Selective oxidation of glycerol to lactic acid over activated carbon supported Pt catalyst in alkaline solution

Article abstract of DOI:10.1016/S1872-2067(15)61055-5

Pt/activated carbon (Pt/AC) catalyst combined with base works efficiently for lactic acid production from glycerol under mild conditions. Base type (LiOH, NaOH, KOH, or Ba(OH)₂) and base/glycerol molar ratio significantly affected the catalytic performance. The corresponding lactic acid selectivity was in the order of LiOH > NaOH > KOH > Ba(OH)₂. An increase in LiOH/glycerol molar ratio elevated the glycerol conversion and lactic acid selectivity to some degree, but excess LiOH inhibited the transformation of glycerol to lactic acid. In the presence of Pt/AC catalyst, the maximum selectivity of lactic acid was 69.3% at a glycerol conversion of 100% after 6 h at 90 °C, with a LiOH/glycerol molar ratio of 1.5. The Pt/AC catalyst was recycled five times and was found to exhibit slightly decreased glycerol conversion and stable lactic acid selectivity. In addition, the experimental results indicated that reaction intermediate dihydroxyacetone was more favorable as the starting reagent for lactic acid formation than glyceraldehyde. However, the Pt/AC catalyst had adverse effects on the intermediate transformation to lactic acid, because it favored the catalytic oxidation of them to glyceric acid.

Full text of DOI:10.1016/S1872-2067(15)61055-5

ChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509
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ꢀ ꢀ ꢀ
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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
Selectiveꢀoxidationꢀofꢀglycerolꢀtoꢀlacticꢀacidꢀoverꢀactivatedꢀcarbonꢀ
supportedꢀPtꢀcatalystꢀinꢀalkalineꢀsolutionꢀ
a,c
a,#
a,c
a,b,
ChenꢀZhangꢀ ,ꢀTaoꢀWangꢀ ,ꢀXiaoꢀLiuꢀ ,ꢀYunjieꢀDingꢀ *
ꢀ
aꢀDalianꢀNationalꢀLaboratoryꢀforꢀCleanꢀEnergy,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀDalianꢀ116023,ꢀLiaoning,ꢀChinaꢀ
bꢀStateꢀKeyꢀLaboratoryꢀofꢀCatalysis,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀDalianꢀ116023,ꢀLiaoning,ꢀChinaꢀ
cꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciences,ꢀBeijingꢀ100049,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Pt/activatedꢀcarbonꢀ(Pt/AC)ꢀcatalystꢀcombinedꢀwithꢀbaseꢀworksꢀefficientlyꢀforꢀlacticꢀacidꢀproductionꢀ
Receivedꢀ6ꢀJanuaryꢀ2016ꢀ
Acceptedꢀ30ꢀJanuaryꢀ2016ꢀ
Publishedꢀ5ꢀAprilꢀ2016ꢀ
fromꢀglycerolꢀunderꢀmildꢀconditions.ꢀBaseꢀtypeꢀ(LiOH,ꢀNaOH,ꢀKOH,ꢀorꢀBa(OH)
molarꢀratioꢀsignificantlyꢀaffectedꢀtheꢀcatalyticꢀperformance.ꢀTheꢀcorrespondingꢀlacticꢀacidꢀselectivityꢀ
wasꢀinꢀtheꢀorderꢀofꢀLiOHꢀ>ꢀNaOHꢀ>ꢀKOHꢀ>ꢀBa(OH) .ꢀAnꢀincreaseꢀinꢀLiOH/glycerolꢀmolarꢀratioꢀele‐
2
)ꢀandꢀbase/glycerolꢀ
2
vatedꢀtheꢀglycerolꢀconversionꢀandꢀlacticꢀacidꢀselectivityꢀtoꢀsomeꢀdegree,ꢀbutꢀexcessꢀLiOHꢀinhibitedꢀ
theꢀtransformationꢀofꢀglycerolꢀtoꢀlacticꢀacid.ꢀInꢀtheꢀpresenceꢀofꢀPt/ACꢀcatalyst,ꢀtheꢀmaximumꢀselec‐
tivityꢀ ofꢀ lacticꢀ acidꢀ wasꢀ 69.3%ꢀ atꢀ aꢀ glycerolꢀ conversionꢀ ofꢀ 100%ꢀ afterꢀ 6ꢀ hꢀ atꢀ 90ꢀ °C,ꢀ withꢀ aꢀ Li‐
OH/glycerolꢀmolarꢀratioꢀofꢀ1.5.ꢀTheꢀPt/ACꢀcatalystꢀwasꢀrecycledꢀfiveꢀtimesꢀandꢀwasꢀfoundꢀtoꢀexhibitꢀ
slightlyꢀdecreasedꢀglycerolꢀconversionꢀandꢀstableꢀlacticꢀacidꢀselectivity.ꢀInꢀaddition,ꢀtheꢀexperimentalꢀ
resultsꢀindicatedꢀthatꢀreactionꢀintermediateꢀdihydroxyacetoneꢀwasꢀmoreꢀfavorableꢀasꢀtheꢀstartingꢀ
reagentꢀ forꢀ lacticꢀ acidꢀ formationꢀ thanꢀ glyceraldehyde.ꢀ However,ꢀ theꢀ Pt/ACꢀ catalystꢀ hadꢀ adverseꢀ
effectsꢀonꢀtheꢀintermediateꢀtransformationꢀtoꢀlacticꢀacid,ꢀbecauseꢀitꢀfavoredꢀtheꢀcatalyticꢀoxidationꢀofꢀ
themꢀtoꢀglycericꢀacid.ꢀ
Keywords:ꢀ
Glycerolꢀ
Lacticꢀacidꢀ
Platinumꢀ
Activatedꢀcarbonꢀ
Oxidationꢀ
Baseꢀtype
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
portantꢀbuildingꢀblockꢀchemicalꢀthatꢀisꢀwidelyꢀusedꢀinꢀtheꢀfood,ꢀ
cosmetics,ꢀ andꢀ pharmaceuticalꢀ industries.ꢀ Notably,ꢀ polylacticꢀ
acidꢀhasꢀtheꢀpotentialꢀtoꢀ replaceꢀconventionalꢀoil‐basedꢀ poly‐
ethyleneꢀterephthalateꢀ(PET)ꢀplasticsꢀbecauseꢀofꢀitsꢀbiodegra‐
dabilityꢀ andꢀ biocompatibilityꢀ [7].ꢀ Itꢀ isꢀ estimatedꢀ thatꢀ theꢀ
worldwideꢀ demandꢀ forꢀ LAꢀ willꢀ reachꢀ 600ꢀ ktꢀ inꢀ 2020ꢀ [8].ꢀ Atꢀ
present,ꢀLAꢀisꢀmainlyꢀproducedꢀbyꢀfermentationꢀfromꢀcarbohy‐
drates;ꢀhowever,ꢀthisꢀprocessꢀisꢀtime‐consumingꢀandꢀinvolvesꢀ
complexꢀseparationꢀstepsꢀ[9].ꢀAsꢀaꢀresult,ꢀtheꢀchemicalꢀtrans‐
formationꢀofꢀglycerolꢀtoꢀLAꢀisꢀattractingꢀextensiveꢀeffortsꢀfromꢀ
theꢀacademicꢀandꢀindustrialꢀcommunities.ꢀ
Biofuelꢀ synthesisꢀ viaꢀ transesterificationꢀ ofꢀ plantꢀ orꢀ animalꢀ
oilꢀ hasꢀ becomeꢀ aꢀ promisingꢀ alternativeꢀ routeꢀ forꢀ sustainableꢀ
energyꢀ production,ꢀ andꢀ alsoꢀ producesꢀ glycerolꢀ asꢀ aꢀ majorꢀ
by‐productꢀ duringꢀ theꢀ manufacturingꢀ process.ꢀ Therefore,ꢀ theꢀ
transformationꢀofꢀglycerolꢀintoꢀvalue‐addedꢀchemicalsꢀisꢀvitalꢀtoꢀ
theꢀ overallꢀ competitivenessꢀ ofꢀ theꢀ biofuelꢀ industryꢀ [1,2].ꢀ Theꢀ
structuralꢀcharacteristicꢀofꢀtripleꢀhydroxylꢀgroupsꢀmakesꢀglyc‐
erolꢀanꢀexcellentꢀchemicalꢀfeedstockꢀforꢀtheꢀsynthesisꢀofꢀversa‐
tileꢀhigh‐valueꢀderivatives,ꢀsuchꢀasꢀlacticꢀacidꢀ(LA),ꢀglycericꢀacidꢀ
(GLYA),ꢀandꢀ1,3‐propanediolꢀ[3–6].ꢀInꢀparticular,ꢀLAꢀisꢀanꢀim‐
Theꢀ chemicalꢀ productionꢀ ofꢀ LAꢀ fromꢀ glycerolꢀ hasꢀ beenꢀ in‐
*
ꢀ
ꢀCorrespondingꢀauthor.ꢀTel/Fax:ꢀ+86‐411‐84379143;ꢀE‐mail:ꢀdyj@dicp.ac.cnꢀ
Correspondingꢀauthor.ꢀTel/Fax:ꢀ+86‐411‐84379143;ꢀE‐mail:ꢀwangtao@dicp.ac.cnꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21176236).ꢀ
DOI:ꢀ10.1016/S1872‐2067(15)61055‐5ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ37,ꢀNo.ꢀ4,ꢀAprilꢀ2016ꢀ ꢀ ꢀ

ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
503ꢀ
vestigatedꢀthroughꢀdifferentꢀapproaches,ꢀincludingꢀhydrother‐
malꢀ reactionsꢀ [10–12],ꢀ hydrogenolysisꢀ methodsꢀ [13,14]ꢀ andꢀ
catalyticꢀ selectiveꢀ aerobicꢀ oxidationsꢀ [3,15,16].ꢀ Kishidaꢀ etꢀ al.ꢀ
methodꢀ[3].ꢀInꢀaꢀtypicalꢀexperiment,ꢀ3ꢀgꢀofꢀACꢀ(TangshanꢀUnitedꢀ
Carbon,ꢀ China)ꢀ wasꢀ suspendedꢀinꢀ300ꢀmLꢀofꢀ deionizedꢀwaterꢀ
withꢀvigorousꢀstirring,ꢀandꢀ0.03ꢀgꢀofꢀPtꢀasꢀH
ShanghaiꢀJiuyue,ꢀChina)ꢀsolutionꢀwasꢀadded.ꢀAfterꢀ0.5ꢀh,ꢀanꢀex‐
cessꢀamountꢀofꢀNaBH ꢀ(>ꢀ98%,ꢀTianjinꢀHainachuanꢀScienceꢀandꢀ
2 6
PtCl ꢀ(Ptꢀ≥ꢀ38%,ꢀ
[10]ꢀreportedꢀhydrothermalꢀdecompositionꢀofꢀglycerolꢀtoꢀLAꢀinꢀ
theꢀpresenceꢀofꢀNaOHꢀatꢀ300ꢀ°C,ꢀwhereꢀtheꢀLAꢀmolarꢀyieldꢀcouldꢀ
reachꢀ90%.ꢀMeanwhile,ꢀtheꢀcatalyticꢀhydrogenolysisꢀofꢀglycerolꢀ
toꢀLAꢀhasꢀbeenꢀexploredꢀoverꢀRuꢀandꢀPtꢀcatalystsꢀatꢀ200ꢀ°Cꢀun‐
4
Technology,ꢀ China)ꢀ solutionꢀ wasꢀ introducedꢀ dropwise.ꢀ Theꢀ
suspendedꢀ blackꢀ solutionꢀ wasꢀ stirredꢀ forꢀ 6ꢀ h.ꢀ Afterward,ꢀ theꢀ
derꢀ4ꢀMPaꢀH
2
ꢀinꢀbasicꢀsolutions,ꢀachievingꢀyieldsꢀnoꢀhigherꢀthanꢀ
blackꢀprecipitateꢀwasꢀfilteredꢀandꢀwashedꢀwithꢀdeionizedꢀwaterꢀ

58%ꢀ[13].ꢀUnfortunately,ꢀsevereꢀreactionꢀconditionsꢀ(includingꢀ
3
untilꢀCl ꢀwasꢀnotꢀdetectableꢀwithꢀAgNO ꢀsolution.ꢀTheꢀsolidꢀwasꢀ
highꢀtemperatureꢀandꢀpressure)ꢀhaveꢀbeenꢀmajorꢀconcernsꢀinꢀ
scalingꢀupꢀtheꢀreaction.ꢀThus,ꢀtheꢀselectiveꢀoxidationꢀofꢀglycerolꢀ
toꢀlacticꢀacidꢀinꢀbasicꢀaqueousꢀsolutionꢀisꢀstillꢀattractiveꢀunderꢀ
mildꢀreactionꢀconditions.ꢀShenꢀetꢀal.ꢀ[3]ꢀfirstꢀreportedꢀaꢀone‐potꢀ
driedꢀatꢀ120ꢀ°Cꢀforꢀ12ꢀh.ꢀACꢀwasꢀwashedꢀwithꢀdeionizedꢀwaterꢀ
toꢀremoveꢀsurfaceꢀashꢀandꢀgroundꢀtoꢀ100–200ꢀmeshꢀbeforeꢀuse.ꢀ
2.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ
2
Au‐Pt/TiO ‐catalyzedꢀaerobicꢀoxidationꢀofꢀglycerolꢀatꢀ90ꢀ°Cꢀinꢀ
NaOHꢀwithꢀaꢀLAꢀyieldꢀofꢀaroundꢀ86%.ꢀSimilarꢀresultsꢀhaveꢀbeenꢀ
Metalꢀanalysisꢀwasꢀcarriedꢀoutꢀbyꢀinductivelyꢀcoupledꢀplas‐
maꢀopticalꢀemissionꢀspectroscopyꢀ(ICP‐OES)ꢀonꢀaꢀPerkinꢀElmerꢀ
Optimaꢀ7300ꢀDV,ꢀandꢀshowedꢀthatꢀtheꢀPtꢀloadingꢀofꢀtheꢀcatalystꢀ
wasꢀ 0.9ꢀ wt%ꢀ (designedꢀ loadingꢀ wasꢀ 1ꢀ wt%).ꢀ Theꢀ glycerol/Ptꢀ
molarꢀratioꢀwasꢀcalculatedꢀbasedꢀonꢀtheꢀ0.9ꢀwt%ꢀloading.ꢀPhys‐
icalꢀadsorptionꢀwasꢀcarriedꢀoutꢀonꢀaꢀQuantachromeꢀAutosorb‐1ꢀ
instrument.ꢀ Theꢀ Brunauer–Emmett–Tellerꢀ (BET)ꢀ methodꢀ wasꢀ
usedꢀtoꢀcalculateꢀtheꢀspecificꢀsurfaceꢀareas.ꢀTheꢀt‐plotꢀmethodꢀ
wasꢀappliedꢀtoꢀcalculateꢀtheꢀexternalꢀandꢀmicroꢀsurfaceꢀareas.ꢀ
Totalꢀporeꢀvolumeꢀwasꢀcalculatedꢀbasedꢀonꢀtheꢀamountꢀofꢀni‐
achievedꢀ onꢀ Au/CeO
2
ꢀ andꢀ Pt‐Au/CeO ꢀ catalystsꢀ underꢀ basicꢀ
2
conditionsꢀ[15,16].ꢀ
Generally,ꢀtheꢀproductionꢀofꢀLAꢀfromꢀglycerolꢀoxidationꢀoverꢀ
supportedꢀ nobleꢀ metalꢀ catalystsꢀ isꢀ assistedꢀ byꢀ concentratedꢀ
NaOHꢀsolution,ꢀtypicallyꢀwithꢀaꢀNaOHꢀtoꢀglycerolꢀmolarꢀratioꢀofꢀ
4ꢀ[16–18].ꢀHowever,ꢀtoꢀdate,ꢀ thereꢀhaveꢀbeenꢀfewꢀ reportsꢀonꢀ
glycerolꢀoxidationꢀtoꢀlacticꢀacidꢀinꢀdifferentꢀalkalineꢀsolutions.ꢀ
Inꢀ anꢀ Au‐Pt/C‐catalyzedꢀ 1,2‐propanediolꢀ oxidationꢀ process,ꢀ
Ryabenkovaꢀetꢀal.ꢀ[19]ꢀreportedꢀthatꢀtheꢀpresenceꢀofꢀLiOHꢀaf‐
fordedꢀ theꢀ highestꢀ lactateꢀ yieldꢀ amongstꢀ theꢀ differentꢀ alkalisꢀ
trogenꢀadsorbedꢀatꢀaꢀrelativeꢀpressureꢀ(p/p
)ꢀofꢀ0.99.ꢀBeforeꢀtheꢀ
0
(
LiOH,ꢀNaOH,ꢀKOH,ꢀCsOH,ꢀandꢀRbOH).ꢀGivenꢀthatꢀeachꢀhydrox‐
test,ꢀsamplesꢀwereꢀoutgassedꢀatꢀ250ꢀ°Cꢀforꢀ12ꢀh.ꢀTransmissionꢀ
electronꢀ microscopyꢀ (TEM)ꢀ wasꢀ conductedꢀ withꢀ aꢀ JEM‐2100ꢀ
electronꢀ microscopeꢀ operatingꢀ atꢀ 200ꢀ kV.ꢀ Theꢀ metalꢀ particleꢀ
sizeꢀdistributionꢀwasꢀcalculatedꢀbyꢀcountingꢀapproximatelyꢀ140ꢀ
particlesꢀ inꢀ TEMꢀ images.ꢀ COꢀ pulseꢀ chemisorptionꢀ wasꢀ per‐
formedꢀonꢀaꢀ150‐mgꢀsampleꢀinꢀaꢀquartzꢀU‐tubeꢀonꢀanꢀAltamiraꢀ
Instrumentsꢀ AMI‐300ꢀ withꢀ aꢀ thermalꢀ conductivityꢀ detectionꢀ
(TCD)ꢀ deviceꢀ andꢀ anꢀ OmniStarꢀ GSDꢀ 320ꢀ massꢀ spectrometer.ꢀ
ideꢀalkaliꢀpossessesꢀaꢀspecificꢀionicꢀradius,ꢀtheirꢀrespectiveꢀal‐
kaliꢀ solubility,ꢀ solutionꢀ viscosity,ꢀ andꢀ oxygenꢀ solubilityꢀ mayꢀ
affectꢀtheꢀcatalyticꢀreactionꢀbehaviorꢀ[20,21].ꢀ
Carbonꢀmaterialsꢀhaveꢀbeenꢀwidelyꢀusedꢀasꢀsupportsꢀinꢀhet‐
erogeneousꢀ catalysisꢀ becauseꢀ ofꢀ theirꢀ uniqueꢀ advantages,ꢀ in‐
cludingꢀlargeꢀspecificꢀsurfaceꢀarea,ꢀstabilityꢀinꢀbothꢀacidicꢀandꢀ
basicꢀsolutions,ꢀandꢀeasyꢀrecoveryꢀofꢀtheꢀnobleꢀmetal.ꢀUntilꢀre‐
cently,ꢀ carbon‐supportedꢀ catalystsꢀ wereꢀ investigatedꢀ toꢀ pro‐
duceꢀLAꢀfromꢀglycerolꢀoxidation;ꢀhowever,ꢀGLYAꢀwasꢀgeneratedꢀ
asꢀ theꢀ majorꢀ product.ꢀ Forꢀ example,ꢀ Chornajaꢀ etꢀ al.ꢀ [17]ꢀ andꢀ
Ketchieꢀ etꢀ al.ꢀ [18]ꢀ reportedꢀ lessꢀ thanꢀ 5%ꢀ LAꢀ selectivityꢀ overꢀ
Pd/Cꢀ andꢀ Au/Cꢀ catalysts,ꢀ respectively.ꢀ Heeresꢀ etꢀ al.ꢀ [16]ꢀ alsoꢀ
investigatedꢀtheꢀconversionꢀofꢀglycerolꢀtoꢀLAꢀoverꢀAu/Cꢀcata‐
lystsꢀandꢀobtainedꢀ27%ꢀLAꢀselectivity,ꢀwhichꢀwasꢀtheꢀhighestꢀ
yieldꢀ onꢀ carbon‐supportedꢀ catalystsꢀ atꢀ theꢀ time.ꢀ Therefore,ꢀ
furtherꢀinvestigationꢀofꢀcarbon‐supportedꢀcatalystꢀisꢀattractiveꢀ
fromꢀbothꢀacademicꢀandꢀindustrialꢀperspectives.ꢀ
Afterꢀ10%ꢀH
/Arꢀreductionꢀatꢀ200ꢀ°Cꢀforꢀ1ꢀhꢀandꢀArꢀpostꢀflush,ꢀ
2
10%ꢀ CO/Heꢀ pulseꢀ chemisorptionꢀ wasꢀ initiatedꢀ atꢀ 30ꢀ °C.ꢀ Aꢀ
CO/Ptꢀstoichiometryꢀofꢀ1ꢀwasꢀusedꢀforꢀcalculationsꢀ[22].ꢀ
2.3.ꢀ ꢀ Glycerolꢀoxidationꢀreactionꢀ
Theꢀ glycerolꢀ oxidationꢀ reactionꢀ wasꢀ carriedꢀ outꢀ inꢀ aꢀ
three‐neckꢀ flaskꢀ (100ꢀ mL)ꢀ atꢀ atmosphericꢀ pressureꢀ inꢀ anꢀ oilꢀ
bath.ꢀAꢀknownꢀamountꢀofꢀbaseꢀandꢀcatalystꢀ(0.25ꢀg)ꢀwereꢀaddedꢀ
intoꢀglycerolꢀsolutionꢀ(25ꢀg,ꢀ10ꢀwt%).ꢀWhenꢀtheꢀsolutionꢀtem‐
Herein,ꢀweꢀreportꢀaꢀstudyꢀonꢀglycerolꢀoxidationꢀtoꢀproduceꢀ
LAꢀoverꢀPt/activatedꢀcarbonꢀ(Pt/AC)ꢀcatalystꢀinꢀalkalineꢀaque‐
peratureꢀstabilized,ꢀO
magneticꢀstirringꢀatꢀ800ꢀr/min.ꢀAfterꢀtheꢀreaction,ꢀtheꢀaqueousꢀ
solutionꢀwasꢀfiltered,ꢀneutralizedꢀwithꢀH SO ꢀaqueousꢀsolution,ꢀ
2
ꢀflowꢀwasꢀinitiatedꢀatꢀ100ꢀmL/minꢀwithꢀ
ousꢀsolutionꢀunderꢀO
2
ꢀatꢀatmosphericꢀpressure.ꢀTheꢀeffectsꢀofꢀ
2
4
baseꢀtypeꢀ(LiOH,ꢀNaOH,ꢀKOH,ꢀandꢀBa(OH)
2
)ꢀandꢀbase/glycerolꢀ
andꢀdilutedꢀwithꢀdeionizedꢀwater.ꢀTheꢀproductsꢀwereꢀanalyzedꢀ
byꢀ high‐performanceꢀ liquidꢀ chromatographyꢀ (HPLC)ꢀ onꢀ anꢀ
Agilentꢀ1100ꢀinstrumentꢀequippedꢀwithꢀaꢀrefractiveꢀindexꢀde‐
tectorꢀ (RID).ꢀ Theꢀ analysisꢀ usedꢀ anꢀ Alltechꢀ OA‐1000ꢀ columnꢀ
molarꢀ ratioꢀ onꢀ catalyticꢀ performanceꢀ wereꢀ alsoꢀ investigated.ꢀ
Weꢀ expectꢀ thatꢀ thisꢀ workꢀ willꢀ formꢀ theꢀ basisꢀ ofꢀ aꢀ practicalꢀ
methodꢀ forꢀ LAꢀ productionꢀ fromꢀ glycerolꢀ usingꢀ AC‐supportedꢀ
catalysts.ꢀ
withꢀaꢀseparationꢀtemperatureꢀofꢀ80ꢀ°C.ꢀH
2
SO ꢀaqueousꢀsolutionꢀ
4
(0.005ꢀmol/L)ꢀwasꢀusedꢀasꢀtheꢀmobileꢀphaseꢀatꢀaꢀflowꢀrateꢀofꢀ
2
.ꢀ ꢀ Experimentalꢀ
0.5ꢀmL/min.ꢀAllꢀproductsꢀwereꢀidentifiedꢀbyꢀcomparingꢀreten‐
tionꢀtimesꢀwithꢀthoseꢀofꢀpureꢀmaterials;ꢀquantificationꢀwasꢀbyꢀ
theꢀexternalꢀstandardꢀmethod.ꢀ Glycerolꢀ conversionꢀandꢀliquidꢀ
productꢀselectivityꢀwereꢀcalculatedꢀaccordingꢀtoꢀtheꢀliteratureꢀ
withꢀtheꢀcarbonꢀbalanceꢀgenerallyꢀmoreꢀthanꢀ90%ꢀunlessꢀoth‐
2.1.ꢀ ꢀ Catalystꢀpreparationꢀ
Pt/ACꢀcatalystꢀwasꢀpreparedꢀbyꢀaꢀdeposition–precipitationꢀ

504ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
erwiseꢀ notedꢀ [23].ꢀ Theꢀ spentꢀ catalystꢀ wasꢀ separated,ꢀ washedꢀ
thoroughlyꢀwithꢀdeionizedꢀwater,ꢀandꢀdriedꢀbeforeꢀuseꢀinꢀrecy‐
clingꢀexperiments.ꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ EffectsꢀofꢀPt/ACꢀandꢀNaOHꢀonꢀglycerolꢀoxidationꢀtoꢀlacticꢀ
acidꢀ
TheꢀPt/AC‐catalyzedꢀglycerolꢀoxidationꢀwasꢀconductedꢀandꢀ
theꢀ resultsꢀ areꢀ summarizedꢀ inꢀ Tableꢀ 1.ꢀ Inꢀ allꢀ reactions,ꢀ theꢀ
productsꢀwereꢀobtainedꢀasꢀsalts,ꢀbutꢀforꢀsimplicityꢀandꢀcompar‐
isonꢀtheyꢀ wereꢀ markedꢀ asꢀtheꢀ acidꢀforms.ꢀTheꢀcoexistenceꢀofꢀ
Pt/ACꢀ andꢀ NaOHꢀ ledꢀ toꢀ LAꢀ production,ꢀ givingꢀ 58.5%ꢀ glycerolꢀ
conversionꢀ andꢀ 44.9%ꢀ LAꢀ selectivity.ꢀ By‐productsꢀ wereꢀ alsoꢀ
detected,ꢀincludingꢀGLYA,ꢀtartronicꢀacidꢀ(TA),ꢀglycolicꢀacidꢀ(GA),ꢀ
oxalicꢀacidꢀ(OA),ꢀaceticꢀacidꢀ(AA),ꢀandꢀformicꢀacidꢀ(FA).ꢀReactionꢀ
intermediatesꢀsuchꢀasꢀglyceraldehydeꢀ(GlA),ꢀdihydroxyacetoneꢀ
Schemeꢀ1.ꢀProposedꢀreactionꢀpathwayꢀforꢀglycerolꢀconversionꢀtoꢀlacticꢀ
acidꢀandꢀby‐productsꢀonꢀPt/AC.ꢀ
DHAꢀtoꢀLAꢀorꢀGLYAꢀremainsꢀunclear.ꢀTheirꢀrespectiveꢀselectivi‐
tyꢀtowardꢀLAꢀmayꢀprovideꢀusefulꢀinformationꢀinꢀtheꢀdesignꢀofꢀ
anꢀimprovedꢀcatalystꢀsystem.ꢀ
(DHA),ꢀandꢀpyruvaldehydeꢀ(PyA),ꢀifꢀatꢀallꢀpresent,ꢀcouldꢀnotꢀbeꢀ
detectedꢀunderꢀtheꢀreactionꢀconditions.ꢀ
Forꢀaꢀbetterꢀunderstandingꢀofꢀtheꢀrolesꢀthatꢀtheꢀmetalꢀcata‐
lystꢀandꢀbaseꢀplayedꢀinꢀtheꢀoxidationꢀreaction,ꢀsingleꢀvariableꢀ
analysesꢀwereꢀperformedꢀwithoutꢀPt/ACꢀorꢀbaseꢀ(Tableꢀ1).ꢀInꢀ
theꢀabsenceꢀofꢀPt/ACꢀcatalyst,ꢀNaOHꢀconvertedꢀaꢀtraceꢀamountꢀ
ofꢀglycerolꢀtoꢀformꢀGAꢀ(33.4%)ꢀasꢀtheꢀmainꢀproduct,ꢀtogetherꢀ
withꢀ17.5%ꢀselectivityꢀforꢀLAꢀandꢀ24.6%ꢀselectivityꢀforꢀGLYA.ꢀInꢀ
aꢀbase‐freeꢀenvironment,ꢀglycerolꢀconversionꢀwasꢀ18.6%ꢀwithꢀ
ToꢀgainꢀinsightꢀintoꢀtheꢀformationꢀpathwayꢀforꢀLAꢀandꢀGLYAꢀ
fromꢀGlAꢀorꢀDHA,ꢀaꢀseriesꢀofꢀexperimentsꢀwereꢀperformedꢀinꢀ
2
NaOHꢀ aqueousꢀ solutionꢀ underꢀ anꢀ O ꢀ atmosphereꢀ withꢀ eitherꢀ
GlAꢀorꢀDHAꢀasꢀtheꢀstartingꢀreagent.ꢀAtꢀ5ꢀminꢀofꢀreactionꢀtime,ꢀ
GlAꢀorꢀDHAꢀhadꢀdisappearedꢀcompletelyꢀandꢀtheꢀmainꢀproductsꢀ
wereꢀLAꢀandꢀGLYA,ꢀwithꢀsmallꢀamountsꢀofꢀotherꢀproductsꢀ(TA,ꢀ
GA,ꢀOA,ꢀandꢀFA;ꢀnotꢀshownꢀhere).ꢀFigureꢀ1ꢀ(filledꢀsymbols)ꢀde‐
pictsꢀtheꢀplotꢀofꢀLA/GLYAꢀmolarꢀratioꢀasꢀaꢀfunctionꢀofꢀreactionꢀ
timeꢀ onꢀ streamꢀ inꢀ theꢀ presenceꢀ ofꢀ theꢀ baseꢀ butꢀ withoutꢀ theꢀ
metalꢀ catalyst.ꢀ DHAꢀ reactionꢀ showedꢀ higherꢀ LA/GLYAꢀ molarꢀ
ratiosꢀthanꢀthatꢀofꢀGlAꢀreaction,ꢀindicatingꢀthatꢀDHAꢀasꢀtheꢀsub‐
strateꢀ wasꢀ relativelyꢀ moreꢀ favorableꢀ thanꢀ GlAꢀ toꢀ formꢀ LA.ꢀ Inꢀ
general,ꢀDHAꢀcanꢀproduceꢀLAꢀatꢀlowꢀtemperaturesꢀofꢀ15–140ꢀ
°C;ꢀ however,ꢀ GlAꢀ generatesꢀ LAꢀ atꢀ higherꢀ temperaturesꢀ ofꢀ
200–300ꢀ°Cꢀ[13,27–29].ꢀTheꢀlatterꢀreactionꢀprobablyꢀneedsꢀtoꢀ
overcomeꢀaꢀhighꢀenergyꢀbarrierꢀbecauseꢀtheꢀformationꢀofꢀLAꢀisꢀ
favoredꢀ fromꢀ GlAꢀ atꢀ higherꢀ temperature.ꢀ Anotherꢀ possibilityꢀ
mayꢀbeꢀrelatedꢀtoꢀtheꢀtransformationꢀrate,ꢀwhichꢀcouldꢀbeꢀin‐
86.3%ꢀselectivityꢀforꢀGLYAꢀoverꢀPt/ACꢀcatalyst,ꢀandꢀtheꢀtargetꢀ
LAꢀwasꢀnotꢀdetected.ꢀTheꢀresultsꢀdemonstrateꢀthatꢀPt/ACꢀcata‐
lystꢀ playsꢀ aꢀ decisiveꢀ roleꢀ inꢀ glycerolꢀ activation,ꢀ probablyꢀ be‐
causeꢀtheꢀprimaryꢀH‐eliminationꢀoccursꢀmuchꢀmoreꢀeasilyꢀonꢀaꢀ
metallicꢀcatalystꢀthanꢀinꢀbasicꢀsolutionꢀaloneꢀ[24].ꢀTheꢀroleꢀofꢀ
theꢀbaseꢀisꢀtoꢀincreaseꢀtheꢀrateꢀofꢀglycerolꢀoxidationꢀbyꢀaidingꢀ
theꢀ initialꢀ deprotonationꢀ overꢀ theꢀ Ptꢀ catalyst,ꢀ andꢀ favorablyꢀ
shiftꢀtheꢀequilibriumꢀbyꢀformingꢀsaltꢀproductsꢀ[24].ꢀMeanwhile,ꢀ
theꢀbaseꢀalsoꢀfavorsꢀtheꢀintramolecularꢀCannizzaroꢀrearrange‐
mentꢀoverꢀLAꢀproductionꢀ[3,12].ꢀThisꢀsuggestsꢀthatꢀtheꢀcollab‐
orationꢀofꢀtheꢀmetalꢀcatalystꢀandꢀbaseꢀisꢀindispensableꢀforꢀLAꢀ
productionꢀfromꢀglycerolꢀoxidation,ꢀwhichꢀisꢀinꢀlineꢀwithꢀLiu’sꢀ
reportꢀ[25].ꢀ
TheꢀglycerolꢀoxidationꢀpathwaysꢀthatꢀleadꢀtoꢀLAꢀandꢀGLYAꢀ
areꢀ differentꢀ (Schemeꢀ 1).ꢀ Glycerolꢀ isꢀ firstꢀ dehydrogenatedꢀ toꢀ
GlAꢀandꢀDHAꢀintermediatesꢀbyꢀtheꢀcoordinationꢀofꢀPt/ACꢀandꢀ
base.ꢀ Theyꢀ thenꢀ undergoꢀ eitherꢀ base‐catalyzedꢀ dehydrationꢀ
togetherꢀwithꢀintramolecularꢀCannizzaroꢀrearrangementꢀtoꢀLA,ꢀ
orꢀ furtherꢀ metal‐catalyzedꢀ oxidationꢀ toꢀ GLYA,ꢀ TA,ꢀ andꢀ C–Cꢀ
cleavageꢀ productsꢀ suchꢀ asꢀ GAꢀ orꢀ FAꢀ [3,16,26].ꢀ However,ꢀ theꢀ
mechanismꢀ forꢀ theꢀ transformationꢀ ofꢀ intermediatesꢀ GlAꢀ andꢀ
10
DHA+NaOH
DHA+Pt/AC+NaOH
GlA+NaOH
8
GlA+Pt/AC+NaOH
6
4
2
0
Tableꢀ1ꢀ
Comparisonꢀofꢀcatalystꢀandꢀbaseꢀperformancesꢀinꢀglycerolꢀoxidation.ꢀ
n
NaOH/ꢀ Conversionꢀ
Selectivityꢀ(%)ꢀ
0
10
20
30
40
50
60
Catalystꢀ
n
glycerol
ꢀ
(%)ꢀ
58.5ꢀ
ꢀ 5.9ꢀ
18.6ꢀ
LAꢀ GLYAꢀ TAꢀ GAꢀ OA AA FA
44.9 18.4ꢀ 7.9ꢀ 14.1ꢀ 1.6 2.1 11.0
17.5 24.6ꢀ 0ꢀ 33.4ꢀ 0ꢀ 4.0 20.5
Reaction time (min)
Pt/ACꢀ
Noneꢀ
Pt/ACꢀ
4ꢀ
4ꢀ
Fig.ꢀ1.ꢀLA/GLYAꢀmolarꢀratioꢀvariationꢀwithꢀorꢀwithoutꢀPt/ACꢀinꢀNaOHꢀ
solution.ꢀ Reactionꢀ conditions:ꢀ substrateꢀ =ꢀ 0.1ꢀ mol/Lꢀ DHAꢀ orꢀ GlA,ꢀ
NaOH/substrateꢀmolarꢀratioꢀ=ꢀ4:1,ꢀmPt/AC/msubstrateꢀsolutionꢀ=ꢀ1:1000,ꢀotherꢀ
conditionsꢀsameꢀasꢀTableꢀ1.ꢀ
Noneꢀ
0ꢀ 86.3ꢀ 0.1ꢀ 13.4ꢀ 0.1 0.1
0
Reactionꢀconditions:ꢀtꢀ=ꢀ90ꢀ°C,ꢀpꢀ=ꢀ0.1ꢀMPa,ꢀ6ꢀh,ꢀFO2ꢀ=ꢀ100ꢀmL/min,ꢀstir‐
ringꢀspeedꢀ=ꢀ800ꢀr/min,ꢀnglycerol/nPtꢀ=ꢀ2400.ꢀ

ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
505ꢀ
ferredꢀfromꢀLookhart’sꢀobservationꢀthatꢀDHAꢀwasꢀdehydratedꢀ
muchꢀ fasterꢀ thanꢀ GlAꢀ [30].ꢀ Furthermore,ꢀ theꢀ LA/GLYAꢀ molarꢀ
ratioꢀ wasꢀ almostꢀ constantꢀ asꢀ reactionꢀ timeꢀ increased,ꢀ whichꢀ
indicatesꢀ thatꢀ theꢀ furtherꢀ oxidationꢀ ofꢀ GLYAꢀ toꢀ TAꢀ andꢀ C–Cꢀ
spillingꢀofꢀproductsꢀoccurredꢀrelativelyꢀslowly,ꢀandꢀthusꢀmain‐
tainedꢀaꢀstableꢀLA/GLYAꢀratio.ꢀ
Figureꢀ1ꢀ(openꢀsymbols)ꢀshowsꢀLA/GLYAꢀmolarꢀratioꢀvaria‐
tionsꢀinꢀNaOHꢀaqueousꢀsolutionꢀwithꢀPt/ACꢀcatalyst.ꢀForꢀDHAꢀ
reaction,ꢀtheꢀLA/GLYAꢀmolarꢀratioꢀdroppedꢀslightlyꢀfromꢀ5.5ꢀtoꢀ
Tableꢀ2ꢀ
GlycerolꢀoxidationꢀreactionꢀwithꢀdifferentꢀbasesꢀoverꢀPt/ACꢀcatalyst.ꢀ
n
base
/
Conversion
(%)ꢀ
Selectivityꢀ(%)ꢀ
LA GLYAꢀ TAꢀ GAꢀ OA AA FA
Baseꢀ
nglycerol
LiOHꢀ
NaOHꢀ
KOHꢀ
2ꢀ
2ꢀ
2ꢀ
1ꢀ
60.4ꢀ
62.6ꢀ
63.4ꢀ
41.8ꢀ
60.1ꢀ 17.9ꢀ 4.5ꢀ ꢀ 7.5ꢀ 2.8 1.4 ꢀ 5.8
51.2ꢀ 13.6ꢀ 5.4ꢀ 11.9ꢀ 5.7 1.8 10.4
43.3ꢀ 17.1ꢀ 5.8ꢀ 11.3ꢀ 2.8 5.0 14.7
24.8ꢀ 29.3ꢀ 0.2ꢀ 20.9ꢀ 0.9 5.0 18.9
Ba(OH)
2
Reactionꢀconditions:ꢀtꢀ=ꢀ90ꢀ°C,ꢀpꢀ=ꢀ0.1ꢀMPa,ꢀ6ꢀh,ꢀFO2ꢀ=ꢀ100ꢀmL/min,ꢀstir‐
ringꢀspeedꢀ=ꢀ800ꢀr/min,ꢀnglycerol/nPtꢀ=ꢀ2400.ꢀ
5.3.ꢀ Inꢀ contrast,ꢀ forꢀ GlAꢀ asꢀ substrate,ꢀ theꢀ LA/GLYAꢀ ratioꢀ de‐
ꢀ
creasedꢀ remarkablyꢀ fromꢀ 4ꢀ toꢀ lessꢀ thanꢀ 2.ꢀ Obviously,ꢀ whenꢀ
Pt/ACꢀwasꢀadded,ꢀLAꢀformationꢀwasꢀinhibitedꢀandꢀGLYAꢀpro‐
ductionꢀwasꢀfacilitatedꢀregardlessꢀofꢀGlAꢀorꢀDHAꢀasꢀsubstrate.ꢀ
Interestingly,ꢀPt/ACꢀcatalystꢀacceleratedꢀtheꢀtransformationꢀofꢀ
GlAꢀtoꢀGLYAꢀoverꢀthatꢀofꢀDHA.ꢀChornajaꢀetꢀal.ꢀ[17]ꢀalsoꢀreportedꢀ
thatꢀ theꢀ rateꢀ ofꢀ GlAꢀ oxidationꢀ toꢀ GLYAꢀ wasꢀ higherꢀ thanꢀ GlAꢀ
wereꢀ62.6%ꢀandꢀ51.2%,ꢀrespectively.ꢀInꢀKOHꢀaqueousꢀsolution,ꢀ
theꢀglycerolꢀconversionꢀwasꢀsimilarꢀtoꢀLiOHꢀandꢀNaOH,ꢀbutꢀLAꢀ
selectivityꢀ decreasedꢀ toꢀ 43.3%.ꢀ Ba(OH) ꢀ showedꢀ muchꢀ lowerꢀ
2
glycerolꢀ conversionꢀ (41.8%)ꢀ andꢀ LAꢀ selectivityꢀ (24.8%).ꢀ Theꢀ
formerꢀthreeꢀhydroxidesꢀhaveꢀlowerꢀelectricꢀcharge,ꢀlowerꢀmo‐
lecularꢀ weight,ꢀ andꢀ smallerꢀ structureꢀ thanꢀ Ba(OH) ,ꢀ whichꢀ
2
transformationꢀ toꢀ LAꢀ usingꢀ aꢀ Pd/Al
2
O ꢀ catalystꢀ inꢀ alkalineꢀ
3
mightꢀenableꢀthemꢀtoꢀdissociateꢀandꢀmoveꢀrapidlyꢀinꢀtheꢀreac‐
tionꢀ solution,ꢀ providingꢀ dissociatedꢀ hydroxylꢀ ionsꢀ toꢀ promoteꢀ
theꢀ reactionꢀ networks.ꢀ Inꢀ contrast,ꢀ theꢀ higherꢀ electricꢀ chargeꢀ
aqueousꢀsolution.ꢀThus,ꢀweꢀdepictꢀtheꢀpossibleꢀpathwayꢀforꢀLAꢀ
productionꢀasꢀshownꢀinꢀSchemeꢀ2.ꢀDHAꢀisꢀfirstlyꢀdehydratedꢀtoꢀ
PyAꢀinꢀbasicꢀsolution,ꢀfollowedꢀbyꢀaꢀbase‐catalyzedꢀrearrange‐
mentꢀofꢀPyAꢀtoꢀLA,ꢀandꢀaccompaniedꢀwithꢀDHAꢀisomerizationꢀtoꢀ
GlAꢀandꢀfurtherꢀoxidationꢀtoꢀGLYAꢀoverꢀPt/ACꢀcatalyst.ꢀInꢀotherꢀ
words,ꢀDHAꢀmayꢀtakeꢀoneꢀstepꢀlessꢀthanꢀGlAꢀtowardꢀLA,ꢀwhichꢀ
mayꢀ contributeꢀ toꢀ itsꢀ betterꢀ assistanceꢀ forꢀ LAꢀ production.ꢀ
Therefore,ꢀ byꢀ carefulꢀ controlꢀ ofꢀ alkalineꢀ conditions,ꢀ aꢀ higherꢀ
DHA/GlAꢀ ratioꢀ mayꢀ beꢀ achieved,ꢀ whichꢀ wouldꢀ facilitateꢀ theꢀ
selectivityꢀtoꢀLA.ꢀ
andꢀlargerꢀionicꢀradiusꢀofꢀBa(OH)
LAꢀdecompositionꢀtoꢀC ꢀandꢀC ꢀproductsꢀ[11].ꢀTherefore,ꢀalka‐
li‐metalꢀ hydroxidesꢀ wereꢀ aꢀ betterꢀ choiceꢀ thanꢀ alkaline‐earthꢀ
hydroxideꢀBa(OH) ꢀforꢀLAꢀproduction.ꢀ
2
ꢀmightꢀfavorꢀtheꢀundesirableꢀ
1
2
2
Althoughꢀtheꢀthreeꢀalkali‐metalꢀhydroxidesꢀshowedꢀsimilarꢀ
glycerolꢀconversions,ꢀtheirꢀLAꢀselectivitiesꢀwereꢀobviouslyꢀdif‐
ferentꢀinꢀtheꢀorderꢀofꢀKOHꢀ<ꢀNaOHꢀ<ꢀLiOHꢀ(Tableꢀ2).ꢀThisꢀsug‐
gestsꢀ aꢀ mechanismꢀ wherebyꢀ theꢀ metalꢀ ionꢀ exertsꢀ significantꢀ
influenceꢀonꢀtheꢀoxidationꢀbehavior.ꢀChangesꢀinꢀtheꢀmetalꢀionꢀ
radiusꢀcausesꢀseveralꢀphysicochemicalꢀproperties,ꢀsuchꢀasꢀsolu‐
tionꢀalkalinity,ꢀsolubilityꢀofꢀoxygen,ꢀandꢀviscosityꢀ[21,32].ꢀ
3.2.ꢀ ꢀ Effectꢀofꢀdifferentꢀhydroxidesꢀonꢀglycerolꢀoxidationꢀtoꢀlacticꢀ
acidꢀ
Inꢀ Groupꢀ IA,ꢀ alkalinityꢀ isꢀ positivelyꢀ relatedꢀ withꢀ radiusꢀ
lengthꢀ (Tableꢀ 3).ꢀ Theꢀ strongerꢀ alkalinityꢀ mightꢀ improveꢀ theꢀ
deprotonationꢀ processꢀ duringꢀ theꢀ glycerolꢀ oxidationꢀ reaction.ꢀ
Thus,ꢀ theirꢀ glycerolꢀ conversionsꢀ exhibitedꢀ theꢀ sameꢀ orderꢀ asꢀ
theirꢀalkalinitiesꢀandꢀradii.ꢀTheꢀhighestꢀLAꢀselectivityꢀwasꢀob‐
tainedꢀinꢀLiOHꢀaqueousꢀmedium,ꢀwhichꢀmightꢀbeꢀrelatedꢀtoꢀtheꢀ
oxygenꢀsolubilityꢀinꢀsolution.ꢀWeꢀtestedꢀtheꢀoxygenꢀsolubilityꢀinꢀ
basicꢀreactionꢀsolutionꢀandꢀfoundꢀthatꢀLiOHꢀsolutionꢀdissolvedꢀ
moreꢀoxygenꢀthanꢀNaOHꢀandꢀKOHꢀ(Tableꢀ3),ꢀwhichꢀwasꢀcon‐
sistentꢀwithꢀBattino’sꢀreportꢀ[33].ꢀAccordingꢀtoꢀDavisꢀetꢀal.ꢀ[34],ꢀ
Theꢀuseꢀofꢀaꢀbaseꢀisꢀaꢀcrucialꢀfactorꢀinꢀglycerolꢀoxidationꢀtoꢀ
LA,ꢀ soꢀ weꢀ furtherꢀinvestigatedꢀ theꢀeffectꢀofꢀ alkaliꢀtypeꢀonꢀtheꢀ
performanceꢀ ofꢀ glycerolꢀ oxidationꢀ overꢀ Pt/ACꢀ catalystꢀ (Tableꢀ
2
).ꢀThreeꢀalkali‐metalꢀhydroxidesꢀ(LiOH,ꢀNaOH,ꢀandꢀKOH)ꢀandꢀ
oneꢀ alkaline‐earthꢀ hydroxideꢀ Ba(OH)
2
ꢀ wereꢀ used.ꢀ Otherꢀ alka‐
line‐earthꢀhydroxidesꢀwereꢀnotꢀadoptedꢀbecauseꢀofꢀtheirꢀpoorꢀ
solubilitiesꢀ[11,31].ꢀWhenꢀLiOHꢀwasꢀusedꢀasꢀtheꢀbase,ꢀtheꢀglyc‐
erolꢀconversionꢀwasꢀ60.4%ꢀandꢀLAꢀselectivityꢀwasꢀ60.1%ꢀafterꢀ
ꢀh,ꢀwhichꢀwasꢀtheꢀhighestꢀamongꢀtheꢀfourꢀalkalis.ꢀWhenꢀNaOHꢀ
wasꢀ introduced,ꢀ theꢀ glycerolꢀ conversionꢀ andꢀ LAꢀ selectivityꢀ
6
theꢀroleꢀofꢀO
2
ꢀisꢀtoꢀassistꢀtheꢀregenerationꢀofꢀhydroxideꢀionsꢀviaꢀ
O
OH
O
OH
H
O
O
-
OH , -H2O
HO
-
HO
H
HO
H
HO
HO
H
OH , -H2O HO
H
H
O
OH
OH
+H2O
DHA
GlA
OH
-
HO
OH +O2
Pt/AC
H
-H2O
O
O
O
OH-
HO
OH
H
intramolecular OH
Cannizzaro
rearrangement
OH
GLYA
Schemeꢀ2.ꢀPossibleꢀDHAꢀandꢀGlAꢀconversionꢀpathwayꢀtowardꢀLAꢀandꢀGLYA.ꢀ
OH
O
PyA
LA

506ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
Atꢀ lowꢀ LiOH/glycerolꢀ molarꢀ ratios,ꢀ theꢀ reactionꢀ productsꢀ
Tableꢀ3ꢀ
Comparisonꢀofꢀionicꢀradius,ꢀviscosity,ꢀksca,ꢀandꢀoxygenꢀsolubility.ꢀaꢀ
wereꢀalmostꢀacidic,ꢀindicatingꢀthatꢀtheꢀamountꢀofꢀbaseꢀmightꢀbeꢀ
insufficientꢀ toꢀ aidꢀ theꢀ dehydrogenationꢀ reactionꢀ fromꢀ theꢀ hy‐
droxylꢀgroupsꢀofꢀglycerolꢀandꢀtoꢀfurtherꢀcatalyzeꢀtheꢀCannizzaroꢀ
rearrangementꢀ toꢀ LAꢀ formation.ꢀ Suchꢀ anꢀ insufficiencyꢀ wouldꢀ
suppressꢀ bothꢀ glycerolꢀ conversionꢀ andꢀ LAꢀ selectivity.ꢀ Whenꢀ
moreꢀLiOHꢀwasꢀadded,ꢀtheꢀdehydrogenationꢀreactionꢀproceed‐
edꢀfasterꢀtowardꢀintermediatesꢀGlAꢀandꢀDHA.ꢀSimultaneously,ꢀ
theꢀ base‐catalyzedꢀ rearrangementꢀ ofꢀ intermediatesꢀ wasꢀ pro‐
motedꢀtoꢀgenerateꢀmoreꢀLA.ꢀ
WhenꢀLiOH/glycerolꢀmolarꢀratiosꢀwereꢀaboveꢀ1.5,ꢀtheꢀglyc‐
erolꢀ conversionꢀ droppedꢀ drastically.ꢀ Thisꢀ mayꢀ beꢀ aꢀ resultꢀ ofꢀ
declinesꢀ inꢀ massꢀ transferꢀ rateꢀ andꢀ oxygenꢀ solubility,ꢀ whichꢀ
wereꢀcausedꢀbyꢀincreasedꢀbaseꢀratioꢀandꢀviscosityꢀ[20,35].ꢀTheꢀ
oxygenꢀdiffusivityꢀandꢀoxygenꢀsolubilityꢀdeclineꢀrapidlyꢀowingꢀ
toꢀtheꢀLiOHꢀconcentrationꢀincrease.ꢀThus,ꢀtheꢀoxidationꢀdehy‐
drogenationꢀonꢀtheꢀPt/ACꢀcatalystꢀmayꢀbeꢀaffected,ꢀleadingꢀtoꢀ
lowerꢀ glycerolꢀ conversionꢀ andꢀ correspondingꢀ GlAꢀ orꢀ DHAꢀ in‐
termediates.ꢀTheꢀLAꢀselectivityꢀalsoꢀdroppedꢀbecauseꢀtheꢀextraꢀ
baseꢀ mayꢀ facilitateꢀ glycerolꢀ transformationꢀ toꢀ GlA,ꢀ whichꢀ isꢀ
likelyꢀtoꢀformꢀmoreꢀGLYAꢀinꢀtheꢀpresenceꢀofꢀPt/AC.ꢀ
ꢀb
Viscosityꢀcꢀ
(mPa·s)ꢀ ꢀ
1.66ꢀ
1.50ꢀ
1.16ꢀ
ꢀd
sca ꢀ
Oxygenꢀsolubilityꢀe
Ionicꢀradius ꢀ
pm)ꢀ ꢀ
k
Baseꢀ
(
(L/mol)ꢀ
0.091ꢀ
0.181ꢀ
0.176ꢀ
ꢀ
(mg/L)ꢀ ꢀ
30.1ꢀ
29.1ꢀ
LiOHꢀ
NaOHꢀ
KOHꢀ
ꢀ 76ꢀ
102ꢀ
138ꢀ
28.8ꢀ
aꢀBecauseꢀwaterꢀisꢀinꢀabsoluteꢀmajorityꢀ(90ꢀwt%)ꢀinꢀreactionꢀsolution,ꢀ
allꢀtheꢀphysicochemicalꢀparametersꢀareꢀconsideredꢀvalid.ꢀ
b
ꢀ
Theoreticalꢀ6‐coordinateꢀionicꢀradius.ꢀVariationꢀtrendꢀatꢀotherꢀcoor‐
dinateꢀnumbersꢀisꢀsimilarꢀ[32].ꢀ
c
ꢀCalculatedꢀbyꢀlinearꢀinterpolationꢀonꢀliteratureꢀdataꢀbetweenꢀ0.7ꢀandꢀ4ꢀ
mol/Lꢀatꢀ25ꢀ°Cꢀ[20].ꢀ
d
ꢀTheꢀoxygenꢀsolubilityꢀcouldꢀbeꢀrepresentedꢀasꢀkscaꢀ(i.e.,ꢀtheꢀSetschenowꢀ
saltꢀ effectꢀ parameter);ꢀ theseꢀ dataꢀ wereꢀ acquiredꢀ forꢀ baseꢀ concentra‐
tionsꢀofꢀ0.8–1.2ꢀmol/Lꢀ[35].ꢀ
e
ꢀ
Dataꢀ obtainedꢀ byꢀ iodometricꢀ methodꢀ (Chineseꢀ GBꢀ 7489‐87,ꢀ totallyꢀ
equivalentꢀtoꢀISOꢀ5813:1983)ꢀafterꢀ20ꢀminꢀoxygenꢀbubblingꢀandꢀ2ꢀminꢀ
standingꢀatꢀroomꢀtemperatureꢀ(20ꢀ°C)ꢀwithꢀbase/glycerolꢀratioꢀofꢀ0.5.ꢀ
OtherꢀconditionsꢀidenticalꢀtoꢀthoseꢀdescribedꢀinꢀTableꢀ2ꢀexceptꢀthatꢀnoꢀ
catalystꢀwasꢀaddedꢀtoꢀavoidꢀdisturbance.ꢀ
ꢀ
theꢀcatalyticꢀdecompositionꢀofꢀaꢀperoxideꢀintermediateꢀoverꢀPtꢀ
sites.ꢀ Whenꢀ moreꢀ oxygenꢀ isꢀ dissolved,ꢀ theꢀ hydroxideꢀ ionsꢀ re‐
generateꢀfasterꢀandꢀpromoteꢀLAꢀproductionꢀinꢀtheꢀpresenceꢀofꢀ
Pt/ACꢀcatalyst.ꢀBesides,ꢀitꢀisꢀpossibleꢀthatꢀaꢀsmallerꢀmetalꢀionꢀ
radiusꢀmightꢀfavorꢀtheꢀglycerolꢀdehydrogenationꢀtowardꢀmoreꢀ
DHA,ꢀthusꢀenhancingꢀLAꢀformation,ꢀandꢀthisꢀproposalꢀstillꢀre‐
quiresꢀverification.ꢀ
3
.4.ꢀ ꢀ Effectꢀofꢀreactionꢀtimeꢀonꢀglycerolꢀoxidationꢀtoꢀlacticꢀacidꢀ
Figureꢀ 2ꢀ showsꢀ theꢀ glycerolꢀ conversionꢀ andꢀ variationꢀ inꢀ
productꢀ selectivityꢀ asꢀ aꢀ functionꢀ ofꢀ reactionꢀ timeꢀ atꢀ theꢀ opti‐
mizedꢀLiOH/glycerolꢀratioꢀofꢀ1.5.ꢀGlycerolꢀwasꢀconvertedꢀcom‐
pletelyꢀwithinꢀ6ꢀh.ꢀThereꢀwasꢀaꢀnear‐linearꢀincreaseꢀinꢀglycerolꢀ
conversion,ꢀwhichꢀimpliedꢀthatꢀPt/ACꢀmaintainedꢀactivityꢀdur‐
ingꢀ theꢀ oxidationꢀ reaction.ꢀ Furthermore,ꢀ LAꢀ hadꢀ theꢀ highestꢀ
selectivityꢀ atꢀ anyꢀ glycerolꢀ conversionꢀ amongꢀ theꢀ reactionꢀ
products,ꢀindicatingꢀthatꢀLAꢀwasꢀtheꢀdominantꢀproduct.ꢀTheꢀLAꢀ
selectivityꢀreachedꢀaꢀmaximumꢀ(69.3%)ꢀafterꢀ6ꢀhꢀandꢀthenꢀde‐
creasedꢀslightly.ꢀTheꢀAAꢀselectivityꢀincreasedꢀslightly,ꢀimplyingꢀ
thatꢀLAꢀwasꢀnotꢀstableꢀandꢀmightꢀdecomposeꢀtoꢀAA.ꢀItꢀwasꢀnot‐
edꢀthatꢀtheꢀselectivityꢀofꢀGLYAꢀdecreasedꢀremarkablyꢀbecauseꢀ
ofꢀtheꢀconsecutiveꢀoxidationꢀofꢀGLYAꢀtoꢀTAꢀandꢀOA.ꢀ
3.3.ꢀ ꢀ EffectꢀofꢀLiOH/glycerolꢀmolarꢀratioꢀonꢀglycerolꢀoxidationꢀtoꢀ
lacticꢀacidꢀ
Furtherꢀ optimizationꢀ reactionsꢀ wereꢀ performedꢀ inꢀ LiOHꢀ
mediumꢀatꢀdifferentꢀLiOH/glycerolꢀmolarꢀratiosꢀandꢀtheꢀresultsꢀ
areꢀshownꢀinꢀTableꢀ4.ꢀBeforeꢀreachingꢀaꢀmolarꢀratioꢀofꢀ1.5,ꢀbothꢀ
glycerolꢀ conversionꢀ andꢀ LAꢀ selectivityꢀ wereꢀ enhancedꢀ withꢀ
elevatedꢀLiOHꢀconcentration,ꢀandꢀtheꢀmaximumꢀLAꢀselectivityꢀ
wasꢀ69.3%ꢀatꢀ100%ꢀglycerolꢀconversion.ꢀHowever,ꢀfurtherꢀele‐
vationꢀ ofꢀ theꢀ LiOH/glycerolꢀ molarꢀ ratioꢀ causedꢀ aꢀ decreaseꢀ inꢀ
bothꢀ reactionꢀ activityꢀ andꢀ LAꢀ selectivity.ꢀ Glycerolꢀ conversionꢀ
droppedꢀsignificantlyꢀtoꢀ69.3%ꢀatꢀaꢀmolarꢀratioꢀofꢀ1.75ꢀandꢀfur‐
therꢀdroppedꢀtoꢀ60.4%ꢀatꢀaꢀratioꢀofꢀ2.ꢀTheꢀLAꢀselectivityꢀgradu‐
allyꢀdecreasedꢀfromꢀ69.3%ꢀtoꢀ60.1%ꢀwhenꢀtheꢀLiOH/glycerolꢀ
molarꢀ ratioꢀ increasedꢀ fromꢀ 1.5ꢀ toꢀ 2.0.ꢀ Thisꢀ indicatesꢀ thatꢀ theꢀ
optimumꢀLiOH/glycerolꢀmolarꢀratioꢀwasꢀ1.5ꢀunderꢀourꢀreactionꢀ
conditions,ꢀ withꢀ relativelyꢀ highꢀ LAꢀ selectivityꢀ atꢀ fullꢀ glycerolꢀ
conversion.ꢀ
TheꢀstabilityꢀofꢀtheꢀPt/ACꢀcatalystꢀwasꢀtestedꢀinꢀaꢀrecyclingꢀ
experimentꢀforꢀfiveꢀruns.ꢀAsꢀshownꢀinꢀFig.ꢀ3,ꢀtheꢀglycerolꢀcon‐
100
100
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
LA
Tableꢀ4ꢀ
GlycerolꢀoxidationꢀreactionꢀatꢀdifferentꢀLiOH/glycerolꢀmolarꢀratios.ꢀ
LiOH/glycerolꢀ Conversionꢀ
molarꢀratioꢀ
Selectivityꢀ(%)ꢀ
AA
GLYA
GA
FA
TA
OA
(%)ꢀ
73.6ꢀ
89.7ꢀ
100ꢀ
69.3ꢀ
60.4ꢀ
LAꢀ GLYAꢀ TAꢀ GAꢀ OAꢀ AA FA
52.6ꢀ 17.1ꢀ 5.0ꢀ 13.5ꢀ 3.2ꢀ 3.0 5.6
56.7ꢀ 15.2ꢀ 6.1ꢀ 11.1ꢀ 3.4ꢀ 2.9 4.6
69.3ꢀ ꢀ 8.0ꢀ 9.4ꢀ 5.9ꢀ 2.5ꢀ 1.4 3.5
61.8ꢀ 15.8ꢀ 4.4ꢀ 8.0ꢀ 2.6ꢀ 1.5 5.9
60.1ꢀ 17.9ꢀ 4.5ꢀ 7.5ꢀ 2.8ꢀ 1.4 5.8
1
1
1
1
2
.0ꢀ
.25ꢀ
.5ꢀ
.75ꢀ
.0ꢀ
10
0
0
2
4
6
8
10
12
Reaction time (h)
Fig.ꢀ2.ꢀVariationꢀofꢀtheꢀglycerolꢀconversionꢀandꢀproductꢀselectivityꢀwithꢀ
timeꢀonꢀstream.ꢀReactionꢀconditions:ꢀtꢀ=ꢀ90ꢀ°C,ꢀpꢀ=ꢀ0.1ꢀMPa,ꢀFO2ꢀ=ꢀ100ꢀ
mL/min,ꢀstirringꢀspeedꢀ=ꢀ800ꢀr/min,ꢀnglycerol/nPtꢀ=ꢀ2400.ꢀ
Reactionꢀconditions:ꢀtꢀ=ꢀ90ꢀ°C,ꢀpꢀ=ꢀ0.1ꢀMPa,ꢀ6ꢀh,ꢀFO2ꢀ=ꢀ100ꢀmL/min,ꢀstir‐
ringꢀspeedꢀ=ꢀ800ꢀr/min,ꢀnglycerol/nPtꢀ=ꢀ2400.ꢀ ꢀ

ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
507ꢀ
1
00
100
90
(
a)
(b)
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
(
a)
2
h
(b)
4
h
(c) 7 h
80
70
60
50
40
30
20
10
0
5
0
(c)
50
40
30
20
10
(d)
40
30
2
0
0
0
1
1
2
3
Run
4
5
00
1
2
3
4
5
6
7
8
9 10 11 12
0
1
2
3
4
5
6
7
8
9 10 11 12
diameter (nm)
diameter (nm)
Fig.ꢀ3.ꢀRecyclingꢀtestsꢀofꢀPt/ACꢀcatalystꢀforꢀ4‐hꢀglycerolꢀoxidationꢀreac‐
tion.ꢀ Reactionꢀ conditions:ꢀ tꢀ =ꢀ 90ꢀ °C,ꢀ pꢀ =ꢀ 0.1ꢀ MPa,ꢀ FO2ꢀ=ꢀ 100ꢀ mL/min,
stirringꢀspeedꢀ=ꢀ800ꢀr/min,ꢀnglycerol/nPtꢀ=ꢀ2400.ꢀ
Fig.ꢀ5.ꢀTEMꢀimagesꢀofꢀ(a)ꢀfreshꢀandꢀ(b)ꢀspentꢀ5‐timeꢀPt/ACꢀcatalysts;ꢀPtꢀ
particleꢀsizeꢀdistributionsꢀofꢀ(c)ꢀfreshꢀandꢀ(d)ꢀspentꢀ5‐timeꢀPt/ACꢀcata‐
lysts.ꢀ
versionꢀdecreasedꢀfromꢀ63.6%ꢀtoꢀ52.9%ꢀafterꢀfiveꢀruns,ꢀbutꢀtheꢀ
selectivityꢀ ofꢀ LAꢀ wasꢀ stillꢀ aroundꢀ 60%.ꢀ Metalꢀ analysisꢀ byꢀ
ICP‐OESꢀrevealedꢀthatꢀPtꢀleachingꢀwasꢀbelowꢀtheꢀlimitꢀofꢀdetec‐
tionꢀ andꢀ negligible.ꢀ However,ꢀ theꢀ specificꢀ surfaceꢀ areaꢀ ofꢀ theꢀ
Pt/ACꢀcatalystꢀdecreasedꢀafterꢀfiveꢀrunsꢀ(Tableꢀ5),ꢀwhichꢀmightꢀ
beꢀ ascribedꢀ toꢀ chelationꢀ ofꢀ productꢀ onꢀ theꢀ catalystꢀ surface,ꢀ
whichꢀwouldꢀpreventꢀtheꢀglycerolꢀfromꢀaccessingꢀtheꢀPtꢀactiveꢀ
sitesꢀ [36].ꢀ Theꢀ poreꢀ sizeꢀ distributionꢀ basedꢀ onꢀ theꢀ NL‐DFTꢀ
methodꢀ alsoꢀ confirmedꢀ theꢀ possibilityꢀ ofꢀ reactantꢀ blockageꢀ
becauseꢀ theꢀ numberꢀ ofꢀ poresꢀ aroundꢀ 1.9ꢀ nmꢀ decreasedꢀ afterꢀ
reactionꢀ(Fig.ꢀ4).ꢀInꢀaddition,ꢀtheꢀaverageꢀparticleꢀsizeꢀofꢀPtꢀin‐
creasedꢀ fromꢀ 4.4ꢀ toꢀ 5.5ꢀ nmꢀ afterꢀ fiveꢀ runsꢀ (Fig.ꢀ 5).ꢀ COꢀ pulseꢀ
chemisorptionꢀ ofꢀ theꢀ freshꢀ andꢀ spentꢀ catalystꢀ alsoꢀ confirmedꢀ
theꢀ slightꢀ agglomerationꢀ ofꢀ Pt,ꢀ withꢀ theꢀ averageꢀ particleꢀ sizeꢀ
increasingꢀ fromꢀ 7.1ꢀ toꢀ 11.7ꢀ nm;ꢀ Ptꢀ dispersionꢀ declinedꢀ fromꢀ
16.8%ꢀ toꢀ 10.2%,ꢀ whichꢀ mayꢀ influenceꢀ theꢀ catalystꢀ activityꢀ toꢀ
someꢀdegreeꢀ[37].ꢀFurtherꢀdetailedꢀinvestigationꢀisꢀnecessaryꢀtoꢀ
elucidateꢀtheꢀdeactivationꢀmechanism.ꢀ
4.ꢀ ꢀ Conclusionsꢀ
Lacticꢀacidꢀwasꢀpreparedꢀasꢀtheꢀmajorꢀproductꢀbyꢀtreatmentꢀ
ofꢀ glycerolꢀ inꢀ alkalineꢀ aqueousꢀ solutionꢀ inꢀ theꢀ presenceꢀ ofꢀ aꢀ
Pt/ACꢀcatalyst.ꢀTheꢀpromotionꢀeffectꢀofꢀLiOHꢀwasꢀstrongerꢀthanꢀ
Tableꢀ5ꢀ
theꢀotherꢀbasesꢀ(NaOH,ꢀKOHꢀandꢀBa(OH)
2
)ꢀinꢀtermsꢀofꢀglycerolꢀ
Theꢀspecificꢀsurfaceꢀareasꢀandꢀtotalꢀporeꢀvolumesꢀofꢀfreshꢀandꢀ spentꢀ
Pt/ACꢀcatalysts.ꢀ
conversionꢀtoꢀLA.ꢀReactionꢀintermediateꢀDHAꢀwasꢀmoreꢀfavor‐
ableꢀasꢀtheꢀstartingꢀreagentꢀforꢀLAꢀformationꢀthanꢀGlA,ꢀbutꢀtheꢀ
Pt/ACꢀcatalystꢀacceleratedꢀfurtherꢀoxidationꢀofꢀDHAꢀandꢀGlAꢀtoꢀ
GLYA.ꢀInꢀaddition,ꢀtheꢀPt/ACꢀcatalystꢀretainedꢀhighꢀactivityꢀandꢀ
LAꢀselectivityꢀafterꢀfiveꢀrunsꢀinꢀaꢀcatalystꢀrecyclingꢀexperiment.ꢀ
ꢀ
a
2
ꢀ
ꢀb
2
ꢀ
2
ꢀc
3
ꢀ
Catalystꢀ
Freshꢀ
Spentꢀ
S
BET ꢀ(m /g) ꢀ Smacro ꢀ(m /g) ꢀ Smicroꢀ(m /g)ꢀ
V
total ꢀ(cm /g)
970.8ꢀ
687.0ꢀ
278.7ꢀ
221.4ꢀ
692.1ꢀ
465.6ꢀ
0.65ꢀ
0.54ꢀ
aꢀ
CalculatedꢀbyꢀtheꢀBETꢀmethod.ꢀ
Calculatedꢀbyꢀtheꢀt‐plotꢀmethod.ꢀ
bꢀ
cꢀ
Referencesꢀ
Calculatedꢀ basedꢀ onꢀ theꢀ amountꢀ ofꢀ nitrogenꢀ adsorbedꢀ atꢀ aꢀ relativeꢀ
pressureꢀ(p/p )ꢀofꢀ0.99.
0
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GreenꢀChem.,ꢀ2011,ꢀ13,ꢀ1960–1979.ꢀ
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0.10
0.08
0.06
0.04
0.02
0.00
Fresh
Spent 5-time
[
[
[
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Pore diameter (nm)
Fig.ꢀ4.ꢀPoreꢀsizeꢀdistributionsꢀofꢀfreshꢀandꢀspentꢀPt/ACꢀcatalysts.ꢀ
[9] R.ꢀP.ꢀJohn,ꢀK.ꢀM.ꢀNampoothiri,ꢀA.ꢀPandey,ꢀAppl.ꢀMicrobiol.ꢀBiotech‐

508ꢀ
ChenꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ502–509ꢀ
ꢀ
GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2016,ꢀ37:ꢀ502–509ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(15)61055‐5
Selectiveꢀoxidationꢀofꢀglycerolꢀtoꢀlacticꢀacidꢀoverꢀactivatedꢀ
carbonꢀsupportedꢀPtꢀcatalystꢀinꢀalkalineꢀsolutionꢀ
Food
additive
ꢀ
ꢀ
Biodiesel
byproduct
ChenꢀZhang,ꢀTaoꢀWang*,ꢀXiaoꢀLiu,ꢀYunjieꢀDing*ꢀ
DalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences;ꢀ
UniversityꢀofꢀChineseꢀAcademyꢀofꢀSciencesꢀ
Cosmetics
additive
Pt/AC + LiOH
90 C, 0.1 MPa O2
Glycerol
o
Pt/activatedꢀcarbonꢀcatalystꢀworksꢀefficientlyꢀforꢀlacticꢀacidꢀpro‐
ductionꢀ fromꢀ glycerolꢀ underꢀ mildꢀ conditions.ꢀ Differentꢀ alkalisꢀ
greatlyꢀinfluenceꢀbothꢀglycerolꢀconversionꢀandꢀlacticꢀacidꢀselectiv‐
ity,ꢀamongꢀwhichꢀLiOHꢀisꢀoptimal.ꢀ
Lactic acid
yield > 65%
PLA
ꢀ
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