Conversion of saccharides into levulinic acid and 5-hydroxymethylfurfural over WO3-Ta2O5 catalysts

Article abstract of DOI:10.1039/c5ra26147c

Bimetallic oxide catalysts WO₃-Ta₂O₅ are active in converting saccharides into 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) in one-pot reactions. The product selectivity varies at different WO₃ to Ta₂O₅ ratios. FTIR measurements indicate the presence of Lewis acid sites and the strength of the Lewis acid sites varies when the WO₃ to Ta₂O₅ ratio changes. The result suggests that conversion of carbohydrates into HMF and LA can be realized using a single catalytic system by adjusting the catalyst's acidic properties.

Full text of DOI:10.1039/c5ra26147c

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Conversion of saccharides into levulinic acid and 5-
hydroxymethylfurfural over WO3–Ta2O5 catalysts†
Cite this: RSC Adv., 2016, 6, 49760
a
b
a
ac
*
Qishun Liu,‡ Fengli Yang,‡ Heng Yin and Yuguang Du
Received 8th December 2015
Accepted 7th April 2016
DOI: 10.1039/c5ra26147c
www.rsc.org/advances
Bimetallic oxide catalysts WO3–Ta2O5 are active in converting isomerization, dehydration, and rehydration. Several homoge-
saccharides into 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) neous and heterogeneous catalytic systems containing Brønsted
in one-pot reactions. The product selectivity varies at different WO3 to or Lewis acid catalysts for the conversion of biomass into HMF
Ta2O5 ratios. FTIR measurements indicate the presence of Lewis acid have been reported.9–12 Most of the reported LA preparation
sites and the strength of the Lewis acid sites varies when the WO3 to methods use mineral acids (HCl, H2SO4, H3PO4, etc.) as cata-
Ta2O5 ratio changes. The result suggests that conversion of carbo- lysts at higher temperatures (about 250 C).13 Although homo-
ꢀ
hydrates into HMF and LA can be realized using a single catalytic geneous Brønsted acid-catalyzed conversion of saccharides into
system by adjusting the catalyst's acidic properties.
LA is a well-established process with many large scale units in
operation, the harsh reaction conditions, difficulties in
handling the liquid acidic waste, as well as the low product
selectivity makes this process undesirable.
Introduction
Processes using heterogeneous catalysts are generally more
environmentally friendly than those which use mineral acids as
the catalyst.14,15 Nevertheless, the yield of LA is generally lower
when heterogeneous acid catalysts are used.16–18 For example,
the highest yield of LA reported in the literature is 43% when
a LZY zeolite catalyst was used in converting fructose.19 Zhang
et al. utilised MFI-type zeolite with different SiO2/Al2O3 ratios as
catalysts in the dehydration of glucose to LA, reporting the
highest LA yield of 35.8%.20 Zhang et al. also found that the
strength of acidic sites and the mesoporosity of the zeolites had
a signicant effect on LA formation.20
We have reported that tantalum compounds are water-
tolerant solid acids which exhibit unique acidic properties
and good stability in water-containing system.11 Furthermore,
WO3 is an efficient catalyst for the dehydration of alcohols.21
However, research on WO3–Ta2O5 has not been widely pub-
lished. We report within this paper that tungsten–tantalum
mixed oxides (hereinaer WO3–Ta2O5), prepared by co-
precipitation, is a reusable heterogeneous catalyst for the
Future supplies of chemicals, materials, and energy depend on
developing renewable alternatives to petroleum. Carbohydrates
are a key renewable biomass component and an important
potential source of chemical intermediates, however, selectively
converting carbohydrates to desired platform chemicals is
difficult. Therefore, it is particularly important to develop new
catalysts for that purpose.
5-Hydroxymethylfurfural (HMF) and levulinic acid (LA) are
key platform chemicals; both can be obtained from biomass-
based carbohydrate chemistry and further upgraded to high
quality fuels and value-added chemicals.1–5 LA is considered as
one of top 12 bio-derived feedstocks by the United States
Department of Energy (DOE) for its applications as fuel addi-
tives, polymers, and resin precursors.6,7 It is well accepted that
HMF is a product of facile acid-catalyzed dehydration of
carbohydrates while LA is a product of subsequent rehydration
of HMF.8 The reaction pathway is shown in Scheme 1.
Direct conversion of carbohydrates into HMF and LA
involves multiple steps including but not limited to hydrolysis,
aNatural Products & Glyco-Biotechnology Research Group, Liaoning Provincial Key
Laboratory of Carbohydrates, Dalian 116023, China. E-mail: 252391742@163.com;
Fax: +86 411 84379060; Tel: +86 411 84379061
bJiangsu University of Technology, China
cInstitute of Process Engineering, Chinese Academy of Science, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra26147c
‡ Contributed equally to this work.
Scheme 1 Conversion of saccharides into HMF or LA.
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conversion of saccharides into value-added chemicals. decreases the LA yield. E.g., the LA yield was 76% using 20%
Furthermore, WO3–Ta2O5 is active in one-pot synthesis of LA WO3–Ta2O5, indicating that too high a content of WO3 is
from Jerusalem artichoke juice.
unfavorable for the formation of LA.
It is commonly understood that the acidic property of
heterogeneous catalysts is important for saccharide dehydra-
tion. The WO3–Ta2O5 catalyst was characterized using pyridine-
FTIR. The pyridine-FTIR spectra show that the peak intensity at
1450 cmÀ1 (attributed to pyridinium ions formed on Lewis acid
sites) became weaker when the percentage of WO3 increased.
This suggested that the formation of HMF was stimulated by the
Lewis acid, which is consistent with Nakajima's ndings.22 With
more WO3 added, the formation of HMF was inhibited.
Conversely, a suitable ratio of WO3 was favorable in forming
levulinic acid—the rehydration product of HMF—indicating
that the role of WO3 is similar to homogeneous acid, such as
H2SO4.22,23
Glucose, such as aldohexose is more difficult to convert into
HMF or LA than fructose. But it would be signicant to use
glucose as reactant to convert into chemicals and platforms on
a larger scale. Results using glucose as a reactant were shown in
Fig. S1 and S2.† It can be seen that the trends of LA and HMF
yields are similar to that of conversion of fructose. 5% WO3–
Ta2O5 showed the best selectivity to LA. The highest LA yield was
21%. The highest HMF yield (39%) was obtained using 0.5%
WO3–Ta2O5 as the catalyst. In addition, all the reactant
conversion rates are more than 95% catalyzed by WO3–Ta2O5
with different WO3 to Ta2O5 ratio, indicating formation of
byproducts (i.e. humins, insoluble products etc.) in these
reactions.24,25
Results and discussion
The effect of WO3 ratio on the yield of LA and HMF
The catalytic activity of WO3–Ta2O5 at different WO3 to Ta2O5
ratios was investigated. The results show that WO3–Ta2O5 at all
ratios are catalytic active in the conversion of monosaccharides
to HMF and LA. The yield of products (HMF and LA) varies at
different WO3 to Ta2O5 ratios (see Fig. 1). The HMF yield
increases when WO3 to Ta2O5 decreases. The HMF yield reached
61% using 0.5% WO3 in WO3–Ta2O5 as the catalyst (hereinaer
“0.5% WO3–Ta2O5”). It has been previously reported that the
HMF yield reached 90% using fructose as a reactant and
a tantalum catalyst containing no WO3,11 which suggests that
the presence of WO3 may be unfavourable to HMF. As for LA—
the product of HMF rehydration—its yield increased initially
and then decreased when WO3 was increased in the ratio. The
highest LA yield is 89%, which was achieved when fructose was
used as a reactant and catalyzed by 5% WO3–Ta2O5. Such a high
LA yield has not been reported in aqueous heterogeneous
catalytic systems. Therefore, more WO3 in WO3–Ta2O5
In addition to pyridine-FTIR, characterizations were carried
out using X-ray diffraction, TEM, and NH3-TPD. The
morphology of the samples was studied using TEM. Fig. S4† is
a TEM micrograph. The images reveal that the catalysts are
amorphous at different WO3 to Ta2O5 ratios, which is consistent
with the XRD results (see Fig. S5†). Tantalum oxide in this form
contains mainly Lewis acids and displays better acidic proper-
ties on saccharide dehydration into HMF.26 The addition of
WO3 may inhibit the Lewis acid sites from binding with pyri-
dine thus weakening the peak intensity of 1450 cmÀ1. There
ꢀ
ꢀ
were two desorption proles (50–300 C, 300–600 C) over the
temperature range of 50–600 ꢀC in the NH3-TPD proles
(Fig. S6†), suggesting the catalyst contains weak, moderate, and
strong acid sites on its surface. In order to ensure that the
catalyst remains amorphous, all the samples were treated at
300 ꢀC, thus the proles at 50–300 ꢀC are important to our
experiments and the 5% WO3–Ta2O5 catalyst has the maximum
amount of acid sites within this temperature range, which could
be the reason why the 5% WO3–Ta2O5 ratio has a better catalytic
performance than catalysts at other ratios.
The effect of temperature on the LA and HMF yields
Fig. 2 shows the effect of temperature on the LA and HMF yields
when using the ratio of 5% WO3–Ta2O5. The LA yield is directly
related to the reaction temperature. The LA yield was 89% at the
reaction temperature of 180 ꢀC. When the reaction temperature
was 160 ꢀC, the highest LA yield was 69%, with an extended
Fig. 1 The effect of WO3 on LA yields (A) and HMF yields (B). Reaction
condition: fructose (F):1.2 g, WO3–Ta2O5: 0.1 g, 20 ml of water, 30 ml
of 2-butanol, 180 ꢀC, 800 rpm. Yields were determined by HPLC
analysis.
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generated LA was converted into other by-products. Further-
more, the amount of HMF was small with the longer reaction
time directly affecting the decrease in the HMF yield. The
rehydration of HMF also produced formic acid, and its molar
yield should have been equivalent to that of LA. Incongruously,
the yield of formic acid was less than that of LA. This discrep-
ancy may be caused by the formic acid generated as Brønsted
acid catalyst consumed by hydrogenation with HMF, or as
a reagent for other reactions.28 Glucose or fructose as isomeri-
zation products were also detected when fructose and glucose
as reactants (see Fig. 3 and S7†), indicating that the isomeri-
zation occurred in this reaction system. The similar phenomena
were obtained when glucose was catalyzed by these catalysts.
Jerusalem artichoke juice was also used as the reactant in
addition to glucose and fructose. This non-food feedstock grows
well on marginal lands and has high tolerance for cold and
drought as well as resistance to wind and sand, and the easy
cultivation and relatively low input requirements make Jer-
usalem artichoke juice a promising feedstock for biofuels and
intermediates chemicals. Therefore, the Jerusalem artichoke
has been considered as one of the greatest potential raw
materials for production of biofuels and chemicals.29 The total
saccharide (main components were fructose and glucose with
ratios of 3.75 : 1) concentration of Jerusalem artichoke was 6%
aer pre-treatment (including membrane process, resin
exchange methods, and enzymatic hydrolysis method) as the
protein and ions might be disadvantageous for the activity of
the catalyst.30 The LA yield was 82% using pre-treated Jerusalem
artichoke juice catalyzed by 5% WO3–Ta2O5 (see Fig. S8†). The
results conrm that the heterogeneous catalysts are effective to
produce HMF and LA from biomass in a single catalytic system,
which is a challenge.31 It provides new ideas for transformation
biomass into biochemicals by heterogeneous catalysts.
Fig. 2 Effect of reaction temperature on LA and HMF yields. Reaction
condition: fructose: 1.2 g, WO3–Ta2O5 (5%): 0.1 g, 20 ml of water, 30
ml of 2-butanol, 800 rpm. Yields were determined by HPLC analysis.
reaction time. Conversely, the yield of HMF is lower at a higher
reaction temperature. The HMF yield was 10% of HMF at the
reaction temperature of 180 ꢀC and 23% of HMF at 160 ꢀC,
using 5% WO3–Ta2O5 as the catalyst for both temperatures. This
indicates that HMF was converted into LA more quickly at
a lower temperature. Additionally, the HMF yield decreased
when the reaction time was increased due to the rehydration of
HMF into LA or other by-products. These results show that
a higher temperature promotes the formation of LA. The reac-
tion temperature is modest relative to the reaction temperature
required when using homogeneous acids as catalysts.
Saccharides as the reactant
Fructose was rst catalyzed by 5% WO3–Ta2O5 and the products
were analysed by HPLC. The highest LA yield of 89% was ob-
tained (see Fig. 3), which was much higher than the reported LA
yield using other solid acids as the catalyst.27 The yield of LA
increased initially and then decreased; which suggests that the
Catalyst recycling
Recycling of catalyst is very important in green chemistry so that
the catalyst stability and reusability were tested. In the case of
Fig. 3 Product yields from fructose catalyzed by 5%WO3–Ta2O5.
Reaction condition: fructose: 1.2 g, WO3–Ta2O5 (5%): 0.1 g, 20 ml of Fig. 4 WO3–Ta2O5 (5%) recycling experiments. Reaction condition for
water, 30 ml of 2-butanol, 180 ꢀC, 800 rpm. Yields were determined by each batch: fructose: 1.2 g, 20 ml of water, 30 ml of 2-butanol, 180 ꢀC,
HPLC analysis.
800 rpm. Yields were determined by HPLC analysis.
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5% WO3–Ta2O5 aer each reaction, the catalyst was separated,
washed with deionized water, and dried at 60 C for 12 hours
volume 1-results of screening for potential candidates from
sugars and synthesis gas, 2004.
ꢀ
prior to being reused in the next run. As shown in Fig. 4, the
reaction using the fresh 5% WO3–Ta2O5 proceeds efficiently
produced a LA yield of 89%. The reused catalyst has not shown
signicant loss of activity. The yield of LA was 56% in the
second use, 52% in the third use, and 53% in the fourth use. In
7 B. Girisuta, L. P. B. M. Janssen and H. J. Heeres, Green Chem.,
2006, 8, 701–709.
8 F. M. Jin and H. Enomoto, Energy Environ. Sci., 2011, 4, 382–
397.
9 B. R. Caes and R. T. Raines, ChemSusChem, 2011, 4, 353–356.
addition, the HMF yield was 8% in the rst use, which increased 10 V. Degirmenci, E. A. Pidko, P. C. M. M. Magusin and
sharply to 41% in the second use, 43% in the third use, and 46% E. J. M. Hensen, ChemCatChem, 2011, 3, 969–972.
in the fourth use. Moreover, the sum of the LA and HMF yields 11 F. Yang, Q. Liu, M. Yue, X. Bai and Y. Du, Chem. Commun.,
little changed in the rst four uses but decreased in the h 2011, 47, 4469–4471.
uses, which may be attributed to catalyst deactivation. The exact 12 A. S. Amarasekara and C. C. Ebede, Bioresour. Technol., 2009,
mechanism of catalyst deactivation requires further studies.
100, 5301–5304.
13 M. Brasholz, K. von Kanel, C. H. Hornung, S. Saubern and
J. Tsanaktsidis, Green Chem., 2011, 13, 1114–1117.
14 Y. Takeuchi, F. M. Jin, K. Tohji and H. Enomoto, J. Mater.
Sci., 2008, 43, 2472–2475.
15 J.-P. Lange, Angew. Chem., Int. Ed., 2015, 54, 13186–13197.
16 B. Chamnankid, C. Ratanatawanate and K. Faungnawakij,
Chem. Eng. J., 2014, 258, 341–347.
17 H. Z. Chen, B. Yu and S. Y. Jin, Bioresour. Technol., 2011, 102,
3568–3570.
18 D. W. Rackemann and W. O. S. Doherty, Biofuels, Bioprod.
Bioren., 2011, 5, 198–214.
Conclusions
The WO3–Ta2O5 catalyst at different WO3 to Ta2O5 ratios and
different acid strengths was synthesized and evaluated in the
conversion of monosaccharide and Jerusalem artichoke juice
into HMF and LA in a water-containing biphasic system. There
apparently are few Brønsted acid sites on the tungsten oxide
incorporated in the tantalum compound and the Lewis acid
declined with the increase in WO3. The ratio of WO3 inuenced
the products distribution while 5% WO3–Ta2O5 showed the best
activity and selectivity to LA. The catalyst is also active in the
conversion of Jerusalem artichoke juice. Experiments using
recycled catalysts indicate that the WO3–Ta2O5 catalyst can be
recycled and reused. It is believed that the carbohydrate dehy-
dration into HMF and HMF rehydration into LA continues in
the presence of the acid sites on the catalyst. Further studies are
in progress.
19 J. Jow, G. L. Rorrer, M. C. Hawley and D. T. A. Lamport,
Biomass, 1987, 14, 185–194.
20 W. Zeng, D. G. Cheng, H. H. Zhang, F. Q. Chen and
X. L. Zhan, React. Kinet., Mech. Catal., 2010, 100, 377–384.
21 Y. K. Kim, R. Rousseau, B. D. Kay, J. M. White and
Z. Dohnalek, J. Am. Chem. Soc., 2008, 130, 5059–5061.
22 K. Nakajima, Y. Baba, R. Noma, M. Kitano, J. N. Kondo,
S. Hayashi and M. Hara, J. Am. Chem. Soc., 2011, 133,
4224–4227.
23 X. Chan, W. Nan, D. Mahajan and T. Kim, Catal. Commun.,
2015, 72, 11–15.
24 C. Sievers, I. Musin, T. Marzialetti, M. B. V. Olarte,
P. K. Agrawal and C. W. Jones, ChemSusChem, 2009, 2,
665–671.
Acknowledgements
This work was nancially supported by the National Natural
Science Foundation of China (project 21406020), National High
Technology Research and Development Program of China
(2014AA022004) and Natural Science Foundation of Jiangsu
Province (project BK20140257).
25 B. F. M. Kuster, Starch/Staerke, 1990, 42, 314–321.
26 T. Ushikubo and K. Wada, Appl. Catal., 1990, 67, 25–38.
27 S. Suacharoen and D. N. Tungasmita, J. Chem. Technol.
Biotechnol., 2013, 88, 1538–1544.
Notes and references
1 A. J. Crisci, M. H. Tucker, M. Y. Lee, S. G. Jang, J. A. Dumesic
and S. L. Scott, ACS Catal., 2011, 1, 719–728.
2 J. Lewkowski, ARKIVOC, 2001, 2, 17–54.
3 D. M. Alonso, J. Q. Bond and J. A. Dumesic, Green Chem.,
2010, 12, 1493–1513.
4 J. J. Bozell and G. R. Petersen, Green Chem., 2010, 12, 539–
554.
5 A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and
C. A. M. Afonso, Green Chem., 2011, 13, 754–793.
6 G. Petersen, T. Werpy, A. Aden, J. Bozell, J. Holladay, J. White
and A. Manheim, Top value added chemicals from biomass
28 T. Thananatthanachon and T. B. Rauchfuss, Angew. Chem.,
Int. Ed., 2010, 49, 6616–6618.
29 S.-Z. Li and C. Chan-Halbrendt, Appl. Energy, 2009, 86, S162–
S169.
30 S. J. Kay and S. F. Nottingham, Biology and Chemistry of
Jerusalem Artichoke, CRC Press, Boca Raton, 2007.
31 M. G. Mazzotta, D. Gupta, B. Saha, A. K. Patra, A. Bhaumik
and M. M. Abu-Omar, ChemSusChem, 2014, 7, 2342–2350.
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