Influence of supports for selective production of 2,5-dimethylfuran via bimetallic copper-cobalt catalyzed 5-hydroxymethylfurfural hydrogenolysis

Article abstract of DOI:10.1016/S1872-2067(17)62789-X

The hydrogenolysis of carbon–oxygen bonds is an important model reaction in upgrading biomass-derived furanic compounds to transportation fuels. One of these model reactions, namely conversion of 5-hydroxymethylfurfural (HMF) to the gasoline additive 2,5-dimethylfuran (DMF), is especially attractive. In this study, bimetallic Cu-Co catalysts supported on CeO₂, ZrO₂, and Al₂O₃ were used for the selective hydrogenolysis of HMF to DMF. The structures of the fresh and used catalysts were studied using X-ray diffraction, the Brunauer-Emmett-Teller method, transmission electron microscopy, temperature-programmed reduction by H₂, temperature-programmed desorption of NH₃, and CHNS analysis. The structures were correlated with the catalytic activities. The Cu-Co/CeO₂ catalyst produced mainly 2,5-bis(hydroxymethyl)furan via reduction of C=O bonds on large Cu particles. The Cu-Co/Al₂O₃ catalyst gave the best selectivity for DMF, as a result of a combination of highly dispersed Cu, mixed copper–cobalt oxides, and suitable weak acidic sites. Cu-Co/ZrO₂ had low selectivity for DMF and produced a combination of various over-hydrogenolysis products, including 2,5-dimethyltetrahydrofuran and 5,5-oxybis(methylene)-bis(2-methylfuran), because of the presence of strong acidic sites. The reaction pathways and effects of various operating parameters, namely temperature, H₂ pressure, and time, were studied to enable optimization of the selective conversion of HMF to DMF over the Cu-Co/Al₂O₃ catalyst.

Full text of DOI:10.1016/S1872-2067(17)62789-X

ChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
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
ꢀ
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
Influenceꢀofꢀsupportsꢀforꢀselectiveꢀproductionꢀofꢀ2,5‐dimethylfuranꢀ
viaꢀbimetallicꢀcopper‐cobaltꢀcatalyzedꢀ5‐hydroxymethylfurfuralꢀ ꢀ
hydrogenolysisꢀ
SanjayꢀSrivastava,ꢀG.ꢀC.ꢀJadeja,ꢀJigishaꢀParikhꢀ*
ꢀ
DepartmentꢀofꢀChemicalꢀEngineering,ꢀSardarꢀVallabhbhaiꢀNationalꢀInstituteꢀofꢀTechnology,ꢀSurat‐395007,ꢀGujarat,ꢀIndiaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Theꢀ hydrogenolysisꢀ ofꢀ carbon–oxygenꢀ bondsꢀ isꢀ anꢀ importantꢀ modelꢀ reactionꢀ inꢀ upgradingꢀ bio‐
mass‐derivedꢀ furanicꢀ compoundsꢀ toꢀ transportationꢀ fuels.ꢀ Oneꢀ ofꢀ theseꢀ modelꢀ reactions,ꢀ namelyꢀ
conversionꢀofꢀ5‐hydroxymethylfurfuralꢀ(HMF)ꢀtoꢀtheꢀgasolineꢀadditiveꢀ2,5‐dimethylfuranꢀ(DMF),ꢀisꢀ
Receivedꢀ16ꢀDecemberꢀ2016ꢀ
Acceptedꢀ10ꢀJanuaryꢀ2017ꢀ
Publishedꢀ5ꢀAprilꢀ2017ꢀ
especiallyꢀattractive.ꢀInꢀthisꢀstudy,ꢀbimetallicꢀCu‐CoꢀcatalystsꢀsupportedꢀonꢀCeO
,ꢀZrO ,ꢀandꢀ Al O
2 2 2 3ꢀ
wereꢀusedꢀforꢀtheꢀselectiveꢀhydrogenolysisꢀofꢀHMFꢀtoꢀDMF.ꢀTheꢀstructuresꢀofꢀtheꢀfreshꢀandꢀusedꢀ
catalystsꢀwereꢀstudiedꢀusingꢀX‐rayꢀdiffraction,ꢀtheꢀBrunauer‐Emmett‐Tellerꢀmethod,ꢀtransmissionꢀ
Keywords:ꢀ
electronꢀ microscopy,ꢀ temperature‐programmedꢀ reductionꢀ byꢀ H
sorptionꢀofꢀNH ,ꢀandꢀCHNSꢀanalysis.ꢀTheꢀstructuresꢀwereꢀcorrelatedꢀwithꢀtheꢀcatalyticꢀactivities.ꢀTheꢀ
Cu‐Co/CeO ꢀcatalystꢀproducedꢀmainlyꢀ2,5‐bis(hydroxymethyl)furanꢀviaꢀreductionꢀofꢀC=Oꢀbondsꢀonꢀ
largeꢀCuꢀparticles.ꢀTheꢀCu‐Co/Al ꢀcatalystꢀgaveꢀtheꢀbestꢀselectivityꢀforꢀDMF,ꢀasꢀaꢀresultꢀofꢀaꢀcombi‐
nationꢀ ofꢀ highlyꢀ dispersedꢀ Cu,ꢀ mixedꢀ copper–cobaltꢀ oxides,ꢀ andꢀ suitableꢀ weakꢀ acidicꢀ sites.ꢀ
Cu‐Co/ZrO hadꢀ lowꢀ selectivityꢀ forꢀ DMFꢀ andꢀ producedꢀ aꢀ combinationꢀ ofꢀ variousꢀ
2
,ꢀ temperature‐programmedꢀ de‐
5‐Hydroxymethylfurfuralꢀ
3
Hydrogenationꢀ
Hydrogenolysisꢀ
Copper‐cobaltꢀ
Bimetallicꢀ
2
O
2 3
2
ꢀ
Biofuels
over‐hydrogenolysisꢀproducts,ꢀincludingꢀ2,5‐dimethyltetrahydrofuranꢀandꢀ5,5‐oxybis(methylene)‐
bis(2‐methylfuran),ꢀbecauseꢀofꢀtheꢀpresenceꢀofꢀstrongꢀacidicꢀsites.ꢀTheꢀreactionꢀpathwaysꢀandꢀeffectsꢀ
2
ofꢀvariousꢀoperatingꢀparameters,ꢀnamelyꢀtemperature,ꢀH ꢀpressure,ꢀandꢀtime,ꢀwereꢀstudiedꢀtoꢀena‐
bleꢀoptimizationꢀofꢀtheꢀselectiveꢀconversionꢀofꢀHMFꢀtoꢀDMFꢀoverꢀtheꢀCu‐Co/Al
2 3
O ꢀcatalyst.ꢀ
©ꢀ2017,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1.ꢀ ꢀ Introductionꢀ
2‐methyltetrahydrofuran,ꢀ pentane,ꢀ andꢀ 2,5‐dimethylfuranꢀ
(
DMF)ꢀ [3–6].ꢀ HMFꢀ isꢀ aꢀ valuableꢀ chemicalꢀ becauseꢀ itꢀ canꢀ beꢀ
convertedꢀ toꢀ aꢀ varietyꢀ ofꢀ chemicalsꢀ suchꢀ asꢀ
2,5‐bis(hydroxymethyl)furanꢀ (BHMF),ꢀ 2‐hydroxymethyl‐
5‐methylfuranꢀ(5‐MFOL),ꢀDMF,ꢀandꢀ2,5‐dimethyltetrahydrofu‐
ranꢀ (DMTHF)ꢀ (Schemeꢀ 1)ꢀ [7–9].ꢀ DMFꢀ isꢀ anꢀ importantꢀ com‐
poundꢀbecauseꢀitꢀhasꢀpotentialꢀuseꢀinꢀgasolineꢀblendsꢀandꢀcanꢀ
beꢀ convertedꢀ toꢀ p‐xyleneꢀ throughꢀ aꢀ Diels‐Alderꢀ reactionꢀ withꢀ
ethyleneꢀ[10–12].ꢀ ꢀ
Energyꢀ crises,ꢀ depletionꢀ ofꢀ fossilꢀ fuelꢀ reserves,ꢀ andꢀ globalꢀ
warmingꢀhaveꢀincreasedꢀinterestꢀinꢀtheꢀproductionꢀofꢀbiobasedꢀ
materialsꢀ[1].ꢀInꢀconfrontingꢀtheseꢀchallenges,ꢀbiorefinedꢀmate‐
rialsꢀ haveꢀ emergedꢀ asꢀ anꢀ alternativeꢀ toꢀ industrialꢀ carbon.ꢀ Inꢀ
biorefining,ꢀ lignocellulosicꢀ biomassꢀ isꢀ transformedꢀ intoꢀ val‐
ue‐addedꢀ chemicalsꢀ andꢀ fuelsꢀ [2].ꢀ Theꢀ hydrogena‐
tion/hydrogenolysisꢀ ofꢀ furansꢀ suchꢀ asꢀ furfuralꢀ (FAL)ꢀ andꢀ
ꢀ
ꢀ
5
‐hydroxymethylfurfuralꢀ (HMF)ꢀ hasꢀ beenꢀ widelyꢀ studiedꢀ forꢀ
Preciousꢀ metals,ꢀ i.e.ꢀ Pt,ꢀ Pd,ꢀ Rh,ꢀ Ru,ꢀ andꢀ Au,ꢀ areꢀ theꢀ mainꢀ
metalsꢀ withꢀ potentialꢀ usesꢀ inꢀ theꢀ hydrogenationꢀ ofꢀ HMFꢀ toꢀ
theꢀproductionꢀofꢀbiobasedꢀfuelsꢀsuchꢀasꢀ2‐methylfuranꢀ(2‐MF),ꢀ
*ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+91‐261‐2251689;ꢀE‐mail:ꢀjk_parikh@yahoo.co.inꢀ
DOI:ꢀ10.1016/S1872‐2067(17)62789‐Xꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ38,ꢀNo.ꢀ4,ꢀAprilꢀ2017ꢀ ꢀ ꢀ

700ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
DMF;ꢀPdꢀandꢀRuꢀhaveꢀbeenꢀreportedꢀtoꢀgiveꢀtheꢀbestꢀselectivi‐
tiesꢀ forꢀ DMFꢀ [9,13–17].ꢀ Theꢀ firstꢀ reportedꢀ catalystꢀ forꢀ hydro‐
genationꢀofꢀHMFꢀtoꢀDMFꢀwasꢀCuRu/C,ꢀwhichꢀgaveꢀ71%ꢀyieldsꢀofꢀ
DMFꢀ fromꢀ twoꢀ differentꢀ startingꢀ materialsꢀ [9,18].ꢀ Itꢀ wasꢀ re‐
portedꢀ thatꢀ theꢀ activityꢀ ofꢀ thisꢀ catalystꢀ graduallyꢀ decreasedꢀ
becauseꢀofꢀdeactivationꢀofꢀactiveꢀcentresꢀand/orꢀtheꢀpresenceꢀofꢀ
chlorideꢀionsꢀ[9].ꢀThananatthanachonꢀandꢀRauchfussꢀreportedꢀ
theꢀ conversionꢀ ofꢀ HMFꢀ toꢀ DMFꢀ usingꢀ Pd/Cꢀ asꢀ aꢀ catalystꢀ andꢀ
formicꢀacidꢀasꢀanꢀadditiveꢀ[8].ꢀAnꢀexcellentꢀyield,ꢀi.e.ꢀ93%,ꢀwithꢀ
thereforeꢀbeꢀeffectiveꢀinꢀtheꢀproductionꢀofꢀDMFꢀbyꢀhydrogena‐
tion/hydrogenolysisꢀofꢀHMF.ꢀInꢀourꢀpreviousꢀwork,ꢀweꢀhydro‐
genatedꢀFALꢀtoꢀ2‐MFꢀoverꢀbimetallicꢀCu‐Coꢀcatalystsꢀsupportedꢀ
onꢀ SiO
2
,ꢀ H‐ZSM‐5,ꢀ andꢀ Al
2
O
3
ꢀ [29].ꢀ Cu‐Co/Al
2
O ꢀ wasꢀ theꢀ bestꢀ
3
hydrogenolysisꢀ catalystꢀ becauseꢀ ofꢀ theꢀ presenceꢀ ofꢀ smallꢀ Cuꢀ
particlesꢀ andꢀ Cu–Coxꢀmixedꢀphases,ꢀandꢀsynergiesꢀamongꢀCu,ꢀ
Co,ꢀandꢀAl
Theꢀpresentꢀworkꢀwasꢀundertakenꢀbasedꢀonꢀtheꢀbackgroundꢀ
describedꢀ above.ꢀ Inꢀ thisꢀ study,ꢀ insteadꢀ ofꢀ usingꢀ SiO ꢀ andꢀ
H‐ZSM‐5ꢀ asꢀ supports,ꢀ materialsꢀ whichꢀ stabilizeꢀ metalꢀ disper‐
sionꢀ andꢀ improveꢀ oxygenꢀ storageꢀ (e.g.ꢀ CeO ꢀ andꢀ ZrO )ꢀ wereꢀ
examinedꢀandꢀcomparedꢀwithꢀAl ꢀasꢀsupportsꢀforꢀCu‐Coꢀbi‐
2 3
O .ꢀ ꢀ
2
9
9%ꢀHMFꢀconversionꢀwasꢀachieved,ꢀbutꢀonlyꢀwhenꢀformicꢀacidꢀ
andꢀH
SO ꢀwereꢀused.ꢀHowever,ꢀbecauseꢀofꢀtheirꢀhighlyꢀcorro‐
siveꢀnatureꢀandꢀenvironmentalꢀconcerns,ꢀtheꢀuseꢀofꢀbothꢀformicꢀ
acidꢀandꢀH SO ꢀisꢀrestricted.ꢀLuijkxꢀetꢀal.ꢀ[19]ꢀusedꢀaꢀcombina‐
2
4
2
2
O
2 3
2
4
metallicꢀcatalysts.ꢀTheꢀstructuresꢀofꢀtheseꢀsynthesizedꢀcatalystsꢀ
wereꢀ studiedꢀ usingꢀ X‐rayꢀ diffractionꢀ (XRD),ꢀ theꢀ Brunau‐
er–Emmett–Tellerꢀ (BET)ꢀ method,ꢀ transmissionꢀ electronꢀ mi‐
tionꢀofꢀPd/CꢀandꢀHClꢀtoꢀreduceꢀHMFꢀtoꢀDMF;ꢀTheꢀresultsꢀwereꢀ
similarꢀtoꢀthoseꢀreportedꢀbyꢀRauchfussꢀetꢀal.ꢀ[8].ꢀZuꢀetꢀal.ꢀ[15]ꢀ
usedꢀRu/Co
toꢀDMFꢀatꢀ130ꢀ°Cꢀandꢀ0.7ꢀMPa;ꢀtheyꢀclearlyꢀidentifiedꢀtheꢀrolesꢀ
ofꢀ Ruꢀ andꢀ CoO ,ꢀ whichꢀ areꢀ responsibleꢀ forꢀ reductionꢀ andꢀ hy‐
drogenolysisꢀofꢀcarbonylꢀandꢀhydroxylꢀgroups,ꢀrespectively.ꢀ
Becauseꢀofꢀtheꢀhighꢀcostꢀofꢀnobleꢀmetals,ꢀresearchꢀonꢀpre‐
cious‐metal‐freeꢀcatalystsꢀwhichꢀcanꢀeffectivelyꢀconvertꢀHMFꢀtoꢀ
DMFꢀisꢀneeded.ꢀYangꢀetꢀal.ꢀ[20]ꢀobtainedꢀaꢀ76%ꢀyieldꢀofꢀDMFꢀ
3
O
4
ꢀasꢀaꢀcatalystꢀforꢀtheꢀselectiveꢀconversionꢀofꢀHMFꢀ
croscopyꢀ(TEM),ꢀtemperature‐programmedꢀdesorptionꢀofꢀNH
(NH ‐TPD),ꢀ temperature‐programmedꢀ reductionꢀ byꢀ
(H
theseꢀcatalystsꢀinꢀtheꢀhydrogenolysisꢀofꢀHMFꢀtoꢀDMFꢀwereꢀin‐
vestigated.ꢀCu‐Co/Al ꢀcatalystsꢀwereꢀbestꢀforꢀtheꢀhydrogen‐
olysisꢀ ofꢀ biomass‐derivedꢀ HMFꢀ toꢀ DMF;ꢀ DMFꢀ wasꢀ selectivelyꢀ
obtainedꢀinꢀ78%ꢀyieldꢀunderꢀmildꢀconditions.ꢀTheꢀHMFꢀconver‐
sionꢀandꢀDMFꢀselectivityꢀwereꢀoptimizedꢀbasedꢀonꢀtheꢀreactionꢀ
pathwaysꢀandꢀeffectsꢀofꢀtheꢀreactionꢀparameters,ꢀnamelyꢀtem‐
3
ꢀ
3
H
2
ꢀ
x
2
‐TPR),ꢀandꢀCHNSꢀanalysis.ꢀTheꢀactivitiesꢀandꢀselectivitiesꢀofꢀ
O
2 3
overꢀNi/Co
toꢀthoseꢀ reportedꢀ forꢀRuꢀ andꢀ CoO
Cu–Znꢀ alloy,ꢀ Cu/MgO/Al ,ꢀ Ru‐modifiedꢀ Cu/MgO/Al
3
O
4
ꢀcatalysts;ꢀtheꢀrolesꢀofꢀNiꢀandꢀCoO
ꢀ byꢀ Zuꢀ etꢀ al.ꢀ [15].ꢀ Cu/ZnO,ꢀ
,ꢀ andꢀ
x
ꢀwereꢀsimilarꢀ
x
O
2 3
O
2 3
perature,ꢀH ꢀpressure,ꢀandꢀtime.ꢀ ꢀ
2
Cu–PMOꢀcatalystsꢀhaveꢀbeenꢀexaminedꢀinꢀtheꢀhydrogenationꢀofꢀ
HMFꢀtoꢀDHMFꢀandꢀDMFꢀ[21–23].ꢀHowever,ꢀtheꢀdevelopmentꢀofꢀ
low‐costꢀandꢀenvironmentallyꢀbenignꢀrobustꢀcatalyticꢀsystemsꢀ
forꢀthisꢀreactionꢀisꢀstillꢀinꢀprogress.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2.1.ꢀ ꢀ Materialsꢀ ꢀ
Recently,ꢀ supportedꢀ bimetallicꢀ Cu‐Coꢀ nanoclustersꢀ haveꢀ
emergedꢀ asꢀ versatileꢀ catalyticꢀ systemsꢀ forꢀ hydrogena‐
tion/hydrogenolysisꢀ reactionsꢀ becauseꢀ ofꢀ theꢀ presenceꢀ ofꢀ
Tetrahydrofuranꢀ(THF),ꢀHMF,ꢀandꢀallꢀtheꢀproductsꢀshownꢀinꢀ
Schemeꢀ1ꢀ(allꢀGCꢀgrade)ꢀwereꢀpurchasedꢀfromꢀSigma‐Aldrich,ꢀ
Cu(0),ꢀ CoO
beenꢀreportedꢀthatꢀearly‐transition‐metalꢀoxidesꢀsuchꢀasꢀCoO
ReO ,ꢀ andꢀ MoO ꢀ canꢀ effectivelyꢀ splitꢀ C–Oꢀ andꢀ O–Hꢀ bondsꢀ
15,19,35,36].ꢀ Aꢀ combinationꢀ ofꢀ Cuꢀ metalꢀ andꢀ CoO ꢀ couldꢀ
x
ꢀ species,ꢀ andꢀ mixedꢀ oxideꢀ phasesꢀ [24–34].ꢀ Itꢀ hasꢀ
Mumbai,ꢀIndia.ꢀTheꢀsupports,ꢀi.e.ꢀCeO
99%),ꢀwereꢀpurchasedꢀfromꢀSterlingꢀChemicalꢀPvt.,ꢀLtd.,ꢀSurat,ꢀ
India.ꢀBimetallicꢀCu‐CoꢀcatalystsꢀwithꢀCu:Coꢀmolarꢀratiosꢀofꢀ1,ꢀ2,ꢀ
2
,ꢀZrO
2
,ꢀandꢀAl O3ꢀ(purityꢀ
2
x
,ꢀ
x
x
[
x
andꢀ 4ꢀ wereꢀ synthesizedꢀ onꢀ CeO
2
,ꢀ ZrO
2
,ꢀ andꢀ Al
2 3
O ꢀ atꢀ fixedꢀ Cuꢀ
O
O
O
5
,5-OBMB-2MF
O
O
+
H
2
2
O
-
H
5
-MF
O
-
H
OH
+
H2
O
HO
O
O
O
O
HMF
O
5-MFOL
DMF
DMTHF
-
H
2
+
H2
O
HO
OH
BHMF
Schemeꢀ1.ꢀReactionꢀpathwayꢀinꢀDMFꢀsynthesisꢀfromꢀHMF.ꢀ

ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
701ꢀ
loadingsꢀofꢀ10ꢀwt%ꢀbyꢀimpregnationꢀwithꢀaqueousꢀsolutionsꢀofꢀ
Co(NO ·6H OꢀandꢀCu(NO ·6H O.ꢀDetailsꢀofꢀtheꢀsynthesisꢀandꢀ
)
3 2
2
)
3 2
2
i
characterizationꢀofꢀtheꢀsupportedꢀbimetallicꢀCu‐Coꢀcatalystsꢀareꢀ
availableꢀelsewhereꢀ[29].ꢀ
h
g
f
e
2
.2.ꢀ ꢀ Catalyticꢀactivityꢀstudyꢀ
d
c
b
Hydrogenationꢀ ofꢀ HMFꢀ wasꢀ performedꢀ inꢀ aꢀ 100‐mLꢀ auto‐
claveꢀ reactorꢀ (Amarꢀ Equipmentꢀ Pvt.,ꢀ Ltd.,ꢀ Mumbai,ꢀ India).ꢀ
Briefly,ꢀtheꢀcatalystꢀ(0.5ꢀg)ꢀwasꢀreducedꢀatꢀ280ꢀ±ꢀ2ꢀ°CꢀinꢀaꢀH
flowꢀatꢀ1ꢀMPaꢀforꢀ3ꢀh.ꢀTheꢀreactorꢀwasꢀcooledꢀtoꢀroomꢀtemper‐
atureꢀandꢀflushedꢀwithꢀN .ꢀTheꢀreactorꢀwasꢀchargedꢀwithꢀHMFꢀ
2.5ꢀmmol)ꢀinꢀTHFꢀ(20ꢀmL).ꢀTheꢀcatalyticꢀactivitiesꢀofꢀtheꢀpre‐
paredꢀ catalystsꢀ wereꢀ investigatedꢀ atꢀ 160–230ꢀ °Cꢀ underꢀ aꢀ H
2
ꢀ
a
2
(
Al O3
2
2
ꢀ
ZrO2
CeO2
70
pressureꢀ ofꢀ 3.0ꢀ MPaꢀ withꢀ stirringꢀ atꢀ 1000ꢀ r/min.ꢀ Theꢀ repro‐
ducibilityꢀofꢀeachꢀreactionꢀwasꢀcheckedꢀbyꢀrepeatingꢀitꢀtwice.ꢀ
ProductꢀsamplesꢀwereꢀanalysedꢀusingꢀaꢀSigmaꢀGCꢀsystemꢀwithꢀaꢀ
flameꢀ ionizationꢀ detectorꢀ (FID).ꢀ Anꢀ AB‐5ꢀ capillaryꢀ columnꢀ ofꢀ
dimensionsꢀ30ꢀmꢀ×ꢀ0.25ꢀmmꢀ×ꢀ0.5ꢀμmꢀwasꢀused.ꢀInꢀaꢀtypicalꢀ
procedure,ꢀtheꢀinitialꢀovenꢀtemperatureꢀwasꢀheldꢀatꢀ50ꢀ°Cꢀforꢀ2ꢀ
minꢀandꢀincreasedꢀtoꢀ300ꢀ°Cꢀatꢀaꢀrampingꢀrateꢀofꢀ10ꢀ°C/minꢀandꢀ
heldꢀforꢀ2ꢀmin.ꢀTheꢀproductꢀsuspensionꢀ(1ꢀμL)ꢀwasꢀinjectedꢀintoꢀ
2
0
30
40
50
60
80
o
2
/( )
Fig.ꢀ1.ꢀWideꢀangleꢀXRDꢀpatternsꢀofꢀsupportsꢀCeO
metallicꢀCuꢀ(10ꢀwt%)ꢀ(a,ꢀc,ꢀe)ꢀandꢀCoꢀ(10wt%)ꢀ(b,ꢀd,ꢀf)ꢀsupportedꢀonꢀ
CeO ,ꢀZrO ꢀandꢀAl ꢀrespectively,ꢀandꢀbimetallicꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀ(g,ꢀh
i)ꢀcatalystsꢀsupportedꢀonꢀCeO ,ꢀZrO ꢀandꢀAl ꢀrespectively,ꢀcalcinedꢀatꢀ
50ꢀ°C.ꢀ
2
,ꢀZrO
2
,ꢀAl
2
O
3
,ꢀmono‐
2
2
O
2 3
theꢀcapillaryꢀcolumnꢀusingꢀaꢀ20:1ꢀsplitꢀratio,ꢀwithꢀN
ꢀasꢀtheꢀcar‐
2
2
2
2
O
3
rierꢀ gas.ꢀ Theꢀ carbonꢀ balanceꢀ wasꢀ calculatedꢀ inꢀ eachꢀ runꢀ byꢀ
measuringꢀtheꢀcarbonꢀinꢀtheꢀliquidꢀphaseꢀusingꢀGC‐FID;ꢀitꢀwasꢀ
foundꢀtoꢀbeꢀ>92%ꢀinꢀeachꢀrunꢀbecauseꢀofꢀunidentifiedꢀproducts.ꢀ
Theꢀunidentifiedꢀproductsꢀwereꢀquantifiedꢀbyꢀsubtractingꢀtheꢀ
overallꢀcarbonꢀbalanceꢀatꢀeachꢀstepꢀfromꢀ100%.ꢀTheꢀfollowingꢀ
equationꢀwasꢀusedꢀtoꢀdetermineꢀtheꢀamountꢀofꢀcarbonꢀinꢀtheꢀ
reactionꢀmixture:ꢀcarbonꢀbalanceꢀ(%)ꢀ=ꢀmolesꢀofꢀcarbonꢀafterꢀ
reactionꢀ(reactantꢀandꢀproducts)/molesꢀofꢀcarbonꢀbeforeꢀreac‐
tionꢀ(reactant)ꢀꢀ100.ꢀ
4
patternsꢀofꢀtheꢀmonometallicꢀCuꢀandꢀCoꢀcatalystsꢀoverꢀallꢀthreeꢀ
supportsꢀshowedꢀdiffractionꢀpeaksꢀfromꢀCuOꢀatꢀ2θꢀ=ꢀ35.5°ꢀandꢀ
38.7°,
monoclinicꢀ copperꢀ oxideꢀ (JCPDSꢀ 80‐1917ꢀ andꢀ 45‐0937),ꢀ andꢀ
fromꢀCo ꢀatꢀ2θꢀ=ꢀ37°,ꢀ44°,ꢀandꢀ56°ꢀ(JCPDSꢀ43‐1003)ꢀ[28,29].ꢀ ꢀ
ꢀ
which areꢀ assignedꢀ toꢀ theꢀ (111)ꢀ andꢀ (111)ꢀ planesꢀ ofꢀ
ꢀ
3 4
O
SpecificꢀXRDꢀpatternsꢀwereꢀobservedꢀforꢀdopedꢀCu‐Coꢀoverꢀ
allꢀ threeꢀ supportsꢀ (Fig.ꢀ 1).ꢀ Forꢀ theꢀ calcinedꢀ catalysts,ꢀ eitherꢀ
segregatedꢀCuOꢀorꢀaꢀspinelꢀoxideꢀconsistingꢀofꢀCo
wasꢀ clearlyꢀ observed.ꢀ Becauseꢀ ofꢀ theirꢀ similarꢀ cubicꢀ frame‐
worksꢀ andꢀ unitꢀ cellꢀ parametersꢀ (Co ,ꢀ aꢀ =ꢀ 8.177ꢀ Åꢀ andꢀ
CuCo ,ꢀaꢀ=ꢀ8.122ꢀÅ),ꢀCo ꢀandꢀCuCo ꢀareꢀnotꢀeasilyꢀdistin‐
guishableꢀ basedꢀ onꢀ theirꢀ XRDꢀ patternsꢀ [29].ꢀ Theꢀ Cu‐Co/CeO
andꢀ Cu‐Co/ZrO2ꢀ catalystsꢀ showedꢀ weakꢀ butꢀ clearꢀ diffractionꢀ
peaksꢀatꢀ2θꢀ=ꢀ35.5°ꢀandꢀ38.7°, whichareꢀassignedꢀtoꢀtheꢀ(111)ꢀ
andꢀ(111)ꢀplanesꢀofꢀmonoclinicꢀcopperꢀoxideꢀ(JCPDSꢀ80‐1917ꢀ
andꢀ45‐0937),ꢀandꢀdiffractionꢀpeaksꢀattributedꢀtoꢀCo ꢀatꢀ2θꢀ=ꢀ
37°,ꢀ44°,ꢀandꢀ56°ꢀ(JCPDSꢀ43‐1003).ꢀForꢀCu‐Co/Al ,ꢀtheꢀweakꢀ
diffractionꢀpeaksꢀatꢀ2θꢀ=ꢀ35.5°ꢀandꢀ38.7°areꢀattributedꢀtoꢀhighlyꢀ
dispersedꢀ Cuꢀ onꢀ porousꢀ Al ꢀ [28,29].ꢀ Theꢀ full‐widthsꢀ atꢀ
half‐maximumꢀ (FWHM)ꢀ ofꢀ theꢀ diffractionꢀ peakꢀ atꢀ 2θꢀ =ꢀ 37°,ꢀ
whichꢀ isꢀ attributedꢀ toꢀ CuCoO ,ꢀ increasedꢀ inꢀ theꢀ orderꢀ CeO2ꢀ<ꢀ
;ꢀthisꢀisꢀbecauseꢀCu‐Co/Al ꢀhasꢀtheꢀsmallestꢀcrys‐
3
O
4
/CuCo
2
O
4
ꢀ
3
.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3 4
O
2 4
O
3.1.ꢀ ꢀ Catalystꢀstructureꢀ ꢀ
2
O
4
O
3 4
2
ꢀ
3.1.1.ꢀ ꢀ XRDꢀresultsꢀ ꢀ
Theꢀeffectsꢀofꢀtheꢀsupportꢀonꢀtheꢀcrystallineꢀphasesꢀofꢀtheꢀ
ꢀ
ꢀ
bimetallicꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀcatalystsꢀwereꢀinvestigatedꢀusingꢀ
XRD.ꢀ Theꢀ XRDꢀ patternsꢀ ofꢀ theꢀ calcinedꢀ andꢀ reducedꢀ catalystsꢀ
3 4
O
areꢀshownꢀinꢀFigs.ꢀ1–3.ꢀTheꢀXRDꢀpatternsꢀofꢀtheꢀZrO
catalystsꢀ showꢀ theꢀ presenceꢀ ofꢀ face‐centredꢀ cubicꢀ (fcc)ꢀ ZrO
andꢀ (fcc)ꢀ CeO ꢀ crystallineꢀ structuresꢀ (Fig.ꢀ 1),ꢀ basedꢀ onꢀ theꢀ
JCPDSꢀfilesꢀ(JCPDSꢀ83‐0936ꢀandꢀJCPDSꢀ81‐0792)ꢀ[37].ꢀHowever,ꢀ
noꢀ(fcc)ꢀstructureꢀwasꢀobservedꢀforꢀAl ;ꢀonlyꢀaꢀweakꢀdiffrac‐
tionꢀpeakꢀatꢀ2θꢀ=ꢀ67°ꢀindicatedꢀtheꢀpresenceꢀofꢀAl .ꢀToꢀgainꢀ
2
ꢀandꢀCeO
2
ꢀ
ꢀ
O
2 3
2
ꢀ
2
O
2 3
O
2 3
4
2
O
3
ZrO2ꢀ<ꢀAl
O
2 3
O
2 3
furtherꢀ insightsꢀ intoꢀ theꢀ effectsꢀ ofꢀ theꢀ supportsꢀ onꢀ activeꢀ siteꢀ
formationꢀ inꢀ theꢀ bimetallicꢀ catalysts,ꢀ weꢀ examinedꢀ theꢀ XRDꢀ
patternsꢀofꢀmonometallicꢀCuꢀ(10ꢀwt%)ꢀandꢀCoꢀ(10ꢀwt%)ꢀonꢀallꢀ
threeꢀ supportsꢀ andꢀ comparedꢀ themꢀ withꢀ theꢀ patternsꢀ ofꢀ theꢀ
bimetallicꢀcounterpartsꢀ(Fig.ꢀ1).ꢀTheꢀintensitiesꢀofꢀtheꢀdiffrac‐
tionꢀpeaksꢀfromꢀallꢀthreeꢀsupportsꢀdecreasedꢀafterꢀdopingꢀwithꢀ
tals.ꢀ ꢀ
Inꢀ theꢀ caseꢀ ofꢀ theꢀ reducedꢀ catalystsꢀ (Fig.ꢀ 2),ꢀ Cu‐Co/ZrO2ꢀ
showedꢀweakꢀdiffractionꢀpeaksꢀfromꢀ(fcc)ꢀCuꢀmetalꢀandꢀCu O.ꢀ
However,ꢀdiffractionꢀpeaksꢀfromꢀ(fcc)ꢀCu Oꢀwereꢀnotꢀobservedꢀ
forꢀ theꢀ otherꢀ twoꢀ catalysts,ꢀ i.e.,ꢀ Cu‐Co/CeO2ꢀandꢀ Cu‐Co/Al ;ꢀ
2
2
O
2 3
theyꢀonlyꢀdisplayedꢀdiffractionꢀpeaksꢀfromꢀ(fcc)ꢀCuꢀmetal.ꢀTheꢀ
10ꢀwt%ꢀCuꢀandꢀ10ꢀwt%ꢀCoꢀinꢀtheꢀmonometallicꢀcatalysts.ꢀTheꢀ
FWHMsꢀofꢀtheꢀstrongestꢀpeak,ꢀatꢀ2θꢀ=ꢀ44.3°,ꢀdecreasedꢀinꢀtheꢀ
intensitiesꢀdecreasedꢀfurtherꢀafterꢀdopingꢀsimultaneouslyꢀwithꢀ
CuꢀandꢀCo.ꢀThisꢀimpliesꢀthatꢀtheꢀcrystallinitiesꢀofꢀtheꢀsupportsꢀ
decreasedꢀ asꢀ aꢀ resultꢀ ofꢀ highꢀ metalꢀ loadings.ꢀ Theꢀ diffractionꢀ
orderꢀofꢀCeO2ꢀ<ꢀZrO2ꢀ<ꢀAl
clesꢀ inꢀ Cu‐Co/Al ꢀ areꢀ smallerꢀ thanꢀ thoseꢀ inꢀ theꢀ otherꢀ twoꢀ
catalysts.ꢀTheꢀsizesꢀofꢀtheꢀCuꢀmetalꢀcrystallitesꢀinꢀtheꢀreducedꢀ
2
O
3
.
ꢀ
Thisꢀconfirmsꢀthatꢀtheꢀmetalꢀparti‐
O
2 3

702ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
o
Cu-Co/Al O3
#
o
2
o
#
#

Co/Al O
o
2
3
o
o
Cu-Co/ZrO2


Cu-Co/Al O
2
3
0
o Cu

Cu O
2
Cu/Al O
0
2
3

Cu
0

Co /CoO
Cu-Co/CeO2
# Co O /CoO
3
4
Al O
2
3
2
0
30
40
o50
/( )
60
70
80
2
20
30
40
50 o
60
70
80
2
/( )
Fig.ꢀ2.ꢀ Wideꢀ angleꢀ XRDꢀ patternsꢀ ofꢀ Cu‐Coꢀ (Cu/Coꢀ =ꢀ 1)ꢀ catalystsꢀ sup‐
portedꢀonꢀCeO ,ꢀZrO ꢀandꢀAl 3ꢀreducedꢀatꢀ280ꢀ°C.ꢀ
2
2
2
O
Fig.ꢀ 3.ꢀ Wideꢀ angleꢀ XRDꢀ patternsꢀ ofꢀ Al
0wt%)ꢀandꢀbimetallicꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀreducedꢀatꢀ280ꢀ°Cꢀforꢀcom‐
parison.ꢀ
2
O ꢀ supportedꢀ monoꢀ (Cuꢀ &ꢀ Co,ꢀ
3
1
catalystsꢀwereꢀcalculatedꢀusingꢀtheꢀScherrerꢀformula,ꢀbasedꢀonꢀ
theꢀCuꢀ(111)ꢀpeakꢀatꢀ2θꢀ=ꢀ44.3°.ꢀTheꢀCeO ‐supportedꢀcatalystꢀ
hadꢀtheꢀlargestꢀCuꢀparticles,ꢀofꢀaverageꢀsizeꢀ25ꢀnm;ꢀtheꢀaverageꢀ
Cuꢀ particleꢀ sizeꢀ forꢀ theꢀ Al ‐supportedꢀ catalystꢀ wasꢀ 15ꢀ nm.ꢀ
Theꢀdifferencesꢀamongꢀtheꢀphasesꢀandꢀcrystalliteꢀsizesꢀobtainedꢀ
withꢀdifferentꢀsupportsꢀcanꢀbeꢀattributedꢀtoꢀtheꢀnatureꢀofꢀtheꢀ
supportsꢀ and/orꢀ metal–supportꢀ interactions.ꢀ Theꢀ oxideꢀ sup‐
portsꢀusedꢀinꢀthisꢀstudyꢀinteractꢀweaklyꢀwithꢀCuꢀandꢀCo,ꢀandꢀtheꢀ
2
area,ꢀporeꢀvolume,ꢀandꢀporeꢀsizeꢀofꢀCeO
andꢀ Coꢀ wereꢀ smallerꢀ thanꢀ thoseꢀ forꢀ theꢀ otherꢀ twoꢀ supports;ꢀ
Al ꢀshowedꢀtheꢀlargestꢀreductionsꢀinꢀsurfaceꢀarea,ꢀporeꢀvol‐
ume,ꢀandꢀporeꢀsize.ꢀTheꢀdifferencesꢀamongꢀtheꢀtexturalꢀproper‐
tiesꢀofꢀtheꢀsynthesizedꢀcatalystsꢀcanꢀbeꢀattributedꢀtoꢀtheꢀnatureꢀ
ofꢀ theꢀ supportsꢀ andꢀ theirꢀ interactionsꢀ withꢀ bothꢀ metals.ꢀ Theꢀ
2
ꢀafterꢀdopingꢀwithꢀCuꢀ
O
2 3
O
2 3
orderꢀofꢀtheꢀinteractionꢀstrengthsꢀisꢀCeO
Theꢀ strongerꢀ interactionsꢀ betweenꢀ bothꢀ theꢀ metalsꢀ andꢀ CeO
producedꢀlargeꢀsegregatedꢀCuOꢀandꢀCo 4ꢀphases,ꢀwhereasꢀtheꢀ
strongꢀinteractionsꢀbetweenꢀcopperꢀandꢀcobaltꢀoxidesꢀandꢀtheirꢀ
weakerꢀinteractionsꢀ withꢀ Al ꢀpromotedꢀformationꢀofꢀmixedꢀ
copper‐cobaltꢀoxides.ꢀToꢀunderstandꢀtheꢀsynergyꢀbetweenꢀCuꢀ
andꢀ Coꢀ overꢀ Al ,ꢀ theꢀ reducedꢀ bimetallicꢀ Cu‐Coꢀ (Cu/Coꢀ =ꢀ 1)ꢀ
catalystꢀwasꢀcomparedꢀwithꢀitsꢀmonometallicꢀcounterparts,ꢀi.e.ꢀ
Cuꢀ (10ꢀ wt%)/Al ꢀ andꢀ Coꢀ (10ꢀ wt%)/Al ꢀ (reducedꢀ atꢀ 280ꢀ
C),ꢀasꢀshownꢀinꢀFig.ꢀ3.ꢀTheꢀmonometallicꢀCuꢀcatalystꢀcontainedꢀ
2
ꢀ>ꢀZrO2ꢀ>ꢀAl
2
O
3
ꢀ[38].ꢀ
smallꢀ declineꢀinꢀtheꢀ poreꢀvolumeꢀ andꢀ poreꢀ sizeꢀofꢀ CeO ꢀafterꢀ
dopingꢀcouldꢀbeꢀtheꢀresultꢀofꢀdepositionꢀofꢀmetalꢀparticlesꢀonꢀ
theꢀ externalꢀ surfaceꢀ ofꢀ theꢀ supportꢀ ratherꢀ thanꢀ inꢀ theꢀ pores.ꢀ
2
2
ꢀ
3
O
However,ꢀ theꢀ Al
2
O ‐supportedꢀ catalystꢀ showedꢀ largeꢀ reduc‐
3
O
2 3
tionsꢀinꢀ poreꢀvolumeꢀ andꢀ poreꢀ size;ꢀthisꢀcanꢀ beꢀ attributedꢀtoꢀ
depositionꢀofꢀmetalꢀparticlesꢀonꢀtheꢀsurfaceꢀandꢀinꢀtheꢀpores.ꢀItꢀ
2
O
3
canꢀbeꢀassumedꢀthatꢀCeO
surfaceꢀbecauseꢀitꢀhasꢀstrongꢀinteractionsꢀwithꢀbothꢀtheꢀmetalsꢀ
usedꢀ inꢀ thisꢀ study.ꢀ However,ꢀ comparedꢀ withꢀ CeO ,ꢀ Al ꢀ hasꢀ
2
ꢀcanꢀstabilizeꢀmetalꢀparticlesꢀonꢀtheꢀ
2
O
3
O
2 3
2
O
2 3
°
weakꢀinteractionꢀwithꢀCuꢀandꢀCo,ꢀandꢀthisꢀmayꢀresultꢀinꢀhighlyꢀ
dispersedꢀmetalꢀparticles.ꢀTheseꢀresultsꢀareꢀinꢀagreementꢀwithꢀ
thoseꢀreportedꢀbyꢀWangꢀetꢀal.ꢀ[39],ꢀwhoꢀsuggestedꢀthatꢀstrongꢀ
interactionsꢀbetweenꢀCuꢀandꢀCoꢀandꢀweakerꢀinteractionsꢀwithꢀ
largeꢀ Cuꢀ crystalsꢀ butꢀ theꢀ monometallicꢀ Coꢀ catalystꢀ containedꢀ
bothꢀoxideꢀandꢀmetallicꢀformsꢀbecauseꢀofꢀtheꢀreducingꢀcondi‐
tionsꢀusedꢀinꢀthisꢀ study.ꢀ Monometallicꢀ Co
aboveꢀ450ꢀ°C.ꢀInꢀcontrastꢀtoꢀtheꢀmonometallicꢀcatalysts,ꢀbime‐
tallicꢀCu‐Co/Al ꢀ(Cu/Coꢀ=ꢀ1)ꢀgaveꢀdiffractionꢀpeaksꢀfromꢀCuꢀ
and/orꢀCoꢀmetalꢀandꢀpartiallyꢀreducedꢀCoO .ꢀTheꢀlowꢀintensitiesꢀ
ofꢀtheꢀdiffractionꢀpeaksꢀfromꢀCuꢀmetalꢀsuggestꢀthatꢀco‐dopingꢀofꢀ
CoꢀandꢀCuꢀonꢀporousꢀAl ꢀsignificantlyꢀdecreasedꢀtheꢀsizeꢀofꢀ
3 4
O ꢀisꢀreducedꢀatꢀorꢀ
Al
2
O
3
ꢀleadꢀtoꢀhighlyꢀdispersedꢀmetalꢀparticlesꢀonꢀporousꢀAl
O .ꢀ
2 3
O
2 3
Thisꢀmayꢀresultꢀinꢀaꢀhighꢀsurfaceꢀareaꢀcomparedꢀwithꢀthoseꢀofꢀ
theꢀotherꢀtwoꢀcatalysts.ꢀ
x
O
2 3
3.1.3.ꢀ ꢀ Morphologyꢀ ꢀ ꢀ
theꢀ metalꢀ crystallites.ꢀ Theꢀ particleꢀ sizeꢀ ofꢀ monometallicꢀ Cu,ꢀ
basedꢀ onꢀ theꢀ peakꢀ atꢀ 44.3°,ꢀ wasꢀ 25–30ꢀ nm.ꢀ However,ꢀ asꢀ re‐
portedꢀearlier,ꢀtheꢀcorrespondingꢀsizeꢀwasꢀ15ꢀnmꢀforꢀbimetallicꢀ
TEMꢀimagesꢀofꢀ freshlyꢀreducedꢀCu‐Coꢀ (Cu/Coꢀ =ꢀ1)ꢀonꢀdif‐
ferentꢀsupportsꢀareꢀshownꢀinꢀFig.ꢀ4.ꢀTheꢀdispersionꢀandꢀmor‐
Tableꢀ1ꢀ
Cu‐Co/Al
agreementꢀwithꢀpreviouslyꢀreportedꢀresultsꢀforꢀCu‐Coꢀcatalystsꢀ
24–34].ꢀ
2
O ꢀ (Cu/Coꢀ =ꢀ 1).ꢀ Theseꢀ observationsꢀ areꢀ inꢀ goodꢀ
3
Texturalꢀ andꢀ structuralꢀ characteristicsꢀ ofꢀ supportsꢀ andꢀ supportedꢀ
Cu‐Coꢀcatalysts.ꢀ
[
Cu:Coꢀa Cu:Coꢀbꢀ
wt%) (wt%)ꢀ
S
ꢀ
V
ꢀ
D
ꢀ
d ꢀ
BET
p
p
p
Samplesꢀ
CeO
Ref.
2
(
(m /g)ꢀ (mL/g)ꢀ (nm) (nm)
112ꢀ
132ꢀ
166.1ꢀ
82.6ꢀ
94.4ꢀ
113.5ꢀ
3.1.2.ꢀ ꢀ Texturalꢀpropertiesꢀ ꢀ
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.28ꢀ 3.2
0.38ꢀ 4.6
0.54ꢀ 6.6
0.18ꢀ 2.6
0.24ꢀ 3.4
0.32ꢀ 4.6
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
TheꢀtexturalꢀpropertiesꢀofꢀtheꢀsupportsꢀandꢀtheꢀCu‐Coꢀcata‐
ZrO
Al
Cu‐Co/ꢀCeO
Cu‐Co/ZrO
2
ꢀ
2 2 2 3
lystsꢀ supportedꢀ byꢀ CeO ,ꢀ ZrO ,ꢀ andꢀ Al O ꢀ areꢀ summarizedꢀ inꢀ
2 3
O ꢀ
[29]
ꢀ
ꢀ
2
10:10 9.2:8.4ꢀ
10:10 10.6:10.2
10:10 10.4:9.9
25ꢀ
20ꢀ
15ꢀ [29]
Tableꢀ1.ꢀBecauseꢀofꢀitsꢀorderedꢀporousꢀstructure,ꢀAl
highestꢀBETꢀsurfaceꢀarea,ꢀi.e.ꢀ166ꢀm /g,ꢀandꢀaꢀporeꢀvolumeꢀofꢀ
2
O ꢀhadꢀtheꢀ
3
2
ꢀ
2
Cu‐Co/ꢀAl
2
O
3
3
2
0
.54ꢀcm /g.ꢀCeO
2
ꢀhadꢀtheꢀlowestꢀBETꢀsurfaceꢀarea,ꢀ(112ꢀm /g)ꢀ
a
ꢀ
Loadingꢀratioꢀusedꢀinꢀtheꢀsynthesis.ꢀ
EvaluatedꢀbyꢀEDXꢀanalysis.ꢀ
3
andꢀ poreꢀ volume,ꢀ (0.28ꢀ cm /g).ꢀ Theꢀ decreasesꢀ inꢀ theꢀ surfaceꢀ
b
ꢀ

ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
703ꢀ
Cu-Co/CeO
2
Cu-CoZrO
2
2 3
Cu-Co/Al O
20 nm
20 nm
20 nm
Fig.ꢀ4.ꢀTEMꢀmicrographsꢀofꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀcatalystsꢀsupportedꢀonꢀCeO
2
ꢀ(a),ꢀZrO
2
ꢀ(b)ꢀandꢀAl
2
O ꢀ(c).ꢀ
3
phology/orderingꢀofꢀtheꢀCu‐Coꢀnanoparticlesꢀonꢀdifferentꢀsup‐
portsꢀvaryꢀdependingꢀonꢀtheꢀnatureꢀofꢀtheꢀsupportꢀandꢀtheꢀdis‐
creteꢀ interactionsꢀ betweenꢀ theꢀ supportꢀ andꢀ bothꢀ Cuꢀ andꢀ Co.ꢀ
Agglomeratedꢀ largeꢀ metalꢀ crystallitesꢀ (25–30ꢀ nm)ꢀ wereꢀ ob‐
peak,ꢀatꢀaroundꢀ400ꢀ°C,ꢀisꢀattributedꢀtoꢀtheꢀreductionꢀofꢀCo
speciesꢀonꢀtheꢀZrO ꢀsurface.ꢀ
Theꢀ TPRꢀ profileꢀ forꢀ Cu‐Co/Al O ꢀ wasꢀ differentꢀ fromꢀ thoseꢀ
forꢀtheꢀotherꢀtwoꢀcatalysts,ꢀandꢀreductionꢀoccurredꢀatꢀaꢀlowerꢀ
temperature;ꢀ thisꢀ isꢀ ascribedꢀ toꢀ theꢀ reductionꢀ ofꢀ mixedꢀ cop‐
per‐cobaltꢀ oxidesꢀ andꢀ smallꢀ Cuꢀ particles.ꢀ Theseꢀ observationsꢀ
areꢀ supportedꢀ byꢀ theꢀ XRDꢀ andꢀ TEMꢀ results.ꢀ Theꢀ presenceꢀ ofꢀ
multipleꢀ reductionꢀ peaksꢀ indicatesꢀ two‐stepꢀ reductionꢀ ofꢀ Cuꢀ
3
O ꢀ
4
2
2
3
servedꢀ inꢀ theꢀ CeO
interactionsꢀ betweenꢀ CeO
lar‐sizedꢀbutꢀsegregated,ꢀnon‐uniformlyꢀ distributedꢀCu‐Coꢀ na‐
noparticlesꢀwereꢀobservedꢀonꢀZrO .ꢀCu‐Co/Al ꢀhadꢀwellꢀdis‐
persed,ꢀordered,ꢀuniformlyꢀsphericalꢀsmallꢀnanoparticles.ꢀTheꢀ
metalꢀ particlesꢀ inꢀ Cu‐Co/Al ꢀ wereꢀ mainlyꢀ ofꢀ uniformꢀ sizeꢀ
aboutꢀ 20ꢀ nm.ꢀ Thisꢀ morphology/orderingꢀ ofꢀ Cu‐Coꢀ nanoparti‐
clesꢀonꢀCeO ,ꢀZrO ,ꢀandꢀAl ꢀcanꢀbeꢀexplainedꢀbasedꢀonꢀaꢀcom‐
2
‐supportedꢀ catalystꢀ becauseꢀ ofꢀ theꢀ strongꢀ
2
ꢀ andꢀ theꢀ metalꢀ particles.ꢀ Simi‐
2
O
2 3
andꢀ partialꢀ reductionꢀ ofꢀ CuCo
threeꢀ supports,ꢀ Al ꢀ hasꢀ theꢀ weakestꢀ interactionsꢀ withꢀ theꢀ
copper‐cobaltꢀoxideꢀphasesꢀandꢀthisꢀenhancesꢀtheꢀreducibilityꢀ
ofꢀtheꢀcopperꢀoxidesꢀandꢀmixedꢀCuCo ,ꢀwhichꢀincreasesꢀtheꢀ
numberꢀofꢀCu–CoO ꢀsitesꢀinꢀCu‐Co/Al .ꢀToꢀclarifyꢀtheꢀeffectꢀofꢀ
synergyꢀ betweenꢀ Cuꢀ andꢀ Coꢀ onꢀ theꢀ reductiveꢀ properties,ꢀ theꢀ
reductionꢀprofilesꢀofꢀmonometallicꢀCuꢀ(10ꢀwt%)/Al ꢀandꢀCoꢀ
(10ꢀ wt%)/Al ꢀ wereꢀ alsoꢀ obtainedꢀ (Fig.ꢀ 5),ꢀ andꢀ comparedꢀ
2 4 3 4
O /Co O ꢀ [16,35].ꢀ Amongꢀ theꢀ
O
2 3
O
2 3
2
2
O
2 3
O
2 4
binationꢀofꢀaꢀporousꢀstructureꢀandꢀmetal‐supportꢀinteractions.ꢀ
Theꢀ moreꢀ uniformꢀ distributionsꢀ ofꢀ Cu‐Coꢀ particlesꢀ onꢀ theꢀ
x
O
2 3
Al
formlyꢀporousꢀAl
thanꢀtheꢀmetal–supportꢀinteractionsꢀinꢀtheꢀotherꢀcasesꢀ[29].ꢀ
2 3
O ꢀsupportꢀcanꢀbeꢀascribedꢀtoꢀtheꢀinteractionsꢀbetweenꢀuni‐
O
2 3
2 3
O ꢀandꢀbothꢀCuꢀandꢀCoꢀspeciesꢀbeingꢀweakerꢀ
O
2 3
withꢀ thoseꢀ ofꢀ theirꢀ bimetallicꢀ counterparts.ꢀ Theꢀ differencesꢀ
amongꢀtheseꢀreductiveꢀbehavioursꢀwereꢀdiscussedꢀatꢀlengthꢀinꢀ
3.1.4.ꢀ ꢀ Reductiveꢀpropertiesꢀ ꢀ
ourꢀ previousꢀ workꢀ [29].ꢀ Tableꢀ 2ꢀ showsꢀ theꢀ experimentalꢀ H ꢀ
2
Theꢀ reductiveꢀ propertiesꢀ ofꢀ Cu‐Co/CeO
2
,ꢀ Cu‐Co/ZrO
2
,ꢀ andꢀ
consumptionsꢀduringꢀTPR.ꢀItꢀcanꢀbeꢀdeducedꢀthatꢀCoꢀandꢀCuꢀareꢀ
bothꢀ essentiallyꢀ completelyꢀ reducedꢀ byꢀ 400ꢀ °Cꢀ onꢀ allꢀ threeꢀ
2 3 2
Cu‐Co/Al O ꢀ wereꢀ investigatedꢀ usingꢀ H ‐TPR.ꢀ Metal‐supportꢀ
interactionsꢀplayꢀaꢀvitalꢀroleꢀinꢀstabilizingꢀandꢀreducingꢀmetalꢀ
oxidesꢀ toꢀ metallicꢀ sites.ꢀ Inꢀ particular,ꢀ forꢀ bimetallicꢀ catalyticꢀ
systems,ꢀtheꢀinteractionsꢀbetweenꢀeachꢀmetalꢀcomponentꢀandꢀ
theꢀ supportꢀ significantlyꢀ affectsꢀ theꢀ chemicalꢀ environmentꢀ ofꢀ
theꢀ metalsꢀ and/orꢀ theꢀ reductionꢀ temperature.ꢀ Weaklyꢀ inter‐
actingꢀ metalꢀ oxideꢀ speciesꢀ areꢀ easilyꢀ reducedꢀ toꢀ theꢀ metallicꢀ
stateꢀ[38].ꢀConversely,ꢀifꢀtheꢀmetalꢀoxidesꢀareꢀstronglyꢀadsorbedꢀ
onꢀtheꢀ support,ꢀtheyꢀ areꢀ difficultꢀtoꢀreduce,ꢀ andꢀthisꢀleadsꢀtoꢀ
incompleteꢀ reductionꢀ andꢀ formationꢀ ofꢀ low‐valenceꢀ metalsꢀ
supports,ꢀ withꢀ Cu‐Co/CeO ꢀ beingꢀ slightlyꢀ lessꢀ reducedꢀ (82%)ꢀ
comparedꢀwithꢀtheꢀotherꢀtwoꢀ(88%ꢀandꢀ96%).ꢀ
2
3.1.5.ꢀ ꢀ Surfaceꢀacidityꢀ ꢀ
Theꢀ surfaceꢀ aciditiesꢀ ofꢀ theꢀ bimetallicꢀ Cu‐Coꢀ (Cu/Coꢀ =ꢀ 1)ꢀ
2 2
catalystsꢀsupportedꢀonꢀCeO ꢀandꢀZrO ꢀwereꢀdeterminedꢀusingꢀ
Co/Al O
2
3
[
37,38].ꢀTheꢀreductiveꢀpropertiesꢀofꢀtheꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀcat‐
alystsꢀ supportedꢀ onꢀ CeO
ꢀ andꢀ ZrO ꢀ wereꢀ determinedꢀ usingꢀ
‐TPRꢀ andꢀ theꢀ profilesꢀ wereꢀ comparedꢀ withꢀ thatꢀ ofꢀ
Cu‐Co/Al ꢀ [29]ꢀ (Fig.ꢀ 5).ꢀ Theꢀ natureꢀ ofꢀ theꢀ supportꢀ signifi‐
2
2
Cu-Co/Al O
2
3
H
2
O
2 3
Cu-Co/ZrO2
cantlyꢀaffectedꢀtheꢀreducibilityꢀofꢀtheꢀbimetallicꢀcatalysts.ꢀTheꢀ
differencesꢀamongꢀtheꢀreductionꢀtemperaturesꢀshowedꢀthatꢀtheꢀ
Cu-Co/CeO2
Cu/Al O
CeO
actionꢀwithꢀbothꢀmetals.ꢀAl
whichꢀwereꢀdeconvolutedꢀtoꢀseveralꢀpeaks.ꢀTheꢀTPRꢀprofileꢀofꢀ
theꢀ ZrO ‐supportedꢀ catalystꢀ showedꢀ threeꢀ majorꢀ reductionꢀ
peaks.ꢀTheꢀfirstꢀpeak,ꢀatꢀ200ꢀ°C,ꢀisꢀattributedꢀtoꢀtheꢀreductionꢀofꢀ
smallꢀCuOꢀparticles,ꢀwhichꢀinteractꢀweaklyꢀwithꢀZrO .ꢀTheꢀsec‐
ondꢀpeak,ꢀatꢀ250–370ꢀ°C,ꢀisꢀascribedꢀtoꢀtheꢀreductionꢀofꢀlargerꢀ
CuOꢀparticles,ꢀ whichꢀareꢀstronglyꢀ attachedꢀtoꢀZrO .ꢀ Theꢀ thirdꢀ
2
ꢀ(broadꢀhumpꢀatꢀ220–370ꢀ°C)ꢀsupportꢀhadꢀstrongerꢀinter‐
2
3
2 3
O ꢀandꢀZrO2ꢀshowedꢀbroadꢀhumpsꢀ
2
1
00
200
300
400
500
600
o
Temperature ( C)
2
Fig.ꢀ5.ꢀ H
2
‐TPRꢀpatternsꢀofꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀcatalystsꢀ supportedꢀonꢀ
ꢀandꢀAl 3ꢀcalcinedꢀatꢀ450ꢀ°C.ꢀ
2
CeO
2
,ꢀZrO
2
2
O

704ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
Tableꢀ2ꢀ
QuantitativeꢀHydrogenꢀconsumptionꢀduringꢀTPR.ꢀ
Cu-Co/ZrO2
Cu/Coꢀaꢀ
ꢀconsumptionꢀ Metalꢀre‐
wt%/wt%)ꢀ (mmol/g.cat)ꢀ ducedꢀ(%)
H
2
Cu-Co/Al O
2
3
Samplesꢀ
Cu‐Co/CeO
Ref.
(
2
ꢀ
ꢀ
1ꢀ
1ꢀ
1ꢀ
32.6ꢀ
44.3ꢀ
53.8ꢀ
82ꢀ
88ꢀ
96ꢀ
—ꢀ
—ꢀ
[29]
Cu‐Co/ZrO
Cu‐Co/Al
2
2
O
3
ꢀ
aꢀLoadingꢀratioꢀusedꢀinꢀtheꢀsynthesis.ꢀ
ꢀ
NH
Cu‐Co/Al
acidicꢀsites,ꢀbasedꢀonꢀtheꢀNH
classifiedꢀasꢀweakꢀ(<ꢀ250ꢀ°C),ꢀmediumꢀ(250–400ꢀ°C),ꢀandꢀstrongꢀ
>ꢀ400ꢀ°C)ꢀacidicꢀsites.ꢀTheꢀoverallꢀacidityꢀofꢀaꢀcatalystꢀcanꢀbeꢀ
calculatedꢀfromꢀtheꢀrelativeꢀpeakꢀareasꢀinꢀtheꢀNH ‐desorptionꢀ
curvesꢀ[29].ꢀCu‐Co/CeO ꢀ(Cu/Coꢀ=ꢀ1)ꢀhadꢀfewꢀweakꢀandꢀstrongꢀ
acidicꢀsites,ꢀandꢀhadꢀonlyꢀmediumꢀacidity.ꢀCu‐Co/Al ꢀ(Cu/Coꢀ
ꢀ1)ꢀshowedꢀthreeꢀpeaksꢀ(atꢀ145,ꢀ335,ꢀandꢀ555ꢀ°C),ꢀwhichꢀcanꢀ
3
‐TPDꢀ andꢀ theꢀ resultsꢀ wereꢀ comparedꢀ withꢀ thoseꢀ forꢀ
ꢀ(Fig.ꢀ6ꢀandꢀTableꢀ3).ꢀGenerally,ꢀtheꢀstrengthsꢀofꢀtheꢀ
ꢀdesorptionꢀtemperature,ꢀcanꢀbeꢀ
Cu-Co/CeO2
O
2 3
3
1
00
200
300
400
500
600
700
(
o
Temperature ( C)
3
Fig.ꢀ 6.ꢀNH
3
‐TPDꢀ patternsꢀofꢀCu‐Coꢀ(Cu/Co=1)ꢀcatalystsꢀsupportedꢀonꢀ
3ꢀcalcinedꢀatꢀ450ꢀ°C.ꢀ
2
CeO ,ꢀZrO ꢀandꢀAl O
2
2
2
O
2 3
=
beꢀascribedꢀtoꢀNH
acidicꢀsites.ꢀCu‐Co/ZrO
1
desorptionꢀbyꢀweakꢀandꢀstrongꢀacidicꢀsitesꢀ(Fig.ꢀ6ꢀandꢀTableꢀ3).ꢀ
Aꢀcomparisonꢀofꢀtheꢀresultsꢀforꢀtheꢀthreeꢀcatalystsꢀshowsꢀthatꢀ
3
ꢀdesorptionꢀfromꢀweak,ꢀmedium,ꢀandꢀstrongꢀ
ꢀ(Cu/Coꢀ=ꢀ1)ꢀshowedꢀtwoꢀpeaksꢀ(minorꢀ
00–250ꢀ°C,ꢀmajorꢀ350–550ꢀ°C),ꢀwhichꢀcanꢀbeꢀascribedꢀtoꢀNH
formanceꢀofꢀtheseꢀcatalystsꢀwithꢀthatꢀofꢀCu‐Co/Al
2
O ꢀ(Cu/Coꢀ=ꢀ
3
2
1)ꢀinꢀtheꢀhydrogenation/hydrogenolysisꢀofꢀHMFꢀtoꢀDMFꢀatꢀ200ꢀ
°Cꢀandꢀ3.0ꢀMPaꢀ(Fig.ꢀ7).ꢀTheꢀsupportꢀplaysꢀaꢀsignificantꢀroleꢀinꢀ
theꢀ selectiveꢀ hydrogenation/hydrogenolysisꢀ ofꢀ HMFꢀ toꢀ DMF.ꢀ
3
ꢀ
Cu‐Co/CeO
sion)ꢀ andꢀ Cu‐Co/Al
(98%ꢀconversion)ꢀinꢀHMFꢀhydrogenation.ꢀTheꢀorderꢀofꢀtheꢀcat‐
alyticꢀactivitiesꢀ wasꢀ CeO ꢀ<ꢀZrO ꢀ<ꢀAl .ꢀHMFꢀcontainsꢀthreeꢀ
2
ꢀshowedꢀtheꢀlowestꢀcatalyticꢀactivityꢀ(78%ꢀconver‐
Cu‐Co/Al
mmol/gꢀcat.ꢀTheꢀorderꢀofꢀtheꢀtotalꢀaciditiesꢀwasꢀAl
CeO .ꢀItꢀisꢀworthꢀnotingꢀthatꢀfiveꢀdifferentꢀtypesꢀofꢀOHꢀgroupsꢀ
areꢀ presentꢀ onꢀ theꢀ surfaceꢀ ofꢀ γ‐Al ,ꢀ givingꢀ aꢀ netꢀ electricꢀ
2 3
O ꢀ (Cu/Coꢀ =ꢀ 1)ꢀ hadꢀ theꢀ maximumꢀ acidity,ꢀ i.e.ꢀ 0.49ꢀ
2 3
O ꢀ showedꢀ theꢀ highestꢀ catalyticꢀ activityꢀ
2 3
O
ꢀ>ꢀZrO ꢀ>ꢀ
2
2
2
2
O
2 3
O
2 3
functionalꢀ groups,ꢀ namelyꢀ C=O,ꢀ O–H,ꢀ andꢀ theꢀ furanꢀ ringꢀ
(Schemeꢀ1).ꢀOverꢀCuꢀcatalysts,ꢀHMFꢀhydrogenationꢀproceedsꢀbyꢀ
reductionꢀofꢀtheꢀC=OꢀbondꢀtoꢀgiveꢀtheꢀdiolꢀintermediateꢀBHMF.ꢀ
FurtherꢀhydrogenolysisꢀofꢀBHMFꢀleadsꢀtoꢀtheꢀformationꢀofꢀDMFꢀ
viaꢀ anotherꢀintermediate,ꢀi.e.ꢀ 5‐MFOLꢀ[20–23].ꢀNagarajaꢀetꢀal.ꢀ
[44]ꢀproposedꢀthatꢀtheꢀpresenceꢀofꢀaꢀlargerꢀamountꢀofꢀmetallicꢀ
CuꢀthanꢀofꢀCuOꢀpromotedꢀreductionꢀofꢀtheꢀC=OꢀbondꢀinꢀFALꢀtoꢀ
giveꢀfurfurylꢀalcohol.ꢀInꢀourꢀpreviousꢀwork,ꢀweꢀalsoꢀobservedꢀ
thatꢀtheꢀconversionꢀofꢀFALꢀtoꢀfurfurylꢀalcoholꢀviaꢀC=Oꢀreductionꢀ
increasedꢀwithꢀincreasingꢀamountꢀofꢀsurfaceꢀmetallicꢀCuꢀ[27].ꢀ
Theꢀactivitiesꢀofꢀallꢀthreeꢀcatalystsꢀusedꢀinꢀthisꢀstudyꢀcanꢀthere‐
foreꢀbeꢀexplainedꢀbasedꢀonꢀ(1)ꢀtheꢀdegreeꢀofꢀreduction,ꢀi.e.ꢀtheꢀ
chargeꢀ(σ),ꢀdependingꢀonꢀtheꢀnumberꢀofꢀAlꢀneighboursꢀandꢀAlꢀ
coordinationꢀ [40,41].ꢀ Theꢀ removalꢀ ofꢀ OHꢀ groupsꢀ duringꢀ
high‐temperatureꢀtreatmentꢀ(calcination)ꢀcreatesꢀunsaturatedꢀ
surfaceꢀcations,ꢀwithꢀmainlyꢀtetrahedrallyꢀ[Al(IV)]ꢀandꢀoctahe‐
drallyꢀ[Al(VI)]ꢀcoordinatedꢀAlꢀ[42,43].ꢀBothꢀLewisꢀandꢀBrønstedꢀ
acidicꢀ sitesꢀ mayꢀ thereforeꢀ beꢀ presentꢀ onꢀ Al
theꢀdegreeꢀofꢀdehydration.ꢀ ꢀ
2
O3,ꢀ dependingꢀonꢀ
3.2.ꢀ ꢀ Catalyticꢀactivityꢀ ꢀ
3.2.1.ꢀ ꢀ CatalystꢀscreeningꢀforꢀHMFꢀhydrogenationꢀtoꢀDMFꢀ
Weꢀ previouslyꢀ reportedꢀ aꢀ liquid‐phaseꢀ hydrogenationꢀ ofꢀ
amountꢀ ofꢀ surfaceꢀ metallicꢀ Cuꢀ species,ꢀ indicatedꢀ byꢀ H
sumptionꢀ duringꢀ TPR,ꢀ andꢀ (2)ꢀ theꢀ numberꢀ ofꢀ copper‐cobaltꢀ
mixedꢀ oxideꢀ sitesꢀ available.ꢀ Cu‐Co/CeO ꢀ gaveꢀ theꢀ lowestꢀ H
consumption,ꢀ andꢀ Cu‐Co/Al ꢀconsumedꢀtheꢀ highestꢀvolumeꢀ
ofꢀH .ꢀ
2
ꢀ con‐
FALꢀtoꢀ2‐MFꢀusingꢀaꢀhighlyꢀefficientꢀnon‐nobleꢀmetal,ꢀenviron‐
mentallyꢀbenign,ꢀbimetallicꢀCu‐Coꢀcatalystꢀ[29].ꢀTheꢀadvantageꢀ
ofꢀthisꢀcatalyticꢀsystem,ꢀwhichꢀwasꢀpreparedꢀusingꢀanꢀimpreg‐
nationꢀ method,ꢀ overꢀ otherꢀ Cu‐basedꢀ catalystsꢀ hasꢀ beenꢀ thor‐
2
2
ꢀ
O
2 3
2
oughlyꢀdiscussed.ꢀInꢀourꢀpreviousꢀwork,ꢀweꢀfoundꢀthatꢀSiO
H‐ZSM‐5ꢀsupportsꢀgaveꢀlowꢀselectivitiesꢀforꢀC–Oꢀhydrogenoly‐
sis.ꢀInꢀthisꢀstudy,ꢀweꢀthereforeꢀusedꢀmaterialsꢀwhichꢀcanꢀstabi‐
2
ꢀandꢀ
Inꢀtermsꢀofꢀproductꢀselectivity,ꢀtheꢀmainꢀcompoundsꢀidenti‐
fiedꢀinꢀtheꢀliquidꢀreactionꢀproductsꢀwereꢀBHMF,ꢀ5‐MF,ꢀ5‐MFOL,ꢀ
andꢀDMF,ꢀoverꢀallꢀthreeꢀcatalysts.ꢀHowever,ꢀtheꢀselectivityꢀforꢀ
theꢀdesiredꢀproductꢀ(DMF)ꢀisꢀaffectedꢀbyꢀtheꢀsupport,ꢀtheꢀsec‐
lizeꢀmetalꢀdispersionꢀandꢀimproveꢀoxygenꢀstorage,ꢀi.e.ꢀCeO ꢀandꢀ
2
ZrO2,ꢀasꢀsupportsꢀforꢀCu‐Coꢀ(Cu/Coꢀ=ꢀ1)ꢀandꢀcomparedꢀtheꢀper‐
2
ondꢀmetal,ꢀorꢀboth.ꢀForꢀexample,ꢀCu‐Co/CeO ꢀgaveꢀtheꢀhighestꢀ
Tableꢀ3ꢀ
2 2 2 3
Acidityꢀofꢀbi‐metallicꢀCu‐CoꢀcatalystsꢀsupportedꢀonꢀCeO ,ꢀZrO ,ꢀandꢀAl O ,ꢀusingꢀammonia‐TPDꢀmethod.ꢀ
Cu/Coꢀ*ꢀ
Samplesꢀ
Amountꢀofꢀammoniaꢀdesorbedꢀ(mmol/g.cat)ꢀ
TotalꢀAcidityꢀ
(mmol/g.cat)ꢀ
Ref.ꢀ
(
wt%/wt%)ꢀ
<200
ꢀ
°Cꢀ
250–450ꢀ°Cꢀ
>450ꢀ°Cꢀ
Cu‐Co/CeO
Cu‐Co/ZrO
Cu‐Co/Al
ꢀLoadingꢀratioꢀusedꢀinꢀtheꢀsynthesis.ꢀ
2
ꢀ
ꢀ
1ꢀ
1ꢀ
1ꢀ
0.03ꢀ
0.08ꢀ
0.13ꢀ
0.18ꢀ
0.04ꢀ
0.21ꢀ
0.04ꢀ
0.28ꢀ
0.14ꢀ
0.25ꢀ
0.40ꢀ
0.49ꢀ
—
—
[29]ꢀ
ꢀ
ꢀ
2
2
O
3
ꢀ
*

ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
705ꢀ
sionꢀbecauseꢀofꢀtheꢀstrongꢀinteractionsꢀbetweenꢀCuꢀandꢀCo.ꢀAꢀ
combinationꢀ ofꢀ Cu–CoO ꢀ wasꢀ foundꢀ toꢀ beꢀ effectiveꢀ inꢀ theꢀ
one‐stepꢀ hydrogenationꢀ ofꢀ FALꢀ toꢀ 2‐MFꢀ viaꢀ reductionꢀ ofꢀ theꢀ
C=OꢀbondꢀfollowedꢀbyꢀC–Oꢀhydrogenolysisꢀ[29].ꢀTheseꢀpreviousꢀ
reportsꢀandꢀtheꢀpresentꢀexperimentalꢀfindingsꢀsuggestꢀthatꢀtheꢀ
improvedꢀdispersionꢀofꢀCuꢀinꢀtheꢀpresenceꢀofꢀCoꢀandꢀtheꢀsyn‐
HMF
IV
I
II
VI
III
Oth
1
00
x
V
8
6
4
2
0
0
0
0
0
ergyꢀbetweenꢀCuꢀandꢀCoO
tionsꢀbetweenꢀCuꢀandꢀCoꢀfacilitateꢀtheꢀhydrogenolysisꢀofꢀHMFꢀ
toꢀDMF.ꢀThisꢀisꢀsupportedꢀbyꢀtheꢀXRD,ꢀBET,ꢀandꢀH ‐TPRꢀresults.ꢀ
MetallicꢀCuꢀandꢀmixedꢀCu‐CoꢀparticlesꢀcanꢀthereforeꢀactivateꢀH
toꢀenableꢀpartialꢀreductionꢀofꢀCo 4,ꢀwhichꢀisꢀdifficultꢀtoꢀreduceꢀ
atꢀlowꢀtemperatures.ꢀThisꢀreducibilityꢀofꢀtheꢀbimetallicꢀcatalystsꢀ
x
ꢀspeciesꢀasꢀaꢀresultꢀofꢀstrongꢀinterac‐
2
2
ꢀ
3
O
isꢀresponsibleꢀforꢀtheꢀenhancedꢀactivityꢀofꢀtheꢀCu‐Co/Al
2
O ꢀcat‐
3
Cu-Co/CeO2
Cu-Co/ZrO2
Catalyst
Cu-Co/Al O
2 3
alyst.ꢀ ꢀ
Cu‐Co/ZrO
producedꢀaꢀcombinationꢀofꢀring‐saturationꢀandꢀover‐
olysisꢀ productsꢀ suchꢀ asꢀ DMTHFꢀ andꢀ otherꢀ by‐products.ꢀ Theꢀ
propertiesꢀofꢀZrO ꢀandꢀtheꢀpresenceꢀofꢀstrongꢀacidicꢀsitesꢀmayꢀ
2
ꢀ hadꢀ lowꢀ selectivityꢀ forꢀ DMFꢀ (aboutꢀ 40%)ꢀ andꢀ
Fig.ꢀ 7.ꢀ Catalyticꢀ activityꢀ forꢀ hydrogenolysisꢀ ofꢀ HMFꢀ overꢀ supported
bi‐metallicꢀcopper‐cobaltꢀcatalyst.ꢀReactionꢀconditions:ꢀ200ꢀ°C,ꢀ3.0ꢀMPa,ꢀ
ꢀ
hydrogen‐
8
(
ꢀ h,ꢀ Catalystꢀ 0.5ꢀ g,ꢀ HMFꢀ 2.5ꢀ mmol,ꢀ THFꢀ 20ꢀ mL.ꢀ I—5‐Methylfurfural
5‐MF),ꢀ II—bis(hydroxymethꢀ yl‐furan)ꢀ (BHMF),ꢀ III—5‐methylfurfuryl
alcoholꢀ (5‐MFOL),ꢀ IV—5,5‐oxybis(methylene)bis(2‐methylfuran),
V—2,5‐dimethylfuranꢀ (DMF),ꢀ VI—2,5‐dimethyltetrahydrofuran
DMTHF),ꢀOthꢀ=ꢀFOL,ꢀMFꢀandꢀfewꢀofꢀunknownꢀproducts.ꢀ
2
beꢀresponsibleꢀforꢀthisꢀbehaviour;ꢀtheꢀstrongꢀacidicꢀsitesꢀmayꢀ
causeꢀsideꢀreactionsꢀsuchꢀasꢀringꢀopeningꢀorꢀringꢀsaturation.ꢀBuiꢀ
etꢀal.ꢀ[51]ꢀreportedꢀthatꢀringꢀopeningꢀbyꢀhydrolyticꢀcleavageꢀofꢀ
theꢀfuranicꢀC–OꢀbondꢀwasꢀusuallyꢀpromotedꢀbyꢀBrønstedꢀacidicꢀ
sitesꢀ inꢀ acidicꢀ materials.ꢀ Inꢀ addition,ꢀ tracesꢀ ofꢀ
(
selectivityꢀ forꢀ BHMFꢀ becauseꢀ ofꢀ preferentialꢀ reductionꢀ ofꢀ theꢀ
C=OꢀbondꢀinꢀHMF.ꢀSmallꢀamountsꢀofꢀhydrogenolysisꢀproductsꢀ
suchꢀ asꢀ 5‐MF,ꢀ 5‐MFOL,ꢀ andꢀ DMF,ꢀ andꢀ smallꢀ amountsꢀ ofꢀ theꢀ
productsꢀFOLꢀandꢀMF,ꢀwhichꢀwereꢀproducedꢀbyꢀdecarbonyla‐
tionꢀ followedꢀ byꢀ hydrogenolysis,ꢀ wereꢀ alsoꢀ detected.ꢀ
5,5‐oxybis(methylene)bis(2‐methylfuran),ꢀformedꢀbyꢀdehydra‐
tionꢀofꢀ5‐MOL,ꢀwereꢀalsoꢀobservedꢀwithꢀCu‐Co/ZrO
2
.ꢀThisꢀisꢀinꢀ
agreementꢀwithꢀaꢀpreviousꢀreportꢀ[15].ꢀ ꢀ
Weꢀstudiedꢀtheꢀhydrogenolysisꢀofꢀ5‐methylfurfuralꢀ(5‐MF)ꢀ
overꢀtheꢀsameꢀcatalystsꢀandꢀunderꢀtheꢀsameꢀreactionꢀconditionsꢀ
Cu‐Co/Al
2
O ꢀ wasꢀ theꢀ mostꢀ activeꢀ inꢀ polarizingꢀ O–Hꢀ andꢀ C–Oꢀ
3
bonds,ꢀresultingꢀinꢀDMFꢀproductionꢀviaꢀsequentialꢀhydrogena‐
tion/hydrogenolysisꢀofꢀHMF.ꢀTheseꢀresultsꢀshowꢀthatꢀCuꢀeffec‐
tivelyꢀ promotesꢀ hydrogenationꢀ andꢀ moderatelyꢀ promotesꢀ hy‐
drogenolysis.ꢀ Inꢀ addition,ꢀ Cuꢀ canꢀ breakꢀ theꢀ C=Oꢀ bondꢀ duringꢀ
hydrogenationꢀ ofꢀ FALꢀ andꢀ HMFꢀ [21,28,44].ꢀ Itꢀ hasꢀ alsoꢀ beenꢀ
reportedꢀthatꢀCuꢀmetalꢀgivesꢀselectiveꢀproductionꢀofꢀpropyleneꢀ
glycolꢀviaꢀglycerolꢀhydrogenolysisꢀ[43].ꢀSithisaꢀetꢀal.ꢀ[44]ꢀpro‐
(
Fig.ꢀ 8)ꢀ toꢀ exploreꢀ theꢀ reactionꢀ pathwaysꢀ andꢀ clarifyꢀ theꢀ rea‐
sonsꢀforꢀtheꢀsuperiorꢀhydrogenolysisꢀactivitiesꢀofꢀsomeꢀofꢀtheꢀ
catalysts.ꢀTheꢀhydrogenolysisꢀactivityꢀofꢀCu‐Co/CeO ꢀwasꢀinfe‐
riorꢀtoꢀthoseꢀofꢀtheꢀotherꢀtwoꢀcatalysts.ꢀAboutꢀ86%ꢀ5‐MFꢀwasꢀ
convertedꢀoverꢀCu‐Co/CeO ,ꢀwithꢀ32%ꢀselectivityꢀforꢀDMF.ꢀTheꢀ
2
2
majorꢀ productꢀ selectivityꢀ wasꢀ forꢀ 5‐MFOLꢀ (48%),ꢀ formedꢀ viaꢀ
reductionꢀ ofꢀ theꢀ C=Oꢀ bondꢀ inꢀ 5‐MF.ꢀ Followingꢀ theꢀ trendꢀ ob‐
servedꢀforꢀHMFꢀhydrogenation,ꢀCu‐Co/Al
1
posedꢀthatꢀaldehydesꢀwereꢀpreferentiallyꢀadsorbedꢀinꢀtheꢀη (O)ꢀ
2
O ꢀshowedꢀexcellentꢀ
3
configurationꢀonꢀCuꢀmetal,ꢀwhichꢀallowsꢀinteractionsꢀbetweenꢀ
surfaceꢀCuꢀandꢀtheꢀoxygenꢀofꢀtheꢀFALꢀcarbonylꢀgroup,ꢀtoꢀyieldꢀ
furfurylꢀalcohol.ꢀItꢀhasꢀalsoꢀbeenꢀreportedꢀthatꢀsurfaceꢀCuꢀcanꢀ
hydrogenolysisꢀ activityꢀ andꢀ producedꢀ aboutꢀ 82%ꢀ DMFꢀ withꢀ
5-MF
DMF
5-MFOL
Oth
induceꢀ O−Hꢀ bondꢀ scissionꢀ toꢀ formꢀ stableꢀ alkoxideꢀ (CH
termediatesꢀduringꢀmethanolꢀdecompositionꢀ[45].ꢀ
3
O)ꢀ in‐
100
80
Theꢀaboveꢀfindingsꢀsuggestꢀthatꢀtheꢀincreasedꢀselectivityꢀofꢀ
Cu‐Co/Al ꢀforꢀDMFꢀproductionꢀviaꢀC–OꢀandꢀO–Hꢀhydrogenol‐
ysisꢀcanꢀbeꢀattributedꢀtoꢀsynergyꢀbetweenꢀsurfaceꢀmetallicꢀCuꢀ
sitesꢀandꢀpartiallyꢀreducedꢀCoO ꢀsites.ꢀTheꢀXRDꢀandꢀTPRꢀresultsꢀ
showꢀthatꢀ Cu‐Co/Al ꢀhasꢀtheꢀmaximumꢀamountsꢀofꢀsurfaceꢀ
O
2 3
60
40
20
0
x
O
2 3
metallicꢀCuꢀandꢀmixedꢀoxideꢀphases,ꢀresultingꢀinꢀanꢀincreasedꢀ
rateꢀofꢀhydrogenolysisꢀ[29].ꢀItꢀhasꢀbeenꢀreportedꢀthatꢀtheꢀre‐
ducedꢀformsꢀofꢀspinelꢀCuCoO
persedꢀ onꢀ CoO ꢀ [34,35].ꢀ Itꢀ hasꢀ alsoꢀ beenꢀ reportedꢀ thatꢀ ear‐
ly‐transition‐metalꢀ oxidesꢀ suchꢀ asꢀ ReO ,ꢀ MoO ,ꢀ andꢀ CoO ꢀ areꢀ
4
ꢀcatalystsꢀinvolveꢀmetallicꢀCuꢀdis‐
x
x
x
x
Cu-Co/CeO2
Cu-Co/ZrO2
Catalyst
Cu-Co/Al O
2
3
effectiveꢀ catalystsꢀ inꢀ theꢀ hydrogenolysisꢀ ofꢀ biomass‐derivedꢀ
componentsꢀ[35,36].ꢀPreviousꢀstudiesꢀ[47,48]ꢀhaveꢀshownꢀthatꢀ
Fig.ꢀ 8.ꢀ Catalyticꢀ activityꢀ forꢀ hydrogenolysisꢀ ofꢀ 5‐methylfurfuralꢀ overꢀ
supportedꢀbi‐metallicꢀcopper‐cobaltꢀcatalysts.ꢀReactionꢀconditions:ꢀ200
dissociativeꢀadsorptionꢀofꢀH ꢀonꢀCu(0)ꢀhasꢀaꢀlowꢀactivationꢀen‐
2
ergyꢀ[49].ꢀSimilarꢀeffectsꢀhaveꢀbeenꢀobservedꢀforꢀpromotionꢀofꢀ
Cuꢀ catalystsꢀ withꢀ nobleꢀ metalsꢀ [50].ꢀ Recently,ꢀ ourꢀ groupꢀ re‐
portedꢀthatꢀanꢀincreaseꢀinꢀtheꢀCoꢀloadingꢀincreasedꢀCuꢀdisper‐
°
C,ꢀ 3.0ꢀ MPa,ꢀ 8ꢀ h,ꢀ Catalystꢀ 0.5ꢀ g,ꢀ 5‐MFꢀ 2.5ꢀ mmol,ꢀ THFꢀ 20ꢀ mL.
Oth=5,5‐oxybis(methylene)bis(2‐methylfuran),ꢀ 2,5‐dimethyltetrahy‐
drofuranꢀ(DMTHF),ꢀFOL,ꢀMFꢀandꢀfewꢀofꢀunknownꢀproducts.ꢀ
ꢀ

706ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
9
9%ꢀconversionꢀofꢀ5‐MF.ꢀHowever,ꢀalthoughꢀ99%ꢀconversionꢀ
ofꢀ5‐MFꢀwasꢀachievedꢀoverꢀCu‐Co/ZrO ,ꢀtheꢀselectivityꢀforꢀDMFꢀ
56%)ꢀ wasꢀ lowꢀ andꢀ largeꢀ amountsꢀ ofꢀ ring‐saturationꢀ andꢀ
2
100
(
ring‐openingꢀ productsꢀ wereꢀ obtained.ꢀ Theseꢀ resultsꢀ areꢀ inꢀ
agreementꢀwithꢀthoseꢀobtainedꢀforꢀone‐stepꢀhydrogenolysisꢀofꢀ
HMFꢀtoꢀDMF.ꢀ ꢀ
80
60
40
3.2.2.ꢀ ꢀ EffectsꢀofꢀCu/CoꢀmolarꢀratioꢀonꢀHMFꢀhydrogenolysisꢀ ꢀ
HMF
DMF
TheꢀeffectꢀofꢀtheꢀCu/Coꢀmolarꢀratioꢀonꢀtheꢀcatalyticꢀactivityꢀ
ofꢀ bimetallicꢀ Cu‐Co/Al
2
O ꢀ wasꢀ investigatedꢀ byꢀ studyingꢀ cata‐
3
lystsꢀwithꢀvariousꢀmolarꢀratioꢀ(Cu/Coꢀ=ꢀ1,ꢀ2,ꢀandꢀ4)ꢀatꢀ200ꢀ°Cꢀ
andꢀ 3.0ꢀ MPa.ꢀ Theꢀ resultsꢀ wereꢀ comparedꢀ withꢀ thoseꢀ forꢀ theꢀ
1
60 170 180 190 200o 210 220 230 240
monometallicꢀ Cuꢀ (10ꢀ wt%)/Al
counterpartsꢀ (Tableꢀ 4).ꢀ Theꢀ catalyticꢀ activityꢀ ofꢀ Coꢀ (10ꢀ
wt%)/Al ꢀwasꢀlow,ꢀwhichꢀconfirmsꢀthatꢀCo ꢀspeciesꢀaloneꢀ
haveꢀ littleꢀ effectꢀ onꢀ HMFꢀ hydrogenolysisꢀ underꢀ theꢀ presentꢀ
conditions.ꢀThisꢀresultꢀisꢀinꢀagreementꢀwithꢀthatꢀreportedꢀbyꢀZuꢀ
2
O
3
ꢀ andꢀ Coꢀ (10ꢀ wt%)/Al
2
O ꢀ
3
Temperature ( C)
Fig.ꢀ9.ꢀEffectꢀofꢀtemperatureꢀonꢀtheꢀconversionꢀofꢀ HMFꢀ toꢀ DMFꢀoverꢀ
Cu‐Co/Al ꢀ (Cu/Coꢀ =ꢀ 1).ꢀ Reactionꢀ conditions:ꢀ 3.0ꢀ MPa,ꢀ 8ꢀ h,ꢀ Catalystꢀ
.5g,ꢀHMFꢀ2.5ꢀmmol,ꢀTHFꢀ20ꢀmL.ꢀ
O
2 3
O
3 4
O
2 3
0
etꢀal.ꢀ[15],ꢀwhoꢀfoundꢀthatꢀCo
HMFꢀhydrogenation.ꢀWhenꢀ10ꢀwt%ꢀCu/Al
3
O
4
ꢀhadꢀlowꢀcatalyticꢀactivityꢀinꢀ
3
.3.1.ꢀ ꢀ Effectsꢀofꢀtemperatureꢀ
Theꢀeffectꢀofꢀtemperatureꢀonꢀtheꢀselectiveꢀhydrogenolysisꢀofꢀ
2 3
O
ꢀwasꢀused,ꢀBHMF,ꢀ
formedꢀ viaꢀ activationꢀ ofꢀ theꢀ carbonylꢀ group,ꢀ wasꢀ theꢀ majorꢀ
productꢀ(45.5%).ꢀHowever,ꢀtheꢀbimetallicꢀcatalystsꢀgaveꢀlowerꢀ
selectivitiesꢀforꢀBHMFꢀandꢀincreasedꢀselectivitiesꢀforꢀDMF;ꢀtheꢀ
DMFꢀ selectivityꢀ reachedꢀ aꢀ maximumꢀ ofꢀ aboutꢀ 68.4%ꢀ overꢀ
HMFꢀtoꢀDMFꢀwasꢀstudiedꢀoverꢀtheꢀtemperatureꢀrangeꢀ160–230ꢀ
CꢀatꢀaꢀconstantꢀH ꢀpressureꢀofꢀ3.0ꢀMPaꢀ(Fig.ꢀ9).ꢀTheꢀHMFꢀcon‐
versionꢀwasꢀlowꢀ(68%)ꢀatꢀ160ꢀ°C,ꢀbutꢀincreasedꢀwithꢀincreasingꢀ
temperature.ꢀItꢀreachedꢀtheꢀmaximum,ꢀi.e.ꢀ100%ꢀatꢀ220ꢀ°C,ꢀandꢀ
remainedꢀconstantꢀwithꢀfurtherꢀtemperatureꢀincreasesꢀtoꢀ230ꢀ
°
2
Cu‐Co/Al
formedꢀoverꢀallꢀtheꢀcatalysts,ꢀandꢀitꢀwasꢀconvertedꢀtoꢀDMFꢀviaꢀ
‐MFꢀandꢀMFOLꢀbyꢀsubsequentꢀhydrogenationꢀandꢀhydrogen‐
2
O ꢀ (Cu/Coꢀ =ꢀ 1).ꢀ BHMFꢀ wasꢀ theꢀ mainꢀ intermediateꢀ
3
°
C.ꢀTheseꢀresultsꢀcanꢀbeꢀattributedꢀtoꢀanꢀincreaseꢀinꢀtheꢀreactionꢀ
rateꢀbecauseꢀofꢀfacilitationꢀofꢀC=Oꢀbondꢀbreakingꢀoverꢀmetallicꢀ
Cu,ꢀresultingꢀinꢀincreasedꢀactivationꢀofꢀmolecularꢀH ꢀinꢀtheꢀre‐
5
olysisꢀunderꢀtheꢀpresentꢀconditionsꢀ[22–26].ꢀItꢀcanꢀbeꢀdeducedꢀ
thatꢀhydrogenationꢀofꢀtheꢀC=Oꢀbondꢀfollowedꢀbyꢀhydrogenoly‐
sisꢀofꢀC–OꢀandꢀO–HꢀbondsꢀinꢀHMFꢀisꢀfavouredꢀatꢀhigherꢀtemper‐
aturesꢀbecauseꢀofꢀactivationꢀofꢀtheꢀC–OꢀandꢀO–Hꢀbonds,ꢀwhichꢀ
resultsꢀinꢀformationꢀofꢀDMFꢀasꢀtheꢀmajorꢀproductꢀandꢀBHMF,ꢀ
MFA,ꢀandꢀMFOLꢀasꢀminorꢀproductsꢀoverꢀbimetallicꢀCu‐Coꢀcata‐
lystsꢀ[46].ꢀTheseꢀresultsꢀcanꢀbeꢀexplainedꢀbasedꢀonꢀpreviouslyꢀ
2
actionꢀmixtureꢀ[22,23].ꢀHydrogenationꢀofꢀtheꢀC=Cꢀbondꢀ(bondꢀ
energyꢀ=ꢀ615ꢀkJ/mol)ꢀisꢀeasierꢀthanꢀC=Oꢀbondꢀ(bondꢀenergyꢀ=ꢀ
715ꢀkJ/mol)ꢀhydrogenationꢀ[45].ꢀHowever,ꢀtheꢀpresenceꢀofꢀtheꢀ
conjugatedꢀ furanꢀ ringꢀ makesꢀ hydrogenationꢀ ofꢀ theꢀ C=Oꢀ bondꢀ
easierꢀ thanꢀ C=Cꢀ bondꢀ hydrogenationꢀ inꢀ theꢀ selectiveꢀ hydro‐
genationꢀofꢀHMFꢀtoꢀDMF,ꢀwhichꢀisꢀgenerallyꢀpromotedꢀatꢀhigherꢀ
temperaturesꢀ[46].ꢀAtꢀ160ꢀ°CꢀtheꢀselectivityꢀforꢀDMFꢀwasꢀlowꢀ
reportedꢀXRD,ꢀH
‐TPR,ꢀandꢀX‐rayꢀabsorptionꢀnear‐edgeꢀstruc‐
2
tureꢀstudies,ꢀwhichꢀshowedꢀthatꢀtheꢀamountsꢀofꢀsurfaceꢀmetallicꢀ
CuꢀandꢀmixedꢀCu‐CoꢀphasesꢀincreasedꢀwithꢀincreasingꢀCoꢀload‐
ing;ꢀthisꢀisꢀresponsibleꢀforꢀtheꢀenhancedꢀhydrogenolysisꢀactivityꢀ
ofꢀtheꢀbimetallicꢀcatalystsꢀ[29].ꢀ ꢀ
(
40.6%),ꢀwithꢀformationꢀofꢀby‐productsꢀsuchꢀasꢀBHMF,ꢀ5‐MF,ꢀ
andꢀ5‐MFOL.ꢀHowever,ꢀwithꢀincreasingꢀtemperature,ꢀtheꢀselec‐
tivityꢀforꢀDMFꢀimprovedꢀsignificantlyꢀandꢀreachedꢀaꢀmaximumꢀ
ofꢀ78%ꢀatꢀ220ꢀ°C.ꢀItꢀisꢀworthꢀnotingꢀthatꢀhydrogenationꢀofꢀtheꢀ
C=OꢀbondꢀinꢀHMFꢀwasꢀfavouredꢀatꢀlowꢀtemperaturesꢀoverꢀCuꢀ
catalystsꢀbecauseꢀofꢀtheꢀhigherꢀactivationꢀenergiesꢀofꢀC–Oꢀandꢀ
O–H,ꢀ resultingꢀ inꢀ theꢀ formationꢀ ofꢀ BHMFꢀ asꢀ aꢀ majorꢀ product.ꢀ
However,ꢀ higherꢀ temperaturesꢀ promoteꢀ C–Oꢀ andꢀ O–Hꢀ hydro‐
genolysis,ꢀwhichꢀresultsꢀinꢀfurtherꢀconversionꢀofꢀBHMFꢀtoꢀDMF.ꢀ
2
Weꢀthenꢀstudiedꢀtheꢀeffectsꢀofꢀtemperature,ꢀH ꢀpressure,ꢀandꢀ
2 3
timeꢀonꢀreactionsꢀusingꢀtheꢀCu‐Co/Al O ꢀ(Cu/Coꢀ=ꢀ1)ꢀcatalystꢀtoꢀ
improveꢀtheꢀDMFꢀyield.ꢀ
3.3.ꢀ ꢀ Effectsꢀofꢀoperatingꢀparametersꢀ
Tableꢀ4ꢀ
EffectꢀofꢀCu/CoꢀmolarꢀratioꢀonꢀhydrogenolysisꢀofꢀHMF.ꢀ
Cu/Coꢀ*ꢀ
wt%/wt%)ꢀ
Selectivityꢀ(%)ꢀ
HMFꢀConversionꢀ
(%)ꢀ
Catalystꢀ
(
DMFꢀ
38.5ꢀ
68.4ꢀ
56.6ꢀ
43.0ꢀ
10.5ꢀ
BHMFꢀ
45.5ꢀ
ꢀ 5.4ꢀ
16.2ꢀ
35.0ꢀ
35.0ꢀ
5‐MFꢀ
ꢀ 3.5ꢀ
ꢀ 8.6ꢀ
10.4ꢀ
10.0ꢀ
ꢀ 8.5ꢀ
5‐MFOLꢀ
ꢀ 2.5ꢀ
12.8ꢀ
Othꢀ
10.0ꢀ
ꢀ 4.8ꢀ
ꢀ 4.6ꢀ
ꢀ 8.5ꢀ
39.5ꢀ
Cu/Al O
2 3
ꢀ
—ꢀ
1ꢀ
2ꢀ
92.7ꢀ
99.9ꢀ
98.4ꢀ
98.2ꢀ
42.7ꢀ
Cu‐Co/Al
Cu‐Co/Al
Cu‐Co/Al
2
2
2
O ꢀ
3
O ꢀ
3
O ꢀ
3
12.2ꢀ
4ꢀ
ꢀ 3.5ꢀ
ꢀ 6.5ꢀ
Co/Al
ꢀLoadingꢀratioꢀusedꢀinꢀtheꢀsynthesis.ꢀ
Reactionꢀconditions:ꢀ200ꢀ°C,ꢀ3.0ꢀMPa,ꢀ8ꢀh,ꢀCatalystꢀ0.5ꢀg,ꢀHMFꢀ2.5ꢀmmol,ꢀTHFꢀ20ꢀmL.ꢀ
O
2 3
ꢀ
—ꢀ
*
HMF:ꢀ5‐hydroxymethylfuran;ꢀDMF:ꢀ2,5‐dimethylfuran;ꢀBHMF:ꢀ2,5‐bisꢀhydroxymethylfuran;ꢀ5‐MF:ꢀ5‐methylfurfural;ꢀ5‐MFOL:ꢀ5‐methylfurfurylꢀalco‐
hol;ꢀOth:ꢀFOL,ꢀMFꢀandꢀfewꢀofꢀunknown.ꢀ

ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
707ꢀ
Aꢀ highꢀ temperatureꢀ isꢀ thereforeꢀ importantꢀ forꢀ C–Oꢀ andꢀ O–Hꢀ
hydrogenolysisꢀ ofꢀ theꢀ intermediatesꢀ BHMF,ꢀ 5‐MF,ꢀ and/orꢀ
100
5‐MFOL.ꢀ Furtherꢀ increasesꢀ inꢀ temperatureꢀ resultedꢀ inꢀ
over‐hydrogenolysisꢀ productsꢀ andꢀ theꢀ yieldꢀ ofꢀ DMFꢀ dropped.ꢀ
ThisꢀsuggestsꢀthatꢀtheꢀconversionꢀofꢀHMFꢀtoꢀDMFꢀhadꢀreachedꢀaꢀ
maximumꢀatꢀ220ꢀ°C,ꢀandꢀtheꢀeffectꢀofꢀfurtherꢀincreasesꢀinꢀtheꢀ
reactionꢀtemperatureꢀwasꢀinsignificant.ꢀAꢀreactionꢀtemperatureꢀ
ofꢀ220ꢀ°Cꢀwasꢀthereforeꢀusedꢀinꢀsubsequentꢀexperiments.ꢀ
8
0
60
40
20
0
HMF
DMF
3
.3.2.ꢀ ꢀ EffectsꢀofꢀH ꢀpressureꢀ
2
Inꢀhydrogenation/hydrogenolysisꢀreactions,ꢀtheꢀsolubilityꢀofꢀ
,ꢀasꢀwellꢀasꢀotherꢀparametersꢀ(temperatureꢀandꢀtime),ꢀisꢀim‐
H
2
2
4
6
8
10
2
portant.ꢀAꢀhighꢀH ꢀpressureꢀisꢀneededꢀtoꢀaccelerateꢀtheꢀhydro‐
Time (h)
genationꢀofꢀbiobasedꢀmoleculesꢀ[22].ꢀTheꢀoptimumꢀH
2
ꢀpressureꢀ
Fig.ꢀ 11.ꢀ Effectꢀ ofꢀ timeꢀ onꢀ theꢀ conversionꢀ ofꢀ HMFꢀ toꢀ DMFꢀ overꢀ
Cu‐Co/Al ꢀ(Cu/Coꢀ=ꢀ1).ꢀReactionꢀconditions:ꢀ3.0ꢀMPa,ꢀ220ꢀ°C,ꢀCatalyst
.5ꢀg,ꢀHMFꢀ2.5ꢀmmol,ꢀTHFꢀ20ꢀmL.ꢀ
forꢀselectiveꢀhydrogenationꢀofꢀHMFꢀtoꢀDMFꢀwasꢀidentifiedꢀbyꢀ
performingꢀ reactionsꢀ atꢀ 220ꢀ °Cꢀ andꢀ variousꢀ pressuresꢀ inꢀ theꢀ
rangeꢀ10–40ꢀbarꢀ(Fig.ꢀ10).ꢀTheꢀconversionꢀandꢀselectivityꢀbothꢀ
increasedꢀwithꢀincreasingꢀpressureꢀupꢀtoꢀ30ꢀbar,ꢀandꢀreachedꢀ
O
2 3
0
5‐MF,ꢀandꢀ5‐MFOLꢀtoꢀDMF.ꢀWhenꢀtheꢀreactionꢀtimeꢀwasꢀfurtherꢀ
1
00%ꢀ andꢀ 78%,ꢀ respectively.ꢀ Theꢀ HMFꢀ conversionꢀ didꢀ notꢀ
changeꢀ significantlyꢀ withꢀ furtherꢀ increasesꢀ inꢀ pressure.ꢀ Theꢀ
conversionꢀofꢀHMFꢀtoꢀDMFꢀincreasedꢀwithꢀincreasingꢀH ꢀpres‐
sureꢀupꢀtoꢀ3.0ꢀMPaꢀbecauseꢀofꢀtheꢀincreasingꢀsolubilityꢀofꢀH ꢀinꢀ
increasedꢀ toꢀ 10ꢀ h,ꢀ theꢀ HMFꢀ conversionꢀ remainedꢀ constantꢀ atꢀ
00%;ꢀhowever,ꢀtheꢀselectivityꢀforꢀDMFꢀdecreasedꢀslightly.ꢀThisꢀ
1
2
canꢀ beꢀ attributedꢀ toꢀ theꢀ formationꢀ ofꢀ increasingꢀ amountsꢀ ofꢀ
by‐productsꢀwhenꢀtheꢀreactionꢀtimeꢀincreasedꢀbeyondꢀaꢀcertainꢀ
value.ꢀAꢀreactionꢀtimeꢀofꢀ8ꢀhꢀwasꢀthereforeꢀusedꢀinꢀsubsequentꢀ
experiments.ꢀTheꢀtransformationꢀofꢀHMFꢀtoꢀDMFꢀproceedsꢀviaꢀ
theꢀ intermediatesꢀ BHMFꢀ orꢀ 5‐MF,ꢀ andꢀ thenꢀ 5‐MFOL.ꢀ Conver‐
sionꢀofꢀbothꢀintermediatesꢀtoꢀDMFꢀisꢀconsideredꢀtoꢀbeꢀslowꢀandꢀ
requiresꢀmoreꢀtimeꢀoverꢀCu‐basedꢀcatalysts.ꢀ ꢀ
2
theꢀ reactionꢀ mixture.ꢀ However,ꢀ pressuresꢀ aboveꢀ 3.0ꢀ MPaꢀ didꢀ
notꢀ significantlyꢀ changeꢀ theꢀ HMFꢀ conversionꢀ becauseꢀ ofꢀ theꢀ
largerꢀamountꢀofꢀchemisorbedꢀhydrogenꢀ(Hads)ꢀonꢀtheꢀcatalyst,ꢀ
whichꢀbecameꢀsaturated.ꢀHowever,ꢀaboveꢀ3.0ꢀMPa,ꢀaꢀslightꢀde‐
creaseꢀinꢀDMFꢀselectivityꢀwasꢀobserved.ꢀThisꢀcanꢀbeꢀattributedꢀ
toꢀfurtherꢀopeningꢀandꢀhydrogenationꢀofꢀtheꢀfuranꢀring.ꢀAꢀH ꢀ
2
pressureꢀofꢀ3.0ꢀMPaꢀwasꢀthereforeꢀchosenꢀforꢀsubsequentꢀex‐
periments.ꢀ ꢀ
3.4.ꢀ ꢀ StabilityꢀofꢀcatalystsꢀinꢀHMFꢀhydrogenolysisꢀ ꢀ
TheꢀCu‐Co/Al
2 3
O ꢀcatalyst,ꢀwhichꢀgaveꢀtheꢀbestꢀcatalyticꢀper‐
3.3.3.ꢀ ꢀ Effectsꢀofꢀtimeꢀ
formance,ꢀwasꢀrecycledꢀtwiceꢀtoꢀevaluateꢀitsꢀstability.ꢀTheꢀHMFꢀ
conversionꢀandꢀselectivityꢀforꢀDMFꢀdroppedꢀfromꢀ100%ꢀtoꢀ62%ꢀ
andꢀ78%ꢀtoꢀ42%,ꢀrespectively,ꢀinꢀtheꢀsecondꢀrunꢀ(Tableꢀ5).ꢀTheꢀ
decreaseꢀinꢀtheꢀcatalyticꢀactivityꢀwasꢀinvestigatedꢀbyꢀexaminingꢀ
theꢀdifferencesꢀbetweenꢀtheꢀstructuresꢀofꢀtheꢀspentꢀandꢀfreshlyꢀ
reducedꢀ catalystsꢀ usingꢀ TEMꢀ andꢀ CHNSꢀ analysis.ꢀ TEMꢀ andꢀ
CHNSꢀ analysisꢀ showedꢀ theꢀ presenceꢀ ofꢀ carbonꢀ afterꢀ use.ꢀ Theꢀ
TEMꢀresultsꢀshowedꢀthatꢀcarbonꢀwasꢀdepositedꢀonꢀtheꢀactiveꢀ
sitesꢀ andꢀ theꢀ particleꢀ sizeꢀ increasedꢀ afterꢀ theꢀ secondꢀ cycle;ꢀ
theseꢀfactorsꢀcouldꢀcauseꢀtheꢀsignificantꢀdropꢀinꢀtheꢀactivityꢀofꢀ
theꢀcatalyst.ꢀTheseꢀobservationsꢀagreeꢀwithꢀourꢀpreviousꢀworkꢀ
onꢀFALꢀhydrogenation,ꢀinꢀwhichꢀcokeꢀformationꢀwasꢀobservedꢀ
TheꢀeffectsꢀofꢀtimeꢀonꢀtheꢀHMFꢀconversionꢀandꢀtheꢀselectivi‐
tyꢀforꢀDMFꢀwereꢀinvestigatedꢀoverꢀtheꢀrangeꢀ2–10ꢀhꢀatꢀ220ꢀ°Cꢀ
andꢀ3.0ꢀMPa.ꢀFig.ꢀ11ꢀshowsꢀthatꢀonlyꢀ21%ꢀconversionꢀofꢀHMFꢀ
andꢀ5.6%ꢀselectivityꢀforꢀDMFꢀwereꢀachievedꢀinꢀ2ꢀh.ꢀWhenꢀtheꢀ
reactionꢀ timeꢀ wasꢀ prolongedꢀ fromꢀ 2ꢀ toꢀ 8ꢀ h,ꢀ theꢀ conversionꢀ
reachedꢀ 100%ꢀ andꢀ theꢀ selectivityꢀ increasedꢀ toꢀ 78%.ꢀ Theꢀ in‐
creasedꢀselectivityꢀforꢀDMFꢀwithꢀtimeꢀcorrespondsꢀtoꢀconver‐
sionꢀ ofꢀ increasingꢀ amountsꢀ ofꢀ intermediatesꢀ suchꢀ asꢀ BHMF,ꢀ
100
[
29].ꢀToꢀconfirmꢀtheꢀreasonsꢀforꢀtheꢀlossꢀofꢀcatalyticꢀactivity,ꢀtheꢀ
80
60
40
20
Tableꢀ5ꢀ
Reusabilityꢀ ofꢀ Cu‐Co/Al
ofꢀHMFꢀtoꢀDMF.ꢀ
2
O3ꢀ(Cu/Co=1)ꢀ catalystꢀ towardꢀ hydrogenolysisꢀ
HMF
DMF
ConversionꢀofꢀHMFꢀ
%)ꢀ
SelectivityꢀofꢀDMFꢀ
(%)ꢀ
Catalystsꢀ
(
Cu‐Co/Al
aꢀCu‐Co/Al
aꢀCu‐Co/Al
2
O
3
ꢀ(Fresh)ꢀ
100ꢀ
78.0ꢀ
54.0ꢀ
42.6ꢀ
72.2ꢀ
st
2
O
O
3
ꢀ1 ꢀcycleꢀ
ꢀ ꢀ ꢀ 78.4ꢀ
ꢀ ꢀ ꢀ 62.4ꢀ
ꢀ ꢀ ꢀ 94.6ꢀ
nd
1
2
3
4
2
3
ꢀ2 ꢀcycleꢀ
Hydrogen pressure (MPa)
bꢀCu‐Co/Al
st
2
O ꢀ1 ꢀcycleꢀ
3
aꢀ
bꢀ
Withoutꢀcalcinations.ꢀ Withꢀcalcinations.ꢀ
Fig.ꢀ10.ꢀEffectꢀofꢀhydrogenꢀpressureꢀonꢀtheꢀconversionꢀofꢀHMFꢀtoꢀDMF
Reactionꢀ Conditions:ꢀ 220ꢀ °C,ꢀ 3.0ꢀ MPa,ꢀ Catalystꢀ 0.5ꢀ g,ꢀ HMFꢀ 2.5ꢀ mmol,
THFꢀ20ꢀmL,ꢀ8ꢀh.ꢀ
overꢀCu‐Co/Al ꢀ(Cu/Coꢀ=ꢀ1).ꢀReactionꢀconditions:ꢀ220ꢀ°C,ꢀ8ꢀh,ꢀCatalyst
.5ꢀg,ꢀHMFꢀ2.5ꢀmmol,ꢀTHFꢀ20ꢀmL.ꢀ
2
O
3
0

708ꢀ
SanjayꢀSrivastavaꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ699–709ꢀ
2 3
usedꢀcatalystꢀ(Cu‐Co/Al O ꢀafterꢀtheꢀsecondꢀcycle)ꢀwasꢀcalcinedꢀ
theseꢀpromisingꢀresults,ꢀfurtherꢀstudiesꢀwillꢀfocusꢀonꢀtheꢀreac‐
atꢀ500ꢀ°Cꢀandꢀactivatedꢀinꢀsituꢀatꢀ280ꢀ°Cꢀtoꢀremoveꢀdeposits,ꢀ
andꢀthenꢀtestedꢀunderꢀsameꢀreactionꢀconditions.ꢀAsꢀexpected,ꢀ
theꢀconversionꢀofꢀHMFꢀandꢀselectivityꢀforꢀDMFꢀbothꢀincreased,ꢀ
toꢀ 94%ꢀ andꢀ 72%,ꢀ respectively.ꢀ Itꢀ canꢀ thereforeꢀ beꢀ concludedꢀ
thatꢀtheꢀcatalystꢀlostꢀactivityꢀbecauseꢀcokeꢀformedꢀduringꢀHMFꢀ
hydrogenationꢀcoveredꢀtheꢀactiveꢀsitesꢀonꢀtheꢀcatalyst.ꢀ
tionꢀmechanismꢀandꢀkineticsꢀofꢀHMFꢀconversion.ꢀ
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2 3
GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2017,ꢀ38:ꢀ699–709ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(17)62789‐X
Influenceꢀofꢀsupportsꢀforꢀselectiveꢀproductionꢀofꢀ2,5‐dimethylfuranꢀviaꢀbimetallicꢀcopper‐cobaltꢀcatalyzedꢀ
5‐hydroxymethylfurfuralꢀhydrogenolysisꢀ
ꢀ
SanjayꢀSrivastava,ꢀG.ꢀC.ꢀJadeja,ꢀJigishaꢀParikh*ꢀ
SardarꢀVallabhbhaiꢀNationalꢀInstituteꢀofꢀTechnology,ꢀIndiaꢀ
ꢀ
Theꢀpresentꢀstudyꢀexploredꢀtheꢀuseꢀofꢀnon‐noble,ꢀenvironmentallyꢀbenign,ꢀbimetallicꢀcopper‐cobaltꢀcatalystsꢀinꢀtheꢀselectiveꢀproductionꢀofꢀ
,5‐dimethylfuranꢀviaꢀ5‐hydroxymethylfurfuralꢀhydrogenolysis.ꢀ
2

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