co变换催化剂

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