催化劑表面碳物種及表征

1、何謂積碳以含碳化合物為原料的催化反應(yīng)的第一步通常是在催化劑表面上進(jìn)行吸附形成含碳物種，如含碳物種經(jīng)過(guò)分解、聚合等反應(yīng)生成碳或焦炭沉積在催化劑表面，既所謂的積碳或結(jié)焦。積碳會(huì)堵塞催化劑的活性位或催化劑的孔道，從而導(dǎo)致催化劑的失活！常發(fā)生積碳的催化反應(yīng)催化裂化Pt重整加氫精制輕油制氫積碳形態(tài)積碳的形態(tài)一般分為無(wú)定形碳、層狀石墨碳、管須狀結(jié)晶碳以及粘稠狀液態(tài)碳或焦油。積碳原因熱裂解催化裂解深度脫氫烯烴聚合熱裂解積碳是氣相有機(jī)原料在高溫下熱裂解形成煙炱、焦油，它們?cè)诖呋瘎┍砻嫔仙捎行虻幕驘o(wú)序的碳；催化積碳是在催化劑的作用下，烴類化合物發(fā)生催化積碳反應(yīng)，它與催化劑的性質(zhì)密切相關(guān)。氧化物、硫化物上主要是

2、酸性積碳，積碳速率與催化劑的表面酸堿性有關(guān)；金屬上的積碳是通過(guò)烴類深度脫氫和脫氫環(huán)化聚合產(chǎn)生積碳，金屬顆粒大小、分散度、合金化影響積碳；金屬負(fù)載酸性載體催化劑的催化積碳則兩者同時(shí)存在。積碳防止合金化，如Pt重整催化劑中添加第二組分金屬形成合金，可減緩催化劑的積碳；添加助劑，Pt重整催化劑采用少量Cl改性，可以減緩酸性積碳；利用載體活性組分的相互作用，降低積碳；對(duì)于酸性催化劑或載體，添加堿性助劑（K20、MgO），減弱酸性積碳通入水蒸氣，消碳；添加其他元素如稀土，加速消碳，防止積碳。積碳失活再生燒碳催化劑因?yàn)榉e碳而失活，其催化劑再生通常采用燒碳的方法可以部分恢復(fù)催化劑的活性。燒碳條件如氣氛、溫度

3、、氣體組分等都會(huì)影響到再生后催化劑的結(jié)構(gòu)、物化性質(zhì)以及催化性能，因此必須嚴(yán)加控制。幾條注意事項(xiàng)（三步驟）：除催化劑上的烴類和揮發(fā)物，必須在惰性氣氛下進(jìn)行；除去硫和輕質(zhì)碳，必須在低溫250-350度下先使金屬氧化除去硫，同時(shí)某些聚合物和輕質(zhì)碳也隨之除去；最后除碳，根據(jù)碳的量以及類型在較高溫度下進(jìn)行。積碳表征催化劑積碳表征手段一覽表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表征手段具體介紹Temperature-ProgrammedTechniquesTemperature-ProgrammedOxidation(TPO)可獲取信息：providesdirectinformationregardingcokeoxid

8、ationrateobtainusefulinformationsuchas:location,composition(hydrogen/carbonratio)andmorphology(highlydispersedormultidimensionalparticles).具體如：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).尤其適用于H2為反應(yīng)物的催化反應(yīng)一-CharacterizationofcokebyTPHyisofspecialinterestwhenhydrogenisoneofthereactants,如：reforming,dehydrogenationmethanolsynthesisFischer-TropschsynthesisTemperature-ProgrammedGasificat

11、ion與TPO相似，采用載氣如He、Ar,也可以采用CO2代替O2ElectronMicroscopyThelocalization,natureandstructureofcokedepositshavebeenexaminedwithelectronmicroscopy。Typically,theelectronmicroscopyalonedoesnotprovidemuchinformation,andisgenerallyusedincombinationwithrelatedspectroscopiesElectronEnergyLossSpectrocopy(EELS)EELS能

12、夠提供的信息：providesanalyticalandstructuralinformation,similartothatgivenbyX-rayabsorptionspectroscopy;detectthelocationofthecoke(由于EELS具有高分辨率1nm2);providesqualitativeinformationregardingthetypeofcokepresentonthecatalyst(與參照樣品對(duì)比).局限性：usedonlyinfewcasestocharacterizecokedepositsonheterogeneuscatalystsInfr

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

14、erialsontheworkingcatalyst.局限性：limitedinformationonthenatureofcarbonaceousdepositsbecauseoftheircomplexityandofthedifficultytoassignunambiguouslyanIRbandtoparticularspecies。波數(shù)歸屬情況氏沁衣、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a(chǎn)fbraatic2970/2

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

18、llowstheanalysisofcatalystswithlowcokecontent(0.30.5wt%)thepossibilityoffollowingthegraphitizationofamorphouscarbon.缺點(diǎn)：結(jié)果解析困難；surfacefluorescence干擾UV-RamanSpectrometry(UV-RS).解決了傳統(tǒng)Raman的缺點(diǎn)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等進(jìn)行分析洗脫物。缺點(diǎn)：thecokecouldbemodifiedduringthisprocedure常采用的溶劑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優(yōu)點(diǎn)：Thistechniquehastheadvantagethatthecokecontentandthereforethecoke

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

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

24、thylgrvupalquaternarycarbonsecondaryandtertiaryparaffinicCcirbonaromaticC-Hgroupsaromiiii匚C-Hgroupssp2bendedcarbonEtlkylinedaroniLitics,carbonbridgesbiwccnaiv)maticEingsxubstiimcdamtnaticcarbons,bridgedciirbonsiticondensedaromLitics.olcfiincCHgroupspoly毀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.缺點(diǎn)：thesensitivityofthistypeofdeterminationisratherlow，beingitdifficulttodeterminethefractionand/oramountofcokeinthecrystallineform.SecondaryIonMassSpectrometry(SIMS)SIMSisamongthefewsurfacesensitivetechniqueswh

28、icharecapableofdetectinghydrogencontentofthedeposits.IthasbeenusedincombinationwithAEStoanalysecokeonmetalfoils缺點(diǎn)：However,itwasnotpossibletoobtaintherealH/CratioofthecarbondepositSorptionCapacity:SurfaceAreaandPoreVolume原理：Adsorptionmeasurementsallowthedeterminationofcokelocation.Whenthevolumeoccupi

29、edbycokeismuchsmallerthanthevolumeinaccessibletoadsorbates,itmeansthatthereisaporeblockage.缺點(diǎn)：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