促进钾盐为水煤气变换反应的钌_交流催化剂

co变换催化剂

PromotedpotassiumsaltsbasedRu/ACcatalystsforwatergasshift

reaction

YajuanMaa,BingLiua, ,MengmengJinga,RenyuanZhangb,JunyuChena,YuhuaZhanga,JinlinLia,

KeyLaboratoryofCatalysisandMaterialsSciencesoftheStateEthnicAffairsCommission&MinistryofEducation,CollegeofChemistryandMaterialScience,South-CentralUniversityforNationalities,Wuhan430074,PRChinab

CollegeofChemistryandChemicalEngineering,XiaMenUniversity,XiaMen361005,PRChina

a

highlights

TheadditionofpotassiumsaltimprovedtheRu/ACactivityoverWGSreaction. COconversionincreasedfrom13.6%forRu/ACto56.1%forK2CO3-Ru/ACat300°C. Theincreaseoftheactivitywasduetothereductiontemperatureofthecatalyst. Thehighhygroscopicabilityofthesaltalsoincreasedthecatalystactivity.

articleinfoabstract

Inthiswork,wehavepreparedseveralkindsofpotassiumsaltsdopedRu/ACcatalystsandsystematicallystudiedtheircatalyticactivitiestowardswater–gasshift(WGS)reaction.ActivitytestingindicatedthatK2CO3dopedRu/ACcatalyst(Ru-K2CO3/AC)showedhighercatalyticperformancethanKOHandKOAcdopedRu/ACcatalysts,methaneselectivitydecreasedmostafterdopingKOH.AlthoughtheparticlesizeofRunanoparticlesinRu-K2CO3/ACcatalystwaslargerthanthatoftheparentRu/ACcatalyst,H2-TPRindicatedthatRuOxwasreducedatmuchlowertemperature,suggestingaweakerinteractionbetweenRuOxandthesurfacefunctionalgroupofactivecarbonafterthedopingofK2CO3.Thus,Runanoparticlesinteractedstrongerwiththereactionmolecules(COandH2O),leadingahighercatalyticactivity.Inaddi-tion,thedopingofK2CO3onthesurfaceofRu/ACcatalystalsoincreasedtheconcentrationofwateraroundRuactivesiteduetothehygroscopicability.Interestingly,itwasalsofoundthatthepreparedmethodalsogreatlyaffectedthecatalystactivity.Iftheactivecarbonwas rstlycoatedwithK2CO3,fol-loweddepositionofRumetalnanoparticles,(calledRu/K2CO3-ACcatalyst),theactivitydecreasedremarkablyascomparedtoRu-K2CO3/AC.ThelowcatalyticactivityofRu/K2CO3-ACwasmainlyduetotheaggregationofRunanoparticles.

Ó2015ElsevierB.V.Allrightsreserved.

Articlehistory:

Received27June2015

Receivedinrevisedform19October2015Accepted26October2015

Availableonline14November2015Keywords:

Water–gas-shiftreactionRutheniumbasedcatalystsPotassiumsaltsDoping

1.Introduction

Thewater–gasshift(WGS)reaction(CO+H2O?H2+CO2,DH=41.2kJmolÀ1)isoneofthemostfundamentalreactionsfortheremovalofCOandproductionofhighpurityH2fromsyngas.Thisreactioncanbeusedfortheupgradingofthereformedgasinfuelcells,asitiseffectivetoreduceCOtoaverylowcontent,avoidingthepoisoningofPtelectrodes[1].Inaddition,WGSreac-tionhasalsoplayedakeyroleinadjustingtheH2/COratioforFis-cher–Tropsch(FT)processes[2]andprovidinghydrogen-richCorrespondingauthors.Tel./fax:+862767842572.

E-mailaddresses:liubing@(B.Liu),lijl@(J.Li).

/10.1016/j.cej.2015.10.119

1385-8947/Ó2015ElsevierB.V.Allrightsreserved.

streamsforfuelcells[3].Industrially,inordertoproducehighpur-ityH2atthehighestpossibleCOconversion,two-stagemethodisappliedinWGSreaction:ahightemperatureshiftreactionoperat-ingat300–450°CbytheuseofFe-basedcatalysts(e.g.,Fe2O3/Cr2O3)andalowtemperatureshiftreactionoperatingat200–270°CbytheuseofCu-basedcatalysts(e.g.,Cu/ZnO/Al2O3)[4].However,someproblemsstillremaininthecomicaltwo-stageWGScatalysts.ThecatalyticactivityofFe2O3/Cr2O3isrelativelowatlowreactiontemperatures.Furthermore,theFe2O3/Cr2O3containsabout1–2wt.%hexavalentchromium(Cr6+),whichishighlytoxictohumans,organismsandtheenvironment[5].TheCu/ZnO/Al2O3catalystsdeactivatedatanoxidizingatmosphere[6].Therefore,theneedforthedevelopmentofhighactiveWGScatalystsstillremainsanimportantgoalinWGSreactions.

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156Y.Maetal./ChemicalEngineeringJournal287(2016)155–161

SomenoblemetalsespeciallyPt,Pd,AuandRucatalystshavebeenusedasalternativesforWGSreactionstocircumventthenamedlimitationsofthecommercialWGScatalysts[7–10].Amongthem,paredwithPtcatalysts,Rucatalystsaremuchcheaper,thustheuseofRucatalystswillbepromisingasaneco-nomicalwayintheindustrialWGSreactions.Infact,homogeneousRucatalystshavebeenusedforWGSreactionsforalongtime,whichcanbeoperatedatlowtemperature,achievinghighequilib-riumconversion.However,WGSreactionoverhomogeneouscata-lystswasmainlycarriedoutunderhighCOpressures(>10bar)ineetal.preparedahomogeneousRu3(CO)12catalystandapplieditinWGSreaction.Aratioof150molofH2producedpermoleofRu3(CO)12over30daysbythissystem[11].Comparedwiththehomogeneouscat-alysts,theRubasedheterogeneousWGScatalystssometimesshowedevenmuchhigherhighcatalyticactivitytowardsWGSreaction[12].Forexample,Shindeetal.[13]preparedhighlyactiveandcokeresistantZr0.93Ru0.05O2catalyst,andapplieditinWGSreaction.Thiscatalystcanafforded99%conversionofCOwith100%H2selectivitybelow290°C.AlackofCOmethanationactivityisattributedtotheionicnatureofRuspecies(Ru4+).

Inrecentyears,someresearchersfoundthatthecatalystactiv-ityofheterogeneouscatalystsoverWGSreactioncouldbeimprovedbythemodi cationofthecatalystsurfacewithalkaliadditives,especiallypotassiumsalts[14–17].Forexample,thecat-alyticactivitiesofseveralkindsofPtcatalystscanbeenhancedbythedopingofNa+,K+,Li+,Rb+,Cs+[16,18].ThemainroleofalkalicationswasclaimedthatitcanweakentheC–Hbondofformate,thusfacilitatingCO2desorptionfromthecatalystsurface[15].ItisalsobelievedthattheintroductionofalkaligeneratednewactivesitessuchasPt–alkali–Ox(OH)yclustertopromotetheWGSreac-tion[18].Wateriseasilydissociatedontheseclusterstoafford–OH,whichisthenreactedwithCOatlowtemperatures.TheactiveenergyofwaterdissociationishigherthanotherstepsinWGSreaction[19].TheformationofPt–alkali–Ox(OH)yclustercanlowertheactiveenergyofwaterdissociationstep.Besidestheimprove-mentofthecatalystactivity,thealkaliadditionwasalsofoundtoimprovethePt@SiO2catalyststabilityincyclicoperations[20].Inourpreviouswork,wehavealsofoundthatthecatalyticactivityofRunanoparticlessupportedonactivecarbon(Ru/AC)wasalsogreatlyenhancedbytheadditionofK2CO3[21].AlthoughthehighercatalyticactivityofRu/ACafterthedopingofK2CO3wasobtained,manyissuesarestilldeservedtostudysuchasthesourceofpotassiumsaltsandthecatalystpreparedmethodsontheactiv-ityofRu/ACcatalyst,aswellasthedeepinsightintothedifferencesinthesecatalyststowardWGSreaction.Herein,wehavepreparedseveralkindsofpotassiumsaltsdopedRu/ACcatalystsbytwodif-ferentmethodsandsystematicallystudiedtheircatalyticactivitiestowardswater–gasshift(WGS)reaction.Moreimportantly,thedifferenceinthecatalyticactivitiesoftheseas-preparedcatalystswasalsotriedtobeunderstoodbyvarioustechnologies.

2.Experimentalsection2.1.Materialsandmethod

30wt.%HNO3waspurchasedfromAladdinChemicalReagentCo.,Ltd(ShanghaiChina).Ethanol(99.5%),K2CO3(99.9%)KOAc(99.9%),KOH(99.9%)andethyleneglycol(EG)werepurchasedfromSinopharmChemicalReagentCo.,Ltd(ShanghaiChina).Ru(NO)(NO3)3(10wt.%)andactivecarbon(AC)werepurchasedfromAlfaAesarchemicalsCo.,Ltd(Shanghai,China).AllofthechemicalreagentsexceptACwereusedasreceivedwithoutfurtherpuri cation.

2.2.Catalystsynthesis

Ru/ACcatalystwaspreparedaccordingtothemethodasdescribedinourpreviousworkwithaslightmodi cation[21].ACwas rstlytreatedwith30wt.%HNO3at90°Cfor4h.ForthepreparationofRu/ACcatalyst,Ru(NO)(NO3)3(0.2g,Ru:10wt.%)inEGsolution(30mL)andAC(1g)waswelladdedanddispersedinthesolutionwithultrasonic-assistancefor30min.Then,themixturewasstirredat160°Cfor6h.Aftercoolingtoroomtemper-ature,themixturewas ltrated,washedseveraltimesbyethanolanddriedatroomtemperature.TheRucontentwas2wt.%inthe-oryandthecatalystwasnamedasRu/AC.

Thealkalidopingcatalystswerepreparedbytwodifferentmethods.Onmethodisthepost-modi cationoftheas-preparedRu/ACcatalysts.Brie y,theRu/ACcatalyst(1.0g)wasimpregnatedwithofacertainamountofaqueousK2CO3for24hatroomtem-perature,anddriedat160°Cfor4h.ThecatalystwasabbreviatedasRu-K2CO3/AC.Methodforthemodi cationoftheRu/ACcatalystwithKOHandKOAcwasthesameasthepreparationofRu-K2CO3/AC,whichwerenamedasRu-KOH/ACandRu-KOAc/AC,respec-tively.Ineachcase,themolratioofRutoKwassettobe1:10.ThecontentofKwas7.6%,7.4%and7.3%forRu-KOH/AC,Ru-K2CO3/ACandRu-KOAc/ACcatalystsdetectedbyICP.ThecontentofRuwasabout1.8%forthethreecatalystsdetectedbyICP.

Ontheotherhand,thesupportwas rsttreatedwithK2CO3beforethedepositionofRunanoparticles.ACwas rstimpreg-natedwiththesameamountofK2CO3,andthendriedat160°Cfor4h.Then,theK2CO3treatedACwasaddedinRu(NO(NO3)3EGsolution,andotherstepswerethesamefortheRu/ACcatalystasdescribedabove.Theas-preparedcatalystwasdenotedasRu/K2CO3-AC.

2.3.Catalystcharacterization

Fouriertransforminfrared(FT-IR)spectraofthesampleswerecollectedusingaNicoletFouriertransforminfraredspectrometer(NEXUS470).Fortheanalyses,thepowdersamplesweremixedwithpotassiumbromide(KBr)powderandpressedintodiskswithoutanypretreatment.

H2-temperatureprocessedreduction(H2-TPR)wasexperimentswerecarriedoutusingAMI-200fromZetonAltamiraCompany.Thesample(50mg)inaquartzreactorwaspurgedwith30ml/minArwhileheatingataramprateof10°/minto150°Candmain-tainingthattemperaturefor1htoremovetracesofwater.Aftercoolingto50°thesamplewasreducedina owof10vol.%H2/Ar(30ml/min)whileheatingfrom50°to500°atarateof10°/min.BETsurfaceareaofthepreparedmaterialswasdeterminedbyphysisorptionofN2at77KbyusingaquantachromeAutosorb-1-C-MSinstrument.ThetotalporevolumesandtheaverageporesizeswereobtainedbyusingtheBarrett–Joyner–Halendamethod.Transmissionelectronmicroscopy(TEM)imagesofthecatalystsampleswereobtainedwithaFEITecnaiG20instrument.Thesam-pleswerepreparedbydirectlysuspendingthecatalystinethanolwithultrasonictreatment.Acoppermicroscopegridcoveredwithperforatedcarbonwasdippedintothesolutionandthendried.TheICP-AESanalysiswasperformedonOptima4300DV,Perkine-ElmertodeterminethecontentofRuandKintheiongelcatalysts.

2.4.TypicalprocedureforWGSreaction

Theactivityofallpreparedcatalystswasevaluatedinacontin-uoustestrigwithon-lineanalysisoftheef uentgasesviaAgilentMicroGC3000AGC.Inatypicalrun,0.4goftheas-preparedcata-lystwasplacedinastainless-steeltubular xedbedreactorandcontactedwithacontinuousgas ow(40mL/min)consistingof

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Y.Maetal./ChemicalEngineeringJournal287(2016)155–161157

60%N2,30%H2Oand10%COatatmosphere.Thecatalystwasini-tiallyheatedinCO/N2atmospherefromroomtemperatureto300°Cbeforesteamwasaddedtothemixture.Thereactionwas rstlyconductedat300°Cforabout5htoobtainstablecatalyticactivitybeforethetemperaturewasdecreasedupto200°Ctostudytheeffectoftemperatureoncatalystactivity.

3.Resultsanddiscussion

3.1.EffectsofpotassiumadditiononactivityforWGSreactionInitially,theRu/ACcatalyststreatedwithdifferentkindsofpotassiumsalts(KOH,K2CO3,KOAc)werestudiedforWGSreac-tions.COconversionsatdifferentreactiontemperatureoverthesecatalystsweredepictedinFig.1.Thereactionwas rstlyconductedat300°Cforabout5htoobtainstablecatalyticactivitybeforethetemperaturewasdecreasedupto200°Ctostudytheeffectoftem-peratureoncatalystactivity.Theactivitytestwaskeptforatleast2hateverytemperature.Noobviouslydeactivationwasfoundatourexperimentcondition.Forallofthecatalysts,paredwiththeparentRu/ACcatalyst,thethreekindsofpotassiumsaltdopedRu/ACcat-alystsshowedanenhancedactivityatthesamereactiontempera-ture.TheseresultsindicatedthatthedopingofalkaliimprovedtheactivityofRu/ACcatalysttowardsWGSreaction.Atlowreactiontemperaturebelow220°C,thesealkalidopedRu/ACcatalystsexhibitedonlyamarginalincreaseinCOconversion.However,thesepotassiumdopedRu/ACcatalystsshowedmuchhighercat-alyticactivitythantheparentRu/ACcatalystbeyond220°C.Itisalsonotedthatthekindofpotassiumsaltshowedagreatin uenceontheactivityofthesealkalidopedRu/ACcatalysts.Ru-K2CO3/ACandRu-KOAc/ACcatalystsdemonstratedmuchhigherWGSactiv-itythanRu-KOH/ACcatalystwiththesameratioofRutoKof1:10.Forinstance,COconversionwasattainedin44.8%withRu-KOH/ACcatalystat300°C,whilethosereached51.8%and56.1%underthesamereactionconditionsfortheRu-KOAc/ACandRu-K2CO3/AC,respectively.Thereasonsofthedifferentcatalyticactivityofthesecatalystswillbeillustratedinthefollowingpart.ThemethaneselectivityovervariouscatalystsasafunctionofreactiontemperaturewasshowninFig.S1.Therewasnomethaneinproductionbelow275°Cforallthetestedcatalystsinour

experimentcondition.Themethaneselectivityincreasedwiththeincreaseofthereactiontemperature,butstilllessthan2%at300°C.TheadditionofKOHdecreasedthemethaneselectivity,forinstance,theSCH4decreasedfrom1.7%to0.7%afterKOHdopingat300°C.Theadditionofpotassiumsalt(K2CO3,KOAc)didn’thaveanobviouseffectontheselectivityofmethaneatourtestedcondition.

ThehighestTOFobtainedfromourcatalystswas76hÀ1for2%Ru-K2CO3/ACat300°C.AsshowninTable1,theWGSactivitywasmuchhigherthanthe3%Ru-K2CO3/SiO2catalystsinRef.[34],whichTOFwas35hÀ1.OurcatalystWGSactivitywasalittlelowerthanthePt/KOH/Al2O3catalyst22,however,theactivitywastestedatmuchhigherpressure(5bar)intheirworkthanours(atmosphere).

Fig.2showstheTEMimagesofRu/ACandK2CO3-Ru/ACcatalysts.AsobservedinFig.2,Runanoparticleswereuniformlydistributedonthesupportsofthetwokindsofcatalysts,andnodistinctaggregationofRunanoparticleswasobservedintheTEMimagesofthetwocatalysts.TheparticlessizedistributionofRunanoparticleswasalsoestimatedbythemeasurementoftheRuparticlesfromthegivenareaoftheTEMimage.TEManalysispro-videddirectinformationonthesizeoftheRunanoparticlesintherangefrom1to5nm,andtheaverageofparticlesizewasesti-matedtobe2.4nm.AfterdopingwithK2CO3,theaverageparticlesizeofRunanoparticlesincreasedto3.2nmforK2CO3-Ru/ACcat-alyst,indicatingthedopingofK2CO3ontheactivecarboncausedthegrowthofRunanoparticles.Similarphenomenonwasalsoobservedbyotherresearchers[22].Kuscheandco-workersfoundthatthesizeofPtnanoparticlesinPt/Al2O3catalystincreasedfrom3.2nmto4.4nmafterdopingAl2O3withKOH.Xiongetal.foundalkalipromoters(alkali:Li,Na,KorCs)alsoledtoanincreaseincrystallitesizeoftheironoxideinFe/CNTcatalyst[23].ThepossiblereasonfortheslightincreaseoftheRunanoparticlessizewasthattheas-preparedRu/ACcatalystafterthedopingofK2CO3wassubjectedtobeheatedat160°C,whichresultedinthemove-mentofRunanoparticles,leadingtoagrowingsizeofRunanoparticles.

BETmeasurementswereusedtocharacterizethetexturestruc-tureofsupportandcatalysts,andtheresultsareshowninTable2andFig.S2.TheaverageporediameteroftheRu/ACandK2CO3-Ru/ACcatalystswasclosetothesupportactivecarbon.However,thesurfaceareaandporevolumedecreasedofthetwocatalystsweremuchlowerthanthesupport,indicatingRuorpotassiumsaltentersintotheporecanalofactivatedcarbon.Interesting,theBETsurfaceandporevolumeoftheK2CO3-Ru/ACcatalystshowedaveryslightdecreaseascomparedwithRu/ACcatalyst,whichfur-therindicatedthatthepotassiumsalt(K2CO3)wasdopedonthesurfaceoftheRu/ACcatalyst.

H2-TPRmeasurementsareusedtoprobethenatureandthereducibilityofthecatalysts.TheTPRpro lesoftheRu/ACcatalystandthepotassiumdopedRu/ACcatalystsaredepictedinFig.3.AlthoughRunanoparticlesareinitsmetallicformunderreducingpreparationconditions,theRunanoparticlescanbeoxidizedtohighvalencestatewhenexposedtooxygenduringstorage[24].XPSresultscon rmedmetallicRu(0)andRuO2wereco-existedintheRu/ACandRu-K2CO3/ACcatalysts.Twopeakswereclearlyobservedinthereductionpro leofRu/ACcatalystfrom180to

Table1

WGSactivitycomparisonwithliteratures.CatalystsTOF(hÀ1)ReactionconditionReferences2%Ru-K2CO3/AC76T=300°C,P=atmosphereOurworkPt-KOH/Al2O3

95T=230°C,P=5bar

Ref.[22]3%Ru-K2CO3/SiO2

35

T=250°C,P=atmosphere

Ref.[34]

co变换催化剂

Table2

ResultsofN2adsorptionmeasurementsofthecatalysts.CatalystACRu/AC

Ru-K2CO3/AC

Surfacearea(cm2/g)792564558

Porediameter(nm)2.82.83.0

Porevolume(cm3/g)0.5480.3880.384

asprecursor[25].ComparedwiththeTPRpro leoftheRu/ACcat-alyst,the rstreductionpeakofallthepotassiumsaltsdopedRu/ACcatalystsdividedintotwopeaksandshiftedtolowertempera-ture,thesecondreductionpeakwasmuchweaker.Forinstance,thelowtemperaturereductionpeakofRu-K2CO3/ACappearedat93°Cand201°C,whilethosewereobservedat122°Cand247°CforRu-KOAc/AC,100°Cand201°CforRu-KOH/AC,respec-tively.TheH2consumptionofthecatalystsduringH2-TPRexperi-mentwascalculatedbystandardH2pulseexperiment,andtheresultsareshowninTable3.Itonlyneed1mmolH2for50mg2%Ru/ACcatalystduringH2-TPRexperimentifRuwastotallyoxi-dizedintoRuO2.Obviously,theH2consumptionduringH2-TPRexperimentwasmuchlowerthanthecalculateddata,whichindi-catedthatRuwaspartiallyoxidizedduringstorage.TheH2con-sumptionofRu-K2CO3/ACandRu-KOAc/ACwaslargerthanRu-KOH/AC,andallofthemwerelargerthanRu/AC.TheseresultsindicatedthatRuwasfurtheroxidizedafterdopingpotassium,andtheoxidationdegreeofpotassiumsalt(K2CO3,Ru-KOAc)dop-ingcatalystwaslargerthanKOHdopingcatalyst.

TheinteractionbetweentheRuOxnanoparticlesandactivecar-bonwascomparativelyweakandhigherdispersiondegreeofRuparticleleadtolowerreductiontemperature[26].However,iftheactivecarbonwasfunctionalizedbythetreatment

with

Table3

ThepeakpositionandH2consumptioncalculatedfromH2-TPRexperiment.CatalystsRu/AC

Ru-KOH/ACRu-K2CO3/ACRu-KOAc/AC

T(K)Peak–10093122

1

T(K)Peak270201201247

2

T(K)Peak330341339350

3

H2consumption(lmol)27313536

400°Cwithtwomaximumpeaksat270and330°C,respectively.Thesesignalscanbeassignedtothereductionofwell-dispersedRuOxoxidespecies,andsimilarresultswerealsoobservedintheTPRpro lesofRu/c-Al2O3,inwhichalsoRu(NO)(NO3)3wasused

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Y.Maetal./ChemicalEngineeringJournal287(2016)155–161159

HNO3,RuOxstronglyinteractedwiththesurfacefunctionalgroupoftheactivecarbon,andthereductionofRuOxtoRu0particleswasdif cultandreducedatmuchhightemperature[27].ThedecreaseofthereductiontemperatureofRuOxafterthedopingofpotassiumsaltsindicatedthatpotassiumsaltsalsohadthecon-tactwithRuOx,thuscausedaweakerinteractionofRuOxwithsup-portandreducedthereductiontemperatureofRuOx.Evinetal.foundsimilarphenomenonasours,inwhichthereductiontemper-atureofPtoverPt/CeO2catalystsbecamelowerandwiderafterdopingwithalkali(Li,Na,K,Rb,Cs)[28].Therefore,accordingtotheTMEandH2-TPRresults,thedopingofpotassiumsaltontheRu/ACcatalystcausedanincreaseoftheRunanoparticlesize,andthepresenceofpotassiumsaltdecreasedtheinteractionoftheRuOxandthesurfacefunctionalgroupofactivecarbon,whichresultedinalowerreductiontemperatureoftheoxidizedRunanoparticles.Potassiumionsstabilizehighdispersed,oxidizedRuspeciesontheactivatedcarbonsurface,maybeformedanewRu-O-Kactivatedsite.Suchspecies(Na+,K+)havebeenreportedtocatalyzetheWGSreactiononPt/SiO2catalysts[18].

FT-IRspectraofpotassiumsaltsdopedRu/ACcatalystsandtheRu/ACcatalystarerecordedintheregionfrom800to4000cmÀ1.AsshowninFig.4,thestrongbandat1090cmÀ1ispresentinallthesamples,whichisassignedtotheasymmetricandsymmetricvibrationsfromNOÀ3remainedinthesupportAC[29],astheACsupportwasactivatedbyHNO3beforetheloadingofRunanopar-ticles.Thebandat1560cmÀ1intheK2CO3-Ru/ACandKOAc-Ru/ACcatalystsisassignedtot(OCO)asymmetricandsymmetricvibra-tions,whichshouldbecausedbythedopingofK2CO3andKOAcinthecatalysts[30,31].Itisnotedthebandat1630cmÀ1alsoappearinthepotassiumsaltspromotedsamples,whichcanbeassignedtoO–H–Obendingvibrationofthephysicallyadsorbedwater[32].Inaddition,thebroadbandbetween2500and3500cmÀ1inthepotassiumsaltsdopedRu/ACcatalystsisalsocausedbythevibrationsofthephysicallyadsorbedwater,whilethatismuchweakerintheRu/ACcatalyst.TheseresultsindicatedthatthetreatmentofRu/ACcatalystswithpotassiumsaltsenhancedwaterconcentrationinthesurfaceofthecatalysts,

onthealuminasurface,whichincreasedtheavailabilityofH2Oatthecatalyticallyactivesites[24].AccordingtotheresultsobtainedfromFT-IRspectrum,theenhancementofwaterconcen-trationaroundtheactivesitesduetothehygroscopicnatureofthesaltcoatingshouldbetheonereasonofthesigni cantimprove-mentofthecatalyticactivityofalkalidopingRu/ACcatalysts.Inaddition,thedopingofpotassiumsaltonRu/ACcatalystsincreasedalittletheRuOxparticlesize,andtheinteractionbetweenRuOxnanoparticlesandsurfacefunctionalgroupofsupportdecreased.ThelowerinteractionsofthemetalnanoparticleswiththesupportinverselypromotedCOcontactadsorptionontheactivesites(RuOxnanoparticles),affordingahighercatalyticactivity.Watanabeetal.alsocon rmedthissupposebyFT-IRresults.Alkaliadditionwasabletostrengthenthemetal-CObondbyincreasingthebackdona-tionofthemetalelectronsintothe2panti-bondingorbitalofadsorbedCO[33].

parisonoftheactivityofK2CO3promotedRu/ACcatalystspreparedbytwodifferentmethods

TofurtherstudytheeffectofalkalidopedRu/ACcatalystsontheWGSactivity,westudiedthedifferentpreparationmethodsofK2CO3dopingRu/ACcatalystsforWGSreaction.Ru/K2CO3-ACindi-catedthattheACsupportwas rstlytreatedbyK2CO3,followingbytheintroductionofRunanoparticlesonthesupport,whileK2CO3-Ru/ACdenotedasRu/ACwas nallytreatedbyK2CO3.AsshowninFig.5thepreparationmethodgreatlyaffectedthecata-lystactivityinWGSreactioneventhoughtheweightpercentageofKisalmostthesameinthethreecatalysts.TheactivityofK2CO3-Ru/ACwasmuchhigherthanthoseofRu/paredwiththeparentRu/ACcatalyst,aslightimprovementwasobservedovertheRu/K2CO3-ACcatalyst.

Inordertogetsomeinsightsintothehugedifferenceofthecat-alyticactivitycausedbythepreparationmethods,somecharacter-izationofthesecatalystswerestudied.TEMimagesoftheRu/K2CO3-ACcatalystwereshowninFig.6.ItisobservedthatRu

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Journal287(2016)155–161

wasstrongbase.ItisreportedthatRu(NO)(NO3)3existedintheformof[RuNO(NO3)4H2O]Àor[RuNO(NO2)(NO3)2(OH)H2O]Àinsolution[34].Thus,thesenegativeRuprecursorscouldhardlybeadsorbedonthesurfaceoftheK2CO3-treactedAC,andthentheRunanoparticlesinthesolutiontendedtoaggregateandthendepositedintothesupportwithalargeparticleandalowdisper-sion.Withthesameamountoftheactivecomponent,theaggrega-tionofmetalnanoparticlesresultedinalowratioofexposedactivesitestopromotethecatalyticreaction,thusalowercatalyticactiv-itywasobserved.Therefore,theaggregationofmetalnanoparticlesshouldbetheonereasonoftheobservedlowWGSactivityoftheRu/K2CO3-ACcatalyst.4.Conclusions

Inthiswork,aseriesofpotassiumsaltdopedRu/ACcatalystswerepreparedandstudiedtheircatalyticactivityoverWGSreac-tion.Itwasfoundthatthekindofpotassiumsaltsigni cantaffectedtheRu/ACcatalyticactivity.Ru-K2CO3/ACshowedhighercatalyticperformancethanRu-KOAc/ACandRu-KOH/ACcatalysts.TheCOconversiongreatlyincreasedfrom13.6%forRu/ACcatalystto56.1%forK2CO3-Ru/ACcatalystat300°C.Thesigni cantincreaseofthecatalyticactivityoftheK2CO3-Ru/paredwithK2CO3-Ru/ACcatalyst,theRu/K2CO3-ACcatalystgavemuchlowerWGSactiv-ity.ThelowcatalyticactivityofRu/K2CO3-ACwasmainlyduetotheaggregationofRunanoparticles.Acknowledgement

TheProjectwassupportedbyNationalNaturalScienceFounda-tionofChina(No.21206200).AppendixA.Supplementarydata

Supplementarydataassociatedwiththisarticlecanbefound,intheonlineversion,at/10.1016/j.cej.2015.10.119.

Reference

[1]B.Liu,H.Y.Xu,Z.H.Zhang,Platinumbasedcore–shellcatalystsforsourwater–

gasshiftreaction,mun.26(2012)159–163.

[2]G.P.vanderLaan,A.A.C.M.Beenackers,Intrinsickineticsofthegas–solid

Fischer–Tropschandwatergasshiftreactionsoveraprecipitatedironcatalyst,Appl.Catal.AGen.193(2000)39–53.

[3]V.Galvitaa,K.Sundmachera,Cyclicwatergasshiftreactor(CWGS)forcarbon

monoxideremovalfromhydrogenfeedgasforPEMfuelcells,Chem.Eng.J.134(2007)168–174.

[4]F.Meshkani,M.Rezaei,Preparationofmesoporousnanocrystallineironbased

catalystsforhightemperaturewatergasshiftreaction:effectofpreparationfactors,Chem.Eng.J.260(2015)107–116.

[5]D.L.Trimm,Minimisationofcarbonmonoxideinahydrogenstreamforfuel

cellapplication,Appl.Catal.AGen.296(2005)1–11.

[6]M.V.Twigg,M.S.Spencer,Deactivationofsupportedcoppermetalcatalystsfor

hydrogenationreactions,Appl.Catal.AGen.212(2001)161–174.

[7]B.Liu,A.Goldbach,H.Y.Xu,Sourwater–gasshiftreactionoverPt/CeO2

catalysts,Catal.Today171(2011)304–311.

[8]Z.J.Mei,Y.Li,M.H.Fan,L.Zhao,J.Zhao,EffectoftheinteractionsbetweenPt

speciesandceriaonPt/ceriacatalystsforwatergasshift:theXPSstudies,Chem.Eng.J.259(2015)293–302.

[9]W.D.Williams,M.Shekhar,W.S.Lee,V.Kispersky,W.N.Delgass,F.H.Ribeiro,S.

M.Kim,E.A.Stach,J.T.Miller,L.F.Allard,MetalliccorneratomsingoldclusterssupportedonrutilearethedominantactivesiteduringwaterÀgasshiftcatalysis,J.Am.Chem.Soc.132(2010)14018–14020.

[10]T.Huang,B.Liu,Z.H.Zhang,Y.H.Zhang,J.L.Li,Preparationofcon nedRu-iongelcatalystsandtheirapplicationforalowtemperaturewater–gasshiftreaction,RSCAdv.4(2014)28529–28536.

[11]ine,R.G.Rinker,P.C.Ford,Catalysisbyrutheniumcarbonylinalkaline

solution:thewatergasshiftreaction,J.Am.Chem.Soc.99(1977)252–253.[12]S.Werner,N.Szesni,M.Kaiser,R.W.Fischer,M.Haumann,P.Wasserscheid,

Ultra-low-temperaturewater-gasshiftcatalysisusingsupportedionicliquidphase(SILP)materials,ChemCatChem2(2010)1399–1402.

[13]V.M.Shinde,G.Madras,ProductionofsyngasfromsteamreformingandCO

removalwithwatergasshiftreactionovernanosizedZr0.95Ru0.05O2-dsolidsolution,Inter.J.HydrogenEnergy38(2013)13961–13973.

[14]M.Yang,S.Li,Y.Wang,J.A.Herron,Y.Xu,L.F.Allard,S.Lee,J.Huang,M.

Mavrikakis,M.Flytzani-Stephanopoulos,CatalyticallyactiveAu-O(OH)xspeciesstabilizedbyalkaliionsonzeolitesandmesoporousoxides,Science346(2014)1498–1501.

[15]J.M.Pigos,C.J.Brooks,G.Jacobs,B.H.Davis,Lowtemperaturewater–gasshift:

theeffectofalkalidopingontheC–HbondofformateoverPt/ZrO2catalysts,Appl.Catal.AGen.328(2007)14–26.

[16]J.H.Pazmin

ˇo,M.Shekhar,W.D.Williams,M.C.Akatay,J.T.Miller,W.N.Delgass,F.H.Ribeiro,MetallicPtasactivesitesforthewater–gasshiftreactiononalkali-promotedsupportedcatalysts,J.Catal.286(2012)279–286.

[17]R.T.Figueiredo,M.S.Santos,H.M.C.Andrade,J.L.G.Fierro,Effectofalkali

cationsontheCuZnOAl2O3lowtemperaturewatergas-shiftcatalyst,Catal.Today172(2011)166–170.

[18]Y.P.Zhai,D.Pierre,R.Si,W.L.Deng,P.Ferrin,A.U.Nilekar,G.W.Peng,J.A.

Herron,D.C.Bell,H.Saltsburg,M.Mavrikakis,M.Flytzani-Stephanopoulos,Alkali-stabilizedPt-OHxspeciescatalyzelow-temperaturewater-gasshiftreactions,Science329(2010)1633–1636.

[19]J.A.Rodriguez,P.Liu,J.Hrbek,J.e.Evans,M.Pérez,Watergasshiftreactionon

CuandAunanoparticlessupportedonCeO2(111)andZnO(000I

):intrinsicactivityandimportanceofsupportinteractions,Angew.Chem.Int.Ed.46(2007)1329–1332.

[20]Y.Wang,Y.P.Zhai,D.Pierre,M.Flytzani-Stephanopoulos,Silica-encapsulated

platinumcatalystsforthelow-temperaturewater-gasshiftreaction,Appl.Catal.B127(2012)342–350.

[21]B.Liu,T.Huang,Z.H.Zhang,Z.Wang,Y.H.Zhang,J.L.Li,Theeffectofthealkali

additiveonthehighlyactiveRu/Ccatalystforwatergasshiftreaction,Catal.Sci.Technol.4(2014)1286–1292.

[22]M.Kusche,K.Bustillo,F.Agel,P.Wasserscheid,Highlyeffectivept-based

water-gasshiftcatalystsbysurfacemodi cationwithalkalihydroxidesalts,ChemCatChem7(2015)766–775.

[23]H.F.Xiong,M.A.Motchelaho,M.Moyo,L.L.Jewell,N.J.Coville,EffectofGroupI

alkalimetalpromotersonFe/CNTcatalystsinFischer–Tropschsynthesis,Fuel150(2015)687–696.

[24]Z.P.Yan,L.Lin,S.J.Liu,Synthesisofc-valerolactonebyhydrogenationof

biomass-derivedlevulinicacidoverRu/Ccatalyst,EnergyFuels23(2009)3853–3858.

[25]K.Baranowska,J.Okal,N.Miniajluk,Effectofrheniumonruthenium

dispersionintheRu–Re/g-Al2O3catalysts,Catal.Lett.144(2014)447–459.[26]M.F.Ran,Y.Liu,W.Chu,Z.B.Liu,A.Borgna,HighdispersionofRunanoparticles

supportedoncarbonnanotubessynthesizedbywater-assistedchemicalvapordepositionforcellobioseconversion,mun.27(2012)69–72.

[27]J.Xiong,X.F.Dong,L.L.Li,COselectivemethanationinhydrogen-richgas

mixturesovercarbonnanotubesupportedRu-basedcatalysts,J.Nat.GasChem.21(2012)445–451.

[28]H.N.Evin,G.Jacobs,J.Ruiz-Martinez,U.M.Graham,A.Dozier,G.Thomas,B.H.

Davis,Lowtemperaturewater-gasshift/methanolsteamreforming:alkalidopingtofacilitatethescissionofformateandmethoxyC–HbondsoverPt/ceriacatalyst,Catal.Lett.122(2008)9–19

.

co变换催化剂

Y.Maetal./ChemicalEngineeringJournal287(2016)155–161

[29]P.A.Bazula,A.H.Lu,J.Nitz,F.Schuth,Surfaceandporestructuremodi cation

oforderedmesoporouscarbonsviaachemicaloxidationapproach,MicroporousMesoporousMater.108(2008)266–275.

[30]A.M.DuartedeFarias,A.P.M.G.Barandas,R.F.Perez,M.A.Fraga,Water–gas

shiftreactionovermagnesia-modi edPt/CeO2catalysts,J.PowerSources165(2007)854–860.

[31]R.Knapp,S.A.Wyrzgol,A.Jentys,J.A.Lercher,Water–gasshiftcatalysts

basedonionicliquidmediatedsupportedCunanoparticles,J.Catal.276(2010)280–291.

161

[32]H.Abdulhamid,E.Fridell,J.Dawody,M.Skoglundh,InsituFTIRstudyofSO2

interactionwithPt/BaCO3/Al2O3NOxstoragecatalystsunderleanandrichconditions,J.Catal.241(2006)200–210.

[33]R.Watanabe,Y.J.Sakamoto,K.Yamamuro,S.Tamura,E.Kikuchi,Y.Sekine,

RoleofalkalimetalinahighlyactivePd/alkali/Fe2O3catalystforwatergasshiftreaction,Appl.Catal.AGen.457(2013)1–11.

[34]T.Niu,L.H.Zhang,Y.Liu,HighlydispersedRuonK-dopedmeso-macroporous

SiO2forthepreferentialoxidationofCOinH2-richgases,Inter.J.HydrogenEnergy39(2014)13800–13807.

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