Catalytic oxidation of glycerol to tartronic acid over Au/HY catalyst under mild conditions

Article abstract of DOI:10.1016/S1872-2067(14)60132-7

Gold nanoclusters or nanoparticles on various supports (CeO₂, activated carbon, HY, REY, and NaY) were investigated for glycerol oxidation in the aqueous phase under mild conditions. Compared with other catalysts, Au/HY showed remarkable catalytic performance in forming dicarboxylic acid (tartronic acid) over the monocarboxylic acid (glyceric acid) or the C-C cleavage product (oxalic acid). Au/HY achieved 98% conversion of glycerol and 80% yield of tartronic acid at 60 °C under 0.3 MPa O₂. Further characterization showed that the small size of Au clusters is the key factor for the high oxidation performance. In situ Fourier transform infrared spectroscopy revealed that glycerol was first transformed to glyceric acid, and then glyceric acid was directly oxidized to tartronic acid.

Full text of DOI:10.1016/S1872-2067(14)60132-7

ChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
ava i l a b l e a t w w w. s c i e n c ed 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
CatalyticꢀoxidationꢀofꢀglycerolꢀtoꢀtartronicꢀacidꢀoverꢀAu/HYꢀcatalystꢀ
underꢀmildꢀconditionsꢀ
ꢀa,ꢀb
ꢀa
ꢀa,b
ꢀa
ꢀa
ꢀa
ꢀa,
JiayingꢀCai ,ꢀHongꢀMa ,ꢀJunjieꢀZhang ,ꢀZhongtianꢀDu ,ꢀYizhengꢀHuang ,ꢀJinꢀGao ,ꢀJieꢀXu *
ꢀ
aꢀDalianꢀNationalꢀLaboratoryꢀforꢀCleanꢀEnergy,ꢀStateꢀKeyꢀLaboratoryꢀofꢀCatalysis,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀ ꢀ
Dalianꢀ116023,ꢀLiaoning,ꢀChinaꢀ
bꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences,ꢀBeijingꢀ100049,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Goldꢀnanoclustersꢀorꢀnanoparticlesꢀonꢀvariousꢀsupportsꢀ(CeO ,ꢀactivatedꢀcarbon,ꢀHY,ꢀREY,ꢀandꢀNaY)ꢀ
2
Receivedꢀ30ꢀMarchꢀ2014ꢀ
Acceptedꢀ28ꢀAprilꢀ2014ꢀ
Publishedꢀ20ꢀOctoberꢀ2014ꢀ
wereꢀinvestigatedꢀ forꢀ glycerolꢀ oxidationꢀ inꢀ theꢀ aqueousꢀphaseꢀ underꢀ mildꢀ conditions.ꢀ Comparedꢀ
withꢀotherꢀcatalysts,ꢀAu/HYꢀshowedꢀremarkableꢀcatalyticꢀperformanceꢀinꢀformingꢀdicarboxylicꢀacidꢀ
(tartronicꢀacid)ꢀoverꢀtheꢀmonocarboxylicꢀacidꢀ(glycericꢀacid)ꢀorꢀtheꢀC–Cꢀcleavageꢀproductꢀ(oxalicꢀ
acid).ꢀAu/HYꢀachievedꢀ98%ꢀconversionꢀofꢀglycerolꢀandꢀ80%ꢀyieldꢀofꢀtartronicꢀacidꢀatꢀ60ꢀ°Cꢀunderꢀ0.3ꢀ
MPaꢀO .ꢀFurtherꢀcharacterizationꢀshowedꢀthatꢀtheꢀsmallꢀsizeꢀofꢀAuꢀclustersꢀisꢀtheꢀkeyꢀfactorꢀforꢀtheꢀ
highꢀoxidationꢀperformance.ꢀInꢀsituꢀFourierꢀtransformꢀinfraredꢀspectroscopyꢀrevealedꢀthatꢀglycerolꢀ
wasꢀfirstꢀtransformedꢀtoꢀglycericꢀacid,ꢀandꢀthenꢀglycericꢀacidꢀwasꢀdirectlyꢀoxidizedꢀtoꢀtartronicꢀacid.
2
Keywords:ꢀ
Catalyticꢀoxidationꢀ
Glycerolꢀ
Goldꢀ
Tartronicꢀacid
©ꢀ2014,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
glycerolꢀintoꢀTARACꢀusingꢀoxygenꢀasꢀoxidantꢀandꢀwaterꢀasꢀsol‐
ventꢀunderꢀmildꢀconditions.ꢀHowever,ꢀlittleꢀresearchꢀhasꢀbeenꢀ
reportedꢀonꢀthisꢀtopic.ꢀ
Asꢀaꢀmajorꢀbyproductꢀinꢀbiodieselꢀproduction,ꢀglycerolꢀhasꢀ
receivedꢀgreatꢀattentionꢀwithꢀtheꢀrapidꢀglobalꢀdevelopmentꢀofꢀ
biodieselꢀ[1–5].ꢀGlycerolꢀhasꢀbeenꢀrecognizedꢀasꢀanꢀimportantꢀ
biomass‐basedꢀ buildingꢀ blockꢀ forꢀ valuableꢀ C3ꢀ molecules.ꢀ Theꢀ
surplusꢀofꢀglycerolꢀhasꢀinspiredꢀresearchersꢀtoꢀdevelopꢀefficientꢀ
methodsꢀ toꢀ useꢀ glycerolꢀ [6–9].ꢀ Becauseꢀ glycerolꢀ isꢀ aꢀ highlyꢀ
functionalizedꢀmoleculeꢀcontainingꢀthreeꢀhydroxylꢀgroups,ꢀitꢀisꢀ
feasibleꢀ toꢀ convertꢀ glycerolꢀ intoꢀ valuableꢀ oxygenatedꢀ deriva‐
tivesꢀ viaꢀ catalyticꢀ oxidation,ꢀ suchꢀ asꢀ tartronicꢀ acidꢀ (TARAC),ꢀ
glycericꢀ acidꢀ (GLYA),ꢀ andꢀ dihydroxyacetoneꢀ (DIHA)ꢀ [6,10,11].ꢀ
Amongꢀtheseꢀcompounds,ꢀTARACꢀisꢀaꢀhighꢀvalue‐addedꢀchemi‐
calꢀthatꢀisꢀwidelyꢀusedꢀasꢀaꢀpharmaceuticalꢀandꢀanti‐corrosiveꢀ
protectiveꢀ agent,ꢀ asꢀ wellꢀ asꢀ forꢀ theꢀ monomerꢀ ofꢀ biopolymersꢀ
Currently,ꢀ supportedꢀ preciousꢀ metalꢀ catalystsꢀ areꢀ usedꢀ inꢀ
glycerolꢀoxidation.ꢀAu/C,ꢀPd/C,ꢀandꢀPt/Cꢀareꢀeffectiveꢀforꢀpro‐
ducingꢀGLYAꢀbutꢀinefficientꢀforꢀproducingꢀTARACꢀ[16–22].ꢀRe‐
cently,ꢀ Zopeꢀ etꢀ al.ꢀ [17]ꢀ employedꢀ anꢀ Au/TiO
ꢀ catalystꢀ forꢀ theꢀ
2
oxidationꢀofꢀglycerolꢀandꢀachievedꢀ100%ꢀconversionꢀwithꢀ20%ꢀ
selectivityꢀ ofꢀ sodiumꢀ tartronate.ꢀ Kimuraꢀ etꢀ al.ꢀ [14]ꢀ reportedꢀ
thatꢀglycerolꢀoxidationꢀoverꢀPd/Pt‐basedꢀcatalystꢀyieldedꢀ58%ꢀ
disodiumꢀ tartronate.ꢀ Theseꢀ studiesꢀ indicateꢀ thatꢀ theꢀ unsatis‐
factoryꢀ yieldꢀ ofꢀ TARACꢀ resultsꢀ fromꢀ theꢀ difficultyꢀ inꢀ furtherꢀ
oxidationꢀ ofꢀ GLYAꢀ andꢀ theꢀ occurrenceꢀ ofꢀ C–Cꢀ cleavageꢀ orꢀ de‐
carboxylation.ꢀToꢀachieveꢀaꢀhighꢀyieldꢀofꢀTARAC,ꢀitꢀisꢀimperativeꢀ
toꢀdevelopꢀnewꢀefficientꢀheterogeneousꢀcatalystsꢀavoidingꢀC–Cꢀ
cleavageꢀorꢀdecarboxylation.ꢀItꢀisꢀalsoꢀimportantꢀtoꢀinvestigateꢀ
theꢀreactionꢀpathwayꢀofꢀdicarboxylicꢀacidꢀformation.ꢀ ꢀ
[12–15].ꢀ Itꢀ isꢀ challengingꢀ andꢀ importantꢀ toꢀ developꢀ
cost‐efficientꢀandꢀenvironmentallyꢀfriendlyꢀmethodsꢀtoꢀoxidizeꢀ
*ꢀ
Correspondingꢀauthor.ꢀTel/Fax:ꢀ+86‐411‐84379245;ꢀE‐mail:ꢀxujie@dicp.ac.cnꢀ ꢀ ꢀ
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(20803074,ꢀ21233008)ꢀandꢀtheꢀ"StrategicꢀPriorityꢀResearchꢀPro‐
gram–ClimateꢀChange:ꢀCarbonꢀBudgetꢀandꢀRelatedꢀIssues"ꢀofꢀtheꢀChineseꢀAcademyꢀofꢀSciencesꢀ(XDA050102).ꢀ
DOI:ꢀ10.1016/S1872‐2067(14)60132‐7ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ35,ꢀNo.ꢀ10,ꢀOctoberꢀ2014ꢀ ꢀ ꢀ

1654ꢀ
JiayingꢀCaiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660ꢀ
Inꢀ ourꢀ previousꢀ study,ꢀ weꢀ foundꢀ thatꢀ gold‐basedꢀ catalystsꢀ
Tableꢀ1ꢀ ꢀ
areꢀ effectiveꢀ forꢀ alcoholꢀ oxidationꢀ [23].ꢀ Moreover,ꢀ weꢀ haveꢀ
successfullyꢀencapsulatedꢀ1‐nmꢀAuꢀnanoclustersꢀinꢀtheꢀsuper‐
CatalyticꢀoxidationꢀofꢀglycerolꢀoverꢀAuꢀcatalystsꢀwithꢀdifferentꢀsupports.
D
Au
ꢀ
Conversionꢀ
Productꢀyieldꢀ(%)ꢀ
TARACꢀ OXALA Others
Catalystꢀ
Au/ACꢀ
cageꢀ ofꢀ HYꢀ zeolite.ꢀ Au/HYꢀ showedꢀ highꢀ efficiencyꢀ inꢀ 5‐
ꢀ
hy‐
(nm)
15ꢀ
10ꢀ
ꢀ 6ꢀ
ꢀ 2ꢀ
ꢀ 1ꢀ
(%)ꢀ
90ꢀ
98ꢀ
98ꢀ
99ꢀ
98ꢀ
ꢀ 4ꢀ
GLYAꢀ
80ꢀ
ꢀ 2ꢀ
26ꢀ
ꢀ 5ꢀ
droxymethyl‐2‐furfuralꢀ oxidation,ꢀ achievingꢀ 99%ꢀ yieldꢀ ofꢀ 2,5‐
ꢀ
ꢀ 6ꢀ
24ꢀ
43ꢀ
69ꢀ
80ꢀ
ꢀ 0ꢀ
ꢀ 2ꢀ
55ꢀ
ꢀ 4ꢀ
ꢀ 6ꢀ
12ꢀ
ꢀ 0ꢀ
ꢀ 2ꢀ
17ꢀ
25ꢀ
19ꢀ
ꢀ 3ꢀ
ꢀ 0ꢀ
Au/CeO
Au/NaYꢀ
Au/REYꢀ
Au/HYꢀ
HYꢀ
2
ꢀ
furandicarboxylicꢀacidꢀ[24].ꢀInꢀthisꢀstudy,ꢀinspiredꢀbyꢀitsꢀexcel‐
lentꢀ performanceꢀ inꢀ convertingꢀ hydroxylꢀ groupsꢀ toꢀ carboxylꢀ
groups,ꢀweꢀinvestigatedꢀsupportedꢀAuꢀcatalystsꢀforꢀtheꢀoxida‐
tionꢀofꢀglycerol.ꢀWeꢀcomparedꢀtheꢀcatalyticꢀperformanceꢀofꢀAuꢀ
onꢀdifferentꢀsupports,ꢀinvestigatedꢀtheꢀoxidationꢀpathway,ꢀandꢀ
exploredꢀtheꢀconversionꢀprocessꢀofꢀGLYAꢀtoꢀTARAC.ꢀ ꢀ
ꢀ 3ꢀ
ꢀ 4ꢀ
—ꢀ
2
Reactionꢀconditions:ꢀ0.23ꢀgꢀglycerolꢀinꢀ4.6ꢀgꢀH O,ꢀ0.4ꢀgꢀNaOH,ꢀ0.3ꢀgꢀcata‐
2
lystꢀ(1.5ꢀwt%ꢀAu),ꢀ60ꢀ°C,ꢀ p(O )=ꢀ0.3ꢀMPa,ꢀ9ꢀh,ꢀtheꢀAu/glycerolꢀmolarꢀ
ratioꢀ1/150.ꢀ
GLYA:ꢀGlycericꢀacid;ꢀTARAC:ꢀTartronicꢀacid;ꢀOXALA:ꢀOxalicꢀacid.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2
.1.ꢀ ꢀ Catalystꢀpreparationꢀandꢀcharacterizationꢀ
niedꢀbyꢀC–CꢀcleavageꢀwithꢀformicꢀacidꢀandꢀOXALAꢀasꢀtheꢀdeg‐
radationꢀproducts.ꢀInꢀtheꢀcaseꢀofꢀAu/AC,ꢀglycerolꢀwasꢀefficientlyꢀ
oxidizedꢀtoꢀGLYAꢀwithꢀ80%ꢀyield,ꢀbutꢀtheꢀyieldꢀofꢀTARACꢀwasꢀ
lowꢀ(6%),ꢀwhichꢀisꢀconsistentꢀwithꢀpreviousꢀstudiesꢀthatꢀGLYAꢀ
wasꢀ theꢀ mainꢀ productꢀ overꢀ Au/ACꢀ [16].ꢀ Forꢀ theꢀ Au/HY,ꢀ
Au/REY,ꢀ andꢀ Au/NaYꢀ catalysts,ꢀ thereꢀ wasꢀ aꢀ higherꢀ yieldꢀ ofꢀ
Theꢀcatalystsꢀwereꢀpreparedꢀbasedꢀonꢀtheꢀmethodsꢀinꢀourꢀ
previousꢀworkꢀ[24].ꢀAꢀcertainꢀamountꢀofꢀsupportꢀwasꢀaddedꢀtoꢀ
HAuCl ꢀaqueousꢀsolutionꢀ(50ꢀmL,ꢀ0.1ꢀmol/L).ꢀAfterꢀstirringꢀatꢀ
0ꢀ°Cꢀforꢀ2ꢀh,ꢀsodiumꢀcitrateꢀsolutionꢀwasꢀadded.ꢀTheꢀobtainedꢀ
4
6
mixtureꢀ wasꢀ stirredꢀ forꢀ anotherꢀ 2ꢀ h.ꢀ Afterꢀ centrifugationꢀ andꢀ
washingꢀwithꢀdistilledꢀwater,ꢀtheꢀsampleꢀwasꢀtreatedꢀatꢀ100ꢀ°Cꢀ
TARACꢀ thanꢀ forꢀ theꢀ Au/ACꢀ andꢀ Au/CeO ꢀ catalysts.ꢀ Goldꢀ
2
nanoclustersꢀonꢀHYꢀzeoliteꢀhadꢀextremelyꢀhighꢀactivity,ꢀachiev‐
ingꢀ98%ꢀconversionꢀwithꢀ80%ꢀyieldꢀofꢀTARAC.ꢀHowever,ꢀtheꢀHYꢀ
supportꢀaloneꢀonlyꢀhadꢀveryꢀlowꢀactivity.ꢀOverꢀtheꢀAu/REYꢀcat‐
alyst,ꢀ90%ꢀconversionꢀwithꢀ69%ꢀyieldꢀofꢀTARACꢀwasꢀachieved,ꢀ
andꢀAu/NaYꢀonlyꢀgaveꢀ43%ꢀyieldꢀofꢀTARAC.ꢀ ꢀ
inꢀH ꢀatmosphereꢀ(0.1ꢀMPa)ꢀforꢀ6ꢀh.ꢀTheꢀAuꢀloadingꢀforꢀtheseꢀ
2
catalystsꢀwasꢀ1.5ꢀwt%.ꢀ ꢀ
Transmissionꢀelectronꢀmicroscopyꢀ(TEM)ꢀstudiesꢀwereꢀper‐
formedꢀinꢀaꢀFEIꢀTecnaiꢀG2ꢀF30ꢀS‐Twinꢀelectronꢀmicroscope.ꢀTheꢀ
real‐timeꢀ inꢀ situꢀ Fourierꢀ transformꢀ infraredꢀ spectroscopyꢀ
AsꢀshownꢀinꢀFig.ꢀ1,ꢀtheꢀAuꢀparticleꢀsizeꢀvariesꢀimmenselyꢀonꢀ
(FT‐IR)ꢀmeasurementsꢀwereꢀcarriedꢀoutꢀwithꢀaꢀMettlerꢀToledoꢀ
differentꢀsupports.ꢀForꢀACꢀandꢀCeO ꢀsupports,ꢀAuꢀparticlesꢀhadꢀ
2
ReactIRꢀ 45mꢀ spectrometer.ꢀ Anꢀ Infraredꢀ Associatesꢀ liquidꢀ ni‐
trogen‐cooledꢀ AgXꢀ fiberꢀ conduitꢀ diamond‐attenuatedꢀ totalꢀ re‐
flectionꢀprobeꢀwasꢀused.ꢀ
averageꢀ sizesꢀ ofꢀ 15ꢀ andꢀ 10ꢀ nm,ꢀ respectively.ꢀ Theirꢀ differentꢀ
catalyticꢀ performanceꢀ mayꢀ beꢀ attributedꢀ toꢀ theꢀ differencesꢀ inꢀ
C–Cꢀcleavageꢀactiveꢀsitesꢀonꢀtheꢀsupportsꢀandꢀtheꢀmetalꢀsupportꢀ
interaction.ꢀForꢀAu/HY,ꢀtheꢀAuꢀnanoclustersꢀhadꢀaꢀsizeꢀaroundꢀ
1ꢀnm,ꢀwhichꢀhasꢀbeenꢀdemonstratedꢀbyꢀdetailedꢀcharacteriza‐
tionsꢀ inꢀ ourꢀ previousꢀ studyꢀ [24].ꢀ Itꢀ seemsꢀ thatꢀ theꢀ yieldꢀ ofꢀ
TARACꢀincreasedꢀfromꢀ43%ꢀtoꢀ80%ꢀwhenꢀtheꢀAuꢀnanoparticleꢀ
sizeꢀdecreasedꢀfromꢀ6ꢀtoꢀ1ꢀnm.ꢀTheseꢀresultsꢀsuggestꢀthatꢀtheꢀ
formationꢀofꢀTARACꢀcanꢀbeꢀsignificantlyꢀincreasedꢀbyꢀdecreas‐
ingꢀ theꢀ Auꢀ particleꢀ size.ꢀ Therefore,ꢀ theꢀ smallꢀ sizeꢀ ofꢀ theꢀ Auꢀ
nanoclustersꢀ isꢀ theꢀ mainꢀ reasonꢀ forꢀ theꢀ formationꢀ ofꢀ TARACꢀ
whenꢀchoosingꢀYꢀtypeꢀzeoliteꢀasꢀsupport.ꢀ
2.2.ꢀ ꢀ Glycerolꢀoxidationꢀandꢀproductꢀanalysisꢀ ꢀ
Aꢀ typicalꢀ reactionꢀ procedureꢀ wasꢀ asꢀ follows.ꢀ Glycerolꢀ (2.5ꢀ
mmol),ꢀ H Oꢀ (4.6ꢀ g),ꢀ NaOHꢀ (0.4ꢀ g),ꢀ andꢀ catalystꢀ (0.3ꢀ g,ꢀ 0.023ꢀ
2
mmol)ꢀ wereꢀ addedꢀ intoꢀ theꢀ autoclave.ꢀ Theꢀ autoclaveꢀ wasꢀ
chargedꢀwithꢀdioxygenꢀ(0.3ꢀMPa),ꢀmaintainedꢀatꢀ60ꢀ°Cꢀforꢀ9ꢀh,ꢀ
andꢀthenꢀcooled.ꢀTheꢀreactionꢀmixtureꢀwasꢀacidifiedꢀandꢀana‐
lyzedꢀbyꢀhigh‐performanceꢀliquidꢀchromatographyꢀ(HPLC)ꢀonꢀaꢀ
Watersꢀ2695ꢀsystem.ꢀ ꢀ
3.2.ꢀ ꢀ Reactionꢀcourseꢀandꢀproposedꢀcatalyticꢀrouteꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
Inꢀtheꢀreaction,ꢀTARACꢀmayꢀbeꢀproducedꢀeitherꢀbyꢀtheꢀcon‐
3
.1.ꢀ ꢀ Catalyticꢀperformanceꢀ ꢀ
secutiveꢀreactionꢀinꢀwhichꢀglycerolꢀisꢀfirstꢀconvertedꢀtoꢀGLYAꢀ
andꢀthenꢀtoꢀTARAC,ꢀorꢀbyꢀparallelꢀreactionsꢀwhereꢀtwoꢀhydrox‐
ylꢀgroupsꢀareꢀsimultaneouslyꢀoxidizedꢀandꢀglycerolꢀisꢀdirectlyꢀ
transformedꢀ toꢀ TARACꢀ inꢀ oneꢀ step.ꢀ Forꢀ theꢀ Au/ACꢀ catalyst,ꢀ
glycerolꢀwasꢀefficientlyꢀoxidizedꢀtoꢀGLYAꢀwithꢀproductionꢀofꢀaꢀ
smallꢀamountꢀofꢀTARACꢀ(Tableꢀ1).ꢀMoreover,ꢀglycerolꢀoxidationꢀ
overꢀ Au/HYꢀ showedꢀ 10%ꢀ yieldꢀ ofꢀ GLYA.ꢀ Itꢀ isꢀ proposedꢀ thatꢀ
GLYAꢀmayꢀbeꢀtheꢀintermediateꢀsubstance.ꢀToꢀstudyꢀtheꢀprocess,ꢀ
theꢀinfluenceꢀofꢀreactionꢀtimeꢀonꢀtheꢀcatalyticꢀperformanceꢀofꢀ
Au/HYꢀwasꢀinvestigated.ꢀAsꢀshownꢀinꢀFig.ꢀ2(a),ꢀtheꢀconversionꢀ
ofꢀglycerolꢀincreasedꢀwithꢀtimeꢀandꢀreachedꢀ98%ꢀafterꢀ3ꢀh.ꢀTheꢀ
yieldꢀofꢀGLYAꢀincreasedꢀinꢀtheꢀinitialꢀ2ꢀhꢀandꢀreachedꢀaꢀmaxi‐
mumꢀ valueꢀ ofꢀ 38%.ꢀ Thenꢀ theꢀ amountꢀ ofꢀ GLYAꢀ graduallyꢀ de‐
Initially,ꢀweꢀemployedꢀAuꢀcatalystsꢀwithꢀdifferentꢀsupportsꢀ
(CeO
2
,ꢀ activatedꢀ carbonꢀ (AC),ꢀ HY,ꢀ REY,ꢀ andꢀ NaY)ꢀ onꢀ glycerolꢀ
oxidationꢀreactionꢀatꢀ60ꢀ°Cꢀunderꢀ0.3ꢀMPaꢀO
2
ꢀinꢀwater.ꢀAsꢀtheꢀ
reactionsꢀwereꢀconductedꢀinꢀalkalineꢀsolution,ꢀtheꢀfinalꢀprod‐
uctsꢀ wereꢀ inꢀ theꢀ formꢀ ofꢀ glycerate,ꢀ tartronate,ꢀ andꢀ oxalate.ꢀ
Thus,ꢀacidificationꢀtoꢀtheꢀcarboxylicꢀacidꢀformꢀwasꢀrequiredꢀforꢀ
analysis.ꢀ Theꢀ catalystsꢀ hadꢀ remarkablyꢀ differentꢀ performanceꢀ
forꢀglycerolꢀoxidationꢀ(Tableꢀ1).ꢀWhenꢀgoldꢀwasꢀsupportedꢀonꢀ
CeO ,ꢀitꢀgaveꢀ98%ꢀconversion.ꢀHowever,ꢀtheꢀmainꢀproductꢀwasꢀ
oxalicꢀ acidꢀ (OXALA,ꢀ 55%ꢀ yield),ꢀ andꢀ theꢀ yieldꢀ ofꢀ TARACꢀ wasꢀ
onlyꢀ24%,ꢀsuggestingꢀthatꢀtheꢀoxidationꢀprocessꢀwasꢀaccompa‐
2

ꢀ
JiayingꢀCaiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660ꢀ
1655ꢀ
0
.5
.4
.3
.2
.1
.0
(
a)
(b)
0
0.3
0.2
0.1
0.0
0
0
0
0
1
0
15 20 25
50 nm
1
00 nm
8.5
11 14.5
Diameter (nm)
Diameter (nm)
0
.5
.4
.3
.2
.1
0.0
0
.4
.3
.2
.1
(
c)
(d)
0
0
0
0
0
0
0
20 nm
0.0
1
2
3
4
0
5
10
15
20 nm
Diameter (nm)
Diameter (nm)
ꢀ
2
Fig.ꢀ1.ꢀRepresentativeꢀTEMꢀimagesꢀandꢀsizeꢀdistributionsꢀofꢀ(a)ꢀAu/AC,ꢀ(b)ꢀAu/CeO ,ꢀ(c)ꢀAu/REY,ꢀandꢀ(d)ꢀAu/NaY.ꢀ
creased,ꢀ andꢀ theꢀ yieldꢀ wasꢀ lowꢀ (2%)ꢀ afterꢀ 9ꢀ h.ꢀ Theꢀ trendꢀ ofꢀ
GLYAꢀ concentrationꢀ wentꢀ throughꢀ aꢀ volcanoꢀ curve,ꢀ whichꢀ isꢀ
consistentꢀwithꢀtheꢀcharacterꢀofꢀconsecutiveꢀreaction,ꢀsuggest‐
ingꢀthatꢀ glycerolꢀmayꢀfirstꢀconvertꢀtoꢀGLYAꢀandꢀthenꢀGLYAꢀisꢀ
oxidizedꢀtoꢀTARACꢀ[22].ꢀ
Real‐timeꢀ inꢀ situꢀ FT‐IRꢀ spectroscopyꢀ furtherꢀ confirmsꢀ theꢀ
conversionꢀofꢀtheꢀmonocarboxylicꢀacidꢀtoꢀtheꢀdicarboxylicꢀacidꢀ
duringꢀtheꢀglycerolꢀoxidationꢀprocessꢀoverꢀAu/HYꢀ(Fig.ꢀ2).ꢀBe‐
foreꢀtheꢀreaction,ꢀtheꢀIRꢀspectraꢀofꢀglycerol,ꢀTARAC,ꢀGLYA,ꢀandꢀ
theꢀ Au/HYꢀ catalystꢀ wereꢀ recordedꢀ underꢀ reactionꢀ conditionsꢀ
(Fig.ꢀ2(b))ꢀ[25].ꢀInꢀtheꢀbeginning,ꢀonlyꢀtheꢀcharacteristicꢀpeaksꢀ
ofꢀ glycerolꢀ andꢀ theꢀ catalystꢀ areꢀ observedꢀ atꢀ 1045ꢀ andꢀ 1640ꢀ
−1
cm ,ꢀrespectively.ꢀAfterꢀ1ꢀhꢀreactionꢀtime,ꢀIRꢀbandsꢀatꢀ1340ꢀandꢀ
−1
1600ꢀcm ꢀappearedꢀ(Fig.ꢀ2(b)ꢀandꢀ(c)),ꢀindicatingꢀtheꢀproduc‐
tionꢀofꢀTARAC.ꢀInꢀaddition,ꢀtheꢀintensityꢀofꢀtheꢀglycerolꢀpeakꢀatꢀ
−1
1045ꢀcm ꢀdecreasedꢀwithꢀtimeꢀ(Fig.ꢀ2(d)).ꢀItꢀshouldꢀbeꢀnotedꢀ
1
00
100
80
60
40
20
0
(
a)
(b)
Tatronic acid
8
6
4
2
0
0
0
0
0
Glyceric acid
Glycerol
Catalyst
1040
Conversion
TARAC
GLYA
1340
10 h
8 h
OXALA
6
4
h
h
2 h
1
0
h
h
1600
1400
1200
1000
800
0
1
2
3
4
5
6
7
8
9
1
Time (h)
Wavenumber (cm )
ꢀ
ꢀ ꢀ
(c)
(d)
1
800 1700 1600 1500 1400 1300 1200
1200
1150
1100
1050
1000
950
−1
−1
Wavenumber (cm )
Wavenumber (cm )
ꢀ
Fig.ꢀ2.ꢀReactionꢀcourseꢀ(a)ꢀandꢀaꢀsegmentꢀofꢀtheꢀinꢀsituꢀFT‐IRꢀspectraꢀ(b−d)ꢀforꢀglycerolꢀoxidationꢀonꢀtheꢀAu/HYꢀcatalyst.ꢀ

1656ꢀ
JiayingꢀCaiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660ꢀ
−1
thatꢀalthoughꢀtheꢀpeakꢀofꢀGLYAꢀatꢀ1420ꢀcm ꢀmaintainedꢀaꢀlowꢀ
intensity,ꢀ itꢀ initiallyꢀ increasedꢀ andꢀ thenꢀ decreasedꢀ duringꢀ theꢀ
reaction.ꢀ ꢀ
Glycerol
TARAC
Throughꢀcalculation,ꢀtheꢀglycerolꢀoxidationꢀrateꢀwasꢀcalcu‐
latedꢀtoꢀbeꢀ44ꢀmolglycerolꢀ/(molAuh)ꢀforꢀtheꢀinitialꢀ2ꢀh.ꢀTheꢀgen‐
erationꢀ ratesꢀ ofꢀ TARACꢀ andꢀ GLYAꢀ wereꢀ 20ꢀ andꢀ 19ꢀ molproduct
ꢀ
/(molAuh),ꢀrespectively.ꢀTheꢀsimilarꢀrateꢀvaluesꢀforꢀTARACꢀandꢀ
GLYAꢀcanꢀbeꢀexplainedꢀbyꢀtheꢀfactꢀthatꢀtheyꢀwereꢀobtainedꢀviaꢀ
resembleꢀoxidationꢀprocessesꢀandꢀtheꢀreactionꢀwasꢀcomposedꢀ
ofꢀ consecutiveꢀ processesꢀ [26].ꢀ Eachꢀ stepꢀ ofꢀ theꢀ consecutiveꢀ
processꢀinvolvesꢀtheꢀoxidationꢀofꢀoneꢀhydroxylꢀgroup.ꢀ ꢀ
Oxidationꢀ ofꢀ GLYAꢀ accompanyingꢀ withꢀ real‐timeꢀ inꢀ situꢀ
FT‐IRꢀ experimentsꢀ wasꢀ performedꢀ toꢀ determineꢀ whetherꢀ itꢀ
couldꢀbeꢀfurtherꢀoxidizedꢀtoꢀTARACꢀ(Fig.ꢀ3).ꢀDuringꢀtheꢀfirstꢀ6ꢀh,ꢀ
GLYAꢀwasꢀgraduallyꢀoxidizedꢀtoꢀTARAC.ꢀTheꢀreactionꢀachievedꢀ
GLYA
Schemeꢀ1.ꢀProposedꢀreactionꢀpathwayꢀforꢀtheꢀformationꢀofꢀTARACꢀoverꢀ
Au/HYꢀcatalyst.ꢀ
9
5%ꢀconversionꢀwithꢀ75%ꢀyieldꢀofꢀTARACꢀ(Fig.ꢀ3(a))ꢀafterꢀ9ꢀh,ꢀ
−1
whichꢀ isꢀ consistentꢀ withꢀ theꢀ peakꢀ atꢀ 1115ꢀ cm ꢀ (GLYA)ꢀ de‐
−1
3.3.ꢀ ꢀ Effectsꢀofꢀpressureꢀandꢀtemperatureꢀonꢀglycerolꢀoxidationꢀ ꢀ
creasingꢀandꢀpeakꢀatꢀ1340ꢀcm ꢀ(TARAC)ꢀincreasingꢀinꢀtheꢀre‐
al‐timeꢀinꢀsituꢀFT‐IRꢀspectrumꢀ(Fig.ꢀ3(b))ꢀwithinꢀ5ꢀhꢀoxidationꢀ
reactionꢀ time.ꢀ Thisꢀ experimentꢀ suggestsꢀ thatꢀ GLYAꢀ isꢀ theꢀ in‐
termediateꢀinꢀglycerolꢀoxidation.ꢀInꢀaddition,ꢀthereꢀisꢀnoꢀdetec‐
tionꢀofꢀaldehaydeꢀproductionꢀsuchꢀasꢀglyceraldehyde.ꢀTheꢀpro‐
posedꢀ reactionꢀ pathwayꢀ forꢀ glycerolꢀ oxidationꢀ isꢀ shownꢀ inꢀ
Schemeꢀ1.ꢀGlycerolꢀwasꢀfirstꢀdirectlyꢀoxidizedꢀtoꢀGLYA,ꢀandꢀthenꢀ
GLYAꢀwasꢀfurtherꢀoxidizedꢀtoꢀTARAC.ꢀ
Theꢀeffectꢀofꢀoxygenꢀpressureꢀonꢀglycerolꢀoxidationꢀwasꢀin‐
vestigated,ꢀandꢀtheꢀresultsꢀareꢀshownꢀinꢀFig.ꢀ4.ꢀTheꢀconversionꢀ
ofꢀglycerolꢀgraduallyꢀincreasedꢀwithꢀincreasingꢀpressureꢀfromꢀ
.1ꢀtoꢀ0.5ꢀMPa.ꢀInꢀaddition,ꢀtheꢀyieldꢀofꢀTARACꢀincreasedꢀfromꢀ
0%ꢀtoꢀ80%ꢀwhenꢀtheꢀO
ꢀpressureꢀwasꢀincreasedꢀfromꢀ0.1ꢀtoꢀ
.3ꢀMPa.ꢀHowever,ꢀfurtherꢀincreasingꢀtheꢀpressureꢀtoꢀ0.5ꢀMPaꢀ
didꢀnotꢀfurtherꢀincreaseꢀtheꢀyieldꢀofꢀTARAC.ꢀInꢀfact,ꢀtheꢀyieldꢀofꢀ
TARACꢀdecreasedꢀtoꢀ58%ꢀatꢀ0.5ꢀMPa,ꢀwhichꢀmayꢀbeꢀcausedꢀbyꢀ
over‐oxidation.ꢀHence,ꢀtheꢀoptimumꢀO ꢀpressureꢀwasꢀ0.3ꢀMPa.ꢀ
Figureꢀ5ꢀshowsꢀtheꢀeffectꢀofꢀreactionꢀtemperatureꢀonꢀglycer‐
olꢀoxidationꢀoverꢀAu/HY.ꢀAtꢀ20ꢀandꢀ40ꢀ°C,ꢀtheꢀyieldꢀofꢀTARACꢀ
wasꢀ lessꢀ thanꢀ 60%.ꢀ Increasingꢀ theꢀ temperatureꢀ tendedꢀ toꢀ in‐
creaseꢀ theꢀ yieldꢀ ofꢀ TARAC.ꢀ However,ꢀ atꢀ 80ꢀ °Cꢀ theꢀ yieldꢀ ofꢀ
0
3
0
2
1
00
100
80
60
40
20
0
2
(a)
8
6
4
2
0
0
0
0
0
Conversion
Tartronic acid
Oxalic acid
100
(a)
80
60
40
0
2
4
6
8
Time (h)
0.1 MPa
.3 MPa
0
2
0
0.5 MPa
(b)
GLYA
0
0
1
2
3
4
5
6
7
8
9
TARAC
Catalyst
Time (h)
1
00
(b)
80
60
40
20
0
0
0
0
.1 MPa
.3 MPa
.5 MPa
1
600
1
340
6
1
h
h
1
600
1400
Wavenumber (cm )
1200
1000
800
0
1
2
3
4
5
6
7
8
9


Time (h)
Fig.ꢀ3.ꢀReactionꢀcourseꢀ(a)ꢀandꢀaꢀsegmentꢀofꢀtheꢀinꢀsituꢀFT‐IRꢀspectra
b)ꢀforꢀGLYAꢀoxidationꢀoverꢀtheꢀAu/HYꢀcatalyst.
(
Fig.ꢀ4.ꢀEffectꢀofꢀpressureꢀonꢀglycerolꢀconversionꢀandꢀTARACꢀproduction

ꢀ
JiayingꢀCaiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660ꢀ
1657ꢀ
rivedꢀ hydroxylꢀ compounds.ꢀ Furtherꢀ applicationꢀ ofꢀ theꢀ Au/HYꢀ
catalystꢀ toꢀ theꢀ oxidationꢀ ofꢀ otherꢀ biomass‐derivedꢀ hydroxylꢀ
compoundsꢀisꢀinꢀprogress.ꢀ
1
00
(a)
8
6
4
2
0
0
0
0
0
o
2
0 C
o
40 C
Referencesꢀ
o
6
8
0 C
o
0 C
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4.ꢀ ꢀ Conclusionsꢀ
[
Weꢀ haveꢀ successfullyꢀ fabricatedꢀ anꢀ Au/HYꢀ catalystꢀ forꢀ theꢀ
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versionꢀ andꢀ 80%ꢀ yieldꢀ ofꢀ TARACꢀ underꢀ mildꢀ conditions.ꢀ Theꢀ
highꢀ efficiencyꢀ ofꢀ Au/HYꢀ inꢀ theꢀ productionꢀ ofꢀ TARACꢀ wasꢀ at‐
tributedꢀ toꢀ theꢀ smallꢀ sizeꢀ ofꢀ theꢀ Auꢀ nanoclustersꢀ onꢀ theꢀ HYꢀ
support.ꢀ Real‐timeꢀ inꢀ situꢀ FT‐IRꢀ experimentsꢀ combiningꢀ withꢀ
reactionꢀcourseꢀrevealedꢀthatꢀglycerolꢀwasꢀinitiallyꢀoxidizedꢀtoꢀ
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[
[20] DimitratosꢀN,ꢀLopez‐SanchezꢀJꢀA,ꢀLennonꢀD,ꢀPortaꢀF,ꢀPratiꢀL,ꢀVillaꢀA.ꢀ
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[23] MaꢀH,ꢀNieꢀX,ꢀCaiꢀJꢀY,ꢀChenꢀC,ꢀGaoꢀJ,ꢀMiaoꢀH,ꢀXuꢀJ.ꢀSciꢀChinaꢀChem,ꢀ
GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2014,ꢀ35:ꢀ1653–1660ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(14)60132‐7
Catalyticꢀoxidationꢀofꢀglycerolꢀtoꢀtartronicꢀacidꢀ
overꢀAu/HYꢀcatalystꢀunderꢀmildꢀconditionsꢀ
Aqueous solution
JiayingꢀCai,ꢀHongꢀMa,ꢀJunjieꢀZhang,ꢀZhongtianꢀDu,ꢀ ꢀ
ꢀ
YizhengꢀHuang,ꢀJinꢀGao,ꢀJieꢀXu*ꢀ ꢀ ꢀ
DalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀ ꢀ
ChineseꢀAcademyꢀofꢀSciences;ꢀ ꢀ
UniversityꢀofꢀChineseꢀAcademyꢀofꢀSciencesꢀ ꢀ
Tartronicꢀ acidꢀ hasꢀ beenꢀ producedꢀ asꢀ theꢀ dominantꢀ
productꢀ inꢀ glycerolꢀ oxidationꢀ overꢀ Au/HYꢀ catalyst.ꢀ
Real‐timeꢀinꢀsituꢀFT‐IRꢀshowedꢀthatꢀglycerolꢀwasꢀfirstꢀ
oxidizedꢀtoꢀglycericꢀacidꢀandꢀthenꢀtoꢀtartronicꢀacid.ꢀ
Glycerol
Tartronic acid
Gold

1658ꢀ
JiayingꢀCaiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1653–1660ꢀ
2
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013,ꢀ19:ꢀ14215ꢀ
ꢀ
[
Pageꢀnumbersꢀreferꢀtoꢀtheꢀcontentsꢀinꢀtheꢀprintꢀversion,ꢀwhichꢀincludeꢀ
bothꢀtheꢀ Englishꢀ andꢀChineseꢀ versionsꢀ ofꢀtheꢀ paper.ꢀ Theꢀ onlineꢀversionꢀ
onlyꢀhasꢀtheꢀEnglishꢀversion.ꢀTheꢀpagesꢀwithꢀtheꢀChineseꢀversionꢀareꢀonlyꢀ
availableꢀinꢀtheꢀprintꢀversion.ꢀ
2
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26] KimuraꢀH,ꢀYokotaꢀY,ꢀSawamotoꢀY.ꢀCatalꢀLett,ꢀ2005,ꢀ99:ꢀ133ꢀ
[