A selective and economic carbon catalyst from waste for aqueous conversion of fructose into 5-hydroxymethylfurfural

Article abstract of DOI:10.1039/C6RA00154H

It is of vital importance to design stable and selective heterocatalysts for aqueous production of platforms from biomass-derived sugars. This paper describes a selective aqueous conversion of fructose to HMF using carbon catalysts from pulping waste sodium ligninsulfonate (SLS). The effect of carbonization atmospheres (N₂ flow, static air and air flow) on the structure, porosity, compositions and acidic properties of carbon catalysts were investigated by thermogravimetry-mass spectrum analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Boehm titrations, N₂ adsorption–desorption isotherms and elemental analysis. The carbonization in air flow favored the formation of more oxygen-containing functional groups and micropores, while more sulfonic groups and meso-/macro-pores were formed during carbonization in a static air atmosphere. Both oxygen- and sulfur-containing groups were acid sites, and their total amount was the largest when carbonized in air flow, followed by static air and N₂ flow. The positive correlation between the acid amounts and fructose conversion of carbon catalysts clearly demonstrated the catalytic effect of the acid sites. The steric hindrance of micropores in carbon catalysts restricted the formation of humins and promoted the HMF selectivity compared with meso-/macro-pores.

Full text of DOI:10.1039/C6RA00154H

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PAPER
A selective and economic carbon catalyst from
waste for aqueous conversion of fructose into
5-hydroxymethylfurfural†
Cite this: RSC Adv., 2016, 6, 30160
Tiansheng Deng,‡a Jiangong Li,‡a Qiqi Yang,b Yongxing Yang,a Guangqiang Lv,a
c
c
c
a
a
*
*
Ying Yao, Limin Qin, Xianlong Zhao, Xiaojing Cui and Xianglin Hou
It is of vital importance to design stable and selective heterocatalysts for aqueous production of platforms from
biomass-derived sugars. This paper describes a selective aqueous conversion of fructose to HMF using carbon
catalysts from pulping waste sodium ligninsulfonate (SLS). The effect of carbonization atmospheres (N2 flow,
static air and air flow) on the structure, porosity, compositions and acidic properties of carbon catalysts were
investigated by thermogravimetry-mass spectrum analysis, X-ray photoelectron spectroscopy, Fourier
transform infrared spectroscopy, Boehm titrations, N2 adsorption–desorption isotherms and elemental
analysis. The carbonization in air flow favored the formation of more oxygen-containing functional groups
and micropores, while more sulfonic groups and meso-/macro-pores were formed during carbonization in
a static air atmosphere. Both oxygen- and sulfur-containing groups were acid sites, and their total amount
was the largest when carbonized in air flow, followed by static air and N2 flow. The positive correlation
between the acid amounts and fructose conversion of carbon catalysts clearly demonstrated the catalytic
effect of the acid sites. The steric hindrance of micropores in carbon catalysts restricted the formation of
humins and promoted the HMF selectivity compared with meso-/macro-pores.
Received 4th January 2016
Accepted 13th March 2016
DOI: 10.1039/c6ra00154h
www.rsc.org/advances
water)8,11,15 have been demonstrated as the reaction media, and
high HMF yields were achieved with the aids of various acid
catalysts including heteropoly acids,21 solid acids,10,12,20,22 ion
Introduction
The increasing shortage of fossil fuels and environmental
pollution have stimulated the search for safe and clean energies
and chemicals.1 The potential of biomass as a complement
feedstock for fossil resources has been developed because of its
abundant and renewable nature.2 However, biomass resources
cannot be utilized directly as fuels due to their low energy
density and complex chemical compositions.3 Increasing efforts
have been contributed to convert biomass materials including
lignincellulose and saccharides to valuable chemicals,4 among
which the production of 5-hydroxymethylfurfural (HMF) has
attracted much attention.5 HMF is considered as an important
platform chemical, which can convert to levulinic acid, dime-
thylfuran and other biofuels with high heating values.6
exchange resins,14 zeolites,15 and acidic ionic liquid.16 In
comparison with organic solvents, water is an environmentally
friendly solvent and it is efficient especially for dissolving
saccharides. Despite of its green and convenient nature, the
studies using water as the reaction medium are few and
scarce.9–11,20 One of the main challenges for using water as
solvent is that the high polarity and strong hydrogen bonding
interaction of water make many solid acid catalysts unstable,
leading to the loss of acid sites in the catalyst. Therefore,
homogeneous catalysts are commonly applied in aqueous
system. Homogeneous catalysis showed high catalytic effi-
ciency, yet the challenges in the catalyst recycling and separa-
tion greatly lower their potential in the commercial
application.12 To tackle these problems, heterogeneous catalysts
including mesoporous TiO2,9 H3PO4 treated Nb2O3,18 alumino-
silicate catalysts15 and heterogeneous zirconium phosphate,17
were developed to catalyze the conversion of fructose into HMF.
Although these catalysts were easily separated, they suffered
from low stability. As efficient and stable catalysts, various
carbon-based catalysts, such as p-styrenesulfonic acid to carbon
nanotubes,13 and graphene oxide19,24 were developed for fruc-
tose dehydration into HMF. However, the expensive carbon
material and the complexity in the synthesis of catalyst limit
their further application in large-scale industrial production.
One of major routes for HMF production is based on acid
catalytic dehydration process of fructose.5,7–23 Organic
solvents,7,9,14,16,22 ionic liquids10 and biphasic systems (organic/
aThe Biorenery Research and Engineering Center, Institute of Coal Chemistry,
Chinese Academy of Sciences, Taiyuan, 030001, P. R. China. E-mail: cuixj@sxicc.ac.
cn; houxl@sxicc.ac.cn
bTaiyuan University of Technology, Taiyuan, P. R. China
cTaiyuan Institute of Technology, Taiyuan, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra00154h
‡ Authors contributed equally.
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Another big challenge for HMF synthesis from carbohydrates in in a 80 ml Erlenmeyer ask, and the mixture was ultrasonicated
water is related to the HMF selectivity. In fact, water promotes for 8 h. The carbon catalysts were then washed by deionized
the by-products formation, such as levulinic acid, formic acid water until a pH of 7 was reached. Finally, the carbon catalysts
and polymerized products (humins).25–27
were dried at 100 ꢀC for 12 h. The phosphoric acid-functionalized
Sodium ligninsulfonate (SLS) is popular and could be carbon catalysts obtained in static air atmosphere, air ow, and
collected from industrial sewage, such as from pulp liquor.28 N2 ow were designated as Ct1, Ct2, and Ct3.
Therefore, SLS derived activated carbon is more economical
The conversion of fructose was performed in a Teon-lined
compared with carbon nanotube and graphene materials. More autoclave with a content of 10 ml. In each test, a certain
importantly, we noticed that SLS possesses aromatic structures, amount of fructose was dissolved in water, followed by the
and it is rich in sulfonate groups, ether, hydroxyl, and other addition of a certain amount of catalyst. The mixture was
oxidation groups. The acidic oxygen- and sulfur-containing maintained at the desired temperature (120–170 ꢀC) and under
functional groups, have been demonstrated as the active sites vigorous stirring. High pressure liquid chromatography (LC-
for the dehydration of fructose into HMF.11–13,24,29 Therefore, the 10AT, Shimadzu) was used to analyze the products. The
acidic oxygen- and sulfur-containing functional groups in SLS concentration of HMF was analyzed by an UV detector (SPD-
could be preserved aer appropriate carbonization process and 10A, Shimadzu) and a 4.6 mm ID250 mm Kromstar C18
catalyze the conversion of fructose into HMF. Furthermore, the reverse-phase column. The mobile phase and the column
textural properties of the carbonized catalysts that are crucial to temperature was acetonitrile solution (70 vol%) with a ow rate
the selective conversion of sugars in water, could be tuned by of 0.6 ml minÀ1 and 25 ꢀC, respectively. Fructose concentration
carbonization conditions.
was obtained by a reective index detector (RID-10A, Shimadzu)
In the article, SLS was applied as the raw material to fabricate and SC 1011 sugar column (Shodex, Japan). The mobile phase
the acidic carbon catalysts for the selective conversion of fruc- was deionized water with a ow rate of 1 ml minÀ1, and the
tose into HMF in aqueous solution. Three atmospheres were column temperature was 80 ꢀC. Standard solutions of HMF and
applied for the carbonization of SLS, including N2 ow, static air fructose were used to obtain the calibration curves to calculate
atmosphere and air ow. The structure, porosity, compositions their concentrations by the external standard method.
and acidic properties of the carbon catalysts aer carbonization
were investigated by TG-MS, XRD, IR, Boehm titrations, N2
adsorption–desorption isotherms and elemental analysis, and
Elemental analysis of the samples was carried out using Ele-
the fructose conversion and HMF selectivity can be correlated
with the acidic properties and porosity of the catalysts, respec-
tively. Yield of 59.9% for HMF can be obtained from fructose in
water, and the catalyst were stable aer reusing for ve times.
Catalyst characterization
mentar instrument (Vario Macro Cube, Germany). The powder
X-ray diffraction (XRD) patterns were recorded on a X-ray
photoelectron spectroscopy (Kratos, UK). Fourier transform
infrared spectra of the samples was obtained on a FT-IR ana-
lyser (BRUKER TENSOR 27, Germany). The pore structure of the
Experimental
Materials
samples were obtained through analyzing N2 adsorption–
desorption isotherms (BEL BELSORP-max, Japan). N2 adsorp-
tion–desorption isotherms was analysed by physical adsorption
Fructose (99%) and 5-hydroxymethylfurfural (HMF) (99%) were
apparatus (Tristar 3000, USA). The samples were degassed at
obtained from Amresco, J&K Scientic Company and Kermel
100 ꢀC for 8 h prior to the analysis. Thermogravimetric and
chemical reagent company (Tianjin, China); sodium ligninsul-
mass spectrum analysis (TG-MS) was performed on a Evolution
fonate was purchased from Sigma-Aldrich Corp (USA); phos-
16/18 (Setaram Instrumentation, France) and OMNI star
phoric acid (84 wt%) was from Tianda chemical Corp (Tianjin,
(Pfeiffer Vacuum, Germany). The carrier gas was argon. The
China); hydrochloric acid (36 wt%) was obtained from Tianli
chemical reagent Co., Ltd. (Tianjin, China); sodium carbonate
(99 wt%) was acquired from Beichen Fangzheng chemical
reagent Corp (Tianjin, China); sodium hydroxide (96 wt%) was
purchased from Henxing chemical reagent Co., Ltd. (Tianjin,
China); sodium bicarbonate (99%) was from Beijing Huagong
Corp (Beijing, China).
À1
ꢀ
ꢀ
temperature was raised from 25 C to 1000 C by 10 ꢀC min
.
Results and discussion
The decomposition behavior of SLS
The mass loss behavior and the phase evolutions of SLS during
the carbonization process were investigated by TG-MS. As
shown in Fig. 1S and 2S in ESI,† two major stages for the mass
loss of SLS were detected by TG, that is, two low-temperature
Catalyst preparation and testing
The preparation procedures of phosphoric acid-functionalized peaks ranging from 150 to 400 ꢀC, and a high-temperature
carbon catalysts were as follows: 1 g of sodium ligninsulfonate peak ranging from 500 to 900 ꢀC. MS results indicated that
(designated as SLS) was mixed with 2 ml of phosphoric acids, carbon oxide (CO), carbon dioxide (CO2) and methane (CH4)
followed by heating in a tube furnace at 500 ꢀC for 2 h statically, were generated below 400 ꢀC. Sulfur dioxide (SO2) was detected
or in a nitrogen or air ow with a rate of 80 ml minÀ1. The when the temperature increased to 230 ꢀC, which can be
heating rate was 18 ꢀC minÀ1. Aer being cooled down, the ob- attributed to the decomposition of sulfonate groups of SLS. The
tained carbon catalysts was mixed with 30 ml hydrochloric acid second stage mass loss was accompanied by the generation of
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CO and CO2, which resulted from the further decomposition of method, the acid sites with weak, moderate or strong acidity can
the oxidation groups of SLS.
be quantied by acid–base neutralization reaction with strong,
moderate or weak base. In our case, NaHCO3 reacts with the
strong acid sites including carboxylic and sulfonic groups,
Na2CO3 is able to neutralize carboxyl, sulfonic and lactone
groups, and NaOH can react with all acid sites including carboxyl,
sulfonic, lactone and phenolic groups. The amounts of various
acid sites calculated by Boehm's method are listed in Table 1.
As shown in Table 1, Ct2 possessed the most acidic sites
among the three catalysts, whereas the amount of acidic sites in
Ct3 was the least. Noticeably, a positive correlation can be
established between the total content of (O + S) (determined by
ICP) and the amount of total acid sites for the three catalysts,
while such correlation was not found between the oxygen
content and the amount of total acid sites for the three catalysts
(Fig. 5S and 6S, in ESI†). This result indicated that the acid sites
in the catalysts were primarily the oxygen-, and sulfur-
containing groups.
The structure of carbonized catalysts
As indicated by TG-MS results, most of the functional groups of
SLS including oxygen- and sulfur-containing groups decom-
posed in the temperature window of 200–800 ꢀC. It has been
demonstrated that these oxygen- and sulfur-containing
groups,11–13,24,29 particularly carboxyl and sulfonic groups30,31
are catalytic sites for fructose dehydration. Therefore,
ꢀ
a carbonization temperature of 500 C was chosen in order to
retain the functional groups in SLS as much as possible and also
to carbonize SLS as completely as possible. Moreover, a variety
amount of phosphoric acid was added to SLS in the carbon-
ization process to increase the amount of functional groups.32
Three atmospheres were chosen for the carbonization of SLS,
which include statistic atmosphere, the ow of air and the N2
ow. The largest mass decline was observed for SLS during
carbonization in air ow, whereas the least one was found when
SLS was carbonized in N2 ow (Table 1S, in ESI†). This result
indicated more obvious combustion of SLS in air. In addition,
the XRD patterns of SLS and the carbonized catalysts are shown
in Fig. 3S in ESI.† An obvious peak at 23ꢀ and a broad peak at
43ꢀ appeared in the carbonized catalysts, which were ascribed to
002 plane and 100 plane of activated carbon structure, respec-
tively.33 Therefore, the carbonization at 500 ꢀC led to the
formation of activated carbon.
The porosity of the carbonized catalysts
As shown in Fig. 7S in ESI,† Ct1 and Ct3 exhibited type II
absorption isotherm and Ct2 exhibited type I absorption
isotherm. The textural properties and pore size distributions of
the three catalysts are shown in Table 2 and Fig. 8S.† Ct2
possessed the highest percentage of micropores, while Ct1 and
Ct3 were richer in mesopores and macropores. The carboniza-
tion in N2 ow facilitated the formation of the meso- and macro-
pores, and that in the static air atmosphere favored the
formation of both the micro- and mesopores. It is possible that
The distribution of functional groups in carbonized catalysts
The functional groups in phosphoric acid-functionalized
carbon catalysts were investigated by FT-IR (Fig. 4S in ESI†).
Vibration at 1715 cmÀ1 can be attributed to carboxyl group
(nC]O), while the band from 1500 cmÀ1 to 1600 cmÀ1 and out of
plane bending band at 738 cmÀ1 and 812 cmÀ1 indicate the
presence of aromatic structures; the bands of 1360 (dO–H), 1088
(nC–O) and 651 cmÀ1 (gO–H), correspond to hydroxyl of phenol
groups, while those for ester bonds (–CO–O–) are at 1280 and
1146 cmÀ1; the bands of 1210 (nas) and 1045 cmÀ1 (ns) can be
attributed to sulfonic groups, while that appearing at 1311 cmÀ1
is the evidence of hydroxyl groups.34–36
There existed sulfonic groups, hydroxyl of phenol groups and
aromatic structures in the spectrum of SLS. The carbonization
in the three atmospheres caused a decline in the band inten-
sities of sulfonic groups and hydroxyl of phenol groups, which
is in accordance with the TG-MS results. Meanwhile, the
carbonization process led to the formation of carboxyl groups in
the three catalysts.
Table 1 The amounts of acid sites in catalysts determined by Boehm
titrationsa
Carboxyl + sulfonicb Lactonec
Phenolicd
Total
Catalyst mmol gÀ1 mmol gÀ1 mmol gÀ1 mmol gÀ1
Ct1
Ct2
Ct3
1.2
1.7
0.6
1.8
1.5
1.7
5.0
10.7
4.2
8.0
13.9
6.5
a
The acid sites were titrated by NaHCO3 (carboxyl, sulfonic), Na2CO3
(carboxyl, sulfonic and lactone) and NaOH (carboxyl, sulfonic, lactone
b
c
and phenolic), according to ref. 36. Strong acid sites. Moderate
acid sites. d Weak acid sites.
Table 2 The textural properties of the carbonized catalysts
ABET
Amicro
Vtotal
Vmicro
Dc
nm
a
b
a
Catalyst
m2 gÀ1
m2 gÀ1
cm3 gÀ1
cm3 gÀ1
The elemental compositions of SLS and the three phosphoric
acid-functionalized carbon catalysts were investigated by ICP-
OES. As shown in Table 2S in ESI,† the carbonization process
caused the decrease in the contents of oxygen and sulfur in the
samples. Combined with FT-IR result, it was concluded that Ct1
catalyst contained more sulfonic groups while Ct2 had more
oxygen-containing groups.
Ct1
Ct2
Ct3
Ct2d
1054.6
559.4
1198.3
551.8
404.3
316.5
286.3
311.6
1.18
0.32
1.73
0.32
0.17
0.13
0.12
0.13
4.5
2.3
5.8
2.2
a
The data were from t-plot reports. b Total pore volume of pores that are
c
d
less than 323.5 nm diameter. Average pore width. Ct2 aer 5-cycled
To quantify the amount of strong and weak surface acidic sites
in the catalysts, Boehm's method was applied.37,38 In the Boehm's
reaction, reaction condition: 170 ꢀC, 0.5 mmol fructose, 5 ml water, 4.5 h.
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the majority of meso- and macro-pores in Ct2 were either was observed on Ct2 (Fig. 1A). Aer reaction for 4.5 h at 170 ꢀC,
burned when carbonization in the air ow, as indicated by the HMF selectivity was highest on Ct2, followed by Ct1 and Ct3
great mass loss in this process (Table 1S, in ESI†).
(entries 1–3 in Table 3).
As conrmed by BET results (Table 2), the microporous
surface area of Ct2 contributed to 56.6% of the total surface area,
which was higher than those of Ct1 and Ct3 (38.3% and 23.9%
respectively). Moreover, the average pore size of Ct2 was the
smallest among all the catalysts. A positive relationship can be
established between HMF selectivity and the ratio of micropo-
rous to the total surface area, while such correlation was not
found between HMF selectivity and the total surface area, or
HMF selectivity and the microporous volume (Fig. 1C and 10S in
ESI†). These results indicated the promotional effect of the
micropores on the HMF selectivity. The promotional effect of
micropores on HMF selectivity was also observed in zeolite
catalyst systems.39 The major byproduct was humins in all the
test runs in this work. Humins is demonstrated to originate from
the polymerization of fructose and HMF.40–42 By considering the
macromolecular nature of humins, it is reasonable to deduce
Dehydration of fructose into 5-HMF
The fructose conversions on the three catalysts increased
gradually and all reached more than 92% aer reaction for 4.5 h
(Fig. 9S in ESI†). It has been demonstrated that both the weak
and strong acid sites including oxygen- and sulfur-containing
functional groups are active towards fructose dehydra-
tion.11–13,24,26–28 The acid amount as a function of the fructose
conversion was examined to gain insight into the effect of acid
amount on fructose conversion (Fig. 1B). A positive correlation
can be established, which clearly demonstrated the catalytic
effect of the acid sites on the fructose conversion.
The HMF yield and selectivity of the three catalysts are
shown in Fig. 1A and 9S in ESI.† The HMF yield of Ct1 and Ct3
climbed to the maximums at 2.5 and 3 h respectively. In
contrast, an increasing enhancement in HMF yield up to 4.5 h
Fig. 1 (A) HMF yield on the three catalysts; correlation of (B) the total acid amount with fructose conversion, and (C) the ratio of the microporous
surface area to the total surface area with HMF selectivity.
Table 3 Dehydration of fructose into 5-HMF on the carbonized catalystsa
Entry
Catalyst
Temp. ꢀ
C
Fructose mmol
Cat. loading mg
HMF yield mol%
HMF selectivity mol%
Fructose conv. mol%
1
2
3
4
5
6
7
8
Ct1
Ct2
Ct3
Ct1
Ct1
Ct1
Ct2
Ct2
Ct2
Ct3
Ct3
Ct3
Ct1
Ct1
Ct2
Ct2
Ct3
Ct3
170
170
170
160
140
120
160
140
120
160
140
120
170
170
170
170
170
170
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
2.0
0.5
2.0
0.5
2.0
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
49.9
55.0
46.3
41.4
7.8
0.8
50.9
7.2
52.0
55.0
50.0
61.3
30.8
3.3
68.3
32.5
4.1
57.8
24.1
3.0
70.7
69.4
71.1
59.9
61.6
42.7
96.0
100.0
92.6
67.5
25.3
24.1
74.5
22.1
13.8
63.4
28.0
26.2
70.9
70.3
78.2
100.0
75.5
94.4
9
0.6
36.6
6.7
10
11
12
13
14
15
16
17
18
0.8
50.1
48.8
55.6
59.9
46.5
40.3
a
Reaction condition: 5 ml of water, 4.5 h.
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that the micropores restricted the formation of the humins, and catalyst, leading to the decrease in the BET surface area and the
as a result promoted HMF selectivity. pore volume of catalysts. The BET analysis of the used catalyst
In addition, the effects of reaction conditions including was performed, and the results were listed in the Table 2. Both
temperature, fructose concentration, and catalyst loading on the BET surface area and the pore volume of the used catalyst
the HMF yield were investigated. The temperature played an were similar to those of the fresh one. This result clearly indi-
important role in fructose dehydration. Bꢀoth the fructose cated that the adsorption of humins was trace. These results
conversion were low at the range of 120–140 C, and they were indicated the great potential of the carbon catalysts Ct2 for the
obviously enhanced at 160–170 ꢀC (Table 3, entries 1–12; larger-scale selective conversion of fructose in aqueous
Fig. 11S in ESI†). Interestingly, the HMF selectivity of the three solution.
catalysts was promoted with increasing temperature. It is likely
that at lower reaction temperatures, more fructose molecules
were just adsorbed on the catalyst without further conversion.
Conclusions
Therefore, the calculated fructose conversion was higher than We have demonstrated a selective aqueous conversion of fruc-
the real one, causing a lower calculated HMF selectivity.
tose into HMF by using carbon catalysts from pulping waste
The effect of catalyst loading and substrate concentration on sodium ligninsulfonate. The distribution of functional groups
the fructose dehydration were also investigated (Table 3, entries and the porosity of the carbon catalysts were greatly dependent
1–3, 13–18; Fig. 12S in ESI†). HMF yields of the catalysts were on the carbonization atmosphere. The carbonization in air ow
similar with 0.5 or 1.0 mmol fructose in the reaction system. The favored the formation of more oxygen-containing functional
HMF yield of Ct1 and Ct3 declined with further increase in the groups and micropores, while more sulfonic groups and meso-/
amount of fructose to 2.0 mmol. In comparison, the HMF yield macro-pores were formed during carbonization in static air
of Ct2 increased. In comparison with Ct1 and Ct3, the higher atmosphere. These oxygen- and sulfur-containing groups were
ratio of microporous to the total surface area in Ct2 restricted the identied to be the acid sites. The total amount of acid sites
formation of the humins, which may account for the enhance- increased with the increase in the oxygen concentration in the
ment of HMF yield at high fructose concentrations. As shown in atmosphere. More meso- and macro-pores were formed during
Fig. 12S in ESI,† an obvious improvement in the HMF yield carbonization in the N2 ow, while micropores were predomi-
occurred when catalyst loading was increased from 3 mg to 5 mg, nant when carbonization in the air ow.
indicating that HMF formation was promoted with more acid
A positive correlation can be established between the acid
sites. However, the HMF yield declined at high catalyst loadings amounts and the fructose conversions of the carbon catalysts,
(20 mg). This result is likely due to the acceleration of side which clearly demonstrated the catalytic effect of the acid sites.
reactions (the formation of humins) at high catalyst loading.
The HMF selectivity was dependent on the porosity of the
Five-cycled testings were carried out to investigate catalyst carbon catalysts. In comparison with the meso- and macro-
stability on fructose dehydration. As shown in Fig. 2, all the pores, the steric hindrance of micropores restricts the forma-
three catalysts showed high stability. Particularly, more than 54 tion of humins (the main byproduct), resulting in the promo-
mol% of HMF yield can be achieved aer the Ct2 catalyst were tion in the HMF selectivity. More than 54 mol% of HMF yield
reused for ve times.
(98.4% of the original HMF yield) can be obtained aer the
Taking into account the sorbent nature of the carbon cata- catalyst were reused for ve times, indicating the promising
lyst, the humins may be adsorbed on the catalyst. By consid- future of the carbon catalyst for larger-scale production of HMF
ering the large size of the humins, the adsorbed humins would from fructose.
cause the blockage of micropores and some mesopores in the
Acknowledgements
This work was nancially supported by the National Key Basic
Research Program of China (973 program) (no. 2012CB215305),
Science Foundation for Youths of Shanxi (No. 2014021014-5)
and the National Natural Science Foundation of China (No.
21303240).
References
1 M. Chatterjee, T. Ishizaka and H. Kawanami, Green Chem.,
2014, 16, 1543.
2 G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106,
4044–4098.
3 Y.-B. Huang and Y. Fu, Green Chem., 2013, 15, 1095.
4 J. Y. Chan and Y. Zhang, ChemSusChem, 2009, 2, 731–734.
5 H. Zhao, J. E. Holladay, H. Brown and Z. C. Zhang, Science,
2007, 316, 1597–1600.
Fig. 2 Five-cycled stability testing on the three catalysts. Reaction
condition: 170 ꢀC, 0.5 mmol fructose, 5 ml water, 4.5 h.
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6 Y. Yang, C.-w. Hu and M. M. Abu-Omar, Green Chem., 2012, 26 T. S. Deng, X. J. Cui, Y. Q. Qi, Y. X. Wang, X. L. Hou and
14, 509–513. Y. L. Zhu, Chem. Commun., 2012, 48, 5494–5496.
7 J. Wang, T. Qu, M. Liang and Z. Zhao, RSC Adv., 2015, 5, 27 J. S. Kruger, V. Nikolakis and D. G. Vlachos, Appl. Catal., A,
106053–106060. 2014, 469, 116–123.
8 S. Wang, H. Lin, J. Chen, Y. Zhao, B. Ru, K. Qiu and J. Zhou, 28 Y. Roman-Leshkov, J. N. Chheda and J. A. Dumesic, Science,
RSC Adv., 2015, 5, 84014–84021. 2006, 312, 1933–1937.
9 S. Dutta, S. De, A. K. Patra, M. Sasidharan, A. Bhaumik and 29 X. Zhang, M. Wang, Y. Wang, C. Zhang, Z. Zhang, F. Wang
B. Saha, Appl. Catal., A, 2011, 409–410, 133–139. and J. Xu, Chin. J. Catal., 2014, 35, 703–708.
10 L. Hu, G. Zhao, X. Tang, Z. Wu, J. Xu, L. Lin and S. Liu, 30 B. R. Caes, M. J. Palte and R. T. Raines, Chem. Sci., 2013, 4,
Bioresour. Technol., 2013, 148, 501–507. 196–199.
11 V. V. Ordomsky, J. van der Schaaf, J. C. Schouten and 31 S. Kang, J. Ye, Y. Zhang and J. Chang, RSC Adv., 2013, 3, 7360.
´
T. A. Nijhuis, ChemSusChem, 2012, 5, 1812–1819.
12 X. Qi, M. Watanabe, T. M. Aida and R. L. Smith Jr, Catal.
Commun., 2009, 10, 1771–1775.
13 R. Liu, J. Chen, X. Huang, L. Chen, L. Ma and X. Li, Green
Chem., 2013, 15, 2895–2903.
14 X. H. Qi, M. Watanabe, T. M. Aida and R. L. Smith, Ind. Eng.
Chem. Res., 2008, 47, 9234–9239.
15 V. V. Ordomsky, J. van der Schaaf, J. C. Schouten and
T. A. Nijhuis, J. Catal., 2012, 287, 68–75.
32 Y. Chen, S.-R. Zhai, N. Liu, Y. Song, Q.-D. An and X.-W. Song,
Bioresour. Technol., 2013, 144, 401–409.
33 T. Tsoncheva, I. Genova, B. Tsintsarski, M. Dimitrov,
D. Paneva, Z. Zheleva, I. Yordanova, G. Issa, D. Kovacheva,
T. Budinova, H. Kolev, R. Ivanova, I. Mitov and N. Petrov,
React. Kinet., Mech. Catal., 2013, 110, 281–294.
34 J. M. V. Nabais, C. Laginhas, P. J. M. Carrott and
M. M. L. R. Carrott, J. Anal. Appl. Pyrolysis, 2010, 87, 8–13.
35 J. M. V. Nabais, P. Nunes, P. J. M. Carrott, M. M. L. Ribeiro
´
´
´
16 Y. Ma, S. Qing, L. Wang, N. Islam, S. Guan, Z. Gao, X. Mamat,
H. Li, W. Eli and T. Wang, RSC Adv., 2015, 5, 47377–47383.
Carrott, A. M. Garcıa and M. A. Dıaz-Dıez, Fuel Process.
Technol., 2008, 89, 262–268.
17 F. S. Asghari and H. Yoshida, Carbohydr. Res., 2006, 341, 36 J. M. V. Nabais, C. E. C. Laginhas, P. J. M. Carrott and
2379–2387.
M. M. L. Ribeiro Carrott, Fuel Process. Technol., 2011, 92,
234–240.
18 B. Saha and M. M. Abu-Omar, Green Chem., 2014, 16, 24–38.
19 H. Wang, T. Deng, Y. Wang, X. Cui, Y. Qi, X. Mu, X. Hou and 37 H. P. Boehm, E. Diehl, W. Heck and R. Sappok, Angew.
Y. Zhu, Green Chem., 2013, 15, 2379–2383. Chem., Int. Ed. Engl., 1964, 3, 669–677.
20 A. Dibenedetto, M. Aresta, C. Pastore, L. di Bitonto, 38 Z. J. Jiang, Y. Liu, X. P. Sun, F. P. Tian, F. X. Sun, C. H. Liang,
A. Angelini and E. Quaranta, RSC Adv., 2015, 5, 26941–26948. W. S. You, C. R. Han and C. Li, Langmuir, 2003, 19, 731–736.
21 Q. Zhao, Z. Sun, S. Wang, G. Huang, X. Wang and Z. Jiang, 39 C. Moreau, R. Durand, S. Razigade, J. Duhamet, P. Faugeras,
RSC Adv., 2014, 4, 63055–63061. et al., Appl. Catal., A, 1996, 145, 211–224.
22 N. Wang, Y. Yao, W. Li, Y. Yang, Z. Song, W. Liu, H. Wang, 40 K. Shimizu, R. Uozumi and A. Satsuma, Catal. Commun.,
X.-F. Xia and H. Gao, RSC Adv., 2014, 4, 57164–57172. 2009, 10, 1849–1853.
23 A. A. Assanosi, M. M. Farah, J. Wood and B. Al-Duri, RSC 41 C. H. Kuo, A. S. Poyraz, L. Jin, Y. T. Meng, L. Pahalagedara,
Adv., 2014, 4, 39359–39364.
24 H. Wang, Q. Kong, Y. Wang, T. Deng, C. Chen, X. Hou and
Y. Zhu, ChemCatChem, 2014, 6, 728–732.
25 W. Xing, H. H. Ngo, S. H. Kim, W. S. Guo and P. Hagare,
Bioresour. Technol., 2008, 99, 8674–8678.
S. Y. Chen, D. A. Kriz, C. Guild, A. Gudza and S. L. Suib,
Green Chem., 2014, 16, 785–791.
42 L. Wang, H. Wang, F. J. Liu, A. M. Zheng, J. Zhang, Q. Sun,
J. P. Lewis, L. F. Zhu, X. J. Meng and F. S. Xiao,
ChemSusChem, 2014, 7, 402–406.
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