theupper apolar phase (hexane) wasseparated easily from thenonpolar phase(acetonitrile)bydecantationanditssulfurcontentanalyzed bygaschromatography.Reuseofthecatalysttests:After300min ofreaction,thecatalystwasrecoveredbyfiltrationofthemodified mixture,followedbywashing3timestoremovethesolvents.The materialwasthendriedinanovenfor12hat70◦C.

ThereactionproductswereanalyzedbyGC–MS(Agilent).The percentageofdibenzothiopheneconversionwasquantifiedby inte-gratingthedibenzothiophenepeaktothetotalioncontentobtained beforeandafterthereactionwiththecatalyst.GC–MSanalysiswas carriedoutwithaninjector temperatureof250◦C,aninjection volumeof0.2mL,andaflowrateof1.4mLmin−1withanHP-5 column(5%polymethylphenylsiloxane).Eachrunusedaheating curveof110◦Cfor5minthenincreasingby3◦Cmin−1to250◦C. TheconcentrationinpercentageofremainingDBTwasmonitored

usingacalibrationcurve(5points)constructedwithvarious con-centrationsofthiscompound.Thecalibrationcurvewasperformed inthetwosolvents,acetonitrileandhexanewithagoodlinearity (R2_>0.99).

3. Resultsanddiscussion

3.1. Synthesisandcharacterization

Fig.1(A)showsimagesofH2OdropletsontheNb-ampand Nb-hydsurfaces.TheNb-hydsurfacewascompletelywettedbyH2O, andthecontactanglewasmeasuredasapproximately0◦. How-ever,thecontactanglemeasuredforNb-ampwas76◦,showing thatthesurfactant-containingcatalysthadasignificantlydifferent surfacecompositioncomparedtothecatalystwithoutthe surfac-tant.Theseresultsemphasizedthattheadditionofasurfactant increasedthehydrophobiccharacterofthecatalyst,suggestingthat thesurfacegroupsarelessavailabletomakeinteractionswiththe droplet.Thiscan,inturn,stabilizeemulsionsattheliquid–liquid interface,asconfirmedbyopticalmicroscopy(Fig.1(B)).This indi-catesthatthesizeandtypeofquaternaryammoniumcationsplay avitalroleintheformationofametastableemulsiondroplet.We foundthatthesemetastabledropletsarereadilyformedwhenthe modifiedNbO2OHisstirredwithacetonitrileandhexane.These emulsiondropletscanbeeasilyseparatedbycentrifugation,and thecatalystcanthenberecycled.Furthermore,itisseenthat Nb-amppreferentiallymigratestothebiphasicinterfaceofthissolvent system(Fig.1(D)),whileNb-hydshowsnosuchpropensity.The materialwithoutthepresenceof surfactantisnot stableatthe polar/nonpolarinterfaceofthesolvents.

Toobservepossiblemorphologicalchangesinthematerialdue totheuseofthesurfactant,thesampleswereanalyzedby transmis-sionelectronmicroscopy,withimagesshowninFig.1(C)and(D). AsshowninFig.1(C),thematerial(Nb-hyd)presentstheregular morphologyofagglomeratedparticles.Fig.1(D)(Nb-amp)shows poorimagecontrast,whichistypicalofnanoparticlesdispersedin thepresenceofsurfactant.Thiseffectofasurfactantonthesurface ofcatalystshasbeendescribedintheliterature[14].

Thepresenceofthesurfactantmoleculeoverthecatalystwas identifiedbyinfraredspectroscopy(Fig.2).Themoreintensebands intheCTABspectrumarelocatedintheregionbetween3050and 2700cm−1.Thebandsatapproximately2916and2848cm−1are associatedtothesymmetric(␯s)andasymmetric(␯a)stretching modesofCH2,respectively.Thesebandsappearinthespectrum ofNb-ampsample,indicatingthepresenceofthesurfactantinthe catalyststructure.Toidentifythepossiblebondingbetweenthe surfactantandthecatalyst,specificregionsoftheNb-hydand Nb-ampFTIRspectrawereevaluated.Thetwomainspectralregions of interestare at 3600–3000cm−1 and 950–500cm−1. Thefirst isthesumcontributionofdifferenthydroxylgroupabsorptions atthehybridcatalystsurface.Thebandsatabout3412cm−1and 3140cm−1areassignedtotheO Hstretchingvibrationlocalized at thesurface and in the bulk structure, respectively [16]. The extentofO Hbulkorsurfacegroupscanbeevaluatedbasedonthe ratiobetweentheareabeloweachhydroxylbandandtotalarea ofthebands(AOHsurface+AO Hbulk).AfractionofO Hbulkgroups (AO Hbulk/Atotal=0.67)issignificantlylargerthantheO Hsurface groups (AO Hsurface/Atotal=0.32) to Nb-hyd. The ratio between thesefractionsisapproximately2.Aftertheadditionofsurfactant tothecatalyst,theinversionofrelative intensityofthesebands followed, for Nb-amp the high frequency band at 3186cm−1, became more intense. Moreover, two new bands centred at 3541cm−1and3323cm−1besidesthosepresentwererevealedby thedeconvolutionoftheO HstretchingregionrelatedtoNb-amp (Fig.2).Thesebandsinhighfrequencies,whencomparedtothe

Fig.1.(A)ContactanglemeasurementsofH2OdropletsontheNb-ampandNb-hydsurfaces.(B)Opticalmicroscopyimageofacetonitrile-in-hexaneemulsionformedby

sonicating.(C)TEMimageofcatalyst(Nb-hyd).(D)TEMimageofcatalyst(Nb-amp).Itisdetailedin(C)and(D)thecatalystinhexane/acetonitrilemixture.Itisseenthatthe amphiphiliccatalystpreferentiallymigratestotheinterface.

Fig.2.ATR-FTIRspectraofthesurfactantCTAB,amphiphilic(Nb-amp),andhydrophilic(Nb-hyd)catalysts.Theinsetpresentsaclose-upoftheNb-ampandNb-hydspectra, showingdeconvolutedFTIRspectrumofsamples:carbonylstretchingregion.

46 L.C.A.deOliveiraetal./AppliedCatalysisB:Environmental147 (2014) 43–48

Fig.3.TGAanalysesofthecatalystsNb-hydandNb-amp.

Nb-hyd,wereassociatedwithnewlinkageinvolvedintheO H surface(at3541cm−1)andbulk(at3323cm−1)groupsofniobium oxyhydroxide and surfactant. The deconvolution mathematical procedureovercameanoverlappinginabsorptionofthehydroxyl bandfrombulkandsurfacelinkageandnolinkwiththesurfactant. Thefollowing ratio of areas,AOHsurfacelinkageCTAB/AOHsurface and AO Hbulk-linkageCTAB/AOHbulkwasusedtoinvestigatetheextentof O Hgrouplinkagetothesurfactant.Theratioincreaseof0.24–0.75 indicatedthattheCTABlinkageisinvolvedpreferentiallytothe O Hgroupbulk.Furthermore,theratioofthefractionsofO Hbulk (AOHbulk-linkageCTAB+AOHbulk)/(AO HsurfacelinkageCTAB+AOHsurface) andO Hsurfacedecreasedbyapproximately1,whencompared tothevalueofNb-hyd.Thisresultcanbeexplaineddue tothe substitutionoftheO Hgroupsofthebulkbythesurfactantthat promotesstronginteractionsbetweenthehydroxyloftheniobium oxyhydroxideandthesurfactantgroups.

Inaddition,thepossibilityofinteractionsbetweenCTABandthe Nb O,Nb OorNb(O O)groupstoalesserextentcanexplainthe slightchangesobservedinthesecondregionofthetwospectra.The bandsthatappearbetween950and500cm−1areassignedtothe Nb OandO Ostretchingvibrations[15,17–19].TheNb-amp spec-trumshowsalargernumberofshouldersinthisregion,indicating thatthenewinteractionsbetweenthesurfactantandcatalyst inter-ferewiththevibrationalmodesofthesecatalystgroups.

ThethermogravimetricanalysisisshowninFig.3.Both materi-alswithandwithoutsurfactantincorporated,haveaverysimilar weightlossprofileuptoabout250◦C.Thatmasschangemustbe duetothelossofwaterandalsohydroxylgroups.However,above thistemperaturethematerialcontaininghydrophobicgroups (Nb-amp)loses18%ofmass,whilethecatalystNb-hydhasnomassloss. Thus,webelievethatthecatalystNb-amphasacontentof18%by weightofsurfactantsgroupsonitssurface.

3.2. Theoreticalstudies

3.2.1. AbinitiostudyoftheNbO2OHstructure

To understand the structure of this niobium oxyhydroxide materialandhowitssurfaceinteractswiththesurfactant,wehave performedsome theoreticalcalculations using a cluster model. BasedontheNbO2OHstoichiometry,itwasconsideredtoexist asa clusterof 18 Nb atoms withterminal oxygenatoms each attachedtoahydrogenatom.Inaddition,weconsideredthe sur-facetobecoveredbyhydroxylgroups.Themodelhastheformula Nb18O75H62.Becauseitisalargesystem,geometryoptimization wasconductedattheHartree–FocklevelwiththeSBKJCEffective

Fig.4. StructureoftheNb(OH)5H2Omodelspeciesatdifferentlevelsoftheoryand

theNb18O75H62cluster(withoutterminalhydrogenatomsatnon-surfaceedges)

obtainedattheHF/SBKJClevel.Onlysingletstateswereconsidered.

CorePotential(ECP)andtherespectiveSBKJCbasisset.However, wehavetestedthereliabilityofthisleveloftheorybyoptimizing thestructureofNb(OH)5H2OmodelattheHFlevelwiththeSBKJC basissetandalsobyaddingdpolarizationfunctionsontheNbandO atoms(SBKJC+P(d)basisset).Densityfunctionaltheorycalculations withtheX3LYPfunctionalandtheSBKJC+P(d)basissetwerealso performed(Fig.4).Fromthecalculations,wenoticedadistorted octahedralstructure aroundtheNbatoms.TheNb OHdistance wasslightlychangedbytheleveloftheory,whilethedifferencein bondlengthwaslargerforNb-OH2.

Consideringthelongcomputationaltimerequiredforthe opti-mization of this large Nb18O75H62 cluster, we believe that the HF/SBKJCcalculationsareareasonableapproach.Theoctahedral geometryaroundtheNbatomisevenmoredistortedduetothe hydrogen bondsbetween the hydrogen atoms of the hydroxyl groupsandthevicinaloxygenatoms.TheNb Odistancesarein therangeof1.8–2.2 ˚A,whereasmanyhydrogenbondsare approx-imately1.8 ˚A.

3.2.2. StructureofthemodifiedNbO2OHsurface

Thepresentexperimentaldataindicatethatthesurfactantis bound tothe NbO2OH surface according to infrared spectrum. Thus,weneedamodelabletoexplainthestructureofthecatalyst. ConsideringthatthenormalNbO2OHsurfaceisfullycoveredby OH groups, the formation of the peroxo group and adsorption of the surfactant onthe surface can be viewedas the process presentedinFig.5.Thequaternaryammoniumionis boundby anelectrostaticinteractionandwecannoticetheperoxogroups becomeinteractionsites.Toverifythestabilityofthisstructure, wehaveperformedabinitiocalculationsusingasmallercluster, Nb8O37H31, interacting withthe N(CH3)4+ ion. Geometry opti-mizationwasperformedattheHF/SBKJCleveloftheory,andthe obtainedstructureispresentedinFig.5.Itcanbeobservedthat thestructureproposedisstable,andthesurfactantstayscloseto boththeoxoandtheperoxogroups.Thestructureofthesurface peroxogroupsuggeststhattheoxidationprocessisasingleoxygen transfer fromthe surfaceto thesubstrate. The closeproximity betweenthesurfactantandthesurfaceperoxogroupallowsthe oxidationoflowpolaritysubstrates.Infact,thefloppynatureof

Fig.5.FormalprocessfortheamphiphilicNbO2OHsurfaceformationandstructure

oftheNb-ampcatalystmodelledastheinteractionoftheNb8O36H32Br−cluster

(withoutterminalhydrogenatomsatnon-surfaceedges)withtheN(CH3)4+ion

obtainedattheHF/SBKJClevel.

theminimumenergystructurebetweenthesurfactantcationand thesurface allows itseasy mobility. Asconsequence, no steric repulsionshouldbeobservedbetweenthesurfactantcationand thesulphidereactantduringtheoxidationreaction.Thepresent proposaliscompatiblewiththeexperimentallyobservedreaction. 3.3. Catalytictests

To illustrate the application of the hybrid catalyst in a liq-uid/liquid reaction system,we chosethe selective oxidation of dibenzothiophene(DBT)asamodelreaction.DBTwasusedasa modelmoleculebecauseitisrepresentativeofthemoststable sul-furousmoleculesinoilandconstitutesthemajorityofthesulfurous moleculesremainingindieselafterHDStreatment[8].Fig.6shows theconversionofDBTovertimeatroomtemperatureusingthe Nb-ampcatalyst.

These results demonstrate that DBT is almost completely oxidizedintothecorrespondingsulphoneby90minat25◦C.Only stoichiometricH2O2isconsumed,andtheturnovernumber(TON) isestimatedtobehigherthan218.Theseresultsindicatethatthe Nb-ampcatalystintheemulsionisveryactiveandselectivefor theoxidationofDBTtothesulphoneevenatroomtemperature. The catalystwithout surfactant incorporation (Nb-hyd) didnot presentahighoxidationcapacity(ca.19%after60min)because itremainedinthepolarphase,disallowingthereactionwithDBT dissolvedinthenonpolarphase.Sincetheperoxogroupsreplace the acidgroup onthe surface [20] it is possible to obtainthe peroxogroupamountconsideringthedecreasingintheacidsites after theH2O2 treatment (asdescribed in Section2)to obtain theNb-ampcatalyst.ThetitrationofNaOH(0.0097mol/L)excess withHCl (0.0084mol/L)showedthattheacidsitesamountwas 7.11×1019_and5.47×1019_H+_{sites/gforNb-ampbeforeandafter}

Fig.6.ProfileofDBTremovalanddetailsofamphiphilicniobiumoxyhydroxide particlesattheinterfaceofbiphasicsystem.

H2O2 treatment,respectively.Theperoxogroupamountscanbe obtainedbythedifferencebetweenthesevalues,i.e.,1.64×1019 peroxosites/g.Consideringthat10mgofcatalystinthereactions wasused,thenumberandperoxositesare1.64×1017_.Whereas thenumberofmoleculesconvertedafter300minofreactionwas 3.27×1019_{,thevalueofTONisapproximately218.}

Fig.7showsthesulfur-specificgaschromatography(GC–MS) analysesofDBTinhexanebeforeandafterthecatalyticoxidationat 60min.Itisworthwhiletonoteallofthesulfurousmoleculeswere almostcompletelyoxidizedintosulphones,which consequently werecompletelyextractedinsitubythepolarextractant.Theused catalystwaseasilyseparatedfromthereactionsystembyfiltration. Afterfourcycles,thecatalystshowedalmostthesamecatalytic performanceasunusedmaterial,indicatingthatthecatalystcan berecycledandreusedforthisreaction.

Theadvantageofoperatinginabiphasicsystemwiththe cat-alystattheliquid/liquidinterfaceisthepossibilityofconducting theprocessinasinglestepinsteadoftwobyskippingthe sepa-ration.Theoxidizedmoleculeswithhigherpolaritymigratetothe polarphaseafterreactionwiththeperoxospeciesonthecatalyst (Fig.6detail),facilitatingtheirseparation fromthehydrocarbon molecules. It is important to note that surface modification of

Fig.7. ChromatogramsofstandardDBTinhexanebeforereaction,acetonitrilephase afterreaction,andhexanephaseafterreaction.

48 L.C.A.deOliveiraetal./AppliedCatalysisB:Environmental147 (2014) 43–48 niobiumhasonlybeenshownwiththesyntheticroutepresentedin

thiswork.Thismeansthattheformationofniobiumoxyhydroxide insteadofniobium oxidepermitsthegenerationofthe peroxo-species(oxidizingagent)whilealsofacilitatingtheanchoringofthe surfactantmolecule(hydrophobizationofthecatalyst).Ourresults highlighttheapplicationsofsolidcatalystsbasedonmodified nio-biumcompoundslocalizedattheinterfaceoftwoliquidphases. Finally,theresultspresentedinthisworkopenanewfieldofstudy usingnewcompoundsofniobium.Theseversatilecompoundsmay bemodifiedthroughgenerationofoxidizinggroupsasshownhere orimpregnatedwithothermetalsaimingtowardstheirapplication indifferenttypesofcatalyticreactions.

4. Conclusion

Anewniobiumoxyhydroxidehasbeenmodifiedandstudied asaheterogeneouscatalystforoxidativedesulphurizationdueto theproductionofoxidizinggroupsonthecatalyst.Furthermore, thismaterialwasconvertedtoafamilyofsolidcatalyststhatcan stabilizeinwater/oilemulsionsandcatalyzereactionsatthe liq-uid/liquidinterfacebyanchoringasurfactant.Thematerialwas thenabletoefficientlyremoveasulfurouscompoundundermild andbiphasicconditions.TheoreticalcalculationsandFTIRanalyses showedthattheperoxidegroupandsurfactantspeciesare anchor-ing,replacing–OHonthecatalyst.Furthermore,unexpecteddata showedthattheperoxidegroupisnotaradical,asreportedbysome authors.Thisresultsuggeststhattheoxidationprocessisasingle oxygentransferencefromthesurfacetothesubstratewithno rad-icalinvolvement.Finally,theresultspresentedinthisworkopena newfieldofstudyusingnewcompoundsofniobium.These versa-tilecompoundsmaybemodifiedthroughgenerationofoxidizing groupsasshownhereorimpregnatedwithothermetalsaiming towardstheirapplicationindifferenttypesofcatalyticreactions.

Inaddition,thepossibilityoftransformationintoanamphiphilic materialenablesitswiderusetobeemployedinvariousindustrial processes.

Acknowledgments

ThisworkwassupportedbytheCNPq,FAPEMIG,CAPESand Pro-ReitoriadePesquisa-UFMG.

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