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(3)

Step1:CO(g)MCOadsStep2:O2(g)M2Oads

Step3:COads+OadsMCO2-adsStep

CO2-adsMCO2(g)

Intheabovereactions,steps1and2areactuallytheactivationofCOandO2bytheirstrongadsorptionontothecatalystsurface.ThefollowingreactionbetweenactivatedCOadsandOadsyieldsCO2.Ithasbeenprovedthattheas-preparedco-loadedCuMnZTsamplewithhigherCuspeciesincorporationcangreatlypromotethecatalyticef?ciencyofCOoxidation,andthepossiblesynergeticmechanismsarediscussedasfollows:

1.COcompetitiveadsorption/activationbytheactivesites:ithasbeencon?rmedthatCOcanbeeasilyadsorbedontotheCu+sitesinsteadofthesitesoccupiedbyCu2+/Cu0orMn4+[39–42].TheadsorptionofCOontotheCu+sitesimpliestheactivationofCOmolecules.TheexistenceofCu+intheCuM-nZT-csamplehasbeenprovedintheXPSanalysis(Fig.7(b)),whichismainlyresultedfromtheredoxcouplingreactionofCu2++Mn3+=Cu++Mn4+.

2.Oxygenadsorptionandactivation:underthepresenceofCOinthereactionsystem,alargenumberofoxygenvacanciescanbegeneratedbythesmallamountofCuoxidespeciesincorporatedintoZTframework,accompaniedbythevalencechangeoftita-niumspeciesfromTi4+toTi3+intheCuMnZTsample,forthesakeofchargecompensation.Theseoxygenvacancieswould

bepresentedpreferentiallyonthesurfaceofZTmatrix,whichcouldadsorboxygenmoleculesfromthecircumstanceandacti-vatethemintoOads,asshowninstep2.

3.ThereactionsbetweenCOadsandOadsonthesurfaceand/ortheinterfacebetweenCuoxidesandMnoxidesandZTmatrixleadtothecompletionofCOoxidation,asshowninstep3.Thisstep,aswellastheabovesteps,couldbebene?tfromthelargesur-faceareaofthemesoporousZTsampleaswellasthehighdis-persionofCuandMnspeciesinZTmatrix.AsindicatedthatpartofCuspeciescoulddisperseintotheinnerporesurfaceatrelativelyhighCu-loadingamount,whichbecameinclosecontactwiththelater-introducedMnspecieswithinthemesoporechannels.Duringthereaction,COmoleculesweread-sorbedandactivatedintoCOadsontheactivemetalsitessuchasCu+.WhileO2moleculeswereadsorbedandactivatedintoOadsonoxygenvacanciesatthesurfaceofZTframework,thenthead-sorbedCOadsandOadscouldbeeasilytransformedintoCO2withthehelpoftheredoxcouplingofCu2++Mn3+=Cu++Mn4+andtheoxygenvacanciesintheCuMnZTsample.

4.Conclusions

CuandMnspecieshavebeensuccessfullyincorporatedintomesoporousZTmatrixwithhomogeneousdispersionasdesigned,inwhichCuspecieswasincorporatedintotheZTframeworkbytheco-hydrolysiswithZrandTiprecursor,andMnspecieswashomo-geneouslydispersedintothemesoporouschannelsofZTviaaninsituredoxreactionofKMnO4withtheretainedsurfactantwithinthemesoporouschannels.ThesmallamountofCuspecies(lessthan2.2wt%)remainedintheZTframeworkafterhydrothermaltreatmentcouldpromotethecondensationofZr/Tiprecursorsandconsequentlygreatlyenhancedthechemicalstabilityofmes-oporousZTwallagainstthecorrosionbyKMnO4forthelaterMn-loading.ComparativelyexcessamountofCuspeciesmayseg-regateoutoftheZTframeworkintothemesoporousnetworkofZTmatrixatincreasedCucontentofP2.2wt%andbecameinclosecontactwithlaterintroducedMnspecies.Theco-loadedCuMnZTcatalystsattheCucontentofP2.2wt%presentedtheremarkablyenhancedcatalyticactivitytowardsCOoxidationthanthatofsin-gleCuorMnloadedcounterparts.ApossiblesynergeticcatalyticeffectamongCu,MnspeciesandmesoporousZrO2–TiO2matrixwasproposedfortheco-loadedCuMnZTcatalystsattheCucon-tentofP2.2wt%,inwhichCOmoleculeswereactivatedbyadsorb-ingonCu+sitesgeneratedintheredoxcouplingreactionofCu2++Mn3+=Cu++Mn4+,asprovedbyH2-TPRandXPSanalyses.Meanwhile,O2moleculescouldbeactivatedbyadsorbingontotheoxygenvacanciesgeneratedbytheCuoxidedopinginZrO2–TiO2andvalencechangeoftitaniumspeciesfromTi4+toTi3+intheCuMnZT

samples.

120Y.Gongetal./MicroporousandMesoporousMaterials173(2013)112–120

Acknowledgements

TheauthorsgratefullyacknowledgethesupportofthisresearchbytheNationalKeyBasicResearchProgramofChina(2013CB933200),theChinaNationalFundsforDistinguishedYoungScientists(51225202),theNationalNaturalScienceFounda-tionofChina(grant.51202278),theNaturalScienceFoundationofShanghai(12ZR1435200).References

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