Ca Doping E ff ect on the Competition of NH 3 − SCR and NH 3 Oxidation Reactions over Vanadium-Based Catalysts - Zheng et al. - 2021 - U

《Ca Doping E ff ect on the Competition of NH 3 − SCR and NH 3 Oxidation Reactions over Vanadium-Based Catalysts - Zheng et al. - 2021 - U》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

pubs.acs.org/JPCCArticleCaDopingEffectontheCompetitionofNH3−SCRandNH3OxidationReactionsoverVanadium-BasedCatalystsYangZheng,YangyangGuo,*JianWang,LeiLuo,andTingyuZhu*CiteThis:J.Phys.Chem.C2021,125,6128−6136ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:TheCapoisoningeffectconstrainsvanadium-basedcatalystsfromfurtherapplicationinhigh-calciumcontentfluegas,andthedeactivationeffectofCaOonV2O5−WO3/TiO2(VWT)andV2O5/TiO2(VT)catalystshasbeeninvestigatedfromanewperspective.AstheNH3selectivecatalyticreduction(NH3−SCR)resultsshowed,theNOconversionat400°Cdeclinedby71.7%forVTandby34.8%forVWTafterCaOdoping,andthedecreaseinNOconversionforNH3−SCRattemperaturesgreaterthan300°CwasmainlycausedbythecompetitionoftheNH3oxidationreaction.ThecharacterizationofcatalystsbyNH3−SCR,XRD,Ramanspectroscopy,H2-TPR,NH3-TPD,andTEMshowedthatthenumberofsurfaceacidsitesdecreasedandthattheoxidationandreductionpropertiesofthecatalystsalldeterioratedafterCaOdoping,whichistheprimaryreasonforthedecreaseinNOconversion.CaOalsoaffectedNH3oxidation,andtheL-NH3adsorbedonCaOfavoredtheNH3oxidationreaction,asDRIFTSshowed.NH3reactionpathwayschangedbyCaOdopingbecauseNH3oxidationbecomesmorecompetitiveattemperaturesgreaterthan300°C.Densityfunctionaltheory(DFT)calculationsconfirmedtheNOformationpathwayonCaO,andthecompetitionmechanismofNH3−SCRandNH3oxidationreactionshasbeendescribed,whichhashardlybeenreported.3171.INTRODUCTIONmaterialsinfluegascanreachashighas1kg/Nm,andthe18SelectivecatalyticreductionwithNH3(NH3−SCR)hasbeendepositionofCaspeciesonSCRcatalystsisinevitable.Liet19widelyusedasaneffectivemethodtocontrolstationarysourceal.systematicallystudiedtheeffectofCapoisoningonaNOemissions.1−4VO/TiO(VT)catalystshavebeenV2O5−WO3/TiO2(VWT)catalystandfoundthatthedopingx252commerciallyappliedfordecadesduetotheirhighdeNOofCaspeciesnotonlydecreasestheBETsurfacearea,thexamountofsurfacechemisorbedoxygenandtheV5+reducibilityactivity,excellentN2selectivity,goodthermalstability,andstrongtolerancetoSO.5−7However,theiractivitygraduallybutalsoleadstosomeCaWOformation,causingbulkDownloadedviaUNIVOFNEWMEXICOonMay15,2021at21:04:42(UTC).24decreasesafterlong-termexposuretoflyashcontainingtungstenspeciesandpassivatingsurfaceacidsitesonthe12poisonoussubstancessuchasalkalimetalsoralkaline-earthcatalyst.Wangetal.believedthatCamainlyblockedthemetals,whichconstrainsVTcatalystsfromfurtherapplicationporesofthecatalystsandreducedtheredoxactivityoftheSeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.8−1020insomeindustries,suchascementproduction.catalysts.Nicosiaetal.attributedthedeactivationofVWTThepoisoningeffectsofsomealkalimetals,suchasKandcatalystsbyalkaliandalkaliearthmetalstoCaorKoccupying8,9,11−15Na,onVTcatalystshavebeenextensivelystudied.Itisthenonatomicholesitesofthe(010)V2O5surface,boththegenerallybelievedthatalkalimetaldopingcandecreasetheBrønstedacidandV5+Ositesbeingblocked,whiletheBrønstedacidsiteamount,thespecificsurfacearea,andthebyproductofN2Oabove500°CwasnotinfluencedbytheactiveV5+sitereducibilityoncatalysts,leadingtoareductionpoisoningcompounds.inNH3adsorptionandadecayinreactivitywithNOx.N2isthedesiredproductfortheSCRreaction,whileN2OTherefore,withrespecttotheantialkalipoisoningmodificationbyproductscommonlyexist,especiallyonSCRcatalystswithofNH3−SCRcatalysts,theimprovementinacidityandredoxstrongredoxperformanceorunderhigherreactiontemper-performanceisthemainfocus,andlittleattentionhasbeengiventothechemicalpropertiesoftoxicsubstances.Comparedwithalkalimetals,therearefewstudiesontheReceived:January25,2021alkaliearthmetalCapoisoningeffect.ItiscommonlyacceptedRevised:February23,2021thatCaislesstoxicthanKandNa.16However,theCaPublished:March16,2021poisoningphenomenonisamoreseriousproblemforcementkilnsorcirculatingfluidizedbedboilerswithhigh-calciumcontentcoalburning.TheCaOconcentrationofparticle©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.jpcc.1c006776128J.Phys.Chem.C2021,125,6128−6136

1TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleFigure1.(a)NO/NH3conversions(dottedlineforNH3andsolidlineforNO)and(b)N2Oproduction/N2selectivityintheNH3−SCRreactionoverVWT,VT,Ca-VWT,andCa-VTsamples.Reactioncondition:[NH]=[NO]=500ppm,[O]=5vol%,andGHSV=100000h−1.321,2122atures.Zhangetal.suspectedthatNH3oxidationoftheVWTorVTcatalystwereimpregnatedwithCa(NO3)2competitionwithNH3−SCRwasthemainreasonfortheaqueoussolutionastheCaOprecursor.Afterstirringfor4h,decreaseinN2selectivity,andtheN2selectivitywasimprovedthepoisonedcatalystwasdriedat110°Cfor12handthenduetothereducedredoxactivityafterKpoisoning.Similarly,calcinedat500°Cfor4h.Allofthefinalsampleswereground19Lietal.alsofoundthatdifferentCaspecieshaddifferentandsievedto40−60meshforactivityevaluation.effectsonN2selectivity,whichcorrespondstoNH3oxidationThecatalystspreparedabovewerecharacterizedbyXRD,activity.ApartfromN2O,NH3mayalsobeoxidizedtoNO,Raman,XPS,BET,TEMandHRTEM,H2-TPR,NH3-TPD,21resultinginalowerNOxconversionefficiency.EspeciallyinandinsituDRIFTS,andthetestconditionsaredetailedinthethepresenceofCaO,theNH3conversionefficiencytoNOcanSupportingInformation.reachashighas90%at700−1100°Cunderoxygen-rich2.2.CatalystActivity.Thecatalyticactivitieswere23,24conditions.Comparedwithalkalimetals,thepoisoninginvestigatedbyafixed-bedreactor,thereactiontemperatureeffectofthealkaliearthmetalCaonthecompetitionreactionwas100−400°C,andthefeedstreamconsistedof500ppmofbetweenNH3−SCRandNH3oxidationreactionsisoflessNO,500ppmofNH3,and5vol%O2,withN2balance.Atotal25concernandlacksmechanisticanalysis.Ourpreviousworkof100mgofcatalystwasused,andthetotalflowratewas200studiedtheeffectofcementkilnashoncommercialVWTmLmin−1,withagaseoushourlyspacevelocity(GHSV)ofcatalystsandfoundthattheCaOincementkilnashhada100000h−1.TheoutletsignalsofNO,NO,NH,NO,and232strongpoisingeffectonNOconversions,whiletheCaOH2OweredetectedcontinuouslybyaTensor27FTIRdopingeffectonNH3oxidationduringtheSCRreactionwasspectrometer.Spectrawerecollectedwith16scansatanotinvestigated.resolutionof2cm−1.TheNH-oxidationtestsweresimilarto3ToextensivelyinvestigatetheCaOdopingeffectontheSCRtheNH3−SCRtestsperformedwithoutNO.reaction,freshVWTandVTcatalystsdopedwithCaOwereTheNOandNH3conversionsandN2selectivitycalculationprepared.NOconversionhasbeenevaluated,withN2formulasareshownintheSupportingInformation.selectivitycomparedsimultaneously.NH3oxidationexperi-2.3.ComputationalMethods.TheViennaAbInitio26,27mentswerecarriedouttofurtherinvestigatetheCaOeffectonPackage(VASP5.4.4)wasemployedtoperformallofthethecompetitionofNH3−SCRandNH3oxidationreactions.InDFTcalculationswithinthegeneralizedgradientapproxima-28situdiffusereflectioninfraredFouriertransformspectroscopytion(GGA)usingthePBEformulation.Theprojected29,30(DRIFT)anddensityfunctionaltheory(DFT)calculationsaugmentedwave(PAW)potentialswerechosentowereadoptedtoexplorethepoisoningmechanism.describetheioniccoresandconsidervalenceelectronsusingaplanewavebasissetwithakineticenergycutoffof400eV.2.EXPERIMENTALSECTIONPartialoccupanciesoftheKohn−ShamorbitalswereallowedusingtheGaussiansmearingmethodandawidthof0.05eV.2.1.CatalystPretreatmentandPoisoningProcess.Theelectronicenergywasconsideredself-consistentwhentheTheVWTandVTcatalystswith3wt%V2O5and5wt%energychangewassmallerthan10−5eV.GeometryWO3(whenused)loadingsandcommercialTitaniaP25astheoptimizationwasconsideredconvergentwhentheforcesupportwerepreparedbytheimpregnationmethod.Typically,changewassmallerthan0.02eV/Å.Grimme’sDFT-D3acertainamountofammoniummetavanadateandoxalateormethodology31wasusedtodescribethedispersioninter-ammoniummetatungstatewasdissolvedinthesolutionwithactions.desiredproportions.Then,agivenmassofP25powderwasThedetailedstructuralparametersareshownintheimpregnatedinthissolutionwithstrongstirringfor4h.TheSupportingInformation.obtainedsolutionwasdriedovernightat110°C,followedbycalcinationat500°Cfor4hinair.3.RESULTSANDDISCUSSIONTheCaO-dopedVWT(Ca-VWT)andVT(Ca-VT)catalystswerealsopreparedbytheimpregnationmethod,3.1.CatalystActivity.3.1.1.NH3−SCRTest.TheSCRandtheCa/Vmolarratiowassetto1:1.Briefly,equalamountsperformanceofthecatalystsispresentedinFigure1.TheNO6129https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

2TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleFigure2.NH3oxidationexperimentsperformedon(a)VT,(b)Ca-VT,and(C)CaO(dottedlineforNH3conversionandsolidlineforNOselectivity).Reactioncondition:[NH]=500ppm,[O]=5vol%,andGHSV=100000h−1.32conversiononVWTobviouslymovedtoalowertemperatureconversion,NOselectivityandproductdistributionareshownthanthatonVT.ThehighestNOconversionswere99.3%atinFigures2andS1,andCaOwasadoptedforcomparison.32325°C,89.8%at375°C,72.6%at350°C,and24.3%at300TheNH3oxidation-relatedreactionsareshownbelow:°ConVWT,VT,Ca-VWT,andCa-VT,respectively.CaO3additionhadanobviouspoisoningeffectonNOremoval,and2NH3222+→+ON3HO2(1)theNOconversiononCa-VTdeclinedby72%at300°CcomparedwiththatonVT;theNOconversiononCa-VWT2NH322+→+2ONO3H2O(2)declinedby35%at300°CcomparedwiththatonVWT.TheresultsindicatedthatthepresenceofWinthecatalystcannot5onlywidenthereactiontemperaturewindowandenhancethe2NH32+→+O2NO3H2O2(3)DeNOxefficiencybutalsoimprovetheCapoisoningresistance.AccordingtoFigure2,NH3conversionincreasedwithFromFigure1a,thecompetitionofNH3oxidationgreatlyincreasingtemperature,andtheactivityfollowedthesequencedeactivatedtheNOconversionattemperaturesgreaterthanVT>Ca-VT>CaO.VT,Ca-VTandCaOachievedmaximum300°C.NH3oxidationonCa-VTwasgreatlypromotedNH3conversionsof92.3%,74.5%,and64.1%at400°C,becauseNH3conversionbecame12.8timeshigherthanNOrespectively.ComparingpanelsaandbFigure2,theNOconversionat400°C,showingthatWcandecreasetheextentselectivityincreasedfrom2.38%to30.05%at400°CafteroftheNH3oxidationreaction.BasedontheN2OproductionCaOdoping.Figure2(c)demonstratesthatpureCaOcouldandN2selectivityshowninFigure1b,theN2selectivitiesofcatalyzeNH3oxidation,andtheNOselectivitywas34%at400°C.However,theN2OamountwasgreatlyreducedafterCaOVWT,VT,andCa-VWTweresimilar.WhiletheCa-VTdoping.TheproductdistributionofCa-VTwassimilartothatcatalystwasquitedifferent,theN2selectivitydecreasedfirstofCaO,indicatingthattheNH3oxidationreactionpathwayandthenincreasedslowlyattemperaturesgreaterthan300°C.hadbeenchangedbyCaO.AsthetotalNOconversionrateforCa-VTdecreasedatCombinedwithFigure1,itcanbeconcludedthatthetemperaturesgreaterthan325°C,N2OformationwasdecreaseinNOconversionforNH3−SCRattemperaturesinhibited,whileNOgenerationwasenhanced,indicatingthatgreaterthan300°CismainlycausedbythecompetitionoftheCaOadditioncanalsoaffecttheNH3oxidationreaction.NH3oxidationreaction.CaOadditionimprovedNO3.1.2.NH3OxidationTest.AccordingtoFigure1,theformationandinhibitedN2OformationbyNH3oxidation,competitionbetweenNH3oxidationandtheNH3−SCRcausingNOconversionintheNH3−SCRreactiontogreatlyreactioncanbeaffectedbyCaO,soNH3oxidationwasalsodecreaseathightemperature,whiletheN2selectivitywasevaluatedtoinvestigatetheCaOadditioneffect.TheNH3improved.6130https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

3TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleFigure3.ContributionsoftheSCRreaction,theNSCRreaction,andtheN−NreactiontoNH3conversionduringNOreductionover(a)VTand(b)Ca-VT.ThenonselectivecatalyticreductiontoN2O(NSCR)andthecatalyticoxidationofNH3toNO(N−Nreaction)33simultaneouslyoccurredduringtheNH3−SCRprocess.NH3conversion(δNH3)andNOconversion(δNO)canbedescribedasfollows:δNH3=++δδδSCRNSCRNN−(4)δNO=+−δδδSCRNSCRN−N(5)whereδSCR,δNSCR,andδN−NarethecontributionsoftheSCRreaction,theNSCRreaction,andthecatalyticoxidationofNH3toNO,respectively.Accordingtoreactions4and5,δN−Ncanbecalculatedasfollows:δδNH−NO3δNN−=2(6)Meanwhile,thecontributionsoftheSCRreactionandtheNSCRreactioncanbecalculatedaccordingtotheformationofFigure4.XRDpatternsoftheVWT,Ca-VWT,VT,andCa-VTN2andN2O,respectively.catalysts.AccordingtothecalculatedresultinFigure3,NH3conversionwasobviouslyrestrainedafterCaOdoping,anditsdistributionwasgreatlychanged.FortheNH3−SCRandfoundinRamanspectraandHRTEMimages,asshowninNSCRreactions,thecontributionsgreatlydecreasedforCa-FiguresS3−S4.VT,especiallyathighertemperatures,andtheSCRandNSCRTheNH3−SCRandNH3oxidationexperimentsshownincontributionsat350°Cdecreasedfrom78.6%to32.6%andFigureS5indicatedthatCaWO4hadalmostnoactivity,whilefrom12.9%to6.6%,respectively.WhiletheN−NreactionCaWO4formationcouldbeoneofthereasonsfortheNOcontributionincreasedobviouslyabove300°C,itscontribu-conversiondecreaseonCa-VWT.tionat350°Cincreasedfrom2.1%to19.1%,showingthatthe3.2.2.BETandXPSCharacterization.TheresultsoftheNH3reactionpathwayshadbeenchangedbyCaOdoping,andBETsurfaceareaandporevolumeofthefoursamplesaretheNH3oxidationreactionoccurredmoreeasilythanNH3−showninTable1.WiththedopingofCaO,theporevolumeSCRattemperaturesgreaterthan300°C.showedaslightdecrease,whichindicatedthatCaOcould3.2.CharacterizationoftheCatalysts.3.2.1.XRDcovertheactivesitesonthecatalystsurface.ThecontentofWCharacterization.NormalizedXRDpatternsoftheVWT,onthesurfacedecreasedby18.9%afterCadopingforVWT,Ca-VWT,VT,andCa-VTcatalystsareshowninFigure4.ThewhichmayberelatedtoCaWO4formationaccordingtothedominantanataseTiO2phase(25.3°,37.9°,47.8°,and54.3°)XRDresults.wasobservedinallcatalysts,andbothvanadiumoxideandThesurfacechemisorbedoxygen(O)andtheV5+amountβtungstenoxidewerewelldispersedonTiO2.Withthedopingwereimportantfactorsthatdeterminedtheoxidationand35,36ofCaO,scheelitephaseCaWO4(PDF-ICDD41-1431)reductionpropertiesofthecatalyst,respectively.XPSformedontheCa-VWTsample,showingthatCaspeciescananalysesofO1sandV2pareillustratedintheSupportingreactwithWOxtoformCaWO4,whichleadstoadecreaseinInformation,andtheresultsareshowninTable1.TheOβ/thecontentofCaOandWO3inCa-VWTanddestroysthe(Oα+Oβ)ratiosforVTandVWTbothdecreasedafterCaOsurfaceWOxdispersion,weakeningthestrengtheningeffectofaddition;forVT,theOβ/(Oα+Oβ)ratiodecreasedby18.5%,WOonVWTcatalystactivity.34TheCaWOspecieswasalsoandforVWT,itdecreasedby30.3%.TheV5+/V4+ratio346131https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

4TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleTable1.BETandXPSResultsoftheVWT,Ca-VWT,VT,andCa-VTCatalystssurfaceatomicconcentration(%)sampleS(m2/g)porevolume(cm3/g)VWTiO/(O+O)V5+/V4+BETβαβVWT56.000.421.923.6827.530.330.80Ca-VWT55.500.342.232.9728.510.230.50VT57.180.482.4933.750.270.62Ca-VT57.000.402.7430.950.220.54decreasedby12.9%forVTand37.5%forVWTafterCaOaddition.TheseresultsindicatethattheoxidationandreductionpropertiesrepresentedbytheOβ/(Oα+Oβ)andV5+/V4+ratiosbothdecreasedfortheCa-poisonedcatalysts.AsshowninFigure5,theTi2pXPSspectradisplayedbindingenergies(BE)atapproximately464.8eV(Ti2p1/2)Figure6.H2-TPRcurvesoftheVWT,Ca-VWT,VT,andCa-VTcatalysts.toCa0forCa-VWT.ComparingthecurvesofVWTandVTshowsthatthereductionpeakofVmovedfrom430to456°Candtoapproximately530°CafterCaOdoping,showingthatCaOdopingreducedtheVreducibility,whichwasconsistentFigure5.Ti2pXPSanalysesoftheVWT,Ca-VWT,VT,andCa-VTwiththeV2pXPSresults.catalysts.3.2.4.NH3-TPDCharacterization.NH3adsorptionontheacidsitesofthecatalystisthefirststepoftheNH3−SCRandand459.0eV(Ti2p3/2),bothofwhichcorrespondedtotheNH3oxidationreactions,andtheNH3adsorptionamountand3739characteristicpeaksofanataseTiO2.TheBEoftheTi2pdistributionareimportanttoreactionactivity.TheresultsofpeakfortheVWTcatalystshiftedtoahigherrangethanthattheNH3-TPDanalysesareshowninFigure7andTable2.forVT,suggestinganelectrondensitydecreasearoundtheTiAccordingtothecomparisonofVWTandVT,theinthecatalystsaftertheintroductionofW.Incontrast,theBEintroductionofWincreasedthetotalacidamountfrom303oftheTi2ppeakfortheCa-VWTandCa-VTcatalystsshiftedto365μmol/m2.Inparticular,thenumberofstrongacidsitestoalowerrange,suggestingelectrondensityenrichmentincreasedby45%duetotheintroductionofW.CaOdopingaroundtheTiinthecatalystduetoCaaddition.TheCadecreasedthetotalacidamountfrom365to214μmol/m2fordopingeffectonWwasconsistentwithTi,asillustratedinVWTandfrom303to150μmol/m2forVT.Inparticular,theFigureS8.Therefore,Caactedasanelectrondonorgroup,numberofweakacidsitesdecreasedby67%forVWTand74%whichincreasedtheelectronclouddensityonthecatalystandforVTafterCaOdoping.wasnotconducivetoNH3adsorption.3.2.5.InSituDRIFTSofNH3Desorption.Tostudythe3.2.3.H2-TPRCharacterization.TheredoxabilitiesofthedifferenteffectsofCaOdopingonthestrongandweakacidcatalystswereevaluatedbyH2-TPR,asshowninFigure6.Insitesofthecatalysts,insituDRIFTSofNH3desorptionwastheVWTprofile,thefirstpeakat430°Cwasassignedtotheinvestigated.Figure8showsthedesorptionofNH3from100reductionofV5+toV3+.Thesecondpeakat498°Cwasto500°C.Thebandsatapproximately3700cm−1(3500−assignedtothereductionofW6+toW4+.38Thepeakcentered4000cm−1)couldbeassignedtoO−Hstretching.40Thebandsatapproximately775°Cwassubsequentlycausedbytheat3250and3395cm−1(3100−3400cm−1)representedthehydrogenconsumedbythetransformationofW4+toW0.The-NHstretchingofcoordinatedNH.Thepeaksat1603and3reductionpeaksofV5+toV3+werepresentat456,537,and1223cm−1inFigure8arepresentedthe−NHvibrationof2528°CforVT,Ca-VWT,andCa-VT,respectively.TheNH3adsorbedontheLewisacidsitesgeneratedfromV.ThereductionpeakofW6+toW4+wassuperimposedonthebandsat1426cm−1indicatedNH+onBrønstedacidsites.4reductionpeakofV5+toV3+forCa-VWT.ThepeaksofCa-TheNHadsorptionpeaksbelongingtoBrønstedacids(14263VWTandCa-VTattemperatureshigherthan850°Cwerecm−1)wereobviouslyweakenedwhenthetemperatureassignedtothereductionofCa2+toCa0.Thereductionpeakincreasedfrom100to300°C.TheLewisacidsitesbecameofW4+toW0wassuperimposedonthereductionpeakofCa2+extremelyweakwhenthetemperatureincreasedfrom300to6132https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

5TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleBecausetheCaOsurfaceeasilyabsorbedH2Omolecules,astronginvertedpeakat3500−4000cm−1appearedinFigure8(b).Correspondingly,theL-NH3adsorptionpeakatapproximately1600cm−1overlapswiththedecreasedpeakofHO,resultinginaninvertedpeakat1619cm−1,butthe2overallpeakintensitywaspositive.Thestrongadsorptionpeakat3100−3400cm−1couldalsoprovetheadsorptionofL-NH.3TheL-NH3andB-NH3adsorptionsitesat1199and1439cm−1providedbyVOshiftedslightlyforCa-VT,theB-NH253adsorptionsitesat1439cm−1becameweaker,andthecorrespondingweakacidcontentobservedinNH3-TPDdecreased.Inaddition,bandsat1133and1390cm−1appearedafterCaOdoping,representingtheNH3adsorbedonthe41LewisacidsitesgeneratedfromCaO.TheNH3adsorptionpeaksbelongingtoBrønstedacidsat1439cm−1disappearedquicklywhenthetemperatureincreasedfrom100to200°C;thebandsat1133,1199,1390cm−1and3100−3400cm−1,whichbelongedtoLewisacidsites,disappearedwhenthetemperatureincreasedto400°C.AsCaOpossessedabundantLewisacidsitesforNH341adsorption,thedecreaseinthenumberofstrongacidsiteswaslessthanthatofweakacidsitesforCacatalystsaccordingtoFigure7,whilethepeakattributedtothestronglyadsorbedNH3correspondingtoCaOshiftedfromapproximately280to240°C.Additionally,notethattheL-NH3adsorbedonCaOfavoredtheNH3oxidationreactionbutshowednoSCRactivityintheNH3−SCRreaction.Figure7.NH3-TPDcurvesobtainedforthecatalysts.3.3.CaODopingMechanismDiscussion.ToelucidateTable2.AcidSiteAnalysisthereactionmechanismofNH3ontheCaOsurface,DFTcalculationswerecarriedout,andtheresultsareshowninsampleC(μmol/m2)aC(μmol/m2)C(μmol/m2)WSTotalFigure9.Accordingtothecomputationalresults,NH3couldVWT136229365adsorbonsurfaceCaOsites,andpathwayC,representedbyVT145158303theblueline,wasthemostlikelypathway.Inthereaction,theCa-VWT45169214adsorbedNH3wasactivatedbythedissociationofanHatomCa-VT38112150andsubsequentlyreactedwithO2,resultingintheformationofaCW:weakacidsites(100−220°C).CS:strongacidsites(220−350intermediateNH2OandthendissociationofanHatomto°C),andCTotal=CM+CS.generateNHO.AnHatomdissociatedagainfromintermediateNHOtoformfinalproductNO.Thecalculation400°C.AccordingtotheNH3-TPDacidstrengthanalysisinresultsalsoshowedthatthefinalrelativeenergywashigherFigure7,itcanbeconcludedthattheweakacidwasmainlythantheinitialrelativeenergy,indicatingthatthereactionofsuppliedbyBrønstedacidsandthatthestrongacidwasmainlyCaOcatalyzingNH3oxidationtoNOwasendothermic,whichsuppliedbyLewisacids.wasconsistentwiththeresultinFigure2.Figure8.DRIFTSspectraofVT(a)andCa-VT(b)after500ppmofNH3adsorptiontreatedwithN2atdifferenttemperatures.6133https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

6TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticle4.CONCLUSIONThedeactivationeffectofCaOonVWTandVTcatalystsforNH3−SCRhasbeeninvestigated.TheNH3−SCRtestshowsthattheNOconversiondeclinedby71.7%and34.8%at400°CafterCaOdopingforVTandVWT,respectively.TheNH3oxidationtestshowedthatN2Oformationwasinhibited,whileNOgenerationwasenhancedforCa-VTattemperaturesgreaterthan300°C.ThedecreaseinNOconversionforNH3−SCRattemperaturesgreaterthan300°CismainlycausedbythecompetitionoftheNH3oxidationreaction.ThecharacterizationofcatalystsbyBETshowedthattheporevolumeslightlydecreasedafterCaOdoping,andXRD,RamanspectroscopyandTEMrevealedCaWO4formationonCa-VWT,weakeningthepromotionaleffectofWO3onVWTcatalystactivity.TheO/(O+O)ratioandV5+/V4+ratioβαβFigure9.EnergyprofileandoptimizedstructuresofintermediatesdeterminedbyXPSindicatedthattheoxidationandreductionandproductsinNH3oxidationprocessonCaO/V2O5(pathwaysA,propertiesofthecatalystsbothdecreasedfortheCa-poisonedB,andCarerepresentedbyblack,red,andbluelines,respectively.).catalysts.TheH2-TPRresultsverifiedthatVreducibilitywasreducedafterCaOdoping.NH3-TPDshowsthatCaOTheE-RmechanismwasfurtherprovenbytheDRIFTSdecreasedthetotalacidamountby16.7%forCa-VWTandspectraofVTandCa-VTaftertheadsorptionofdifferent30.1%forCa-VT.Thedecreaseinthenumberofstrongacidatmospheresat250°Cfor15min,asillustratedinFigureS10.siteswaslessthanthatofweakacidsitesforCa-dopedThus,forV2O5activespecies,theNH3−SCRreactionfollowedcatalysts,andtheL-NH3adsorbedonCaOfavoredtheNH342,43theclassicalTopsøemechanism.AfterCadopingontheoxidationreaction,asDRIFTSshowed.catalysts,theacidityandredoxactivityofthecatalystbothTheNH3reactionpathwayswerechangedbyCaOdoping,decreased,andNH3adsorptionandtheredoxreactionandNH3oxidationbecamemorecompetitiveattemperaturesweakened,causingadecreaseinNOconversion.greaterthan300°C.DFTcalculationsconfirmedthattheNOForVTorVWTcatalysts,NH3adsorbedonV2O5toformformationpathwayonCaOfollowsNH3(ads.)→NH2→[NH2]species,whichcouldbefurtheroxidizedto[NH]NH2O→NHO→NO,andthecompetitionmechanismofspeciesbythesubtractionofahydrogenatom,andthen,theNH3−SCRandNH3oxidationreactionshasbeendescribed.[NH]speciescouldcombinetoformN2H2speciesandcould44generateN2OorN2+H2O,asillustratedinFigure10.■ASSOCIATEDCONTENTTherefore,N2OisthemainbyproductofNH3oxidationover*sıSupportingInformationVTandVWTcatalysts,asshowninFigure2.TheSupportingInformationisavailablefreeofchargeathttps://pubs.acs.org/doi/10.1021/acs.jpcc.1c00677.Experimentaldetails,RamanspectraandTEMimagesofthecatalysts,NH3oxidationtestsofVWTandCa-VWT,NH3−SCRandNH3oxidationtestsofCaWO4,andinsituDRIFTofNH3andNOadsorptiononcatalysts(PDF)■AUTHORINFORMATIONCorrespondingAuthorsYangyangGuo−CASKeyLaboratoryofGreenProcessandEngineering,InstituteofProcessEngineering,InnovationFigure10.CompetitionmechanismofNH3−SCRandNH3oxidationAcademyforGreenManufacture,ChineseAcademyofreactionsoverCa-dopedvanadium-basedcatalysts.Sciences,Beijing100190,China;orcid.org/0000-0002-8584-6210;Email:yyguo@ipe.ac.cnFortheCaO-dopedVWTandVTcatalysts,competitionTingyuZhu−CASKeyLaboratoryofGreenProcessandbetweentheNH3−SCRandNH3oxidationreactionschanges,Engineering,InstituteofProcessEngineering,InnovationandtheoxidationpathwayofNH3includesbothV2O5-drivenAcademyforGreenManufacture,ChineseAcademyofandCaO-drivenpathways.TheV2O5-drivenpathwayistheSciences,Beijing100190,China;CenterforExcellenceinsameasthatoffreshcatalysts,althoughitsactivitydecreasedRegionalAtmosphericEnvironment,InstituteofUrbanduetothereductioninredoxactivitybyCaO.FortheCaO-Environment,ChineseAcademyofSciences,Xiamen361021,drivenpathway,CaOfavoredthestrongadsorptionofNH3,China;Phone:+86-10-82544821;Email:tyzhu@ipe.ac.cnandNH3wasoxidizedbyCaOaccordingtothepathwayNH3(ads.)→NH2→NH2O→NHO→NO,andtheAuthorsreactionbyproductsaremainlyNO,asshowninFigure2.TheYangZheng−CASKeyLaboratoryofGreenProcessandCaOdopingeffectontheNH3oxidationreactioncouldbeEngineering,InstituteofProcessEngineering,InnovationanotherimportantreasonfortheNOconversiondecrease,AcademyforGreenManufacture,ChineseAcademyofwhichhashardlybeenreported.Sciences,Beijing100190,China;UniversityofChinese6134https://dx.doi.org/10.1021/acs.jpcc.1c00677J.Phys.Chem.C2021,125,6128−6136

7TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleAcademyofSciences,Beijing100049,China;orcid.org/(11)Zhang,J.;Huang,Z.;Du,Y.;Wu,X.;Shen,H.;Jing,G.Alkali-0000-0002-9723-5687Poisoning-ResistantFe2O3/MoO3/TiO2CatalystfortheSelectiveJianWang−CASKeyLaboratoryofGreenProcessandReductionofNObyNH3:TheRoleoftheMoO3SafetyBufferinEngineering,InstituteofProcessEngineering,InnovationProtectingSurfaceActiveSites.Environ.Sci.Technol.2020,54,595−AcademyforGreenManufacture,ChineseAcademyof603.(12)Wang,D.;Luo,J.;Yang,Q.;Yan,J.;Zhang,K.;Zhang,W.;Sciences,Beijing100190,China;orcid.org/0000-0002-Peng,Y.;Li,J.;Crittenden,J.DeactivationMechanismofMulti-0315-5257poisonsinCementFurnaceFlueGasonSelectiveCatalyticReductionLeiLuo−CASKeyLaboratoryofGreenProcessandCatalysts.Environ.Sci.Technol.2019,53,6937−6944.Engineering,InstituteofProcessEngineering,Innovation(13)Xiang,J.;Du,X.;Wan,Y.;Chen,Y.;Ran,J.;Zhang,L.Alkali-AcademyforGreenManufacture,ChineseAcademyofDrivenActiveSiteShiftofFastSCRwithNH3onV2O5−WO3/TiO2Sciences,Beijing100190,ChinaCatalystViaaNovelEley−RidealMechanism.Catal.Sci.Technol.Completecontactinformationisavailableat:2019,9,6085−6091.https://pubs.acs.org/10.1021/acs.jpcc.1c00677(14)Wang,X.;Cong,Q.;Chen,L.;Shi,Y.;Shi,Y.;Li,S.;Li,W.TheAlkaliResistanceofCunbtiCatalystforSelectiveReductionofNObyNH3:AComparativeInvestigationwithVWTiCatalyst.Appl.Catal.,NotesB2019,246,166−179.Theauthorsdeclarenocompetingfinancialinterest.(15)Liu,S.;Guo,R.;Sun,X.;Liu,J.;Pan,W.;Shi,X.;Wang,Z.;Liu,X.;Qin,H.SelectiveCatalyticReductionofNOxoverCe/TiZrOx■ACKNOWLEDGMENTSCatalyst:ThePromotedKResistancebyTiZrOxSupport.Mol.Catal.ThisresearchwasfinanciallysupportedbytheNationalKey2019,462,19−27.ResearchandDevelopmentProgramofChina(16)Zhu,N.;Shan,W.;Shan,Y.;Du,J.;Lian,Z.;Zhang,Y.;He,H.,[2017YFC021080401],theNationalScienceFoundationofEffectsofAlkaliandAlkalineEarthMetalsonCu-SSZ-39CatalystforChina[51778600],DepartmentofScienceandTechnologyoftheSelectiveCatalyticReductionofNOxwithNH3.Chem.Eng.J.HebeiProvince[19273715D],andtheNationalEngineering2020,388.LaboratoryforFlueGasPollutantsControlTechnologyand(17)Fu,S.;Song,Q.;Yao,Q.StudyontheCatalysisofCaCO3intheSNCRDeNOxProcessforCementKilns.Chem.Eng.J.2015,262,Equipment[NEL-KF-2019017].9−17.■(18)Wang,X.B.;Zhou,J.;Wang,J.;Ding,A.F.;Gui,K.T.;REFERENCESThomas,H.R.TheEffectofDifferentCaPrecursorsontheActivity(1)Zhu,W.;Tang,X.;Gao,F.;Yi,H.;Zhang,R.;Wang,J.;Yang,C.;ofManganeseandCeriumOxidesSupportedonTiO2forNONi,S.TheEffectofNon-SelectiveOxidationontheMn2Co1OxAbatement.React.Kinet.,Mech.Catal.2020,129,153−164.CatalystsforNH3-SCR:PositiveandNon-Positive.Chem.Eng.J.(19)Li,X.;Li,X.;Yang,R.T.;Mo,J.;Li,J.;Hao,J.ThePoisoning2020,385,123797−123807.EffectsofCalciumonV2O5-WO3/TiO2CatalystfortheSCR(2)Tan,W.;Wang,J.;Li,L.;Liu,A.;Song,G.;Guo,K.;Luo,Y.;Reaction:ComparisonofDifferentFormsofCalcium.Mol.Catal.Liu,F.;Gao,F.;Dong,L.GasPhaseSulfationofCeria-ZirconiaSolid2017,434,16−24.SolutionsforGeneratingHighlyEfficientandSO2ResistantNH3-(20)Kröcher,O.;Elsener,M.ChemicalDeactivationofV2O5/SCRCatalystsforNORemoval.J.Hazard.Mater.2020,388,WO3−TiO2SCRCatalystsbyAdditivesandImpuritiesfromFuels,121729−121729.LubricationOils,andUreaSolution.Appl.Catal.,B2008,77,215−(3)Yang,J.;Li,M.;Guo,Y.SpatiallyNanoconfinedArchitectures:A227.PromisingDesignforSelectiveCatalyticReductionofNOx.(21)Kong,M.;Liu,Q.;Jiang,L.;Tong,W.;Yang,J.;Ren,S.;Li,J.;ChemCatChem2020,12,5599−5610.+Tian,Y.KDeactivationofV2O5-WO3/TiO2CatalystDuring(4)Zhan,S.;Zhang,H.;Zhang,Y.;Shi,Q.;Li,Y.;Li,X.EfficientSelectiveCatalyticReductionofNOwithNH3:EffectofVanadiumNH3-SCRRemovalofNOxwithHighlyOrderedMesoporousContent.Chem.Eng.J.2019,370,518−526.WO3(x)-CeO2atLowTemperatures.Appl.Catal.,B2017,203,(22)Zhang,S.;Liu,S.;Hu,W.;Zhu,X.;Qu,R.;Wu,W.;Zheng,C.;199−209.Gao,X.NewInsightintoAlkaliResistanceandLowTemperature(5)Zhu,N.;Shan,W.;Lian,Z.;Zhang,Y.;Liu,K.;He,H.AActivationonVanadia-TitaniaCatalystsforSelectiveCatalyticSuperiorFe-V-TiCatalystwithHighActivityandSO2ResistanceforReductionofNO.Appl.Surf.Sci.2019,466,99−109.theSelectiveCatalyticReductionofNOxwithNH3.J.Hazard.Mater.(23)Zhang,Y.N.;Wang,Y.L.;Cui,S.P.;Wang,W.;Zhao,Y.N.2020,382,120970−120979.(6)Wang,H.;Ning,P.;Zhang,Y.;Ma,Y.;Wang,J.;Wang,L.;EffectofCaOonSNCRReactionwithNH3asReducingAgent.Mater.Sci.Forum2016,847,249−255.Zhang,Q.HighlyEfficientWO3-FeOxCatalystsSynthesizedUsinga(24)Xu,M.;Wu,Y.;Wu,H.;Ouyang,H.;Lu,Q.CatalyticNovelSolvent-FreeMethodforNH3-SCR.J.Hazard.Mater.2020,388,121812−121812.OxidationofNH3overCirculatingAshintheSelectiveNon-Catalytic(7)Liang,Q.;Li,J.;He,H.;Yue,T.;Tong,L.EffectsofSOandReductionProcessDuringCirculatingFluidizedBedCombustion.2H2OonLow-TemperatureNOConversionoverF-V2O5-WO3/TiO2Fuel2020,271,117546−117553.Catalysts.J.Environ.Sci.2020,90,253−261.(25)Guo,Y.;Luo,L.;Mu,B.;Wang,J.;Zhu,T.Ash-andAlkali-(8)Fang,Q.;Zhu,B.;Sun,Y.;Song,W.;Xu,M.EffectsofAlkaliPoisoningMechanismsforCommercialVanadium-Titanic-BasedMetalPoisoningandCobaltModificationontheNH3AdsorptionCatalysts.Ind.Eng.Chem.Res.2019,58,22418−22426.Behavi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