工业催化原理-英文课件chapter31

Chapter3Adsorptionincatalyzedreaction•§3.1PhysisorptionandchemisorptionphysicaladsorptionchemicaladsorptioninteractionforceVanderWaalsvalencebondheatofadsorption~20KJ/mol40-400KJ/molactivationenergynoyesspeedofadsorptionrapidslowselectivitynoyeslayersofadsorbatemultilayersmonolayeradsorptiontemp.77KroomtemperatureapplicationsBETmethoddeterminingthemeasuringsurfacedispersionofmetalareaandporeinasupporteddistributioncatalystsurfacearea§3.1Physisorptionandchemisorption•potentialenergycurve•Lennard-JonesequationforphysisorptionE(r)=-A/r-6+B/r12negativesignrepresentsattractionwhilepositivetermstandsforrepulsion•Morseformulaforchemisorption§3.1Physisorptionandchemisorption•potentialenergycurve•Ea=21KJ/molactivationenergyfortransferphysisorptiontochemisorption•qc=34KJ/molheatofchemisorption,exothermic•Ed=55KJ/molactivationenergyfordesorption,Ed=Ea+qc§3.1Physisorptionandchemisorption•ThetransferofphysisorptiontochemisorptionatpointF,atransitionstatewasformed,whereitisthepathwayofminumumpotentialenergyofformationofchemisorbedspecies.•ActuaryitdoesnotneedtoovercomethedissociateenergyofH2D=103KJ/mol.§3.2Chemisorbedstate•Chemisorbedstategenerallymeansthechemicalstate,electronstructureandgeometricconfigurationofamolecule(oratom)adsorbedonthesolidsurface.•Duetotheinteractionbetweenadsorbateandsurface,theelectronandgeometrystructureofadsorbateusuallywilldeferfromtheoriginals.•However,thestudyofchemisorbedstateisfarfromsufficientbecauseoftheresearchdifficulty§3.2.1Adsorbedstateofcarbonmonoxide•Ingeneral,anadsorbedmoleculecanexistmorethanonestate.e.g.carbonmonoxideadsorbedonthesurfaceofmetalRutheniumlinear(Cu,Pt…)twinbridge(Ni,Pd…)线式双重式桥式§3.2.1Adsorbedstateofcarbonmonoxide•molecularadsorption(roomtemperatureonPt,Ni,Cu,Fe…)CO(gas)CO*•dissociateadsorption(onW,Mo,TiorathighertemperatureonNi,Fe…)CO(gas)[CO]C*+O*•differentadsorbedstateswillcausedifferentcatalyticactivities.CO+H2CH3OH(Pd,Cu/ZnO)molecularadsorptionCO+H2hydrocarbons(Fecatalyst)dissociateadsorption§3.2.2Adsorbedstateofoxygen•OxygenadsorbedonmetalsOOOOO||\/OMMM-type-typelinear(end-on)side-on§3.2.2Adsorbedstateofoxygen•OxygenadsorbedonmetalsWhileadsorbedoxygenmoleculeintheside-onstate,especiallyin-type,eachoxygenatomwasbondedtometalatomrespectivelytoformatriangleconfiguration.Thedistancebetweentwooxygenatomswasincreasedandthebondstrengthdecreasedhencetoenhancethereactionactivity.§3.2.2AdsorbedstateofoxygenAdsorbedStateOOstrengthconstantoriginaloxygen11.810-7/Nnm-1oxygenadsorbedonPd4.1510-7/Nnm-1oxygenadsorbedonNi3.410-7/Nnm-1oxygenadsorbedonPt3.2610-7/Nnm-1•thesmallerconstant,thehigherreactionactivitythereforesupportedPlatinumisagoodoxidationcatalyst.§3.2.3Adsorbedstateofhydrogen•Thereexistfourdifferenttypesofadsorbedspeciesonplatinummetalsurface•Ingeneral,itisbelievedthathydrogencouldadsorbedonmetalsurfaceinbothmolecularandatomicformsthroughnormaladsorptionordissociatedadsorptionrespectively.H|HHHHH||||／＼PtPtPtPtPtPt§3.2.3Adsorbedstateofhydrogen•ThermaldesorptionspectrumofhydrogenonW(111),tungsten,hasfourpeaksindicatingfourpossibleadsorbedstates.§3.3Adsorptionheat•Theheatofadsorptionisasignificantpropertyforcharacterizationofthetypeofsorptionandofthedegreeofheterogeneityofasurface.•§3.3.1Differentialandintegralheatofadsorption•Integralheatofadsorptionistheaveragevalueofthermaleffectsoverthealldegreesofsurfacecoveragetillequilibrium.Itcanbemeasuredbyacalorimetricmethod.§3.3.1Differentialandintegralheatofadsorption•Differentialheatofadsorption,whichisaninstantvalueofheatofadsorptionatashortperiod,canbecalculatedbyClausius-Clapeyronequation(lnP/T)=q/RT2ln(P2/P1)=q/R·(1/T1-1/T2)•qistheheatofadsorptionatthecoverage,itcanbededucedfromthe-Pcurve,surfacecoveragevsgaspressureatadsorptionequilibrium.§3.3.2Relationshipofadsorptionheatandactivationenergywithsurfacecoverage•therearethreemaincasesbetweenq,heatofadsorption,and-surfacecoverage1.idealcase:thevalueofqshowsaconstantwithvariedForexample,oxygenonmetalsurface.2.qlinearlydecreasesasincreasesq=qo-3.qdecreaseslogarithmicallyasincreasesq=qo-│ln(1-)│isnottoolarge§3.3.2Relationshipofadsorptionheatandactivationenergywithsurfacecoverageqθ1.Ideacase2.Linearcase3.Logarithmiccase§3.3.2Relationshipofadsorptionheatandactivationenergywithsurfacecoverage•therearemainlytwosituationsofEaandEd,activationenergyofsorptionwithcoverage1.linearcaseEa=Eao+Ed=Edo-2.logarithmicallycaseEa=Eao+’│ln(1-)│Ed=Edo-’│ln(1-)│•atanycertainvalueofcoverage,itisalwayssatisfiedEd=Ea+q§3.3.2RelationshipofadsorptionheatandactivationenergywithsurfacecoverageEd=Ea+q