催化剂表面碳物种及表征

1、何谓积碳以含碳化合物为原料的催化反应的第一步通常是在催化剂表面上进行吸附形成含碳物种，如含碳物种经过分解、聚合等反应生成碳或焦炭沉积在催化剂表面，既所谓的积碳或结焦。积碳会堵塞催化剂的活性位或催化剂的孔道，从而导致催化剂的失活！常发生积碳的催化反应催化裂化Pt重整加氢精制轻油制氢积碳形态积碳的形态一般分为无定形碳、层状石墨碳、管须状结晶碳以及粘稠状液态碳或焦油。积碳原因热裂解催化裂解深度脱氢烯烃聚合热裂解积碳是气相有机原料在高温下热裂解形成烟炱、焦油，它们在催化剂表面上生成有序的或无序的碳；催化积碳是在催化剂的作用下，烃类化合物发生催化积碳反应，它与催化剂的性质密切相关。氧化物、硫化物上主要是

2、酸性积碳，积碳速率与催化剂的表面酸碱性有关；金属上的积碳是通过烃类深度脱氢和脱氢环化聚合产生积碳，金属颗粒大小、分散度、合金化影响积碳；金属负载酸性载体催化剂的催化积碳则两者同时存在。积碳防止合金化，如Pt重整催化剂中添加第二组分金属形成合金，可减缓催化剂的积碳；添加助剂，Pt重整催化剂采用少量Cl改性，可以减缓酸性积碳；利用载体活性组分的相互作用，降低积碳；对于酸性催化剂或载体，添加碱性助剂（K20、MgO），减弱酸性积碳通入水蒸气，消碳；添加其他元素如稀土，加速消碳，防止积碳。积碳失活再生烧碳催化剂因为积碳而失活，其催化剂再生通常采用烧碳的方法可以部分恢复催化剂的活性。烧碳条件如气氛、温度

3、、气体组分等都会影响到再生后催化剂的结构、物化性质以及催化性能，因此必须严加控制。几条注意事项（三步骤）：除催化剂上的烃类和挥发物，必须在惰性气氛下进行；除去硫和轻质碳，必须在低温250-350度下先使金属氧化除去硫，同时某些聚合物和轻质碳也随之除去；最后除碳，根据碳的量以及类型在较高温度下进行。积碳表征催化剂积碳表征手段一览表TeeimiqueAppircatimiIR,FT-IR.DRIFTS-Fundionulgroupsofcoke(ntdure)AcidsitedeactivationSThM-EELSCokelocationElectronMicroscopyLocation,st

4、ructureTPOTPHyTPHc-morphology,kineticparameterlocationTGA-cokereactivity-volatil亡compcnmd翼oxygencontent,latticeoxygenreactivityCokeExtriictioii-CompositionofSolublefraction-CoklocationLRSUV-RSStructuiepregrttphitieorhighlyorganized)AveragedimensionofcrystaBite(tnonophasiccarbonJDissolutioaofSupportC

5、okecompositionandstructureXRDCrysOLlirjestructurecokelocationAESAinonn：ofcoke(approximatety)FractionofamorphousgraphiticVscarbidic/moleculanSIMSHydrogen.contentofthecarbondeposits(qualitative)Sorptioncapacity-cokelocation(poremouthorsiteporevolumeaniysisblockingl(uncertaintyincokedensity)-microormes

6、oporeblockingrCCPMAS-NMR-typeofchemicalgroupsincoRe(nature)lHNMR-HCdistribution,ofhvdrogenintokcti9XeNMR沔iMASNMRXPSUV-VIS(aliphatic,aromatic,etc)-Cokedistribution-Cokedistributioncokelocationinzeolites!FunctionalgroupsofcokedeiectionofcarbciiiuiTiionsNeutronscatteringandAttenuationcokecontentreqnire

7、stlieCHbeknown)C/H(requiresthe%Cbeknown)Cokedistribution(requiresadditionalexjwrirneiiiiiliftforttiatiori)TEOM(microbalanceEPRweigtitgainCokeNature,radicalsduringcokelorniation表征手段具体介绍Temperature-ProgrammedTechniquesTemperature-ProgrammedOxidation(TPO)可获取信息：providesdirectinformationregardingcokeoxid

8、ationrateobtainusefulinformationsuchas:location,composition(hydrogen/carbonratio)andmorphology(highlydispersedormultidimensionalparticles).具体如：DeterminationofH/CRatioDeterminationofCokeLocation.DeterminationofOxidationKineticsDeterminationofMorphologyDeterminationofCokeAmount方法：detectionofCO2byather

9、malconductivitydetector(TCD)afteritisseparatedfromoxygenandwaterinaGCcolumn;detectionofCO,CO2andhydrocarbonaceouscompoundsaftermethanation;quantificationofCO2withamassspectrometer;monitoringtemperatureincrementaboveareferencesample,indifferentialthermalanalysis(DTA)equipment;measurementofweightlossi

10、nthermalgravimetricanalysis(TGA)equipment.detectionofCO2byFTIRTemperature-ProgrammedHydrogenation(TPHy).尤其适用于H2为反应物的催化反应一-CharacterizationofcokebyTPHyisofspecialinterestwhenhydrogenisoneofthereactants,如：reforming,dehydrogenationmethanolsynthesisFischer-TropschsynthesisTemperature-ProgrammedGasificat

11、ion与TPO相似，采用载气如He、Ar,也可以采用CO2代替O2ElectronMicroscopyThelocalization,natureandstructureofcokedepositshavebeenexaminedwithelectronmicroscopy。Typically,theelectronmicroscopyalonedoesnotprovidemuchinformation,andisgenerallyusedincombinationwithrelatedspectroscopiesElectronEnergyLossSpectrocopy(EELS)EELS能

12、够提供的信息：providesanalyticalandstructuralinformation,similartothatgivenbyX-rayabsorptionspectroscopy;detectthelocationofthecoke(由于EELS具有高分辨率1nm2);providesqualitativeinformationregardingthetypeofcokepresentonthecatalyst(与参照样品对比).局限性：usedonlyinfewcasestocharacterizecokedepositsonheterogeneuscatalystsInfr

13、aredTechniques(FTIR,DRIFTS)能够提供的信息：obtainedwiththesetechniquesisthechemicalidentityofcompoundsthatformthecoke,suchasolefinic,rmationregardingthelocationofcokecanbeobtainedbyfollowingthesignalofcertaincatalystsurfacegroups,suchasBronstedOH.observethedepositionofcarbonaceousmat

14、erialsontheworkingcatalyst.局限性：limitedinformationonthenatureofcarbonaceousdepositsbecauseoftheircomplexityandofthedifficultytoassignunambiguouslyanIRbandtoparticularspecies。波数归属情况氏沁衣、用1)伽IgnttK笊740-760Mono-siibstiti!tcdarcmatics790-840CHdeformationinalkenes10361045vCCCH?inclirbutenesiCbondnIMOlinear

15、butenes120WiggingCH2longchuiipnratlins1336waggingCHiC4=dimeric1370-1380bumchedchainoligonrtrs1385aromatics-卩isCH3139()olefinicspecies1410linearbutenes1420.1430linearbutenes/ft=CHvinyl1437CH?asymmetricdeforinaiion(attachedtoaromatics1450/1463aromaticskeletalringbreathing5CH51471CHjdeformation(attache

16、dtouromatics)15131524yC=Caromatics1583.159YC=Caroniatics；polyaromatics1589niycrocristiillinepolycycliciiromatics1615.1617；C=Caroniatios；polyaroniatici1622C1=Cstretchniginbutenes1630.1625Cbondtt/oieiinicspecies2865saturatedCHStretching2925saturatedCHstretching2960saturatedCHpolyoleins十afbraatic2970/2

17、990saturatedCH5tretchingCHolcii11itspecies3045/305SvCHaromatic5)LaserRamanSpectroscopyClassicalLaserRamanSpectroscopy(LRS)提供信息：provideinformationregardingcokestructure(pregraphiticorhighlyorganized)andontheaveragedimensionofthecrystallite,aslongasamonophasiccarbonisproduced优点：thehighsensitivitythata

18、llowstheanalysisofcatalystswithlowcokecontent(0.30.5wt%)thepossibilityoffollowingthegraphitizationofamorphouscarbon.缺点：结果解析困难；surfacefluorescence干扰UV-RamanSpectrometry(UV-RS).解决了传统Raman的缺点Table2Ranntabuihlretaiucdliy(lrairbonsRanidnshift(cmRtiinaubandasigtrnieiilx1605-1615!36O-14iO1200-12101545-1550

19、1483RingrichesofpolypiroinulkspecieRingstreTchesofpolyarnmalicspeciesC-CstretchesofpolyaromalicspeciesCCstretchesOfconjugatedolefinsIn-phaseC=CstreichofcyclopcinadicnlspeciesDissolutionoftheSupportandSolventExtraction原理：afterthedissolutionofthesupportwithastrongacid,thecokeisextractedwithdifferentso

20、lvents,然后采用GC、MS等进行分析洗脱物。缺点：thecokecouldbemodifiedduringthisprocedure常采用的溶剂Tabk3Cokejiinctiomilitymuls&hcutaffinityrrrjfjj.xfwrf(ftfrtpfnnids1Hesatie1Henaiie-benzene(E5i15)ChlorGrormChloroform-dietliylether(90:10)Dteihyletier-eth；H)(il73i7Chiorofami-ethanolFyridine-ethatliplS：nttrtdhvdracarbonArotii

21、aLicJiydrocsrbonsPohiTiironiaik.norr-biisich-ctcrocyctcMonophenolsllasicnitrogpnatedheterocyclesHigldyfundioiialnioi-cculesPolyphenolsMoleculeswith址highcontentofNandONeutronScatteringandAttenuation可提供信息：measurecokecontentandC/Hratio优点：Thistechniquehastheadvantagethatthecokecontentandthereforethecoke

22、profilealongthecatalystbed,canbemeasuredin-situ.NuclearMagneticResonance(NMR)提供信息：TheNMRtechniqueisapowerfultechniquetoinvestigatethenatureofcarbonaceousdepositsdetectbindingsbetweenaromaticrings,alkylfragments,andeventertiarycarbeniumion-likespecies.缺点：TheinformationprovidedbyNMRisnotquantitative.种

23、类：13CCP/MAS-NMR.1920Talk4t3CCPMASNMRsignalussiLfnHrentsSitfuaifppNiAssi(fninenrmethylgroupconnectedwithsecondarycarbon,aliphaticmethylgroupboundtop-aralliniccarbonHHthylgrcupin3dto;iroirbrt!iesecondarycarbon,aliphaticmethylgroupbmmdtoMcfiniGc凤bonCHZgrouplinkedtomethylgroupsotherparaHiiiicCH；groupsme

24、thylgrvupalquaternarycarbonsecondaryandtertiaryparaffinicCcirbonaromaticC-Hgroupsaromiiii匚C-Hgroupssp2bendedcarbonEtlkylinedaroniLitics,carbonbridgesbiwccnaiv)maticEingsxubstiimcdamtnaticcarbons,bridgedciirbonsiticondensedaromLitics.olcfiincCHgroupspoly毁11;、ibOinnt沁CObondaroniLiric30and323030-50125L

25、28130B513841140-501601HNMRalsousedtostudyHYzeolitescokedwithn-heptane129XeNMRThistechniquehasbeenusedtostudycokelocationonzeolitecatalysts29SiMASNMR.AugerElectronSpectroscopy(AES)Augerelectronspectroscopy(AES)wasusedincombinationwithsecondaryionmassspectrometry(SIMS)todistinguishbetweenfourtypesofca

26、rbonaceousdeposits,onmetalfoils(rhodium,iridiumandplatinum).Thefoilswerecokedbyexposingtoethyleneatlowpressure.Augerspectroscopycandistinguishbetweenmolecularorcarbidicontheonehand,andgraphiticoramorphouscarbonontheother.X-Raydiffraction(XRD)CokestructurecanbecharacterizedbyX-Raydiffractionanalysis.

27、Thistechniquemakesitpossibletodetermineifthereiscokewithcrystallinestructureonthecatalyst.缺点：thesensitivityofthistypeofdeterminationisratherlow，beingitdifficulttodeterminethefractionand/oramountofcokeinthecrystallineform.SecondaryIonMassSpectrometry(SIMS)SIMSisamongthefewsurfacesensitivetechniqueswh

28、icharecapableofdetectinghydrogencontentofthedeposits.IthasbeenusedincombinationwithAEStoanalysecokeonmetalfoils缺点：However,itwasnotpossibletoobtaintherealH/CratioofthecarbondepositSorptionCapacity:SurfaceAreaandPoreVolume原理：Adsorptionmeasurementsallowthedeterminationofcokelocation.Whenthevolumeoccupi

29、edbycokeismuchsmallerthanthevolumeinaccessibletoadsorbates,itmeansthatthereisaporeblockage.缺点：However,inmanycasestheadsorptionstudyiscarriedoutatadifferenttemperaturethanthereaction,andthereforediffusivitycouldbequitedifferent.Anotheraspectthatshouldbetakenintoaccountisthatifthepretreatmentforadsorp

30、tionmeasurementrequirestemperatureshigherthanthereactiontemperature,animportantfractionofcarbonaceousdepositscouldbestrippedoffthecatalystand,therefore,theporevolumemeasuredinthiswaywillbehigherthantheactualvolumeunderreactionconditions.X-RayPhoto-electronSpectroscopy(XPS)UltraViolet-VisibleSpectroscopy(UV-VIS)TheUV-VISspectroscopycanbeusedtodeterminethechemicalidentityofthecokecomponentes.UV-VIS,unlikeNMRandIR,caneasilydetectalkylandalkenylcarbeniumions,essentiallyduetoitsmuchhighersensitivity55.Thisisusuallycarriedoutundervaccum,andtherefore,themorevolatilecompoundscould