Selective Glucose-to-Fructose Isomerizationover Modified
Zirconium UiO-66 in Alcohol Media
Matheus DornelesdeMello and MichaelTsapatsis*
Biomass is an alternative carbon source to fossil fuels for the
production of platform chemicals,
such as 5-hydroxymethyl-
furfural (HMF), which can be used as polymer precursors and
in the synthesis of pharmaceuticals.
One of the routes avail-
able to produce HMF passes through the hydrolysis of cellu-
lose to glucose, followed by glucoseisomerization to fructose,
and finally dehydration of fructose to HMF.
Glucose is the
most abundant and cheapest monosaccharide available. How-
ever,the industrial enzyme-catalyzed glucoseisomerization
owing to thermodynamic limitations presentin
its high cost, and low catalyst stability,
offers opportunities for novel processes based on non-enzy-
Considerableeffort has been devoted in the past years to
improveyields and selectivity in fructosebyinvestigationof
differentsystems, includinghomogeneous acids and bases,
and heterogeneouscatalysts. Davis and co-workersintroduced
the use of substituted BEA zeolites as efficient Lewis acidcata-
lysts for glucoseisomerization. Since then, Sn-BEA and several
variations have been deeply investigated,
wide range of possibilities regarding activity,selectivity,and
even reactionmechanisms depending on the catalyst–reaction
media pair under study.
It is accepted that glucose isomerizationtofructoseon
Lewis acid sites occurs through aMeerwein–Ponndorf–Verley–
Oppenaher (MPVO) mechanism that involves the concerted re-
ductionofacarbonyl and the oxidation of adjacentalcohol
through ahydride transfer.
First, glucose diffuses from the
externalliquid phase onto the active sites, followed by adsorp-
tion and ring-openingofglucose on these sites. All these steps
are assumed to be quasi-equilibrated.
After that, coordina-
tion of glucose to an active site leads to the C2-to-C1hydride
transfer,which is assumed to be the rate-determining step.
Fructose is then desorbed and diffuses backtothe external
Another possible primary product in the reactionisman-
nose, the epimer of glucose. If sodium was incorporated into
the activesite of Sn-BEA,
or if borates were used as cata-
glucose epimerized to mannosethroughanintramo-
lecular carbon shift, known as the Bilik reaction. It is also possi-
ble to form mannose from areverse 1,2-hydride transfer from
fructose, asitwas observed for CrCl
andother metal halides
As an attempttofind new heterogeneous catalysts with
Lewis acidityfor glucoseisomerization,metal–organic frame-
works (MOFs) have drawn significant attention owing to their
high tunability and density of active sites.
MOFs are com-
posed of metal clusters connected by organic linkers, which
can have their characteristics modified upon different choices
of metals and linkers.
However,anobstacle for the applica-
tions of MOFs can be their limitedstability.
The zirconium MOF UiO-66
is one of the MOFs with high-
est reported stability, both chemical and thermal.
[23, 25, 26]
clusters can act as Lewis acid sites, as it was observed for the
cyclization of benzaldehyde and aldol condensation.
modified UiO-66with Brønsted acid sites has been studied for
glucoseisomerization to fructose in water,achieving high se-
lectivity at 48 %glucose conversion.
Asimilar synthesis pro-
cedure was used to make an active catalyst for fructosedehy-
dration to HMF,showing high activity and stabilityatreaction
Modulated zirconiummetal–organic framework UiO-66 is
shown to catalyze the isomerizationofd-glucose to d-fructose
in alcohol media. Fructose selectivity can change depending
on solvent choice. We hypothesize that the difference in selec-
tivity is related to acombined effect of adsorption and solva-
tion effects, which may lead to the high formation of alkylglu-
cosides in depletion of fructose if methanol or ethanol are
used. Afructoseselectivity of 72 %at82% glucoseconversion
in 1-PrOH was achieved. The reaction mechanismwas investi-
gated using nuclear magnetic resonance spectroscopy. We
demonstrate that UiO-66isomerizes glucose to fructose
throughanintramolecular C2–C1 hydridetransfer.Inaddition,
we show that modulated UiO-66 is ahighly active and stable
catalystatthe reactionconditions, showinggreat potentialfor
other sugar reactions.
[a] M. D. de Mello, Prof. M. Tsapatsis
Department of Chemical Engineering and Materials Science
University of Minnesota
421 WashingtonAvenue SE, Minneapolis,MN55455 (USA)
Supporting informationand the ORCID identification number(s) for the
author(s) of this article can be found underhttps://doi.org/10.1002/
ChemCatChem 2018, 10,2417 –2423 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim2417