Catalytic performance enhancement by alloying Pd with Pt on ordered mesoporous manganese oxide for methane combustion

Article abstract of DOI:10.1016/S1872-2067(16)62567-6

Ordered mesoporous Mn₂O₃(meso-Mn₂O₃) and meso-Mn₂O₃-supported Pd, Pt, and Pd-Pt alloy x(Pd_yPt)/meso-Mn₂O₃; x = (0.10?1.50) wt%; Pd/Pt molar ratio (y) = 4.9?5.1 nanocatalysts were prepared using KIT-6-templated and poly(vinyl alcohol)-protected reduction methods, respectively. The meso-Mn₂O₃had a high surface area, i.e., 106 m²/g, and a cubic crystal structure. Noble-metal nanoparticles (NPs) of size 2.1?2.8 nm were uniformly dispersed on the meso-Mn₂O₃surfaces. Alloying Pd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd_5.1Pt)/meso-Mn₂O₃gave the best performance; T_10%, T_50%, and T_90%(the temperatures required for achieving methane conversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of 20000 mL/(g·h). The effects of SO₂, CO₂, H₂O, and NO on methane combustion over 1.41(Pd_5.1Pt)/meso-Mn₂O₃were also examined. We conclude that the good catalytic performance of 1.41(Pd_5.1Pt)/meso-Mn₂O₃is associated with its high-quality porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interactions between Pd-Pt alloy NPs and the meso-Mn₂O₃support.

Full text of DOI:10.1016/S1872-2067(16)62567-6

ChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105
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a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
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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
ꢀ
ꢀ
Article
CatalyticꢀperformanceꢀenhancementꢀbyꢀalloyingꢀPdꢀwithꢀPtꢀonꢀ ꢀ
orderedꢀmesoporousꢀmanganeseꢀoxideꢀforꢀmethaneꢀcombustionꢀ
ꢀ
ꢀ#
PengꢀXu,ꢀZhixingꢀWu,ꢀJiguangꢀDeng,ꢀYuxiꢀLiu,ꢀShaohuaꢀXie,ꢀGuangshengꢀGuo*,ꢀHongxingꢀDai
ꢀ
BeijingꢀKeyꢀLaboratoryꢀforꢀGreenꢀCatalysisꢀandꢀSeparation,ꢀKeyꢀLaboratoryꢀofꢀBeijingꢀonꢀRegionalꢀAirꢀPollutionꢀControl,ꢀKeyꢀLaboratoryꢀofꢀAdvancedꢀ
FunctionalꢀMaterials,ꢀEducationꢀMinistryꢀofꢀChina,ꢀandꢀLaboratoryꢀofꢀCatalysisꢀChemistryꢀandꢀNanoscience,ꢀDepartmentꢀofꢀChemistryꢀandꢀChemicalꢀEngi‐
neering,ꢀCollegeꢀofꢀEnvironmentalꢀandꢀEnergyꢀEngineering,ꢀBeijingꢀUniversityꢀofꢀTechnology,ꢀBeijingꢀ100124,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Orderedꢀ mesoporousꢀ Mn
2
O
3
ꢀ (meso‐Mn
2
O
3
)ꢀ andꢀ meso‐Mn
2
O ‐supportedꢀ Pd,ꢀ Pt,ꢀ andꢀ Pd‐Ptꢀ alloyꢀ
3
Receivedꢀ31ꢀAugustꢀ2016ꢀ
Acceptedꢀ25ꢀSeptemberꢀ2016ꢀ
Publishedꢀ5ꢀJanuaryꢀ2017ꢀ
x(Pd
y
Pt)/meso‐Mn
2
O ;ꢀ xꢀ=ꢀ(0.101.50)ꢀ wt%;ꢀ Pd/Ptꢀ molarꢀ ratioꢀ (y)ꢀ =ꢀ 4.95.1ꢀ nanocatalystsꢀ wereꢀ
3
preparedꢀusingꢀKIT‐6‐templatedꢀandꢀpoly(vinylꢀalcohol)‐protectedꢀreductionꢀmethods,ꢀrespectively.ꢀ
Theꢀmeso‐Mn
2
2 3
O ꢀhadꢀaꢀhighꢀsurfaceꢀarea,ꢀi.e.,ꢀ106ꢀm /g,ꢀandꢀaꢀcubicꢀcrystalꢀstructure.ꢀNoble‐metalꢀ
nanoparticlesꢀ(NPs)ꢀofꢀsizeꢀ2.12.8ꢀnmꢀwereꢀuniformlyꢀdispersedꢀonꢀtheꢀmeso‐Mn
2
O ꢀsurfaces.ꢀAl‐
3
loyingꢀPdꢀwithꢀPtꢀenhancedꢀtheꢀcatalyticꢀactivityꢀinꢀmethaneꢀcombustion;ꢀ1.41(Pd5.1Pt)/meso‐Mn
gaveꢀtheꢀbestꢀperformance;ꢀT10%,ꢀT50%,ꢀandꢀT90%ꢀ(theꢀtemperaturesꢀrequiredꢀforꢀachievingꢀmethaneꢀ
conversionsꢀofꢀ10%,ꢀ50%,ꢀandꢀ90%)ꢀwereꢀ265,ꢀ345,ꢀandꢀ425ꢀ°C,ꢀrespectively,ꢀatꢀaꢀspaceꢀvelocityꢀofꢀ
2
O
3
Keywords:ꢀ
Orderedꢀmesoporousꢀmanganeseꢀoxide
Pd‐Ptꢀalloyꢀnanoparticleꢀ
Supportedꢀnobleꢀmetalꢀcatalystꢀ
Strongꢀmetal‐supportꢀinteractionꢀ
Methaneꢀcombustionꢀ
2
1
1
0000ꢀ mL/(gh).ꢀ Theꢀ effectsꢀ ofꢀ SO
2
,ꢀ CO
2
,ꢀ H O,ꢀ andꢀ NOꢀ onꢀ methaneꢀ combustionꢀ overꢀ
2
.41(Pd5.1Pt)/meso‐Mn
2
O
3
ꢀwereꢀalsoꢀexamined.ꢀWeꢀconcludeꢀthatꢀtheꢀgoodꢀcatalyticꢀperformanceꢀofꢀ
ꢀisꢀassociatedꢀwithꢀitsꢀhigh‐qualityꢀporousꢀstructure,ꢀhighꢀadsorbedꢀoxy‐
.41(Pd5.1Pt)/meso‐Mn
O
2 3
genꢀ speciesꢀ concentration,ꢀ goodꢀ low‐temperatureꢀ reducibility,ꢀ andꢀ strongꢀ interactionsꢀ betweenꢀ
Pd‐PtꢀalloyꢀNPsꢀandꢀtheꢀmeso‐Mn ꢀsupport.ꢀ
O
2 3
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1.ꢀ ꢀ Introductionꢀ
tion,ꢀe.g.,ꢀsuppressionꢀofꢀNO ꢀandꢀCOꢀandꢀemissionsꢀandꢀmoreꢀ
x
efficientꢀenergyꢀuse.ꢀPd‐basedꢀcatalystsꢀareꢀcommonlyꢀusedꢀforꢀ
methaneꢀ combustionꢀ becauseꢀ ofꢀ theirꢀ excellentꢀ
low‐temperatureꢀcatalyticꢀactivitiesꢀ[4,5].ꢀPdOꢀisꢀbelievedꢀtoꢀbeꢀ
anꢀimportantꢀactivity‐controllingꢀfactorꢀinꢀcatalyzingꢀtheꢀoxida‐
tionꢀofꢀhydrocarbons,ꢀandꢀtheꢀreductionꢀofꢀPdOꢀtoꢀmetallicꢀPd0ꢀ
atꢀhighꢀtemperaturesꢀdecreasesꢀtheꢀcatalyticꢀactivityꢀ[6,7];ꢀforꢀ
example,ꢀHellmanꢀetꢀal.ꢀ[8]ꢀfoundꢀthatꢀtheꢀPdOꢀ(101)ꢀfacetꢀwasꢀ
Methaneꢀ isꢀ widelyꢀ consideredꢀ toꢀ beꢀ theꢀ cleanestꢀ availableꢀ
hydrocarbonꢀ energyꢀ sourceꢀ forꢀ transportationꢀ andꢀ industrialꢀ
applicationsꢀ[1].ꢀMethaneꢀitself,ꢀhowever,ꢀisꢀaꢀgreenhouseꢀgas,ꢀ
withꢀaꢀglobalꢀwarmingꢀeffectꢀ21–23ꢀtimesꢀgreaterꢀthanꢀthatꢀofꢀ
CO ꢀ[2],ꢀandꢀmoreꢀseriousꢀpollutantsꢀ(e.g.,ꢀCO,ꢀnitrogenꢀoxides,ꢀ
2
andꢀunburnedꢀhydrocarbons)ꢀareꢀalwaysꢀdetectedꢀinꢀtheꢀoutletsꢀ
ofꢀmethaneꢀflameꢀcombustionꢀ[3].ꢀCatalyticꢀcombustionꢀofꢀme‐
thaneꢀhasꢀmanyꢀadvantagesꢀoverꢀconventionalꢀflameꢀcombus‐
0
moreꢀ reactiveꢀ thanꢀ metallicꢀ Pd ꢀ inꢀ methaneꢀ combustion.ꢀ
Pd‐basedꢀcatalysts,ꢀhowever,ꢀhaveꢀsomeꢀmajorꢀdrawbacks:ꢀ(1)ꢀ
*
ꢀ
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐10‐67396118;ꢀfax:ꢀ+86‐10‐67391983;ꢀE‐mail:ꢀguogs@bjut.edu.cnꢀ ꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐10‐67396118;ꢀfax:ꢀ+86‐10‐67391983;ꢀE‐mail:ꢀhxdai@bjut.edu.cnꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀPh.D.ꢀProgramꢀFoundationꢀofꢀMinistryꢀofꢀEducationꢀofꢀChinaꢀ(20131103110002);ꢀtheꢀNNSFꢀofꢀChinaꢀ(21377008),
NationalꢀHighꢀTechnologyꢀResearchꢀandꢀDevelopmentꢀProgramꢀ(863ꢀProgram,ꢀ2015AA034603),ꢀFoundationꢀonꢀtheꢀCreativeꢀResearchꢀTeamꢀCon‐
structionꢀ Promotionꢀ Projectꢀ ofꢀ Beijingꢀ Municipalꢀ Institutions,ꢀ andꢀ Scientificꢀ Researchꢀ Baseꢀ Construction‐Scienceꢀ andꢀ Technologyꢀ Creationꢀ Plat‐
form‐NationalꢀMaterialsꢀResearchꢀBaseꢀConstruction.ꢀ
DOI:ꢀ10.1016/S1872‐2067(16)62567‐6ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ38,ꢀNo.ꢀ1,ꢀJanuaryꢀ2017ꢀ ꢀ ꢀ

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
93ꢀ
theyꢀoftenꢀhaveꢀpoorꢀstabilityꢀinꢀsteady‐stateꢀmethaneꢀcombus‐
tionꢀprocessesꢀ[9,10],ꢀandꢀ(2)ꢀtheirꢀexposureꢀtoꢀwaterꢀorꢀsul‐
fur‐containingꢀcompoundsꢀcanꢀsignificantlyꢀreduceꢀtheꢀactivityꢀ
aqueousꢀsolutionꢀ(50ꢀwt%,ꢀ20.00ꢀmmol)ꢀwasꢀaddedꢀunderꢀvig‐
orousꢀstirring.ꢀTheꢀmixtureꢀwasꢀstirredꢀatꢀ65ꢀ°Cꢀforꢀ3ꢀh.ꢀAꢀpow‐
derꢀwasꢀobtainedꢀbyꢀfiltrationꢀandꢀdryingꢀtheꢀresidueꢀatꢀroomꢀ
temperatureꢀ(rt).ꢀTheꢀprecursor@silicaꢀcompositeꢀwasꢀplacedꢀ
inꢀaꢀcrucibleꢀandꢀcalcinedꢀinꢀaꢀmuffleꢀfurnaceꢀfromꢀrtꢀtoꢀ600ꢀ°Cꢀ
atꢀ aꢀ rampingꢀ rateꢀ ofꢀ 1ꢀ °C/min;ꢀ thisꢀ temperatureꢀ wasꢀ main‐
tainedꢀ forꢀ 6ꢀ h.ꢀ Theꢀ silicaꢀ templateꢀ wasꢀ removedꢀ byꢀ etchingꢀ
twiceꢀ withꢀ hotꢀ NaOHꢀ aqueousꢀ solutionꢀ (2.00ꢀ mol/L).ꢀ Tem‐
viaꢀformationꢀofꢀinactiveꢀPd(OH) ꢀandꢀstableꢀpalladiumꢀsulfateꢀ
2
phasesꢀ[5,11,12].ꢀTheseꢀproblemsꢀcanꢀbeꢀovercomeꢀbyꢀaddingꢀaꢀ
secondꢀmetalꢀtoꢀgenerateꢀaꢀ bimetallicꢀ alloyꢀ catalyst.ꢀ Pt‐basedꢀ
catalystsꢀareꢀalsoꢀgoodꢀcatalystsꢀforꢀtheꢀcombustionꢀofꢀhydro‐
carbons.ꢀTheꢀadditionꢀofꢀPtꢀcanꢀincreaseꢀtheꢀlow‐temperatureꢀ
methaneꢀcombustionꢀactivityꢀorꢀhinderꢀtheꢀgrowthꢀofꢀPdꢀorꢀPdOꢀ
particlesꢀ[13].ꢀDopingꢀofꢀaꢀsupportedꢀPdꢀcatalystꢀwithꢀaꢀsmallꢀ
amountꢀ ofꢀ Ptꢀ improvesꢀ theꢀ thermalꢀ stabilityꢀ [14,15]ꢀ andꢀ en‐
hancesꢀresistanceꢀtoꢀsulfurꢀorꢀwater‐vaporꢀpoisoningꢀ[12].ꢀ ꢀ
Transition‐metalꢀ oxidesꢀ (e.g.,ꢀ Mnꢀ [16,17],ꢀ Coꢀ [18],ꢀ Cu,ꢀ Cr,ꢀ
andꢀNiꢀ[19])ꢀhaveꢀalsoꢀbeenꢀusedꢀasꢀcatalystsꢀinꢀmethaneꢀcom‐
bustion;ꢀ theyꢀ areꢀ cheaper,ꢀ moreꢀ stableꢀ atꢀ highꢀ temperaturesꢀ
plate‐freeꢀmeso‐Mn
ingꢀwithꢀdeionizedꢀwaterꢀandꢀethanol,ꢀandꢀdryingꢀatꢀ80ꢀ°C.ꢀ
Orderedꢀmeso‐Mn ‐supportedꢀPd‐Ptꢀalloyꢀcatalystsꢀwereꢀ
preparedꢀviaꢀaꢀPVAꢀ(MWaver.ꢀ=ꢀ10000ꢀg/mol)‐protectedꢀreduc‐
tionꢀ routeꢀ withꢀ NaBH ꢀ asꢀ aꢀ reducingꢀ agentꢀ [31].ꢀ Theꢀ typicalꢀ
preparationꢀ procedureꢀ wasꢀ asꢀ follows.ꢀ Aꢀ desiredꢀ amountꢀ ofꢀ
PVAꢀ wasꢀ addedꢀ toꢀ anꢀ aqueousꢀ solutionꢀ ofꢀ PdCl ꢀ andꢀ H PtCl
(100ꢀmg/L,ꢀPd/Ptꢀmolarꢀratioꢀ=ꢀ5.0)ꢀinꢀanꢀiceꢀbath;ꢀtheꢀmixtureꢀ
wasꢀstirredꢀvigorouslyꢀforꢀ20ꢀmin.ꢀAꢀcertainꢀamountꢀofꢀNaBH ꢀ
2 3
O ꢀwasꢀobtainedꢀbyꢀcentrifugation,ꢀwash‐
O
2 3
4
2
2
4
ꢀ
[11],ꢀandꢀmoreꢀresistantꢀtoꢀsulfurꢀpoisoningꢀ[19]ꢀthanꢀsupport‐
edꢀ noble‐metalꢀ catalysts.ꢀ Amongꢀ theꢀ transition‐metalꢀ oxideꢀ
catalystsꢀdevelopedꢀsoꢀfar,ꢀmanganeseꢀoxidesꢀhaveꢀbeenꢀwidelyꢀ
studiedꢀasꢀpossibleꢀalternativeꢀcatalystsꢀforꢀmethaneꢀcombus‐
tionꢀbecauseꢀofꢀtheirꢀvariedꢀandꢀmultipleꢀoxidationꢀstatesꢀandꢀ
oxygen‐storageꢀ capacitiesꢀ [20].ꢀ Han'sꢀ groupꢀ [17]ꢀ reportedꢀ
4
aqueousꢀsolutionꢀ(0.1ꢀmol/L)ꢀwasꢀquicklyꢀaddedꢀtoꢀtheꢀmixedꢀ
solution,ꢀ generatingꢀ aꢀ dark‐brownꢀ noble‐metalꢀ sol.ꢀ Aꢀ desiredꢀ
amountꢀofꢀmeso‐Mn
2
O ꢀpowderꢀwasꢀaddedꢀtoꢀtheꢀnoble‐metalꢀ
3
solꢀ (theoreticalꢀ Pd‐Ptꢀ loadingsꢀ =ꢀ (0.1,ꢀ 1.0,ꢀ andꢀ1.5)ꢀwt%)ꢀandꢀ
theꢀ mixtureꢀ wasꢀ stirredꢀ forꢀ 6ꢀ h.ꢀ Theꢀ mixtureꢀ wasꢀ filtered,ꢀ
washedꢀwithꢀdeionizedꢀwater,ꢀandꢀdriedꢀatꢀ80ꢀ°Cꢀforꢀ12ꢀh.ꢀTheꢀ
driedꢀpowdersꢀwereꢀcalcinedꢀinꢀaꢀmuffleꢀfurnaceꢀfromꢀrtꢀtoꢀ600ꢀ
°C,ꢀatꢀaꢀrampingꢀrateꢀofꢀ1ꢀ°C/min,ꢀandꢀthenꢀthisꢀtemperatureꢀ
completeꢀ conversionꢀ ofꢀ methaneꢀ overꢀ α‐Mn
2
O ꢀ atꢀ ca.ꢀ 600ꢀ °C,ꢀ
3
andꢀthisꢀcatalystꢀhasꢀultrahighꢀstability.ꢀMachockiꢀandꢀcowork‐
ersꢀ [21]ꢀ foundꢀ thatꢀ Ag‐loadedꢀ manganese‐lanthanumꢀ oxidesꢀ
showedꢀ goodꢀ catalyticꢀ activitiesꢀ inꢀ methaneꢀ combustion,ꢀ andꢀ
4+
3+
theꢀreactionꢀrateꢀwasꢀrelatedꢀtoꢀtheꢀsurfaceꢀMn /Mn ꢀmolarꢀ
ratio.ꢀ ꢀ
wasꢀ maintainedꢀ forꢀ 6ꢀ h;ꢀ x(Pd
y
Pt)/meso‐Mn
2
O ꢀ samplesꢀ wereꢀ
3
obtained.ꢀ Inductivelyꢀ coupledꢀ plasmaꢀ atomicꢀ emissionꢀ spec‐
troscopyꢀ(ICPAES)ꢀshowedꢀthatꢀtheꢀactualꢀloadingsꢀ(x)ꢀofꢀtheꢀ
nobleꢀmetalsꢀwereꢀ(0.07,ꢀ0.72,ꢀandꢀ1.41)ꢀwt%,ꢀrespectively,ꢀandꢀ
theꢀcorrespondingꢀyꢀvaluesꢀwereꢀ4.9,ꢀ5.1,ꢀandꢀ5.1.ꢀ ꢀ
Recently,ꢀourꢀgroupꢀinvestigatedꢀaꢀnumberꢀofꢀnanosizedꢀorꢀ
porousꢀ catalystsꢀ (e.g.,ꢀ Au‐Pd/meso‐Co
Co ꢀ [23],ꢀ Au‐Pd/3DOMꢀ Mn ꢀ [24],ꢀ Au/3DOMꢀ Mn
Au/meso‐Mn ꢀ [26],ꢀ Au‐Pd/meso‐Cr ꢀ [27],ꢀ andꢀ Ag/Mn
3
O
4
ꢀ [22],ꢀ Au‐Pd/3DOMꢀ
O
3 4
O
2 3
2 3
O ꢀ [25],ꢀ
O
2 3
2
O
3
2 3
O ꢀ
Forꢀ comparison,ꢀ xPd/meso‐Mn
2
O
3
,ꢀ xPt/meso‐Mn
2
O ,ꢀ andꢀ
3
nanowiresꢀ[28]),ꢀandꢀfoundꢀthatꢀmostꢀofꢀthemꢀ(especiallyꢀtheꢀ
bimetallicꢀcatalysts)ꢀperformedꢀwellꢀinꢀtheꢀoxidationꢀofꢀtypicalꢀ
volatileꢀorganicꢀcompoundsꢀand/orꢀCO.ꢀWeꢀintroducedꢀaꢀsmallꢀ
amountꢀofꢀPtꢀtoꢀgenerateꢀPd‐Ptꢀalloyꢀnanoparticlesꢀ(NPs)ꢀandꢀ
loadedꢀ themꢀ viaꢀ aꢀ poly(vinylꢀ alcohol)ꢀ (PVA)‐protectedꢀ reduc‐
x(Pd Pt)/bulk‐Mn ꢀ samplesꢀ wereꢀ alsoꢀ preparedꢀ usingꢀ theꢀ
sameꢀmethod.ꢀICP‐AESꢀshowedꢀthatꢀtheꢀactualꢀPd,ꢀPt,ꢀandꢀPd‐Ptꢀ
loadingsꢀ (x)ꢀ wereꢀ (1.40,ꢀ 1.42,ꢀ andꢀ 0.70)ꢀ wt%ꢀ inꢀ
y
2 3
O
xPd/meso‐Mn
respectively;ꢀ theꢀ actualꢀ Pd/Ptꢀ molarꢀ ratioꢀ (y)ꢀ inꢀ
x(Pd Pt)/bulk‐Mn ꢀwasꢀ4.9.ꢀ ꢀ
2 3 2 3 y 2 3
O ,ꢀ xPt/meso‐Mn O ,ꢀ andꢀ x(Pd Pt)/bulk‐Mn O ,ꢀ
tionꢀrouteꢀonꢀKIT‐6‐derivedꢀorderedꢀmesoporousꢀMn
2 3
O ꢀ(me‐
y
O
2 3
so‐Mn )ꢀ withꢀ specificꢀ redoxꢀ propertiesꢀ toꢀ overcomeꢀ theꢀ
2 3
O
drawbacksꢀofꢀPd‐basedꢀcatalysts.ꢀWeꢀinvestigatedꢀtheirꢀphysi‐
cochemicalꢀ propertiesꢀ andꢀ evaluatedꢀ theirꢀ catalyticꢀ perfor‐
2.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ
mancesꢀ inꢀ methaneꢀ combustion.ꢀ Orderedꢀ meso‐Mn
2
O
3
ꢀ hasꢀ aꢀ
X‐rayꢀ diffractionꢀ (XRD)ꢀ patternsꢀ ofꢀ theꢀ samplesꢀ wereꢀ rec‐
ordedꢀ usingꢀ aꢀ Brukerꢀ D8ꢀ Advanceꢀ diffractometerꢀ withꢀ CuꢀKαꢀ
radiationꢀandꢀaꢀNiꢀfilterꢀ(ꢀ=ꢀ0.15406ꢀnm).ꢀElementalꢀanalysesꢀ
ofꢀ theꢀ noble‐metalꢀ loadingsꢀ wereꢀ performedꢀ usingꢀ ICP‐AESꢀ
(ThermoꢀElectronꢀIRISꢀIntrepidꢀER/Sꢀspectrometer).ꢀTransmis‐
sionꢀ electronꢀ microscopyꢀ (TEM)ꢀ andꢀ selected‐areaꢀ electronꢀ
diffractionꢀ(SAED)ꢀwereꢀperformedꢀusingꢀaꢀJEOL‐2010ꢀinstru‐
mentꢀ operatedꢀ atꢀ 200ꢀ kV.ꢀ High‐angleꢀ annularꢀ dark‐fieldꢀ andꢀ
scanningꢀ transmissionꢀ electronꢀ microscopyꢀ (HAADF‐STEM)ꢀ
wereꢀusedꢀtoꢀacquireꢀHAADFꢀandꢀelementꢀmappingꢀimagesꢀ(FEIꢀ
G2ꢀ 80‐200/Chemi‐STEMꢀ Cs‐correctedꢀ transmissionꢀ electronꢀ
microscopeꢀ withꢀ probeꢀ corrector).ꢀ Theꢀ Brunau‐
er‐Emmett‐Tellerꢀ(BET)ꢀsurfaceꢀareasꢀofꢀtheꢀsamplesꢀwereꢀde‐
good‐qualityꢀ porousꢀ structureꢀ andꢀ aꢀhighꢀ surfaceꢀarea,ꢀthere‐
foreꢀitsꢀuseꢀasꢀaꢀsupportꢀforꢀmetalꢀalloyꢀcatalystsꢀwithꢀaꢀuniformꢀ
particleꢀdistributionꢀimprovesꢀtheꢀcatalyticꢀactivityꢀandꢀstabil‐
ity.ꢀToꢀtheꢀbestꢀofꢀourꢀknowledge,ꢀthereꢀhaveꢀbeenꢀnoꢀreportsꢀofꢀ
theꢀ preparationꢀ ofꢀ three‐dimensionalꢀ orderedꢀ me‐
so‐Mn
2
O ‐supportedꢀmetalꢀalloyꢀcatalystsꢀandꢀtheirꢀuseꢀasꢀme‐
3
thaneꢀcombustionꢀcatalysts.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2.1.ꢀ ꢀ Catalystꢀpreparationꢀ
Mesoporousꢀ silicaꢀ (KIT‐6)ꢀ andꢀ orderedꢀ meso‐Mn
2 3
O ꢀ wereꢀ
terminedꢀ basedꢀ onꢀ N
ꢀ adsorptionꢀ atꢀ 196ꢀ °Cꢀ (Micromeriticsꢀ
2
synthesizedꢀusingꢀpreviouslyꢀreportedꢀproceduresꢀ[29,30].ꢀInꢀaꢀ
typicalꢀsynthesis,ꢀKIT‐6ꢀ(1.0ꢀg)ꢀwasꢀsuspendedꢀinꢀtolueneꢀ(50ꢀ
ASAPꢀ2020ꢀanalyzer);ꢀtheꢀsamplesꢀwereꢀoutgassedꢀatꢀ250ꢀ°Cꢀforꢀ
2.5ꢀhꢀunderꢀvacuumꢀbeforeꢀtheꢀmeasurements.ꢀTheirꢀpore‐sizeꢀ
distributionsꢀwereꢀcalculatedꢀbasedꢀonꢀtheꢀdesorptionꢀbranchesꢀ
mL).ꢀTheꢀmixtureꢀwasꢀstirredꢀatꢀ65ꢀ°Cꢀforꢀ0.5ꢀhꢀandꢀMn(NO
) ꢀ
3 2

94ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
ofꢀ theꢀ isotherms.ꢀ X‐rayꢀ photoelectronꢀ spectroscopyꢀ (XPS;ꢀ VGꢀ
CLAMꢀ4ꢀMCDꢀanalyzer)ꢀwasꢀusedꢀtoꢀdetermineꢀtheꢀMnꢀ2p,ꢀOꢀ1s,ꢀ
Pdꢀ3d,ꢀPtꢀ4f,ꢀandꢀCꢀ1sꢀbindingꢀenergiesꢀ(BEs)ꢀofꢀsurfaceꢀspecies,ꢀ
usingꢀMgꢀKꢀ(hvꢀ=ꢀ1253.6ꢀeV)ꢀasꢀtheꢀexcitationꢀsource.ꢀ ꢀ
controllerꢀwasꢀusedꢀtoꢀintroduceꢀ100ꢀppmꢀSO
andꢀ1.0ꢀvol%ꢀNOꢀfromꢀtheꢀcorrespondingꢀSO ,ꢀCO
indersꢀ(balancedꢀwithꢀN )ꢀintoꢀtheꢀreactionꢀsystem.ꢀWaterꢀva‐
porꢀ(3.0ꢀvol%ꢀH O)ꢀwasꢀintroducedꢀbyꢀpassingꢀtheꢀfeedꢀstreamꢀ
2
,ꢀ5.0ꢀvol%ꢀCO
2
,ꢀ
2
2
,ꢀandꢀNOꢀcyl‐
2
2
Temperature‐programmedꢀ H
mentsꢀ wereꢀ performedꢀ usingꢀ aꢀ chemicalꢀ adsorptionꢀ analyzerꢀ
Autochemꢀ IIꢀ 2920,ꢀ Micromeritics).ꢀ Beforeꢀ theꢀ TPRꢀ measure‐
ments,ꢀtheꢀcatalystꢀ(4060ꢀmesh,ꢀca.ꢀ0.050ꢀg)ꢀwasꢀloadedꢀintoꢀaꢀ
quartzꢀfixed‐bedꢀU‐shapedꢀmicroreactorꢀ(i.d.ꢀ=ꢀ4ꢀmm)ꢀandꢀpre‐
2
ꢀ reductionꢀ (H
2
‐TPR)ꢀ experi‐
throughꢀaꢀwaterꢀsaturatorꢀatꢀaꢀcertainꢀtemperature.ꢀTheꢀreac‐
tantsꢀ andꢀ productsꢀ wereꢀ analyzedꢀ onlineꢀ usingꢀ aꢀ gasꢀ chro‐
matographꢀ(GC‐14C,ꢀShimadzu)ꢀequippedꢀwithꢀaꢀflameꢀioniza‐
tionꢀdetectorꢀandꢀaꢀthermalꢀconductivityꢀdetector;ꢀaꢀStabilwaxꢀ
columnꢀ(lengthꢀ30ꢀm)ꢀwasꢀusedꢀforꢀmethaneꢀseparationꢀandꢀaꢀ
Carboxenꢀ1000ꢀcolumnꢀ(lengthꢀ3ꢀm)ꢀwasꢀusedꢀforꢀpermanentꢀ
gasꢀdetection.ꢀTheꢀ balanceꢀofꢀ carbonꢀthroughoutꢀtheꢀcatalyticꢀ
systemꢀ wasꢀ estimatedꢀ toꢀ beꢀ 99.5%.ꢀ Theꢀ catalyticꢀ activitiesꢀ ofꢀ
theꢀsamplesꢀwereꢀevaluatedꢀbasedꢀonꢀtheꢀtemperaturesꢀ(T10%,ꢀ
(
treatedꢀinꢀO ꢀflowꢀ(20ꢀmL/min)ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀh.ꢀAfterꢀcoolingꢀ
2
toꢀrtꢀinꢀtheꢀsameꢀatmosphere,ꢀtheꢀsystemꢀwasꢀpurgedꢀwithꢀHeꢀ
flowꢀ(30ꢀmL/min)ꢀforꢀ15ꢀmin.ꢀTheꢀpretreatedꢀsampleꢀwasꢀex‐
posedꢀ toꢀ aꢀ flowꢀ (50ꢀ mL/min)ꢀ ofꢀ 5%ꢀ H
fromꢀrtꢀtoꢀ900ꢀ°Cꢀatꢀaꢀrampingꢀrateꢀofꢀ10ꢀ°C/min.ꢀChangesꢀinꢀtheꢀ
ꢀconcentrationꢀinꢀtheꢀeffluentꢀwereꢀmonitoredꢀonlineꢀusingꢀ
2
‐95%ꢀ Arꢀ andꢀ heatedꢀ
T50%,ꢀandꢀT90%)ꢀrequiredꢀforꢀachievingꢀmethaneꢀconversionsꢀofꢀ
H
2
10%,ꢀ50%,ꢀandꢀ90%.ꢀTheꢀmethaneꢀconversionꢀwasꢀdefinedꢀasꢀ
(cinletꢀꢀcoutlet)/cinletꢀꢀ100%,ꢀwhereꢀcinletꢀandꢀcoutletꢀareꢀtheꢀme‐
thaneꢀ concentrationsꢀ inꢀ theꢀ inletꢀ andꢀ outletꢀ feedꢀ streams,ꢀ re‐
spectively.ꢀ ꢀ
theꢀchemicalꢀadsorptionꢀanalyzer.ꢀTheꢀreductionꢀpeakꢀwasꢀcal‐
ibratedꢀagainstꢀthatꢀforꢀcompleteꢀreductionꢀofꢀaꢀknownꢀstand‐
ard,ꢀi.e.,ꢀpowderedꢀCuOꢀ(Aldrich,ꢀ99.995%).ꢀ ꢀ
Theꢀ Fourier‐transformꢀ infraredꢀ (FT‐IR)ꢀ spectrumꢀ ofꢀ
1
.41(Pd5.1Pt)/meso‐Mn
recordedꢀinꢀtheꢀrangeꢀ4004000ꢀcm ꢀatꢀaꢀresolutionꢀofꢀ4ꢀcm ꢀ
Brukerꢀ Vertexꢀ 70ꢀ spectrometer).ꢀ Beforeꢀ theꢀ spectrumꢀ wasꢀ
recorded,ꢀtheꢀsampleꢀwasꢀactivatedꢀinꢀO ꢀandꢀmethane,ꢀwithꢀtheꢀ
introductionꢀofꢀ100ꢀppmꢀSO ,ꢀ5.0ꢀvol%ꢀCO ,ꢀ3.0ꢀvol%ꢀH O,ꢀandꢀ
.0ꢀvol%ꢀNO.ꢀ
2
O
3
ꢀ(1ꢀwt%ꢀsampleꢀ+ꢀ99ꢀwt%ꢀKBr)ꢀwasꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
–1
–1
(
3.1.ꢀ ꢀ Crystalꢀphaseꢀcomposition,ꢀmorphology,ꢀsurfaceꢀarea,ꢀandꢀ
particleꢀsizeꢀdistributionꢀ ꢀ ꢀ
2
2
2
2
1
Fig.ꢀ1ꢀshowsꢀtheꢀXRDꢀpatternsꢀofꢀtheꢀpreparedꢀsamples.ꢀAꢀ
comparisonꢀwithꢀtheꢀXRDꢀpatternꢀofꢀaꢀstandardꢀMn
2 3
O ꢀsampleꢀ
2.3.ꢀ ꢀ Catalyticꢀevaluationꢀ
(JCPDSꢀ PDF#ꢀ 41‐1442)ꢀ showsꢀ thatꢀ allꢀ theꢀ Braggꢀ diffractionꢀ
peaksꢀ(Fig.ꢀ1(a))ꢀofꢀtheꢀmeso‐Mn
samplesꢀcanꢀbeꢀindexedꢀtoꢀaꢀcubicꢀcrystalꢀstructure.ꢀ ꢀ
TheꢀsizesꢀofꢀtheꢀMn ꢀ(Tableꢀ1)ꢀcrystallitesꢀinꢀmeso‐Mn
andꢀ theꢀ supportedꢀ noble‐metalꢀ samples,ꢀ calculatedꢀ usingꢀ theꢀ
Scherrerꢀ equation,ꢀ wereꢀ inꢀ theꢀ rangeꢀ 19.120.3ꢀ nm,ꢀ whereasꢀ
2
O
3
ꢀandꢀx(Pd
y
Pt)/meso‐Mn
2
O
3
ꢀ
ꢀ
Theꢀcatalyticꢀactivitiesꢀofꢀtheꢀsamplesꢀwereꢀevaluatedꢀusingꢀ
aꢀcontinuous‐flowꢀfixed‐bedꢀquartzꢀtubularꢀmicroreactorꢀ(i.d.ꢀ=ꢀ
.0ꢀ mm).ꢀ Theꢀ sampleꢀ (40–60ꢀ mesh,ꢀ 50ꢀ mg)ꢀ wasꢀ dilutedꢀ withꢀ
quartzꢀsandꢀ(40–60ꢀmesh,ꢀ0.25ꢀg)ꢀtoꢀminimizeꢀtheꢀeffectsꢀofꢀhotꢀ
spots.ꢀBeforeꢀtheꢀtest,ꢀeachꢀsampleꢀwasꢀtreatedꢀinꢀO ꢀflowꢀ(20ꢀ
mL/min)ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀh.ꢀTheꢀreactantꢀmixtureꢀconsistedꢀofꢀ
.5ꢀvol%ꢀCH ꢀ+ꢀ20ꢀvol%ꢀO ꢀ+ꢀ77.5ꢀvol%ꢀN ꢀ(balance),ꢀandꢀtheꢀ
totalꢀflowꢀwasꢀ16.6ꢀmL/min,ꢀgivingꢀaꢀCH /O ꢀmolarꢀratioꢀofꢀ1/8ꢀ
andꢀaꢀspaceꢀvelocityꢀ(SV)ꢀofꢀca.ꢀ20000ꢀmL/(gh).ꢀAꢀmassꢀflowꢀ
O
2 3
2
O
3
6
2
thatꢀ ofꢀ Mn
2
O
3
ꢀ inꢀ 0.07(Pd4.9Pt)/bulk‐Mn
2
O ꢀ wasꢀ 70.7ꢀ nm.ꢀ Noꢀ
3
diffractionꢀsignalsꢀfromꢀnoble‐metalꢀphasesꢀwereꢀdetectedꢀbe‐
causeꢀofꢀtheꢀlowꢀloadingsꢀofꢀnobleꢀmetalsꢀandꢀtheirꢀgoodꢀdis‐
persion.ꢀTheꢀdiffractionꢀpeakꢀatꢀ2θꢀ=ꢀca.ꢀ1°ꢀinꢀtheꢀsmall‐angleꢀ
2
4
2
2
4
2
XRDꢀpatternꢀ(Fig.ꢀ1(b))ꢀofꢀmeso‐Mn
2
O ꢀandꢀtheꢀsupportedꢀno‐
3
(a)
(b)
(7)
(7)
(6)
(6)
(
5)
(
5)
4)
3)
2)
(
(4)
(
(
(3)
2)
1)
(
(
(1)
1
0
20
30
40
2
50
/( )
60
70
80
0.6
1.2
1.8
2.4
3.0
3.6
o
o
2/( )
,ꢀ (2)ꢀ 0.07(Pd4.9Pt)/meso‐Mn ,ꢀ (3)ꢀ 0.72(Pd5.1Pt)/meso‐Mn
,ꢀandꢀ(7)ꢀ0.07(Pd4.9Pt)/bulk‐Mn
Fig.ꢀ 1.ꢀ (a)ꢀ Wide‐angleꢀ andꢀ (b)ꢀ small‐angleꢀ XRDꢀ patternsꢀ ofꢀ (1)ꢀ meso‐Mn
.41(Pd5.1Pt)/meso‐Mn ,ꢀ(5)ꢀ1.40Pd/meso‐Mn ,ꢀ(6)ꢀ1.42Pt/meso‐Mn
O
2 3
2
O
3
2
3
O ,ꢀ (4)ꢀ
1
2
O
3
O
2 3
O
2 3
2
O .ꢀ
3

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
95ꢀ
Tableꢀ1ꢀ
BETꢀsurfaceꢀareas,ꢀporeꢀvolumes,ꢀaverageꢀporeꢀsizes,ꢀMn
2
O ꢀcrystalliteꢀsizesꢀ(DMn2O3),ꢀnoble‐metalꢀparticleꢀsizes,ꢀrealꢀPdꢀorꢀPtꢀcontents,ꢀandꢀrealꢀPd/Ptꢀ
3
molarꢀratiosꢀofꢀsamples.ꢀ
a
Nobelꢀmetalꢀ
particleꢀsizeꢀbꢀ
Surfaceꢀareaꢀ
Poreꢀvolumeꢀ Averageꢀporeꢀ
D
Mn2O3ꢀ ꢀ ꢀ
RealꢀPd/Ptꢀ
contentꢀ ꢀ(wt%)ꢀ molarꢀratioꢀ ꢀ
RealꢀPd/Ptꢀ ꢀ
Sampleꢀ
2
3
c
c
(m /g)ꢀ
(cm /g)ꢀ
0.37ꢀ
0.40ꢀ
0.38ꢀ
0.36ꢀ
0.35ꢀ
0.35ꢀ
0.03ꢀ
sizeꢀ(nm)ꢀ
11.2ꢀ
12.6ꢀ
ꢀ 9.6ꢀ
ꢀ 9.6ꢀ
ꢀ 9.3ꢀ
ꢀ 9.9ꢀ
—ꢀ
(nm)ꢀ
19.5ꢀ
19.6ꢀ
19.1ꢀ
19.4ꢀ
20.2ꢀ
20.3ꢀ
70.7ꢀ
2 3
meso‐Mn O ꢀ
105.6ꢀ
ꢀ 95.3ꢀ
ꢀ 76.5ꢀ
ꢀ 85.1ꢀ
ꢀ 89.9ꢀ
ꢀ 83.5ꢀ
ꢀ ꢀ 4.5ꢀ
—ꢀ
—ꢀ
—/—ꢀ
0.051/0.019ꢀ
0.53/0.19ꢀ
1.04/0.37ꢀ
1.40/—ꢀ
—ꢀ
4.9ꢀ
5.1ꢀ
5.1ꢀ
—ꢀ
0
0
1
1
1
.07(Pd4.9Pt)/meso‐Mn
2
2
2
O
O
O
3
3
3
ꢀ
ꢀ
ꢀ
.72(Pd5.1Pt)/meso‐Mn
.41(Pd5.1Pt)/meso‐Mn
2.4ꢀ
2.2ꢀ
2.8ꢀ
2.5ꢀ
2.1ꢀ
.40Pd/meso‐Mn
.42Pt/meso‐Mn
.07(Pd4.9Pt)/bulk‐Mn
2
O
3
ꢀ
ꢀ
2
O
3
—/1.42ꢀ
0.051/0.019ꢀ
—ꢀ
4.9ꢀ
0
2
O
3
ꢀ
a
ꢀ
DataꢀwereꢀcalculatedꢀaccordingꢀtoꢀtheꢀScherrerꢀequationꢀusingꢀtheꢀFWHMꢀofꢀtheꢀ(222)ꢀlineꢀofꢀMn
2
O ;ꢀ
3
bꢀ
DataꢀwereꢀestimatedꢀaccordingꢀtoꢀtheꢀTEMꢀimages;ꢀ ꢀ
cꢀDataꢀwereꢀdeterminedꢀbyꢀtheꢀICP‐AESꢀtechnique.ꢀ
ꢀ
ble‐metalꢀsamplesꢀindicatesꢀformationꢀofꢀanꢀorderedꢀmesopo‐
rousꢀstructure,ꢀbutꢀnoꢀsmall‐angleꢀXRDꢀpeaksꢀwereꢀdetectedꢀinꢀ
Fig.ꢀ2ꢀshowsꢀtheꢀTEMꢀimagesꢀandꢀSAEDꢀpatternsꢀofꢀtheꢀsam‐
ples.ꢀTheꢀmeso‐Mn ꢀandꢀsupportedꢀnoble‐metalꢀsamplesꢀhadꢀ
high‐qualityꢀorderedꢀmesoporousꢀstructuresꢀwithꢀaꢀporeꢀsizeꢀofꢀ
O
2 3
0
.07(Pd4.9Pt)/bulk‐Mn
2
O .ꢀ ꢀ
3
Fig.ꢀ 2.ꢀ TEMꢀ imagesꢀ andꢀ SAEDꢀ patternsꢀ (insets)ꢀ ofꢀ (a,ꢀ b)ꢀ meso‐Mn
2
O
3
,ꢀ (c,ꢀ d)ꢀ 0.07(Pd4.9Pt)/meso‐Mn
,ꢀandꢀ(m,ꢀn)ꢀ0.07(Pd4.9Pt)/bulk‐Mn
2
O
3
,ꢀ (e,ꢀ f)ꢀ 0.72(Pd5.1Pt)/meso‐Mn
.ꢀ
2
O ,ꢀ (g,ꢀ h)ꢀ
3
1
.41(Pd5.1Pt)/meso‐Mn ,ꢀ(i,ꢀj)ꢀ1.40Pd/meso‐Mn ,ꢀ(k,ꢀl)ꢀ1.42Pt/meso‐Mn
2
O
3
2
O
3
O
2 3
O
2 3

96ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
ca.ꢀ14ꢀnmꢀ(Fig.ꢀ2(b)ꢀandꢀ(d)).ꢀNoble‐metalꢀNPsꢀwereꢀhighlyꢀdis‐
persedꢀonꢀtheꢀMn ꢀsurfaces.ꢀTheꢀparticleꢀsizesꢀofꢀmoreꢀthanꢀ
0ꢀnoble‐metalꢀNPsꢀinꢀtheꢀsupportedꢀsamplesꢀwereꢀmeasured;ꢀ
theꢀresultsꢀareꢀshownꢀinꢀTableꢀ1ꢀandꢀFig.ꢀ3.ꢀTheꢀaverageꢀsizesꢀofꢀ
theꢀ noble‐metalꢀ NPsꢀ inꢀ theꢀ supportedꢀ samplesꢀ wereꢀ inꢀ theꢀ
rangeꢀ2.22.8ꢀnm.ꢀTheꢀmultipleꢀbrightꢀelectronꢀdiffractionꢀringsꢀ
inꢀtheꢀSAEDꢀpatternsꢀ(Fig.ꢀ2(a),ꢀ(c),ꢀ(e),ꢀ(g),ꢀ(i),ꢀ(k),ꢀandꢀ(m))ꢀofꢀ
theꢀsamplesꢀindicateꢀthatꢀtheseꢀmaterialsꢀwereꢀpolycrystalline.ꢀ
Fig.ꢀ4ꢀshowsꢀtheꢀHAADF‐STEMꢀandꢀelementꢀmappingꢀimagesꢀ
pore‐sizeꢀ distributionsꢀ ofꢀ theꢀ samples.ꢀ Theꢀ meso‐Mn
2
O ꢀ andꢀ
3
O
2 3
supportedꢀnoble‐metalꢀ samplesꢀhadꢀtypeꢀIVꢀisothermsꢀwithꢀ aꢀ
hysteresisꢀ loopꢀ inꢀ theꢀ relativeꢀ pressureꢀ rangeꢀ 0.51.0ꢀ (Fig.ꢀ
5(a)),ꢀindicatingꢀgenerationꢀofꢀaꢀmesoporousꢀstructureꢀinꢀtheseꢀ
samples.ꢀTheꢀpore‐sizeꢀdistributionꢀcurvesꢀ(Fig.ꢀ5(b))ꢀhadꢀtwoꢀ
peaks,ꢀinꢀtheꢀrangesꢀ26ꢀandꢀ1016ꢀnm,ꢀrespectively.ꢀ
7
Theꢀ BETꢀ surfaceꢀ areasꢀ andꢀ poreꢀ volumesꢀ ofꢀ meso‐Mn
andꢀ theꢀ supportedꢀ noble‐metalꢀ samplesꢀ wereꢀ inꢀ theꢀ rangesꢀ
2
O ꢀ
3
2
3
76.5105.6ꢀ m /gꢀ andꢀ 0.350.40ꢀ cm /g,ꢀ respectively,ꢀ muchꢀ
2
3
ofꢀ 1.41(Pd5.1Pt)/meso‐Mn
Pd‐Ptꢀ alloyꢀ wasꢀ formedꢀ usingꢀ theꢀ PVA‐protectedꢀ reductionꢀ
strategyꢀwithꢀNaBH ꢀasꢀtheꢀreducingꢀagent.ꢀ
Fig.ꢀ 5ꢀ showsꢀ theꢀ N ꢀ adsorption‐desorptionꢀ isothermsꢀ andꢀ
2 3
O .ꢀ Theꢀ figureꢀ clearlyꢀ showsꢀ thatꢀ aꢀ
higherꢀ thanꢀ thoseꢀ (4.52ꢀ m /gꢀ andꢀ 0.03ꢀ cm /g)ꢀ ofꢀ
0.70(Pd4.9Pt)/bulk‐Mn (Tableꢀ 1).ꢀ Theꢀ me‐
so‐Mn ‐supportedꢀ noble‐metalꢀ catalystsꢀ wereꢀ preparedꢀ us‐
ingꢀ theꢀ incipientꢀ wetnessꢀ impregnationꢀ method,ꢀ followedꢀ byꢀ
2 3
O ꢀ
4
O
2 3
2
60
40
20
0
(
a)
Average d = 2.4 nm
(b)
Average d = 2.2 nm
60
40
20
0
1
2
3
1
2
3
Noble metal particle size (nm)
Noble metal particle size (nm)
60
40
20
0
60
(
c)
Average d = 2.8 nm
(d)
Average d = 2.5 nm
(e)
Average d = 2.1 nm
60
40
20
0
40
20
0
1
2
3
4
1
2
3
4
1
2
3
Noble metal particle size (nm)
Noble metal particle size (nm)
Noble metal particle size (nm)
Fig.ꢀ 3.ꢀ Noble‐metalꢀ particleꢀ sizeꢀ distributionsꢀ ofꢀ (a)ꢀ 0.72(Pd5.1Pt)/meso‐Mn
.42Pt/meso‐Mn ,ꢀandꢀ(e)ꢀ0.07(Pd4.9Pt)/bulk‐Mn .ꢀ
2
O
3
,ꢀ (b)ꢀ 1.41(Pd5.1Pt)/meso‐Mn
2
O
3
,ꢀ (c)ꢀ 1.40Pd/meso‐Mn
2
O ,ꢀ (d)ꢀ
3
1
O
2 3
O
2 3
(
a)
e)
(b)
(f)
(c)
(g)
(d)
(
(h)
Fig.ꢀ4.ꢀ(a–d)ꢀHAADF‐STEMꢀimagesꢀandꢀ(e–h)ꢀelementꢀmappingꢀimagesꢀofꢀ1.41(Pd5.1Pt)/meso‐Mn
2
O .ꢀ
3

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
97ꢀ
2
1
1
1
0
.1
.8
.5
.2
.9
(
a)
(b)
(
6)
(6)
(
5)
4)
3)
2)
(5)
4)
3)
(
(
(
0.6
(
(
(2)
(1)
0
.3
.0
(1)
0
0.0
0.2
0.4
0.6
0.8
1.0
0
10
20
Pore diameter (nm)
30
40
Relative pressure (p/p0)
Fig.ꢀ 5.ꢀ (a)ꢀ N
2
ꢀ adsorption‐desorptionꢀ isothermsꢀ andꢀ (b)ꢀ pore‐sizeꢀ distributionsꢀ ofꢀ (1)ꢀ meso‐Mn
2
O
3
,ꢀ (2)ꢀ 0.07(Pd4.9Pt)/meso‐Mn
.ꢀ
2 3
O ,ꢀ (3)ꢀ
0.72(Pd5.1Pt)/meso‐Mn ,ꢀ(4)ꢀ1.41(Pd5.1Pt)/meso‐Mn ,ꢀ(5)ꢀ1.40Pd/meso‐Mn ,ꢀandꢀ(6)ꢀ1.42Pt/meso‐Mn
O
2 3
O
2 3
O
2 3
2
O
3
calcinationꢀatꢀ600ꢀ°Cꢀforꢀ6ꢀh.ꢀDuringꢀimpregnationꢀandꢀcalcina‐
tion,ꢀchangesꢀinꢀtheꢀporousꢀstructureꢀoccurredꢀandꢀtheꢀqualityꢀ
ofꢀtheꢀmesoporousꢀstructureꢀdecreased,ꢀleadingꢀtoꢀchangesꢀinꢀ
theꢀsurfaceꢀareasꢀofꢀtheꢀsamples.ꢀ
3+
(a) Mn 2p3/2
(b) O 1s
2+
Mn
4+
Mn
Mn
O
latt
O
ads
(7)
(7)
(
6)
(6)
(5)
(5)
(
4)
3)
2)
1)
(4)
(3)
(
(
(2)
(
(1)
638
640
642
644
646
648
527
529
531
533
535
537
Binding energy (eV)
Binding energy (eV)
(c) Pd 3d
(d) Pt 4f
337.3
71.7
74.6
75.7
72.6
342.6
335.4
340.8
(5)
(
6)
(
4)
(4)
(3)
(
3)
333
336
339
342
345
348
70
72
74
76
78
80
Binding energy (eV)
Binding energy (eV)
Fig.ꢀ 6.ꢀ(a)ꢀ Mnꢀ 2p3/2,ꢀ (b)ꢀ Oꢀ 1s,ꢀ (c)ꢀ Pdꢀ 3d,ꢀ andꢀ (d)ꢀ Ptꢀ 4fꢀXPSꢀofꢀ (1)ꢀ meso‐Mn
2
O
3
,ꢀ (2)ꢀ 0.07(Pd4.9Pt)/meso‐Mn
2
O
3
,ꢀ (3)ꢀ 0.72(Pd5.1Pt)/meso‐Mn
2
O ,ꢀ (4)ꢀ
3
1
.41(Pd5.1Pt)/meso‐Mn ,ꢀ(5)ꢀ1.40Pd/meso‐Mn ,ꢀ(6)ꢀ1.42Pt/meso‐Mn ,ꢀandꢀ(7)ꢀ0.07(Pd4.9Pt)/bulk‐Mn
2
O
3
2
O
3
2
O
3
2
O .ꢀ
3

98ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
3.2.ꢀ ꢀ Surfaceꢀcomposition,ꢀmetalꢀoxidationꢀstate,ꢀandꢀoxygenꢀ
speciesꢀ
233
4
04
XPSꢀ isꢀ anꢀ effectiveꢀ techniqueꢀ forꢀ investigatingꢀ theꢀ surfaceꢀ
elementꢀcontents,ꢀmetalꢀoxidationꢀstates,ꢀandꢀadsorbedꢀoxygenꢀ
speciesꢀofꢀanꢀoxideꢀcatalyst.ꢀFig.ꢀ6ꢀshowsꢀtheꢀMnꢀ2p3/2,ꢀOꢀ1s,ꢀPdꢀ
d,ꢀandꢀPtꢀ4fꢀXPSꢀofꢀtheꢀsamples.ꢀEachꢀsampleꢀgaveꢀanꢀasym‐
(
7)
2
07
2
76
8
6
(
6)
1
68
1
36
3
85
metricꢀMnꢀ2p3/2ꢀXPSꢀsignalꢀ(Fig.ꢀ6(a)),ꢀwhichꢀwasꢀdecomposedꢀ
toꢀthreeꢀcomponentsꢀwithꢀBEꢀ=ꢀ640.0,ꢀ641.3,ꢀandꢀ642.8ꢀeVꢀto‐
getherꢀwithꢀaꢀweakꢀshake‐upꢀsatelliteꢀatꢀBEꢀ=ꢀ644.7ꢀeV,ꢀassign‐
(
5)
1
34
168
80
(4)
1
57
2+
3+
4+
ableꢀ toꢀ surfaceꢀ Mn ,ꢀ Mn ,ꢀ andꢀ Mn ꢀ speciesꢀ [32,33],ꢀ respec‐
tively.ꢀ Fig.ꢀ 6(b)ꢀ showsꢀ thatꢀ eachꢀ sampleꢀ gaveꢀ aꢀ broad,ꢀ asym‐
metricꢀOꢀ1sꢀXPSꢀpeak,ꢀwhichꢀwasꢀdecomposedꢀintoꢀtwoꢀcom‐
ponents,ꢀatꢀBEꢀ=ꢀ529.6ꢀandꢀ531.2ꢀeV,ꢀascribableꢀtoꢀsurfaceꢀlat‐
85
(3)
(2)
210
9
5


2
ticeꢀoxygenꢀ(Olatt)ꢀandꢀadsorbedꢀoxygenꢀ(Oads,ꢀe.g.,ꢀO
2
,ꢀO
2
,ꢀorꢀ

O )ꢀspeciesꢀ[21,34],ꢀrespectively.ꢀCurveꢀfittingꢀenabledꢀdecon‐
volutionꢀ ofꢀ theꢀ asymmetricꢀ Pdꢀ 3dꢀ andꢀ Ptꢀ 4fꢀ XPSꢀ signalsꢀ ofꢀ
397
400o
558
600
(
1)
0
1
.72(Pd5.1Pt)/meso‐Mn
2 3
O ,ꢀ
1.41(Pd5.1Pt)/meso‐Mn
O ,ꢀ
2 3
0
100
200
300
500
700
.40Pd/meso‐Mn ,ꢀ andꢀ 1.42Pt/meso‐Mn
2
O
3
2 3
O ꢀ intoꢀ fourꢀ com‐
Temperature ( C)
ponents,ꢀatꢀBEꢀ=ꢀ335.4,ꢀ337.3,ꢀ340.8,ꢀandꢀ342.6ꢀeVꢀandꢀatꢀBEꢀ=ꢀ
1.7,ꢀ 72.6,ꢀ 74.6,ꢀ andꢀ 75.7ꢀ eVꢀ (Fig.ꢀ 6(c)ꢀ andꢀ (d)),ꢀ respectively.ꢀ
TheꢀsignalsꢀatꢀBEꢀ=ꢀ335.5ꢀandꢀ340.8ꢀeVꢀareꢀassignedꢀtoꢀsurfaceꢀ
Fig.ꢀ
.07(Pd4.9Pt)/meso‐Mn
1.41(Pd5.1Pt)/meso‐Mn
1.42Pt/meso‐Mn
7.ꢀ
H
2
‐TPRꢀ
profilesꢀ ofꢀ (1)ꢀ
meso‐Mn
2
O
3
,ꢀ
(2)ꢀ
7
0
2
O
O
3
,ꢀ (3)ꢀ 0.72(Pd5.1Pt)/meso‐Mn
,ꢀ (5)ꢀ 1.40Pd/meso‐Mn
.ꢀ
2
O
3
,ꢀ (4)ꢀ
2
3
2
O ,ꢀ (6)ꢀ
3
0
2 3
O ,ꢀandꢀ(7)ꢀ0.07(Pd4.9Pt)/bulk‐Mn
O
2 3
metallicꢀPd ꢀspeciesꢀandꢀthoseꢀatꢀBEꢀ=ꢀ337.8ꢀandꢀ342.9ꢀeVꢀareꢀ
2+
attributedꢀ toꢀ surfaceꢀ Pd ꢀ speciesꢀ [35].ꢀ Similarly,ꢀ theꢀ compo‐
nentsꢀatꢀBEꢀ=ꢀ71.7ꢀeVꢀandꢀ74.6ꢀeVꢀareꢀascribedꢀtoꢀsurfaceꢀmetal‐
performance.ꢀ Strongꢀ interactionsꢀ canꢀ occurꢀ betweenꢀ theꢀ no‐
ble‐metalꢀorꢀalloyꢀNPsꢀandꢀtheꢀMn O ꢀsupportꢀ(possiblyꢀviaꢀtheꢀ
reactionꢀPdꢀ(PtꢀorꢀPd‐Pt)ꢀ+ꢀ2Mn4+ꢀꢀPd2+ꢀ(Pt2+ꢀorꢀPd2+‐Pt2+)ꢀ+ꢀ
0
licꢀPt ꢀspecies,ꢀandꢀthoseꢀatꢀBEꢀ=ꢀ72.6ꢀeVꢀandꢀ75.7ꢀeVꢀareꢀas‐
2 3
2+
cribedꢀtoꢀsurfaceꢀoxidizedꢀPtꢀ(Pt )ꢀ[36,37].ꢀTheꢀPdꢀ3dꢀandꢀPtꢀ4fꢀ
XPSꢀ ofꢀ theꢀ otherꢀ samplesꢀ areꢀ notꢀ shownꢀ becauseꢀ theirꢀ weakꢀ
signalsꢀcouldꢀnotꢀbeꢀdecomposedꢀaccurately.ꢀ ꢀ
3+
4+
3+
2Mn ),ꢀ thereforeꢀ theꢀ surfaceꢀ Mn /Mn ꢀ molarꢀ ratiosꢀ wereꢀ
similarꢀ (0.600.67)ꢀ atꢀ similarꢀ loadingsꢀ ((1.401.42)ꢀ wt%)ꢀ ofꢀ
Pd,ꢀPt,ꢀorꢀPd‐PtꢀNPs.ꢀ
XPSꢀwasꢀusedꢀforꢀquantitativeꢀanalysisꢀofꢀtheꢀsamplesꢀtoꢀde‐
termineꢀtheꢀsurfaceꢀelementꢀcontents;ꢀtheꢀresultsꢀareꢀsumma‐
rizedꢀ inꢀ Tableꢀ 2.ꢀ Theꢀ Oads/Olattꢀ molarꢀ ratiosꢀ decreasedꢀ inꢀ theꢀ
3.3.ꢀ ꢀ Low‐temperatureꢀreducibilityꢀ
orderꢀ1.41(Pd5.1Pt)/meso‐Mn
0.69)ꢀ >ꢀ 0.72(Pd5.1Pt)/meso‐Mn
.42Pt/meso‐Mn ꢀ(0.63)ꢀ>ꢀ0.07(Pd4.9Pt)/meso‐Mn
ꢀ 0.07(Pd4.9Pt)/bulk‐Mn ꢀ (0.52)ꢀ >ꢀ meso‐Mn ꢀ (0.45);ꢀ thisꢀ
sequenceꢀ correspondsꢀ toꢀ theꢀ orderꢀ ofꢀ theꢀ catalyticꢀ perfor‐
mancesꢀ(discussedꢀbelow).ꢀ ꢀ
2
O
3
ꢀ(0.77)ꢀ>ꢀ1.40Pd/meso‐Mn
(0.65)ꢀ
ꢀ(0.53)ꢀ
2
O
>ꢀ
3
ꢀ
(
1
>
2 3
O ꢀ
Accordingꢀtoꢀtheꢀliteratureꢀ[32,42],ꢀtheꢀreductionꢀofꢀmanga‐
O
2 3
O
2 3
neseꢀ oxidesꢀ canꢀ beꢀ dividedꢀ intoꢀ consecutiveꢀ steps:ꢀ Mn
Mn ꢀ →ꢀ MnO.ꢀ However,ꢀ theꢀ reductionꢀ peaksꢀ inꢀ theꢀ H
profileꢀ mayꢀ alsoꢀ ariseꢀ fromꢀ reductionꢀ ofꢀ speciesꢀ inꢀ differentꢀ
localꢀenvironmentsꢀ[42].ꢀFig.ꢀ7ꢀshowsꢀtheꢀH ‐TPRꢀprofilesꢀofꢀtheꢀ
samples,ꢀandꢀtheirꢀH ꢀconsumptionsꢀareꢀsummarizedꢀinꢀTableꢀ2.ꢀ
Thereꢀwereꢀtwoꢀmainꢀreductionꢀpeaks,ꢀcenteredꢀatꢀ397ꢀandꢀ
558ꢀ°C,ꢀforꢀmeso‐Mn ,ꢀattributableꢀtoꢀtheꢀreductionꢀofꢀMn
toꢀMn ꢀandꢀofꢀMn ꢀtoꢀMnOꢀ[32,42,43],ꢀrespectively.ꢀAfterꢀ
2 3
O ꢀ →ꢀ
O
2 3
O
2 3
O
3 4
2
‐TPRꢀ
2
Aꢀcatalystꢀwithꢀaꢀhigherꢀadsorbedꢀoxygenꢀspeciesꢀconcentra‐
2
tionꢀ promotesꢀ redox‐basedꢀ reactionsꢀ [38‒40].ꢀ Generally,ꢀ O ꢀ
2
moleculesꢀcanꢀbeꢀadsorbedꢀatꢀtheꢀoxygenꢀvacanciesꢀofꢀaꢀmetalꢀ
oxideꢀ[41].ꢀPd,ꢀPt,ꢀorꢀPd‐Ptꢀloadingꢀenhancedꢀtheꢀadsorbedꢀox‐
O
2 3
2 3
O ꢀ
O
3 4
O
3 4
ygenꢀ
speciesꢀ
concentrationsꢀ
ofꢀ
theꢀ
samples;ꢀ
noble‐metalꢀloading,ꢀtheꢀreductionꢀpeaksꢀofꢀtheꢀsamplesꢀshiftedꢀ
toꢀ lowerꢀ temperatures,ꢀ particularlyꢀ inꢀ theꢀ caseꢀ ofꢀ
1.41(Pd5.1Pt)/meso‐Mn
2 3
O
ꢀ hadꢀ theꢀ highestꢀ adsorbedꢀ oxygenꢀ
speciesꢀ concentration,ꢀ andꢀ thereforeꢀ gaveꢀ theꢀ bestꢀ catalyticꢀ
1.41(Pd5.1Pt)/meso‐Mn
2 3
O .ꢀ
Thisꢀ
indicatesꢀ
improvedꢀ
Tableꢀ2ꢀ
2
SurfaceꢀelementꢀcontentsꢀofꢀsamplesꢀandꢀH ‐TPRꢀresults.ꢀ
Surfaceꢀelementꢀcompositionꢀ(molarꢀratio)ꢀ
H
2
ꢀconsumptionꢀ(mmol/g)ꢀ
Aboveꢀ120ꢀ°Cꢀ
14.85ꢀ
Sampleꢀ
4
+
3+
2+
Pd /Pd0
2+
0
Mn /Mn
0.65ꢀ
O
ads/Olatt
0.45ꢀ
0.53ꢀ
0.65ꢀ
0.77ꢀ
0.69ꢀ
0.63ꢀ
0.52ꢀ
ꢀ
Pt /Pt ꢀ
—ꢀ
Belowꢀ120ꢀ°C
—ꢀ
Totalꢀ
14.85ꢀ
12.89ꢀ
13.19ꢀ
14.15ꢀ
13.71ꢀ
12.24ꢀ
14.10ꢀ
meso‐Mn
2 3
O ꢀ
—ꢀ
0
0
1
1
1
0
.07(Pd4.9Pt)/meso‐Mn
2
2
2
O
O
O
3
3
3
ꢀ
ꢀ
ꢀ
0.48ꢀ
0.57ꢀ
—ꢀ
—ꢀ
0.68ꢀ
1.19ꢀ
12.21ꢀ
12.00ꢀ
.72(Pd5.1Pt)/meso‐Mn
.41(Pd5.1Pt)/meso‐Mn
5.40ꢀ
4.50ꢀ
11.48ꢀ
—ꢀ
0.96ꢀ
1.18ꢀ
—ꢀ
0.92ꢀ
—ꢀ
0.67ꢀ
0.61ꢀ
0.60ꢀ
0.49ꢀ
2.34ꢀ
2.19ꢀ
0.82ꢀ
—ꢀ
11.81ꢀ
11.52ꢀ
11.42ꢀ
14.10ꢀ
.40Pd/meso‐Mn
.42Pt/meso‐Mn
.07(Pd4.9Pt)/bulk‐Mn
2
O
3
ꢀ
ꢀ
2
O
3
2
O ꢀ
3
—ꢀ

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
99ꢀ
low‐temperatureꢀ reducibility.ꢀ Theꢀ reductionꢀ shouldersꢀ belowꢀ
20ꢀ°Cꢀcanꢀbeꢀascribedꢀtoꢀtheꢀreductionꢀofꢀoxidizedꢀnobleꢀmet‐
als,ꢀandꢀthoseꢀaboveꢀ120ꢀ°Cꢀcanꢀbeꢀassignedꢀtoꢀtheꢀreductionꢀofꢀ
Mn ꢀtoꢀMn ꢀorꢀfurtherꢀtoꢀMnO.ꢀTheꢀtotalꢀH ꢀconsumptionsꢀ
14.1014.85ꢀ mmol/g)ꢀ ofꢀ theꢀ meso‐Mn andꢀ
.07(Pd4.9Pt)/bulk‐Mn ꢀ samplesꢀ wereꢀ closeꢀ toꢀ orꢀ slightlyꢀ
higherꢀ thanꢀ thoseꢀ (12.2414.15ꢀ mmol/g)ꢀ ofꢀ theꢀ me‐
so‐Mn ‐supportedꢀ noble‐metalꢀ samples;ꢀ theꢀ latterꢀ gaveꢀ aꢀ
low‐temperatureꢀ(belowꢀ120ꢀ°C)ꢀH ꢀconsumptionꢀofꢀ0.682.34ꢀ
mmol/g,ꢀshowingꢀthatꢀtheꢀlow‐temperatureꢀreducibilitiesꢀofꢀtheꢀ
porousꢀMn ‐supportedꢀsamplesꢀwereꢀbetterꢀthanꢀthoseꢀofꢀtheꢀ
bulk‐Mn ‐supportedꢀ andꢀ noble‐metal‐freeꢀ samples.ꢀ Theꢀ
.41(Pd5.1Pt)/meso‐Mn sampleꢀ showedꢀ theꢀ bestꢀ
low‐temperatureꢀreducibility.ꢀ ꢀ
moreꢀconvenientꢀtoꢀcompareꢀtheꢀcatalyticꢀactivitiesꢀofꢀtheꢀsam‐
plesꢀusingꢀT10%,ꢀT50%,ꢀandꢀT90%;ꢀtheseꢀdataꢀareꢀsummarizedꢀinꢀ
Tableꢀ3.ꢀ ꢀ
1
2
O
3
3
O
4
2
Theꢀ1.41(Pd5.1Pt)/meso‐Mn
2
O ꢀsampleꢀperformedꢀbest,ꢀgiv‐
3
(
0
2 3
O ꢀ
ingꢀT10%,ꢀT50%,ꢀandꢀT90%ꢀvaluesꢀofꢀ265,ꢀ345,ꢀandꢀ425ꢀ°C,ꢀrespec‐
tively,ꢀ atꢀ SVꢀ =ꢀ 20000ꢀ mL/(gh).ꢀTheꢀT90%ꢀvaluesꢀwereꢀ495ꢀ°Cꢀ
2 3
O
overꢀ
0.72(Pd5.1Pt)/meso‐Mn
1.40Pd/meso‐Mn
1.41(Pd5.1Pt)/meso‐Mn
1.42Pt/meso‐Mn
2
O
3
,ꢀ
485ꢀ
460ꢀ
°Cꢀ
°Cꢀ
overꢀ
overꢀ
2
O
3
2 3
O ,ꢀ
andꢀ
2
2 3
O .ꢀ Theꢀ methaneꢀ conversionꢀ overꢀ
2 3
O ꢀ decreasedꢀ withꢀ increasingꢀ SVꢀ (Fig.ꢀ
2
O
3
8(b)),ꢀasꢀaꢀresultꢀofꢀshorteningꢀofꢀtheꢀcontactꢀtime.ꢀ ꢀ
Generally,ꢀitꢀisꢀmoreꢀaccurateꢀtoꢀuseꢀtheꢀturnoverꢀfrequen‐
ciesꢀ(TOFs)ꢀandꢀspecificꢀreactionꢀratesꢀtoꢀevaluateꢀtheꢀinherentꢀ
2
O
3
1
2
O ꢀ
3
catalyticꢀactivities.ꢀForꢀtheꢀMn
lysts,ꢀnobleꢀmetalsꢀandꢀMn ꢀareꢀtheꢀactiveꢀsites,ꢀandꢀitꢀisꢀdif‐
ficultꢀ toꢀ calculateꢀ theꢀ TOFsꢀ ofꢀ suchꢀ samplesꢀ accurately.ꢀ Theꢀ
TOF ꢀvaluesꢀ[=ꢀzC /n ,ꢀwhereꢀzꢀisꢀtheꢀconversionꢀatꢀaꢀcertainꢀ
temperature,ꢀ C ꢀ (mol/s)ꢀ isꢀ theꢀ initialꢀ methaneꢀ concentration,ꢀ
andꢀn ꢀ(mol)ꢀisꢀtheꢀmolarꢀamountꢀofꢀmetalꢀorꢀoxideꢀ(Mꢀ=ꢀPd,ꢀPt,ꢀ
Pd‐Ptꢀ orꢀ Mn )]ꢀ andꢀ theꢀ specificꢀ reactionꢀ ratesꢀ atꢀ aꢀ typicalꢀ
temperatureꢀ (400ꢀ °C)ꢀ wereꢀ calculatedꢀ basedꢀ onꢀ theꢀ activityꢀ
dataꢀandꢀamountsꢀofꢀPdꢀand/orꢀPtꢀandꢀMn ꢀinꢀtheꢀsamples;ꢀ
2 3
O ‐supportedꢀnoble‐metalꢀcata‐
O
2 3
3.4.ꢀ ꢀ Catalyticꢀperformanceꢀ
M
0
M
Inꢀaꢀblankꢀexperimentꢀ(onlyꢀquartzꢀsandꢀwasꢀloadedꢀinꢀtheꢀ
microreactor),ꢀnoꢀmethaneꢀconversionꢀwasꢀdetectedꢀunderꢀtheꢀ
conditionsꢀ2.5ꢀvol%ꢀCH ,ꢀCH /O ꢀmolarꢀratioꢀ=ꢀ1/8,ꢀSVꢀ=ꢀ20000ꢀ
0
M
4
4
2
O
2 3
mL/(gh),ꢀlessꢀthanꢀ600ꢀ°C,ꢀi.e.,ꢀnoꢀhomogeneousꢀreactionsꢀoc‐
curredꢀinꢀ theꢀ catalyticꢀ systemꢀ underꢀtheꢀ conditionsꢀused.ꢀFig.ꢀ
O
2 3
8
(a)ꢀandꢀ(b)ꢀshowꢀtheꢀcatalyticꢀactivitiesꢀofꢀtheꢀobtainedꢀsam‐
plesꢀ andꢀ theꢀ effectꢀ ofꢀ theꢀ SVꢀ onꢀ theꢀ catalyticꢀ activityꢀ ofꢀ
.41(Pd5.1Pt)/meso‐Mn ꢀ inꢀ methaneꢀ combustion,ꢀ respec‐
tively.ꢀ ꢀ
theꢀresultsꢀareꢀsummarizedꢀinꢀTableꢀ3.ꢀFig.ꢀ9ꢀshowsꢀtheꢀspecificꢀ
reactionꢀratesꢀnormalizedꢀperꢀgramꢀofꢀcatalyst,ꢀnobleꢀmetal,ꢀorꢀ
1
O
2 3
Mn
1.41(Pd5.1Pt)/meso‐Mn
nobleꢀ metalꢀ andꢀ theꢀ highestꢀ specificꢀ reactionꢀ ratesꢀ (6.39ꢀ
mol/(gs)ꢀforꢀcatalystꢀandꢀ6.48ꢀmmol/(gs)ꢀforꢀMn )ꢀatꢀ400ꢀ
ꢀandꢀspecificꢀ
2 3
O
.ꢀ Fig.ꢀ 9ꢀ andꢀ theꢀ dataꢀ inꢀ Tableꢀ 3ꢀ showsꢀ thatꢀ
–1
2
O ꢀhadꢀtheꢀhighestꢀTOFꢀ(1.02ꢀms )ꢀforꢀ
3
Fig.ꢀ8(a)ꢀshowsꢀthatꢀtheꢀcatalyticꢀactivityꢀincreasedꢀmonot‐
onouslyꢀ withꢀ increasingꢀ temperature,ꢀ andꢀ loadingꢀ ofꢀ no‐
ble‐metalꢀ NPsꢀ improvedꢀ theꢀ catalyticꢀ activity.ꢀ Atꢀ similarꢀ no‐
ble‐metalꢀNPꢀloadings,ꢀtheꢀcatalyticꢀactivityꢀofꢀtheꢀsampleꢀload‐
edꢀwithꢀPd‐PtꢀalloyꢀNPsꢀwasꢀbetterꢀthanꢀthoseꢀofꢀtheꢀsamplesꢀ
O
2 3
–1
°C;ꢀhowever,ꢀtheꢀhighestꢀTOFꢀ(0.50ꢀms )ꢀforꢀMn
2 3
O
reactionꢀ rateꢀ normalizedꢀ perꢀ gramꢀ ofꢀ nobleꢀ metalꢀ (4.11ꢀ
mmol/(gs))ꢀ atꢀ 400ꢀ °Cꢀ wereꢀ achievedꢀ overꢀ
loadedꢀ withꢀ Pdꢀ onlyꢀ (1.40Pd/meso‐Mn
1.42Pt/meso‐Mn ).ꢀ Theꢀ 0.70(Pd4.9Pt)/meso‐Mn
outperformedꢀ theꢀ 0.70(Pd4.9Pt)/bulk‐Mn ꢀ sample.ꢀ Theꢀ
.41(Pd5.1Pt)/meso‐Mn ꢀsampleꢀgaveꢀtheꢀbestꢀperformance.ꢀ
Theseꢀresultsꢀshowꢀthatꢀtheꢀpresenceꢀofꢀaꢀporousꢀstructureꢀandꢀ
theꢀalloyingꢀofꢀnobleꢀmetalsꢀimprovedꢀtheꢀcatalyticꢀactivity.ꢀItꢀisꢀ
2
O
3
)ꢀ orꢀ Ptꢀ onlyꢀ
0.07(Pd4.9Pt)/meso‐Mn
izedꢀperꢀgramꢀofꢀcatalystꢀorꢀMn
inꢀ aꢀ similarꢀ mannerꢀ toꢀ theꢀ catalyticꢀ activitiesꢀ ofꢀ theꢀ samples.ꢀ
Theꢀonlyꢀdifferenceꢀwasꢀinꢀtheꢀcaseꢀofꢀtheꢀspecificꢀreactionꢀratesꢀ
normalizedꢀ perꢀ gramꢀ ofꢀ nobleꢀ metal,ꢀ inꢀ whichꢀ theꢀ
2
O
3
.ꢀTheꢀspecificꢀreactionꢀratesꢀnormal‐
ꢀ(Fig.ꢀ9(a)ꢀandꢀ(b))ꢀchangedꢀ
(
O
2 3
2 3
O ꢀ sampleꢀ
O
2 3
2
O
3
1
O
2 3
0.07(Pd4.9Pt)/meso‐Mn
2
O
3
ꢀandꢀ0.07(Pd4.9Pt)/bulk‐Mn
2
O ꢀsam‐
3
100
100
(b)
(a)
1
.41(Pd Pt)/meso-Mn O
80
60
40
20
0
(1)
2)
3)
4)
5)
6)
7)
80
60
40
20
0
5.1
2
3
(
(
(
(
(
(
SV (mL/(gh))
2
3
4
0000
0000
0000
200
250
300
350
400o
450
500
550
200
250
300
350
400
450
500
o
Temperature ( C)
Temperature ( C)
Fig.ꢀ8.ꢀ(a)ꢀMethaneꢀconversionꢀasꢀfunctionꢀofꢀreactionꢀtemperatureꢀforꢀ(1)ꢀmeso‐Mn
4)ꢀ1.41(Pd5.1Pt)/meso‐Mn ,ꢀ(5)ꢀ0.07(Pd4.9Pt)/bulk‐Mn ,ꢀ(6)ꢀ1.40Pd/meso‐Mn
effectꢀofꢀSVꢀonꢀmethaneꢀoxidationꢀoverꢀ1.41(Pd5.1Pt)/meso‐Mn .ꢀ
2
O
3
,ꢀ(2)ꢀ0.07(Pd4.9Pt)/meso‐Mn ,ꢀ(3)ꢀ0.72(Pd5.1Pt)/meso‐Mn
2
O
3
2
O ,ꢀ
3
(
O
2 3
O
2 3
2
O
3
,ꢀandꢀ(7)ꢀ1.42Pt/meso‐Mn ꢀatꢀSVꢀ=ꢀ20000ꢀmL/(gh);ꢀandꢀ(b)ꢀ
O
2 3
O
2 3

100ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
Tableꢀ3ꢀ
Catalyticꢀactivities,ꢀTOFꢀvalues,ꢀandꢀspecificꢀreactionꢀratesꢀofꢀsamplesꢀatꢀSVꢀ=ꢀ20000ꢀmL/(gh).ꢀ
Methaneꢀcombustionꢀactivity
ꢀ
ꢀ
ꢀ
Methaneꢀcombustionꢀatꢀ400ꢀ°Cꢀ
T
10%ꢀ
T
50%ꢀ
T
90%ꢀ
TOFNobleꢀmetalꢀ TOFMn2O3ꢀ Specificꢀreactionꢀ Specificꢀreactionꢀ Specificꢀreactionꢀrateꢀ
Sampleꢀ
–
1
(ms–1)
(°C)
ꢀ
(°C)ꢀ
(°C)ꢀ
(ms )ꢀ
ꢀ
rateꢀforꢀcatalystꢀ
rateꢀforꢀMn
2 3
O ꢀ
forꢀnobleꢀmetalꢀ
(mol/(gs))ꢀ
(mol/(gs))ꢀ
(mmol/(gs))ꢀ
meso‐Mn
2
O
3
ꢀ
370ꢀ
320ꢀ
285ꢀ
265ꢀ
280ꢀ
305ꢀ
320ꢀ
455ꢀ
425ꢀ
382ꢀ
345ꢀ
380ꢀ
400ꢀ
455ꢀ
—ꢀ
—ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.23ꢀ
0.45ꢀ
0.75ꢀ
1.02ꢀ
0.80ꢀ
0.62ꢀ
0.40ꢀ
—ꢀ
1.44ꢀ
2.88ꢀ
4.70ꢀ
6.39ꢀ
4.97ꢀ
3.85ꢀ
2.54ꢀ
1.44ꢀ
2.88ꢀ
4.74ꢀ
6.48ꢀ
5.04ꢀ
3.90ꢀ
2.54ꢀ
—ꢀ
0
0
1
1
1
0
ꢀ
.07Pd4.9Pt/meso‐Mn
2
2
2
O
O
O
3
3
3
ꢀ
ꢀ
ꢀ
0.50ꢀ
0.08ꢀ
0.05ꢀ
0.04ꢀ
0.05ꢀ
0.04ꢀ
4.11ꢀ
0.65ꢀ
0.45ꢀ
0.35ꢀ
0.27ꢀ
3.63ꢀ
.72Pd5.1Pt/meso‐Mn
.41Pd5.1Pt/meso‐Mn
485ꢀ
425ꢀ
460ꢀ
495ꢀ
—ꢀ
.40Pd/meso‐Mn
.42Pt/meso‐Mn
2
O
3
ꢀ
2
3
O ꢀ
.07Pd4.9Pt/bulk‐Mn
2
O ꢀ
3
8
8
6
4
2
0
1.8
(
a)
(b)
(c)
1
.5
.2
6
4
2
0
1
0.9
0
.6
.3
0
0.0
2
00 250 300 350 400 450 500 550
200 250 300 350 400 450 500 550
200 250 300 350 400 450 500 550
o
o
o
Temperature ( C)
Temperature ( C)
Temperature ( C)
Fig.ꢀ9.ꢀSpecificꢀreactionꢀratesꢀnormalizedꢀperꢀgramꢀofꢀ(a)ꢀcatalyst,ꢀ(b)ꢀMn
2
O
3
,ꢀandꢀ(c)ꢀnobleꢀmetalꢀasꢀaꢀfunctionꢀofꢀtemperatureꢀforꢀ(◆)ꢀmeso‐Mn
2 3
O ,ꢀ(■)
0
.07(Pd4.9Pt)/meso‐Mn
2
O
3
,ꢀ(●)ꢀ0.72(Pd5.1Pt)/meso‐Mn
2
O
3
,ꢀ(▲)ꢀ1.41(Pd5.1Pt)/meso‐Mn ,ꢀ(ꢁ)ꢀ1.40Pd/meso‐Mn ,ꢀ(◇)ꢀ1.42Pt/meso‐Mn ,ꢀandꢀ(□)
2
O
3
2
O
3
2
O
3
0
.07Pd4.9Pt/bulk‐Mn O .ꢀ
2
3
plesꢀshowedꢀhigherꢀspecificꢀreactionꢀratesꢀnormalizedꢀperꢀgramꢀ
ofꢀnobleꢀmetalꢀaboveꢀ300ꢀ°Cꢀ(Fig.ꢀ9(c)),ꢀpossiblyꢀbecauseꢀofꢀtheꢀ
lowꢀloadingsꢀofꢀnoble‐metalꢀNPs.ꢀTheseꢀresultsꢀalsoꢀsuggestꢀthatꢀ
otherꢀ factorsꢀ (e.g.,ꢀ adsorbedꢀ oxygenꢀ speciesꢀ concentration,ꢀ
low‐temperatureꢀreducibility,ꢀandꢀnobleꢀmetal‐supportꢀinterac‐
tions)ꢀ affectedꢀ theꢀ catalyticꢀ performancesꢀ ofꢀ theꢀ supportedꢀ
samples.ꢀ
theꢀactivityꢀcomparedꢀwithꢀthatꢀofꢀfullyꢀoxidizedꢀPdOꢀparticles.ꢀ
AꢀgoodꢀcontactꢀsurfaceꢀbetweenꢀPdꢀandꢀPdOꢀparticlesꢀisꢀthere‐
foreꢀimportant.ꢀInꢀtheꢀcaseꢀofꢀsupportedꢀbimetallicꢀPd‐Ptꢀcata‐
lysts,ꢀ theꢀ metallicꢀ phaseꢀ isꢀ retained,ꢀ evenꢀ inꢀ anꢀ oxidizingꢀ at‐
mosphere,ꢀbecauseꢀofꢀPd‐Ptꢀalloyꢀformation.ꢀTheꢀcatalyticꢀactiv‐
ityꢀofꢀ1.41(Pd5.1Pt)/meso‐Mn
O3ꢀmightꢀthereforeꢀbeꢀbetterꢀthanꢀ
2
thatꢀ ofꢀ aꢀ monometallicꢀ Pdꢀ catalyst,ꢀ despiteꢀ theꢀ slightlyꢀ lowerꢀ
surfaceꢀ PdOꢀ content.ꢀ Anotherꢀ possibleꢀ reasonꢀ forꢀ theꢀ higherꢀ
activityꢀofꢀtheꢀsupportedꢀ Pd‐Ptꢀalloyꢀcatalystꢀisꢀeasierꢀoxygenꢀ
adsorptionꢀandꢀactivationꢀthanꢀonꢀtheꢀPdOꢀphase.ꢀ
Fig.ꢀ10ꢀshowsꢀtheꢀmethaneꢀconsumptionꢀratesꢀandꢀTOFMn2O3
valuesꢀ ofꢀ theꢀ samplesꢀ atꢀ 300ꢀ andꢀ 400ꢀ °Cꢀ asꢀ aꢀ functionꢀ ofꢀ theꢀ
ads/Olattꢀmolarꢀratio.ꢀEitherꢀtheꢀmethaneꢀconsumptionꢀrateꢀorꢀ
ꢀ
O
theꢀ TOFMn2O3ꢀ increasedꢀ withꢀ increasingꢀ Oadsꢀ concentration,ꢀ
showingꢀthatꢀaꢀhigherꢀOadsꢀconcentrationꢀenhancedꢀtheꢀcatalyticꢀ
performanceꢀ[44].ꢀ ꢀ
Inꢀrecentꢀyears,ꢀaꢀnumberꢀofꢀstudiesꢀofꢀmethaneꢀcombustionꢀ
overꢀMn‐basedꢀandꢀsupportedꢀnoble‐metalꢀcatalystsꢀhaveꢀbeenꢀ
reportedꢀinꢀtheꢀliterature;ꢀtheꢀresultsꢀareꢀshownꢀinꢀTableꢀ4.ꢀ ꢀ
Hutchingsꢀ andꢀ coworkersꢀ [45]ꢀ pointedꢀ outꢀ thatꢀ theꢀ Auꢀ inꢀ
supportedꢀ Au‐Pdꢀ alloyꢀ catalystsꢀ canꢀ actꢀ asꢀ anꢀ electronicꢀ pro‐
moterꢀforꢀPd.ꢀItꢀhasꢀalsoꢀbeenꢀreportedꢀthatꢀtheꢀperformancesꢀ
Clearly,ꢀ
1.41(Pd5.1Pt)/meso‐Mn
La0.7Ag0.3MnO ꢀ [49],ꢀ La0.7Sr0.3MnO
1.0ꢀwt%ꢀPd/Al ꢀ[50],ꢀ1.0ꢀwt%ꢀPd/ZrO
LaMnPdꢀ [51],ꢀ 2ꢀ mol%ꢀ Rhꢀ inꢀ LaMnRhꢀ [51],ꢀ andꢀ 1.1ꢀ wt%ꢀ
ꢀ [52].ꢀ Theꢀ specificꢀ activityꢀ overꢀ
ꢀ wasꢀ muchꢀ higherꢀ thanꢀ thoseꢀ overꢀ
ꢀ[49],ꢀLa0.7Sr0.3MnO ꢀ[49],ꢀLa0.7Ce0.3MnO ꢀ[49],ꢀ1ꢀ
mol%ꢀPdꢀinꢀLaMnPdꢀ[51],ꢀandꢀ2ꢀmol%ꢀRhꢀinꢀLaMnRhꢀ[51],ꢀandꢀ
closeꢀtoꢀthoseꢀoverꢀ1.1ꢀwt%ꢀPt/3DOMꢀCe0.6Zr0.3 ꢀ[52],ꢀbutꢀ
lowerꢀ thanꢀ thoseꢀ overꢀ 1.0ꢀ wt%ꢀ Pd/Al ꢀ [50]ꢀ andꢀ 1.0ꢀ wt%ꢀ
Pd/ZrO ꢀ[50].ꢀ ꢀ
theꢀ
T
50%
ꢀ
andꢀ
ꢀ wereꢀ muchꢀ lowerꢀ thanꢀ thoseꢀ overꢀ
ꢀ [49],ꢀ La0.7Ce0.3MnO ꢀ [49],ꢀ
ꢀ[50],ꢀ1ꢀmol%ꢀPdꢀinꢀ
T
90%
ꢀ
valuesꢀ
overꢀ
2 3
O
3
3
3
ofꢀ bimetallicꢀ Au‐Pd/CeO
betterꢀthanꢀthoseꢀofꢀsingle‐metalꢀAu/CeO
becauseꢀ ofꢀ aꢀ mutualꢀ promotionalꢀ effectꢀ [46].ꢀ Inꢀ theꢀ presentꢀ
work,ꢀ 1.41(Pd5.1Pt)/meso‐Mn ꢀ performedꢀ betterꢀ thanꢀ
.40Pd/meso‐Mn ꢀorꢀ1.42Pt/meso‐Mn ,ꢀ possiblyꢀbecauseꢀ
2
ꢀ catalystsꢀ inꢀ tolueneꢀ oxidationꢀ areꢀ
O
2 3
2
2
ꢀorꢀPd/CeO ꢀcatalystsꢀ
2
Pt/3DOMꢀ Ce0.6Zr0.3
1.41(Pd5.1Pt)/meso‐Mn
La0.7Ag0.3MnO
Y
O
0.1 2
O
2 3
2 3
O
1
O
2 3
O
2 3
3
3
3
ofꢀPd‐Ptꢀinteractions.ꢀPdOꢀisꢀusuallyꢀconsideredꢀtoꢀbeꢀanꢀactivi‐
ty‐controllingꢀ factorꢀ inꢀ catalyzingꢀ hydrocarbonꢀ oxidation.ꢀ Ac‐
cordingꢀ toꢀ theꢀ literatureꢀ [47,48],ꢀ however,ꢀ aꢀ smallꢀ amountꢀ ofꢀ
metallicꢀPdꢀonꢀtheꢀPdOꢀparticlesꢀinꢀpureꢀPdꢀcatalystsꢀenhancesꢀ
Y O
0.1 2
O
2 3
2

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
101ꢀ
8
6
4
2
1.3
(b)
(a)
1.1
0.9
0.7
0.5
o
o
T = 400 C
T = 400 C
o
o
0.3
T = 300 C
T = 300 C
0.1
-
0
-0.1
0
.4
0.5
0.6
O /O molar ratio
0.7
0.8
0.4
0.5
0.6
0.7
0.8
O /O molar ratio
ads
latt
ads
latt
Fig.ꢀ10.ꢀ(a)ꢀMethaneꢀconsumptionꢀratesꢀandꢀ(b)ꢀTOFMn2O3ꢀvaluesꢀatꢀvariousꢀtemperaturesꢀasꢀfunctionꢀofꢀOads/Olattꢀmolarꢀratiosꢀofꢀsamples.ꢀ
Tableꢀ4ꢀ
Comparisonꢀofꢀmethaneꢀoxidationꢀactivitiesꢀofꢀsamplesꢀwithꢀthoseꢀreportedꢀinꢀtheꢀliterature.ꢀ
T
50%
ꢀ
T
90%
ꢀ SpecificꢀactivityꢀatꢀT50%ꢀ SpecificꢀactivityꢀatꢀT90%
Catalystꢀ
.41Pd5.1Pt/meso‐Mn
Reactionꢀconditionꢀ
2.5%ꢀCH ,ꢀSVꢀ=ꢀ20000ꢀmL/(gh)ꢀ
Ref.ꢀ
(°C)ꢀ
(°C)ꢀ
425ꢀ
750ꢀ
780ꢀ
810ꢀ
710ꢀ
650ꢀ
475ꢀ
515ꢀ
598ꢀ
(mol/(gmin))ꢀ
(mol/(gmin))
4.10ꢀꢀ10–4ꢀ
2.66ꢀꢀ10–5ꢀ
2.57ꢀꢀ10–5ꢀ
2.52ꢀꢀ10–5ꢀ
4.72ꢀꢀ10–4ꢀ
5.15ꢀꢀ10–4ꢀ
1.85ꢀꢀ10–5ꢀ
1.79ꢀꢀ10–5ꢀ
4.33ꢀꢀ10–4ꢀ
ꢀ
–
4
1
2 3
O ꢀ
4
345ꢀ
690ꢀ
720ꢀ
740ꢀ
640ꢀ
600ꢀ
425ꢀ
445ꢀ
479ꢀ
2.28ꢀꢀ10 ꢀ
Thisꢀwork
[49]ꢀ
[49]ꢀ
–
5
La0.7Ag0.3MnO
3
ꢀ
1%ꢀCH
1%ꢀCH
1%ꢀCH
5%ꢀCH
5%ꢀCH
4
,ꢀSVꢀ=ꢀ10000ꢀmL/(gh)ꢀ
,ꢀSVꢀ=ꢀ10000ꢀmL/(gh)ꢀ
,ꢀSVꢀ=ꢀ10000ꢀmL/(gh)ꢀ
,ꢀSVꢀ=ꢀ30000ꢀmL/(gh)ꢀ
,ꢀSVꢀ=ꢀ30000ꢀmL/(gh)ꢀ
1.81ꢀꢀ10 ꢀ
–
5
La0.7Sr0.3MnO
3
ꢀ
4
1.69ꢀꢀ10 ꢀ
–
5
La0.7Ce0.3MnO
3
ꢀ
4
1.68ꢀꢀ10 ꢀ
[49]ꢀ
–
4
1
1
1
2
1
.0ꢀwt%ꢀPd/Al
.0ꢀwt%ꢀPd/ZrO
ꢀmol%ꢀPd,ꢀLaMnPdꢀ
ꢀmol%ꢀRh,ꢀLaMnRhꢀ
2
O
3
ꢀ
4
3.57ꢀꢀ10 ꢀ
[50]ꢀ
[50]ꢀ
[51]ꢀ
[51]ꢀ
–
4
2
ꢀ
4
3.88ꢀꢀ10 ꢀ
–5
1%ꢀCH
4
,ꢀSVꢀ=ꢀ5000ꢀmL/(gh)ꢀ
,ꢀSVꢀ=ꢀ5000ꢀmL/(gh)ꢀ
1.21ꢀꢀ10 ꢀ
–5
1%ꢀCH
4
1.17ꢀꢀ10 ꢀ
–4
.1ꢀwt%ꢀPt/3DOMꢀCe0.6Zr0.3
0.1 2
Y O ꢀ
4
2%ꢀCH ,ꢀSVꢀ=ꢀ30000ꢀmL/(gh)ꢀ
2.41ꢀꢀ10 ꢀ
[52]ꢀ
MethaneꢀoxidationꢀoverꢀtheꢀPd‐basedꢀcatalystsꢀcanꢀproceedꢀ
alyticallyꢀstableꢀunderꢀtheꢀreactionꢀconditionsꢀused.ꢀ ꢀ
viaꢀ theꢀ Mars‐vanꢀ Krevelenꢀ mechanism,ꢀ inꢀ whichꢀ theꢀ reactionꢀ
takesꢀplaceꢀviaꢀaꢀredoxꢀcycleꢀofꢀtheꢀcatalystꢀ[19,53,54].ꢀAtꢀlowꢀ
temperatures,ꢀmethaneꢀcanꢀreactꢀwithꢀchemisorbedꢀoxygenꢀtoꢀ
3.5.ꢀ ꢀ EffectsꢀofꢀSO
activityꢀ
2
,ꢀCO
2
,ꢀH O,ꢀandꢀNOꢀadditionꢀonꢀcatalyticꢀ ꢀ
2
yieldꢀCO
oxygensꢀinꢀoxidizedꢀnobleꢀmetalsꢀareꢀinvolvedꢀinꢀmethaneꢀoxi‐
dation,ꢀresultingꢀinꢀcatalystꢀreduction.ꢀTheꢀgas‐phaseꢀO ꢀmole‐
culesꢀcanꢀbeꢀactivatedꢀatꢀtheꢀoxygenꢀvacanciesꢀofꢀMn ꢀorꢀnearꢀ
theꢀinterfaceꢀbetweenꢀoxidizedꢀPdꢀand/orꢀPtꢀandꢀMn ꢀtoꢀgiveꢀ
activeꢀoxygenꢀspecies,ꢀreplenishingꢀtheꢀ latticeꢀ oxygensꢀofꢀoxi‐
dizedꢀ Pdꢀ and/orꢀ Ptꢀ consumedꢀ inꢀ methaneꢀ oxidationꢀ andꢀ
re‐oxidizingꢀ theꢀ reducedꢀ catalyst.ꢀ Inꢀ theꢀ caseꢀ ofꢀ theꢀ
2
ꢀandꢀH
2
O;ꢀhowever,ꢀatꢀhigherꢀtemperatures,ꢀtheꢀlatticeꢀ
TheꢀeffectsꢀofꢀSO
activityꢀwereꢀinvestigatedꢀbyꢀperformingꢀmethaneꢀcombustionꢀ
overꢀ 1.41(Pd5.1Pt)/meso‐Mn ꢀ inꢀ theꢀ presenceꢀ ofꢀ 100ꢀ ppmꢀ
SO ,ꢀ5.0ꢀvol%ꢀCO ,ꢀ3.0ꢀvol%ꢀH O,ꢀorꢀ1.0ꢀvol%ꢀNO;ꢀtheꢀresultsꢀareꢀ
shownꢀinꢀFig.ꢀ12(a).ꢀ
Itꢀ isꢀ clearꢀ thatꢀ theꢀ catalyticꢀ activitiesꢀ ofꢀ
1.41(Pd5.1Pt)/meso‐Mn ꢀinꢀtheꢀpresenceꢀandꢀabsenceꢀofꢀ100ꢀ
ꢀ wereꢀ similar,ꢀ i.e.,ꢀ thisꢀ catalystꢀ wasꢀ
2
,ꢀCO
2
,ꢀwaterꢀvapor,ꢀandꢀNOꢀonꢀtheꢀcatalyticꢀ
2
O
2 3
O
2 3
O
2 3
2
2
2
O
2 3
2 3
Mn O ‐supportedꢀ Pd‐Ptꢀ alloyꢀ catalysts,ꢀ theꢀ metallicꢀ phaseꢀ isꢀ
ppmꢀ SO
2
ꢀ orꢀ 5.0ꢀ vol%ꢀ CO
2
maintained,ꢀ evenꢀ inꢀ anꢀ oxidizingꢀ atmosphere,ꢀ becauseꢀ ofꢀ for‐
mationꢀ ofꢀ aꢀ Pd‐Ptꢀ alloy,ꢀ resultingꢀ inꢀ betterꢀ activityꢀ comparedꢀ
100
withꢀthoseꢀofꢀtheꢀMn
2
O ‐supportedꢀPdꢀorꢀPtꢀcatalyst.ꢀAlloyingꢀofꢀ
3
PdꢀwithꢀPtꢀsignificantlyꢀpromotesꢀtheꢀadsorptionꢀandꢀactivationꢀ
ofꢀoxygen,ꢀpossiblyꢀenhancingꢀtheꢀmigrationꢀofꢀactivatedꢀoxy‐
80
60
2 3
genꢀ toꢀ theꢀ noble‐metalꢀ alloy‐Mn O ꢀ interface.ꢀ Theꢀ excellentꢀ
2 3
catalyticꢀ activityꢀ ofꢀ 1.41(Pd5.1Pt)/meso‐Mn O ꢀ couldꢀ resultꢀ
fromꢀ itsꢀ enhancedꢀ oxygenꢀ activationꢀ abilityꢀ andꢀ betterꢀ
low‐temperatureꢀreducibility.ꢀ
Theꢀ catalyticꢀ stabilityꢀ wasꢀ examinedꢀ byꢀ performingꢀ
on‐streamꢀ
methaneꢀ
combustionꢀ
overꢀ
4
0
0
4
8
12
16
20
24
1.41(Pd5.1Pt)/meso‐Mn
2 3
O
ꢀatꢀ425ꢀ°CꢀandꢀSVꢀ=ꢀ20000ꢀmL/(gh)ꢀ
On-stream reaction time (h)
forꢀ25ꢀh;ꢀtheꢀresultsꢀareꢀshownꢀinꢀFig.ꢀ11.ꢀNoꢀsignificantꢀlossꢀinꢀ
catalyticꢀactivityꢀwasꢀobservedꢀwithinꢀ25ꢀhꢀofꢀon‐streamꢀreac‐
tion.ꢀTheꢀ1.41(Pd5.1Pt)/meso‐Mn
Fig.ꢀ11.ꢀMethaneꢀconversionꢀversusꢀon‐streamꢀmethaneꢀoxidationꢀtimeꢀ
overꢀ1.41(Pd5.1Pt)/meso‐Mn ꢀatꢀSVꢀ=ꢀ20000ꢀmL/(gh)ꢀandꢀatꢀ425ꢀ°C.
O
2 3
ꢀsampleꢀwasꢀthereforeꢀcat‐
2
O
3

102ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
1
00
(
a)
(
b)
SO
2
-, CO
00 ppm SO
.0 vol% CO
.0 vol% H
.0 vol% NO
2
-, H
2
O-, and NO-free
(1)
1
5
3
1
2
2
8
6
4
2
0
0
0
0
0
2
O
(2)
(3)
(4)
(5)
2 3
1.41(Pd5.1Pt)/meso-Mn O
2
00
260
320
380
o
440
500
4000
3400
2800
2200
1600
1000
400
1
Temperature ( C)
Wavenumber (cm )
Fig.ꢀ12.ꢀ(a)ꢀEffectsꢀofꢀ100ꢀppmꢀSO ,ꢀ5.0ꢀvol%ꢀCO ,ꢀ3.0ꢀvol%ꢀH
2
2
2
O,ꢀandꢀ1.0ꢀvol%ꢀNOꢀonꢀmethaneꢀconversionꢀatꢀSVꢀ=ꢀ20000ꢀmL/(gh);ꢀandꢀ(b)ꢀFT‐IRꢀspec‐
traꢀofꢀ1.41(Pd5.1Pt)/meso‐Mn ꢀ(1)ꢀafterꢀactivationꢀinꢀO ꢀflowꢀ(16.6ꢀmL/min)ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀhꢀandꢀafterꢀmethaneꢀcombustionꢀinꢀpresenceꢀofꢀ(2)ꢀ100ꢀ
ppmꢀSO ,ꢀ(3)ꢀ5.0ꢀvol%ꢀCO ,ꢀ(4)ꢀ3.0ꢀvol%ꢀH O,ꢀorꢀ(5)ꢀ1.0ꢀvol%ꢀNO.ꢀ
O
2 3
2
2
2
2
stronglyꢀresistantꢀtoꢀSO
causeꢀtheꢀintroductionꢀofꢀaꢀsmallꢀamountꢀofꢀPtꢀpreventsꢀblock‐
ingꢀofꢀtheꢀactiveꢀsitesꢀbyꢀadsorptionꢀofꢀsulfurꢀorꢀcarbonꢀoxides.ꢀ
2
ꢀorꢀCO
2
ꢀpoisoning.ꢀThisꢀisꢀpossiblyꢀbe‐
andꢀstretchingꢀandꢀbendingꢀvibrationsꢀofꢀMn–Oꢀbonds,ꢀrespec‐
tively.ꢀ Theꢀ absorptionꢀ bandsꢀ atꢀ 1125ꢀ andꢀ 1146ꢀ cm ꢀ [Fig.ꢀ
–1
12(b)(1)]ꢀcanꢀbeꢀassignedꢀtoꢀoxygenꢀspeciesꢀ(e.g.,ꢀO
[18,62].ꢀTheꢀabsorptionꢀbandꢀatꢀ1042ꢀcm ꢀindicatesꢀformationꢀ
2
–ꢀandꢀO 2–)ꢀ
2
0
–1
Corroꢀ etꢀ al.ꢀ [55]ꢀ reportedꢀ thatꢀ theꢀ presenceꢀ ofꢀ Pt ꢀ mightꢀ beꢀ
necessaryꢀtoꢀpreventꢀinteractionsꢀbetweenꢀSO
species.ꢀInꢀtheꢀcaseꢀofꢀ3.0ꢀvol%ꢀwaterꢀvaporꢀaddition,ꢀmethaneꢀ
conversionꢀ overꢀ 1.41(Pd5.1Pt)/meso‐Mn ꢀ decreasedꢀ byꢀ ca.ꢀ
0%,ꢀasꢀaꢀresultꢀofꢀformationꢀofꢀhydroxylꢀgroupsꢀonꢀtheꢀsupportꢀ
surface,ꢀwhichꢀhinderedꢀoxygenꢀexchangeꢀbetweenꢀtheꢀsupportꢀ
andꢀactiveꢀsitesꢀ[56].ꢀItꢀhasꢀbeenꢀreportedꢀthatꢀT50%ꢀincreasedꢀ
2
ꢀandꢀPdꢀsurfaceꢀ
ofꢀSO
3
2–ꢀorꢀSO 2–ꢀspeciesꢀ[19].ꢀNoꢀcorrespondingꢀcarbonateꢀorꢀ
4

OH ꢀ groupsꢀ wereꢀ detectedꢀ (Fig.ꢀ 12(b)(2)ꢀ andꢀ (3)),ꢀ possiblyꢀ
becauseꢀofꢀdecompositionꢀofꢀcarbonateꢀorꢀOH ꢀspeciesꢀatꢀhighꢀ
–
O
2 3
–1
1
temperatures.ꢀTheꢀstrongꢀabsorptionꢀbandꢀatꢀ1140ꢀcm ꢀforꢀtheꢀ
sampleꢀafterꢀmethaneꢀcombustionꢀinꢀtheꢀpresenceꢀofꢀ1.0ꢀvol%ꢀ
NOꢀ canꢀ beꢀ assignedꢀ toꢀ NOꢀ adsorptionꢀ onꢀ theꢀ supportꢀ orꢀ no‐
ble‐metalꢀNPsꢀ[63];ꢀthisꢀdecreasedꢀtheꢀcatalyticꢀactivityꢀofꢀtheꢀ
sampleꢀ[59].ꢀ ꢀ
Fig.ꢀ13ꢀshowsꢀTEMꢀimagesꢀofꢀ1.41(Pd5.1Pt)/meso‐Mn
terꢀactivationꢀinꢀO ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀh,ꢀafterꢀmethaneꢀcombustionꢀ
inꢀtheꢀpresenceꢀofꢀ100ꢀppmꢀSO ,ꢀ5.0ꢀvol%ꢀCO ,ꢀ3.0ꢀvol%ꢀCO ,ꢀorꢀ
byꢀca.ꢀ100ꢀ°CꢀoverꢀPd/Al
vaporꢀ[12],ꢀbyꢀca.ꢀ35ꢀ°CꢀoverꢀPdO/Al
vol%ꢀ waterꢀ vaporꢀ [57],ꢀ andꢀ byꢀ ca.ꢀ 120ꢀ °Cꢀ overꢀ Pd/ZrO
Pd/Zr‐CeO ,ꢀandꢀPd/La‐CeO ꢀinꢀtheꢀpresenceꢀofꢀ18.0ꢀvol%ꢀwa‐
2 3
O
ꢀinꢀtheꢀpresenceꢀofꢀ10.0ꢀvol%ꢀwaterꢀ
ꢀinꢀtheꢀpresenceꢀofꢀ3.0ꢀ
,ꢀ
O
2 3
2
2 3
O ꢀaf‐
2
2
2
terꢀvaporꢀ[58].ꢀTheꢀintroductionꢀofꢀPtꢀthereforeꢀincreasedꢀtheꢀ
resistanceꢀofꢀtheꢀPd‐basedꢀcatalystsꢀtoꢀwaterꢀvaporꢀpoisoning.ꢀ
Anꢀ activityꢀ dropꢀ (ca.ꢀ 30%)ꢀ wasꢀ observedꢀ overꢀ
2
2
2
1.0ꢀvol%ꢀNO,ꢀandꢀafterꢀ25ꢀhꢀofꢀon‐streamꢀreaction.ꢀTheꢀimagesꢀ
clearlyꢀshowꢀthatꢀallꢀtheꢀsamplesꢀmaintainedꢀtheirꢀhigh‐qualityꢀ
mesoporousꢀstructureꢀandꢀtheꢀPd‐PtꢀalloyꢀNPsꢀwereꢀwellꢀdis‐
1
.41(Pd5.1Pt)/meso‐Mn
2
O ꢀinꢀtheꢀpresenceꢀofꢀ1.0ꢀvol%ꢀNO.ꢀTheꢀ
3
introductionꢀ ofꢀ NOꢀ intoꢀ theꢀ reactionꢀ systemꢀ couldꢀ interfereꢀ
withꢀmethaneꢀcombustionꢀbecauseꢀofꢀselectiveꢀcatalyticꢀreduc‐
tionꢀ ofꢀ NOꢀ withꢀ methane,ꢀ whichꢀ couldꢀ occurꢀ simultaneouslyꢀ
withꢀmethaneꢀcombustionꢀ[59]:ꢀ ꢀ
tributedꢀonꢀtheꢀsurfaceꢀofꢀtheꢀmeso‐Mn
theꢀimagesꢀinꢀFig.ꢀ2(g)ꢀandꢀ(h)).ꢀ ꢀ
2
O ꢀsupportꢀ(similarꢀtoꢀ
3
4.ꢀ ꢀ Conclusionsꢀ
CH
4
ꢀ+ꢀ2NOꢀ+ꢀO
CH ꢀ+ꢀ2O
WeꢀusedꢀFT‐IRꢀspectroscopyꢀtoꢀelucidateꢀtheꢀsurfaceꢀspeciesꢀ
inꢀ1.41Pd5.1Pt/meso‐Mn ꢀafterꢀactivationꢀinꢀanꢀO ꢀflowꢀ(16.6ꢀ
mL/min)ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀhꢀandꢀafterꢀmethaneꢀcombustionꢀinꢀtheꢀ
presenceꢀofꢀ100ꢀppmꢀSO ,ꢀ5.0ꢀvol%ꢀCO ,ꢀ3.0ꢀvol%ꢀH O,ꢀandꢀ1.0ꢀ
2
ꢀ→ꢀCO
2
ꢀ+ꢀ2H
2
Oꢀ+ꢀN
Oꢀ
2
ꢀ
4
2
ꢀ→ꢀCO
2
ꢀ+ꢀ2H
2
Weꢀpreparedꢀmeso‐Mn
2
O
3
ꢀandꢀx(Pd
y
Pt)/meso‐Mn
2
O ꢀnano‐
3
catalystsꢀusingꢀKIT‐6‐templatingꢀandꢀPVA‐protectedꢀreductionꢀ
2
O
3
2
methods,ꢀrespectively.ꢀTheꢀporousꢀsamplesꢀhadꢀsurfaceꢀareasꢀofꢀ
2
77106ꢀm /gꢀandꢀnoble‐metalꢀNPsꢀofꢀsizeꢀ23ꢀnm,ꢀandꢀwereꢀ
2
2
2
highlyꢀ dispersedꢀ onꢀ theꢀ surfacesꢀ ofꢀ theꢀ cubicꢀ crystallineꢀ me‐
vol%ꢀNO;ꢀtheꢀspectraꢀareꢀshownꢀinꢀFig.ꢀ12(b).ꢀAccordingꢀtoꢀtheꢀ
literatureꢀ[18,60,61],ꢀtheꢀabsorptionꢀbandsꢀatꢀ3400,ꢀ2360ꢀandꢀ
so‐Mn
performanceꢀ
1.41(Pd5.1Pt)/meso‐Mn
265ꢀ °C,ꢀ T50%ꢀ =ꢀ 345ꢀ °C,ꢀ andꢀ T90%ꢀ =ꢀ 425ꢀ °Cꢀ atꢀ SVꢀ =ꢀ 20000ꢀ
mL/(gh)).ꢀIntroductionꢀofꢀaꢀsmallꢀamountꢀofꢀPtꢀincreasedꢀre‐
2
O
3
ꢀsupport.ꢀAlloyingꢀPdꢀwithꢀPtꢀenhancedꢀtheꢀcatalyticꢀ
inꢀ methaneꢀ combustion;ꢀ
ꢀshowedꢀtheꢀhighestꢀactivityꢀ(T10%ꢀ=ꢀ
–1
2
340,ꢀ1625,ꢀ1410,ꢀandꢀ930ꢀcm ꢀcanꢀbeꢀascribedꢀtoꢀtheꢀstretch‐
O
2 3
–
ingꢀvibrationsꢀofꢀOH ,ꢀatmosphericꢀ CO
2
,ꢀ bendingꢀvibrationsꢀofꢀ
adsorbedꢀwaterꢀmolecules,ꢀstretchingꢀvibrationsꢀofꢀC–Hꢀbonds,ꢀ

ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
103ꢀ
Fig.ꢀ13.ꢀTEMꢀimagesꢀofꢀ1.41(Pd5.1Pt)/meso‐Mn
presenceꢀofꢀ(c,ꢀd)ꢀ100ꢀppmꢀSO ,ꢀ(e,ꢀf)ꢀ5.0ꢀvol%ꢀCO
ꢀ20000ꢀmL/(gh).ꢀ
2
O
2
3
ꢀ(a,ꢀb)ꢀafterꢀactivationꢀinꢀO
,ꢀ(g,ꢀh)ꢀ3.0ꢀvol%ꢀH O,ꢀorꢀ(i,ꢀj)ꢀ1.0ꢀvol%ꢀNO;ꢀandꢀ(k,ꢀl)ꢀafterꢀ25ꢀhꢀofꢀon‐streamꢀreactionꢀatꢀ425ꢀ°CꢀandꢀSVꢀ
2
ꢀflowꢀ(16.6ꢀmL/min)ꢀatꢀ250ꢀ°Cꢀforꢀ1ꢀh;ꢀafterꢀmethaneꢀcombustionꢀinꢀtheꢀ
2
2
=
sistanceꢀtoꢀSO
2
,ꢀCO
2
,ꢀandꢀwaterꢀvaporꢀpoisoning.ꢀHowever,ꢀNOꢀ
[8] A.ꢀHellman,ꢀA.ꢀResta,ꢀN.ꢀM.ꢀMartin,ꢀJ.ꢀGustafson,ꢀA.ꢀTrinchero,ꢀP.ꢀA.ꢀ
Carlsson,ꢀO.ꢀBalmes,ꢀR.ꢀR.ꢀFelici,ꢀR.ꢀvanꢀRijn,ꢀJ.ꢀW.ꢀM.ꢀFrenken,ꢀJ.ꢀN.ꢀ
Andersen,ꢀE.ꢀLundgren,ꢀH.ꢀGrönbeck,ꢀJ.ꢀPhys.ꢀChem.ꢀLett.,ꢀ2012,ꢀ3,ꢀ
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additionꢀ negativelyꢀ affectedꢀ methaneꢀ combustionꢀ becauseꢀ ofꢀ
selectiveꢀcatalyticꢀreductionꢀofꢀNOꢀwithꢀmethane.ꢀItꢀisꢀconclud‐
edꢀthatꢀaꢀlargeꢀsurfaceꢀarea,ꢀhighꢀadsorbedꢀoxygenꢀspeciesꢀcon‐
centration,ꢀ goodꢀ low‐temperatureꢀ reducibility,ꢀ andꢀ strongꢀ in‐
[9] A.ꢀ Ersson,ꢀ H.ꢀ Kusar,ꢀ R.ꢀ Carroni,ꢀ T.ꢀ Griffin,ꢀ S.ꢀ Järås,ꢀ Catal.ꢀ Today,ꢀ
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teractionsꢀbetweenꢀtheꢀPd‐PtꢀalloyꢀNPsꢀandꢀmeso‐Mn
responsibleꢀ forꢀ theꢀ excellentꢀ catalyticꢀ performanceꢀ ofꢀ
.41(Pd5.1Pt)/meso‐Mn .ꢀ
2
O ꢀwereꢀ
3
[10] K.ꢀ Persson,ꢀ A.ꢀ Ersson,ꢀ K.ꢀ Jansson,ꢀ N.ꢀ Iverlund,ꢀ S.ꢀ Järås,ꢀ J.ꢀ Catal.,ꢀ
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104ꢀ
PengꢀXuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ92–105ꢀ
GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2017,ꢀ38:ꢀ92–105ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(16)62567‐6
CatalyticꢀperformanceꢀenhancementꢀbyꢀalloyingꢀPdꢀwithꢀPtꢀonꢀorderedꢀmesoporousꢀmanganeseꢀoxideꢀforꢀmethaneꢀcombustionꢀ
ꢀ
ꢀ
PengꢀXu,ꢀZhixingꢀWu,ꢀJiguangꢀDeng,ꢀYuxiꢀLiu,ꢀShaohuaꢀXie,ꢀGuangshengꢀGuo*,ꢀHongxingꢀDai*ꢀ ꢀ
BeijingꢀUniversityꢀofꢀTechnologyꢀ
ꢀ
AlloyingꢀPdꢀwithꢀPtꢀenhancedꢀtheꢀcatalyticꢀperformanceꢀinꢀmethaneꢀcombustion.ꢀ1.41(Pd5.1Pt)/meso‐Mn
2
O ꢀshowedꢀtheꢀhighestꢀactivityꢀ
3
becauseꢀofꢀitsꢀlargeꢀsurfaceꢀarea,ꢀhighꢀOadsꢀconcentration,ꢀgoodꢀlow‐temperatureꢀreducibility,ꢀandꢀstrongꢀPd‐PtꢀalloyꢀandꢀMn
2
O ꢀinterac‐
3
tions.ꢀ
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