Heterogeneous Nb-containing catalyst/: N, N -dimethylacetamide-salt mixtures: Novel and efficient catalytic systems for the dehydration of fructose

Article abstract of DOI:10.1039/c6ra09664f

The development of efficient catalytic systems for the dehydration of carbohydrates to produce 5-hydroxymethylfurfural (HMF) is a very attractive topic. In this work, we synthesized a novel Nb-containing catalyst by the reaction of niobium chloride and nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb-NTMPA. The synthesized Nb-NTMPA was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption, and Fourier transform infrared spectroscopy and used as the heterogeneous catalyst for the dehydration of fructose into HMF using the mixture of N,N-dimethylacetamide (DMA) and salts as the reaction solvent. It was found that Nb-NTMPA was very active for the reaction and a HMF yield of 85.6% could be achieved in a DMA-NaBr mixture under the optimal reaction conditions. Further study indicated that the salts could affect the activity of the reaction systems by the formation of DMA·M⁺ (M = Li, Na and K) macrocations and weakly ion-paired halide ions. Moreover, Nb-NTMPA/DMA-salt systems could also be used in the production of HMF from inulin and sucrose with satisfactory yields.

Full text of DOI:10.1039/c6ra09664f

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DOI: 10.1039/C6RA09664F
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ARTICLE
Heterogeneous Nb-containing catalyst/N,N-dimethylacetamide-
salts mixtures: Novel and efficient catalytic systems for
dehydration of fructose
Received 00th January 20xx,
Accepted 00th January 20xx
Zhimin Xue,*a Bobo Cao,b Wancheng Zhao,c Jinfang Wang,c Tingting Yuc and Tiancheng Mu*c
DOI: 10.1039/x0xx00000x
Development of efficient catalytic systems for dehydration of carbohydrates to produce 5-hydroxymethylfurfural (HMF) is
a very attractive topic. In this work, we synthesized a novel Nb-containing catalyst by the reaction of niobium chloride and
nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb-NTMPA. The synthesized Nb-NTMPA was characterized by
powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2
adsorption-desorption, and Fourier transform infrared spectroscopy and used as the heterogeneous catalyst for the
dehydration of fructose into HMF using the mixture of N,N-dimethylacetamide (DMA) and salts as the reaction solvent. It
was found that Nb-NTMPA was very active for the reaction and a HMF yield of 85.6% could be achieved in DMA-NaBr
mixture at the optimal reaction conditions. Further study indicated that the salts could affect the activity of the reaction
systems by the formation of DMA·M+ (M=Li, Na and K) macrocations and weakly ion-paired halide ions. Moreover, Nb-
NTMPA/DMA-salts systems could be also used in the production of HMF from inulin and sucrose with satisfactory yields.
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catalysts are difficult, which limit the wide application of these
catalysts. In order to overcome the separation problem, numerous
heterogeneous catalysts have been designed for the dehydration of
Introduction
Conversion of renewable and abundant biomass resources into
liquid fuels and value-added chemicals has attracted much
attention in recent years.1-5 Among various processes explored for
biomass transformation, dehydration of carbohydrates, an
important type of biomass, to produce 5-hydroxymethylfurfural
(HMF) is one of the most successful routes.6-9 As one of the top
building block compounds obtained from biomass,10 HMF can be
transformed into many kinds of value-added compounds and
materials,11-14 which are currently produced mainly from petroleum.
In the production of HMF from carbohydrates, dehydration of
fructose is the most promising and efficient method.
Up to now, various catalysts, including homogeneous and
heterogeneous catalysts, have been developed for the dehydration
of fructose to produce HMF. Homogeneous catalysts include
mineral or organic acids,15 various Lewis acids,16,17 and ionic
liquids.18-21 Generally, these homogeneous catalysts are effective
for the dehydration. But the separation and recovery of the
fructose, such as acid resins,22,23 Tin-Beta zeolite,24 lignosulfonic
acid25 sulfated zirconia,26 Nb-containing compounds,27 sulfonated
carbon,28,29 graphene oxide,30 supported ionic liquids,31,32 zirconium
phosphonate,33 metal-organic frameworks,34 and Fe3O4-SBA-SO3H,35
etc. Regardless of these developments, it remains to be a hot topic
to obtain HMF from fructose over heterogeneous catalysts
efficiently.
Among the above catalysts, Nb-containing compounds are an
important type of heterogeneous catalysts for the dehydration of
fructose into HMF because of their high stability and strong acid
properties. For example, Nb2O5 has been proved to be an effective
catalyst for fructose dehydration in DMSO and a HMF yield of 86.2%
could be achieved at 120 oC with a reaction time of 2 h.36 Niobic
acid and niobium phosphate could also be used as catalysts for the
dehydration of fructose to produce HMF in the aqueous phase or
water/2-butanol biphasic system.37 It was found that niobium
phosphate had higher catalytic activity than niobic acid, which was
resulted from the higher effective acidity on the surface of niobium
phosphate. Moreover, sulfated mesoporous niobium oxide showed
a much higher activity for the dehydration than commercial Nb2O5
because of its higher surface area and acidity.38 Recently, a new
kind of mesoporous niobium phosphates was synthesized and
exhibited excellent activity in the dehydration of fructose to HMF in
water.39 These achievements of Nb-containing compounds provide
an attractive way for designing new heterogeneous Nb-containing
catalysts for the production of HMF from fructose.
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Except for catalysts, solvents also have important effect on the nm, 25.2 m2g-1, and 0.14 cm3g-1, respectively. As shown in Fig. 1d,
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activity and selectivity for the formation of HMF from fructose. The the N2 adsorption-desorption isotherm showed the
DOI: 10.1039/C6RtAy0p9e664IVF
dehydration of fructose could be conducted in various solvents characteristic of mesoporous materials.48,49 The hysteresis loop was
systems, including traditional organic solvents,40,41 water,42 an intermediate between typical H1 and H2-type in the P/P0 range
multiphase systems,43,44 and ionic liquids.45 Since alkylimidazolium from 0.4 to 0.9, suggesting large uniform mesopores with a cage
chloride ionic liquids were found to be an efficient solvent for like pore structure connected by windows with a small size,49,50
dehydration of carbohydrates into HMF, ionic liquids as the which was characteristic of mesoporous materials according to
dehydration solvents have attracted dramatic attention. However, IUPAC classification.39,48 Additionally, the pore size distribution
the expensive price of ionic liquids limited its large-scale application. indicated the existence of large mesopores in the prepared Nb-
Therefore, seeking new solvents is still a very attractive topic in the NTMPA (Fig. 1e).
formation of HMF from the dehydration of fructose. Recent reports
indicated that N,N-dimethylacetamide (DMA)46 and caprolactam
(CPL)47 containing lithium chloride were privileged solvents for HMF
production because of the formation of DMA·Li+ or CPL·Li+
macrocations resulted in a high concentration of weakly ion-paired
halide ions,46 which could promote the dehydration of fructose.
However, these solvent systems have not been applicated into the
heterogeneously catalytic fructose dehydration.
As discussed above, there have been many catalysts and
solvents for the dehydration of fructose to produce HMF.
Consideration of catalysts and solvents as a whole is the key and
interesting point to obtain high HMF selectivity and yield from the
dehydration of fructose. More efforts should be paid on this aspect.
In this work, we synthesized a Nb-containing catalyst by the
reaction
of
niobium
chloride
(NbCl5)
and
nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb-
NTMPA (Scheme 1). The as-prepared Nb-NTMPA could be used as
an efficient heterogeneous catalyst for the dehydration of fructose
to produce HMF in DMA-salts mixtures. It was found that the
niobium phytic was very active and stable for the dehydration of
fructose with a maximum yield of 85.6% using DMA-NaBr mixture
as the reaction solvent. Meanwhile, we also discovered that the
type of salts had significant impact on the activity of the reaction
systems.
Fig. 1. Characterization of the synthesized Nb-NTMPA. Powder XRD pattern
(a), SEM image (b), TEM image (c), N2 adsorption-desorption isotherm (d),
and the pore size distribution (e).
N
N
O
O
P
O
P O
O
P
P
O
P
P
O
O
O O
O
O
O
O
O
O
O
O
H2O3P
N
PO3H2
Furthermore, X-ray photoelectron spectroscopy (XPS) showed
the characteristic peaks of Nb5+ (207.4 eV for Nb 3d5/2 and 210.2 eV
for Nb 3d3/2, Fig. 2a) and P5+ (133.6 eV for P 2p, Fig. 2b), suggesting
the presence of Nb5+ and P5+ in the prepared catalyst. In addition,
Fourier transform-infrared (FT-IR) technique showed one strong
band at 1017 cm-1, suggesting the formation of Nb-O-P networks in
the synthesized catalyst (Fig. 2c).39 Meanwhile, an additional band
was also found at 615 cm-1, which was assigned to Nb-O stretching
modes.39
+
NbCl5
Nb5+
Nb5+
Nb-NTMPA
Nb5+
PO3H2
NTMPA
Scheme 1. The preparation of Nb-NTMPA.
Results and Discussion
Catalyst characterization
The synthetic procedure for Nb-NTMPA was presented in detail in
the Experimental section. The prepared Nb-NTMPA was firstly
examined by X-ray diffraction (XRD) method. The XRD pattern
showed one broad diffraction peak, indicating that the obtained
Nb-NTMPA was amorphous (Fig. 1a). The scanning electron
microscopy (SEM, Fig. 1b) and transmission electron microscopy
(TEM, Fig. 1c) demonstrated that the Nb-NTMPA was featureless.
Meanwhile, N2 adsorption-desorption examination indicated that
the Nb-NTMPA prepared was porous (Fig. 1d), and the average pore
diameter, the Brunauer-Emmett-Teller (BET) surface area, and the
pore volume calculated from the N2 adsorption-desorption were 5.5
Fig. 2. XPS spectra of Nb 3d (a), XPS spectra of P 2p (b), and FT-IR spectra of
the prepared Nb-NTMPA (c).
Effect of various salts on the dehydration activity
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The effect of various salts on the dehydration of fructose was firstly with the homogeneous NbCl5 (Entry 2, Table 1V)iewanArdticlebOenttliener
o
DOI: 10.1039/C6RA09664F
examined over Nb-NTMPA at 100 C with a reaction time of 1.5 h, performance than Nb2O5 (Entry 3, Table 1).
and the results were given in Table 1. It could be seen that the yield
There were two reasons for the higher activity of Nb-NTMPA
of HMF was very low in the absence of salts (Entry 1, Table 1).
than Nb2O5, including higher acidity and lower crystallinity. Firstly,
When salts with halide ion were added, the activity of the catalytic
the acidity of the prepared Nb-NTMPA and Nb2O5 was examined by
system was increased dramatically (Entries 2-7, Table 1). When the
NH3-TPD method. The results in Fig. 3 suggested that the acidity of
anion of the salts was Cl-, the activity order of the salts was found to
Nb-NTMPA (0.22 mmol/g) was higher than Nb2O5 (0.03 mmol/g),
be LiCl>KCl>NaCl (Entries 2, 4 and 6, Table 1), which was consistent
which were calculated based on the desorbed NH3 (Fig. 3) at the
o
temperatures from 100 oC to 350 C. Further, the acid strength and
with the order of the solubility of these salts in DMA. The higher
solubility could be beneficial for the formation of DMA·M+ (M=Li,
amounts of Nb-NTMPA and Nb2O5 were determined by the n-
butylamine titration method accurately,36 and the results in Table
Na and K) macrocations and weakly ion-paired chloride ions, and
thus promoted the dehydration of fructose. When the anion of the
S1 indicated the higher acidity of Nb-NTMPA than Nb2O5, which was
salts was changed to Br-, the difference of the activity was not
consistent with the NH3-TPD examination. In addition, the pyridine
noticeable (Entries 3, 5 and 7, Table 1). Meanwhile, we found that
absorption FT-IR analysis indicated that there existed both Lewis
(193 μmol/g) and Brønsted acid (21 μmol/g) sites in Nb-NTMPA (Fig.
the salts with Br- ion had better performance than the salts with Cl-
ion when they had the same cation. This may be resulted from that
S1). The Brønsted acid sites were resulted from the small amount of
Br- had weaker binding force with the cation than Cl-, which had
non-coordinated P-OH species of the phosphate groups of NTMPA,
been proved that weakly ion-paired halide ions favored the reaction.
which also promoted the dehydration of fructose. In contrast, there
-
2-
In addition, the salts with NO3 and SO4 did not show positive
effect, which further indicated that the halide ions could promote
the dehydration of fructose by the formation of hydrogen bonds
between halide ions and the hydroxyl groups in fructose.46 Based on
the results shown in Table 1, we chose NaBr for further study on
the activity of Nb-NTMPA. In addition, we observed the formation
of humin in our reaction system, which were likely generated
through self-polymerization of HMF or cross-polymerization
between fructose and HMF.51-53 Meanwhile, small amount of
levulinic acid and formic acid could also be detected, which were
generated from the rehydration of the formed HMF.
were only Lewis acid sites (64 μmol/g) existed in Nb2O5, which was
less than those in Nb-NTMPA according to the results shown in Fig.
S1. The higher activity of Nb-NTMPA was beneficial for the
dehydration of fructose into HMF with a higher reaction rate, which
could decrease the formation of humin from the polymerization of
HMF with fructose, and thus provided a higher selectivity of HMF
than Nb2O5. Secondly, the prepared Nb-NTMPA had lower
crystallinity than the used Nb2O5 (Fig. S2), which was favorable for
fructose to be in contact with the activity center of the Nb-NTMPA,
and thus promote the dehydration of fructose with a higher activity.
These two reasons resulted in that Nb-NTMPA had better activity
than Nb2O5 at the same reaction conditions.
Table 1. Effect of various salts on the conversion of fructose to HMF.a
Table 2. Dehydration of fructose catalyzed by various catalysts.a
Entry
1
Solvent
DMA
Conversion (%)
Yield (%)b
3.6
Entry
Catalyst
None
Conversion (%)
Yield (%)b
1.9
6.1
96.4
100
39.7
100
47.7
98.6
7.8
2
DMA+LiCl
DMA+LiBr
DMA+NaCl
DMA+NaBr
DMA+KCl
53.6
81.9
29.9
85.6
39.4
80.5
4.3
1
2
3
4
5
6
3.6
100
97.3
100
98
3
NbCl5
80.5
4
Nb2O5
73.4
5
Nb-NTMPA
Nb-NTMPA (2nd
Nb-NTMPA (3rd)
85.6
6
)
82.3
7
DMA+KBr
DMA+KNO3
DMA+K2SO4
DMA+NaNO3
DMA+Na2SO4
95
80.2
aReaction conditions: 0.1 g fructose, 50 mg catalyst, 2 g DMA, NaBr 0.2
g, reaction time 1.5 h, reaction temperature 100 oC. bYields were
determined by HPLC.
8
9
6.3
3.4
10
5.9
4.8
11
4.2
2.7
aReaction conditions: 0.1 g fructose, 50 mg Nb-NTMPA, 2 g DMA, salts
0.2 g, reaction time 1.5 h, reaction temperature 100 oC. bYields were
determined by HPLC.
Activity of different Nb-containing catalysts in DMA-NaBr mixtures
The performance of various Nb-containing catalysts for the
dehydration of fructose in DMA-NaBr mixtures was studied (Table
2). The yield of HMF was very low in the absence of any catalysts
(Entry 1, Table 2). According to the experimental data, the as-
prepared Nb-NTMPA (Entry 4, Table 1) had similar catalytic activity
Fig. 3. NH3-TPD spectra of Nb-NTMPA (a) and Nb2O5 (b). Due to the
o
decomposition temperature of Nb-NTMPA was about 350 C obtained from
the thermogravimetric analysis (Fig. S3). Therefore, we conducted NH3-TPD
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examination from 100 oC to 350 oC. The acidity of Nb-NTMPA and Nb2O5
can be calculated based on the desorbed NH3.
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DOI: 10.1039/C6RA09664F
100
80
60
40
20
0
The reusability of Nb-NTMPA was examined at the optimized
reaction conditions (Entries 4-7, Table 2). It was obvious that Nb-
NTMPA suffered a minor decrease in activity within 3 cycles, which
was probably caused by the loss of Nb-NTMPA when recovered
from reaction systems and the active center occupied by humin
adsorbed on the catalyst. We also examined the content of niobium
in the reaction mixtures after the catalyst was removed and ca. 77
ppm of niobium (about 1.12 atom% Nb) was detected after the
third run. Thus, we thought that partial leaching of niobium
segments from the bulk catalyst phase could also reduce the
activity of the catalyst. The Nb-NTMPA recovered after reusing
three times was characterized by FT-IR (Fig. 4a), XRD (Fig. 4b), SEM
(Fig. 4c), and TEM (Fig. 4d). It can be seen that the properties of Nb-
NTMPA were not changed notably after being used. Additionally, N2
adsorption-desorption (Table S2) and XPS (Table S3 and Fig. S4)
examinations proved that the surface characteristics and textural
properties of fresh and three-times used Nb-NTMPA remained
almost unchanged.
0.0
0.2
0.4
0.6
0.8
1.0
The amount of NaBr (g)
Fig. 5. Influence of NaBr amounts. Reaction conditions: 0.1 g fructose, 50 mg
Nb-NTMPA, 2 g DMA, reaction time 1.5 h, reaction temperature 100 oC.
Effect of reaction temperatures and reaction time on the
dehydration reaction
Fig. 6 shows the influence of reaction temperature on the
dehydration of fructose to produce HMF in DMA-NaBr mixtures
catalyzed by Nb-NTMPA at 60 oC, 80 oC and 100 oC. As shown in Fig.
6, we could find that the dehydration reaction was accelerated by
increasing temperature, which was favorable to achieving higher
yield in a shorter reaction time. When the reaction was conducted
at 100 oC, the yield increased dramatically with time at the
beginning, and reached the maximum (85.6%) at 1.5 h with a
fructose conversion of 100%. Then, the yield decreased slightly with
prolonged time, which may be due to the rehydration of the HMF
produced.
80
60
40
20
0
Fig. 4. The characterization of the recovered Nb-NTMPA after
reused three times. FT-IR spectrum (a), XRD pattern (b), SEM image
(c), and TEM image (d).
Influence of the salts amounts
Based on the results shown in Table 1, salts played a crucial role for
the dehydration of fructose. Further study indicated that the
amount of salts could also affect the yield of HMF. As shown in Fig.
5, the yield of HMF increased to a maximum of 85.6% with an
increase in the amount of NaBr from 0 to 0.2 g which was probably
caused by the increase of DMA·Na+ macrocations and weakly ion-
paired bromide ions in the reaction system. However, the HMF
yield kept almost constant with further increase in the amount of
NaBr from 0.2 to 1 g, hinting that 0.2 g was the optimal NaBr
amount for the reaction at our reaction conditions.
0
30
60
90
120
150
Reaction time (min)
Fig. 6. Influence of reaction temperature on the dehydration of fructose.
Reaction conditions: 0.1 g fructose, 50 mg Nb-NTMPA, 2 g DMA, 0.2 g NaBr.
Black line for 100 oC, red line for 80 oC, and blue line for 60 oC.
Conclusions
In summary, a novel Nb-containing catalyst, Nb-NTMPA, has
been prepared and used as the heterogeneous catalyst for the
dehydration of fructose to synthesize HMF using DMA-salts
mixtures as the reaction solvents. High yield of 85.6% could be
o
obtained from fructose in DMA-NaBr mixture at 100 C with a
reaction time of 1.5 h. The type of salts could affect the activity
of the reaction systems and NaBr showed the best
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performance, which resulted from the formation of DMA·M+ catalysts (0.1475 g) were charged into the quartz reactor, and the
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o
macrocations and weakly ion-paired halide ions. We believe temperature was increased from room temDpeOrIa: 1tu0.r1e03t9o/C165R0A0C96a6t4aF
o
that the simple and efficient catalytic system has potential rate of 10 C/min under a flow of He (50 cm3/min), and then the
o
application for producing HMF from dehydration of catalyst was kept at 150 C for 4 h. After that, the temperature was
carbohydrates.
decreased to 50 oC. NH3/He (10/90, 50 cm3/min) was pulsed into
o
the reactor at 50 C under a flow of He (10 cm3/min) until the acid
sites were saturated with NH3. The adsorbed NH3 was removed by a
flow of He (50 cm3/min). When the baseline was stable, the
temperature was increased from 50 oC to 350 oC at a rate of 10
oC/min.
Experimental
Materials
Fructose (99%), sucrose (99%) and LiCl (99%) were purchased
from Alfa Aesar. Inulin (95%), Nb2O5 (99.5%), niobium (V)
chloride (99+%) and LiBr (99+%) were provided by J&K
Scientific Ltd. N,N-Dimethylformamide (DMF), N,N-
dimethylacetamide (DMA), NaBr, NaCl, KBr, KCl, KNO3, NaNO3,
Na2SO4 and K2SO4 were A. R. grade and were obtained from
Conversion of carbohydrates into HMF
In a typical experiment, known amounts of carbohydrates,
catalyst and salts were added in DMA (2 g) in a flask of 10 mL
sealed with a glass stopper. The mixture was stirred at a fixed
temperature for desired time. Then the mixture was cooled to
room temperature immediately. The samples were analyzed
by HPLC to obtain the yields. The yield of HMF was calculated
by the following equation:
Sinopharm
Chemical
Reagent
Beijing
Co.,
Ltd.
Nitrilotris(methylenephosphonic acid) (ca. 2.2 mol/l) was
purchased from TCI (Shanghai) Development Co., Ltd. All
chemicals were used as received.
Synthesis of Nb-NTMPA
Niobium
chloride
(12
mmol)
and
nitrilotris(methylenephosphonic acid) (NTMPA, 10 mmol) were
dissolved in DMF (600 mL) in a flask of 1000 mL. Then,
triethylamine (120 mmol) was added into the solution
dropwisely with a time of 1 h. After that, the mixture was
firstly stirred for 10 h at room temperature and then aged
under static conditions at 60 oC for 3 h. Finally, the slight
yellow precipitate was separated by filtration, thoroughly
washed with DMF, ethanol and ethyl ether. Before the
characterization and utilization, the sample was washed by
ethanol at 90 oC through Soxhlet extraction for 72 h to remove
DMF completely. After that, the niobium phytic was dried at
80 oC under vacuum for 12 h.
Analysis methods for fructose conversion and HMF yield
The amount of HMF was analyzed by HPLC with Shimadzu LC-
15C pump, Shimadzu UV-Vis SPD-15C detector at 282.0 nm,
o
and a Supelcosil LC-18 5ìm column at 35 C. Before analyzed,
the reaction mixture was diluted to 1000 mL. Methanol/water
solution (50/50 V/V) was used as the mobile phase at a flow
rate of 0.8 mL/min. The conversion of fructose was analyzed
by HPLC with Shimadzu LC-20AT pump and Shimadzu RID-10A
detector with a Benson BP-800 H+ carbonhydrate column at 50
oC. Before analyzed, the reaction mixture was diluted to 500
mL. 5 mM H2SO4 aqueous solution was used as the mobile
phase at flow rate of 0. 6 mL/min.
Catalyst characterization
Reusability of Nb-NTMPA
FT-IR spectra were recorded on Bruker Tensor 27 IR
spectrometer and the sample was prepared by the KBr pellet
method. The BET surface area measurement and pore analysis
were carried out by N2 adsorption at 77 K with Micromeritics
ASAP 2020 V3.00 H (USA) surface area analyser. X-ray
diffraction (XRD) measurements were conducted on an X-ray
diffractometer (D/MAX-RC, Japan) operated at 40 kV and 200
mA with Cu Kα (λ=0.154 nm) radiation. XPS measurements
were carried out on an ESCAL Lab 220i-XL specrometer at a
pressure of ~3×10-9 mbar (1 mbar=100 Pa) using Al Kα as the
excitation source (hν = 1486.6 eV) and operated at 15 kV and
20 mA. The scanning electron microscopy (SEM)
measurements were performed on a Hitachi S-4800 Scanning
Electron Microscope operated at 15 kV. The samples were
spray-coated with a thin layer of platinum before observation.
The transmission electron microscopy (TEM) images were
obtained using a TEM JeoL-1011 with an accelerating voltage
of 120 kV. The sample was dispersed in ethanol with the aid of
sonication and dropped on an amorphous carbon film,
supported on a copper grid, for the TEM analysis. Temperature-
programmed desorption of ammonia (NH3-TPD) was performed on
Micromeritics’ AutoChem 2950 HP Chemisorption Analyzer. The
In the experiments to test the reusability of Nb-NTMPA, the
catalyst was recovered by centrifugation, washed using DMA,
ethanol and ethyl ether. After drying under vacuum at 80 C
o
for 12 h, the catalyst was reused for the next run.
Acknowledgements
The authors thank National Natural Science Foundation of
China (21503016, 21473252) for financial support.
Notes and references
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4
P. Gallezot, Chem. Soc. Rev., 2012, 41, 1538-1558.
R. A. Sheldon, Green Chem., 2014, 16, 950-963.
M. Besson, P. Gallezot and C. Pinel, Chem. Rev., 2014, 114
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C. Li, X. Zhao, A. Wang, G. W. Huber and T. Zhang, Chem. Rev.,
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DOI: 10.1039/C6RA09664F
Graphical abstract
Heterogeneous Nb-containing catalyst/N,N-dimethylacetamide-salts mixtures could
be used as efficient catalytic system for for dehydration of fructose to produce
5-hydroxymethylfurfural.