CO2 hydrogenation to methanol over Cu/Zn/Al/Zr catalysts prepared by liquid reduction

Article abstract of DOI:10.1016/S1872-2067(17)62793-1

Cu/Zn/Al/Zr catalysts containing Cu in three valence states (Cu²⁺, Cu⁺ and Cu⁰) were prepared using a liquid reduction method and subsequently calcined at different temperatures. The effects of the calcination temperature on the catalyst structure, interactions among components, reducibility and dispersion of Cu species, surface properties and exposed Cu surface area were systematically investigated. These materials were also applied to the synthesis of methanol via the hydrogenation of CO₂. The results show that a large exposed Cu surface area promotes catalytic CO₂ conversion and that there is a close correlation between the Cu⁺/Cu⁰ ratio and the selectivity for methanol. A calcination temperature of 573 K was found to produce a Cu/Zn/Al/Zr catalyst exhibiting the maximum activity during the synthesis of methanol.

Full text of DOI:10.1016/S1872-2067(17)62793-1

ChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725
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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
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Article
2
CO ꢀhydrogenationꢀtoꢀmethanolꢀoverꢀCu/Zn/Al/Zrꢀcatalystsꢀ ꢀ
preparedꢀbyꢀliquidꢀreductionꢀ
ꢀa,b
ꢀa,
ꢀa,c
ꢀa,c
ꢀa,c
ꢀa,c
XiaosuꢀDong ,ꢀFengꢀLi *,ꢀNingꢀZhao ,ꢀYishengꢀTan ,ꢀJunweiꢀWang ,ꢀFukuiꢀXiao
ꢀ
aꢀStateꢀKeyꢀLaboratoryꢀofꢀCoalꢀConversion,ꢀInstituteꢀofꢀCoalꢀChemistry,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀTaiyuanꢀ030001,ꢀShanxi,ꢀChinaꢀ
bꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences,ꢀBeijingꢀ100049,ꢀChinaꢀ ꢀ
cꢀNationalꢀEngineeringꢀResearchꢀCenterꢀforꢀCoal‐BasedꢀSynthesis,ꢀInstituteꢀofꢀCoalꢀChemistry,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀTaiyuanꢀ030001,ꢀShanxi,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
2+
+
0
Articleꢀhistory:ꢀ
Cu/Zn/Al/ZrꢀcatalystsꢀcontainingꢀCuꢀinꢀthreeꢀvalenceꢀstatesꢀ(Cu ,ꢀCu ꢀandꢀCu )ꢀwereꢀpreparedꢀusingꢀ
aꢀliquidꢀreductionꢀmethodꢀandꢀsubsequentlyꢀcalcinedꢀatꢀdifferentꢀtemperatures.ꢀTheꢀeffectsꢀofꢀtheꢀ
calcinationꢀtemperatureꢀonꢀtheꢀcatalystꢀstructure,ꢀinteractionsꢀamongꢀcomponents,ꢀreducibilityꢀandꢀ
dispersionꢀofꢀCuꢀspecies,ꢀsurfaceꢀpropertiesꢀandꢀexposedꢀCuꢀsurfaceꢀareaꢀwereꢀsystematicallyꢀinves‐
tigated.ꢀTheseꢀmaterialsꢀwereꢀalsoꢀappliedꢀtoꢀtheꢀsynthesisꢀofꢀmethanolꢀviaꢀtheꢀhydrogenationꢀofꢀ
Receivedꢀ18ꢀDecemberꢀ2016ꢀ
Acceptedꢀ23ꢀJanuaryꢀ2017ꢀ
Publishedꢀ5ꢀAprilꢀ2017ꢀ
CO
2
.ꢀTheꢀresultsꢀshowꢀthatꢀaꢀlargeꢀexposedꢀCuꢀsurfaceꢀareaꢀpromotesꢀcatalyticꢀCO ꢀconversionꢀandꢀ
2
Keywords:ꢀ
+
0
thatꢀthereꢀisꢀaꢀcloseꢀcorrelationꢀbetweenꢀtheꢀCu /Cu ꢀratioꢀandꢀtheꢀselectivityꢀforꢀmethanol.ꢀAꢀcalci‐
nationꢀtemperatureꢀofꢀ573ꢀKꢀwasꢀfoundꢀtoꢀproduceꢀaꢀCu/Zn/Al/Zrꢀcatalystꢀexhibitingꢀtheꢀmaximumꢀ
activityꢀduringꢀtheꢀsynthesisꢀofꢀmethanol.ꢀ
Liquidꢀreductionꢀmethodꢀ
Cu/Zn/Al/Zrꢀcatalystꢀ
Carbonꢀdioxideꢀhydrogenationꢀ
Methanol
©ꢀ2017,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
(1356ꢀ K)ꢀ andꢀ lowꢀ Tammannꢀ temperatureꢀ (678ꢀ K)ꢀ ofꢀ copper,ꢀ
theꢀ aggregationꢀ ofꢀ metallicꢀ copperꢀ particlesꢀ duringꢀ theꢀ highꢀ
temperatureꢀcalcination,ꢀreductionꢀandꢀreactionꢀprocessesꢀhaveꢀ
becomeꢀ significantꢀ challengesꢀ [6,7].ꢀ Metallicꢀ Cuꢀ catalystsꢀ areꢀ
Sinceꢀglobalꢀwarmingꢀcausedꢀbyꢀtheꢀcontinuallyꢀincreasingꢀ
CO
survival,ꢀnewꢀtechnologiesꢀbasedꢀonꢀCO
haveꢀrecentlyꢀreceivedꢀmuchꢀattention.ꢀTheꢀconversionꢀofꢀCO
toꢀusefulꢀchemicalsꢀandꢀfuelsꢀmayꢀbeꢀoneꢀofꢀtheꢀmostꢀpromisingꢀ
approachesꢀtoꢀmitigatingꢀthisꢀproblemꢀ[1].ꢀMethanol,ꢀdueꢀtoꢀitsꢀ
importanceꢀinꢀchemicalꢀindustriesꢀandꢀitsꢀpotentialꢀasꢀanꢀenvi‐
ronmentallyꢀfriendlyꢀenergyꢀcarrier,ꢀhasꢀbecomeꢀtheꢀpreferredꢀ
conversionꢀproductꢀ[2,3].ꢀTherefore,ꢀCO ꢀcatalyticꢀconversionꢀtoꢀ
methanolꢀisꢀaꢀkeyꢀresearchꢀtopic,ꢀalongꢀwithꢀtheꢀoptimizationꢀofꢀ
catalystsꢀforꢀthisꢀpurpose.ꢀ ꢀ
2
ꢀ concentrationꢀ inꢀ theꢀ atmosphereꢀ isꢀ threateningꢀ humanꢀ
2
ꢀcaptureꢀandꢀutilizationꢀ
typicallyꢀpreparedꢀbyꢀreducingꢀCuOꢀwithꢀH ꢀ[8],ꢀalthoughꢀthisꢀ
2
2
ꢀ
involvesꢀaꢀhighlyꢀexothermicꢀreactionꢀandꢀthusꢀthereꢀisꢀtheꢀpo‐
tentialꢀ forꢀ aꢀrunawayꢀreaction.ꢀInꢀaddition,ꢀtheꢀhighꢀtempera‐
turesꢀappliedꢀduringꢀthisꢀprocessꢀ(473ꢀtoꢀ623ꢀK)ꢀcanꢀaccelerateꢀ
theꢀagglomerationꢀofꢀCuꢀspeciesꢀandꢀthusꢀdecreaseꢀtheꢀefficien‐
cyꢀofꢀtheꢀactiveꢀcatalyticꢀsitesꢀ[9].ꢀThereꢀhasꢀrecentlyꢀbeenꢀin‐
terestꢀinꢀapplyingꢀaꢀliquidꢀreductionꢀmethodꢀtoꢀtheꢀpreparationꢀ
ofꢀCu‐basedꢀcatalysts,ꢀbecauseꢀthisꢀmethodꢀisꢀrapidꢀandꢀreadilyꢀ
controlledꢀinꢀcomparisonꢀtoꢀconventionalꢀgasꢀphaseꢀreductionꢀ
2
Cu‐basedꢀcatalystsꢀobtainedꢀfromꢀconventionalꢀco‐
tionꢀ methodsꢀ areꢀ widelyꢀ usedꢀ forꢀ theꢀ synthesisꢀ ofꢀ methanolꢀ
fromꢀCO /H ꢀ[4,5].ꢀHowever,ꢀbecauseꢀofꢀtheꢀlowꢀmeltingꢀpointꢀ
ꢀ
precipita‐
withꢀH
2
ꢀ[10−12].ꢀLiquidꢀreductionꢀwithꢀNaBH ꢀisꢀnormallyꢀcar‐
4
riedꢀoutꢀatꢀlowꢀtemperature,ꢀthusꢀreducingꢀtheꢀagglomerationꢀ
ofꢀ Cuꢀ speciesꢀ andꢀ producingꢀ catalystsꢀ withꢀ smallerꢀ metallicꢀ
2
2
*ꢀCorrespondingꢀauthor.ꢀTel/Fax:ꢀ+86‐351‐4041153;ꢀE‐mail:ꢀlifeng2729@sxicc.ac.cnꢀ
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀKeyꢀScienceꢀandꢀTechnologyꢀProgramꢀofꢀShanxiꢀProvince,ꢀChinaꢀ(MD2014‐10),ꢀtheꢀNationalꢀKeyꢀTechnologyꢀRe‐
searchꢀandꢀDevelopmentꢀProgramꢀ(2013BAC11B00),ꢀandꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21343012).ꢀ
DOI:ꢀ10.1016/S1872‐2067(17)62793‐1ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ38,ꢀNo.ꢀ4,ꢀAprilꢀ2017ꢀ ꢀ ꢀ

718ꢀ
XiaosuꢀDongꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725ꢀ
particlesꢀ[10].ꢀOurꢀownꢀgroupꢀformerlyꢀperformedꢀaꢀsystematicꢀ
studyꢀofꢀtheꢀdifferenceꢀbetweenꢀtheꢀco‐precipitationꢀandꢀliquidꢀ
reductionꢀmethodsꢀwithꢀregardꢀtoꢀtheꢀsubsequentꢀefficiencyꢀofꢀ
Forꢀcomparisonꢀpurposes,ꢀaꢀcatalystꢀwithꢀtheꢀsameꢀcompo‐
sitionꢀwasꢀpreparedꢀbyꢀtheꢀco‐precipitationꢀmethod.ꢀAfterꢀtheꢀ
co‐precipitationꢀ resultingꢀ fromꢀ combiningꢀ metalꢀ nitrateꢀ andꢀ
2
catalyticꢀCO ꢀconversionꢀtoꢀmethanol.ꢀThisꢀpriorꢀworkꢀdemon‐
Na
2
CO ꢀsolutionsꢀatꢀ338ꢀKꢀandꢀpHꢀ7.0,ꢀtheꢀslurryꢀwasꢀagedꢀatꢀ
3
stratedꢀthatꢀaꢀcatalystꢀfabricatedꢀbyꢀtheꢀliquidꢀreductionꢀmeth‐
odꢀcontainedꢀsmallerꢀCuꢀparticlesꢀandꢀexhibitedꢀsuperiorꢀcata‐
lyticꢀactivityꢀandꢀbetterꢀselectivityꢀforꢀmethanolꢀ[12].ꢀ ꢀ
338ꢀ Kꢀ forꢀ 2ꢀ h,ꢀ followedꢀ byꢀ filtering,ꢀ washingꢀ andꢀ drying.ꢀ Theꢀ
driedꢀproductꢀisꢀdenotedꢀasꢀcCZAZ,ꢀwhileꢀcCZAZ‐573ꢀrefersꢀtoꢀ
theꢀdriedꢀproductꢀafterꢀcalcinationꢀforꢀ6ꢀhꢀatꢀ573ꢀKꢀunderꢀaꢀN
2
ꢀ
TheꢀoxidationꢀstatesꢀofꢀCuꢀspeciesꢀareꢀsusceptibleꢀtoꢀchangeꢀ
duringꢀsinteringꢀandꢀcalcinationꢀprocesses.ꢀManyꢀresearchꢀre‐
portsꢀhaveꢀdescribedꢀtheꢀeffectsꢀofꢀcalcinationꢀtemperatureꢀonꢀ
theꢀ structureꢀ andꢀ catalyticꢀ performanceꢀ overꢀ conventionalꢀ
flow.ꢀ
2.2.ꢀ ꢀ Characterizationꢀ ꢀ
2+
Cu‐basedꢀ catalystsꢀ containingꢀonlyꢀCu ꢀ[13−16].ꢀHowever,ꢀtoꢀ
theꢀ bestꢀ ofꢀ ourꢀ knowledge,ꢀ thereꢀ haveꢀ beenꢀ noꢀ reportsꢀ con‐
cerningꢀtheꢀeffectsꢀofꢀcalcinationꢀtemperatureꢀonꢀCu‐basedꢀcat‐
alystsꢀcontainingꢀCuꢀspeciesꢀinꢀmoreꢀhighlyꢀreducedꢀstates.ꢀInꢀ
viewꢀofꢀtheꢀreadyꢀaggregationꢀofꢀmetallicꢀcopperꢀparticles,ꢀcat‐
alystsꢀ preparedꢀ byꢀ liquidꢀ reductionꢀ mayꢀ exhibitꢀ complicatedꢀ
changesꢀwithꢀelevationꢀofꢀtheꢀcalcinationꢀtemperature.ꢀHence,ꢀitꢀ
wouldꢀbeꢀofꢀsignificantꢀinterestꢀtoꢀcarryꢀoutꢀsystematicꢀresearchꢀ
intoꢀtheꢀpropertiesꢀandꢀcatalyticꢀperformanceꢀofꢀcatalystsꢀpre‐
paredꢀbyꢀtheꢀliquidꢀreductionꢀmethodꢀwhileꢀvaryingꢀtheꢀcalci‐
nationꢀtemperature.ꢀ ꢀ ꢀ
Powderꢀ XRDꢀ patternsꢀ wereꢀ acquiredꢀ usingꢀ aꢀ Panalyticalꢀ
X'PertꢀProꢀX‐rayꢀdiffractometerꢀwithꢀCuꢀK ꢀradiation,ꢀoperatingꢀ
atꢀ40ꢀkVꢀandꢀ30ꢀmAꢀandꢀinꢀtheꢀstepꢀmodeꢀ(0.0167°,ꢀ12ꢀs).ꢀSpe‐
cificꢀ surfaceꢀ areasꢀ wereꢀ determinedꢀ fromꢀ N2ꢀ adsorption‐de‐
sorptionꢀisothermsꢀatꢀ77ꢀKꢀusingꢀaꢀMicromeriticsꢀTristarꢀ3000ꢀ
instrument.ꢀThermogravimetricꢀanalysisꢀ(TGA)ꢀwasꢀperformedꢀ
withꢀaꢀSETSYSꢀEVOLUTIONꢀTGAꢀ16/18ꢀinstrumentꢀcoupledꢀtoꢀaꢀ
massꢀspectrometerꢀ(OminStar,ꢀPfeifferꢀVacuum).ꢀPriorꢀtoꢀanal‐
ysis,ꢀtheꢀsamplesꢀwereꢀfirstꢀheatedꢀtoꢀ1000ꢀKꢀatꢀ10ꢀK/minꢀinꢀanꢀ
Arꢀ flow.ꢀ Peaksꢀ atꢀ m/zꢀ =ꢀ 18ꢀ andꢀ 44ꢀ wereꢀ monitoredꢀ becauseꢀ
α
ꢀ
theseꢀresultedꢀfromꢀtheꢀmainꢀpyrolysisꢀproductsꢀH
2
OꢀandꢀCO ,ꢀ
2
Inꢀ theꢀ presentꢀ work,ꢀ Cu/Zn/Al/Zrꢀ precursorsꢀ wereꢀ pre‐
paredꢀbyꢀtheꢀliquidꢀreductionꢀmethodꢀandꢀthenꢀcalcinedꢀatꢀdif‐
ferentꢀ temperatures.ꢀ Theseꢀ catalystsꢀ wereꢀ subsequentlyꢀ ap‐
respectively.ꢀTheꢀmorphologyꢀofꢀeachꢀcatalystꢀwasꢀanalyzedꢀbyꢀ
SEMꢀ withꢀ anꢀ FETꢀ XLꢀ 30S‐FEGꢀ instrumentꢀ atꢀ anꢀ acceleratingꢀ
voltageꢀofꢀ 10.0ꢀ kV.ꢀXPSꢀ wasꢀ performedꢀusingꢀ anꢀAXISꢀ ULTRAꢀ
pliedꢀtoꢀtheꢀsynthesisꢀofꢀmethanolꢀfromꢀCO
acterizedꢀbyꢀX‐rayꢀdiffractionꢀ(XRD),ꢀN ꢀphysisorption,ꢀscanningꢀ
electronꢀmicroscopyꢀ(SEM),ꢀN Oꢀchemisorption,ꢀX‐rayꢀphotoe‐
lectronꢀ spectroscopyꢀ (XPS),ꢀ temperature‐programmedꢀ reduc‐
tionꢀ (TPR),ꢀ andꢀ CO ꢀ temperature‐programmedꢀ desorptionꢀ
TPD).ꢀTheꢀeffectsꢀofꢀcalcinationꢀtemperatureꢀonꢀtheꢀphysico‐
2
/H
2
ꢀandꢀalsoꢀchar‐
DLDꢀ spectrometerꢀ withꢀ aꢀ monochromaticꢀ Alꢀ K ꢀ (1486.8ꢀ eV)ꢀ
source.ꢀ Theꢀ Cꢀ 1sꢀ peakꢀ (284.6ꢀ eV)ꢀ servedꢀ asꢀ theꢀ referenceꢀ toꢀ
calibrateꢀtheꢀbindingꢀenergies.ꢀ ꢀ
TPRꢀdataꢀwereꢀacquiredꢀusingꢀaꢀquartzꢀreactorꢀinꢀconjunc‐
tionꢀwithꢀaꢀthermalꢀconductivityꢀdetectorꢀ(TCD)ꢀtoꢀdetermineꢀ
α
2
2
2
(
theꢀH
atꢀ 423ꢀ Kꢀ underꢀ Arꢀ toꢀ removeꢀ moistureꢀ asꢀ wellꢀ asꢀ otherꢀ ab‐
sorbedꢀimpuritiesꢀandꢀthenꢀreducedꢀinꢀaꢀflowꢀofꢀ10ꢀvol%ꢀH /Arꢀ
atꢀaꢀheatingꢀ rateꢀofꢀ5ꢀ K/minꢀupꢀtoꢀ673ꢀ K.ꢀ CO ‐TPDꢀ wasꢀ con‐
2
ꢀconsumption.ꢀEachꢀsampleꢀ(50ꢀmg)ꢀwasꢀinitiallyꢀheatedꢀ
chemicalꢀ propertiesꢀ andꢀ catalyticꢀ performanceꢀ ofꢀ theseꢀ cata‐
lystsꢀareꢀdiscussedꢀinꢀdetail.ꢀ
2
2
2
.ꢀ ꢀ Experimentalꢀ ꢀ
.1.ꢀ ꢀ Preparationꢀofꢀcatalystsꢀ ꢀ
Cu‐basedꢀ catalystsꢀ havingꢀ theꢀ compositionꢀ ratioꢀ Cu :Zn :
ductedꢀtoꢀassessꢀtheꢀsurfaceꢀbasicꢀproperties,ꢀemployingꢀaꢀmassꢀ
spectrometerꢀ (OminStar,ꢀ Pfeifferꢀ Vacuum).ꢀ Priorꢀ toꢀ measure‐
ment,ꢀeachꢀsampleꢀ(100ꢀmg)ꢀwasꢀfirstꢀactivatedꢀatꢀ503ꢀKꢀforꢀ2ꢀhꢀ
2
underꢀaꢀfeedꢀgasꢀ(H
flowꢀ atꢀ 323ꢀ Kꢀ forꢀ 1ꢀ h.ꢀ Afterꢀ flushingꢀ theꢀ physicallyꢀ adsorbedꢀ
moleculesꢀfromꢀtheꢀcatalystꢀwithꢀanꢀArꢀflow,ꢀCO ‐TPDꢀwasꢀper‐
formedꢀatꢀaꢀtemperatureꢀrampꢀofꢀ10ꢀK/minꢀunderꢀArꢀupꢀtoꢀ723ꢀ
K.ꢀ Theꢀ amountꢀ ofꢀ desorbedꢀ CO ꢀ wasꢀ recordedꢀ byꢀ theꢀ massꢀ
spectrometer.ꢀ Theꢀ exposedꢀ Cuꢀ surfaceꢀ areaꢀ (SCu)ꢀ wasꢀ deter‐
minedꢀbyꢀdissociativeꢀN Oꢀadsorption,ꢀusingꢀaꢀTCDꢀtoꢀmonitorꢀ
theꢀconsumptionꢀofꢀH .ꢀEachꢀsampleꢀ(100ꢀmg)ꢀwasꢀpretreatedꢀ
atꢀ503ꢀKꢀunderꢀaꢀflowꢀofꢀ10ꢀvol%ꢀH /Arꢀforꢀ2ꢀh.ꢀTheꢀreducedꢀ
sampleꢀwasꢀthenꢀcooledꢀtoꢀ323ꢀKꢀandꢀpurgedꢀwithꢀArꢀforꢀ1ꢀh,ꢀ
afterꢀwhichꢀitꢀwasꢀexposedꢀtoꢀ5%ꢀN O/Arꢀforꢀ1ꢀh.ꢀUnderꢀtheseꢀ
conditions,ꢀ allꢀ exposedꢀ metallicꢀ copperꢀ wasꢀ completelyꢀ oxi‐
dizedꢀaccordingꢀtoꢀtheꢀreactionꢀ2Cu(s)ꢀ+ꢀN Oꢀ→ꢀCu O(s)ꢀ+ꢀN ,ꢀ
2 2
:CO ꢀ=ꢀ3:1)ꢀandꢀthenꢀsaturatedꢀusingꢀaꢀCO
2
ꢀ
2+
2+
ꢀ
3+
4+
Al :Zr ꢀ =ꢀ 6:3:0.5:0.5ꢀ wereꢀ preparedꢀ byꢀ theꢀ liquidꢀ reductionꢀ
method.ꢀInꢀaꢀtypicalꢀprocess,ꢀaꢀsolutionꢀofꢀmixedꢀmetalꢀnitratesꢀ
2
(1.0ꢀmol/L,ꢀ100ꢀmL)ꢀandꢀaꢀsolutionꢀofꢀtheꢀNa
2 3
CO ꢀprecipitantꢀ
2
(1.2ꢀmol/L)ꢀwereꢀaddedꢀdropwiseꢀtoꢀdeionizedꢀwaterꢀ(100ꢀmL)ꢀ
withꢀstirringꢀatꢀ338ꢀKꢀandꢀatꢀaꢀconstantꢀpHꢀvalueꢀofꢀ7.0ꢀ±ꢀ0.2.ꢀ
NaBH ꢀ(B/Cuꢀmolarꢀratioꢀ=ꢀ5,ꢀ11.35ꢀg)ꢀwasꢀdissolvedꢀinꢀaꢀNaOHꢀ
solutionꢀ(0.1ꢀmol/L,ꢀ100ꢀmL)ꢀtoꢀprepareꢀaꢀreducingꢀagentꢀsolu‐
tion.ꢀAfterꢀremovingꢀairꢀfromꢀtheꢀreactionꢀmixture,ꢀtheꢀreducingꢀ
agentꢀsolutionꢀwasꢀaddedꢀdropwiseꢀwithꢀstirringꢀatꢀ338ꢀKꢀun‐
2
4
2
2
2
derꢀaꢀN ꢀatmosphere.ꢀTheꢀresultingꢀslurryꢀwasꢀallowedꢀtoꢀageꢀ
2
forꢀ 2ꢀ h,ꢀ andꢀ theꢀ precipitateꢀ wasꢀ removedꢀ byꢀ filtrationꢀ andꢀ
washedꢀseveralꢀtimesꢀwithꢀdeionizedꢀwaterꢀfollowedꢀbyꢀaꢀsingleꢀ
washꢀwithꢀethanol.ꢀTheꢀprecipitateꢀwasꢀthenꢀdriedꢀforꢀ10ꢀhꢀatꢀ
2
2
2
whereꢀCu(s)ꢀrepresentsꢀsurfaceꢀCuꢀatoms.ꢀAfterꢀcoolingꢀtoꢀroomꢀ
temperatureꢀunderꢀanꢀArꢀflow,ꢀtheꢀcatalystꢀwasꢀreducedꢀunderꢀ
3
23ꢀ Kꢀ inꢀ aꢀ vacuumꢀ ovenꢀ toꢀ produceꢀ theꢀ precursorꢀ materials,ꢀ
denotedꢀasꢀCZAZꢀherein.ꢀSamplesꢀofꢀthisꢀCZAZꢀprecursorꢀwereꢀ
calcinedꢀatꢀ423,ꢀ573,ꢀ723ꢀorꢀ873ꢀKꢀforꢀ6ꢀhꢀunderꢀaꢀN ꢀflow,ꢀtoꢀ
aꢀ10ꢀvol%ꢀH /Arꢀflowꢀusingꢀaꢀtemperatureꢀrampꢀofꢀ5ꢀK/minꢀtoꢀ
heatꢀ theꢀ specimenꢀ fromꢀ roomꢀ temperatureꢀ toꢀ 573ꢀ K.ꢀ Theꢀ
2
2
2
amountꢀofꢀconsumedꢀH
2
ꢀisꢀdenotedꢀasꢀnH2.ꢀTheꢀSCuꢀ(m /g)ꢀvalueꢀ
produceꢀspecimensꢀdenotedꢀasꢀCZAZ‐423,ꢀCZAZ‐573,ꢀCZAZ‐723ꢀ
andꢀCZAZ‐873,ꢀrespectively.ꢀ ꢀ
wasꢀcalculatedꢀaccordingꢀtoꢀtheꢀequationsꢀ[17]:ꢀSCuꢀ=ꢀ(nCu×N)ꢀ/ꢀ
(1.4×10 ×W),ꢀwhereꢀSCuꢀisꢀtheꢀexposedꢀcopperꢀsurfaceꢀareaꢀperꢀ
19

ꢀ
XiaosuꢀDongꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725ꢀ
719ꢀ
gramꢀcatalyst,ꢀnCuꢀisꢀtheꢀamountꢀofꢀsurfaceꢀmetallicꢀcopperꢀonꢀ
dothermicꢀnatureꢀandꢀhigherꢀapparentꢀactivationꢀenergyꢀofꢀtheꢀ
RWGSꢀreactionꢀ[20].ꢀInꢀtheꢀcaseꢀofꢀthoseꢀcatalystsꢀsynthesizedꢀ
23
theꢀcatalystꢀ(nCuꢀ=ꢀ2n
H
),ꢀNꢀisꢀAvogadro’sꢀconstantꢀ(6.02×10 ꢀ
2
19
2
atoms/mol),ꢀ 1.4×10 ꢀisꢀtheꢀnumberꢀofꢀcopperꢀatomsꢀperꢀm ,ꢀ
byꢀ liquidꢀ reduction,ꢀ CO ꢀ conversionꢀ andꢀ methanolꢀ selectivityꢀ
2
andꢀWꢀisꢀtheꢀmassꢀofꢀtheꢀtestꢀsample.ꢀ
firstꢀ increaseꢀ andꢀ thenꢀ decreaseꢀ withꢀ increasingꢀ calcinationꢀ
temperature,ꢀandꢀtheꢀCZAZ‐573ꢀexhibitsꢀtheꢀbestꢀcatalyticꢀper‐
formance.ꢀAꢀmaximumꢀmethanolꢀSTYꢀvalueꢀofꢀ0.21ꢀgꢀmL–1ꢀh–1ꢀ
2.3.ꢀ ꢀ Evaluationꢀofꢀcatalystsꢀ ꢀ
togetherꢀwithꢀaꢀCO2ꢀconversionꢀofꢀ24.5%ꢀandꢀaꢀCH OHꢀselectiv‐
3
Activityꢀ measurementsꢀ duringꢀ theꢀ synthesisꢀ ofꢀ methanolꢀ
ityꢀofꢀ57.6%ꢀareꢀobtainedꢀoverꢀtheꢀCZAZ‐573ꢀatꢀaꢀreactionꢀtem‐
peratureꢀofꢀ543ꢀK.ꢀ ꢀ
fromꢀCO
2
/H ꢀwereꢀcarriedꢀoutꢀinꢀaꢀcontinuousꢀflow,ꢀhighꢀpres‐
2
sure,ꢀfixed‐bedꢀreactor.ꢀInꢀeachꢀtrial,ꢀ1.0ꢀgꢀofꢀtheꢀcatalystꢀ(40−60ꢀ
mesh)ꢀwasꢀplacedꢀinꢀaꢀstainlessꢀsteelꢀtubeꢀreactorꢀafterꢀdilutionꢀ
withꢀanꢀequalꢀvolumeꢀofꢀquartzꢀsand.ꢀTheꢀcatalystsꢀsynthesizedꢀ
usingꢀtheꢀliquidꢀreductionꢀmethodꢀwereꢀdirectlyꢀappliedꢀtoꢀac‐
Forꢀcomparisonꢀpurposes,ꢀtheꢀcCZAZ‐573ꢀcatalystꢀpreparedꢀ
byꢀconventionalꢀco‐precipitationꢀwasꢀalsoꢀassessedꢀforꢀactivity.ꢀ
TheꢀsuperiorꢀCO ꢀconversionꢀofꢀtheꢀCZAZ‐573ꢀcatalystꢀrelativeꢀ
2
toꢀ thatꢀ ofꢀ theꢀ cCZAZ‐573ꢀ graduallyꢀ becomesꢀ evidentꢀ withꢀ in‐
creasingꢀ calcinationꢀ temperature.ꢀ Inꢀ addition,ꢀ theꢀ methanolꢀ
selectivityꢀ ofꢀ theꢀ CZAZ‐573ꢀ isꢀ greaterꢀ thanꢀ thatꢀ ofꢀ theꢀ
cCZAZ‐573ꢀ atꢀ theseꢀ threeꢀ reactionꢀ temperatures.ꢀ Theꢀ higherꢀ
activitiesꢀ ofꢀ theꢀ catalystsꢀ madeꢀ usingꢀ theꢀ liquidꢀ reductionꢀ
methodꢀareꢀattributedꢀtoꢀtheꢀpresenceꢀofꢀsmallerꢀcopperꢀparti‐
clesꢀandꢀaꢀlargerꢀquantityꢀofꢀbasicꢀsites;ꢀtheseꢀeffectsꢀhaveꢀbeenꢀ
discussedꢀinꢀdetailꢀinꢀaꢀpreviousꢀresearchꢀreportꢀ[12].ꢀ ꢀ ꢀ
tivityꢀmeasurementsꢀinvolvingꢀCO
withꢀanyꢀfurtherꢀH ꢀreduction.ꢀTheꢀreactionꢀconditionsꢀincludedꢀ
aꢀ temperatureꢀ ofꢀ 503–543ꢀ K,ꢀ aꢀ pressureꢀ ofꢀ 5.0ꢀ MPa,ꢀ n(H ):
2
ꢀhydrogenationꢀtoꢀmethanolꢀ
2
2
ꢀ
–1
n(CO
Theꢀ catalystꢀ obtainedꢀ byꢀ co‐precipitationꢀ wasꢀ reducedꢀ underꢀ
pureꢀH ꢀatꢀatmosphericꢀpressureꢀandꢀ503ꢀKꢀforꢀ4ꢀhꢀpriorꢀtoꢀtheꢀ
2
)ꢀ=ꢀ3:1,ꢀandꢀaꢀgasꢀhourlyꢀspaceꢀvelocityꢀ(GHSV)ꢀ=ꢀ4600ꢀh .ꢀ
2
activityꢀtests.ꢀTheꢀproductsꢀwereꢀquantitativelyꢀanalyzedꢀusingꢀ
gasꢀchromatographyꢀ(GC)ꢀinꢀconjunctionꢀwithꢀaꢀTCD.ꢀGaseousꢀ
productsꢀ(H
columnꢀwhileꢀliquidꢀproductsꢀ(H
withꢀ aꢀ Porapak‐Qꢀ column.ꢀ Theꢀ CO
2
,ꢀCO
2
,ꢀCOꢀandꢀCH
4
)ꢀwereꢀassessedꢀwithꢀaꢀTDX‐01ꢀ
OꢀandꢀCH OH)ꢀwereꢀseparatedꢀ
ꢀ conversionꢀ andꢀ theꢀ car‐
3.2.ꢀ ꢀ Texturalꢀandꢀstructuralꢀpropertiesꢀ ꢀ
2
3
2
TheꢀXRDꢀpatternsꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀareꢀshownꢀinꢀ
Fig.ꢀ1.ꢀTheꢀdiffractionꢀpeaksꢀgeneratedꢀbyꢀtheꢀCZAZꢀprecursorꢀ
andꢀcalcinedꢀsamplesꢀatꢀ2θꢀ=ꢀ43.3°ꢀandꢀ50.4°ꢀcorrespondꢀtoꢀtheꢀ
(111)ꢀ andꢀ (200)ꢀ planesꢀ ofꢀ theꢀ Cuꢀ phaseꢀ (JCPDSꢀ 04‐0836).ꢀ
bon‐basedꢀ selectivitiesꢀ forꢀ methanolꢀ andꢀ COꢀ wereꢀ calculatedꢀ
basedꢀ onꢀ anꢀ internalꢀ normalizationꢀ method.ꢀ Theꢀ spaceꢀ timeꢀ
–1
–1
yieldꢀ(STY,ꢀgꢀmL ꢀh )ꢀforꢀmethanol,ꢀwhichꢀgivesꢀtheꢀamountꢀofꢀ
methanolꢀperꢀmLꢀcatalystꢀperꢀh,ꢀwasꢀcalculatedꢀusingꢀtheꢀequa‐
Characteristicꢀ diffractionꢀ peaksꢀ assignableꢀ toꢀ aꢀ Cu
(JCPDSꢀ 05‐0667)ꢀ areꢀ onlyꢀ observedꢀ inꢀ theꢀ calcinedꢀ samples,ꢀ
implyingꢀthatꢀtheꢀCu OꢀphaseꢀinꢀtheꢀCZAZꢀprecursorꢀisꢀhighlyꢀ
dispersedꢀ andꢀ soꢀ belowꢀ theꢀ XRDꢀ detection,ꢀ andꢀ thatꢀ theꢀ dis‐
persedꢀ Cu Oꢀ particlesꢀ tendꢀ toꢀ aggregateꢀ duringꢀ calcination.ꢀ
Theseꢀresultsꢀsuggestꢀthatꢀtheꢀliquidꢀreductionꢀprocessꢀreducesꢀ
2
Oꢀ phaseꢀ
tion:ꢀSTYꢀ=ꢀ(Wꢀ×ꢀXCH OH)/(tꢀ×ꢀV),ꢀwhereꢀWꢀisꢀtheꢀtotalꢀmassꢀofꢀ
3
H
2
Oꢀandꢀmethanolꢀ(g),ꢀXCH OHꢀisꢀtheꢀmassꢀfractionꢀofꢀmethanol,ꢀtꢀ
2
3
isꢀtheꢀreactionꢀtimeꢀ(h),ꢀandꢀVꢀisꢀtheꢀvolumeꢀofꢀcatalystꢀ(mL).ꢀ
2
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ ꢀ
2+
+
Cu ꢀtoꢀCuꢀandꢀCu .ꢀDiffractionꢀpeaksꢀforꢀtheꢀZnOꢀphaseꢀ(JCPDSꢀ
36‐1451)ꢀareꢀobserved,ꢀwhileꢀAl 3ꢀandꢀZrO ꢀareꢀnotꢀevidentꢀasꢀ
3.1.ꢀ ꢀ CatalyticꢀperformanceꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀ ꢀ ꢀ
2
O
2
separateꢀ phases,ꢀ andꢀ soꢀ mayꢀ haveꢀ beenꢀ highlyꢀ dispersedꢀ inꢀ
amorphousꢀformsꢀorꢀwithꢀveryꢀsmallꢀparticleꢀsizes,ꢀorꢀinteract‐
edꢀwithꢀotherꢀmetalꢀoxidesꢀ[21,22].ꢀWithꢀincreasingꢀcalcinationꢀ
temperature,ꢀ theꢀ characteristicꢀ diffractionꢀ peaksꢀ ascribedꢀ toꢀ
TheꢀcatalyticꢀactivitiesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀcalcinedꢀ
atꢀdifferentꢀtemperatureꢀareꢀsummarizedꢀinꢀTableꢀ1.ꢀAsꢀcanꢀbeꢀ
seen,ꢀtheꢀCO ꢀconversionꢀincreasesꢀwhileꢀtheꢀmethanolꢀselectiv‐
2
ityꢀdecreasesꢀasꢀtheꢀreactionꢀtemperatureꢀisꢀraised,ꢀaꢀresultꢀthatꢀ
isꢀ consistentꢀ withꢀ otherꢀ literatureꢀ reportsꢀ [18−20].ꢀ Methanolꢀ
andꢀCOꢀareꢀtheꢀmainꢀcarbon‐containingꢀproductsꢀunderꢀtheseꢀ
reactionꢀ conditions.ꢀ Aꢀ higherꢀ reactionꢀ temperatureꢀ evidentlyꢀ
theꢀCuꢀandꢀCu Oꢀphasesꢀexhibitꢀanꢀongoingꢀincreaseꢀinꢀintensi‐
2
ty,ꢀowingꢀtoꢀgrainꢀgrowthꢀduringꢀtheꢀthermalꢀtreatmentꢀ[23].ꢀ
Notably,ꢀinꢀtheꢀcaseꢀofꢀtheꢀCZAZ‐873ꢀsample,ꢀtheꢀintensityꢀofꢀtheꢀ
diffractionꢀ peakꢀ atꢀ 2θꢀ =ꢀ43.3°ꢀ assignedꢀtoꢀ Cu(111)ꢀ planesꢀin‐
creasesꢀdramatically,ꢀdemonstratingꢀthatꢀmetallicꢀCuꢀparticlesꢀ
undergoꢀdramaticꢀgrowthꢀatꢀexcessivelyꢀhighꢀtemperatures.ꢀ ꢀ
Fig.ꢀ2ꢀpresentsꢀtheꢀXRDꢀpatternsꢀofꢀtheꢀCu/Zn/Al/Zrꢀcata‐
lystsꢀafterꢀtheꢀtypicalꢀactivationꢀprocedureꢀ(pretreatedꢀatꢀ503ꢀKꢀ
favorsꢀbothꢀactivationꢀandꢀtheꢀconversionꢀofꢀCO
reverseꢀwaterꢀgasꢀshiftꢀ(RWGS)ꢀreactionꢀ(CO ꢀ+ꢀH
isꢀpromotedꢀtoꢀaꢀgreaterꢀextentꢀthanꢀtheꢀsynthesisꢀofꢀmethanolꢀ
CO ꢀ+ꢀ3H ꢀ→ꢀCH OHꢀ+ꢀH O).ꢀThisꢀoccursꢀasꢀaꢀresultꢀofꢀtheꢀen‐
2
,ꢀbecauseꢀtheꢀ
2
2
ꢀ→ꢀCOꢀ+ꢀH O)ꢀ
2
(
2
2
3
2
Tableꢀ1ꢀ
CatalyticꢀperformanceꢀduringꢀCO
2
ꢀhydrogenationꢀtoꢀmethanolꢀatꢀdifferentꢀreactionꢀtemperatureꢀoverꢀvariousꢀCu/Zn/Al/Zrꢀcatalysts.ꢀ
–
1
–1
CO2ꢀconversionꢀ(%)ꢀ
03ꢀKꢀ 523ꢀKꢀ 543ꢀKꢀ
15.2ꢀ
17.3ꢀ
17.7ꢀ
16.2ꢀ
10.9ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
SelectivityꢀforꢀCH
3
OHꢀ(C‐mol%)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
SelectivityꢀforꢀCO(C‐mol%)ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
STYꢀofꢀCH
503ꢀKꢀ 523ꢀK
0.14ꢀ
0.16ꢀ
0.15ꢀ
0.15ꢀ
0.09ꢀ
3
OHꢀ(gꢀmL ꢀh )
Sampleꢀ
5
503ꢀKꢀ
59.4ꢀ
62.1ꢀ
57.5ꢀ
60.3ꢀ
53.0ꢀ
523ꢀKꢀ
57.6ꢀ
60.9ꢀ
55.4ꢀ
58.1ꢀ
51.9ꢀ
543ꢀKꢀ
52.9ꢀ
57.6ꢀ
52.0ꢀ
54.4ꢀ
40.1ꢀ
503ꢀKꢀ
40.6ꢀ
37.9ꢀ
42.5ꢀ
39.7ꢀ
47.0ꢀ
523ꢀKꢀ
42.4ꢀ
39.1ꢀ
44.6ꢀ
41.9ꢀ
48.1ꢀ
543ꢀKꢀ
47.1ꢀ
42.4ꢀ
48.0ꢀ
45.6ꢀ
59.9ꢀ
543ꢀK
0.18ꢀ
0.21ꢀ
0.18ꢀ
0.19ꢀ
0.13ꢀ
CZAZ‐423ꢀ
CZAZ‐573ꢀ
cCZAZ‐573ꢀ
CZAZ‐723ꢀ
CZAZ‐873ꢀ
19.8ꢀ
22.0ꢀ
21.1ꢀ
20.9ꢀ
18.9ꢀ
21.3ꢀ
24.5ꢀ
23.4ꢀ
22.8ꢀ
20.5ꢀ
0.18ꢀ
0.20ꢀ
0.18ꢀ
0.19ꢀ
0.15ꢀ
ꢀ
ꢀ
–1
Reactionꢀconditions:ꢀPꢀ=ꢀ5.0ꢀMPa,ꢀn(H
2
):n(CO
2
)ꢀ=ꢀ3:1,ꢀGHSVꢀ=ꢀ4600ꢀh .

720ꢀ
XiaosuꢀDongꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725ꢀ
Tableꢀ2ꢀ


 ZnO Cu Cu O
2
PhysicochemicalꢀpropertiesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalysts.ꢀ




CZAZ-873






Cuꢀaꢀ
Cuꢀsurfaceꢀareaꢀb Cu /Cu
+
0ꢀcꢀ
BETꢀsurfaceꢀarea
d
Sampleꢀ
2
2
(m /g)ꢀ
(nm)ꢀ
(m /g)ꢀ
(%)ꢀ
CZAZ‐423ꢀ
CZAZ‐573ꢀ
CZAZ‐723ꢀ
CZAZ‐873ꢀ
52.0ꢀ
50.8ꢀ
33.9ꢀ
21.7ꢀ
16.4ꢀ
17.6ꢀ
19.2ꢀ
22.2ꢀ
12.6ꢀ
18.6ꢀ
15.1ꢀ
ꢀ 8.4ꢀ
0.22ꢀ
0.39ꢀ
0.27ꢀ
0.08ꢀ
CZAZ-723
CZAZ-573
aꢀCalculatedꢀfromꢀCu(111)ꢀreflectionsꢀinꢀXRDꢀpatternsꢀ(Fig.ꢀ2)ꢀusingꢀtheꢀ
Scherrerꢀequation.ꢀ
CZAZ-423
CZAZ
bꢀ
FromꢀN
2
Oꢀdissociativeꢀadsorptionꢀmeasurements.ꢀ
cꢀ
Calculatedꢀ byꢀ Cuꢀ LMMꢀ Augerꢀ electronꢀ spectroscopyꢀ ofꢀ theꢀ catalystsꢀ
afterꢀactivationꢀunderꢀaꢀfeedꢀgasꢀatꢀ503ꢀK.ꢀ
ꢀ
2
0
30
40
50
60
70


producesꢀCuꢀspeciesꢀthatꢀareꢀnotꢀfullyꢀreducedꢀunderꢀtheꢀacti‐
vationꢀconditions.ꢀ ꢀ
Fig.ꢀ1.ꢀXRDꢀpatternsꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalysts.ꢀ
Toꢀallowꢀforꢀfurtherꢀinvestigationsꢀofꢀtheꢀthermalꢀdecompo‐
sitionꢀbehaviorsꢀofꢀtheseꢀcatalysts,ꢀtheꢀdriedꢀproductsꢀobtainedꢀ
fromꢀ bothꢀ theꢀ liquidꢀ reductionꢀ andꢀ co‐precipitationꢀ methodsꢀ
wereꢀassessedꢀbyꢀTGAꢀinꢀconjunctionꢀwithꢀmassꢀspectrometryꢀ
(Fig.ꢀ3).ꢀTheꢀcCZAZꢀsample,ꢀhavingꢀaꢀzincian‐malachiteꢀprecur‐
sorꢀstructureꢀ[12],ꢀexhibitsꢀthreeꢀmassꢀlossꢀpeaksꢀwithꢀaꢀtotalꢀ
massꢀ lossꢀ ofꢀ approximatelyꢀ 25.7%.ꢀ Thereꢀ areꢀ labeledꢀ inꢀ theꢀ
figure,ꢀwhereꢀW1,ꢀW2ꢀandꢀW3ꢀcorrespondꢀtoꢀtheꢀlossꢀofꢀphy‐
sisorbedꢀ waterꢀ [25],ꢀ zincian‐malachiteꢀ phaseꢀ decompositionꢀ
withꢀaꢀfeedꢀgas).ꢀItꢀcanꢀbeꢀseenꢀthatꢀtheꢀcharacteristicꢀCu Oꢀdif‐
2
fractionꢀpeaksꢀdisappear,ꢀdemonstratingꢀthatꢀtheꢀcatalystsꢀun‐
dergoꢀaꢀsecondaryꢀvaporꢀphaseꢀreductionꢀduringꢀtheꢀactivationꢀ
procedure.ꢀInꢀaddition,ꢀtheꢀintensityꢀofꢀtheꢀpeaksꢀattributedꢀtoꢀ
theꢀCuꢀphaseꢀincreaseꢀsignificantlyꢀinꢀcomparisonꢀtoꢀthatꢀinꢀFig.ꢀ
1,ꢀasꢀaꢀresultꢀofꢀthisꢀsecondaryꢀreductionꢀandꢀtheꢀaggregationꢀofꢀ
Cuꢀparticlesꢀduringꢀtheꢀhighꢀtemperatureꢀtreatment.ꢀTheꢀaver‐
ageꢀ Cuꢀ grainꢀ crystalꢀ sizesꢀ wereꢀ calculatedꢀ fromꢀ theꢀ Cu(111)ꢀ
reflectionsꢀusingꢀtheꢀScherrerꢀequationꢀandꢀwereꢀfoundꢀtoꢀin‐
creaseꢀalongꢀwithꢀtheꢀcalcinationꢀtemperatureꢀ(Tableꢀ2),ꢀindi‐
catingꢀthatꢀtheꢀcalcinationꢀtemperatureꢀhasꢀaꢀsignificantꢀeffectꢀ
onꢀtheꢀsizeꢀofꢀtheꢀmetallicꢀCuꢀparticles.ꢀ
alongꢀwithꢀtheꢀreleaseꢀofꢀH
ofꢀstableꢀCu/Znꢀhydroxocarbonatesꢀ[22]ꢀwithꢀonlyꢀCO
Inꢀcontrast,ꢀtheꢀCZAZꢀprecursorꢀundergoesꢀaꢀmassꢀlossꢀofꢀaboutꢀ
12.9%.ꢀ Aꢀ broadꢀ H Oꢀ peakꢀ isꢀ observedꢀ whileꢀ littleꢀ CO ꢀ isꢀ re‐
2 2
OꢀandꢀCO ,ꢀandꢀtheꢀdecompositionꢀ
2
ꢀrelease.ꢀ
2
2
Asꢀ shownꢀ inꢀ Tableꢀ 2,ꢀ theꢀ specificꢀ surfaceꢀ areaꢀ decreasesꢀ
leasedꢀ duringꢀ theꢀ thermalꢀ decompositionꢀ process,ꢀ suggestingꢀ
thatꢀ hydroxyꢀ carbonatesꢀ inꢀ thisꢀ materialꢀ areꢀ primarilyꢀ trans‐
formedꢀtoꢀmetal/metalꢀoxidesꢀduringꢀtheꢀliquidꢀreductionꢀpro‐
cess,ꢀinꢀaccordanceꢀwithꢀtheꢀXRDꢀresultsꢀinꢀFig.ꢀ1.ꢀ ꢀ
Fig.ꢀ 4ꢀ presentsꢀ SEMꢀ imagesꢀ ofꢀ Cu/Zn/Al/Zrꢀ catalystsꢀ cal‐
cinedꢀatꢀdifferentꢀtemperatures.ꢀItꢀcanꢀbeꢀseenꢀthatꢀtheꢀcatalystsꢀ
areꢀ composedꢀ ofꢀ eitherꢀ sphericalꢀ orꢀ rod‐likeꢀ particles.ꢀ Withꢀ
increasingꢀcalcinationꢀtemperature,ꢀtheꢀsphericalꢀparticles,ꢀwithꢀ
aꢀsizeꢀdistributionꢀinꢀtheꢀrangeꢀofꢀ30−60ꢀnmꢀinꢀtheꢀCZAZ‐423,ꢀ
growꢀ toꢀ 50−120ꢀ nmꢀ inꢀ theꢀ CZAZ‐873.ꢀ Thisꢀ resultꢀ isꢀ inꢀ goodꢀ
2
2
fromꢀ52.0ꢀm /gꢀforꢀCZAZ‐423ꢀtoꢀ21.7ꢀm /gꢀforꢀCZAZ‐873ꢀwithꢀ
increasingꢀ calcinationꢀ temperature.ꢀ Theꢀ growthꢀ ofꢀ crystalꢀ
grainsꢀand/orꢀtheꢀagglomerationꢀofꢀparticlesꢀatꢀhigherꢀtemper‐
aturesꢀareꢀresponsibleꢀforꢀtheꢀchangesꢀinꢀtheꢀBETꢀsurfaceꢀareaꢀ
andꢀ dCuꢀ [24].ꢀ Theꢀ exposedꢀ Cuꢀ surfaceꢀ areasꢀ determinedꢀ fromꢀ
N Oꢀ dissociativeꢀ adsorptionꢀ measurementsꢀ undergoꢀ aꢀ contin‐
2
uousꢀdecreaseꢀfromꢀCZAZ‐573ꢀtoꢀCZAZ‐873,ꢀdueꢀtoꢀincreasingꢀ
aggregationꢀofꢀCuꢀparticles.ꢀInterestingly,ꢀtheꢀCZAZ‐423ꢀsampleꢀ
hasꢀaꢀrelativelyꢀlowꢀSCuꢀasꢀaꢀresultꢀofꢀtheꢀhighꢀreductionꢀtem‐
peratureꢀappliedꢀtoꢀthisꢀmaterialꢀ(Fig.ꢀ6).ꢀThisꢀhighꢀtemperatureꢀ
agreementꢀwithꢀtheꢀN
ꢀphysisorptionꢀdata.ꢀTheꢀrod‐likeꢀparti‐
2
clesꢀareꢀcomposedꢀofꢀtheꢀZnOꢀphaseꢀaccordingꢀtoꢀhighꢀresolu‐
tionꢀtransmissionꢀelectronꢀmicroscopyꢀ(HRTEM)ꢀandꢀscanningꢀ
TEM‐energyꢀ dispersiveꢀ spectroscopyꢀ resultsꢀ [12].ꢀ Theseꢀ rodsꢀ
areꢀapproximatelyꢀ300−500ꢀnmꢀinꢀlength.ꢀInsteadꢀofꢀpromotingꢀ
strongꢀ interactionsꢀ amongꢀ eachꢀ component,ꢀ asꢀ occursꢀ duringꢀ
theꢀconventionalꢀco‐precipitationꢀmethod,ꢀtheꢀliquidꢀreductionꢀ
processꢀ resultsꢀ inꢀ theꢀ migrationꢀ ofꢀ Cuꢀ speciesꢀ fromꢀ theꢀ
co‐precipitationꢀ slurry,ꢀ suchꢀ thatꢀ theꢀ ZnO,ꢀ undergoingꢀ lessꢀ
bonding,ꢀisꢀinclinedꢀtoꢀgrowꢀintoꢀrod‐likeꢀparticlesꢀwithꢀgoodꢀ
crystallinity.ꢀ ꢀ


ZnO Cu


CZAZ-873








CZAZ-723
CZAZ-573
CZAZ-423
3.3.ꢀ ꢀ XPSꢀanalysisꢀ ꢀ
3
0
40
50
60
70
XPSꢀdataꢀwereꢀacquiredꢀtoꢀdetermineꢀtheꢀsurfaceꢀoxidationꢀ


statesꢀ ofꢀ copperꢀ inꢀ theseꢀ materialsꢀ asꢀ wellꢀ asꢀ theirꢀ chemicalꢀ
compositions.ꢀ Bothꢀ Cuꢀ 2p3/2ꢀ andꢀ Cuꢀ 2p1/2ꢀ peaksꢀ areꢀ evidentꢀ
alongꢀwithꢀtheirꢀsatelliteꢀpeaksꢀinꢀFig.ꢀ5(a),ꢀindicatingꢀtheꢀpres‐
Fig.ꢀ2.ꢀXRDꢀpatternsꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀafterꢀgasꢀphaseꢀacti‐
vation.ꢀ

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721ꢀ
(a)
100
(b)
9
9
8
5
0
5
CZAZ
H O
2
CO2
CZAZ
1
00
W1
9
9
8
8
7
7
5
0
5
0
5
0
W2
H O
2
cCZAZ
W3
cCZAZ
CO2
3
00 400 500 600 700 800 900 1000
Temperature (K)
300 400 500 600 700 800 900 1000
Temperature (K)
Fig.ꢀ3.ꢀ(a)ꢀTGꢀcurvesꢀofꢀCu/Zn/Al/Zrꢀprecursors;ꢀ(b)ꢀMassꢀspectraꢀofꢀtheꢀgaseousꢀreductionꢀproductsꢀgeneratedꢀbyꢀtheseꢀprecursors.ꢀ
2
+
areꢀpresentedꢀFig.ꢀ5(d).ꢀHereꢀaꢀprincipalꢀpeakꢀatꢀ918.8ꢀeVꢀ(Cu0)ꢀ
enceꢀofꢀCu ꢀ[23,26].ꢀTheꢀcharacteristicꢀbindingꢀenergiesꢀofꢀCuꢀ
0
+
2+
+
2p
3/2ꢀ fromꢀ Cu ,ꢀ Cu ꢀ andꢀ Cu ꢀ areꢀ locatedꢀ atꢀ 932.2−933.1,ꢀ
32.0−932.8ꢀandꢀ933.2−934.6ꢀeV,ꢀrespectivelyꢀ[27].ꢀItꢀisꢀnote‐
worthyꢀthatꢀtheꢀCuꢀ2p3/2ꢀpeaksꢀareꢀbroadꢀandꢀbifurcated,ꢀwhichꢀ
suggestsꢀthatꢀtheꢀcatalystsꢀpossessꢀmoreꢀthanꢀoneꢀCuꢀspecies.ꢀ
Theseꢀpeaksꢀcanꢀactuallyꢀbeꢀdeconvolutedꢀintoꢀaꢀlarge,ꢀnarrowꢀ
andꢀaꢀsmallerꢀpeakꢀatꢀ916.8ꢀeVꢀ(Cu )ꢀareꢀobserved.ꢀToꢀassistꢀinꢀ
+
0
9
theseꢀinvestigations,ꢀtheꢀrelativeꢀCu /Cu ꢀratiosꢀofꢀtheꢀcatalystꢀ
surfacesꢀwereꢀcalculatedꢀandꢀareꢀpresentedꢀinꢀTableꢀ2.ꢀTheseꢀ
valuesꢀincreaseꢀinꢀtheꢀorderꢀCZAZ‐873ꢀ<ꢀCZAZ‐423ꢀ<ꢀCZAZ‐723ꢀ
<ꢀCZAZ‐573.ꢀTypically,ꢀCu‐basedꢀcatalystsꢀsimultaneouslyꢀcon‐
0
+
0
+
+
peakꢀatꢀ932.2ꢀeVꢀ(attributedꢀtoꢀCu ꢀand/orꢀCu ꢀspecies)ꢀandꢀaꢀ
tainꢀCu ꢀandꢀCu ꢀonꢀtheirꢀsurfacesꢀafterꢀreduction,ꢀandꢀtheꢀCu ꢀ
speciesꢀmayꢀstronglyꢀinteractꢀwithꢀotherꢀcomponentsꢀ[28,29].ꢀ
Inꢀtheꢀcaseꢀofꢀactivatedꢀcatalystsꢀpreparedꢀbyꢀliquidꢀreduction,ꢀ
2+
small,ꢀbroadꢀpeakꢀaroundꢀ934.5ꢀeVꢀ(assignedꢀtoꢀCu ꢀspecies)ꢀ
28].ꢀCuꢀLMMꢀAugerꢀelectronꢀspectroscopyꢀdataꢀwereꢀalsoꢀac‐
quiredꢀtoꢀassessꢀtheꢀsurfaceꢀCuꢀvalenceꢀstates,ꢀasꢀshownꢀinꢀFig.ꢀ
(b).ꢀAꢀprincipalꢀpeakꢀwithꢀaꢀbroadꢀprofileꢀisꢀevidentꢀatꢀaboutꢀ
16.8ꢀ eV,ꢀ demonstratingꢀ thatꢀ Cu ꢀ isꢀ theꢀ predominantꢀ copperꢀ
[
+
2+
theseꢀsurfaceꢀCu ꢀspeciesꢀmayꢀresultꢀfromꢀtheꢀreductionꢀofꢀCu ꢀ
speciesꢀ stronglyꢀ interactingꢀ withꢀ otherꢀ metalꢀ oxidesꢀ orꢀ mayꢀ
representꢀCu ꢀspeciesꢀthatꢀareꢀdifficultꢀtoꢀreduceꢀtoꢀCu .ꢀTheꢀCu ꢀ
speciesꢀareꢀfromꢀtheꢀreadilyꢀreducedꢀcompoundsꢀCuOꢀandꢀCu O.ꢀ
Thus,ꢀtheꢀvalueꢀofꢀCu /Cu ꢀcanꢀbeꢀanꢀimportantꢀindicationꢀofꢀtheꢀ
interactionꢀbetweenꢀCuꢀspeciesꢀandꢀotherꢀmetalꢀoxides.ꢀ ꢀ
5
9
+
+
0
0
2+
speciesꢀ onꢀ theꢀ surface,ꢀ whileꢀ peaksꢀ attributedꢀ toꢀ Cu ꢀ (917.9ꢀ
2
0
+
0
eV)ꢀandꢀCu ꢀ(918.8ꢀeV)ꢀareꢀindistinguishableꢀowingꢀtoꢀtheirꢀlowꢀ
2+
surfaceꢀ levels.ꢀ Theꢀ Cu ꢀ sitesꢀ haveꢀ evidentlyꢀ beenꢀ completelyꢀ
reducedꢀ toꢀ Cu ꢀ and/orꢀ Cu ꢀ sitesꢀ duringꢀ theꢀ typicalꢀ activationꢀ
0
+
procedure,ꢀasꢀevidencedꢀbyꢀtheꢀabsenceꢀofꢀCuꢀ2pꢀsatelliteꢀpeaksꢀ
inꢀFig.ꢀ5(c).ꢀToꢀdistinguishꢀbetweenꢀCu ꢀandꢀCu ꢀspecies,ꢀtheꢀCuꢀ
LMMꢀAugerꢀelectronꢀspectroscopyꢀdataꢀforꢀactivatedꢀcatalystsꢀ
3.4.ꢀ ꢀ ReducibilityꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀ ꢀ
0
+
TPRꢀmeasurementsꢀwereꢀcarriedꢀoutꢀtoꢀstudyꢀtheꢀreductionꢀ
CZAZ‐423
CZAZ‐723
CZAZ‐573
CZAZ‐873
Fig.ꢀ4.ꢀSEMꢀimagesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalysts.ꢀ

722ꢀ
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9
32.2
916.8
(a)
(b)
9
17.9
934.5
CZAZ-823
918.6
CZAZ-873
CZAZ-723
CZAZ-573
CZAZ-723
CZAZ-573
CZAZ-423
CZAZ-423
925 930 935 940 945 950 955 960 965 970
910
912
914
916
918
920
922
924
Binding energy (eV)
Kinetic energy (eV)
(d)
(c)
CZAZ-873
CZAZ-723
CZAZ-573
CZAZ-873
CZAZ-723
CZAZ-573
CZAZ-423
CZAZ-423
925
930
935
940
945
950
955
960
915
916
917
918
919
920
921
Binding energy (eV)
Kinetic energy (eV)
Fig.ꢀ5.ꢀCuꢀ2pꢀspectraꢀ(a)ꢀandꢀCuꢀLMMꢀAugerꢀelectronꢀspectraꢀ(b)ꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalysts;ꢀCuꢀ2pꢀspectraꢀ(c)ꢀandꢀCuꢀLMMꢀAugerꢀelectronꢀspectraꢀ(d
ofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀafterꢀactivationꢀunderꢀaꢀfeedꢀgas.ꢀ
behaviorꢀ ofꢀ theꢀ catalysts.ꢀ Asꢀ shownꢀ inꢀ Fig.ꢀ 6,ꢀ theseꢀ samplesꢀ
generateꢀaꢀbroadꢀpeakꢀinꢀtheꢀtemperatureꢀrangeꢀfromꢀ420ꢀtoꢀ
liquidꢀreduction,ꢀandꢀitsꢀreductionꢀtemperatureꢀshiftsꢀtoꢀaꢀlow‐
erꢀtemperatureꢀdueꢀtoꢀtheꢀweakenedꢀinteractionsꢀinꢀthisꢀmate‐
rialꢀ[12].ꢀCatalystsꢀobtainedꢀfromꢀliquidꢀreductionꢀandꢀcalcinedꢀ
atꢀdifferentꢀtemperatureꢀdemonstrateꢀthatꢀtheꢀinitialꢀreductionꢀ
temperatureꢀshiftsꢀtoꢀlowerꢀvaluesꢀwithꢀincreasingꢀcalcinationꢀ
temperature.ꢀFurthermore,ꢀtheꢀpeakꢀpatternꢀbecomesꢀsharperꢀ
andꢀmoreꢀsymmetricalꢀonꢀgoingꢀfromꢀ423ꢀtoꢀ723ꢀK.ꢀTheꢀbroadꢀ
peaksꢀindicateꢀtheꢀpresenceꢀofꢀseveralꢀspeciesꢀorꢀstates,ꢀallꢀbe‐
ingꢀreducedꢀatꢀapproximatelyꢀtheꢀsameꢀtemperature,ꢀwhereasꢀ
theꢀsharpꢀpeaksꢀdemonstrateꢀtheꢀexistenceꢀofꢀaꢀsingleꢀspeciesꢀ
orꢀstate.ꢀTheseꢀchangesꢀinꢀpeakꢀpatternsꢀlikelyꢀreflectꢀtheꢀeffectꢀ
ofꢀ theꢀ highꢀ calcinationꢀ temperature,ꢀ whichꢀ producesꢀ aꢀ moreꢀ
homogeneousꢀdistributionꢀofꢀCuꢀspeciesꢀ[30].ꢀ ꢀ
5
50ꢀK,ꢀattributedꢀtoꢀtheꢀreductionꢀofꢀCuOꢀandꢀCu O.ꢀItꢀcanꢀbeꢀ
2
seenꢀ thatꢀ theꢀ catalystsꢀ preparedꢀ byꢀ theꢀ co‐precipitationꢀ andꢀ
liquidꢀ reductionꢀ methodsꢀ showꢀ someꢀ differencesꢀ inꢀ theirꢀ re‐
ductionꢀbehavior.ꢀComparedꢀwithꢀtheꢀcCZAZ‐573ꢀcatalyst,ꢀtheꢀ
reductionꢀ peakꢀ areaꢀ ofꢀ theꢀ CZAZ‐573ꢀ isꢀ decreasedꢀ followingꢀ
CZAZ-873
CZAZ-723
3
.5.ꢀ ꢀ SurfaceꢀbasicityꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀ ꢀ
cCZAZ-573
CZAZ-573
TheꢀCO2ꢀdesorptionꢀprofilesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀaf‐
terꢀ theꢀ typicalꢀ activationꢀ procedureꢀ areꢀ shownꢀ inꢀ Fig.ꢀ 7.ꢀ Theꢀ
profilesꢀcanꢀbeꢀassignedꢀtoꢀthreeꢀscenariosꢀrepresentingꢀthreeꢀ
typesꢀofꢀbasicꢀsites:ꢀweaklyꢀbasicꢀ(surfaceꢀOH ꢀgroups),ꢀmoder‐
CZAZ-423
−
atelyꢀ basicꢀ (metal‐oxygenꢀ pairs,ꢀ suchꢀ asꢀ Zn‐Oꢀ andꢀ Zr‐O)ꢀ andꢀ
stronglyꢀ basicꢀ (lowꢀ coordinationꢀ oxygenꢀ atoms)ꢀ [31,32].ꢀ Theꢀ
differencesꢀ inꢀ theꢀ positionsꢀ ofꢀ theꢀ desorptionꢀ peaksꢀ amongꢀ
4
00
450
500
550
600
650
Temperature (K)
Fig.ꢀ6.ꢀTPRꢀprofilesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalysts.ꢀ

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723ꢀ
CZAZ-573
18
16
14
12
10
CZAZ-873
CZAZ-723
CZAZ-723
CZAZ-423
CZAZ-573
CZAZ-423
CZAZ-873
8
10
12
142
SCu (m /g)
16
18
20
350
400
450
500
550
600
650
700
Temperature (K)
Fig.ꢀ7.ꢀCO
activationꢀprocessꢀunderꢀaꢀfeedꢀgas.ꢀ
2
‐TPDꢀprofilesꢀofꢀtheꢀCu/Zn/Al/Zrꢀcatalystsꢀafterꢀtheꢀtypical
Fig.ꢀ9.ꢀTheꢀrelationshipꢀbetweenꢀtheꢀCO
2
ꢀconversionꢀandꢀSCu.ꢀReactionꢀ
−1
conditions:ꢀPꢀ=ꢀ5.0ꢀMPa,ꢀn(H ):n(CO )ꢀ=ꢀ3:1,ꢀTꢀ=ꢀ523ꢀK,ꢀGHSVꢀ=ꢀ4600ꢀh .
2
2
whileꢀ CO2ꢀ conversionꢀ showedꢀ aꢀ similarꢀ trendꢀ followingꢀ theꢀ
elevationꢀ ofꢀ theꢀ calcinationꢀ temperature,ꢀ asꢀ shownꢀ inꢀ Fig.ꢀ 9.ꢀ
However,ꢀ theꢀ relationshipꢀ betweenꢀ CO2ꢀconversionꢀ andꢀ SCuꢀ isꢀ
notꢀ linear,ꢀ aꢀ resultꢀ thatꢀ isꢀ consistentꢀ withꢀ otherꢀ reportsꢀ
theseꢀ samplesꢀ areꢀ minimalꢀ exceptꢀ inꢀ theꢀ caseꢀ ofꢀ theꢀ stronglyꢀ
basicꢀsitesꢀofꢀtheꢀCZAZ‐423ꢀsample,ꢀsuggestingꢀthatꢀcalcinationꢀ
temperatureꢀhasꢀnoꢀ significantꢀeffectꢀonꢀtheꢀ strengthꢀofꢀbasicꢀ
sites.ꢀ However,ꢀ anꢀ ongoingꢀ decreaseꢀ inꢀ theꢀ amountꢀ ofꢀ basicꢀ
sitesꢀisꢀobservedꢀwithꢀincreasingꢀcalcinationꢀtemperature,ꢀpri‐
marilyꢀattributedꢀtoꢀaꢀdecreaseꢀinꢀtheꢀspecificꢀsurfaceꢀarea.ꢀ ꢀ
[
38−40].ꢀTheseꢀresultsꢀconfirmꢀthatꢀthereꢀmustꢀbeꢀsomeꢀotherꢀ
factorsꢀaffectingꢀtheꢀcatalyticꢀperformanceꢀduringꢀtheꢀsynthesisꢀ
ofꢀmethanolꢀfromꢀCO /H .ꢀ
Itꢀisꢀgenerallyꢀacceptedꢀthatꢀtheꢀcoordination,ꢀchemisorptionꢀ
andꢀactivationꢀofꢀCO ꢀandꢀtheꢀhomogeneousꢀsplittingꢀofꢀhydro‐
2
2
3.6.ꢀ ꢀ Long‐termꢀstabilityꢀtestsꢀ ꢀ
2
0
+
0
+
genꢀtakeꢀplaceꢀonꢀCu ꢀandꢀCu ꢀ[22,33,41−43].ꢀThus,ꢀCu ꢀandꢀCu ꢀ
sitesꢀonꢀtheꢀcatalystꢀsurfaceꢀareꢀimportantꢀinꢀdeterminingꢀtheꢀ
Fig.ꢀ 8ꢀ presentsꢀ theꢀ long‐termꢀ stabilityꢀ testꢀ dataꢀ forꢀ theꢀ
CZAZ‐573ꢀ sampleꢀ duringꢀ theꢀ synthesisꢀ ofꢀ methanolꢀ viaꢀ CO ꢀ
2
−1
catalyticꢀ performanceꢀ duringꢀ CO ꢀ hydrogenationꢀ toꢀ methanolꢀ
2
hydrogenationꢀatꢀ523ꢀK,ꢀ5.0ꢀMPaꢀandꢀaꢀGHSVꢀofꢀ4600ꢀh .ꢀItꢀcanꢀ
beꢀseenꢀthatꢀtheꢀCO ꢀconversionꢀandꢀmethanolꢀselectivityꢀob‐
tainedꢀ fromꢀ theꢀ catalystꢀ remainꢀ stableꢀ duringꢀ aꢀ continuousꢀ
000ꢀ hꢀ trial.ꢀ Theseꢀ resultsꢀ demonstrateꢀ thatꢀ theꢀ CZAZ‐573ꢀ
0
+
[
33,41,42,44].ꢀInꢀcomparisonꢀtoꢀCu ꢀspecies,ꢀCu ꢀspeciesꢀonꢀtheꢀ
2
catalystꢀ surfaceꢀ mayꢀ representꢀ electropositiveꢀ sitesꢀ thatꢀ
+
0
stronglyꢀinteractꢀwithꢀotherꢀcomponents.ꢀAsꢀsuch,ꢀtheꢀCu /Cu ꢀ
ratioꢀcanꢀbeꢀanꢀimportantꢀindicatorꢀofꢀtheꢀinteractionꢀbetweenꢀ
Cuꢀspeciesꢀandꢀotherꢀmetalꢀoxides.ꢀInꢀfact,ꢀitꢀisꢀwellꢀknownꢀthatꢀ
theꢀRWGSꢀreactionꢀisꢀpromotedꢀtoꢀaꢀgreaterꢀextentꢀbyꢀmetallicꢀ
copperꢀthanꢀbyꢀpartiallyꢀoxidizedꢀcopperꢀ[41].ꢀToyirꢀetꢀal.ꢀ[41]ꢀ
preparedꢀGa‐promotedꢀCu‐basedꢀcatalystsꢀwithꢀhighꢀselectivityꢀ
1
sampleꢀshowsꢀsteadyꢀcatalyticꢀperformanceꢀunderꢀtheꢀinvesti‐
gatedꢀreactionꢀconditions.ꢀ ꢀ
Manyꢀ researchersꢀ haveꢀ pointedꢀ outꢀ thatꢀ theꢀ activityꢀ ofꢀ
Cu‐basedꢀ catalystsꢀ duringꢀ CO
closelyꢀ relatedꢀ toꢀ theꢀ exposedꢀ copperꢀ surfaceꢀ areaꢀ (SCu)ꢀ
19,20,30,33−37].ꢀInꢀthisꢀwork,ꢀSCuꢀwasꢀfoundꢀtoꢀfirstꢀincreaseꢀ
andꢀ thenꢀ decreaseꢀ withꢀ increasingꢀ calcinationꢀ temperature,ꢀ
2
ꢀ hydrogenationꢀ toꢀ methanolꢀ isꢀ
forꢀmethanolꢀproductionꢀfromꢀCO
2
/H ꢀandꢀattributedꢀthisꢀselec‐
2
[
+
tivityꢀ toꢀ theꢀ presenceꢀ ofꢀ Cu ꢀ speciesꢀ onꢀ theꢀ catalystꢀ surface.ꢀ
Saitoꢀ etꢀ al.ꢀ [33]ꢀ foundꢀ thatꢀ higherꢀ activitiesꢀ duringꢀ methanolꢀ
synthesisꢀoverꢀaꢀmulticomponentꢀCu/ZnO‐basedꢀcatalystꢀwereꢀ
70
65
60
70
65
60
+
0
obtainedꢀwhenꢀtheꢀvalueꢀCu /Cu ꢀwasꢀapproximatelyꢀ0.7.ꢀInꢀtheꢀ
caseꢀ ofꢀ theꢀ presentꢀ Cu/Zn/Al/Zrꢀ catalystsꢀ preparedꢀ byꢀ liquidꢀ
+
0
reductionꢀwithꢀdifferentꢀcalcinationꢀtemperatures,ꢀtheꢀCu /Cu ꢀ
ratiosꢀ (Tableꢀ 2)ꢀ firstꢀ increaseꢀ thenꢀ decreaseꢀ withꢀ increasingꢀ
calcinationꢀ temperature.ꢀ Theꢀ methanolꢀ selectivityꢀ exhibitꢀ aꢀ
5
5
5
55
25
+
0
similarꢀ trend,ꢀ furtherꢀ verifyingꢀ thatꢀ theꢀ Cu /Cu ꢀ valueꢀ hasꢀ aꢀ
closeꢀ relationshipꢀ withꢀ methanolꢀ selectivity.ꢀ Overall,ꢀ aꢀ highꢀ
2
+
0
valueꢀofꢀCu /Cu ꢀachievedꢀbyꢀselectingꢀanꢀappropriateꢀcalcina‐
tionꢀtemperatureꢀisꢀbeneficialꢀforꢀtheꢀsynthesisꢀofꢀmethanol.ꢀ ꢀ
2
0
5
20
15
1
4.ꢀ ꢀ Conclusionsꢀ ꢀ
0
100 200 300 400 500 600 700 800 900 1000
Reaction time (h)
Cu/Zn/Al/Zrꢀ catalystsꢀ preparedꢀ byꢀ aꢀ liquidꢀ reductionꢀ
methodꢀwereꢀfoundꢀtoꢀcontainꢀthreeꢀCuꢀvalencesꢀ(Cu ,ꢀCu ꢀandꢀ
Fig.ꢀ8.ꢀLong‐termꢀstabilityꢀtestꢀdataꢀforꢀtheꢀCZAZ‐573ꢀcatalystꢀoverꢀ1000
h.ꢀReactionꢀconditions:ꢀPꢀ=ꢀ5.0ꢀMPa,ꢀn(H ):n(CO )ꢀ=ꢀ3:1,ꢀTꢀ=ꢀ523ꢀK,ꢀGHSV
2+
+
2
2
0
+
−
1
Cu ),ꢀ althoughꢀ Cu ꢀ wasꢀ theꢀ predominantꢀ copperꢀ speciesꢀ de‐
=
ꢀ4600ꢀh .ꢀ

724ꢀ
XiaosuꢀDongꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725ꢀ
tectableꢀonꢀtheꢀsurfaceꢀofꢀtheꢀprecursor.ꢀTheꢀcalcinationꢀtem‐
peratureꢀ hadꢀ aꢀ significantꢀ impactꢀ onꢀ theꢀ physicochemicalꢀ
properties.ꢀ Withꢀ increasingꢀ temperature,ꢀ theꢀ specificꢀ surfaceꢀ
areaꢀasꢀwellꢀasꢀtheꢀamountꢀofꢀbasicꢀsitesꢀdecreasedꢀwhileꢀtheꢀCuꢀ
particleꢀsizeꢀincreased,ꢀdueꢀtoꢀhigherꢀratesꢀofꢀCuꢀaggregation.ꢀ
Furthermore,ꢀcalcinationꢀtemperatureꢀwasꢀfoundꢀtoꢀaffectꢀtheꢀ
surfaceꢀdistributionꢀandꢀinteractionꢀofꢀCuꢀspecies,ꢀthusꢀleadingꢀ
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[
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+
0
toꢀsignificantꢀdifferencesꢀinꢀreducibilityꢀandꢀtheꢀCu /Cu ꢀvalue.ꢀ
TheseꢀCu/Zn/Al/Zrꢀcatalystsꢀgeneratedꢀatꢀdifferentꢀcalcinationꢀ
[
2016,ꢀ37,ꢀ484−493.ꢀ
temperaturesꢀ wereꢀ assessedꢀ duringꢀ CO
2
ꢀ hydrogenationꢀ toꢀ
[17] Z.ꢀL.ꢀYuan,ꢀL.ꢀN.ꢀWang,ꢀJ.ꢀH.ꢀWang,ꢀS.ꢀX.ꢀXia,ꢀP.ꢀChen,ꢀZ.ꢀY.ꢀHou,ꢀX.ꢀM.ꢀ
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AꢀCO2ꢀconversionꢀofꢀ24.5%ꢀwasꢀobtainedꢀalongꢀwithꢀaꢀmethanolꢀ
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exhibitedꢀ higherꢀ activityꢀ thanꢀ aꢀ cCZAZ‐573ꢀ sampleꢀ obtainedꢀ
usingꢀ co‐precipitation,ꢀ especiallyꢀ withꢀ regardꢀ toꢀ methanolꢀ se‐
[
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[
[
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CO ꢀhydrogenationꢀtoꢀmethanolꢀoverꢀCu/Zn/Al/Zrꢀcatalystsꢀpreparedꢀbyꢀ ꢀ
2
Calcination temperature (K)
73
liquidꢀreductionꢀ
5
ꢀ
XiaosuꢀDong,ꢀFengꢀLi*,ꢀNingꢀZhao,ꢀYishengꢀTan,ꢀJunweiꢀWang,ꢀFukuiꢀXiaoꢀ
InstituteꢀofꢀCoalꢀChemistry,ꢀChineseꢀAcademyꢀofꢀSciences;ꢀ ꢀ
UniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences;ꢀ ꢀ
NationalꢀEngineeringꢀResearchꢀCenterꢀforꢀCoal‐basedꢀSynthesisꢀ
Cu+
ꢀ
ꢀ
2+
+
0
Cu/Zn/Al/ZrꢀcatalystsꢀcontainingꢀCu ,ꢀCu ꢀandꢀCu ꢀwereꢀpreparedꢀviaꢀaꢀliquidꢀre‐
ductionꢀmethodꢀandꢀthenꢀcalcinedꢀatꢀdifferentꢀtemperatures.ꢀTheseꢀmaterialsꢀwereꢀ
Cu/Zn/Al/Zr catalyst
subsequentlyꢀappliedꢀtoꢀtheꢀsynthesisꢀofꢀmethanolꢀbyꢀtheꢀhydrogenationꢀofꢀCO
assessꢀtheꢀeffectsꢀofꢀvaryingꢀtheꢀcalcinationꢀtemperature.ꢀ
2
ꢀtoꢀ
CO +3H
2
2

ꢀ
XiaosuꢀDongꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ717–725ꢀ
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