铜锰协加载介孔材料ZrO2 TiO2复合材料催化合成及其CO催化氧化性

铜锰协加载介孔材料ZrO2 TiO2复合材料催化合成及其CO催化氧化性能

ACu/Mnco-loadedmesoporousZrO2–TiO2compositeanditsCOcatalyticoxidationproperty

YunGong,HangrongChen?,YuChen,XiangzhiCui,YanZhu,XiaoxiaZhou,JianlinShi?

StateKeyLaboratoryofHighPerformanceCeramicsandSuper?neMicrostructures,ShanghaiInstituteofCeramics,ChineseAcademyofSciences,1295DingxiRoad,Shanghai200050,China

articleinfoabstract

AnovelCu/Mnco-loadedmesoporousZrO2–TiO2(ZT)compositehasbeensuccessfullysynthesized,inwhichCuspecieswere?rstintroducedbyco-hydrolysisofcopperprecursorwithzirconiumandtitaniumprecursors,followingonloadingwithMnspeciesviaaninsituredoxreactionbetweenKMnO4andthesurfactanttemplate.ThepreparedsampleswerecharacterizedbyXRD,N2sorption,TEM,SEM,H2-TPR,UV–visandXPStechniques,etc.COcatalyticoxidationwaschosenasamodelreactiontoinvestigatethedistinctivelysynergeticcatalyticeffectinthepreparedco-loadedsample.Comparedwithsinglecom-ponentofCuorMnloadedsamples,theco-loadedCuMnZTdemonstratedmuchenhancedcatalyticactiv-ityattheCucontentofP2.2wt%.ApossiblesynergeticcatalyticeffectamongtheCu,MnspeciesandmesoporousZrO2–TiO2matrixwasproposedanddiscussedindetail.

ó2013ElsevierInc.Allrightsreserved.

Articlehistory:

Received12December2012Accepted10February2013

Availableonline17February2013Keywords:

MesoporousZrO2–TiO2Amorphous

Cu/Mnco-loadedCOoxidationSynergisticeffect

1.Introduction

Ithasbeenwellestablishedthatthecompositionandstructureofcatalystsupportplayanimportantroleinaffectingthecatalyticperformance,includingtheconversion,selectivitytotargetedproducts,andthereusabilityofcatalysts,etc.Forexample,anappropriatecatalystsupportcouldbeinfavoroftheeffectivedis-persionoftheactivecomponentsandthusgreatlyimprovethecat-alyticactivity[1].Mesoporousmaterialswithhighsurfaceareaanduniformporesizedistributionhavereceivedmuchattentionsincethe?rstsynthesisofmesoporousM41Smaterialsin1992[2–6].Therein,mesoporousmetaloxides,especiallytransitionalmetaloxides,representonekindofthemostimportantandwidelyem-ployedcatalyticcomponentsandsupportsaswell.Amongvariousmetaloxidecatalysts,themesoporouszirconia–titania(abbr.ZT)compositehasattractedmuchattentioninrecentyears[7],duetoitshighsurfacearea,profoundsurfaceacid–baseproperty,highthermalstability,andstrongmechanicalstrengthresultedfromthemutualinteractionbetweenzirconiaandtitania[8–12].Meso-porousZTbinaryoxidewithhighsurfaceareaandstrongsurfaceaciditywasfoundtobehighlypromisinginmanyapplications[13].Inaddition,ithasbeenreportedthatanappropriateratioofZrO2toTiO2couldbeinfavorofincreasingthesurfaceareaandthesurfaceacidity,indespiteofpresentingamorphousphaseor

Correspondingauthors.Tel.:+862152412706;fax:+862152413122(H.Chen),

tel.:+862152412714;fax:+862152413122(J.Shi).

E-mailaddresses:hrchen@mail.sic.ac.cn(H.Chen),jlshi@sunm.shcnc.ac.cn(J.Shi).

1387-1811/$-seefrontmatteró2013ElsevierInc.Allrightsreserved.http://dx.doi.org/10.1016/j.micromeso.2013.02.013

poorcrystallization[14–16].Forexample,whentheweightper-centofTiO2reached34%,thecompositesupportshowedthelarg-estsurfaceareaandsurfaceacidity[17].

Coppermanganesecompositeoxide,suchasamorphousCuMn2O4(hopcalite)iswellknownasthecommercialcatalystfortheoxidationofCO[18,19].Ithasbeenreportedthatasmallamountofcopperspeciescouldnoticeablyimprovethecatalyticperformanceofmanganese-basedcatalystsbyenhancingthefor-mationofoxygenvacanciesandincreasingtheirreducibility,fur-thermore,itwasindicatedthatasynergisticeffectshouldexistintheamorphousCu/Mncomposite[20,21].However,suchamor-phousoxidesstillsufferedfromthosepoorperformances,suchaswater-resistance,anti-poisoning,aswellasdeactivationincaseofcrystallizationoccurrence[18,21–23].Therefore,manyeffortshavebeendevotedtoloadtheamorphousCu/Mncompositeintothesuitablecatalystsupports[24].Hereinto,amesoporouszirco-nia–titaniacompositewithhighsurfaceareas,profoundsurfaceacid-basedproperty,andhighthermalstabilitycouldbeusedasanexcellentcatalystsupport.

Inthiswork,anovelmesoporousZTcompositewithhomoge-neouswormlikepore-sizedistributionhasbeendesignedandsyn-thesizedbyasimplehydrothermalmethodofpre-hydrolyzedzirconiumandtitaniumalkoxides.CuspecieswereincorporatedintothemesoporousZTmatrixthroughaone-potco-hydrolysismethodtogetherwithzirconiumandtitaniumalkoxidesbeforethehydrothermaltreatment.Mnspecieswerepost-loadedintotheas-preparedCuspeciesincorporatedZTprecursorcontainingsurfactantCTAB,byadirectinsituredoxreactionbetweenaqueoussolutionofKMnO4andCTAB.Thisprocesswasschematically

illustratedinScheme1.Suchatwo-stepsuccessionalloadingofCuandMnspeciescouldensurethehomogeneousdispersionofCuandMnspeciesintheZTframeworkand/orintotheinnerporechannels,respectively.ThecatalyticperformancesofCOoxidationreactionforsingleCuorMnloadedsamplesandCu/Mnco-loadedcatalystwereinvestigatedandcompared.Inaddition,thedistinc-tivelysynergisticeffectbetweenCuandMnspeciesintheZTma-trixwasdiscussedindetailandapossiblesynergeticmechanismtowardsCOoxidationamongCuandMnspeciesaswellasmeso-porousZTmatrixwasproposed.2.Experimental2.1.Materials

Cetyltrimethylammoniumbromide[CTAB](Sinopharmchemi-calReagentCo.,China)wasusedasthesurfactant.Zirconiumprop-oxide[Zr(OC3H7)4](Aldrich,70wt%)andtetrabutyltitanate[C16H36O4Ti](ShanghaiLingfengChemicalCo.,China)wereusedastheinorganicsources.Hydrochloricacid[HCl](SinopharmchemicalReagentCo.,China)wasusedtocontrolthealkoxidepre-hydrolysis.

2.2.Preparationofcatalysts

ThemesoporousZTcompositewassynthesizedbya?rstalkox-idepre-hydrolysisandthefollowingsurfactant-assistedhydrother-malmethod.Thetypicalmolarratiowas0.32CTAB:0.7Zr(OC3H7)4:0.3C16H36O4Ti:0.05HCl:120H2O.Brie?y,CTABwas?rstdissolvedintodistilledwaterundervigorousstirringfor2hatroomtemper-ature.Zirconiumpropoxideandtetrabutyltitanatewereaddeddropwiseintothe5MHClunderacertainZr/Timolarratioof7:3,accordingtothereportthatthehighestsurfaceareaandsurfaceaciditycanbeobtainedunderthiscomposition[17].Undercontinu-ousstirringfor2h,themixturewasaddedintothesolutionofCTAB,followedbyfurtherstirringfor2h.Next,themixturewastrans-ferredintoaTe?on-linedautoclaveandheatedat120°Cfor24h.Theas-synthesizedmaterialwas?ltered,washed,driedat80°Candthencalcinedat400°Cfor4h,namedasZT.

Cu/Mnco-loadedsampleswerepreparedbyatwo-steproute.First,Cu(NO3)2á3H2OwasaddedintotheCTABwatersolutionandstirredfor2h,meanwhile,thezirconiumandtitaniumalkox-idesourcesasindicatedabovewerepre-hydrolyzedintheHClsolution.Thesetwosolutionswerethenmixedtogetherandcon-tinuouslystirredfor2h,andafterwardshydrothermallytreatedat120°Cfor24h.Theas-synthesizedmaterialwas?ltered,driedat80°C.TheaboveobtainedpowderwasaddedintoaKMnO4solu-tionunderstirringfor4hat40°CforsubsequentMn-loading.Fi-nally,themixturewaswashedbydistilledwater,driedat80°Candthencalcinedinairat400°Cfor4h,namelyasCuMnZT.

Forcomparison,thereferenceCuZTsamplesweresynthesizedwithoutthefollowingMn-loading.MnZTsampleswereprepared

viatheinsitureactionbetweentheCTABsurfactantintheZTsup-portandKMnO4afterthehydrothermaltreatment[25],afterwardsthefollowingprocedurewasthesameasabove.2.3.Characterizationtechniques

TheCuandMncontentsweremeasuredusingICP-OESonaVistaAXinstrument.TheXRD(X-rayDiffraction)patternsofpreparedsampleswererecordedonaRigakuD/Max-2200PCX-raydiffrac-tometerwithCutarget(40kV,40mA).TheN2adsorptionanddesorptionmeasurementswereperformedusingMicromeriticsTristar-3000at77K.ThetotalsurfaceareaandporevolumewerecalculatedusingtheBETandBJHmethods,respectively.Transmis-sionelectronmicroscopic(TEM)imagesandenergydispersespec-troscopy(EDS)wereobtainedonaJEOL-2010Felectronmicroscopeoperatedat200kV.Theexternalsurfaceareawascalculatedbythet-plotmethod.Scanningelectronmicroscope(SEM)wasperformedonaHitachiS-4800electronmicroscope.Fourier-transforminfra-red(FT-IR)spectrawererecordedonaNicoletAvatar370FT-IRspectrophotometerusingKBrpellets.UV–visabsorptionspectrawererecordedusingaUV-3101PCShimadzuspectroscope.There-doxpropertiesweremeasuredusingtemperatureprogrammedreduction(TPR)ofH2onTP-5080automaticadsorptioninstrument.X-rayphotoelectronspectroscopy(XPS)signalswerecollectedonaVGMicroMKIIinstrumentusingmonochromaticMgKaX-raysat1253.6eVoperatedat150W,andspectrumcalibrationwasper-formedbytakingtheC1selectronpeak(BE=285eV)asinternalreference.