Efficient production of 5-hydroxymethylfurfural from fructose over CuAPO-5 molecular sieves synthesized using an ionothermal method

Article abstract of DOI:10.1039/c9ra07217a

A group of CuAPO-5 molecular sieves with trace Cu were successfully synthesized via an ionothermal method and used for fructose dehydration to 5-hydroxymethylfurfural (HMF) in [BMIM]Br ionic liquid. The 0.06-CuAPO-5 sample displayed excellent performance and a HMF yield of 93.8% was obtained, which could be ascribed to the balance between acid strength and mass transfer efficiency. This work demonstrates that the ionothermal synthesized CuAPO-5 molecular sieve was also a good candidate for the efficient production of HMF.

Full text of DOI:10.1039/c9ra07217a

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Efficient production of 5-hydroxymethylfurfural
from fructose over CuAPO-5 molecular sieves
synthesized using an ionothermal method
Cite this: RSC Adv., 2019, 9, 32848
a
Yan Huang,†abc Pilan Zhang,†a Hualei Hu,
Chunlin Chen,
Danxin Hu,a Jie Yang,a Yexin Zhang,a
*
a
a
a
a
* *
Yong Yang, Jian Zhang and Lei Wang
A group of CuAPO-5 molecular sieves with trace Cu were successfully synthesized via an ionothermal
method and used for fructose dehydration to 5-hydroxymethylfurfural (HMF) in [BMIM]Br ionic liquid.
The 0.06-CuAPO-5 sample displayed excellent performance and a HMF yield of 93.8% was obtained,
which could be ascribed to the balance between acid strength and mass transfer efficiency. This work
demonstrates that the ionothermal synthesized CuAPO-5 molecular sieve was also a good candidate for
the efficient production of HMF.
Received 9th September 2019
Accepted 11th October 2019
DOI: 10.1039/c9ra07217a
rsc.li/rsc-advances
MeSAPO molecular sieves were produced via the hydrothermal
method and catalyzed fructose dehydration in a biphasic
system at 170 ꢀC to obtain no more than 79% yield of HMF.14,15
This unsatised HMF yield was inconsistent with the excellent
performance of MAPO catalysts in other acid-catalyzed dehy-
dration reaction.16 Therefore, more fundamental researches
should be conducted on the synthesis and catalytic role of
MAPO to provide a new choice for HMF production.
Ionothermal method is a novel synthetic choice for the
preparation of molecular sieves, where an ionic liquid can serve
as the reaction solvent and also the structure directing agent
(SDA) during the reaction process.17 The main advantage of
ionothermal method is the removal of competition between the
solvent and SDA for interaction with the growing crystal
surface.18 In addition, the ionothermal reaction can take place
at or near ambient pressure because of the negligible vapor
pressure of ionic liquids.19 This eliminates the safety concerns
associated with high pressures, which is a troublesome problem
in the conventional hydrothermal process.20 Several types of
MAPO materials (including SAPO, CoAPO, MgAPO, and FeAPO)
have been successfully prepared via the ionothermal
method.21–24
1. Introduction
Renewable biomass conversion to useful chemicals has attrac-
ted rapidly increasing attention due to the gradual depletion of
fossil energy resources.1 5-Hydroxymethylfurfural (HMF), one of
the top platform chemicals based on green chemistry by USDOE
in 2010, can be upgraded to produce a wide range of valuable
derivatives such as 2,5-furandicarboxylic acid, 2,5-dime-
thylfuran, and 2,5-bis(hydroxymethyl)furan.2–4 Among the
present synthesis routes to HMF, fructose dehydration is the
most efficient and selective one to allow the large-scale
production in the near future. Many efforts have been taken
to develop a high-performance catalyst for this reaction, but the
highly selective production of HMF is still a big challenge due to
complicated side reactions.5,6
Solid acid catalysts (especially molecular sieves) offer many
advantages including easy catalyst separation, less corrosion
and controllable surface acidity.7–9 Recently, many aluminosil-
icate molecular sieves with different structures (MOR, BEA, LTL,
etc.) have been used in the dehydration of fructose, exhibiting
excellent catalytic performance (Fig. 1).10,11 As another impor-
tant molecular sieves, metal substituted aluminophosphate
molecular sieves (MAPO) have been broadly exploited in catal-
ysis due to their good thermostability and modiable
acidity.12,13 However, only few works have been done on the use
of MAPO in the HMF synthesis so far. For instance, several
aNingbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences,
1219 Zhongguan West Road, Ningbo 315201, China. E-mail: huhualei@nimte.ac.cn;
jzhang@nimte.ac.cn; wanglei@nimte.ac.cn
bShanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050,
China
cUniversity of Chinese Academy of Sciences, Beijing 100049, China
Fig. 1 Conversion of fructose over the solid acid catalysts.
† The rst two authors contributed equally to this work.
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ꢀ
In this work, we report the synthesis of CuAPO-5 molecular of Ar and then cooled down to 100 C. The adsorptionꢀof NH3
sieves by ionothermal method and their utilization in the was performed with the ow of 5% (v/v) NH3/Ar at 100 C. The
dehydration of fructose to HMF in ionic liquid. The 1-butyl-3- NH3 desorption was carried out from 100 ꢀC to 600 ꢀC with
methylimidazolium bromide ([BMIM]Br) ionic liquid was a heating rate of 10 ꢀC minꢁ1. EPR spectra were recorded on
chosen as the reaction media for both catalyst synthesis and the a Bruker Elexsys E500 spectrometer.
dehydration reaction. CuAPO-5 possesses an AFI structure and
˚
12-membered ring pores (7.3 A in size), while Cu atoms are
quite difficult to incorporate into the AFI framework, resulting
in much fewer successful examples than other MAPOs.25
2.4. Catalytic activity test
The catalytic performance in fructose dehydration to 5-hydrox-
CuAPO-5 was usually used to catalyze the selective reduction of
NOx or oxidation of aromatic amines due to its redox property of
Cu,26,27 and, to the best of our knowledge, there is no report on
its application in the acid-catalyzed reactions.
ymethylfurfural was determined in a 100 mL three-neck ask. In
each experiment, 40 g of [BMIM]Br was loaded in ask under
mechanical stirring (400 rpm) and then the ask was heated in
the oil bath at 110 ꢀC for 60 min. Subsequently, 0.40 g of catalyst
was added into the reactor and then stirred at 110 ꢀC for 5 min.
The reaction time started to count as soon as the 4.0 g of fruc-
tose was put into the solution. The reaction mixture was
collected from reactor using pipette. The obtained sample was
2. Experimental
2.1. Materials
Tetraethylammonium hydroxide (TEAOH, 25%), aluminium ltered and diluted for further product analysis.
isopropoxide (AIP, 99.99%), hydrouoric acid (HF, 40%), fruc-
For catalyst recycling tests, the 0.06-CuAPO-5 catalyst was
tose (99%) and 5-hydroxymethylfurfural (HMF, 99%) were separated from the reaction mixture by ltration and washed
purchased from Aladdin Industrial Inc. (Shanghai, China). with deionized water for several times. Subsequently, the recy-
ꢀ
Phosphoric acid (H3PO4, 85%) and cupric acetate (Cu(CH3- cled catalyst was dried in an oven at 120 C for 2 h and then
OO)2$H2O, 98%) were obtained from Sinopharm Chemical calcined in a muffle furnace at 550 ꢀC for 3 h before using in the
Reagent Co. Ltd. (Shanghai, China). Ionic liquids 1-butyl-3- next reaction.
methyl imidazolium bromide ([BMIM]Br, 99%) was purchased
from Lanzhou Zhong Kekaite Co. Ltd. (Lanzhou, China).
The quantitative analysis of fructose was performed by HPLC
using an Bio-Rad aminex column HPX-87H column and RID
2.2. Catalyst synthesis
The synthesis experiment was carried out in a 100 mL round-
bottom ask charged with [BMIM]Br as solvent. Aer adding
ꢀ
the H3PO4, the round-bottom ask was heated to 80 C under
mechanical stirring (400 rpm). Then, TEAOH, Al[OCH(CH3)2]3,
Cu(CH3OO)2$H2O, and HF were added in order under
mechanical stirring to form a solution with a molar ratio of 20
[BMIM]Br : 2.55 P2O5 : 1.5 TEAOH : 1.0 Al2O3 : xCuO : 0.6 HF
(where x ¼ 0.006, 0.012, 0.018, 0.024). Subsequently, the solu-
tion was rapidly heated to 140 ꢀC and then maintained at 140 ꢀC
for 1 h under mechanical stirring (70 rpm). Aer cooled down to
room temperature, the product was ltered and washed with
deionized water for several times. The solid product was dried at
120 ꢀC overnight followed by calcined at 550 ꢀC for 10 h to
obtain CuAPO-5 sample.
2.3. Catalyst characterization
X-ray diffraction (XRD) was conducted on Bruker D8 Advance
with Cu Ka radiation source at l ¼ 1.54056 nm. The N2
adsorption–desorption isotherms at 77 K were performed on
a Quantachrome Autosorb-iQ-C instrument. Morphology of the
synthesized CuAPO-5 samples was examined by a Verios G4 UC
scanning electron microscope (SEM). The compositions of the
sample were determined by the X-ray uorescence technique
(XRF). The XRF analysis was performed on a Rigaku ZSX Primus
II XRF spectrometer. NH3 temperature-programmed desorption
(NH3-TPD) of the catalyst was carried out on a Tianjin XQ TP-
5076 instrument equipped with a mass spectrum detector.
Fig. 2 XRD patterns (a), N2 adsorption–desorption isotherms and pore
The sample (200 mg) was evacuated at 500 ꢀC for 1 h in the ow size distribution inserted (b) of the CuAPO-5 samples.
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detector. H2SO4 (5 mmol Lꢁ1) was used as the mobile phase at
a ow rate of 0.4 mL minꢁ1, and the column temperature was
set at 30 ꢀC. Quantitative analysis of HMF was performed using
Agilent 1260 HPLC Innity instrument equipped with a UV
detector and Agilent ZORBAX Extend-C18 column. A mixture of
water and methanol (95 : 5 (v/v)) was used as the mobile phase
at a ow rate of 1.0 mL minꢁ1, and the column temperature was
ꢀ
maintained at 30 C.
3. Results and discussion
3.1. Catalyst characterization
A series of CuAPO-5 molecular sieves with different Cu contents
were ionothermally prepared. The X-ray diffraction (XRD)
patterns of the CuAPO-5 samples exhibited similar character- Fig. 3 SEM images of the CuAPO-5 samples ((a): 0.03-CuAPO-5; (b):
istics of the AFI structure (Fig. 2a).28 The absence of any indi-
0.06-CuAPO-5; (c): 0.09-CuAPO-5; (d): 0.12-CuAPO-5).
vidual Cu-related phase indicates that the Cu component might
be integrated into the lattice of the AFI structure or its content
was too low to be detected even if agglomerated.25 The type-IV
hysteresis loop can be seen in N2 adsorption–desorption
isotherms (Fig. 2b), demonstrating the presence of meso-
pores.29 This was further conrmed by the pore size distribution
in Fig. 2b.
NH3-TPD is an effective tool to verify the incorporation of
heteroatoms into the AlPO framework.33 As seen in Fig. 4a, all
samples exhibited two desorption peaks, which could be
ascribed to the ammonia adsorbing onto the weak and relatively
stronger acid sites, respectively. With the increase in the copper
content, both the total amount of acid sites and acid strength
gradually increased (Table 1). The strong acid sites should be
attributed to the substitution of heteroatoms for Al3+ in the
framework.32 In addition, the signals of Gt ¼ 2.054 assigned to
the isolated Cu2+ species locating in the framework as tetrahe-
drally coordinated Cu could be observed in the EPR spectrum of
the samples (Fig. 4b).25 Furthermore, its intensity enhanced
with the increasing Cu content, suggesting more copper atoms
located in the framework. Based on the above results, it is
reasonable to conclude that copper was successfully incorpo-
rated into the AFI framework.
Table 1 summarizes the chemical compositions and textural
properties of all CuAPO-5 samples. Although the actual Cu
content in the catalysts gradually raised with the increasing feed
amount of Cu in the gel, only trace Cu could be kept in the
catalysts. This result is quite different from the hydrothermally
synthesized CuAPO-5 catalysts with much higher Cu content,24
which could be related to the fact that the presence of the amine
would go against the incorporation of heteroatoms element in
our case.22 Nevertheless, these tiny amounts of Cu signicantly
altered the physicochemical property of CuAPO-5 samples. The
BET surface area increased from 197.0 to 217.4 m2 gꢁ1 and then
declined to 162.9 m2 gꢁ1 with the increasing Cu content. Fig. 3
depicts the morphologies of all CuAPO-5 samples that were
agglomerated rod-like crystals, which is always observed on the
3.2. Catalytic performance
ionothermally synthesized MAPO-5 molecular sieves.30 Many The catalytic performance of CuAPO-5 catalysts in fructose
cavities could be created within the aggregates to form meso- dehydration to HMF was evaluated in [BMIM]Br at 110 ꢀC
scale porosity during the ionothermal synthesis.31 As the Cu (Fig. 5). In the blank test without catalyst, the conversion of
content increased, the agglomerated species became more fructose was lower than 10% during the rst 30 min and
abundant and bigger, which would cause possible pore block- approached to 31.7% aer the reaction for 60 min, yielding less
ing and induce inferior BET surface area.
than 7% HMF. This result suggested that the [BMIM]Br could
Table 1 Chemical compositions and physicochemical properties of the CuAPO-5 samples
Content of Cu
Number of acid sitese (mmol of NH3 per g)
Samplea SBETb (m2 gꢁ1
)
Vmicro (cm3 gꢁ1
)
Vmeso (cm3 gꢁ1
)
Weak (<200 ꢀC) Strong (200–300 ꢀC) Total acid
c
d
Sample
Gel
0.03-CuAPO-5 1.5% 23 ppm
0.06-CuAPO-5 3.0% 34 ppm
0.09-CuAPO-5 4.5% 52 ppm
0.12-CuAPO-5 6.0% 70 ppm
197.0
217.4
193.1
162.9
0.06
0.07
0.06
0.05
0.13
0.14
0.13
0.12
0.08
0.10
0.11
0.12
0.12
0.12
0.12
0.13
0.20
0.22
0.23
0.25
a
Determined by XRF. b Calculated by BET method. c Estimated by t-plot method. d Calculated by a subtraction of total pore volume at a relative
e
pressure of P/P0 ¼ 0.99 from the micropore pore volume obtained from the t-plot. Determined by NH3 desorption (chemisorbed at 100 ꢀC).
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almost complete conversion of fructose and 90.6% yield of HMF
within 8 min. Aer the reaction for 15 min, the HMF yield
increased to 93.8%. However, for 0.09-CuAPO-5 and 0.12-
CuAPO-5 samples with higher Cu content, both reaction activity
and HMF yield declined to some extent. It should be noted that
the HMF yield on these CuAPO-5 catalysts was higher than most
of the reported zeolitic catalysts (Table 2), suggesting that the
ionothermally prepared CuAPO-5 was also a good candidate for
the efficient production of HMF.
Compared with 0.03-CuAPO-5, 0.06-CuAPO-5 exhibited
higher surface area, pore volume, and stronger acidity, which
were believed to be the positive factors for dehydrating fructose.
Thus, the improved performance on the 0.06-CuAPO-5 sample
is reasonable. Further increase in the Cu content raised the
acidity but dropped the BET surface area and pore volume,
resulting in the inferior performance of 0.09-CuAPO-5 and 0.12-
CuAPO-5. Therefore, for the acid-catalyzed reaction like fructose
dehydration, the acidity was not the only determining factor
and the effect of porosity on mass transfer efficiency should be
highlighted.34 According to the literature, the diffusion limita-
tion in pore channels of molecular sieves would greatly restrict
the conversion of furanic compounds.35 Catalyst reusability is
Table 2 Catalytic performances of the different zeolitic catalysts in
dehydration of fructose to HMF
Catalyst
Solvent
HMF yield (%) Reference
Fig. 4 NH3-TPD profiles (a) and EPR spectrum (b) of the CuAPO-5
samples.
MeSAPO-5
MeSAPO-11
Aqueous/organic phase
H2O, DMSO, MIBK and SBA 78.2
73.9
14
15
H-mordenite H2O/MIBK
74.0
75.1
70.3
84.1
99.1
69.2
93.8
85.5
10
36
36
9
11
37
ZSM-5
MCM-22
KIT-6
KL
H2O/MIBK
H2O/MIBK
DMSO
[BMIM]Br
Water/GBL
catalyze the dehydration reaction,33 but its activity was rather
low under the present reaction conditions. With the presence of
CuAPO-5 catalysts, both fructose conversion and HMF yield
sharply increased. For 0.03-CuAPO-5, 98.3% conversion and
88.7% yield were achieved aer 30 min of reaction. The fructose
conversion and HMF yield nally reached 99.1% and 92.0%,
respectively. 0.06-CuAPO-5 as the most active sample gave an
HY
0.06-CuAPO-5 [BMIM]Br
0.12-CuAPO-5 [BMIM]Br
This work
This work
Fig. 5 The catalytic performances of the samples in dehydration of fructose to HMF. Reaction conditions: 40 g [BMIM]Br, 4.0 g fructose, 0.4 g
catalyst, 110 ꢀC.
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Wong Education Foundation (rczx0800), Fujian Institute of
Innovation of Chinese Academy of Sciences (FJCXY18020202).
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In this work, the trace Cu substituted aluminophosphate
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