Preparation, characterization, and catalytic performance of high efficient CeO2-MnOx-Al2O3 catalysts for NO elimination

Article abstract of DOI:10.1016/S1872-2067(15)61098-1

A series of CeO₂-MnO_x-Al₂O₃ mixed oxide catalysts (Ce:Mn:Al mole ratio = 6:4:x, x = 0.25, 0.5, 1, 2) were prepared by a simple one-step inverse co-precipitation method to investigate the influence of the incorporation of Al³⁺ into CeO₂-MnO_x mixed oxides. CeO₂-MnO_x, CeO₂-Al₂O₃, and MnO_x-Al₂O₃ mixed oxides, and CeO₂ were prepared by the same method for comparison. The samples were characterized by XRD, Raman, N₂ physisorption, H₂-TPR, XPS, and in situ DRIFTS. The catalytic reduction of NO by CO was chosen as a model reaction to evaluate the catalytic performance. The incorporation of a small amount of Al³⁺ into CeO₂-MnO_x mixed oxides resulted in a decrease of crystallite size, with the increase of the BET specific surface area and pore volume, as well as the increase of Ce³⁺ and Mn⁴⁺. The former benefits good contact between catalyst and reactants, and the latter promotes the adsorption of CO and the desorption, conversion and dissociation of adsorbed NO. All these enhanced the catalytic performance for the NO+CO model reaction. A reaction mechanism was proposed to explain the excellent catalytic performance of CeO₂-MnO_x-Al₂O₃ catalysts for NO reduction by CO.

Full text of DOI:10.1016/S1872-2067(15)61098-1

ChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380
ꢀ
ꢀ ꢀ ꢀ
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j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
ꢀ
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Article
Preparation,ꢀcharacterization,ꢀandꢀcatalyticꢀperformanceꢀofꢀhighꢀ ꢀ
efficientꢀCeO
2
‐MnO
x
‐Al
2
O ꢀcatalystsꢀforꢀNOꢀeliminationꢀ
3
ꢀa,
ꢀb,c
ꢀb,c
ꢀb,c
ꢀd
ꢀa
ꢀa,#
XiaojiangꢀYao *,ꢀLuluꢀLi ,ꢀWeixinꢀZou ,ꢀShuohanꢀYu ,ꢀJibinꢀAn ,ꢀHongliꢀLi ,ꢀFumoꢀYang ,ꢀ ꢀ
ꢀb,c,$
LinꢀDong
ꢀ
aꢀKeyꢀLaboratoryꢀofꢀReservoirꢀAquaticꢀEnvironmentꢀofꢀCAS,ꢀChongqingꢀInstituteꢀofꢀGreenꢀandꢀIntelligentꢀTechnology,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀ ꢀ
Chongqingꢀ400714,ꢀChinaꢀ
bꢀKeyꢀLaboratoryꢀofꢀMesoscopicꢀChemistryꢀofꢀMOE,ꢀSchoolꢀofꢀChemistryꢀandꢀChemicalꢀEngineering,ꢀNanjingꢀUniversity,ꢀNanjingꢀ210093,ꢀJiangsu,ꢀChinaꢀ
cꢀJiangsuꢀKeyꢀLaboratoryꢀofꢀVehicleꢀEmissionsꢀControl,ꢀCenterꢀofꢀModernꢀAnalysis,ꢀNanjingꢀUniversity,ꢀNanjingꢀ210093,ꢀJiangsu,ꢀChinaꢀ
dꢀChongqingꢀKeyꢀLaboratoryꢀofꢀEnvironmentalꢀMaterialsꢀandꢀRemediationꢀTechnology,ꢀChongqingꢀUniversityꢀofꢀArtsꢀandꢀSciences,ꢀChongqingꢀ402160,ꢀ
Chinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
AꢀseriesꢀofꢀCeO
2
‐MnO
x
‐Al
2
O ꢀmixedꢀoxideꢀcatalystsꢀ(Ce:Mn:Alꢀmoleꢀratioꢀ=ꢀ6:4:x,ꢀxꢀ=ꢀ0.25,ꢀ0.5,ꢀ1,ꢀ2)ꢀ
3
Receivedꢀ16ꢀFebruaryꢀ2016ꢀ
Acceptedꢀ20ꢀMarchꢀ2016ꢀ
Publishedꢀ5ꢀAugustꢀ2016ꢀ
wereꢀpreparedꢀbyꢀaꢀsimpleꢀone‐stepꢀinverseꢀco‐precipitationꢀmethodꢀtoꢀinvestigateꢀtheꢀinfluenceꢀofꢀ
3+
theꢀ incorporationꢀ ofꢀ Al ꢀ intoꢀ CeO
mixedꢀ oxides,ꢀ andꢀ CeO ꢀ wereꢀ preparedꢀ byꢀ theꢀ sameꢀ methodꢀ forꢀ comparison.ꢀ Theꢀ samplesꢀ wereꢀ
characterizedꢀbyꢀXRD,ꢀRaman,ꢀN ꢀphysisorption,ꢀH ‐TPR,ꢀXPS,ꢀandꢀinꢀsituꢀDRIFTS.ꢀTheꢀcatalyticꢀre‐
ductionꢀofꢀNOꢀbyꢀCOꢀwasꢀchosenꢀasꢀaꢀmodelꢀreactionꢀtoꢀevaluateꢀtheꢀcatalyticꢀperformance.ꢀTheꢀ
2
‐MnO
x
ꢀ mixedꢀ oxides.ꢀ CeO
‐MnO ,ꢀ CeO ‐Al O ,ꢀ andꢀ MnO ‐Al O
2 x 2 2 3 x 2 3
2
2
2
Keywords:ꢀ
Ceria‐basedꢀmixedꢀoxideꢀ
Incorporationꢀ
Electronꢀinteractionꢀ
Adsorptionꢀpropertyꢀ
NOꢀeliminationꢀ
3+
incorporationꢀofꢀaꢀsmallꢀamountꢀofꢀAl ꢀintoꢀCeO
2 x
‐MnO ꢀmixedꢀoxidesꢀresultedꢀinꢀaꢀdecreaseꢀofꢀcrys‐
talliteꢀsize,ꢀwithꢀtheꢀincreaseꢀofꢀtheꢀBETꢀspecificꢀsurfaceꢀareaꢀandꢀporeꢀvolume,ꢀasꢀwellꢀasꢀtheꢀin‐
3+
4+
creaseꢀofꢀCe ꢀandꢀMn .ꢀTheꢀformerꢀbenefitsꢀgoodꢀcontactꢀbetweenꢀcatalystꢀandꢀreactants,ꢀandꢀtheꢀ
latterꢀpromotesꢀtheꢀadsorptionꢀofꢀCOꢀandꢀtheꢀdesorption,ꢀconversionꢀandꢀdissociationꢀofꢀadsorbedꢀ
NO.ꢀAllꢀtheseꢀenhancedꢀtheꢀcatalyticꢀperformanceꢀforꢀtheꢀNO+COꢀmodelꢀreaction.ꢀAꢀreactionꢀmecha‐
nismꢀwasꢀproposedꢀtoꢀexplainꢀtheꢀexcellentꢀcatalyticꢀperformanceꢀofꢀCeO
2
‐MnO
x
‐Al
2
O ꢀcatalystsꢀforꢀ
3
NOꢀreductionꢀbyꢀCO.ꢀ
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
carbonꢀmonoxideꢀ(CO),ꢀandꢀhydrocarbonsꢀ(HCs)ꢀareꢀtheꢀmainꢀ
pollutantsꢀ inꢀ motorꢀ vehicleꢀ exhaust.ꢀ Theyꢀ canꢀ beꢀ efficientlyꢀ
eliminatedꢀ byꢀ three‐wayꢀ catalysisꢀ (TWC)ꢀ technologyꢀ [2‒5].ꢀ
Thereꢀ areꢀ severalꢀ importantꢀ reactionsꢀ inꢀ thisꢀ technology,ꢀ inꢀ
Motorꢀvehiclesꢀbringꢀgreatꢀconvenienceꢀtoꢀpeople,ꢀbutꢀtheyꢀ
alsoꢀcauseꢀseriousꢀatmosphericꢀpollutionꢀ[1].ꢀNitricꢀoxideꢀ(NO),ꢀ
*
ꢀ
$ꢀ
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐23‐65935909;ꢀFax:ꢀ+86‐23‐65935924;ꢀE‐mail:ꢀyaoxj@cigit.ac.cnꢀ ꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐23‐65935909;ꢀFax:ꢀ+86‐23‐65935924;ꢀE‐mail:ꢀfmyang@cigit.ac.cnꢀ ꢀ
Correspondingꢀauthor. Tel:ꢀ+86‐25‐83592290;ꢀFax:ꢀ+86‐25‐83317761;ꢀE‐mail:ꢀdonglin@nju.edu.cnꢀ ꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21507130),ꢀtheꢀOpenꢀProjectꢀProgramꢀofꢀChongqingꢀKeyꢀLaboratoryꢀ
ofꢀEnvironmentalꢀMaterialsꢀandꢀRemediationꢀTechnologyꢀfromꢀChongqingꢀUniversityꢀofꢀArtsꢀandꢀSciencesꢀ(CEK1405),ꢀtheꢀOpenꢀProjectꢀProgramꢀofꢀ
BeijingꢀNationalꢀLaboratoryꢀforꢀMolecularꢀSciencesꢀ(20140142),ꢀtheꢀOpenꢀProjectꢀProgramꢀofꢀJiangsuꢀKeyꢀLaboratoryꢀofꢀVehicleꢀEmissionsꢀControlꢀ
(OVEC001),ꢀtheꢀOpenꢀProjectꢀProgramꢀofꢀChongqingꢀKeyꢀLaboratoryꢀofꢀCatalysisꢀandꢀFunctionalꢀOrganicꢀMoleculesꢀfromꢀChongqingꢀTechnologyꢀandꢀ
BusinessꢀUniversityꢀ(1456029),ꢀandꢀtheꢀChongqingꢀScienceꢀ&ꢀTechnologyꢀCommissionꢀ(cstc2014pt‐gc20002)ꢀ ꢀ
DOI:ꢀ10.1016/S1872‐2067(15)61098‐1ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ37,ꢀNo.ꢀ8,ꢀAugustꢀ2016ꢀ ꢀ ꢀ

1370ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
whichꢀtheꢀcatalyticꢀreductionꢀofꢀNOꢀbyꢀCOꢀ(NO+COꢀmodelꢀreac‐
tion)ꢀattractsꢀmoreꢀattentionꢀdueꢀtoꢀtheꢀsimultaneousꢀelimina‐
tionꢀ ofꢀ NOꢀ andꢀ COꢀ pollutantsꢀ [6,7].ꢀ Inꢀ theꢀ pastꢀ decades,ꢀ sup‐
portedꢀnobleꢀmetalꢀcatalystsꢀwereꢀwidelyꢀappliedꢀforꢀthisꢀreac‐
tion,ꢀandꢀtheyꢀexhibitedꢀexcellentꢀcatalyticꢀperformanceꢀ[8‒10].ꢀ
However,ꢀtheꢀhighꢀcost,ꢀresourceꢀscarcity,ꢀandꢀpoorꢀstabilityꢀofꢀ
nobleꢀmetalsꢀpromptedꢀresearchersꢀtoꢀlookꢀforꢀsubstitutes.ꢀForꢀ
thisꢀpurpose,ꢀlowꢀcostꢀandꢀefficientꢀtransitionꢀmetalꢀoxideꢀcata‐
lystsꢀhaveꢀbecomeꢀtheꢀfocusꢀinꢀrecentꢀyearsꢀ[11,12].ꢀ
2.ꢀ ꢀ Experimentalꢀ ꢀ
2.1.ꢀ ꢀ Catalystꢀpreparationꢀ
Aꢀ seriesꢀ ofꢀ CeO
2
‐MnO
x
‐Al
2
O ꢀ mixedꢀ oxideꢀ catalystsꢀ
3
(Ce:Mn:Alꢀmoleꢀratioꢀ=ꢀ6:4:x,ꢀxꢀ=ꢀ0.25,ꢀ0.5,ꢀ1,ꢀ2)ꢀwereꢀpreparedꢀ
fromꢀ theirꢀ saltꢀ solutionsꢀ asꢀ precursorsꢀ byꢀ aꢀ simpleꢀ one‐stepꢀ
inverseꢀco‐precipitationꢀmethod.ꢀTheꢀdesiredꢀquantitiesꢀofꢀce‐
riumꢀnitrate,ꢀmanganeseꢀnitrateꢀ(50%),ꢀandꢀaluminumꢀnitrateꢀ
wereꢀdissolvedꢀinꢀdistilledꢀwaterꢀseparatelyꢀandꢀmixedꢀtogetherꢀ
byꢀ magneticꢀ stirringꢀ forꢀ 1ꢀ h,ꢀ andꢀ thenꢀ slowlyꢀ addedꢀ intoꢀ theꢀ
excessꢀammoniaꢀ(25%)ꢀwithꢀvigorouslyꢀstirringꢀuntilꢀtheꢀpHꢀ=ꢀ
10.ꢀTheꢀresultingꢀsuspensionꢀwasꢀkeptꢀstirredꢀforꢀanotherꢀ3ꢀh,ꢀ
agedꢀforꢀ24ꢀh,ꢀandꢀthenꢀfiltered,ꢀwashedꢀseveralꢀtimesꢀwithꢀdis‐
tilledꢀwaterꢀuntilꢀtheꢀpHꢀ=ꢀ7.ꢀTheꢀobtainedꢀcakeꢀwasꢀdriedꢀatꢀ
110ꢀ°Cꢀforꢀ12ꢀhꢀandꢀfinallyꢀcalcinedꢀatꢀ500ꢀ°Cꢀinꢀflowingꢀairꢀforꢀ5ꢀ
Theꢀrareꢀearthꢀmetalꢀoxideꢀceriaꢀ(CeO
)ꢀwasꢀwidelyꢀusedꢀforꢀ
2
theꢀNO+COꢀmodelꢀreactionꢀdueꢀtoꢀitsꢀgoodꢀredoxꢀproperty,ꢀhighꢀ
oxygenꢀ storageꢀ andꢀ releaseꢀ capacity,ꢀ andꢀ abundantꢀ surfaceꢀ
oxygenꢀvacanciesꢀ[13‒17].ꢀSomeꢀresearchꢀresultsꢀindicatedꢀthatꢀ
4+
theꢀincorporationꢀofꢀtransitionꢀmetalꢀionsꢀ(suchꢀasꢀZr )ꢀintoꢀtheꢀ
latticeꢀofꢀCeO ꢀtoꢀformꢀaꢀceria‐basedꢀmixedꢀoxideꢀcanꢀincreaseꢀ
theꢀspecificꢀsurfaceꢀareaꢀofꢀCeO ꢀandꢀfurtherꢀimproveꢀitsꢀredoxꢀ
propertyꢀ andꢀ oxygenꢀ storageꢀ andꢀ releaseꢀ capacityꢀ [18‒20].ꢀ
Moreover,ꢀ CeO ‐ZrO ꢀ mixedꢀ oxidesꢀ haveꢀ beenꢀ practicallyꢀ ap‐
2
2
h.ꢀ Inꢀ addition,ꢀ CeO
ides,ꢀandꢀCeO ꢀwereꢀpreparedꢀbyꢀtheꢀsameꢀwayꢀforꢀcomparison.ꢀ
Theseꢀ samplesꢀ areꢀ denotedꢀ asꢀ C .ꢀ Forꢀ example,ꢀ C A ꢀ
2
‐MnO
x
,ꢀ CeO
2
‐Al
2 3 x 2 3
O ,ꢀ MnO ‐Al O ꢀ mixedꢀ ox‐
2
2
2
pliedꢀforꢀtheꢀpurificationꢀofꢀmotorꢀvehicleꢀexhaust.ꢀInꢀourꢀpre‐
viousꢀstudy,ꢀweꢀfoundꢀthatꢀdopingꢀwithꢀionsꢀwithꢀvariableꢀva‐
M A
6 4 x
M
6 4
0.5
representsꢀthatꢀtheꢀmoleꢀratioꢀofꢀCe:Mn:Alꢀisꢀ6:4:0.5.ꢀ
4
+
2+
4+
3+
lenceꢀstatesꢀ(suchꢀasꢀSn /Sn ꢀandꢀTi /Ti )ꢀwasꢀbeneficialꢀtoꢀ
improveꢀ CeO ꢀ becauseꢀ ofꢀ theꢀ electronꢀ transferꢀ betweenꢀ
2
2.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ
4+
3+
Ce /Ce ꢀandꢀtheꢀdopedꢀionsꢀ[21,22].ꢀFurthermore,ꢀmanganeseꢀ
oxideꢀ(MnO
x
)ꢀeasilyꢀgeneratesꢀtheꢀMn /Mn(n–1)+ꢀredoxꢀcouple,ꢀ
n+
XRDꢀ patternsꢀ wereꢀ recordedꢀ onꢀ aꢀ Philipsꢀ X’Pert3ꢀ Powderꢀ
diffractometerꢀ usingꢀ Ni‐filteredꢀ Cuꢀ K ꢀ radiationꢀ (λꢀ =ꢀ 0.15418ꢀ
nm).ꢀ Theꢀ X‐rayꢀ tubeꢀ wasꢀ operatedꢀ atꢀ 40ꢀ kVꢀ andꢀ 40ꢀ mA.ꢀ Theꢀ
dataꢀwereꢀcollectedꢀoverꢀaꢀ2θꢀrangeꢀofꢀ10°‒90°.ꢀTheꢀscanꢀspeedꢀ
wasꢀsetꢀatꢀ10°/minꢀwithꢀaꢀstepꢀsizeꢀofꢀ0.02°.ꢀTheꢀmeanꢀcrystal‐
andꢀ therebyꢀ exhibitsꢀ excellentꢀ catalyticꢀ performanceꢀ inꢀ someꢀ
redoxꢀreactionsꢀ[23‒25].ꢀ ꢀ
α
Recently,ꢀ aꢀ CeO
2
‐MnO ꢀ mixedꢀ oxideꢀ wasꢀ widelyꢀ usedꢀ inꢀ
x
manyꢀimportantꢀreactionsꢀ(suchꢀasꢀNOꢀelimination,ꢀsootꢀcom‐
bustion,ꢀVOCsꢀoxidation,ꢀetc.)ꢀdueꢀtoꢀitsꢀgoodꢀphysicochemicalꢀ
propertyꢀandꢀexcellentꢀcatalyticꢀperformanceꢀ[26‒28].ꢀUsually,ꢀ
theꢀspecificꢀsurfaceꢀareaꢀofꢀaꢀtwo‐componentꢀceria‐basedꢀmixedꢀ
oxideꢀ isꢀ stillꢀ tooꢀ smallꢀ toꢀ satisfyꢀ theꢀ practicalꢀ applicationꢀ re‐
β
liteꢀsizeꢀ(D )ꢀfromꢀtheꢀstrongestꢀpeakꢀofꢀtheseꢀsamplesꢀwasꢀde‐
β
terminedꢀbyꢀD ꢀ=ꢀKλ/βcosθꢀ(Debye‐Scherrerꢀequation),ꢀwhereꢀKꢀ
isꢀtheꢀparticleꢀshapeꢀfactor,ꢀusuallyꢀtakenꢀasꢀ0.89,ꢀλꢀisꢀtheꢀX‐rayꢀ
wavelength,ꢀβꢀisꢀtheꢀfullꢀwidthꢀatꢀhalfꢀmaximumꢀheightꢀ(FWHM)ꢀ
inꢀradians,ꢀandꢀθꢀisꢀtheꢀdiffractionꢀangle.ꢀ
Ramanꢀ spectraꢀ wereꢀ collectedꢀ onꢀ aꢀ Renishawꢀ inViaꢀ Reflexꢀ
LaserꢀRamanꢀspectrometerꢀusingꢀaꢀAr ꢀlaserꢀbeam.ꢀTheꢀRamanꢀ
quirement.ꢀGammaꢀaluminaꢀ(γ‐Al
monlyꢀ usedꢀ catalystꢀ supportꢀ dueꢀ toꢀ itsꢀ largeꢀ specificꢀ surfaceꢀ
areaꢀ andꢀ highꢀ thermalꢀ stabilityꢀ [29].ꢀ Therefore,ꢀ γ‐Al ꢀ wasꢀ
2 3
O )ꢀisꢀoneꢀofꢀtheꢀmostꢀcom‐
+
O
2 3
widelyꢀusedꢀasꢀaꢀsupportꢀtoꢀloadꢀceria‐basedꢀmixedꢀoxidesꢀforꢀ
theꢀpurposeꢀofꢀsatisfyingꢀtheꢀpracticalꢀapplicationꢀinꢀtheꢀpurifi‐
cationꢀofꢀmotorꢀvehicleꢀexhaust.ꢀWeꢀfoundꢀthatꢀtheꢀincorpora‐
tionꢀ ofꢀ Al ꢀ intoꢀ theꢀ latticeꢀ ofꢀ aꢀ ceria‐basedꢀ mixedꢀ oxideꢀ byꢀ aꢀ
co‐precipitationꢀ methodꢀ wasꢀ moreꢀ conduciveꢀ toꢀ improveꢀ theꢀ
physicochemicalꢀ propertyꢀ andꢀ catalyticꢀ performanceꢀ inꢀ ourꢀ
previousꢀworkꢀ[12].ꢀ
spectraꢀ wereꢀ recordedꢀ withꢀ anꢀ excitationꢀ wavelengthꢀ ofꢀ 532ꢀ
nmꢀandꢀtheꢀlaserꢀpowerꢀofꢀ5ꢀmW.ꢀ
TexturalꢀcharacteristicsꢀofꢀtheꢀsamplesꢀwereꢀobtainedꢀbyꢀN2ꢀ
physisorptionꢀatꢀ–196ꢀ°CꢀonꢀaꢀBelsorp‐maxꢀanalyzer,ꢀusingꢀtheꢀ
Brunauer‐Emmet‐Tellerꢀ(BET)ꢀmethodꢀforꢀtheꢀspecificꢀsurfaceꢀ
areaꢀandꢀtheꢀBarrett‐Joyner‐Halendaꢀ(BJH)ꢀmethodꢀforꢀtheꢀporeꢀ
distribution.ꢀPriorꢀtoꢀeachꢀanalysis,ꢀtheꢀcatalystꢀwasꢀdegassedꢀ
underꢀvacuumꢀatꢀ300ꢀ°Cꢀforꢀ4ꢀh.ꢀ
3+
Inꢀ theꢀ presentꢀ work,ꢀ weꢀ preparedꢀ aꢀ seriesꢀ ofꢀ
CeO
2
‐MnO
x
‐Al
2
O
3
ꢀ mixedꢀ oxideꢀ catalystsꢀ byꢀ aꢀ simpleꢀ one‐stepꢀ
H
2
‐TPRꢀ experimentsꢀ wereꢀ performedꢀ inꢀ aꢀ quartzꢀ reactorꢀ
connectedꢀ toꢀ aꢀ thermalꢀ conductivityꢀ detectorꢀ (TCD)ꢀ withꢀ anꢀ
Ar‐H ꢀmixtureꢀ(7.0%ꢀofꢀH ꢀbyꢀvolume,ꢀ30ꢀmL/min)ꢀasꢀreduct‐
ant.ꢀPriorꢀtoꢀtheꢀreduction,ꢀtheꢀsampleꢀ(50ꢀmg)ꢀwasꢀpretreatedꢀ
inꢀaꢀhighlyꢀpurifiedꢀN ꢀstreamꢀatꢀ300ꢀ°Cꢀforꢀ1ꢀhꢀandꢀthenꢀcooledꢀ
inverseꢀco‐precipitationꢀmethod.ꢀTheꢀsamplesꢀwereꢀcharacter‐
izedꢀ byꢀ X‐rayꢀ diffractionꢀ (XRD),ꢀ Ramanꢀ spectroscopy,ꢀ N2ꢀphy‐
sisorption,ꢀ H
2
2
2
ꢀ temperature‐programmedꢀ reductionꢀ (H ‐TPR),ꢀ
2
X‐rayꢀ photoelectronꢀ spectroscopyꢀ (XPS),ꢀ andꢀ inꢀ situꢀ diffuseꢀ
reflectanceꢀ infraredꢀ Fourierꢀ transformꢀ spectroscopyꢀ (inꢀ situꢀ
DRIFTS).ꢀ Theꢀ NO+COꢀ modelꢀ reactionꢀ wasꢀ chosenꢀ toꢀ evaluateꢀ
theꢀcatalyticꢀperformanceꢀofꢀtheꢀsamples.ꢀThisꢀstudyꢀisꢀmainlyꢀ
focusedꢀon:ꢀ(1)ꢀexploringꢀtheꢀinfluenceꢀofꢀtheꢀdopedꢀamountꢀofꢀ
2
toꢀroomꢀtemperature.ꢀAfterꢀthat,ꢀtheꢀTPRꢀstartedꢀfromꢀ50ꢀ°Cꢀtoꢀ
theꢀtargetꢀtemperatureꢀatꢀaꢀrateꢀofꢀ10ꢀ°C/min.ꢀ
XPSꢀanalysisꢀwasꢀperformedꢀonꢀaꢀPHIꢀ5000ꢀVersaProbeꢀsys‐
temꢀusingꢀmonochromaticꢀAlꢀK ꢀradiationꢀ(1486.6ꢀeV)ꢀoperat‐
ingꢀ atꢀ anꢀ acceleratingꢀ powerꢀ ofꢀ 15ꢀ kW.ꢀ Beforeꢀ theꢀ measure‐
ment,ꢀtheꢀsampleꢀwasꢀoutgassedꢀatꢀroomꢀtemperatureꢀinꢀaꢀUHVꢀ
chamberꢀ (<ꢀ 5ꢀ ×ꢀ 10 ꢀ Pa).ꢀ Sampleꢀ chargingꢀ effectsꢀ wereꢀ com‐
pensatedꢀbyꢀcalibratingꢀbindingꢀenergiesꢀ(BE)ꢀwithꢀtheꢀadventi‐
tiousꢀCꢀ1sꢀpeakꢀatꢀ284.6ꢀeV.ꢀThisꢀreferenceꢀgaveꢀBEꢀvaluesꢀwithꢀ
α
3+
Al ꢀ onꢀ theꢀ catalyticꢀ performanceꢀ ofꢀ CeO
2 x 2 3
‐MnO ‐Al O ꢀ mixedꢀ
oxideꢀ catalysts,ꢀ andꢀ (2)ꢀ investigatingꢀ theꢀ interactionꢀ ofꢀ COꢀ
or/andꢀNOꢀwithꢀtheseꢀcatalystsꢀbyꢀinꢀsituꢀDRIFTSꢀinꢀtheꢀtem‐
peratureꢀ rangeꢀ ofꢀ 25‒450ꢀ °Cꢀ toꢀ discussꢀ theꢀ reactionꢀ mecha‐
nism.ꢀ
–7

ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
1371ꢀ
anꢀaccuracyꢀofꢀ0.1ꢀeV.ꢀ
NOꢀconversionꢀ=ꢀ([NO]inꢀ‒ꢀ[NO]out)/[NO]inꢀ×ꢀ100%ꢀ ꢀ ꢀ ꢀ (1)ꢀ
ꢀselectivityꢀ=ꢀ[N out/([N outꢀ+ꢀ[N O]out)ꢀ×ꢀ100%ꢀ ꢀ ꢀ ꢀ (2)ꢀ
whereꢀ[NO]in,ꢀ[NO]out,ꢀ[N out,ꢀandꢀ[N O]outꢀareꢀtheꢀinletꢀconcen‐
–1
Inꢀsituꢀ DRIFTSꢀ wereꢀ collectedꢀ fromꢀ650ꢀtoꢀ4000ꢀ cm ꢀatꢀaꢀ
N
2
2
]
2
]
2
–1
spectralꢀresolutionꢀofꢀ4ꢀcm ꢀ(numberꢀofꢀscans,ꢀ32)ꢀonꢀaꢀNicoletꢀ
700ꢀFT‐IRꢀspectrometerꢀequippedꢀwithꢀaꢀhighꢀsensitivityꢀMCTꢀ
detectorꢀ cooledꢀ byꢀ liquidꢀ N .ꢀ Theꢀ DRIFTSꢀ cellꢀ (Harrick)ꢀ wasꢀ
2
]
2
5
trationꢀofꢀNOꢀandꢀoutletꢀconcentrationꢀofꢀNO,ꢀN
2
,ꢀandꢀN O,ꢀre‐
2
2
spectively.ꢀ
fittedꢀwithꢀaꢀZnSeꢀwindowꢀandꢀaꢀheatingꢀcartridgeꢀthatꢀallowedꢀ
theꢀ sampleꢀ toꢀ beꢀ heatedꢀ toꢀ 450ꢀ °C.ꢀ Theꢀ fineꢀ catalystꢀ powderꢀ
placedꢀonꢀaꢀsampleꢀholderꢀwasꢀcarefullyꢀflattenedꢀtoꢀenhanceꢀIRꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
reflection.ꢀTheꢀsampleꢀwasꢀpretreatedꢀwithꢀaꢀhighlyꢀpurifiedꢀN
2
ꢀ
3.1.ꢀ ꢀ Catalyticꢀactivityꢀandꢀselectivityꢀ(NO+COꢀmodelꢀreaction)ꢀ
streamꢀatꢀ450ꢀ°Cꢀforꢀ1ꢀhꢀtoꢀeliminateꢀphysisorbedꢀwaterꢀandꢀ
otherꢀ impurities.ꢀ Theꢀ sampleꢀ backgroundꢀ atꢀ eachꢀ targetꢀ tem‐
peratureꢀwasꢀcollectedꢀduringꢀtheꢀcoolingꢀprocess.ꢀAtꢀambientꢀ
temperature,ꢀtheꢀsampleꢀwasꢀexposedꢀtoꢀaꢀcontrolledꢀstreamꢀofꢀ
CO‐Arꢀ (10%ꢀ ofꢀ COꢀ byꢀ volume)ꢀ or/andꢀ NO‐Arꢀ (5%ꢀ ofꢀ NOꢀ byꢀ
volume)ꢀatꢀaꢀrateꢀofꢀ5.0ꢀmL/minꢀforꢀ1ꢀhꢀforꢀadsorptionꢀsatura‐
tion.ꢀDesorptionꢀandꢀreactionꢀstudiesꢀwereꢀperformedꢀbyꢀheat‐
ingꢀtheꢀadsorbedꢀspeciesꢀandꢀtheꢀspectraꢀwereꢀrecordedꢀatꢀvar‐
iousꢀ targetꢀ temperaturesꢀ atꢀ aꢀ rateꢀ ofꢀ 10ꢀ °C/minꢀ fromꢀ roomꢀ
temperatureꢀ toꢀ 450ꢀ °Cꢀ byꢀ subtractionꢀ ofꢀ theꢀ correspondingꢀ
backgroundꢀreference.ꢀ
TheꢀcatalyticꢀreductionꢀofꢀNOꢀbyꢀCOꢀwasꢀchosenꢀasꢀtheꢀmod‐
elꢀreactionꢀtoꢀevaluateꢀtheꢀcatalyticꢀperformanceꢀofꢀtheꢀsamples.ꢀ
N
2
Oꢀ(byproduct),ꢀN
TheꢀcatalyticꢀactivityꢀandꢀN
temperatureꢀareꢀexhibitedꢀinꢀFig.ꢀ1.ꢀWithꢀregardꢀtoꢀC
oxide,ꢀwhenꢀtheꢀreactionꢀtemperatureꢀwasꢀnotꢀhigherꢀthanꢀ250ꢀ
°C,ꢀbothꢀ NOꢀ conversionꢀandꢀN ꢀ selectivityꢀ areꢀ negligibleꢀ (lessꢀ
2
,ꢀandꢀCO
ꢀselectivityꢀasꢀaꢀfunctionꢀofꢀreactionꢀ
ꢀmixedꢀ
2
ꢀwereꢀtheꢀmainꢀreactionꢀproducts.ꢀ
2
M
6 4
2
thanꢀ 20%).ꢀ Atꢀ highꢀ temperatureꢀ (>250ꢀ °C),ꢀ theꢀ valuesꢀ wereꢀ
dependentꢀ onꢀ theꢀ increaseꢀ ofꢀ reactionꢀ temperature.ꢀ Fullꢀ NOꢀ
conversionꢀandꢀ100%ꢀN
SomeꢀinterestingꢀphenomenaꢀareꢀobservedꢀinꢀtheꢀAl‐containingꢀ
,ꢀ andꢀ C ꢀ mixedꢀ oxides.ꢀ Weꢀ
foundꢀthatꢀtheꢀintroductionꢀofꢀaꢀsmallꢀamountꢀofꢀAl ꢀintoꢀC
mixedꢀ oxideꢀ resultedꢀ inꢀ theꢀ enhancementꢀ ofꢀ catalyticꢀ perfor‐
mance.ꢀ Theꢀ catalyticꢀ performanceꢀ wasꢀ proportionalꢀ toꢀ theꢀ
2
ꢀselectivityꢀwereꢀobtainedꢀatꢀ450ꢀ°C.ꢀ
2.3.ꢀ ꢀ Catalyticꢀperformanceꢀ
C M A0.25,ꢀ C M A0.5,ꢀ C M A
6 4 6 4 6 4 1
6 4 2
M A
3+
6 4
M ꢀ
TheꢀcatalyticꢀperformanceꢀofꢀtheseꢀcatalystsꢀforꢀtheꢀNO+COꢀ
modelꢀreactionꢀwasꢀdeterminedꢀunderꢀsteadyꢀstateꢀconditionsꢀ
usingꢀaꢀfeedꢀstreamꢀwithꢀaꢀfixedꢀcomposition,ꢀ5%ꢀNO,ꢀ10%ꢀCOꢀ
andꢀ 85%ꢀ Heꢀ byꢀ volumeꢀ asꢀ diluent.ꢀ Theꢀ sampleꢀ (50ꢀ mg)ꢀ wasꢀ
3
+
3+
amountꢀofꢀAl .ꢀHowever,ꢀfurtherꢀincreasingꢀtheꢀamountꢀofꢀAl ꢀ
ledꢀ toꢀ aꢀ negativeꢀ effectꢀ onꢀ theꢀ catalyticꢀ performance,ꢀ whichꢀ
3+
fittedꢀintoꢀaꢀquartzꢀtubeꢀandꢀpretreatedꢀinꢀaꢀhighlyꢀpurifiedꢀN
2
ꢀ
indicatedꢀthatꢀtheꢀadditionꢀofꢀAl ꢀhasꢀanꢀoptimalꢀamount,ꢀi.e.,ꢀ
theꢀC 0.5ꢀmixedꢀoxideꢀexhibitedꢀtheꢀbestꢀNOꢀconversionꢀandꢀ
ꢀ selectivityꢀ amongꢀ theseꢀ samples.ꢀ Moreover,ꢀ C 0.5ꢀ andꢀ
0.5ꢀ mixedꢀ oxidesꢀ wereꢀ preparedꢀ byꢀ theꢀ sameꢀ inverseꢀ
co‐precipitationꢀ methodꢀ forꢀ comparison.ꢀ Theꢀ NOꢀ conversionꢀ
andꢀN ꢀselectivityꢀofꢀtheꢀC 0.5ꢀmixedꢀoxidesꢀareꢀalsoꢀ
presentedꢀinꢀFig.ꢀ1.ꢀTheꢀcatalyticꢀperformanceꢀofꢀtheꢀC 0.5ꢀandꢀ
0.5ꢀ mixedꢀ oxidesꢀ wasꢀ obviouslyꢀ lowerꢀ thanꢀ thatꢀ ofꢀ theꢀ
streamꢀatꢀ300ꢀ°Cꢀforꢀ1ꢀhꢀandꢀthenꢀcooledꢀtoꢀroomꢀtemperature.ꢀ
Afterꢀ that,ꢀ theꢀ mixedꢀ gasesꢀ wereꢀ switchedꢀ on.ꢀ Theꢀ reactionsꢀ
wereꢀcarriedꢀoutꢀatꢀdifferentꢀtemperaturesꢀwithꢀaꢀspaceꢀveloci‐
6
M A
4
N
2
6
A
4
M A
–1
–1
tyꢀofꢀ12000ꢀmLꢀg ꢀh .ꢀAꢀgasꢀchromatographꢀ(GC‐9860)ꢀwithꢀ
twoꢀcolumnsꢀ(length,ꢀ1.75ꢀm;ꢀdiameter,ꢀ3ꢀmm)ꢀandꢀtwoꢀthermalꢀ
conductivityꢀdetectorsꢀ(Tꢀ=ꢀ100ꢀ°C)ꢀwasꢀusedꢀforꢀanalyzingꢀtheꢀ
products.ꢀColumnꢀAꢀwithꢀParopakꢀQꢀwasꢀchosenꢀforꢀseparatingꢀ
2
6
A
0.5ꢀandꢀM A
4
6
A
4
M A
CO
2
ꢀandꢀN
2
OꢀandꢀcolumnꢀBꢀpackedꢀwithꢀ5Aꢀandꢀ13Xꢀmoleculeꢀ
,ꢀ NOꢀ andꢀ CO.ꢀ
ꢀ selectivityꢀ wereꢀ calculatedꢀ byꢀ theꢀ
Mn‐containingꢀ ceria‐basedꢀ mixedꢀ oxides.ꢀ Inꢀ orderꢀ toꢀ getꢀ aꢀ
thoroughꢀ understandingꢀ forꢀ theꢀ reasonꢀ forꢀ differentꢀ catalyticꢀ
performance,ꢀaꢀseriesꢀofꢀcharacterizationsꢀwereꢀperformedꢀonꢀ
theseꢀsamples.ꢀTheꢀresultsꢀareꢀdisplayedꢀandꢀdiscussedꢀinꢀtheꢀ
sieveꢀ (40‒60ꢀ mesh)ꢀ wasꢀ usedꢀ forꢀ separatingꢀ N
Theꢀ NOꢀ conversionꢀ andꢀ N
followingꢀequations:ꢀ
2
2
(a)
(b)
1
00
C6A0.5
100
80
60
40
20
0
C6A0.5
C6M4
C6M4
C6M4A0.25
C6M4A0.5
C6M4A1
C6M4A2
M4A0.5
C6M4A0.25
C6M4A0.5
C6M4A1
C6M4A2
M4A0.5
8
6
4
2
0
0
0
0
0
100
150
200
250
300
350
400
450
100
150
200
250
300
350
400
450
Temperature (C)
Temperature (C)
Fig.ꢀ1.ꢀCatalyticꢀperformanceꢀofꢀtheꢀsamplesꢀforꢀNO+COꢀmodelꢀreaction.ꢀ(a)ꢀNOꢀconversion;ꢀ(b)ꢀN
2
ꢀselectivity.ꢀ

1
372ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
Tableꢀ1ꢀ
followingꢀsections.ꢀ
Crystalliteꢀsize,ꢀlatticeꢀparameter,ꢀandꢀtheꢀmainꢀRamanꢀlineꢀ(F2g)ꢀofꢀtheꢀ
3.2.ꢀ ꢀ Structuralꢀcharacteristicsꢀ(XRDꢀandꢀRaman)ꢀ
samples.ꢀ
Crystalliteꢀsizeꢀ
(nm)ꢀ
10.8ꢀ
Latticeꢀ ꢀ
parameterꢀ(Å)ꢀ
5.4164ꢀ
PositionꢀofꢀF2gꢀ FWHMꢀofꢀF2g
ꢀ
Sample
–1
–1
TheꢀXRDꢀpatternsꢀofꢀtheꢀsamplesꢀareꢀshownꢀinꢀFig.ꢀ2(a).ꢀForꢀ
(cm )ꢀ
463ꢀ
461ꢀ
460ꢀ
459ꢀ
459ꢀ
459ꢀ
459ꢀ
(cm )ꢀ
2
CeO ꢀ
20.2ꢀ
35.1ꢀ
38.3ꢀ
42.4ꢀ
48.5ꢀ
59.4ꢀ
72.2ꢀ
facilitatingꢀcomparison,ꢀtheꢀresultꢀofꢀCeO
figure.ꢀ Weꢀ canꢀ findꢀ thatꢀ CeO ꢀ showedꢀ severalꢀ characteristicꢀ
diffractionꢀ peaksꢀ correspondedꢀ toꢀ theꢀ (111),ꢀ (200),ꢀ (220),ꢀ
311),ꢀ (222),ꢀ (400),ꢀ (331),ꢀ (420),ꢀ (422)ꢀ crystalꢀ planesꢀ ofꢀ theꢀ
cubicꢀfluoriteꢀstructureꢀ[PDF‐ICDDꢀ34‐0394].ꢀTheꢀM
pleꢀ exhibitedꢀ aꢀ seriesꢀ ofꢀ characteristicꢀ diffractionꢀ peaksꢀ as‐
signedꢀtoꢀhausmanniteꢀMn ꢀ[PDF‐ICDDꢀ24‐0734],ꢀwhileꢀonlyꢀ
theꢀbroadꢀdiffractionꢀpeaksꢀattributedꢀtoꢀcubicꢀfluoriteꢀCeO ꢀcanꢀ
beꢀobservedꢀinꢀtheꢀXRDꢀpatternsꢀofꢀtheꢀC ,ꢀC
,ꢀandꢀC ꢀmixedꢀoxides.ꢀTheꢀcharacteristicꢀ
2
ꢀisꢀalsoꢀgivenꢀinꢀthisꢀ
C
C
C
6
6
6
A
M
M
0.5
ꢀ
ꢀ 9.1ꢀ
ꢀ 7.9ꢀ
ꢀ 7.1ꢀ
ꢀ 6.6ꢀ
ꢀ 6.2ꢀ
ꢀ 5.7ꢀ
5.4095ꢀ
5.4023ꢀ
5.3972ꢀ
5.3906ꢀ
5.3871ꢀ
5.3849ꢀ
2
4
ꢀ
4
A
0.25
0.5
1
(
C M A
6
6
6
4
4
A0.5ꢀsam‐
C
C
ꢀ
M
M
4
A
A
4
2
O
3 4
2
areꢀdisplayedꢀinꢀFig.ꢀ2(b).ꢀCeO
cm–1ꢀ attributedꢀ toꢀ theꢀ F2gꢀ vibrationꢀ modeꢀ ofꢀ cubicꢀ fluoriteꢀ
2
ꢀexhibitedꢀaꢀstrongꢀbandꢀatꢀ463ꢀ
A0.5,ꢀC M
6 6 4
6
M A0.25,ꢀ
4
C
6
M A0.5,ꢀC M A
4 6 4 1
M A
6 4 2
structureꢀ [14,33].ꢀ Theꢀ M 0.5ꢀ sampleꢀ showedꢀ aꢀ mainꢀ bandꢀ atꢀ
655ꢀ cm–1ꢀ assignedꢀ toꢀ theꢀ A1gꢀ vibrationꢀ modeꢀ ofꢀ hausmanniteꢀ
Mn ꢀ [34,35].ꢀ However,ꢀ bothꢀ theꢀ Ramanꢀ vibrationꢀ modesꢀ ofꢀ
CeO ꢀandꢀMn ꢀwereꢀdetectedꢀatꢀtheꢀcorrespondingꢀpositionsꢀ
forꢀtheꢀC ,ꢀC ,ꢀandꢀC ꢀsamples.ꢀ
4
A
linesꢀ ofꢀ aluminaꢀ andꢀ manganeseꢀ oxideꢀ wereꢀ absent,ꢀ andꢀ theꢀ
diffractionꢀpeaksꢀofꢀtheseꢀceria‐basedꢀmixedꢀoxidesꢀshiftedꢀtoꢀ
O
3 4
theꢀhighꢀangleꢀdirectionꢀslightlyꢀcomparedꢀwithꢀCeO
2
.ꢀThisꢀsug‐
gestedꢀthatꢀMn ꢀandꢀAl ꢀhaveꢀbeenꢀsuccessfullyꢀincorporatedꢀ
intoꢀtheꢀlatticeꢀofꢀCeO ꢀtoꢀformꢀaꢀuniformꢀsolidꢀsolutionꢀmain‐
2
O
3 4
n+
3+
M
6 4
6 4
M A0.25,ꢀC
6 4 6
M A0.5,ꢀC M
A
4 1
6 4 2
M A
2
Interestingly,ꢀtheꢀRamanꢀbandsꢀofꢀtheseꢀceria‐basedꢀmixedꢀox‐
idesꢀ wereꢀ shiftedꢀ toꢀ theꢀ lowꢀ wavenumberꢀ directionꢀ slightlyꢀ
tainingꢀtheꢀcubicꢀfluoriteꢀstructureꢀand/orꢀhighlyꢀdispersedꢀonꢀ
theꢀ surfaceꢀ ofꢀ theseꢀ samplesꢀ [21,22,27,28,30].ꢀ Theꢀ diffractionꢀ
peaksꢀ ofꢀ theseꢀ ceria‐basedꢀ mixedꢀ oxidesꢀ wereꢀ broaderꢀ andꢀ
2
comparedꢀwithꢀCeO ꢀandꢀMn
3 4
O ꢀ(Tableꢀ1),ꢀwhichꢀfurtherꢀcon‐
firmedꢀ thatꢀ aꢀ fractionꢀ ofꢀ theꢀ Mnn+ꢀ andꢀ Al3+ꢀ wereꢀ successfullyꢀ
weakerꢀthanꢀthoseꢀofꢀCeO
2
ꢀdueꢀtoꢀtheꢀdecreaseꢀofꢀcrystalliteꢀsizeꢀ
incorporatedꢀintoꢀtheꢀlatticeꢀofꢀCeO ,ꢀandꢀtheꢀrestꢀwereꢀhighlyꢀ
dispersedꢀonꢀtheꢀsurfaceꢀofꢀtheꢀsamplesꢀ[22,27].ꢀMoreover,ꢀweꢀ
2
n+
(
Tableꢀ 1),ꢀ whichꢀ indicatedꢀ thatꢀ theꢀ introductionꢀ ofꢀ Mn ꢀ andꢀ
3+
n+
3+
Al ꢀintoꢀtheꢀlatticeꢀofꢀCeO
27,31].ꢀ Especially,ꢀ theꢀ crystalliteꢀ sizeꢀ ofꢀ theꢀ Al‐containingꢀ
,ꢀandꢀC ꢀmixedꢀoxidesꢀwasꢀob‐
viouslyꢀ smallerꢀ thanꢀ thatꢀ ofꢀ theꢀ C ꢀ sample.ꢀ Furthermore,ꢀ
Tableꢀ1ꢀshowsꢀthatꢀtheꢀlatticeꢀparameterꢀofꢀtheseꢀceria‐basedꢀ
mixedꢀoxidesꢀisꢀsmallerꢀthanꢀthatꢀofꢀCeO .ꢀThisꢀwasꢀmainlyꢀbe‐
2
ꢀinhibitedꢀitsꢀgrainꢀgrowthꢀeffectivelyꢀ
canꢀfindꢀthatꢀwhenꢀMn ꢀandꢀAl ꢀwereꢀaddedꢀintoꢀCeO
2
,ꢀtheꢀfullꢀ
[
C
widthꢀatꢀhalfꢀmaximumꢀheightꢀ(FWHM)ꢀvalueꢀofꢀtheꢀceriaꢀF2g
ꢀ
6 4 6 4 6 4
M A0.25,ꢀC M A0.5,ꢀC M A
1
M A
6 4 2
bandꢀwasꢀbroadenedꢀremarkablyꢀ(Tableꢀ1),ꢀwhichꢀwasꢀrelatedꢀ
toꢀ theꢀ increaseꢀ ofꢀ defectꢀ concentrationꢀ andꢀ theꢀ decreaseꢀ ofꢀ
crystalliteꢀ sizeꢀ [21,36].ꢀ Especially,ꢀ theꢀ FWHMꢀ valueꢀ (F2g)ꢀ ofꢀ
M
6 4
2
6 4 6 4 6 4 1 6 4 2
Al‐containingꢀ C M A0.25,ꢀ C M A0.5,ꢀ C M A ,ꢀ andꢀ C M A ꢀ mixedꢀ
4+
3+
2+
causeꢀ theꢀ ionicꢀ radiusꢀ ofꢀ Mn ꢀ (0.54ꢀ Å),ꢀ Mn ꢀ (0.66ꢀ Å),ꢀ Mn ꢀ
6 4
oxidesꢀ wereꢀ obviouslyꢀ largerꢀ thanꢀ thatꢀ ofꢀ theꢀ C M ꢀ sample.ꢀ
3+
4+
(
0.80ꢀÅ),ꢀandꢀAl ꢀ(0.50ꢀÅ)ꢀareꢀsmallerꢀthanꢀthatꢀofꢀCe ꢀ(0.92ꢀÅ),ꢀ
Furthermore,ꢀitꢀcanꢀbeꢀseenꢀfromꢀFig.ꢀ2(b)ꢀthatꢀtheꢀintroductionꢀ
4+
3+
2+
3+
3+
andꢀ theꢀ incorporationꢀ ofꢀ Mn ,ꢀ Mn ,ꢀ Mn ,ꢀ andꢀ Al ꢀ intoꢀ theꢀ
latticeꢀofꢀCeO ꢀresultedꢀinꢀtheꢀshrinkageꢀandꢀdistortionꢀofꢀtheꢀ
ofꢀAl ꢀintoꢀC
6
M ꢀsampleꢀledꢀtoꢀtheꢀRamanꢀintensityꢀofꢀceriaꢀF2gꢀ
4
2
andꢀhausmanniteꢀA1gꢀweakeningꢀremarkably,ꢀwhileꢀtheꢀshiftꢀofꢀ
latticeꢀ[28,31,32].ꢀ
Ramanꢀ spectroscopyꢀ asꢀ aꢀ complementaryꢀ surfaceꢀ charac‐
terizationꢀofꢀXRDꢀwasꢀperformedꢀonꢀtheꢀsamples.ꢀTheꢀresultsꢀ
positionꢀofꢀF2gꢀwasꢀveryꢀslight,ꢀwhichꢀindicatedꢀthatꢀtheꢀexcessꢀ
Al3+ꢀwasꢀhighlyꢀdispersedꢀonꢀtheꢀsurfaceꢀofꢀtheseꢀsamples.ꢀAllꢀ
theꢀobservationsꢀwereꢀconsistentꢀwithꢀtheꢀXRDꢀresults.ꢀBasedꢀ
(a)
F2g
(b)
(111)
Mn3O4
(220)
(200)
(311)
222) (400) (420) (422)
(
331)
(
CeO2
C6A0.5
C6M4


0.1
0.2
C6M4A0.25
C6M4A0.5
C6M4A1
C6M4A2






M4A0.5
200




4 0.5
M A

A1g
10
20
30
40
50
60
70
80
90
400
600
800
1000
1
2 /(  )
Raman shift (cm )
Fig.ꢀ2.ꢀ(a)ꢀXRDꢀpatternsꢀandꢀ(b)ꢀRamanꢀspectraꢀofꢀtheꢀsamples.ꢀ

ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
1373ꢀ
onꢀtheꢀXRDꢀandꢀRamanꢀresults,ꢀweꢀconcludedꢀthatꢀtheꢀintroduc‐
5
43
3+
tionꢀofꢀAl ꢀintoꢀtheꢀC
liteꢀsize.ꢀInꢀaddition,ꢀaꢀfractionꢀofꢀtheꢀAl ꢀwasꢀincorporatedꢀintoꢀ
theꢀlatticeꢀofꢀCeO ,ꢀandꢀtheꢀrestꢀwereꢀhighlyꢀdispersedꢀonꢀtheꢀ
surfaceꢀofꢀtheseꢀsamples.ꢀ
6
M
4
ꢀsampleꢀfurtherꢀdecreasedꢀtheꢀcrystal‐
4
1
0

3+
767
8
C
6
A
0.5
06
2
511

CeO2
00
2
400
600
800
o
Temperature ( C)
2
3.3.ꢀ ꢀ Texturalꢀcharacterizationꢀ(N ꢀphysisorption)ꢀ
M4A0.5


Accordingꢀtoꢀtheꢀresultsꢀofꢀtheꢀcatalyticꢀperformance,ꢀtheꢀin‐
C M A
6
4
0.5
3+
troductionꢀofꢀaꢀsmallꢀamountꢀofꢀAl ꢀintoꢀC
hancedꢀ theꢀ catalyticꢀ performance.ꢀ Especially,ꢀ theꢀ C
mixedꢀoxideꢀpresentedꢀtheꢀbestꢀNOꢀconversionꢀandꢀN ꢀselectiv‐
ity.ꢀ Therefore,ꢀ inꢀ orderꢀ toꢀ exploreꢀ theꢀ influenceꢀ ofꢀ texturalꢀ
propertyꢀonꢀtheꢀcatalyticꢀperformanceꢀofꢀtheseꢀsamples,ꢀC
andꢀC 0.5ꢀmixedꢀoxidesꢀwereꢀchosenꢀasꢀrepresentativeꢀsam‐
plesꢀ forꢀ N2ꢀ physisorptionꢀ measurement.ꢀ Theꢀ resultsꢀ areꢀ pre‐
sentedꢀ inꢀ Fig.ꢀ 3.ꢀ N ꢀ adsorption‐desorptionꢀ isothermsꢀ andꢀ theꢀ
BJHꢀporeꢀdistributionꢀcurvesꢀofꢀCeO ꢀandꢀC 0.5ꢀareꢀalsoꢀexhib‐
6 4
M ꢀmixedꢀoxideꢀen‐


M A ꢀ
6 4 0.5
C6M4
00
2
1
200
300
400
500
600
6 4
M ꢀ
Temperature (C)
‐TPRꢀprofilesꢀofꢀrepresentativeꢀsamples.ꢀ
6
M A
4
Fig.ꢀ4.ꢀH
2
2
ofꢀcatalyticꢀperformance.ꢀ
2
6
A
itedꢀinꢀthisꢀfigureꢀforꢀcomparison.ꢀAllꢀtheꢀsamplesꢀexhibitedꢀtheꢀ
classicalꢀtypeꢀIVꢀaꢀisothermꢀwithꢀaꢀwellꢀdefinedꢀH2ꢀtypeꢀhyste‐
resisꢀloop,ꢀwhichꢀisꢀ theꢀ characteristicꢀofꢀaꢀ wormhole‐likeꢀandꢀ
interstitialꢀ mesoporousꢀ structureꢀ formedꢀ byꢀ nanoparticleꢀ as‐
semblyꢀ [37,38].ꢀ Moreover,ꢀ Fig.ꢀ 3(b)ꢀ showsꢀ thatꢀ theꢀ poreꢀ sizeꢀ
distributionꢀ curvesꢀ ofꢀ theseꢀ samplesꢀ obtainedꢀ byꢀ theꢀ BJHꢀ
methodꢀ exhibitedꢀ oneꢀ singleꢀ peakꢀ centeredꢀ atꢀ 4ꢀ nmꢀ (inꢀ theꢀ
mesoporousꢀrangeꢀofꢀ2‒50ꢀnm),ꢀwhichꢀfurtherꢀindicatedꢀthatꢀ
theseꢀsamplesꢀpossessedꢀaꢀmesoporousꢀstructure.ꢀTheꢀtexturalꢀ
dataꢀofꢀtheseꢀsamplesꢀareꢀalsoꢀdisplayedꢀinꢀFig.ꢀ3.ꢀInterestingly,ꢀ
3.4.ꢀ ꢀ Reductionꢀpropertyꢀ(H ‐TPR)ꢀ
2
Theꢀreductionꢀpropertyꢀofꢀtheꢀcatalystꢀisꢀaꢀkeyꢀfactorꢀinꢀre‐
doxꢀreactions.ꢀHence,ꢀaꢀH ‐TPRꢀtestꢀwasꢀperformedꢀonꢀtheꢀrep‐
resentativeꢀsamplesꢀofꢀtheꢀC ꢀandꢀC 0.5ꢀmixedꢀoxidesꢀforꢀ
2
M
6 4
6
M A
4
obtainingꢀtheꢀreductionꢀpropertyꢀinformation,ꢀasꢀshownꢀinꢀFig.ꢀ
4.ꢀInꢀorderꢀtoꢀgetꢀaꢀbetterꢀunderstandingꢀofꢀtheꢀreductionꢀbe‐
haviorꢀ ofꢀ manganeseꢀ oxide,ꢀ theꢀ H
sampleꢀisꢀalsoꢀdisplayed.ꢀFurthermore,ꢀtheꢀH
CeO ꢀ andꢀ C 0.5ꢀ mixedꢀ oxideꢀ areꢀ exhibitedꢀ forꢀ comparison.ꢀ Itꢀ
canꢀbeꢀseenꢀthatꢀCeO ꢀshowedꢀtwoꢀreductionꢀpeaksꢀatꢀ511ꢀandꢀ
806ꢀ°C,ꢀwhichꢀwereꢀassignedꢀtoꢀtheꢀreductionꢀofꢀsurfaceꢀCeO
andꢀ bulkꢀ CeO ,ꢀ respectivelyꢀ [21,39,40].ꢀ Similarly,ꢀ theꢀ C
2
‐TPRꢀ profileꢀ ofꢀ theꢀ M
4
A
0.5
ꢀ
2
‐TPRꢀprofilesꢀofꢀ
2
6
A
comparedꢀwithꢀCeO
2
,ꢀwhenꢀtheꢀdopedꢀionsꢀwereꢀincorporatedꢀ
2
intoꢀ theꢀ latticeꢀ ofꢀ CeO
2
ꢀ (i.e.,ꢀ C ,ꢀ andꢀ C 0.5ꢀ mixedꢀ
6
A
0.5,ꢀ C
6
M
4
6
M
4
A
2
ꢀ
oxides),ꢀ theꢀ BETꢀ specificꢀ surfaceꢀ areaꢀ increasedꢀ fromꢀ 39.8ꢀ toꢀ
2
A ꢀ
6 0.5
2
8
9.5,ꢀ99.1,ꢀandꢀ106.4ꢀm /g,ꢀaccompaniedꢀwithꢀtheꢀincreaseꢀofꢀ
mixedꢀoxideꢀalsoꢀexhibitedꢀtheꢀtwoꢀreductionꢀpeaks.ꢀHowever,ꢀ
theꢀrelativeꢀareaꢀofꢀtheꢀlow‐temperatureꢀreductionꢀpeakꢀforꢀtheꢀ
theꢀ poreꢀ volumeꢀ fromꢀ 0.1667ꢀ toꢀ 0.2600,ꢀ 0.3102,ꢀ andꢀ 0.4144ꢀ
3
cm /g.ꢀThisꢀwouldꢀbeꢀrelatedꢀtoꢀtheꢀdecreaseꢀofꢀtheꢀcrystalliteꢀ
C
6
A
0.5ꢀ mixedꢀ oxideꢀ wasꢀ obviouslyꢀ largerꢀ thanꢀ thatꢀ ofꢀ CeO
whichꢀwasꢀbecauseꢀofꢀtheꢀdecreaseꢀofꢀcrystalliteꢀsize,ꢀincreaseꢀ
ofꢀBETꢀspecificꢀsurfaceꢀarea,ꢀandꢀtheꢀinteractionꢀbetweenꢀCe4+
2
,ꢀ
sizeꢀofꢀtheseꢀ samplesꢀtoꢀ someꢀ extent.ꢀ Especially,ꢀtheꢀ C
M A ꢀ
6 4 0.5
mixedꢀoxideꢀexhibitedꢀtheꢀlargestꢀBETꢀspecificꢀsurfaceꢀareaꢀandꢀ
poreꢀvolume,ꢀwhichꢀisꢀbeneficialꢀforꢀsufficientꢀcontactꢀbetweenꢀ
catalystꢀandꢀreactants,ꢀandꢀfurtherꢀpromotesꢀtheꢀenhancementꢀ
ꢀ
andꢀAl3+ꢀ[41].ꢀAꢀceria‐basedꢀmixedꢀoxideꢀwithꢀaꢀsmallerꢀcrystal‐
liteꢀsizeꢀhasꢀmoreꢀexposedꢀsurfaceꢀoxygen,ꢀwhichꢀcanꢀreadilyꢀ
(a)
(b)
3
Pore volume = 0.4144 cm /g
C6M4A0.5
3
2
Pore volume = 0.3102 cm /g
BET = 106.4 m /g
C6M4
C6A0.5
CeO2
C6M4A0.5
C6M4
2
BET = 99.1 m /g
3
Pore volume = 0.2600 cm /g
2
BET = 89.5 m /g
C6A0.5
CeO2
3
2
Pore volume = 0.1667 cm /g
BET = 39.8 m /g
0.0
0.2
0.4
0.6
0.8
1.0
0
10
20
30
40
50
0
Relative pressure (p/p )
Pore diameter (nm)
Fig.ꢀ3.ꢀ(a)ꢀN ꢀadsorptionꢀisotherms,ꢀandꢀ(b)ꢀBJHꢀporeꢀdistributionꢀcurvesꢀofꢀrepresentativeꢀsamples.ꢀ
2

1374ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
interactꢀwithꢀhydrogenꢀinꢀtheꢀreductionꢀprocess.ꢀ
ItꢀcanꢀbeꢀseenꢀfromꢀFig.ꢀ4ꢀthatꢀtheꢀM 0.5ꢀsampleꢀexhibitedꢀ
Tableꢀ2ꢀ
4
A
QuantitativeꢀanalysisꢀofꢀH ‐TPRꢀforꢀrepresentativeꢀsamples.ꢀ
2
twoꢀreductionꢀpeaksꢀatꢀ350ꢀandꢀ490ꢀ°C,ꢀwhichꢀwereꢀlabeledꢀasꢀ
αꢀ andꢀ β.ꢀ Theꢀ low‐temperatureꢀ reductionꢀ peakꢀ (α)ꢀ canꢀ beꢀ at‐
Peakꢀtemperatureꢀ
(°C)ꢀ
H
2
ꢀconsumptionꢀ
(μmol/g)ꢀ
Peakꢀareaꢀratioꢀ
/S )ꢀ
Sampleꢀ
(S
α
β
tributedꢀ toꢀ theꢀ reductionꢀ ofꢀ MnO
high‐temperatureꢀ reductionꢀ peakꢀ (β)ꢀ canꢀ beꢀ assignedꢀ toꢀ theꢀ
reductionꢀofꢀMn ꢀtoꢀMnOꢀ[31,32].ꢀAlthoughꢀonlyꢀcrystallineꢀ
Mn ꢀwasꢀobservedꢀinꢀtheꢀXRDꢀpatternꢀofꢀtheꢀM 0.5ꢀsample,ꢀ
MnO /Mn ꢀmayꢀbeꢀhighlyꢀdispersedꢀonꢀtheꢀsurfaceꢀofꢀcrystal‐
lineꢀMn .ꢀThisꢀneedsꢀtoꢀbeꢀfurtherꢀconfirmedꢀbyꢀXPSꢀcharac‐
terization.ꢀTheꢀC ꢀandꢀC 0.5ꢀmixedꢀoxidesꢀalsoꢀpresentedꢀ
twoꢀreductionꢀpeaksꢀ(αꢀandꢀβ).ꢀCombinedꢀwithꢀtheꢀH ‐TPRꢀpro‐
fileꢀofꢀCeO ,ꢀtheseꢀreductionꢀpeaksꢀwereꢀnotꢀonlyꢀattributedꢀtoꢀ
theꢀ reductionꢀ ofꢀ manganeseꢀ oxide,ꢀ butꢀ alsoꢀ containedꢀ theꢀ re‐
ductionꢀofꢀsurfaceꢀCeO ꢀ[31].ꢀInterestingly,ꢀtheꢀreductionꢀpeaksꢀ
ofꢀtheꢀC ꢀandꢀC 0.5ꢀmixedꢀoxidesꢀwereꢀobviouslyꢀshiftꢀtoꢀ
theꢀ lowꢀ temperatureꢀ directionꢀ comparedꢀ withꢀ thoseꢀ ofꢀ theꢀ
0.5ꢀsample,ꢀwhichꢀindicatedꢀthatꢀsomeꢀinteractionꢀmayꢀexistꢀ
2 2 3 3 4
/Mn O ꢀ toꢀ Mn O ,ꢀ andꢀ theꢀ
αꢀ
βꢀ
αꢀ
βꢀ
α+βꢀ
C
C
6
M
4
ꢀ
A
246ꢀ
226ꢀ
350ꢀ
340ꢀ
329ꢀ
490ꢀ
ꢀ 860ꢀ ꢀ 977ꢀ 1837ꢀ
ꢀ 855ꢀ ꢀ 789ꢀ 1644ꢀ
1675ꢀ 2912ꢀ 4587ꢀ
0.88ꢀ
1.08ꢀ
0.58ꢀ
6
M
4
0.5
ꢀ
O
3 4
M A ꢀ
4 0.5
ꢀ
O
3 4
4
A
2
O
2 3
O
3 4
6 4
C M A
0.5ꢀmixedꢀoxideꢀcontainedꢀtheꢀlargestꢀamountꢀofꢀhighꢀva‐
lenceꢀmanganeseꢀ(suchꢀasꢀMn ꢀandꢀMn ).ꢀ
4+
3+
M
6 4
6 4
M A
2
2
3.5.ꢀ ꢀ Surfaceꢀchemicalꢀstateꢀanalysisꢀ(XPS)ꢀ
2
Inꢀ orderꢀ toꢀ furtherꢀ investigateꢀ theꢀ valenceꢀ state,ꢀ surfaceꢀ
composition,ꢀ andꢀ electronꢀ interactionꢀ ofꢀ theseꢀ samples,ꢀ XPSꢀ
wasꢀcarriedꢀoutꢀonꢀtheꢀrepresentativeꢀsamplesꢀofꢀtheꢀC
0.5ꢀmixedꢀoxides.ꢀTheꢀresultsꢀareꢀdisplayedꢀinꢀFig.ꢀ5.ꢀToꢀ
facilitateꢀcomparison,ꢀtheꢀspectraꢀofꢀtheꢀC 0.5ꢀandꢀM 0.5ꢀsam‐
plesꢀareꢀalsoꢀexhibitedꢀinꢀthisꢀfigure.ꢀTheꢀcomplexꢀCeꢀ3dꢀspec‐
trumꢀofꢀtheseꢀsamplesꢀwasꢀfittedꢀbyꢀeightꢀphotoelectronꢀpeaksꢀ
correspondingꢀtoꢀtheꢀfourꢀpairsꢀofꢀspin‐orbitꢀsplitꢀdoubletsꢀwithꢀ
theꢀ assignmentꢀshownꢀinꢀFig.ꢀ 5(a).ꢀItꢀcanꢀ beꢀ seenꢀthatꢀ allꢀtheꢀ
M
6 4
6
M A
4
6
M ꢀandꢀ
4
M
4
A
C
6
M A
4
4+
n+
betweenꢀCe ꢀandꢀMn ꢀtoꢀpromoteꢀtheꢀreductionꢀofꢀmanganeseꢀ
oxide.ꢀEspecially,ꢀtheꢀC 0.5ꢀmixedꢀoxideꢀexhibitedꢀtheꢀlowestꢀ
6
A
4
A
6
4
M A
temperatureꢀ ofꢀ theꢀ reductionꢀ peaksꢀ amongꢀ theseꢀ samples,ꢀ
whichꢀmayꢀbeꢀrelatedꢀtoꢀitsꢀsmallestꢀcrystalliteꢀsize.ꢀQuantita‐
tiveꢀdataꢀfromꢀH
Theꢀ reductionꢀ peakꢀ areaꢀ ratioꢀ (S
rankedꢀ byꢀM ꢀ<ꢀC M A
2
‐TPRꢀforꢀtheseꢀsamplesꢀareꢀlistedꢀinꢀTableꢀ2.ꢀ
/S )ꢀ ofꢀ theseꢀ samplesꢀ wasꢀ
0.5,ꢀwhichꢀindicatedꢀthatꢀtheꢀ
α
β
C A0.5,ꢀ C
6
6
M
4
,ꢀ andꢀ C
6
M A0.5ꢀ mixedꢀ oxidesꢀ exhibitedꢀ sixꢀ strongꢀ
4
4
A
0.5ꢀ<ꢀC
M
6 4
6
4
photoelectronꢀ peaksꢀ labeledꢀ u‴ꢀ andꢀ ν‴,ꢀ u″ꢀ andꢀ ν″,ꢀ uꢀ andꢀ ν,ꢀ
(b)
(
a)
Mn 2p
Ce 3d
Mn2+
Mn3+
Mn4+
u'''
v'''
0
u ,u
0
v ,v
u''
C6A0.5
u'
v''
v'
M4A0.5
C6M4
C6M4
C6M4A0.5
C6M4A0.5
Mn 2p1/2
655
Mn 2p3/2
Ce 3d3/2
Ce 3d5/2
920
910
900
890
880
660
650
645
640
635
Binding energy (eV)
Binding energy (eV)
Al 2p
(c)
O 1s
O'
(d)
7
3.5
O''
M4A0.5
C6M4A0.5
C6M4
M4A0.5
C6A0.5
C6M4A0.5
C6A0.5
7
3.3
7
8
76
74
72
70
68
534
532
530
528
526
524
Binding energy (eV)
Binding energy (eV)
Fig.ꢀ5.ꢀXPSꢀprofilesꢀofꢀrepresentativeꢀsamples.ꢀ(a)ꢀCeꢀ3d;ꢀ(b)ꢀMnꢀ2p;ꢀ(c)ꢀAlꢀ2p;ꢀ(d)ꢀOꢀ1s.ꢀ

ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
1375ꢀ
Tableꢀ3ꢀ
SurfaceꢀcompositionꢀofꢀrepresentativeꢀsamplesꢀbyꢀXPSꢀanalysis.ꢀ
Atomicꢀconcentrationꢀ(at%)ꢀ
Sampleꢀ
Atomicꢀratioꢀ(%)ꢀ
Ce /(Ce +Ce )ꢀ Mn /(Mn +Mn +Mn )
3+
3+
4+
4+
2+
3+
4+
Cꢀ
Ceꢀ
Mnꢀ
—ꢀ
Alꢀ
Oꢀ
O″/O′ꢀ
C
6
C
6
C
6
A
M
M
0.5
ꢀ
41.06ꢀ
40.09ꢀ
38.84ꢀ
26.65ꢀ
11.22ꢀ
10.61ꢀ
10.42ꢀ
—ꢀ
2.05ꢀ
—ꢀ
1.28ꢀ
9.63ꢀ
45.67ꢀ
45.42ꢀ
46.22ꢀ
52.60ꢀ
11.14ꢀ
12.63ꢀ
13.89ꢀ
—ꢀ
—ꢀ
46.89ꢀ
39.58ꢀ
63.09ꢀ
78.03ꢀ
4
ꢀ
ꢀ 3.88ꢀ
ꢀ 3.24ꢀ
11.12ꢀ
29.34ꢀ
32.55ꢀ
24.75ꢀ
4
A
0.5
ꢀ
M A ꢀ
4 0.5
4
+
whichꢀwereꢀascribedꢀtoꢀCe ꢀ[42‒44].ꢀFurthermore,ꢀtwoꢀweakꢀ
TheꢀAlꢀ2pꢀspectrumꢀofꢀtheꢀM
4
A
0.5,ꢀC
6
A
0.5,ꢀandꢀC
6
M A0.5ꢀsam‐
4
3+
photoelectronꢀ peaksꢀ (u′ꢀ andꢀ ν′)ꢀ correspondingꢀ toꢀ Ce ꢀ wereꢀ
alsoꢀobservedꢀonꢀtheꢀthreeꢀsamples,ꢀwhichꢀindicatedꢀthatꢀtheꢀ
chemicalꢀvalenceꢀofꢀCeꢀwasꢀmainlyꢀaꢀ+4ꢀoxidationꢀstate,ꢀandꢀaꢀ
littleꢀofꢀCe ꢀcoexistedꢀ[43‒45].ꢀTheꢀrelativeꢀcontentꢀofꢀCe ꢀinꢀ
theseꢀ samplesꢀ canꢀ beꢀ calculatedꢀ byꢀ theꢀ followingꢀ equationꢀ
basedꢀonꢀtheꢀpeakꢀareaꢀ[22,46]:ꢀ
plesꢀisꢀdisplayedꢀinꢀFig.ꢀ5(c).ꢀAꢀsingleꢀstrongꢀphotoelectronꢀpeakꢀ
centeredꢀatꢀ73.5ꢀeVꢀwasꢀobservedꢀoverꢀtheꢀM 0.5ꢀsample.ꢀTheꢀ
0.5ꢀ samplesꢀ exhibitedꢀ thisꢀ peakꢀ atꢀ aꢀ lowerꢀ
bindingꢀenergyꢀofꢀ73.3ꢀeV,ꢀwhichꢀindicatedꢀthatꢀsomeꢀinterac‐
4
A
C
6
A
0.5ꢀ andꢀ C
6
M A
4
3+
3+
4+
3+
tionꢀexistedꢀbetweenꢀCe ꢀandꢀAl .ꢀThisꢀobservationꢀsuggestedꢀ
3+
thatꢀ theꢀ introductionꢀ ofꢀ reductantꢀ Al ꢀ intoꢀ theꢀ C
6
M ꢀ sampleꢀ
4
Su'  S v'
weakenedꢀtheꢀinteractionꢀofꢀCe4+ꢀandꢀMnn+,ꢀwhichꢀwasꢀharmfulꢀ
3

ꢀ
100%
Ce

(
S  S )
toꢀtheꢀenhancementꢀofꢀcatalyticꢀperformance.ꢀTheꢀhighꢀresolu‐
tionꢀ spectrumꢀ ofꢀ theꢀ Oꢀ 1sꢀ ionizationꢀ featureꢀ ofꢀ theseꢀ repre‐
sentativeꢀsamplesꢀwasꢀnumericallyꢀfittedꢀwithꢀtwoꢀcomponents,ꢀ
whichꢀareꢀexhibitedꢀinꢀFig.ꢀ5(d).ꢀAllꢀtheseꢀsamplesꢀshowꢀaꢀmainꢀ
peakꢀ (O′)ꢀ andꢀ aꢀ shoulderꢀ (O″)ꢀ withꢀ aꢀ higherꢀ bindingꢀ energy,ꢀ
whichꢀwasꢀattributedꢀtoꢀtheꢀcharacteristicꢀlatticeꢀoxygenꢀbond‐
edꢀtoꢀmetalꢀcations,ꢀandꢀsurfaceꢀadsorbedꢀoxygen,ꢀrespectivelyꢀ

u
v
Theꢀ surfaceꢀ atomicꢀ concentrationꢀ andꢀ atomicꢀ ratioꢀ ofꢀ theꢀ
3+
samplesꢀ areꢀ summarizedꢀ inꢀ Tableꢀ 3.ꢀ Theꢀ Ce ꢀ contentꢀ ofꢀ theꢀ
ꢀandꢀC 0.5ꢀmixedꢀoxidesꢀwasꢀobviouslyꢀlargerꢀthanꢀthatꢀ
ofꢀtheꢀC 0.5ꢀsample,ꢀwhichꢀmayꢀbeꢀrelatedꢀtoꢀelectronꢀinterac‐
tion,ꢀdopedꢀamount,ꢀandꢀcrystalliteꢀsize.ꢀEspecially,ꢀtheꢀC A ꢀ
C
6
M
4
6
M A
4
6
A
6
M
4
0.5
3+
mixedꢀ oxideꢀ exhibitedꢀ theꢀ largestꢀ Ce ꢀ content.ꢀ Thereꢀ wereꢀ
threeꢀpossibleꢀreasons,ꢀtheꢀfirstꢀisꢀthatꢀelectronꢀinteractionꢀmayꢀ
[
22,47].ꢀComparedꢀwithꢀtheꢀM 0.5ꢀsample,ꢀtheꢀO′ꢀandꢀO″ꢀpeaksꢀ
4
A
4
+
n+
4+
3+
3+
ofꢀtheꢀC ,ꢀandꢀC M A0.5ꢀmixedꢀoxidesꢀwereꢀshiftedꢀtoꢀ
A0.5,ꢀC M
6 6 4
6
4
beꢀexistedꢀbetweenꢀCe ꢀandꢀMn ꢀ(suchꢀasꢀCe ꢀ+ꢀMn ꢀ↔ꢀCe ꢀ+ꢀ
4+
4+
2+
3+
3+
4+
2+
3+
theꢀ lowꢀ bindingꢀ energyꢀ direction,ꢀ whichꢀ furtherꢀ suggestedꢀ
someꢀ interactionꢀ betweenꢀ ceriumꢀ andꢀ theꢀ dopedꢀ ions.ꢀ Fur‐
thermore,ꢀitꢀcanꢀbeꢀseenꢀfromꢀTableꢀ3ꢀthatꢀtheꢀratioꢀofꢀO″/O′ꢀforꢀ
Mn ,ꢀCe ꢀ+ꢀMn ꢀ↔ꢀCe ꢀ+ꢀMn ,ꢀandꢀ2Ce ꢀ+ꢀMn ꢀ↔ꢀ2Ce ꢀ+ꢀ
4+
4+
Mn )ꢀ[47];ꢀtheꢀsecondꢀisꢀthatꢀtheꢀsubstitutionꢀofꢀCe ꢀ(rꢀ=ꢀ0.92ꢀ
4+
3+
2+
Å)ꢀbyꢀMn ꢀ(rꢀ=ꢀ0.54ꢀÅ),ꢀMn ꢀ(rꢀ=ꢀ0.66ꢀÅ),ꢀMn ꢀ(rꢀ=ꢀ0.80ꢀÅ),ꢀandꢀ
3+
theꢀC
thatꢀforꢀtheꢀC
increaseꢀofꢀdefectꢀconcentrationꢀandꢀtheꢀdecreaseꢀofꢀcrystalliteꢀ
6 4
M A0.5ꢀmixedꢀoxideꢀ(63.09%)ꢀwasꢀobviouslyꢀlargerꢀthanꢀ
Al ꢀ(rꢀ=ꢀ0.50ꢀÅ)ꢀleadsꢀtoꢀtheꢀcontractionꢀofꢀtheꢀlatticeꢀofꢀCeO ꢀ
whileꢀtheꢀspontaneousꢀtransformationꢀofꢀCe ꢀ(rꢀ=ꢀ0.92ꢀÅ)ꢀintoꢀ
largerꢀCe ꢀ(rꢀ=ꢀ1.03ꢀÅ)ꢀcanꢀcompensateꢀforꢀthisꢀlatticeꢀcontrac‐
tionꢀ[19,22];ꢀandꢀtheꢀthirdꢀisꢀthatꢀtheꢀrelativeꢀcontentꢀofꢀCe ꢀinꢀ
theꢀparticlesꢀwasꢀinverselyꢀproportionalꢀtoꢀtheꢀcrystalliteꢀsizeꢀ
2
4+
6 4
M ꢀmixedꢀoxideꢀ(39.58%).ꢀThisꢀwasꢀrelatedꢀtoꢀtheꢀ
3+
3+
3
+
sizeꢀcausedꢀbyꢀtheꢀincorporationꢀofꢀAl ꢀ(supportedꢀbyꢀtheꢀXRDꢀ
andꢀ Ramanꢀ results),ꢀ whichꢀ isꢀ beneficialꢀ forꢀ theꢀ adsorptionꢀ ofꢀ
oxygen.ꢀ
[
48,49],ꢀwhichꢀwasꢀsupportedꢀbyꢀtheꢀXRDꢀresults.ꢀ
TheꢀMnꢀ2pꢀspectrumꢀofꢀtheꢀM ,ꢀandꢀC
4
A
0.5,ꢀC
6
M
4
6
M A0.5ꢀsam‐
4
3
.6.ꢀ ꢀ COꢀor/andꢀNOꢀinteractionꢀwithꢀtheꢀcatalystsꢀ(inꢀsituꢀ
plesꢀ wasꢀ numericallyꢀ fittedꢀ withꢀ sixꢀ photoelectronꢀ peaksꢀ (asꢀ
shownꢀinꢀFig.ꢀ5(b)),ꢀwhichꢀindicatedꢀthatꢀtheꢀMnꢀspeciesꢀexistedꢀ
inꢀtheꢀformꢀofꢀaꢀmixedꢀvalenceꢀmanganeseꢀsystemꢀonꢀtheꢀsur‐
faceꢀ ofꢀ theseꢀ samples.ꢀ Itꢀ canꢀ beꢀ seenꢀ fromꢀ Fig.ꢀ 5(b)ꢀ thatꢀ Mnꢀ
DRIFTS)ꢀ
InꢀsituꢀDRIFTSꢀofꢀCOꢀadsorptionꢀasꢀaꢀfunctionꢀofꢀtemperatureꢀ
wasꢀperformedꢀonꢀtheꢀrepresentativeꢀsamplesꢀofꢀtheꢀC ꢀandꢀ
0.5ꢀ mixedꢀ oxidesꢀ toꢀ understandꢀ theirꢀ reductionꢀ andꢀ ad‐
sorptionꢀproperties.ꢀTheꢀresultsꢀareꢀpresentedꢀinꢀFig.ꢀ6.ꢀWhenꢀ
theꢀC ꢀmixedꢀoxideꢀwasꢀexposedꢀtoꢀCOꢀatꢀroomꢀtemperatureꢀ
(25ꢀ °C),ꢀ itꢀ exhibitedꢀ twoꢀ vibrationꢀ bandsꢀ atꢀ 1304ꢀ andꢀ 1570ꢀ
6
M
4
2p3/2ꢀ containedꢀ threeꢀ characteristicꢀ peaks,ꢀ whichꢀ wereꢀ at‐
2
+
3+
C
6
M A
4
tributedꢀtoꢀthreeꢀMnꢀspecies,ꢀMn ꢀ(640.0ꢀeV),ꢀMn ꢀ(641.3ꢀeV),ꢀ
4+
andꢀMn ꢀ(643.3ꢀeV)ꢀ[47,50].ꢀTheꢀMnꢀ2p1/2ꢀalsoꢀshowedꢀthreeꢀ
M
6 4
Mnꢀspeciesꢀinꢀtheꢀbindingꢀenergyꢀrangeꢀofꢀ650–658ꢀeV.ꢀTableꢀ3ꢀ
4+
showsꢀthatꢀtheꢀrelativeꢀcontentꢀofꢀMn ꢀinꢀtheseꢀsamplesꢀwasꢀ
rankedꢀbyꢀM ꢀ<ꢀC 0.5,ꢀwhichꢀwasꢀconsistentꢀwithꢀ
theꢀresultsꢀofꢀH ‐TPR.ꢀEspecially,ꢀtheꢀC 0.5ꢀmixedꢀoxideꢀex‐
hibitedꢀ theꢀ largestꢀ Mn ꢀ content,ꢀ whichꢀ indicatedꢀ thatꢀ theꢀ in‐
–1
cm ,ꢀ whichꢀ wereꢀ attributedꢀ toꢀ monodentateꢀ carbonateꢀ andꢀ
carboxylate,ꢀ respectivelyꢀ [17,22,52,53].ꢀ Theꢀ intensityꢀ ofꢀ theseꢀ
twoꢀ bandsꢀ weakenedꢀ withꢀ theꢀ increaseꢀ ofꢀ temperature,ꢀ andꢀ
completelyꢀdisappearedꢀatꢀ400ꢀandꢀ300ꢀ°C.ꢀFurthermore,ꢀwhenꢀ
theꢀtemperatureꢀwasꢀincreasedꢀtoꢀ150ꢀ°C,ꢀtwoꢀnewꢀbandsꢀap‐
pearedꢀ atꢀ 1383ꢀ andꢀ 1473ꢀ cm ,ꢀ whichꢀ wereꢀ assignedꢀ toꢀ theꢀ
differentꢀ vibrationꢀ modesꢀ ofꢀ bidentateꢀ carbonateꢀ [52,53].ꢀ In‐
creasingꢀtheꢀtemperatureꢀtoꢀ250ꢀ°Cꢀledꢀtoꢀaꢀnewꢀbandꢀatꢀ1548ꢀ
cm ꢀ correspondingꢀ toꢀ theꢀ vibrationꢀ modeꢀ ofꢀ formate,ꢀ whichꢀ
wasꢀrelatedꢀtoꢀtheꢀsurfaceꢀhydroxylꢀgroupꢀofꢀtheꢀsampleꢀ[53].ꢀ
Interestingly,ꢀ theꢀ intensityꢀ ofꢀ theseꢀ threeꢀ newꢀ bandsꢀ wasꢀ en‐
hancedꢀwithꢀtheꢀincreaseꢀofꢀtemperatureꢀdueꢀtoꢀtheꢀreductionꢀ
A0.5ꢀ<ꢀC M
4 6 4
6
M A
4
2
6
M A
4
4+
3
+
corporationꢀofꢀAl ꢀintoꢀtheꢀC
6
M ꢀmixedꢀoxideꢀledꢀtoꢀtheꢀredoxꢀ
4
4+
3+
3+
4+
4+
2+
3+
cyclesꢀ(Ce ꢀ+ꢀMn ꢀ↔ꢀCe ꢀ+ꢀMn ꢀandꢀ2Ce ꢀ+ꢀMn ꢀ↔ꢀ2Ce ꢀ+ꢀ
–1
4+
Mn )ꢀ toꢀ shiftꢀ toꢀ theꢀ rightꢀ throughꢀ decreasingꢀ theꢀ crystalliteꢀ
4+
size.ꢀMoreover,ꢀitꢀisꢀwidelyꢀreportedꢀthatꢀtheꢀMn ꢀspeciesꢀpos‐
sessedꢀ theꢀ optimalꢀ redoxꢀ propertyꢀ ofꢀ theꢀ manganese‐basedꢀ
catalysts,ꢀ whichꢀ isꢀ beneficialꢀ toꢀ theꢀ enhancementꢀ ofꢀ catalyticꢀ
performanceꢀ forꢀ manyꢀ redoxꢀ reactionsꢀ [47,51].ꢀ Hence,ꢀ theꢀ
–1
4+
largestꢀMn ꢀcontentꢀofꢀC
6
M A0.5ꢀfavoredꢀtheꢀbestꢀcatalyticꢀper‐
4
formanceꢀforꢀNOꢀelimination.ꢀ

1376ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
(a)
(b)
C6M4
6 4
C M A
0.5
1
o
2
4
4
3
3
2
2
1
1
50 C
o
00 C
o
50 C
o
1382
1
473
00 C
o
1
383
o
1472
450 C
50 C
o
1
548
o
4
00 C
00 C
o
o
350 C
50 C
1546
o
o
300 C
00 C
o
o
250 C
2
5 C
o
2
1
1
00 C
o
50 C
o
00 C
o
2
5 C
1
570
1600
Wavenumber (cm )
1304
1573
1600
1299
2000
1800
1400
1200
1000
2000
1800
1400
1200
1000
1
1
Wavenumber (cm )
6 4 6 4
Fig.ꢀ6.ꢀInꢀsituꢀDRIFTSꢀofꢀCOꢀinteractionꢀwithꢀ(a)ꢀC M ꢀandꢀ(b)ꢀC M A0.5ꢀmixedꢀoxides.ꢀ
4
+
3+
ofꢀ Ce ꢀ byꢀ COꢀ toꢀ generateꢀ moreꢀ Ce ꢀ duringꢀ theꢀ heating,ꢀ andꢀ
C
6
M
4
ꢀ mixedꢀ oxideꢀ promotedꢀ theꢀ adsorptionꢀ ofꢀ CO,ꢀ whichꢀ re‐
3+
Ce ꢀ isꢀ beneficialꢀ toꢀ theꢀ adsorptionꢀ ofꢀ COꢀ speciesꢀ [22,54,55].ꢀ
WithꢀregardꢀtoꢀtheꢀC 0.5ꢀmixedꢀoxide,ꢀwhenꢀitꢀwasꢀexposedꢀ
toꢀCOꢀatꢀroomꢀtemperatureꢀandꢀduringꢀtheꢀheating,ꢀallꢀofꢀtheꢀ
vibrationꢀ bandsꢀ ofꢀ monodentateꢀ carbonate,ꢀ carboxylate,ꢀ bi‐
dentateꢀ carbonate,ꢀ andꢀ formateꢀ wereꢀ detected,ꢀ whichꢀ isꢀ veryꢀ
similarꢀtoꢀtheꢀC
(b)ꢀwithꢀFig.ꢀ6(a),ꢀweꢀcanꢀfindꢀthatꢀtheꢀintensityꢀchangeꢀofꢀvi‐
brationꢀbandsꢀforꢀtheꢀC 0.5ꢀmixedꢀoxideꢀwithꢀtheꢀincreaseꢀofꢀ
temperatureꢀwasꢀmoreꢀobviousꢀthanꢀthatꢀforꢀtheꢀC ꢀmixedꢀ
oxide.ꢀ Thisꢀ indicatedꢀ thatꢀ theꢀ incorporationꢀ ofꢀ Al ꢀ intoꢀ theꢀ
sultedꢀ fromꢀ theꢀ improvementꢀ ofꢀ theꢀ reductionꢀ property,ꢀ andꢀ
benefitedꢀtoꢀgenerateꢀmoreꢀCe ꢀduringꢀtheꢀheatingꢀtoꢀadsorbꢀ
COꢀspecies.ꢀ
Itꢀisꢀwellꢀknownꢀthatꢀtheꢀadsorptionꢀandꢀdesorptionꢀproper‐
tyꢀofꢀaꢀdenitrationꢀcatalystꢀforꢀNOꢀisꢀaꢀkeyꢀfactorꢀinꢀtheꢀcatalyticꢀ
reductionꢀofꢀNOꢀbyꢀCO.ꢀTherefore,ꢀinꢀsituꢀDRIFTSꢀofꢀNOꢀadsorp‐
tionꢀwasꢀcarriedꢀoutꢀonꢀtheꢀrepresentativeꢀsamplesꢀofꢀtheꢀC
andꢀC 0.5ꢀmixedꢀoxidesꢀatꢀvariousꢀtemperatures,ꢀasꢀshownꢀ
inꢀFig.ꢀ7.ꢀForꢀtheꢀC ꢀmixedꢀoxide,ꢀwhenꢀitꢀwasꢀexposedꢀtoꢀNOꢀ
3+
6 4
M A
6
M ꢀmixedꢀoxide.ꢀHowever,ꢀonꢀcomparingꢀFig.ꢀ
4
6
6 4
M ꢀ
6 4
M A
6
M A
4
6
M
4
M
6 4
3+
atꢀroomꢀtemperature,ꢀseveralꢀIRꢀbandsꢀappearꢀinꢀtheꢀrangeꢀofꢀ
(a)
(b)
2
C6M4
2
C M A
6
4
0.5
1237
1011
1539
1011
1
355 1211
1356
o
o
4
4
3
3
2
2
1
1
50 C
450 C
o
o
00 C
400 C
o
o
50 C
350 C
o
o
00 C
300 C
o
o
50 C
250 C
o
o
00 C
200 C
o
o
50 C
150 C
o
o
00 C
100 C
o
o
2
5 C
25 C
1574
1
574
1284
1237
1285
1605
1
603
2000
1800
1600
1400
1200
1000
2000
1800
1600
1400
1200
1000
1
1
Wavenumber (cm )
Wavenumber (cm )
6 4 6 4
Fig.ꢀ7.ꢀInꢀsituꢀDRIFTSꢀofꢀNOꢀinteractionꢀwithꢀ(a)ꢀC M ꢀandꢀ(b)ꢀC M A0.5ꢀmixedꢀoxides.ꢀ

ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
1377ꢀ
–
1
1
NO
000–1700ꢀ cm .ꢀ Theꢀ bridgingꢀ bidentateꢀ nitrateꢀ exhibitedꢀ aꢀ
°Cꢀ [56,57].ꢀ Theseꢀ observationsꢀ suggestedꢀ thatꢀ adsorbedꢀ NOꢀ
speciesꢀonꢀtheꢀsurfaceꢀofꢀtheꢀC 0.5ꢀmixedꢀoxideꢀwereꢀmoreꢀ
easilyꢀdesorbedꢀorꢀconvertedꢀorꢀdissociatedꢀwithꢀtheꢀincreaseꢀ
ofꢀ temperatureꢀ thanꢀ thoseꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ C ꢀ mixedꢀ
–1
2
ꢀ symmetricꢀ vibrationꢀ modeꢀ atꢀ 1011ꢀ cm ꢀ andꢀ aꢀ N=Oꢀ
stretchingꢀmodeꢀatꢀ1603ꢀcm .ꢀTheꢀchelatingꢀbidentateꢀnitrateꢀ
displayedꢀtwoꢀbandsꢀofꢀsymmetricꢀandꢀasymmetricꢀvibrationꢀatꢀ
6
M A
4
–1
6
M
4
–1
3+
1
237ꢀandꢀ1574ꢀcm ,ꢀrespectively.ꢀTheꢀlinearꢀnitriteꢀpresentedꢀ
oxide.ꢀTheꢀreasonꢀmayꢀbeꢀthatꢀtheꢀincorporationꢀofꢀAl ꢀintoꢀtheꢀ
–1
4+
aꢀ vibrationꢀ bandꢀ atꢀ 1285ꢀ cm ꢀ [22,56,57].ꢀ Someꢀ interestingꢀ
phenomenaꢀwereꢀobservedꢀinꢀtheꢀheatingꢀprocess.ꢀFirst,ꢀwhenꢀ
theꢀtemperatureꢀincreasedꢀtoꢀ300ꢀ°C,ꢀtheꢀN=Oꢀstretchingꢀmodeꢀ
ofꢀ theꢀ bridgingꢀ bidentateꢀ nitrateꢀ (1603ꢀ cm )ꢀ andꢀ theꢀ linearꢀ
nitriteꢀ (1285ꢀ cm )ꢀ disappearedꢀ completely.ꢀ Second,ꢀ aꢀ newꢀ
bandꢀofꢀfreeꢀNO
peratureꢀ wasꢀ upꢀ toꢀ 400ꢀ °Cꢀ [57].ꢀ Finally,ꢀ theꢀ NO
vibrationꢀbandꢀofꢀtheꢀbridgingꢀbidentateꢀnitrateꢀ(1011ꢀcm ),ꢀasꢀ
wellꢀasꢀtheꢀsymmetricꢀandꢀasymmetricꢀvibrationꢀbandsꢀofꢀtheꢀ
chelatingꢀ bidentateꢀ nitrateꢀ (1237ꢀ andꢀ 1574ꢀ cm )ꢀ weakenedꢀ
withꢀtheꢀtemperature,ꢀbutꢀdidꢀnotꢀcompletelyꢀdisappearꢀevenꢀatꢀ
C M
6
4
ꢀ mixedꢀ oxideꢀ promotedꢀ theꢀ increaseꢀ ofꢀ Mn ꢀ contentꢀ
4+
(supportedꢀbyꢀtheꢀH ‐TPRꢀandꢀXPSꢀresults),ꢀandꢀMn ꢀisꢀcondu‐
2
civeꢀtoꢀtheꢀdesorptionꢀorꢀconversionꢀorꢀdissociationꢀofꢀtheꢀad‐
sorbedꢀNOꢀspeciesꢀbyꢀelectronꢀtransferꢀ[47].ꢀ
InꢀorderꢀtoꢀgetꢀmoreꢀinformationꢀaboutꢀtheꢀreactionꢀofꢀNOꢀ
reductionꢀbyꢀCO,ꢀinꢀsituꢀDRIFTSꢀofꢀNO+COꢀco‐adsorptionꢀwereꢀ
–1
–1
–
–1
3
ꢀionsꢀappearedꢀatꢀ1356ꢀcm ꢀwhenꢀtheꢀtem‐
ꢀ symmetricꢀ
2
recordedꢀ onꢀ theꢀ representativeꢀ samplesꢀ ofꢀ theꢀ C
0.5ꢀ mixedꢀ oxidesꢀ underꢀ simulatedꢀ reactionꢀ conditions.ꢀ
Theꢀ resultsꢀ areꢀ presentedꢀ inꢀ Fig.ꢀ 8.ꢀ Exposingꢀ theꢀ C ꢀmixedꢀ
6 4
M ꢀ andꢀ
–1
C
6
M A
4
M
6 4
–1
oxideꢀtoꢀNOꢀandꢀCOꢀmixedꢀgasesꢀatꢀroomꢀtemperatureꢀledꢀtoꢀ
severalꢀvibrationꢀbandsꢀforꢀnitrateꢀandꢀnitriteꢀthatꢀappearedꢀinꢀ
–1
4
50ꢀ °C.ꢀ Theseꢀ observationsꢀ indicatedꢀ thatꢀ theꢀ adsorbedꢀ NOꢀ
speciesꢀonꢀtheꢀsurfaceꢀofꢀtheꢀC ꢀmixedꢀoxideꢀcanꢀbeꢀdesorbedꢀ
orꢀconvertedꢀorꢀdissociatedꢀduringꢀtheꢀheating.ꢀSimilarly,ꢀwithꢀ
regardꢀtoꢀtheꢀC 0.5ꢀmixedꢀoxide,ꢀallꢀtheꢀvibrationꢀbandsꢀofꢀ
theꢀ rangeꢀ ofꢀ 1000‒1700ꢀ cm ,ꢀ whileꢀ theꢀ vibrationꢀ signalsꢀ ofꢀ
carbonateꢀ andꢀ carboxylateꢀ wereꢀ absent,ꢀ whichꢀ indicatedꢀ thatꢀ
NOꢀ moleculesꢀ preferentiallyꢀ adsorbedꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ
M
6 4
6
M
4
A
C
6
M ꢀmixedꢀoxideꢀdueꢀtoꢀtheirꢀunpairedꢀelectrons,ꢀandꢀinhibitedꢀ
4
theꢀbridgingꢀbidentateꢀnitrate,ꢀchelatingꢀbidentateꢀnitrate,ꢀandꢀ
linearꢀnitriteꢀwereꢀdetectedꢀatꢀroomꢀtemperature.ꢀComparingꢀ
Fig.ꢀ 7(b)ꢀ withꢀ Fig.ꢀ 7(a),ꢀ someꢀ interestingꢀ phenomenaꢀ canꢀ beꢀ
observedꢀ withꢀ theꢀ elevationꢀ ofꢀ temperature.ꢀ First,ꢀ theꢀ N=Oꢀ
theꢀadsorptionꢀofꢀCOꢀ[17,30].ꢀWhenꢀtheꢀtemperatureꢀincreasedꢀ
toꢀ 400ꢀ °C,ꢀ allꢀ theꢀ vibrationꢀ bandsꢀ forꢀ nitrateꢀ andꢀ nitriteꢀ hadꢀ
disappearedꢀcompletelyꢀdueꢀtoꢀtheꢀdesorptionꢀorꢀconversionꢀorꢀ
dissociationꢀofꢀtheꢀadsorbedꢀNOꢀspecies.ꢀTherefore,ꢀsomeꢀactiveꢀ
sitesꢀ wereꢀ exposedꢀ toꢀ adsorbꢀ CO.ꢀ Simultaneously,ꢀ twoꢀ newꢀ
bandsꢀ ofꢀ hydrogencarbonateꢀ andꢀ bidentateꢀ carbonateꢀ ap‐
pearedꢀatꢀ1347ꢀandꢀ1472ꢀcm ,ꢀrespectivelyꢀ[22,52].ꢀCombiningꢀ
withꢀtheꢀresultsꢀofꢀtheꢀcatalyticꢀactivityꢀandꢀselectivity,ꢀweꢀcanꢀ
sayꢀthatꢀtheꢀreactionꢀbetweenꢀadsorbedꢀCOꢀspeciesꢀandꢀgaseousꢀ
NOꢀmoleculesꢀ(aboveꢀ400ꢀ°C)ꢀisꢀmoreꢀbeneficialꢀtoꢀtheꢀreduc‐
–1
stretchingꢀmodeꢀofꢀtheꢀbridgingꢀbidentateꢀnitrateꢀ(1605ꢀcm )ꢀ
–1
andꢀtheꢀlinearꢀnitriteꢀ(1284ꢀcm )ꢀdisappearedꢀatꢀaꢀlowerꢀtem‐
peratureꢀofꢀ200ꢀ°C.ꢀ Second,ꢀwhenꢀtheꢀtemperatureꢀ wasꢀupꢀtoꢀ
–1
3
50ꢀ°C,ꢀtheꢀsymmetricꢀandꢀasymmetricꢀvibrationꢀbandsꢀofꢀtheꢀ
–1
chelatingꢀ bidentateꢀ nitrateꢀ (1237ꢀ andꢀ 1574ꢀ cm )ꢀ hadꢀ disap‐
pearedꢀcompletely.ꢀThird,ꢀfreeꢀNO ꢀionsꢀ(1355ꢀcm )ꢀappearedꢀ
–
–1
3
atꢀ aꢀ lowerꢀ temperatureꢀ ofꢀ 200ꢀ °C.ꢀ Finally,ꢀ twoꢀ newꢀ bandsꢀ ofꢀ
tionꢀofꢀNOꢀtoꢀN
ciesꢀandꢀgaseousꢀCOꢀmoleculesꢀ(belowꢀ400ꢀ°C).ꢀFig.ꢀ8(b)ꢀshowsꢀ
theꢀNO+COꢀco‐adsorptionꢀinꢀsituꢀDRIFTSꢀofꢀtheꢀC 0.5ꢀmixedꢀ
oxide.ꢀ Onlyꢀ NOꢀ speciesꢀ wereꢀ adsorbedꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ
2
ꢀthanꢀtheꢀreactionꢀbetweenꢀadsorbedꢀNOꢀspe‐
–
–)ꢀappearedꢀatꢀ1211ꢀandꢀ
anionicꢀnitrosylꢀ(NO )ꢀandꢀnitroꢀ(NO
2
–1
1539ꢀcm ꢀatꢀ200ꢀ°C,ꢀandꢀweakenedꢀwithꢀtheꢀfurtherꢀelevationꢀ
6
M A
4
ofꢀtemperature,ꢀbutꢀdidꢀnotꢀcompletelyꢀdisappearꢀevenꢀatꢀ450ꢀ
(a)
(b)
C6M4
347
2
6 4
C M A
0.5
1
1347
1472
1
1382
1
472
o
4
4
3
3
2
2
1
1
50 C
1547
o
00 C
o
50 C
1
060
o
o
00 C
450 C
o
400 C
o
o
50 C
3
50 C
o
o
00 C
300 C
o
2
2
50 C
o
50 C
o
00 C
o
o
00 C
150 C
o
1
2
00 C
o
2
5 C
o
5 C
1
574
1284
1237
1574
1604
1284
1
605
1011
1000
1237
1011
1000
2000
1800
1600
1400
1200
1
2000
1800
1600
1400
1200
1
Wavenumber (cm )
Wavenumber (cm )
Fig.ꢀ8.ꢀInꢀsituꢀDRIFTSꢀofꢀCOꢀandꢀNOꢀco‐interactionꢀwithꢀ(a)ꢀC
6
M
4
ꢀandꢀ(b)ꢀC
6
M A0.5ꢀmixedꢀoxides.ꢀ
4

1378ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
C
6
M
4
A
0.5ꢀ mixedꢀ oxideꢀ atꢀ roomꢀ temperature,ꢀ whichꢀ wasꢀ veryꢀ
resultsꢀofꢀtheꢀcatalyticꢀperformance.ꢀHowever,ꢀtheꢀinteractionꢀ
betweenꢀCOꢀandꢀtheꢀCeO ‐MnO ‐Al ꢀcatalystꢀatꢀhighꢀtemper‐
atureꢀ(HT,ꢀaboveꢀ350ꢀ°C)ꢀresultsꢀinꢀtheꢀreductionꢀofꢀtheꢀcatalystꢀ
similarꢀwithꢀtheꢀsituationꢀofꢀtheꢀC ꢀmixedꢀoxideꢀ(Fig.ꢀ8(a)).ꢀ
M
6 4
2
x
O
2 3
Interestingly,ꢀ comparingꢀ withꢀ Fig.ꢀ 8(a),ꢀ weꢀ canꢀ findꢀ thatꢀ theꢀ
vibrationꢀsignalsꢀofꢀtheꢀadsorbedꢀNOꢀspeciesꢀdisappearedꢀatꢀaꢀ
lowerꢀtemperatureꢀofꢀ350ꢀ°C,ꢀwhichꢀwasꢀbecauseꢀtheꢀincorpo‐
3+
toꢀformꢀmoreꢀCe ꢀandꢀoxygenꢀvacancies.ꢀItꢀisꢀwidelyꢀreportedꢀ
3+
thatꢀCe ꢀisꢀbeneficialꢀtoꢀtheꢀadsorptionꢀofꢀCO,ꢀandꢀtheꢀoxygenꢀ
vacancyꢀweakenedꢀtheꢀN–Oꢀbondꢀtoꢀpromoteꢀtheꢀdissociationꢀofꢀ
NOꢀ [22,54,55,58].ꢀ Therefore,ꢀ gaseousꢀ NOꢀ canꢀ beꢀ dissociatedꢀ
intoꢀNꢀandꢀOꢀradicalsꢀbyꢀtheꢀoxygenꢀvacancyꢀtoꢀreactꢀwithꢀad‐
3+
rationꢀofꢀAl ꢀintoꢀtheꢀC
6
M ꢀmixedꢀoxideꢀwasꢀconduciveꢀtoꢀtheꢀ
4
4+
increaseꢀofꢀMn ꢀcontent,ꢀandꢀfurtherꢀpromotedꢀtheꢀdesorptionꢀ
orꢀconversionꢀorꢀdissociationꢀofꢀtheꢀadsorbedꢀNOꢀspeciesꢀ[47].ꢀ
Whenꢀtheꢀtemperatureꢀwasꢀupꢀtoꢀ350ꢀ°C,ꢀCOꢀspeciesꢀwereꢀad‐
sorbedꢀonꢀtheꢀsurfaceꢀofꢀtheꢀC
formateꢀ (1547ꢀ cm ),ꢀ bidentateꢀ carbonateꢀ (1382ꢀ andꢀ 1472ꢀ
cm ),ꢀhydrogencarbonateꢀ(1347ꢀcm ),ꢀandꢀCO
theꢀreducedꢀceriaꢀ(1060ꢀcm )ꢀ[22,52,53].ꢀEspecially,ꢀtheseꢀvi‐
brationꢀ singalsꢀ ofꢀ adsorbedꢀ COꢀ speciesꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ
sorbedꢀCOꢀtoꢀformꢀlargeꢀamountsꢀofꢀN
smallꢀamountꢀofꢀN Oꢀatꢀhighꢀtemperatureꢀ(HT,ꢀaboveꢀ350ꢀ°C).ꢀ
Finally,ꢀtheꢀbyproductꢀN Oꢀcanꢀbeꢀfurtherꢀreducedꢀtoꢀtheꢀfinalꢀ
productꢀN ꢀatꢀtheꢀhigherꢀtemperature.ꢀ
2
ꢀandꢀCO ,ꢀasꢀwellꢀasꢀaꢀ
2
6 4
M A0.5ꢀmixedꢀoxideꢀtoꢀgenerateꢀ
2
–1
2
–1
–1
x
ꢀcoordinatedꢀtoꢀ
2
–1
4.ꢀ ꢀ Conclusionsꢀ
6 4
C M A0.5ꢀmixedꢀoxideꢀwereꢀobviouslyꢀstrongerꢀthanꢀthoseꢀofꢀtheꢀ
6 4
C M ꢀmixedꢀoxide.ꢀThisꢀwasꢀbecauseꢀthatꢀimprovedꢀreductionꢀ
Aꢀ seriesꢀ ofꢀ CeO
2
‐MnO
x
‐Al
2
O ꢀ catalystsꢀ wereꢀ preparedꢀ byꢀ aꢀ
3
propertyꢀofꢀtheꢀC
ductionꢀofꢀCe ꢀbyꢀCOꢀtoꢀgenerateꢀmoreꢀCe ꢀatꢀhighꢀtempera‐
ture,ꢀ andꢀ furtherꢀ promotedꢀ theꢀ adsorptionꢀ ofꢀ COꢀ [22,54,55].ꢀ
6
M
4
A
0.5ꢀmixedꢀoxideꢀwasꢀbeneficialꢀtoꢀtheꢀre‐
simpleꢀ one‐stepꢀ inverseꢀ co‐precipitationꢀ methodꢀ forꢀ investi‐
4+
3+
3+
gatingꢀtheꢀinfluenceꢀofꢀtheꢀincorporationꢀofꢀAl ꢀintoꢀCeO
2
‐MnO ꢀ
x
mixedꢀ oxideꢀ onꢀ theirꢀ physicochemicalꢀ propertyꢀ andꢀ catalyticꢀ
Therefore,ꢀ theꢀ catalyticꢀ performanceꢀ ofꢀ theꢀ C
oxideꢀforꢀNOꢀreductionꢀbyꢀCOꢀwasꢀbetterꢀthanꢀthatꢀofꢀtheꢀC
mixedꢀoxide.ꢀ
6
M A0.5ꢀ mixedꢀ
4
performanceꢀ forꢀ theꢀ NO+COꢀ modelꢀ reaction.ꢀ Theꢀ conclusionsꢀ
n+
3+
6 4
M ꢀ
drawnꢀareꢀasꢀfollows.ꢀ(1)ꢀTheꢀincorporationꢀofꢀMn ꢀandꢀAl ꢀ
intoꢀtheꢀlatticeꢀofꢀCeO ꢀinhibitedꢀitsꢀgrainꢀgrowth,ꢀwhichꢀledꢀtoꢀ
theꢀdecreaseꢀofꢀcrystalliteꢀsize.ꢀEspecially,ꢀtheꢀcrystalliteꢀsizeꢀofꢀ
Al‐containingꢀCeO ‐MnO ‐Al ꢀcatalystsꢀwasꢀobviouslyꢀsmallerꢀ
thanꢀthatꢀofꢀtheꢀCeO ‐MnO ꢀmixedꢀoxide,ꢀwhichꢀindicatedꢀthatꢀ
theꢀintroductionꢀofꢀAl ꢀcanꢀfurtherꢀdecreaseꢀtheꢀcrystalliteꢀsizeꢀ
ofꢀtheꢀCeO ‐MnO ꢀsample.ꢀ(2)ꢀN2ꢀphysisorptionꢀresultsꢀshowedꢀ
thatꢀtheꢀincorporationꢀofꢀAl ꢀintoꢀtheꢀCeO
2
3.7.ꢀ ꢀ ReactionꢀmechanismꢀofꢀNOꢀreductionꢀbyꢀCOꢀoverꢀtheꢀ
2
x
O
2 3
CeO ‐MnO ‐Al ꢀcatalystꢀ
2
x
O
2 3
2
x
3+
Basedꢀonꢀtheꢀcharacterization,ꢀaꢀreactionꢀmechanismꢀofꢀNOꢀ
reductionꢀbyꢀCOꢀoverꢀtheꢀCeO ‐MnO ‐Al ꢀcatalystꢀisꢀproposedꢀ
2
x
3+
2
x
O
2 3
2
‐MnO ꢀmixedꢀoxideꢀ
x
toꢀ furtherꢀ understandꢀ theꢀ excellentꢀ catalyticꢀ performanceꢀ forꢀ
thisꢀmodelꢀreaction,ꢀasꢀshownꢀinꢀFig.ꢀ9.ꢀNOꢀmoleculesꢀareꢀpref‐
erentiallyꢀadsorbedꢀonꢀMn ꢀsitesꢀowingꢀtoꢀtheirꢀunpairedꢀelec‐
increasedꢀ itsꢀ BETꢀ specificꢀ surfaceꢀ areaꢀ andꢀ poreꢀ volumeꢀ re‐
markably,ꢀwhichꢀwasꢀbecauseꢀofꢀtheꢀdecreaseꢀofꢀcrystalliteꢀsize.ꢀ
TheꢀincreaseꢀofꢀBETꢀspecificꢀsurfaceꢀareaꢀandꢀporeꢀvolumeꢀisꢀ
beneficialꢀtoꢀtheꢀcontactꢀbetweenꢀcatalystꢀandꢀreactants,ꢀwhichꢀ
enhancedꢀ catalyticꢀ performance.ꢀ (3)ꢀ Theꢀ relativeꢀ contentꢀ ofꢀ
n+
tronsꢀ toꢀ formꢀ nitrateꢀ andꢀ nitriteꢀ speciesꢀ whenꢀ theꢀ
CeO
2
‐MnO
x
‐Al
2
O ꢀcatalystꢀwasꢀexposedꢀtoꢀNOꢀandꢀCOꢀatꢀroomꢀ
3
3+
3+
temperatureꢀ(25ꢀ°C)ꢀ[58].ꢀTherefore,ꢀtheꢀadsorptionꢀofꢀCOꢀwasꢀ
inhibited,ꢀ whichꢀ wasꢀ supportedꢀ byꢀ theꢀ resultsꢀ ofꢀ NO+COꢀ
co‐adsorptionꢀbyꢀinꢀsituꢀDRIFTS.ꢀInꢀthisꢀsituation,ꢀgaseousꢀCOꢀ
moleculesꢀ canꢀ reactꢀ withꢀ adsorbedꢀ NOꢀ speciesꢀ toꢀ generateꢀ aꢀ
Ce ꢀ increasedꢀ obviouslyꢀ whenꢀ Al ꢀ wasꢀ dopedꢀ intoꢀ theꢀ
CeO ‐MnO ꢀmixedꢀoxide,ꢀwhichꢀwasꢀrelatedꢀtoꢀtheꢀdecreaseꢀofꢀ
2
x
4+
crystalliteꢀsize.ꢀSimultaneously,ꢀtheꢀMn ꢀcontentꢀalsoꢀincreasedꢀ
remarkably,ꢀwhichꢀwasꢀcausedꢀbyꢀtheꢀshiftꢀofꢀtheꢀredoxꢀcyclesꢀ
4
+
3+
3+
4+
4+
2+
3+
4+
2 2 2
smallꢀamountꢀofꢀN ,ꢀandꢀlargeꢀamountsꢀofꢀN OꢀandꢀCO ꢀatꢀlowꢀ
(Ce ꢀ+ꢀMn ꢀ↔ꢀCe ꢀ+ꢀMn ꢀandꢀ2Ce ꢀ+ꢀMn ꢀ↔ꢀ2Ce ꢀ+ꢀMn )ꢀ
3+
temperatureꢀ(LT,ꢀbelowꢀ350ꢀ°C),ꢀwhichꢀisꢀconsistentꢀwithꢀtheꢀ
toꢀtheꢀright.ꢀMoreover,ꢀCe ꢀisꢀbeneficialꢀtoꢀtheꢀadsorptionꢀofꢀCO,ꢀ
whileꢀMn ꢀpromotedꢀtheꢀdesorptionꢀorꢀconversionꢀorꢀdissocia‐
tionꢀofꢀNO.ꢀTherefore,ꢀtheꢀincreaseꢀofꢀCe ꢀandꢀMn ꢀremarkablyꢀ
enhancedꢀtheꢀcatalyticꢀperformanceꢀforꢀNOꢀreductionꢀbyꢀCO.ꢀ(4)ꢀ
4
+
3+
4+
COx
COx
ꢀcatalystꢀwithꢀtheꢀoptimalꢀamountꢀofꢀAl3+ꢀ
2 x 2 3
TheꢀCeO ‐MnO ‐Al O
N
2
(
HT: more)
(Ce:Mn:Alꢀmoleꢀratioꢀ=ꢀ6:4:0.5)ꢀexhibitedꢀtheꢀbestꢀcatalyticꢀper‐
formanceꢀforꢀtheꢀNO+COꢀmodelꢀreaction,ꢀwhichꢀwasꢀrelatedꢀtoꢀ
itsꢀsmallerꢀcrystalliteꢀsize,ꢀlargerꢀBETꢀspecificꢀsurfaceꢀareaꢀandꢀ
poreꢀvolume,ꢀexcellentꢀreductionꢀproperty,ꢀasꢀwellꢀasꢀtheꢀhigherꢀ
NO
CO
COx
CO2
3+
4+
NOx
contentsꢀofꢀCe ꢀandꢀMn .ꢀ
NOx
Referencesꢀ
N O
2
(
LT: more)
NOx
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2
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ꢀ
XiaojiangꢀYaoꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1369–1380ꢀ
GraphicalꢀAbstractꢀ
1379ꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2016,ꢀ37:ꢀ1369–1380ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(15)61098‐1
Preparation,ꢀcharacterization,ꢀandꢀcatalyticꢀperformanceꢀofꢀ
highꢀefficientꢀCeO
2
‐MnO
x
‐Al
2
O ꢀcatalystsꢀforꢀNOꢀeliminationꢀ
3
Al source
ꢀ
XiaojiangꢀYao*,ꢀLuluꢀLi,ꢀWeixinꢀZou,ꢀShuohanꢀYu,ꢀJibinꢀAn,ꢀ ꢀ
100
80
60
40
20
0
ꢀ
ꢀ
HongliꢀLi,ꢀFumoꢀYang*,ꢀLinꢀDong*ꢀ
ChongqingꢀInstituteꢀofꢀGreenꢀandꢀIntelligentꢀTechnology,ꢀChineseꢀ
AcademyꢀofꢀSciences;ꢀNanjingꢀUniversity;ꢀChongqingꢀUniversityꢀofꢀ
ArtsꢀandꢀSciencesꢀ
o
3
50 C
CeO -MnO -Al O
3
mixed oxide
2
x
2
3
+
C M
C M A
6 4 0.5
Theꢀ incorporationꢀ ofꢀ aꢀ smallꢀ amountꢀ ofꢀ Al ꢀ intoꢀ CeO
2
‐MnO
x
ꢀ
6
4
mixedꢀ oxideꢀ improvedꢀ itsꢀ physicochemicalꢀ propertyꢀ andꢀ en‐
hancedꢀ theꢀcorrespondingꢀcatalyticꢀperformanceꢀ forꢀNOꢀreduc‐
tionꢀbyꢀCOꢀefficiently.ꢀ
CeO
mixed oxide
-MnO
2 x
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