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DOI: 10.1002/cssc.201300004
Catalytic Dehydration of Carbohydrates on In Situ
Exfoliatable Layered Niobic Acid in an Aqueous System
under Microwave Irradiation
[
a]
Qingbin Wu, Yani Yan, Qian Zhang, Jinhua Lu, Zhijian Yang, Yahong Zhang, and Yi Tang*
A simple and efficient microwave-assisted HNb O catalytic
ered HNb O8 with the aid of microwave irradiation, which
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process is proposed for the dehydration of carbohydrates in
the aqueous phase. A 5-hydroxymethylfurfural (HMF) yield of
leads to quasi-homogeneous catalytic behavior. Importantly,
the catalytic system is also applicable for the one-pot produc-
tion of HMF from di- and polysaccharides, such as inulin,
through a consecutive hydrolysis–dehydration reaction. Addi-
tionally, the unique restacking feature of the exfoliated HNb O
55.9% was achieved at a high substrate/catalyst weight ratio
of 50 from a 10 wt% fructose solution, which is close to the
yield achieved by homogeneous aqueous systems. The critical
factor for this performance is the fast in situ exfoliation of lay-
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ensures the good reusability of the catalyst.
Introduction
In recent years, sustainable carbon resources have attracted in-
creasing attention because of their potential to replace fossil
fuels. Biomass and biomass-derived chemicals are promising
lysts in aqueous systems is an urgent problem and a challenge
for HMF production from carbohydrates. To date, both homo-
and heterogeneous acidic catalysts have been studied for the
[
1]
[2]
substitutes for a source of petroleum. 5-Hydroxymethylfurfu-
ral (HMF) is one of the most important biomass-derived plat-
dehydration of carbohydrates. Homogeneous catalysts are ef-
[14,15]
ficient,
but heterogeneous catalysts are more promising
[
2]
form chemicals because of its rich chemistry. However, it is
still not yet produced on an industrial scale either because of
the low HMF yield in aqueous systems or the possible environ-
because of their facile separation from the catalytic system as
[16]
well as the low risk of corrosion to equipment. However, the
catalytic efficiency of heterogeneous catalysts is generally
lower than that of homogeneous systems because of the diffi-
culty in exposing sufficient acid sites to the relatively large
volume of reactants and the instability of these acid sites in
[
3]
mental risks and high cost of other solvents. For example,
ionic liquids are efficient solvents for the conversion of bio-
[
4]
mass to HMF, but their large-scale application is limited by
price and potential risks during application and post-treat-
[17]
aqueous solutions.
HNb O is a layered solid acid that has been widely studied
[
5–7]
ment.
In addition, some aprotic organic solvents (e.g., di-
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methylsulfoxide) can drive the equilibrium to HMF because of
its relatively higher solubility in organic solvents, which sup-
as a heterogeneous catalyst for many reactions owing to its
[18,19]
strong acid strength and high stability in water.
However,
[3,8,9]
presses side-reactions, such as the rehydration of fructose.
most reactants cannot enter its interlayer regions to come into
contact with the acid sites because of its relatively small
However, the employment of organic solvents often suffers
from difficulties of product separation as well as environmental
[20]
d spacing. Therefore, a pre-exfoliation process is regarded as
[
2,7,10]
issues.
necessary to expose the acid sites. Nevertheless, because of
À
Water is the most economical and sustainable solvent, but
unfortunately the dehydration of carbohydrates in aqueous
systems is normally reported with low selectivities owing to
undesired reaction pathways to byproducts, for example, in-
soluble humins, soluble polymers, levulinic acid (LA), and
the strong interaction between the Nb O8 sheets, which have
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a high charge density, a long pre-exfoliation period (e.g.,
[20]
3 weeks) is often required. In previous studies, we discov-
ered that the HNb O sheets could self-exfoliate in situ in an
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ethylene oxide (EO) aqueous solution to expose the acid sites
on the HNb O sheets, and this material was employed to cata-
[
11–14]
formic acid (FA).
Thus, the development of efficient cata-
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[21]
lyze EO hydration without pre-exfoliation steps. Unfortunate-
ly, similar ideas have failed for the dehydration of carbohy-
drates owing to their relatively weak effect on the exfoliation
[a] Q. Wu, Y. Yan, Q. Zhang, J. Lu, Z. Yang, Prof. Y. Zhang, Prof. Y. Tang
Department of Chemistry
of HNb O sheets heated in an oil bath (Table S1, Entry 1). The
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,
Collaborative Innovative Center of Chemistry for Energy Materials, and
Laboratory of Advanced Materials
Fudan University, Shanghai, 200433 (PR China)
Fax: (+86)21-65641740
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motivation for this work is to explore an applicable method to
achieve biomass transformation based on the in situ exfoliation
of HNb O sheets.
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Considering the highly efficient energy conversion and di-
E-mail: yitang@fudan.edu.cn
[14,16,22]
electric heating of microwave (MW) irradiation,
herein,
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201300004.
for the first time, a MW-assisted in situ exfoliation process is
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2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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