第九講-無(wú)機(jī)催化原理

第九講機(jī)催化原PartI.ImportanceofTheprincipalthemeincatalysisisthedesiretocontroltherateofchemicalreactionsandthesecondarythemeistounderstandthemechanismofthecontrol.Catalysisplaysaveryimportantroleinawiderangeofandtechnologicalproblems.OneimportantData: industryinthelast50yearshavebeenbasedonCatalysisinmodernTypesofcommercialcatalystsusedinpetroleumTypesofcommercialcatalystsusedinchemicalCatalyticproductionofthetoporganicindustrialApplicationinchemicalfertilizerOutputvalueofchemicalfertilizerindustryaccountsforabout20%ofchemicalindustrialoutputvalue.Nitrogenousfertilizer,phosphatefertilizer,andpotashApplicationinbiomassBiochemicalindustrywouldsubstitutepetrochemicalindustrytogreat mainproducts:fuelethanol,bio-ethylene,biologicalmarshgaspowergeneration,andApplicationinfuelWorkprincipleoffuelFuelcellproductforMP3producedby

Electricfansdrivenbyfuel producedbyAngstromPowerInc..ApplicationfortheuseofPhotocatalysistoothwhiteningsystem

AirNanoZnOmildewand organicmatter

NanoTiO2RareearthThereservesistheRareearthisveryimportant,andmoreexpensivethanOftenusedasWuxiWeifuLidaCatalyticConverter .(無(wú)錫威孚力達(dá)催化凈化 公司CatalyticConverterisalsonamedconverter,clarifierorcarexhaustclarifier,whichakindofdevicetocompletecatalyticApplicationofnanocatalystsforhigheffectivePartII.BasicDefinitionofAnaccelerationordecelerationoftherateofaprocessorreaction,broughtaboutbyacatalyst,usuallypresentinsmall tiesandunaffectedattheendofthereaction.DefinitionofAcatalystisasubstancethatchangesthespeedofachemicalreactionwithoutundergoingapermanentchemicalchangeitselfduringtheprocess.Usually,acatalystpermitsreactionsorprocessestotakeplacemoreeffectivelyorundermilderconditionsthanwouldotherwisebepossible. CatalyticCatalyticInnature,catalyticprocessisachemicalAtleastonereactivemoleculechemicallyinteractswithThereactionratechanges(increaseorThechemicalcomponentisClassificationofClassificationfromtheaspectofindustrial(1)Fertilizermanufacture(2)RefiningPurificationReformingCOshiftMethanationAmmoniasynthesisMethanolAcidmanufactureOxidationReformingFluidCatalyticCrackingCatalyst,HydrocrackingHydrorefiningHydrotreatingAlkylatingPolymerizationOxidationHydrogenationDehydrogenationDehydrationOxoEsterificationIncinerationcatalystforproducesexhaustPowerstationexhaustgastreatingTailgasfromnitricacidplantAutomotiveClassificationfromtheaspectofcatalystactiveNH3synthesisfromN2andFataandoilsPt,OxidationofOxidationofCH3OHtoMetalButanedehydrogenationtoOxidationofSO2toprepareCuO,OilshydrogenationtohigheraliphaticMetalMoS2,WS2,CoS2,Acid,base,AluminaPetroleum1,3-dimethylbenzeneisomerizationto1,4-EthylenereactswithbenzenetoformEthanoldelydrationtosolidphosphoricEthylenehydrationtoCondensationofacetonetodiacetoneRhcomplexCarbonylationofmethanoltoaceticAlkylBasiccompositionsofaAworkingcatalystiscomposedofthreeActivecomponent:mostoftenaSupport:porousmateriallikeAl2O3,SiO2,carbon,TiO2,Promoter:mostoftenametaladdedinsmallOpticalimagesofhomogeneousandnickel-basedcatalystsforPOMSometypicalcatalystElectronElectronpromoterisapromotertochangetheelectronmobilityof Fe3O4- ethylbenzenedehydrogenationExample2.K2OplaysaroleofelectronpromoterinFe-basedcatalystforNH3synthesis.K2Oprovideselectronstocatalyst, reducestheelectronworkfunction(電子逸出功),andthuspromotesthedesorptionofNH3.StructureStructurepromoterisapromotertoimprovethedispersionandthermalstabilityofcatalystbychangingthechemicalcomponent,crystaltexture,porestructure,dispersionstate,andmechanicalstrengthofcatalyst.Example1.Al2O3actsasastructurepromotertopreventthesinteringofinfusedironcatalystforNH3DefinitionofactivationenergyInchemistry,activationenergyisatermintroducedin1889bytheSwedishscientistSvanteArrhenius,thatisdefinedastheenergythatmustbe einorderforachemicalreactiontooccur.Activationenergymayalsobedefinedastheminimumenergyrequiredtostartachemicalreaction.TheactivationenergyofareactionisusuallydenotedbyEa,andgiveninunitsofkilojoulespermole.Activationenergycanbethoughtofastheheightofthepotentialbarrier(sometimescalledtheenergybarrier)separatingtwominimaofpotentialenergy(ofthereactantsandproductsofareaction).Forachemicalreactiontoproceedatareasonablerate,thereshouldexistanappreciablenumberofmoleculeswithenergyequaltoorgreaterthantheactivationenergy.Generallyspeaking,acatalysttypicallyincreasesreactionratesbylowingtheactivationenergy.Definitionofrate-determiningstepTherate-determiningstep(RDS)isachemistrytermforthesloweststepinachemicalreaction.Therate-determiningstepisoftencomparedtotheneckofafunnel;therateatwhichwaterflowsthroughthefunnelisdeterminedbythewidthoftheneck,notbythespeedatwhichwaterispouredin.Insimilarmanner,therateofreactiondependsontherateofthesloweststep.Howeveritisnotclearwhat'sloweststep'means.Forexampledoesitrefertothestepwiththesmallestrateconstant,ifthereactionisreversible,doesitrefertotheratiooftheforwardandreverserateconstantsordoesitsimplyrefertothestepthathasthesmallestflux?Ifthelatterthenatsteadystateallstepscarrythesamefluxandthereforethereisnosloweststep.Inmetabolicpathwaystheratelimitingstepismorewelldefinedandameasure,thefluxcontrolcoefficientisgiventoasteptosignifyhowratelimitingthestepis.Theoryandexperimentalsosuggeststhatthereisnosingleratelimitingstepbutarangeofratelimitingnessacrosstheentirereactionnetwork.PartIII.CatalyticbasicCatalyticreactionSurfacereactionArrheniusReactantReactantOutersurfaceofFigure3-1Stepsofatypicalcatalytic:Externaldiffusionfromthegasstreamtotheoutersurfaceof:Internalporediffusionfromtheoutersurfacetotheinternalporesof:Adsorptionofreactantsontheactive:Reactionofreactantsontheactive:Desorptionof

Surface:Internalporediffusionfromtheinternalporestotheoutersurfaceof:ExternaldiffusionfromtheoutersurfaceofcatalysttothegasExamples:CO+O2→CO2;H2+O2 fromXto fromYto Figure3-3.Therelationshipbetweenactivationenergy(Ea)andenthalpyofformation(ΔH)withandwithoutacatalyst.TheThehighestenergyposition(peakposition)representsthetransitionstate.Withcatalyst,theenergyrequiredtoentertransitionstatedecreases,therebydecreasingtheenergyrequiredtoinitiatethereaction.ArrheniuslnklnkEa/RTlnkAeEa/TheArrheniusequationgives tativebasisoftherelationshipbetweenactivationenergyandtherateatwhichareactionproceeds.K:isthereactionrateA:isthefrequencyfactorfortheR:istheuniversalgasT:isthetemperature(inWhilethisequationsuggeststhattheactivationenergyisindependentontemperature,inregimesinwhichtheArrheniusequationisvalidthisiscancelledbythetemperaturedependenceofk.ThusEacanbeevaluatedfromthereactionratecoefficientatanytemperature(withinthevalidityoftheArrheniusequation).OtherformsofArrheniusDifferential ?IntegralArrheniusequationisoftensuitableforthesituationthatthetemperaturechangesslightly.Ifthetemperaturechangesgreatly,weshouldusemodifiedArrheniusequation:ddlnk lnEa(11 kA(T/T)neEa/0kAe[( )

A,nandEaarenrangesfrom-1to1,andbeobtainedfromβis Figure3-4CatalyticsynthesisofNH3fromN2and2.Relationshipbetweensurfacestructuresofcatalyticmaterialsand結(jié)構(gòu)與性能相ElectronCrystalDefect acidorbasesites(importantforacid-basecatalysis)Skeletonstructure(Example:Sizeeffect(NanoElectronWhybandsoccurinTheelectronsofasingleisolatedatomoccupyatomicorbitals,whichformadiscretesetofenergylevels.Ifseveralatomsarebroughttogetherintoamolecule,theiratomicorbitalssplit,asinacoupledoscillation.Thisproducesanumberofmolecularorbitalsproportionaltothenumberofatoms.Whenalargenumberofatoms(oforder×1020ormore)arebroughttogethertoformasolid,thenumberoforbitals esexceedinglylarge.Consequently,thedifferenceinenergybetweenthem esverysmall.Thus,insolidsthelevelsformcontinuousbandsofenergyratherthanthediscreteenergylevelsoftheatomsinisolation.However,someintervalsofenergycontainnoorbitals,nomatterhowmanyatomsareaggregated,formingbandgaps.Metal:Fe,Co,GaN(3.44eV),Comparisonofthebandgapsforametal,asemiconductorandaninsulator.Comparisonofthebandgapsforametal,asemiconductorandaninsulator.EnergyBand DensityofStatesEffectofelectronstructureonExample:PhotocatalysisistheaccelerationofaphotoreactioninpresenceofaBandgap:3.23<387.5UV-light(<400nm):Inphotogeneratedcatalysis,thephotocatalyticactivity(PCA)dependsontheabilityofthecatalysttocreateelectron–holepairs,whichgeneratefreeradicals(hydroxylradicals:·OH)abletoundergosecondaryreactions.Eigenvalue(EⅠ)oftheouterorbitaloftheBO6

(B=Ti-Ni)Photocatalytic文獻(xiàn) ,白樹(shù)林 2.2CrystalDefectpointlineardefectConductivemechanismofZrO2SurfaceacidorbaseALewisacidisdefinedtobeanyspeciesthatacceptslonepairALewisbaseisdefinedtobeanyspeciesthatdonateslonepairExample:Example:H+isaLewisacid,sinceitcanacceptalonepair,whileOH-NH3areLewisbases,bothofwhichdonatealoneMe3BMe3B+:NH3→Me3B←-BF3+F-→SiF4+2SiF4+2F?→SiF6RClRCl+AlCl3→R++ formationoftheammoniumSkeletonZeolitesaremicroporouscrystallinealuminosilicates,composedofTO4tetrahedra(T=Si,Al)withOatomsconnectingneighboringtetrahedra.Foracompleysiliceousstructure,combinationofTO4(T=Si)unitsinthisfashionleadstosilica(SiO2),whichisanunchargedsolid.UponincorporationofAlintothesilicaframework,the+3chargeontheAlmakestheframeworknegativelycharged,andrequiresthepresenceofextraframeworkcations(inorganicandorganiccationscansatisfythisrequirement)withinthestructuretokeeptheoverallframeworkneutral.Thezeolitecompositioncanbebestdescribedashavingthreecomponents:TheamountofAlwithintheframeworkcanvaryoverawiderangewith=1toComparisonofporesizesofdifferentframework6.Sizeeffect(NanoSpecificsurfaceareaincreasesMeltingpointdecreasesEnergylevelsExample:BET:bulkmaterials(<0.1m2/g);~2nm(~300Meltingpoint:bulkmaterials(1064oC);~2nmExample:Growthofcarbon(a)TypicalSEMand(b)AFMimagesoftheas-grownSWNTsonSi/SiO2substratecoveredwitha30- depositedSiO2film.(c)Ramanspectraofthesamesampleacquiredatthreepositions,withthepeaks303cm-1originatingfromSi/SiO2substrateandusedforcalibration.(d)HRTEMimageofthreeindividualSWNTs(indicatedbyRamanspectraof(A)SWNTswithinthecircletraceareaand(B)MWNTsorcarbonfilementinsidethecircletrace.SEMimagesofalignedlongSWNTarraysfrom(C)SiO2,(D)Al2O3,(E)TiO2,and(F)RandomSWNTsfromTiO2NPs(a),Al2O3NPs(b)andrareearthoxidesEr2O3光催化簡(jiǎn)(C半導(dǎo)體光催化機(jī)概念：光光觸媒[PHOTOCATALYSIS][Photo=Light]觸媒(催化劑)[catalystOH-及O2-自由負(fù)離子。幾乎可分解所有對(duì)人 教授發(fā)現(xiàn)。在一次試驗(yàn)中對(duì)放入水中的氧化鈦結(jié)晶進(jìn)行了光線照射，結(jié)果發(fā)現(xiàn)水被分解成了氧和氫。這一效果作為“本多·藤島效果”（Honda-FujishimaEffect）而聞名于世，該名稱組合了藤島教授和當(dāng)時(shí)他的指導(dǎo)教師 常見(jiàn)的材料種類：TiO2、CdS、WO3、ZnO、ZnSFe2O3、SnO2CdSFe2O3TiO2ZnO光催化制氫1、光催化制氫體系光催光催催化M.Gratzel,etal,Nature,1991,353:737;Nature,1998,395:583;Khan,etal,Science,2002,297:2243;Z.G.Zou,etal.,Nature,2001,光催2、光催化制氫的關(guān)鍵 λ683λ400

3、半導(dǎo)體光催化制氫熱力HH2OH2+G0=238kJ/mol(E=-Go/nF=-1.23Conductione-e-e-Conductione-e-e-e-Bandh+h+h+Bandh+h+h+h+ValenceSeparationofreductionandControlofreverse

4、半導(dǎo)體光催化制氫自197