Comparison of cellobiose and glucose transformation to ethylene glycol

Article abstract of DOI:10.1016/S1872-2067(14)60151-0

Cellobiose was used as a model feedstock to probe the reaction pathways of cellulose to ethylene glycol (EG). Its reactivity was compared with that of glucose using a catalyst composed of H₂WO₄ and Ru/C. EG can be produced by both the direct retro-aldol condensation of cellobiose and the retro-aldol condensation of glucose derived from cellobiose hydrolysis. The direct retro-aldol condensation of cellobiose further promoted the hydrolysis of cellobiose. Cellobiose has a lower reactivity for retro-aldol condensation than glucose, which decreased the formation rate of glycolaldehyde and made it more matched with the subsequent hydrogenation rate, thus leading to increased yield of EG from cellobiose.

Full text of DOI:10.1016/S1872-2067(14)60151-0

ChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
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
Comparisonꢀofꢀcellobioseꢀandꢀglucoseꢀtransformationꢀtoꢀethyleneꢀ
glycolꢀ
ꢀa,b
ꢀa
ꢀa
ꢀa,
ꢀa,b
ꢀa
JunyingꢀZhang ,ꢀXiaofengꢀYang ,ꢀBaolinꢀHou ,ꢀAiqinꢀWang *,ꢀZhenleiꢀLi ,ꢀHuaꢀWang ,ꢀ
TaoꢀZhang ꢀ
ꢀa,#
aꢀStateꢀKeyꢀLaboratoryꢀofꢀCatalysis,ꢀ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:ꢀ
Cellobioseꢀwasꢀusedꢀasꢀaꢀmodelꢀfeedstockꢀtoꢀprobeꢀtheꢀreactionꢀpathwaysꢀofꢀcelluloseꢀtoꢀethyleneꢀ
Receivedꢀ29ꢀAprilꢀ2014ꢀ
Acceptedꢀ10ꢀMayꢀ2014ꢀ
Publishedꢀ20ꢀNovemberꢀ2014ꢀ
glycolꢀ(EG).ꢀItsꢀreactivityꢀwasꢀcomparedꢀwithꢀthatꢀofꢀglucoseꢀusingꢀaꢀcatalystꢀcomposedꢀofꢀH
2
WO
4
andꢀRu/C.ꢀEGꢀcanꢀbeꢀproducedꢀbyꢀbothꢀtheꢀdirectꢀretro‐aldolꢀcondensationꢀofꢀcellobioseꢀandꢀtheꢀ
retro‐aldolꢀcondensationꢀofꢀglucoseꢀderivedꢀfromꢀcellobioseꢀhydrolysis.ꢀTheꢀdirectꢀretro‐aldolꢀcon‐
densationꢀofꢀcellobioseꢀfurtherꢀpromotedꢀtheꢀhydrolysisꢀofꢀcellobiose.ꢀCellobioseꢀhasꢀaꢀlowerꢀreac‐
tivityꢀforꢀretro‐aldolꢀcondensationꢀthanꢀglucose,ꢀwhichꢀdecreasedꢀtheꢀformationꢀrateꢀofꢀglycolalde‐
hydeꢀandꢀmadeꢀitꢀmoreꢀmatchedꢀwithꢀtheꢀsubsequentꢀhydrogenationꢀrate,ꢀthusꢀleadingꢀtoꢀincreasedꢀ
yieldꢀofꢀEGꢀfromꢀcellobiose.ꢀ
Keywords:ꢀ
Cellobioseꢀ
Reactionꢀmechanismꢀ
Glucoseꢀ
Ethyleneꢀglycol
©ꢀ2014,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
andꢀ versatileꢀ dualꢀ componentꢀ catalystꢀ composedꢀ ofꢀ tungsticꢀ
acidꢀandꢀRu/Cꢀ[30]ꢀorꢀRaneyꢀNiꢀ[31],ꢀwhichꢀresultedꢀinꢀtheꢀsig‐
nificantꢀincreaseꢀinꢀrecyclableꢀtimesꢀfromꢀlessꢀthanꢀ3ꢀtoꢀmoreꢀ
thanꢀ30.ꢀOnꢀtheꢀotherꢀhand,ꢀtheꢀunderstandingꢀofꢀtheꢀreactionꢀ
mechanismꢀisꢀapproachingꢀknowledgeꢀofꢀtheꢀnatureꢀofꢀtheꢀac‐
tiveꢀ sites.ꢀ Inꢀ particular,ꢀ theꢀ interplayꢀ betweenꢀ theꢀ tungsticꢀ
compoundꢀandꢀcelluloseꢀisꢀnowꢀbelievedꢀtoꢀbeꢀbyꢀhomogeneousꢀ
catalysisꢀ insteadꢀ ofꢀ heterogeneousꢀ catalysisꢀ andꢀ theꢀ selectiveꢀ
C‐Cꢀcleavageꢀofꢀcelluloseꢀorꢀglucoseꢀfollowsꢀaꢀretro‐aldolꢀcon‐
densationꢀpathwayꢀ[30–35].ꢀ
Inꢀ spiteꢀ ofꢀ theseꢀ advances,ꢀ theꢀ elucidationꢀ ofꢀ theꢀ reactionꢀ
mechanismꢀonꢀ theꢀmolecularꢀlevelꢀhasꢀnotꢀ beenꢀattainedꢀyet.ꢀ
Forꢀexample,ꢀtheꢀproductionꢀofꢀEGꢀfromꢀcelluloseꢀisꢀbelievedꢀtoꢀ
involveꢀthreeꢀconsecutiveꢀreactions:ꢀ(1)ꢀhydrolysisꢀofꢀcelluloseꢀ
toꢀglucose,ꢀ(2)ꢀretro‐aldolꢀcondensationꢀofꢀglucoseꢀtoꢀglycolal‐
dehydeꢀ(GA),ꢀandꢀ(3)ꢀhydrogenationꢀofꢀGAꢀtoꢀEG.ꢀHowever,ꢀitꢀisꢀ
Lignocelluloseꢀisꢀtheꢀmostꢀabundantꢀnon‐edibleꢀbiomassꢀinꢀ
nature,ꢀ andꢀ canꢀ beꢀ aꢀ renewableꢀ hydrocarbonꢀ sourceꢀ forꢀ theꢀ
productionꢀofꢀliquidꢀfuelsꢀandꢀchemicals,ꢀwhichꢀisꢀimportantꢀforꢀ
aꢀ sustainableꢀ societyꢀ [1–22].ꢀ Amongꢀ theꢀ variousꢀ chemicalꢀ
transformationꢀroutesꢀofꢀcellulose,ꢀtheꢀone‐potꢀcatalyticꢀtrans‐
formationꢀofꢀcelluloseꢀandꢀhemicelluloseꢀtoꢀethyleneꢀglycolꢀ(EG)ꢀ
andꢀpropyleneꢀglycolꢀ(PG)ꢀhasꢀattractedꢀconsiderableꢀattentionꢀ
fromꢀbothꢀacademicꢀandꢀindustrialꢀcommunitiesꢀbecauseꢀbothꢀ
EGꢀandꢀPGꢀareꢀcommodityꢀchemicalsꢀwidelyꢀappliedꢀinꢀtheꢀpol‐
yesterꢀindustryꢀ[22–36].ꢀSinceꢀtheꢀfirstꢀreportꢀbyꢀourꢀgroupꢀonꢀ
celluloseꢀconversionꢀtoꢀEGꢀ[23],ꢀmuchꢀprogressꢀhasꢀbeenꢀmadeꢀ
inꢀ catalystꢀ designꢀ andꢀ mechanisticꢀ understandingꢀ bothꢀ fromꢀ
ourꢀ groupsꢀ [24–31]ꢀ andꢀ otherꢀ groupsꢀ [21,36].ꢀ Theꢀ originalꢀ
Ni‐W
C/ACꢀcatalystꢀhasꢀnowꢀbeenꢀreplacedꢀbyꢀaꢀmoreꢀdurableꢀ
2
*
ꢀ
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐411‐84379348;ꢀFax:ꢀ+86‐411‐84685940;ꢀE‐mail:ꢀaqwang@dicp.ac.cnꢀ ꢀ ꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐411‐84379015;ꢀFax:ꢀ+86‐411‐84691570;ꢀE‐mail:ꢀtaozhang@dicp.ac.cnꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21176235,ꢀ21373206,ꢀandꢀ21206159).ꢀ
DOI:ꢀ10.1016/S1872‐2067(14)60151‐0ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ35,ꢀNo.ꢀ11,ꢀNovemberꢀ2014ꢀ ꢀ

1812ꢀ
JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
3
knownꢀthatꢀtheꢀhydrolysisꢀofꢀcelluloseꢀtoꢀglucoseꢀproceedsꢀveryꢀ
slowlyꢀ andꢀ manyꢀ solubleꢀ celloligosaccharidesꢀ areꢀ formedꢀ asꢀ
intermediatesꢀduringꢀtheꢀhydrolysisꢀ[37,38].ꢀInꢀthisꢀcase,ꢀitꢀwillꢀ
beꢀ interestingꢀ toꢀ knowꢀ whetherꢀ theseꢀ celloligosaccharideꢀ in‐
termediatesꢀalsoꢀundergoꢀretro‐aldolꢀcondensationꢀtoꢀproduceꢀ
GAꢀasꢀglucoseꢀdoes,ꢀandꢀifꢀtheyꢀdo,ꢀtoꢀwhatꢀextentꢀdoꢀtheseꢀreac‐
tionsꢀcontributeꢀtoꢀtheꢀtotalꢀproductionꢀofꢀEGꢀfromꢀcellulose.ꢀ
Toꢀaddressꢀtheseꢀquestions,ꢀweꢀmadeꢀaꢀcomparativeꢀstudyꢀ
ofꢀcellobioseꢀandꢀglucoseꢀconversionꢀinꢀtheꢀpresentꢀwork.ꢀCel‐
lobioseꢀ isꢀ aꢀ glucoseꢀ dimerꢀ connectedꢀ withꢀ aꢀ β‐1,4‐glycosidicꢀ
bond.ꢀItꢀisꢀtheꢀ simplestꢀmoleculeꢀthatꢀresemblesꢀtheꢀ celluloseꢀ
structureꢀ [39–42].ꢀ Whenꢀ cellobioseꢀ isꢀ usedꢀ asꢀ theꢀ feedstock,ꢀ
almostꢀ allꢀ theꢀ intermediatesꢀ canꢀ beꢀ identifiedꢀ andꢀ quantified,ꢀ
whichꢀovercomesꢀtheꢀdifficultyꢀinꢀidentifyingꢀtheꢀintermediatesꢀ
inꢀ celluloseꢀ conversion.ꢀ Furthermore,ꢀ cellobioseꢀ hasꢀ oneꢀ
β‐1,4‐glycosidicꢀbondꢀandꢀthereforeꢀallꢀtheꢀreactionsꢀthatꢀoccurꢀ
onꢀ cellulose,ꢀ namely,ꢀ hydrolysis,ꢀ C–Cꢀ bondꢀ cleavage,ꢀ andꢀ hy‐
drogenation,ꢀ alsoꢀ occurꢀ onꢀ cellobiose.ꢀ Therefore,ꢀ cellobioseꢀ isꢀ
anꢀidealꢀprobeꢀmoleculeꢀforꢀtheꢀmechanisticꢀstudyꢀofꢀcelluloseꢀ
conversion.ꢀ
programꢀpackageꢀDMol ꢀinꢀtheꢀMaterialsꢀStudioꢀofꢀAccelrysꢀInc.ꢀ
[43,44].ꢀ Localizedꢀ double‐numericalꢀ basisꢀ setsꢀ withꢀ polariza‐
tionꢀfunctionsꢀ(DNP)ꢀwereꢀused,ꢀwhichꢀareꢀmoreꢀaccurateꢀthanꢀ
butꢀcomparableꢀinꢀsizeꢀtoꢀtheꢀGaussianꢀbasisꢀsetsꢀ6‐31G**.ꢀTheꢀ
non‐localꢀ exchange‐correlationꢀ functionalꢀ ofꢀ BLYPꢀ wasꢀ em‐
–5ꢀ
ployed.ꢀTheꢀconvergencesꢀofꢀenergyꢀandꢀgradientꢀusedꢀ1ꢀꢀ10
hartreeꢀandꢀ2ꢀꢀ10 hartree/Å,ꢀrespectively.ꢀ
–3ꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ Reactionꢀpathwayꢀ
Toꢀunderstandꢀtheꢀreactionꢀpathwaysꢀforꢀtheꢀconversionꢀofꢀ
cellobioseꢀ toꢀ ethyleneꢀ glycol,ꢀ liquidꢀ samplesꢀ wereꢀ takenꢀ fromꢀ
theꢀreactorꢀatꢀfixedꢀtimeꢀintervalsꢀforꢀanalysis.ꢀFig.ꢀ1ꢀpresentsꢀ
theꢀ typicalꢀ HPLCꢀ chromatographꢀ ofꢀ theꢀ liquidꢀ productsꢀ fromꢀ
cellobioseꢀconversionꢀcatalyzedꢀbyꢀH
2
WO ꢀandꢀRu/Cꢀatꢀ453ꢀKꢀ
4
forꢀ20ꢀmin.ꢀAtꢀleastꢀ15ꢀcompoundsꢀwereꢀpresentꢀinꢀtheꢀprocessꢀ
ofꢀ cellobioseꢀ conversionꢀ andꢀ ofꢀ these,ꢀ 14ꢀ compoundsꢀ wereꢀ
identified.ꢀ Amongꢀ these,ꢀ glucosyl‐erythroseꢀ (GE)ꢀ andꢀ gluco‐
syl‐erythritolꢀ(GER)ꢀwereꢀparticularlyꢀinterestingꢀbecauseꢀtheyꢀ
cameꢀfromꢀtheꢀdirectꢀC–Cꢀbondꢀcleavageꢀofꢀcellobioseꢀandꢀnotꢀ
glucoseꢀbyꢀaꢀretro‐aldolꢀreactionꢀpathway.ꢀTheꢀformationꢀofꢀGEꢀ
inꢀcellobioseꢀconversionꢀwasꢀalsoꢀobservedꢀbyꢀAraiꢀgroupꢀun‐
derꢀsub‐ꢀandꢀsuper‐criticalꢀwaterꢀconditionsꢀ[39,40].ꢀTheꢀfor‐
mationꢀ ofꢀ GERꢀ resultedꢀ fromꢀ theꢀ hydrogenationꢀ ofꢀ GEꢀ overꢀ
Ru/C,ꢀ similarlyꢀ toꢀ theꢀ formationꢀ ofꢀ 3‐β‐D‐glucopyranosyl‐ꢀ
D‐glucitolꢀfromꢀcellobioseꢀhydrogenationꢀ[41,42].ꢀInꢀadditionꢀtoꢀ
theꢀ C10ꢀ andꢀ C12ꢀ sugarꢀ andꢀ sugarꢀ alcohols,ꢀ thereꢀ wereꢀ alsoꢀ
C2–C6ꢀ sugarsꢀ (GA,ꢀ glucose,ꢀ mannose,ꢀ andꢀ fructose),ꢀ sugarꢀ al‐
coholsꢀ (sorbitol,ꢀ mannitol,ꢀ andꢀ erythritol),ꢀ andꢀ polyolsꢀ (EG,ꢀ
hydroxyacetone).ꢀInꢀcelluloseꢀconversionꢀtoꢀEG,ꢀmostꢀworkersꢀ
believeꢀthatꢀcelluloseꢀisꢀfirstꢀhydrolyzedꢀtoꢀglucoseꢀandꢀtheꢀre‐
sultantꢀglucoseꢀundergoesꢀretro‐aldolꢀcondensationꢀtoꢀproduceꢀ
GA.ꢀHowever,ꢀinꢀtheꢀpresentꢀwork,ꢀtheꢀdetectionꢀofꢀGEꢀandꢀGERꢀ
unequivocallyꢀindicatedꢀthatꢀGAꢀcanꢀalsoꢀbeꢀproducedꢀdirectlyꢀ
fromꢀtheꢀretro‐aldolꢀcondensationꢀofꢀcellobiose.ꢀByꢀextrapolat‐
ingꢀthisꢀresultꢀtoꢀcelluloseꢀconversion,ꢀweꢀconcludedꢀthatꢀglu‐
2.ꢀ ꢀ Experimentalꢀ
Inꢀallꢀexperiments,ꢀtungsticꢀacidꢀ(H
2
WO ,ꢀSinopharmꢀChem‐
4
icalꢀReagentꢀCo.,ꢀLtd.),ꢀcellobioseꢀ(Jꢀ&ꢀKꢀChemical)ꢀandꢀglucoseꢀ(Jꢀ
ꢀ Kꢀ Chemical)ꢀ wereꢀ usedꢀ asꢀ received.ꢀ Catalyticꢀ reactionsꢀ ofꢀ
&
glucoseꢀ andꢀ cellobioseꢀ wereꢀ performedꢀ inꢀ aꢀ semi‐continuousꢀ
stainlessꢀsteelꢀautoclaveꢀ(ParrꢀInstrumentꢀCompany,ꢀ300ꢀmL)ꢀ
equippedꢀwithꢀsamplingꢀtube,ꢀstirringꢀimpeller,ꢀandꢀtempera‐
tureꢀandꢀpressureꢀcontrolꢀsystems.ꢀInꢀaꢀtypicalꢀreaction,ꢀ0.1ꢀgꢀ
2 4
H WO ,ꢀ0.3ꢀgꢀRu/C,ꢀandꢀ90ꢀmLꢀwaterꢀwereꢀputꢀintoꢀtheꢀauto‐
2
clave.ꢀTheꢀautoclaveꢀwasꢀflushedꢀwithꢀH ꢀforꢀfiveꢀtimesꢀandꢀthenꢀ
sealed.ꢀTheꢀautoclaveꢀwasꢀthenꢀheatedꢀtoꢀtheꢀdesiredꢀtempera‐
ture,ꢀandꢀ10ꢀmLꢀofꢀanꢀaqueousꢀsolutionꢀofꢀglucoseꢀorꢀcellobioseꢀ
atꢀaꢀconcentrationꢀofꢀ1.63ꢀmolcarbon/LꢀwasꢀfedꢀinꢀbyꢀaꢀShimadzuꢀ
LCꢀpumpꢀ(LC‐20A)ꢀatꢀaꢀflowꢀrateꢀofꢀ10ꢀmL/min.ꢀItꢀtookꢀ1ꢀminꢀtoꢀ
finishꢀ theꢀ feedingꢀ process.ꢀ Then,ꢀ pureꢀ H ꢀ gasꢀ wasꢀ chargedꢀ inꢀ
2
untilꢀ aꢀ pressureꢀ ofꢀ 6ꢀ MPa,ꢀ andꢀ theꢀ reactionꢀ wasꢀ startedꢀ byꢀ
strongꢀagitationꢀatꢀ1000ꢀr/min,ꢀandꢀthisꢀpointꢀwasꢀconsideredꢀ
asꢀtheꢀinitialꢀtimeꢀ(tꢀ=ꢀ0).ꢀSamplesꢀwereꢀtakenꢀfromꢀtheꢀreactorꢀ
atꢀfixedꢀtimeꢀintervalsꢀforꢀanalysis.ꢀ ꢀ
Afterꢀ filtrationꢀ throughꢀ aꢀ 0.45ꢀ µmꢀ PTFEꢀ filter,ꢀ theꢀ liquidꢀ
samplesꢀ wereꢀ analyzedꢀ byꢀ aꢀ highꢀ performanceꢀ liquidꢀ chro‐
matographꢀ (HPLC,ꢀ Aglientꢀ 1200)ꢀ inꢀ combinationꢀ withꢀ massꢀ
spectroscopyꢀ(MS),ꢀwithꢀwaterꢀasꢀtheꢀmobileꢀphaseꢀandꢀRIꢀasꢀ
theꢀ detector.ꢀ Forꢀ theꢀ separationꢀ ofꢀ polyols,ꢀ aꢀ Shodexꢀ SC100ꢀ
columnꢀ wasꢀ usedꢀ withꢀ aꢀ waterꢀ flowꢀ rateꢀ ofꢀ 0.6ꢀ mL/minꢀ andꢀ
columnꢀtemperatureꢀofꢀ348ꢀK.ꢀForꢀtheꢀseparationꢀofꢀunsaturat‐
edꢀintermediates,ꢀaꢀCARBOSepꢀCHO‐620ꢀcolumnꢀwasꢀusedꢀwithꢀ
aꢀ waterꢀ flowꢀ rateꢀofꢀ 0.4ꢀ mL/minꢀandꢀ columnꢀ temperatureꢀofꢀ
6
12
7
2
10
1
13
14
15
9
8
1
1
3
16
5
4
0
4
8
12
Retention time (min)
Fig.ꢀ1.ꢀTypicalꢀHPLCꢀanalysisꢀforꢀtheꢀproductsꢀofꢀcellobioseꢀconversionꢀ
catalyzedꢀ byꢀ H WO ꢀ andꢀ Ru/C.ꢀ Reactionꢀ conditions:ꢀ 0.10ꢀ gꢀ H WO ,ꢀ
.30ꢀ gꢀ Ru/AC,ꢀ 453ꢀ K,ꢀ 6ꢀ MPaꢀ H ,ꢀ 20ꢀ min,ꢀ 1000ꢀ r/min.ꢀ 1—Acids;ꢀ
—Cellobiose;ꢀ 3—Glucosyl‐erythrose;ꢀ 4—Glucosyl‐erythritol;ꢀ
—Glucopyranosyl‐D‐glucitol;ꢀ 6—Glucose;ꢀ 7—Mannose;ꢀ 8—Fructose;ꢀ
16
20
24 28
32
348ꢀK.ꢀTheꢀqualitativeꢀanalysisꢀofꢀtheꢀintermediatesꢀandꢀprod‐
uctsꢀwasꢀmadeꢀbyꢀHPLC‐MS.ꢀTheꢀquantitativeꢀanalysisꢀwasꢀbyꢀ
anꢀexternalꢀstandardꢀmethod.ꢀTheꢀyieldsꢀofꢀintermediatesꢀandꢀ
productsꢀwereꢀcalculatedꢀas:ꢀyieldꢀ(%)ꢀ=ꢀ(massꢀofꢀintermediatesꢀ
orꢀproducts)/(massꢀofꢀsugarꢀputꢀintoꢀtheꢀreactor)ꢀꢀ100%.ꢀ
TheꢀGibbsꢀfreeꢀenergyꢀofꢀtheꢀreactionsꢀwasꢀcalculatedꢀwithꢀaꢀ
fullꢀelectronꢀdensityꢀfunctionalꢀtheoryꢀ(DFT)ꢀcalculationꢀbyꢀtheꢀ
2
4
2
4
0
2
5
2
9—Erythritol;ꢀ 10—Glycolaldehyde;ꢀ 11—Mannitol;ꢀ 12—Ethyleneꢀ gly‐
col;ꢀ13—Sorbitol;ꢀ14—Hydroxyacetone;ꢀ15—Unknown.ꢀ

ꢀ
JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
1813ꢀ
CH OH
OH
OH
CH OH
2
2
CH OH
2
H
HO
H
OH
H
Hydrogenation
Retro-aldol
O
O
OH
OH
OH
OH
H
OH
OH
CH2OH
H
OH
CH OH
2
O
Hydrolysis
CH2OH
3
-β-D-glucopyranosyl-D-glucitol
OH
O
OH
OH
OH
CH OH
CH2OH
OH
2
O
CH OH
2
OH
H
OH
CH OH
2
O
OH + O
OH
OH
O
OH
H
OH
O
OH
OH
O
O
OH
OH H
OH
HO
OH
OH
H
OH
OH
HO
GE
GA
H
ꢀ
CH OH
Schemeꢀ3.ꢀReactionꢀ networkꢀofꢀ3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ cata‐
lyzedꢀbyꢀH WO ꢀandꢀRu/C.ꢀ
2
O
Hydrolysis
OH
H
OH H
2
4
HO
H
OH
H
Glucoseꢀisꢀtheꢀbasicꢀunitꢀofꢀcelluloseꢀandꢀitꢀisꢀformedꢀasꢀanꢀ
intermediateꢀinꢀcelluloseꢀconversionꢀtoꢀEG,ꢀwhileꢀcellobioseꢀisꢀ
theꢀsmallestꢀmoleculeꢀpossessingꢀaꢀβ‐1,4‐glycosidicꢀbond.ꢀCel‐
lobioseꢀcanꢀbeꢀconsideredꢀtoꢀrepresentꢀsolubleꢀcelloligosaccha‐
ridesꢀ thatꢀ areꢀ alsoꢀ formedꢀ asꢀ intermediatesꢀ duringꢀ celluloseꢀ
conversionꢀ toꢀ EG.ꢀ Therefore,ꢀ theꢀ comparisonꢀ ofꢀ glucoseꢀ andꢀ
cellobioseꢀ reactivityꢀ willꢀ provideꢀ mechanisticꢀ informationꢀ forꢀ
theꢀcelluloseꢀconversionꢀtoꢀEG.ꢀFirst,ꢀweꢀconductedꢀreactionsꢀatꢀ
aꢀrelativelyꢀlowꢀtemperatureꢀ(393ꢀK)ꢀforꢀ2ꢀhꢀwithꢀaꢀdualꢀcom‐
Glucose
Schemeꢀ 1.ꢀ Primaryꢀ reactionꢀ networkꢀ forꢀ cellobioseꢀ conversionꢀ cata‐
lyzedꢀbyꢀH WO ꢀandꢀRu/C.ꢀ
2
4
coseꢀwouldꢀnotꢀbeꢀtheꢀonlyꢀintermediateꢀsugarꢀduringꢀcelluloseꢀ
conversionꢀ toꢀ EG:ꢀ otherꢀ solubleꢀ celloligosaccharidesꢀ derivedꢀ
fromꢀ theꢀ partialꢀ hydrolysisꢀ ofꢀ celluloseꢀ canꢀ alsoꢀ undergoꢀ C–Cꢀ
bondꢀcleavageꢀtoꢀformꢀGA.ꢀTherefore,ꢀfromꢀtheꢀproductꢀdistri‐
bution,ꢀweꢀproposeꢀtheꢀreactionꢀpathwayꢀillustratedꢀinꢀSchemesꢀ
1–4.ꢀTheꢀprimaryꢀreactionsꢀ(Schemeꢀ1)ꢀareꢀthreeꢀparallelꢀreac‐
ponentꢀcatalystꢀofꢀH
2
WO ꢀandꢀ1%ꢀRu/C.ꢀAsꢀshownꢀinꢀTableꢀ2,ꢀ
4
tionsꢀoccurringꢀsimultaneously:ꢀ(1)ꢀhydrolysisꢀofꢀcellobioseꢀtoꢀ
formꢀtwoꢀmoleculesꢀofꢀglucose,ꢀ(2)ꢀretro‐aldolꢀcondensationꢀofꢀ
cellobioseꢀtoꢀformꢀequal‐molarꢀGEꢀandꢀGA,ꢀandꢀ(3)ꢀhydrogena‐
tionꢀofꢀcellobioseꢀtoꢀ3‐β‐D‐glucopyranosyl‐D‐glucitol.ꢀThen,ꢀtheꢀ
productsꢀfromꢀtheꢀprimaryꢀreactionsꢀundergoꢀsecondaryꢀreac‐
tions.ꢀ Inꢀ theꢀ secondaryꢀ reactions,ꢀ glucose,ꢀ GE,ꢀ andꢀ
bothꢀ theꢀ conversionꢀ andꢀ productꢀ distributionꢀ wereꢀ differentꢀ
whenꢀtheꢀfeedstockꢀwasꢀchangedꢀfromꢀglucoseꢀtoꢀcellobiose.ꢀAtꢀ
thisꢀlowꢀtemperature,ꢀtheꢀcellobioseꢀconversionꢀwasꢀonlyꢀ6.0%ꢀ
whileꢀ theꢀ glucoseꢀ conversionꢀ reachedꢀ 11.1%,ꢀ indicatingꢀ thatꢀ
theꢀintrinsicꢀ reactivityꢀofꢀ cellobioseꢀwasꢀlowꢀ dueꢀtoꢀtheꢀ pres‐
enceꢀ ofꢀ theꢀ β‐1,4‐glycosidicꢀ bond.ꢀ Inꢀ theꢀ caseꢀ ofꢀ cellobiose,ꢀ
3‐β‐D‐glucopyranosyl‐D‐glucitolꢀwasꢀtheꢀmajorꢀproductꢀresult‐
ingꢀfromꢀtheꢀdirectꢀhydrogenationꢀofꢀcellobiose.ꢀTheꢀproductionꢀ
ofꢀaꢀveryꢀsmallꢀamountꢀofꢀsorbitolꢀ(0.16%)ꢀsuggestedꢀthatꢀhy‐
drogenationꢀpredominatedꢀoverꢀtheꢀhydrolysisꢀofꢀcellobioseꢀatꢀ
temperaturesꢀlowerꢀthanꢀ393ꢀK.ꢀSimilarly,ꢀhydrogenationꢀalsoꢀ
occurredꢀwithꢀglucoseꢀtoꢀproduceꢀsorbitolꢀ(9.74%)ꢀandꢀmanni‐
tolꢀ (0.08%).ꢀ Noꢀ C–Cꢀ bondꢀ cleavageꢀ tookꢀ placeꢀ atꢀ 393ꢀ K.ꢀ Ac‐
3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ furtherꢀ undergoꢀ theꢀ severalꢀ
parallelꢀ andꢀ consecutiveꢀ reactionsꢀ shownꢀ inꢀ Schemesꢀ 2–4.ꢀ
Clearly,ꢀevenꢀwithꢀtheꢀsimplestꢀunitꢀofꢀcelluloseꢀcontainingꢀonlyꢀ
oneꢀβ‐1,4‐glycosidicꢀbond,ꢀtheꢀreactionꢀnetworkꢀisꢀratherꢀcom‐
plex,ꢀsoꢀthisꢀwillꢀposeꢀaꢀsignificantꢀchallengeꢀforꢀselectivityꢀcon‐
trolꢀforꢀdesiredꢀproducts.ꢀ
Onꢀtheꢀotherꢀhand,ꢀfromꢀcomparingꢀtheꢀstructureꢀofꢀcellobi‐
ose,ꢀ GEꢀ andꢀ glycosyl‐glycolaldehydeꢀ (GG),ꢀ oneꢀ canꢀ clearlyꢀ seeꢀ
thatꢀ theꢀ accessibilityꢀ toꢀ theꢀ β‐1,4‐glycosidicꢀ bondꢀ followsꢀ theꢀ
orderꢀ GGꢀ >ꢀ GEꢀ >ꢀ cellobiose,ꢀ whichꢀ suggestedꢀ thatꢀ theꢀ ret‐
ro‐aldolꢀcondensationꢀofꢀaldoseꢀatꢀtheꢀreducingꢀendꢀwillꢀfurtherꢀ
promoteꢀtheꢀhydrolysisꢀofꢀtheꢀβ‐1,4‐glycosidicꢀbond.ꢀTheꢀDFTꢀ
calculationꢀofꢀtheꢀGibbsꢀfreeꢀenergiesꢀforꢀtheꢀhydrolysisꢀofꢀtheseꢀ
threeꢀaldosesꢀconfirmedꢀourꢀexpectation,ꢀasꢀshownꢀinꢀTableꢀ1.ꢀ
H
H
H
CH OH
2
Isomerism
H
OH
O
O
HHO
O
+
C
CH OH
CH OH
2
HO
2
H
OH
CH OH
H
OH
O
OH H
2
OH H
CH OH
2
HO
H
H
OH
CH OH
CH OH
2
2
HO
HO
H
H
H
OH
Hydrogenation
H
HO
H
H
+
OH
OH
OH
OH
H
H
CH OH
CH OH
2
2
CH OH
3.2.ꢀ ꢀ Comparisonꢀofꢀglucoseꢀandꢀcellobioseꢀtransformationꢀ
2
O
H
OH
CH OH
OHHO
2
H
H
HO
H
Retro-aldol
O
O
H
H
OH
OH
H
H
+
OHHO
OH
H
OH
CH2OH
O
CH2OH
CH2OH
H
H
Hydrogenation
Retro-aldol
OH
OH
H
OH
O
CH OH
OH H
+
H
H
OH
OH
2
OH
O
HO
OH
HO
H
OH
H
OH
CH OH
2
O
Side products
OH
CH2OH
O
OH
O
CH2OH
CH2OH
O
OH
H
OH
O
OH
OH
O
2
Schemeꢀ4.ꢀReactionꢀnetworkꢀofꢀglucoseꢀcatalyzedꢀbyꢀH WO ꢀandꢀRu/C.ꢀ
4
OH H
O
H2C
C
+
O
H
OH
O
H
HO
HO
HO
OH
OH
H
OH
Tableꢀ1ꢀ
CH2OH
OH2
H
H
H
CH2OH
Hydrolysis
H
O
O
H
H
OH
OH
CH2OH
Gibbsꢀ freeꢀ energyꢀ forꢀ theꢀ hydrolysisꢀ ofꢀ cellobiose,ꢀ glucosyl‐erythroseꢀ
(GE),ꢀandꢀglycosyl‐glycolaldehydeꢀ(GG).ꢀ
OH H
OH HO
+
HO
H
OH
OH
H
H
H
Reactionꢀ
Cellobiose+H
GE+H O→Glucose+Erythroseꢀ
GG+H O→Glucose+GAꢀ
ꢁGꢀ(kcal/mol)ꢀ
ꢀ 5.276ꢀ
HO
O
Side products
2
O→2Glucoseꢀ
OH
OH
2
0.805ꢀ
0.981ꢀ
Schemeꢀ2.ꢀReactionꢀnetworkꢀofꢀglucosyl‐erythroseꢀcatalyzedꢀbyꢀH
2
WO
4
2
andꢀRu/C.ꢀ

1814ꢀ
JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
cordingꢀ toꢀ ourꢀ kineticꢀ studiesꢀ [45,46],ꢀ C–Cꢀ bondꢀ cleavageꢀ ofꢀ
glucoseꢀrequiresꢀanꢀactivationꢀenergyꢀofꢀ141.3ꢀkJ/molꢀwhileꢀtheꢀ
hydrogenationꢀreactionꢀhasꢀaꢀmuchꢀlowerꢀbarrierꢀ(49.6ꢀkJ/mol).ꢀItꢀ
asꢀ ofꢀ 3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ followedꢀ byꢀ theꢀ hydro‐
genationꢀofꢀglucose,ꢀwhileꢀtheꢀEGꢀresultedꢀfromꢀtheꢀretro‐aldolꢀ
condensationꢀofꢀbothꢀcellobioseꢀandꢀglucoseꢀfollowedꢀbyꢀtheꢀhy‐
drogenationꢀofꢀglycolaldehyde,ꢀasꢀshownꢀinꢀSchemesꢀ1ꢀtoꢀ4.ꢀ
Whenꢀtheꢀcellobioseꢀreactionꢀwasꢀperformedꢀatꢀhigherꢀtem‐
peraturesꢀ(433–473ꢀK),ꢀtheꢀreactionꢀrateꢀwasꢀremarkablyꢀen‐
hanced.ꢀForꢀexample,ꢀcellobioseꢀwasꢀcompletelyꢀconvertedꢀforꢀ
360,ꢀ50,ꢀandꢀ15ꢀminꢀatꢀtheꢀreactionꢀtemperatureꢀofꢀ433,ꢀ453,ꢀ
andꢀ473ꢀK,ꢀrespectively.ꢀAtꢀtheꢀsameꢀtime,ꢀtheꢀproductꢀdistribu‐
tionꢀchangedꢀwithꢀincreasingꢀtemperature.ꢀEGꢀratherꢀthanꢀsor‐
bitolꢀbecameꢀtheꢀmainꢀproductꢀatꢀT ≥ꢀ433ꢀK,ꢀindicatingꢀtheꢀC–Cꢀ
bondꢀcleavageꢀreactionꢀprevailedꢀoverꢀhydrogenationꢀatꢀhigherꢀ
temperatures.ꢀNevertheless,ꢀinꢀtheꢀbeginningꢀperiodꢀofꢀtheꢀre‐
action,ꢀ oneꢀ canꢀ stillꢀ observeꢀ theꢀ formationꢀ ofꢀ 3‐β‐D‐gluco‐
pyranosyl‐D‐glucitolꢀandꢀglucose,ꢀandꢀtheꢀlatterꢀbecameꢀmoreꢀ
dominantꢀ withꢀ increasingꢀ temperature,ꢀ suggestingꢀ thatꢀ theꢀ
hydrolysisꢀ ofꢀ cellobioseꢀ wasꢀ moreꢀ promotedꢀ atꢀ anꢀ increasedꢀ
temperature.ꢀItꢀisꢀalsoꢀinterestingꢀtoꢀnoticeꢀthatꢀGAꢀappearedꢀinꢀ
theꢀ productsꢀ ofꢀ theꢀ cellobioseꢀ reactionꢀ atꢀ 453ꢀ andꢀ 473ꢀ K.ꢀ Inꢀ
previousꢀ studiesꢀ ofꢀ celluloseꢀ conversionꢀ [24–31],ꢀ GAꢀ wasꢀ al‐
waysꢀrapidlyꢀhydrogenatedꢀtoꢀEGꢀuponꢀitsꢀformation.ꢀInꢀcon‐
trast,ꢀGAꢀwasꢀnotꢀinstantlyꢀhydrogenatedꢀintoꢀEGꢀinꢀtheꢀpresentꢀ
cellobioseꢀ reaction,ꢀ whichꢀ gaveꢀ theꢀ decreasedꢀ EGꢀ yield.ꢀ Theꢀ
shouldꢀalsoꢀbeꢀpointedꢀoutꢀthatꢀtheꢀpresenceꢀofꢀH
2
WO ꢀinꢀtheꢀ
4
reactionꢀsystemꢀsuppressedꢀtheꢀhydrogenationꢀofꢀbothꢀcellobi‐
oseꢀandꢀglucoseꢀleadingꢀtoꢀtheirꢀlowꢀconversionꢀevenꢀafterꢀ2ꢀhꢀ
forꢀtheꢀreactionꢀatꢀ393ꢀK.ꢀ
Subsequently,ꢀ weꢀ investigatedꢀ theꢀ reactivitiesꢀ ofꢀ cellobioseꢀ
andꢀ glucoseꢀ atꢀ higherꢀ temperaturesꢀ fromꢀ 418ꢀ toꢀ 513ꢀ K.ꢀ Fig.ꢀ 2ꢀ
illustratesꢀtheꢀproductꢀdistributionsꢀfromꢀcellobioseꢀconversionꢀ
atꢀfourꢀdifferentꢀtemperatures.ꢀWhenꢀtheꢀreactionꢀofꢀcellobioseꢀ
proceededꢀ atꢀ 418ꢀ K,ꢀ theꢀ mainꢀ productsꢀ inꢀ theꢀ initialꢀ 240ꢀ minꢀ
wereꢀ 3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ andꢀ glucose,ꢀ whileꢀ theꢀ
otherꢀtwoꢀminorꢀproductsꢀwereꢀsorbitolꢀandꢀEG,ꢀindicatingꢀthatꢀ
theꢀdirectꢀhydrogenationꢀandꢀhydrolysisꢀofꢀcellobioseꢀdominatedꢀ
althoughꢀtheꢀC–Cꢀbondꢀcleavageꢀreactionꢀhadꢀoccurredꢀtoꢀaꢀsmallꢀ
extentꢀ atꢀ thisꢀ temperature.ꢀ However,ꢀ withꢀ increasingꢀ reactionꢀ
time,ꢀbothꢀsorbitolꢀandꢀEGꢀincreasedꢀinꢀtheirꢀyieldsꢀatꢀtheꢀexpenseꢀ
ofꢀ bothꢀ 3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ andꢀ glucose.ꢀ Whenꢀ theꢀ
cellobioseꢀ wasꢀ convertedꢀ completelyꢀ atꢀ 840ꢀ min,ꢀ theꢀ
3‐β‐D‐glucopyranosyl‐D‐glucitolꢀ amountꢀ wasꢀ almostꢀ negligibleꢀ
whileꢀtheꢀsorbitolꢀandꢀEGꢀyieldsꢀwereꢀ42.8%ꢀandꢀ21.7%,ꢀrespec‐
tively.ꢀTheꢀsorbitolꢀcameꢀfromꢀtheꢀhydrolysisꢀofꢀcellobioseꢀasꢀwellꢀ
Tableꢀ2ꢀ
ReactivityꢀofꢀcellobioseꢀandꢀglucoseꢀcatalyzedꢀbyꢀH
2
WO ꢀandꢀ1%ꢀRu/C.ꢀ
4
Yieldꢀ(%)ꢀ
Sorbitolꢀ
0.16ꢀ
Reactantꢀ
Conversionꢀ(%)ꢀ
3
‐β‐D‐glucopyranosyl‐D‐glucitolꢀ
Mannitolꢀ
0ꢀ
0.08ꢀ
EGꢀ
0ꢀ
0ꢀ
1,2‐PGꢀ
0ꢀ
0ꢀ
Cellobioseꢀ
Glucoseꢀ
ꢀ 6.0ꢀ
11.1ꢀ
4.83ꢀ
0ꢀ
9.74ꢀ
2 4 2
Reactionꢀconditions:ꢀ0.1ꢀgꢀH WO ,ꢀ0.3ꢀgꢀ1%Ru/C,ꢀ6ꢀMPaꢀH ,ꢀ1000ꢀr/min,ꢀ393ꢀK,ꢀ2ꢀh.ꢀ
80
60
40
20
0
80
Glucopyranosyl-D-glucitol
Glucopyranosyl-D-glucitol
433 K
418 K
Glucose
Mannose
Sorbitol
EG
120
Glucose
Mannose
Sorbitol
EG
120
60
40
20
0
90
60
30
0
90
60
30
0
60
120 240 360 480 600 720 840
Time (min)
60
120 180 240 300 360 420
Time (min)
ꢀ
8
6
4
2
0
0
0
0
0
80
60
40
20
0
Glucopyranosyl-D-glucitol
Glucose
453 K
Glucopyranosyl-D-glucitol
Glucose
473 K
120
1
9
6
3
0
20
Mannose
Mannose
Glycolaldehyde
Sorbitol
EG
Glycolaldehyde
Sorbitol
EG
90
60
30
0
0
0
0
5
10 20
30 50 70 100 120
Time (min)
2
5
10
15
20
30
WO
40
Time (min)
ꢀ
,ꢀ0.30ꢀgꢀRu/AC,ꢀ6ꢀMPaꢀ
Fig.ꢀ2.ꢀProductꢀdistributionꢀversusꢀtimeꢀforꢀcellobioseꢀconversionꢀatꢀdifferentꢀtemperatures.ꢀReactionꢀconditions:ꢀ0.10ꢀgꢀH
,ꢀ1000ꢀr/min.ꢀ
2
4
H
2

ꢀ
JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
1815ꢀ
underlyingꢀreasonꢀmayꢀlieꢀinꢀthatꢀtheꢀretro‐aldolꢀcondensationꢀ
rateꢀofꢀcellobioseꢀandꢀitsꢀderivedꢀglucoseꢀisꢀmuchꢀhigherꢀthanꢀ
thatꢀofꢀcellulose,ꢀwhichꢀledꢀtoꢀtheꢀproductionꢀofꢀexcessꢀGA.ꢀSinceꢀ
GAꢀ hydrogenationꢀ involvesꢀ heterogeneousꢀ catalysisꢀ overꢀ Ru,ꢀ
theꢀgas‐liquidꢀandꢀliquid‐solidꢀmassꢀtransferꢀrateꢀmayꢀlowerꢀtheꢀ
apparentꢀhydrogenationꢀrateꢀalthoughꢀtheꢀactivationꢀenergyꢀofꢀ
GAꢀhydrogenationꢀwasꢀonlyꢀ42.6ꢀkJ/mol.ꢀIncreasingꢀtheꢀRu/Cꢀ
catalystꢀ amountꢀ orꢀ byꢀ removingꢀ theꢀ possibleꢀ massꢀ transferꢀ
limitationꢀisꢀ anꢀeffectiveꢀwayꢀtoꢀaccelerateꢀGAꢀhydrogenationꢀ
andꢀincreasingꢀtheꢀEGꢀyield.ꢀ
tures.ꢀ Similarꢀ toꢀ theꢀ cellobioseꢀ conversion,ꢀ theꢀ directꢀ hydro‐
genationꢀ ofꢀ glucoseꢀ alsoꢀ significantlyꢀ prevailedꢀ overꢀ theꢀ C–Cꢀ
bondꢀcleavageꢀreactionꢀatꢀaꢀrelativelyꢀlowꢀtemperatureꢀofꢀ418ꢀ
K,ꢀleadingꢀtoꢀtheꢀmajorꢀproductionꢀofꢀsorbitolꢀandꢀminorꢀpro‐
ductionꢀofꢀEG.ꢀWithꢀtheꢀincreaseꢀofꢀtheꢀreactionꢀtemperature,ꢀ
theꢀC–Cꢀbondꢀcleavageꢀreactionꢀofꢀglucoseꢀgraduallyꢀdominatedꢀ
theꢀhydrogenationꢀleadingꢀtoꢀtheꢀmajorꢀproductionꢀofꢀEG,ꢀsimi‐
larꢀ toꢀ theꢀ caseꢀ ofꢀ cellobiose.ꢀ However,ꢀ onꢀ comparingꢀ theꢀ EGꢀ
yieldsꢀinꢀtheꢀglucoseꢀandꢀcellobioseꢀreactionsꢀatꢀtheꢀsameꢀcon‐
ditionsꢀ(Fig.ꢀ4.),ꢀweꢀcanꢀfindꢀthatꢀtheꢀformerꢀisꢀmuchꢀfasterꢀthanꢀ
theꢀlatterꢀinꢀtheꢀinitialꢀperiodsꢀofꢀtheꢀreaction,ꢀsuggestingꢀthatꢀ
Fig.ꢀ3ꢀpresentsꢀtheꢀglucoseꢀconversionꢀatꢀdifferentꢀtempera‐
80
60
40
20
0
140
80
60
40
20
0
140
120
100
80
Sorbitol
EG
418 K
Sorbitol
EG
433 K
1
1
8
6
4
2
0
20
00
0
0
60
0
40
0
20
0
60
120
240
360
480
600
60
120
170
240
300
360
Time (min)
Time (min)
8
6
4
2
0
0
0
0
0
140
80
60
40
20
0
140
120
100
80
4
53 K
Sorbitol
EG
473 K
Sorbitol
EG
Glycolaldehyde
120
Glycolaldehyde
100
80
60
40
20
0
60
40
20
0
5
10
20
30
50
70
100
2
5
10
15
20
30
WO
40
Time (min)
Time (min)
ꢀ
Fig.ꢀ3.ꢀProductꢀdistributionꢀversusꢀtimeꢀforꢀglucoseꢀconversionꢀatꢀdifferentꢀtemperatures.ꢀReactionꢀconditions:ꢀ0.10ꢀgꢀH
000ꢀr/min.ꢀ
2
4
,ꢀ0.30ꢀgꢀRu/AC,ꢀ6ꢀMPaꢀH ,ꢀ
2
1
6
5
4
3
2
1
0
0
0
0
0
0
0
(
a)
(b)
(c)
4
18 K
433 K
453 K
Glucose
Cellobiose
Glucose
Cellobiose
Glucose
Cellobiose
0
300
600
900
75
150
225
300
375
0
30
60
90
120
(f)
Time (min)
Time (min)
Time (min)
75
60
45
30
15
0
(
d)
(e)
4
73 K
493 K
513 K
Glucose
Cellobiose
Glucose
Cellobiose
Glucose
Cellobiose
0
10
20
30
40
0
10
20
30
0
5
10
15
20
Time (min)
Fig.ꢀ4.ꢀEthyleneꢀglycolꢀyieldꢀasꢀaꢀfunctionꢀofꢀreactionꢀtimeꢀforꢀglucoseꢀandꢀcellobioseꢀconversion.ꢀReactionꢀconditions:ꢀ0.10ꢀgꢀH
MPaꢀH ,ꢀ1000ꢀr/min.ꢀ ꢀ
Time (min)
Time (min)
2
WO ,ꢀ0.30ꢀgꢀRu/AC,ꢀ6ꢀ
4
2

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JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
Referencesꢀ
75
60
45
30
15
Glucose
Cellobiose
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Temperature (K)
[
Fig.ꢀ5.ꢀEthyleneꢀglycolꢀyieldsꢀatꢀ100%ꢀcellobioseꢀorꢀglucoseꢀconversion
asꢀaꢀfunctionꢀofꢀtemperature.ꢀReactionꢀconditions:ꢀ0.10ꢀgꢀH WO ,ꢀ0.30ꢀgꢀ
Ru/AC,ꢀ6ꢀMPaꢀH ,ꢀstirringꢀspeedꢀ1000ꢀr/min.ꢀ
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2
[
[
4
13] ZhaoꢀC,ꢀKouꢀY,ꢀLemonidouꢀAꢀA,ꢀLiꢀXꢀB,ꢀLercherꢀJꢀA.ꢀAngewꢀChemꢀIntꢀ
Ed,ꢀ2009,ꢀ48:ꢀ3987ꢀ
theꢀC–Cꢀbondꢀcleavageꢀreactionꢀofꢀglucoseꢀisꢀmuchꢀeasierꢀthanꢀ
thatꢀofꢀcellobiose.ꢀNevertheless,ꢀwithꢀtheꢀincreasingꢀofꢀreactionꢀ
time,ꢀtheꢀEGꢀyieldꢀfromꢀcellobioseꢀconversionꢀsurpassesedꢀthatꢀ
fromꢀglucose.ꢀMoreover,ꢀwithꢀanꢀincreaseꢀofꢀtheꢀreactionꢀtemper‐
ature,ꢀtheꢀintersectingꢀpointꢀofꢀtheꢀEGꢀyieldsꢀofꢀglucoseꢀandꢀcello‐
bioseꢀshiftedꢀtoꢀaꢀshorterꢀreactionꢀtimeꢀ(Fig.ꢀ4(b)–(f)),ꢀsuggestingꢀ
thatꢀaꢀhigherꢀtemperatureꢀisꢀmoreꢀfavorableꢀforꢀtheꢀretro‐aldolꢀ
condensationꢀofꢀcellobioseꢀinꢀcomparisonꢀwithꢀthatꢀofꢀglucose.ꢀAtꢀ
eachꢀtemperature,ꢀtheꢀfinalꢀEGꢀyieldꢀatꢀ100%ꢀconversionꢀofꢀcello‐
bioseꢀwasꢀalwaysꢀhigherꢀthanꢀthatꢀofꢀglucose,ꢀandꢀtheꢀdifferenceꢀ
becameꢀ largerꢀ atꢀ higherꢀ temperatureꢀ (Fig.ꢀ 5.).ꢀ Thisꢀ canꢀ beꢀ ex‐
plainedꢀbyꢀtheꢀslowꢀretro‐aldolꢀcondensationꢀofꢀcellobioseꢀasꢀwellꢀ
asꢀ slowꢀ releaseꢀ ofꢀ glucoseꢀ fromꢀ theꢀ hydrolysisꢀ ofꢀ cellobiose,ꢀ
whichꢀisꢀbetterꢀmatchedꢀwithꢀtheꢀsubsequentꢀhydrogenationꢀofꢀ
GA.ꢀ Onꢀ extrapolatingꢀ thisꢀ toꢀ celluloseꢀ conversion,ꢀ thisꢀ trendꢀ
wouldꢀholdꢀifꢀtheꢀhydrolysisꢀofꢀcelluloseꢀisꢀmuchꢀmoreꢀdifficultꢀ
thanꢀ cellobioseꢀ andꢀ theꢀ resultingꢀ glucoseꢀ concentrationꢀ inꢀ theꢀ
solutionꢀisꢀmuchꢀlower,ꢀi.e.,ꢀtheꢀEGꢀyieldꢀwouldꢀfollowꢀtheꢀorderꢀofꢀ
celluloseꢀ >ꢀ celloligosaccharidesꢀ >ꢀ glucose.ꢀ However,ꢀ thisꢀ trendꢀ
[
14] AlonsoꢀDꢀM,ꢀBondꢀJꢀQ,ꢀDumesicꢀJꢀA.ꢀGreenꢀChem,ꢀ2010,ꢀ12:ꢀ1493ꢀ
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[
9400ꢀ
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Commun,ꢀ2013,ꢀ49:ꢀ5727ꢀ
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XuꢀYꢀP,ꢀLiuꢀZꢀM.ꢀChinꢀJꢀCatal,ꢀ2014,ꢀ35:ꢀ684ꢀ
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[23] JiꢀN,ꢀZhangꢀT,ꢀZhengꢀMꢀY,ꢀWangꢀAꢀQ,ꢀWangꢀH,ꢀWangꢀXꢀD,ꢀChenꢀJꢀG.ꢀ
AngewꢀChemꢀIntꢀEd,ꢀ2008,ꢀ47:ꢀ8510ꢀ
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Chem,ꢀ2010,ꢀ3:ꢀ63ꢀ
canꢀbeꢀchangedꢀbyꢀtuningꢀtheꢀratioꢀofꢀH
2
WO ꢀtoꢀRu/Cꢀasꢀwellꢀasꢀ
4
[
[
[
[
[
26] ZhaoꢀGꢀH,ꢀZhengꢀMꢀY,ꢀWangꢀAꢀQ,ꢀZhangꢀT.ꢀChinꢀJꢀCatal,ꢀ2010,ꢀ31:ꢀ
28ꢀ
27] PangꢀJꢀF,ꢀZhengꢀMꢀY,ꢀWangꢀAꢀQ,ꢀZhangꢀT.ꢀIndꢀEngꢀChemꢀRes,ꢀ2011,ꢀ
0:ꢀ6601ꢀ
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383ꢀ
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:ꢀ939ꢀ
byꢀoptimizingꢀtheꢀreactionꢀconditionsꢀ[34].ꢀ
9
4.ꢀ ꢀ Conclusionsꢀ
5
Fromꢀanꢀinvestigationꢀofꢀtheꢀhydrogenolysisꢀofꢀcellobioseꢀtoꢀ
6
EG,ꢀweꢀelucidatedꢀtheꢀreactionꢀpathwaysꢀinꢀwhichꢀhydrogena‐
tion,ꢀ hydrolysisꢀ andꢀ retro‐aldolꢀ condensationꢀ occurredꢀ simul‐
taneously.ꢀDFTꢀcalculationsꢀsuggestedꢀthatꢀtheꢀretro‐aldolꢀcon‐
densationꢀofꢀaldosesꢀatꢀtheꢀreducingꢀendꢀpromotedꢀtheꢀhydrol‐
ysisꢀofꢀtheꢀβ‐1,4‐glycosidicꢀbond.ꢀTheꢀcomparisonꢀofꢀtheꢀcello‐
bioseꢀ andꢀ glucoseꢀ reactionsꢀ showedꢀ thatꢀ theꢀ retro‐aldolꢀ con‐
densationꢀ ofꢀ cellobioseꢀ isꢀ moreꢀ difficultꢀ thanꢀ thatꢀ ofꢀ glucose,ꢀ
whichꢀloweredꢀtheꢀformationꢀrateꢀofꢀglycolaldehydeꢀandꢀmadeꢀ
itꢀmoreꢀmatchedꢀwithꢀtheꢀsubsequentꢀhydrogenationꢀrate,ꢀthusꢀ
leadingꢀtoꢀincreasedꢀyieldꢀofꢀEGꢀfromꢀcellobiose.ꢀThisꢀtrendꢀcanꢀ
beꢀextrapolatedꢀtoꢀcellulose.ꢀThisꢀstudyꢀprovidedꢀusefulꢀinfor‐
mationꢀforꢀtheꢀmechanisticꢀunderstandingꢀofꢀcelluloseꢀconver‐
sionꢀtoꢀEGꢀandꢀwillꢀguideꢀtheꢀdesignꢀofꢀmoreꢀefficientꢀandꢀselec‐
tiveꢀcatalystꢀformulations.ꢀ
5
30] TaiꢀZꢀJ,ꢀZhangꢀJꢀY,ꢀWangꢀAꢀQ,ꢀZhengꢀMꢀY,ꢀZhangꢀT.ꢀChemꢀCommun,ꢀ
2012,ꢀ48:ꢀ7052ꢀ
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ChemSusChem,ꢀ2013,ꢀ6:ꢀ652ꢀ
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[33] ZhouꢀLꢀK,ꢀPangꢀJꢀF,ꢀWangꢀAꢀQ,ꢀZhangꢀT.ꢀChinꢀJꢀCatal,ꢀ2013,ꢀ34:ꢀ2041ꢀ
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Res,ꢀ2013,ꢀ52:ꢀ9566ꢀ
[
[
[
[
[
35] ZhengꢀMꢀY,ꢀPangꢀJꢀF,ꢀWangꢀAꢀQ,ꢀZhangꢀT.ꢀChinꢀJꢀCatal,ꢀ2014,ꢀ35:ꢀ602ꢀ
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ꢀ
JunyingꢀZhangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1811–1817ꢀ
GraphicalꢀAbstractꢀ
1817ꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2014,ꢀ35:ꢀ1811–1817ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(14)60151‐0
Comparison of cellobiose and glucose transformation to ethylene glycolꢀ
ꢀ
ꢀ
JunyingꢀZhang,ꢀXiaofengꢀYang,ꢀBaolinꢀHou,ꢀAiqinꢀWang*,ꢀZhenleiꢀLi,ꢀHuaꢀWang,ꢀTaoꢀZhang*ꢀ
DalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences;ꢀUniversityꢀofꢀChineseꢀAcademyꢀofꢀSciencesꢀ
CH2OH
O
H
H
H
Hydrolysis
H
OH
Retro-aldol
O
Hydrogenation
O
HO
OH
H
OH HO
+
OH
OH
HO
H
OH
H
H
OH
H
CH2OH
OH
H
OH
OH
CH2OH
OH
OH
CH2OH
O
CH2OH
O
OH
OH
OH
H
HO
H
CH2OH
O
OH
CH2OH
Hydrogenation
Hydrolysis
H
OH
H
OH
OH
OH
H
+
O
O
OH
HO
OH
OH
H
H
OH
H
OH
OH
CH2OH
CH2OH
O
OH
CH2OH
O
H
H
H
Retro-aldol
OH
OH
Hydrolysis
H
OH2
O
O
OH
H
OH HO
O
+
HO
H
OH
H
HO
OH
H
H
OH
Retro-aldol
O
CH2OH
O
OH
CH2OH
O
Hydrolysis
H
OH
H
O
Hydrogenation
H2C
C
OH
H
HO
O
+
OH
H
OH
HO
HO
OH
H
OH
ꢀ
Aꢀnewꢀreactionꢀpathwayꢀwasꢀproposedꢀforꢀcellobioseꢀconversion.ꢀTheꢀretro‐aldolꢀcondensationꢀofꢀcellobioseꢀisꢀmoreꢀdifficultꢀthanꢀthatꢀofꢀ
glucose,ꢀleadingꢀtoꢀincreasedꢀyieldꢀofꢀEGꢀfromꢀcellobiose.ꢀ
EngꢀChemꢀRes,ꢀ1998,ꢀ37:ꢀ357ꢀ
40] SasakiꢀM,ꢀFurukawaꢀM,ꢀMinamiꢀK,ꢀAdschiriꢀT,ꢀAraiꢀK.ꢀIndꢀEngꢀChemꢀ
Res,ꢀ2002,ꢀ41:ꢀ6642ꢀ ꢀ
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2014,ꢀDOI:ꢀ10.1002/aic.14554ꢀ
[
[
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006,ꢀ128:ꢀ8714ꢀ ꢀ
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