催化劑表面碳物種及表征

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行吸附形成含碳物種，如含碳物種經(jīng)過分解、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原料在高溫下熱裂解形成煙炱、焦油，它們在催化劑表面上生成有序的或無序的碳；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；?金屬負載酸性載體催化劑的催化積碳則兩者同時存在。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；?對于酸性催化劑或載體，添加堿性助劑（K2O、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。積碳失活再生一一燒碳催化劑因為積碳而失活，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、氣體組分等都會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（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行。積碳表征催化劑積碳表征手段一覽表AppircatimiItFT-IR.DRIFTS-Fundionulgroupsofcoke(nidure)AcidsitedeactivationSThM-EELSCokelocationElectronMicroscopyLocation,structureTPOTPHyTPHc-morphology,kineticparameter^locationTGA-cokereactivity-volatilecompourids,oxygencontent,latticeoxygenreactivityCokeExtiiictioii-CompositionofSolublefraction-Cok^locationLRSUV-RSStructuie(pregrttphitieorhighlyorganized)Avcrigcdimensionotcrystflllitc(tnonophasiccarbonJDissohitioaofSupportCokecompositionandstructureXRDCrysOLlirjestructurecokelocationAESAinonn：ofcoke(approximatety)FractionofamorphousgraphiticVsciirbidic/moleculanSIMSHydrogen.contentofthecarbondeposits(qualitative)Sorptioncapacity-cokelocation(poremouthorsiteporevolumean^iysisblockingl(uncertaintyincokedensity)-microormesoporeblockingrCCPMAS-NMR-typeofchenifcalgroupsincoRe(nature)lHNMR-HCdistribution.ofhvdrogenintokc明XeNMR*SiMASNMRXPSUV-VIS(alipliatic.aromatic,etc)-Cokedistribution-Cokedistributioncokelocation(inzeolites!FunctionaJgroupsofcokedeiectionofcarbciliumionsNeutronscatteringandAtteniRitioncokecontent{reqnirestlieCHbeknown)C/H(requiresthe%Cbeknown)Cokedistribution(requiresadditionalexjwrirneiiiiiliftforftiatiori)TEOM(microbalance}EPRweigtitgainCokeNatumradicalsduringcokeIbrniation表征手段具體介紹Temperature-ProgrammedTechniquesTemperature-ProgrammedOxidation(TPO)可獲取信息：providesdirectinformationregardingcokeoxidationrateobtainusefulinformationsuchas:location,composition(hydrogen/carbonratio)andmorphology(highlydispersedormultidimensionalparticles).具體如：Determination of H/CRatioDetermination of CokeLocation.Determination of OxidationKineticsDetermination of MorphologyDetermination of CokeAmount方法:

detectionofCO2byathermalconductivitydetector(TCD)afteritisseparatedfromoxygenandwaterinaGCcolumn;detectionofCO,CO2andhydrocarbonaceouscompoundsaftermethanation;quantificationofCO2withamassspectrometer;monitoringtemperatureincrementaboveareferencesample,indifferentialthermalanalysis(DTA)equipment;measurementofweightlossinthermalgravimetricanalysis(TGA)equipment.detectionofCO2byFTIRTemperature-ProgrammedHydrogenation(TPHy).如：尤其適用于H2為反應(yīng)物的催化反應(yīng)一-^CharacterizationofcokebyTPHyisofspecialinterestwhenhydrogenisoneofthereactants,如：reforming,dehydrogenationmethanolsynthesisFischer-TropschsynthesisTemperature-ProgrammedGasification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(與參照樣品對比).局限性：usedonlyinfewcasestocharacterizecokedepositsonheterogeneuscatalystsInfraredTechniques(FTIR,DRIFTS)能夠提供的信息：

obtainedwiththesetechniquesisthechemicalidentityofcompoundsthatformthecoke,suchasolefinic,saturatedorrmationregardingthelocationofcokecanbeobtainedbyfollowingthesignalofcertaincatalystsurfacegroups,suchasBronstedOH.observethedepositionofcarbonaceousmaterialsontheworkingcatalyst.局限性：limitedinformationonthenatureofcarbonaceousdepositsbecauseoftheircomplexityandofthedifficultytoassignunambiguouslyanIRbandtoparticularspecies。波數(shù)歸屬情況740-760Mono-substitutedarcmatics790-840CHdeformationinalkenes10361045vCCCH?]inclirbutenesiC」bondnlinearbutenes120WiggingCH2long pnratlins1336wa典ingCH拱C廣dimeric1370-1380bumchedchainoligonrt^rs1385aromatics-polyaroinatics.'CH31390olefinicspecies1410linearbutenes1420/1430linearbutenes/ft vinyl1437CH?asymmetricdeforinaiion(attachedaromatics^1450/1463aromaticskeletalringbreathing&CH51471CHjdeformation(attachedtouromatics)15131524yC=Caromatics1583,.1595YC=Caroniatics；polyaromatics1589niycrocristiillinepolycycliciiromatics1615.1617■；C=Caroniatics；polyaroniatics;1622C1=Cstretchniginbutenes1630.1625iC]bondtt/olefinicspecies2865saturatedCHStretching2925saturatedCH成『etching2960saturatedCHpolyolefins+afbraatic2970/2990saturatedCHretchingCHolcii11itspecies3045/3Q58vCHaromatic(5)LaserRamanSpectroscopyClassicalLaserRamanSpectroscopy(LRS)提供信息：provideinformationregardingcokestructure(pregraphiticorhighlyorganized)andontheaveragedimensionofthecrystallite,aslongasamonophasiccarbonisproduced優(yōu)點:thehighsensitivitythatallowstheanalysisofcatalystswithlowcokecontent(0.3—0.5wt%)thepossibilityoffollowingthegraphitizationofamorphouscarbon.缺點：?結(jié)果解析困難；?surfacefluorescence干擾UV-RamanSpectrometry(UV-RS).解決了傳統(tǒng)Raman的缺點Table2Ranritabuihl tinmei?/5<retaiuc<1Hainanshift(cmiJRttminrbanda^signtfie/ilxI觸)5-1615 p>?ly^roinulkspeciesRingstreichcsofpolyaromalicspecies1200-1210 C-Cstretchesofpolyaromalicspecies1545-1550 C=CstneKhesof olctim1483 In-phaseC=Cslidchofcyclopenradicny1specksDissolutionoftheSupportandSolventExtraction原理：afterthedissolutionofthesupportwithastrongacid,thecokeisextractedwithdifferentsolvents，然后采用GC、MS等進行分析洗脫物。缺點：thecokecouldbemodifiedduringthisprocedure常采用的溶劑Tahir3CifkeJttniUtHinliiymuls&hcutd(}iixityrrrjfjj.xfwrf1Hesatie1Henaiie-benzene(E5H5)ChlorGrormChl^rokirni-dsclhylcihcr(9ft：!0iDteihylMe(幽no】Chlorofarm-ethanol￡P(guān)yridine-clhiLinD]ArotiiaLicJiydrocsrbonsiironiaik^.norr-biisich&ero/’eki*MonopbenolsHjsicnitrageitaiedlieterocyelesHigldyfunciioiialmoi-cculesPolyphenolsMoiecu屈ivithahighcciatenLofNadd()NeutronScatteringandAttenuation可提供信息：measurecokecontentandC/Hratio優(yōu)點：Thistechniquehastheadvantagethatthecokecontentandthereforethecokeprofilealongthecatalystbed,canbemeasuredin-situ.NuclearMagneticResonance(NMR)提供信息：TheNMRtechniqueisapowerfultechniquetoinvestigatethenatureofcarbonaceousdepositsdetectbindingsbetweenaromaticrings,alkylfragments,andeventertiarycarbeniumion-likespecies.缺點：TheinformationprovidedbyNMRisnotquantitative.種類：13CCP/MAS-NMR.

lilbk4 義。PAJ.4S\MRsi^naidssRfivtreiusSitfuaifppm)Assi(fninenr13面20由2330and323030-50125L28130B5138441I40-[50160metbyIgroupconnectedwithsecondaryenrben.aliphiiticmethylgroupboundtop-aralliniccarbonmethylgreup￡in3<^d〔oaromM仍secondarycarbon,aliphaticmethylgrouphoundto13面20由2330and323030-50125L28130B5138441I40-[50160hy]grvupal aternarycarbonsecondaryandtertiaryparaffinicCcirbonaromaticC-HgroupsaromiiiicC-Hgroupssp2bendedcarboncJkylaiedaroniLitics,carbonbridgesb^iwccnaiv)maticE'ingsxubstiimcdamtnaticcarbons,bridgedciirbonsiticondensedaromLitics.olcfiincCHgroupspolyalkv]yt^liir&imticCObond%aroniLiric1HNMRalsousedtostudyHYzeolitescokedwithn-heptane129XeNMRThistechniquehasbeenusedtostudycokelocationonzeolitecatalysts29SiMASNMR.AugerElectronSpectroscopy(AES)Augerelectronspectroscopy(AES)wasusedincombinationwithsecondaryionmassspectrometry(SIMS)todistinguishbetweenfourtypesofcarbonaceousdeposits,onmetalfoils(rhodium,iridiumandplatinum).Thefoilswerecokedbyexposingtoethyleneatlowpressure.Augerspectroscopycandistinguishbetweenmolecularorcarbidicontheonehand,andgraphiticoramorphouscarbonontheother.X-Raydiffraction(XRD)CokestructurecanbecharacterizedbyX-Raydiffractionanalysis.Thistechniquemakesitpossibletodetermineifthereiscokewithcrystallinestructureonthecatalyst.缺點：thesensitivityofthistypeofdeterminationisratherlow，beingitdifficulttodeterminethefractionand/oramountofcokeinthecrystallineform.SecondaryIonMassSpectrometry(SIMS)SIMSisamongthefewsurfacesensitivetechniqueswhicharecapableofdetectinghydrogencontentofthedeposits.IthasbeenusedincombinationwithAEStoanalysecokeonmetalfoils缺點：However,itwasnotpossibletoobtaintherealH/CratioofthecarbondepositSorptionCapacity:SurfaceAreaandPoreVolume原理：Adsorptionmeasurementsallowthedeterminationofcokelocation.Whenthevolumeoccupiedbycokeismuchsmallerthanthevolumeinaccessibletoadsorbates,itmeansthatthereisaporeblockage.缺點：However,inmanycasestheadsorptionstudyiscarriedoutatadifferenttemperaturethanthereaction,andthereforediffusivitycouldbequitedifferent.Anotheraspectthatshouldbetakenintoaccountisthatifthepretreatmentforadsorptionmeasurementrequirestemperatureshigherthanthereactiontemperature,animportantfractionofcarbonaceousdepositscouldbestrippedoffthecatalystand,therefore,theporevolumemeasuredinthiswaywillbehigherthantheactualvolumeunderreactionconditions.X-RayPhoto-electronSpectroscopy(XPS)UltraViolet-VisibleSpectroscopy(UV-VIS)TheUV-VISspectroscopycanbeusedtodeterminethechemicalidentityofthecokecomponentes.UV-VIS,unlikeNMRandIR,caneasilydetectalkylandalkenylcarbeniumions,essentiallyduetoitsmuchhighersensitivity55.Thisisusuallycarriedoutundervaccum,andtherefore,themorevolatilecompoundscouldbelostunderthesecond