Efficient and Selective Oxidation of 5-Hydroxymethylfurfural into 2, 5-Diformylfuran Catalyzed by Magnetic Vanadium-Based Catalysts with Air as Oxidant

Article abstract of DOI:10.1007/s10562-019-03041-w

Abstract: In this study, a new kind of magnetic vanadium-based catalyst was successfully prepared and employed to produce 2, 5-diformylfuran (DFF) in the liquid phase through selective oxidation of biomass-derived 5-hydroxymethylfurfur (HMF) with air as oxidant. It was found that magnetic Fe₃O₄ nanoparticles supported NH₄·V₃O₈ showed excellent catalytic performance with the achievement of 95.5% HMF conversion along with 82.9% selectivity to DFF under optimal reaction conditions. More importantly, the catalyst could be readily separated from the reaction mixture by a permanent magnet, and recycled several times without the loss of its catalytic activity. Graphic Abstract: The NH₄·V₃O₈/Fe₃O₄ catalyst showed high activity for selective oxidation of 5-hydroxymethylfurfural into 2, 5-diformylfuran.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-019-03041-w

Catalysis Letters
https://doi.org/10.1007/s10562-019-03041-w
Efcient and Selective Oxidation of 5‑Hydroxymethylfurfural into 2,
5‑Diformylfuran Catalyzed by Magnetic Vanadium‑Based Catalysts
with Air as Oxidant
Jinhua Lai1 · Shuolin Zhou1 · Feng Cheng1 · Dongwen Guo1 · Xianxiang Liu1,2 · Qiong Xu1 · Dulin Yin1
Received: 29 June 2019 / Accepted: 16 November 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
In this study, a new kind of magnetic vanadium-based catalyst was successfully prepared and employed to produce 2, 5-difor-
mylfuran (DFF) in the liquid phase through selective oxidation of biomass-derived 5-hydroxymethylfurfur (HMF) with air as
oxidant. It was found that magnetic Fe3O4 nanoparticles supported NH4·V3O8 showed excellent catalytic performance with
the achievement of 95.5% HMF conversion along with 82.9% selectivity to DFF under optimal reaction conditions. More
importantly, the catalyst could be readily separated from the reaction mixture by a permanent magnet, and recycled several
times without the loss of its catalytic activity.
Graphic Abstract
The NH4·V3O8/Fe3O4 catalyst showed high activity for selective oxidation of 5-hydroxymethylfurfural into 2, 5-diformylfuran.
Keywords 5-Hydroxymethylfurfural · 2, 5-Diformylfuran · Selective oxidation · Magnetic catalyst · Biomass
transformation
1 Introduction
* Xianxiang Liu
Due to the increasing demand of petroleum-based
lxx@hunnu.edu.cn
resources for the production of chemicals and fuels, a
* Dulin Yin
great attention has been paid to the utilization of renew-
dulinyin@126.com
able resources as an alternative to fossil resources [1].
1
Biomass is the only renewable organic carbon resource in
nature, whose catalytic conversion can produce important
oxygenated organic compounds to partially replace and
supplement traditional fossil resources [2–4]. HMF is a
very important biomass-based platform compound for the
comprehensive utilization of biomass resources. It can
produce a wide range of widely used furan derivatives
National & Local Joint Engineering Laboratory for New
Petro-chemical Materials and Fine Utilization of Resources,
Key Laboratory of the Assembly and Application of Organic
Functional Molecules of Hunan Province, Hunan Normal
University, Changsha 410081, People’s Republic of China
2
CAS Key Laboratory of Renewable Energy, Guangzhou
Institute of Energy Conversion, Chinese Academy
of Sciences, Guangzhou 510640, People’s Republic of China
Vol.:(0123456789)
1 3

J. Lai et al.
by chemical reactions such as oxidation, hydrogenation,
esterifcation, halogenation, and polymerization [5, 6].
Catalytic oxidation of HMF represents as one of the most
important routes for the utilization of HMF (Scheme 1), as
this process can generate several kinds of import chemi-
cals such as DFF, 5-hydroxymethyl-2-furancarboxylic acid
(HFCA), 5-formyl-2-furancarboxylic acid (FFCA) and
2,5-furandicarboxylic acid (FDCA). However, the selec-
tive oxidation of HMF into a special furan compound is
challenging, although it has received a great deal of atten-
tion. DFF is one of the main products of HMF selective
oxidation, and has been used in the synthesis of high-end
drugs, pesticide antifungal agents, fuorescent materials
and new polymeric materials [7, 8].
oxide-based material [2, 21, 22] and GO-related materials
[23].
Among these catalysts, vanadium-containing catalysts are
noticeable. In the past decade, some methods on the aerobic
oxidation of alcohols using relative cheap V based catalysts
were reported [24–26]. In this work, a new kind of mag-
netic Fe3O4 supported NH4·V3O8 catalyst (NH4·V3O8/Fe3O4)
was successfully prepared and characterized. The activity
of the as prepared NH4·V3O8/Fe3O4 catalyst was evaluated
by the oxidation of HMF into DFF with air as oxidant. The
NH4·V3O8/Fe3O4 catalyst was observed to have a high cata-
lytic activity and selectivity for the selective oxidation of
HMF into DFF.
In the early research on the preparation of DFF by HMF
oxidation, the focus was mainly on traditional oxidants such
as pyridinium chlorochromate (PCC), NaOCl, and BaMnO4
and 2, 2, 6, 6-tetramethylpiperidine-1-oxide (TEMPO) free
radicals [9–11]. Although the traditional oxidant can suc-
cessfully realize the synthesis of DFF by HMF oxidation
under diferent reaction systems, the reaction efect is not
obvious, because it consumes a large amount of oxidants
due to its own defects, the low atomic utilization rate, and of
the generated toxic by-products. This is not in line with the
current background of green chemistry. When using H2O2,
air and oxygen as terminal oxidants, although the atomic uti-
lization rate is high and environmentally friendly, the reac-
tion process is not easy to control, and generally requires
pressurization or high temperature [2, 12]. To conclude, how
to achieve efcient selective oxidation of HMF under mild
conditions has been an important and challenging topic.
In recent years, catalysts for HMF catalytic oxidation are
mainly supported precious metals [13, 14]. Zhu et al. syn-
thesized three novel catalysts using MnO2 as the supporting
material for the oxidation of HMF into DFF in the presence
of O2 [15]. This group further studied the bimetallic Au–Pd
catalyst catalyzed HMF oxidation [16]. Srivastava et al.
[17–20] also have been committed to research in this area
and developed a series of catalysts with excellent catalytic
activity. Precious metals have excellent catalytic properties
for the preparation of DFF systems by HMF oxidation. Due
to the high price of noble metal catalysts, the metallic oxides
catalysts have attracted much attention, such as manganese
2 Experimental
2.1 Materials
5-Hydroxymethylfurfural (99.5%) and 2, 5-diformylfuran
were purchased from Sinopharm Chemical Reagent Co.,
Ltd. (Shanghai, China). NH4VO3, NH3·H2O and FeCl2·4H2O
were purchased from Sinopharm Chemical Reagent Co.,
Ltd (Shanghai, China). All the chemicals were of analytical
grade and used without further purifcation. Ultrapure water
was used for the catalyst preparation and catalytic reactions.
2.2 Catalyst Preparation
The magnetic vanadium-based catalyst was prepared by
using NH4·V3O8 and FeCl2·4H2O as main raw materials.
Typically, NH4·V3O8 (0.458 g) was derived from the pyroly-
sis of NH4VO3 at 180 °C for 12 h, and FeCl2·4H2O (1.000 g)
were refuxed in ultrapure water (20 mL) at 80 °C for 30 min,
and slowly dropped NH3·H2O (2.5%, 10 mL) under high
speed agitation. The black NH4·V3O8/Fe3O4 nanoparticles
were thoroughly washed with ultrapure water, separated by
external magnet, and dried at 80 °C for 2 h.
2.3 Characterizations
Fourier transform infrared spectra (FT-IR) of the samples
were collected by the KBr pellet technique on a Nicolet 370
Scheme 1 General routes for
O
O
O
O
OH
[O]
O
[O]
[O]
[O]
O
the oxidation of HMF into furan
compounds
O
O
O
OH
O
OH
O
HO
HMF
FFCA
DFF
O
FDCA
[O]
O
OH
HO
HFCA
1 3

Efcient and Selective Oxidation of 5‑Hydroxymethylfurfural into 2, 5‑Diformylfuran…
infrared spectrophotometer in the range 400–4000 cm−1.
The crystal structure of the samples were determined by
X-ray difraction (XRD) spectroscopy using Bruker difrac-
tometer with Cu Kα wavelength (λ=1.5418 Å) and difrac-
tion angle (2θ) ranging from 10° to 70°. Thermogravimet-
ric and derivative thermogravimetric (TG-DTG, Germany)
curves were recorded in N2 fow on a Netzsch Model STA
409PC instrument with a heating rate of 20 °C/min from
room temperature to 600 °C using α-Al2O3 as the standard
material. The morphologies of the samples were investigated
by using transmission scanning microscopy (TEM) with
FEI Tecnai G2 F20. The magnetic of the samples was also
investigated using vibrating sample magnetometry (VSM,
Fe3O4
.
NH4 V3O8
.
NH4 V3O8/Fe3O4
4000
3500 3000
2500
2000
1500
1000
500
LakeShore7404).
Wavenumber(cm-1)
2.4 Catalytic Oxidation of HMF
Fig. 1 FT-IR spectra of (a) Fe3O4, (b) NH4·V3O8, and (c) NH4·V3O8/
Fe3O4
The oxidation of HMF in the air under atmospheric pres-
sure was performed in a 10 mL round bottom fask, which
was coupled with a refux condenser using the following
general procedure. Typically, HMF (0.1 mmol, 12.6 mg)
was frstly dissolved into DMSO (5 mL) in the fask with
a magnetic stirrer. Then, 10 mg catalysts were added into
the reaction mixture. The mixture was heated to the desired
temperature while stirring under an air atmosphere. After
reaction, the reaction solution was quantitatively analyzed
by Agilent 1100 HPLC system equipped with Agela Tech-
nologies Venusil XBP C18(L) (4.6×250 mm) and a UV–Vis
(280 nm) detector. The mobile phase was constituted of ace-
tonitrile and 0.1 wt% acetic acid aqueous solution (V:V=15:
85), and the samples was eluted at a rate of 0.5 mL/min at
30 °C. The amount of each compound was quantifed by
external standard calibration curve method. According to
the test results, the oxidation of HMF mainly leads to DFF,
HFCA, FFCA and FDCA.
Fig. 2 XRD patterns of (a) Fe3O4, (b) NH4·V3O8, and (c) NH4·V3O8/
Fe3O4
3 Results and Discussion
largely enhance (311) facet signal at 2θ=35.5º than other
facet signals of the Fe3O4 sample. The XRD spectra of the
pyrolysis product of NH4VO3 revealed that solid NH4·V3O8
is formed according JCPDS card 88-1473. The XRD pat-
tern of NH4·V3O8/Fe3O4 was also collected showing a strong
peak at 2θ=35.6º, in which is diferent from those of Fe3O4
at 2θ=35.5º and NH4·V3O8 at 2θ=27.7º. In addition, some
peaks with low intensity also appeared in NH4·V3O8/Fe3O4,
and all the peaks could be assigned to the corresponding
peaks rather in Fe3O4 or NH4·V3O8. These XRD results con-
frmed that the catalyst NH4·V3O8/Fe3O4 was composed of
Fe3O4 and NH4·V3O8.
3.1 Catalyst Characterization
The functional groups of these samples were identifed by
FT-IR analysis, and the corresponding FT-IR spectra were
depicted in Fig. 1. The FT-IR spectra of diferent NH4·V3O8
illustrated the typical NH4·V3O8 crystal structure. The peak
at 583 cm−1 was the characteristic peak of Fe3O4, which
was the vibration of Fe–O bond [27]. The FT-IR results also
indicated that NH4·V3O8 was successfully supported on the
magnetic Fe3O4 nanoparticles.
The XRD pattern in Fig. 2 illustrated the typical Fe3O4
crystal structure with JCPDS card 88-0315 for the magnetic
Fe3O4 nanoparticles, suggesting that this phase has been suc-
cessfully synthesized. It is seen that the Fe3O4 showed the
The TEM images of NH4·V3O8/Fe3O4 were shown in
Fig. 3. Figure 3b shows that the magnetic Fe3O4 nanopar-
ticles were deposited on the surface NH4·V3O8, and the
1 3

J. Lai et al.
Fig. 3 TEM images of the
NH4·V3O8/Fe3O4 catalyst
0
-1
-2
ꢁꢂ
ꢃꢄ
ꢃꢂ
ꢄ
100
98
Fe3O
.
4 Fe3O
NH4 VV3O2O85
/
/
4F
F
e
e33O44
O
96
ꢂ
200
300
400
500
100
Temperature(ºC)
94
ꢀꢄ
Fe3O4
92
ꢀꢃꢂ
ꢀꢃꢄ
ꢀꢁꢂ
.
NH4 VO8/ Fe3O4
3
90
100
200
300
400
500
600
-10.0k
-5.0k
0.0
Field(G)
5.0k
10.0k
Temperature(ºC)
Fig. 4 TG-DTG curves of (a) Fe3O4 and (b) NH4·V3O8/Fe3O4
Fig. 5 VSM magnetization curve of NH4·V3O8/Fe3O4
nanoparticles have a serious agglomeration phenomenon.
The (111) facet signal at 18.3º corresponded to the 1.5 nm
of facet spacing according to the Fig. 3c.
3.2 Efects of the Solvents on the Oxidation of HMF
The oxidation HMF was further carried out in a variety of
solvents. As shown in Table 1, the solvents were found to
play a crucial role in the conversion of HMF and the selectiv-
ity of DFF. DMSO showed the lowest conversion of 59.6%
with the highest 31.3% DFF selectivity (Table 1, Entry 2),
suggesting that DMSO was a reliable solvent for the selec-
tive oxidation of HMF into DFF. On the other hand, high
conversion of 98.9% albeit with 7.5% DFF selectivity was
obtained in MIBK (Table 1, Entry 4). The reactions carried
in K2CO3 solution and acetonitrile also showed high HMF
conversion but with almost no detectable DFF after oxida-
tion reaction (Table 1, Entry 1 and 2). Therefore, DMSO was
supposed to be a superior solvent for the selective oxidation
of HMF into DFF and will be used in the next step.
The thermogravimetric analysis results of NH4·V3O8/
Fe3O4 and Fe3O4 samples were compared as shown in
Fig. 4. The weight loss lower than 5% at about 237 °C was
observed for Fe3O4, corresponding to the loss of the physi-
cally adsorbed water. In contrast, the NH4·V3O8/Fe3O4 cata-
lyst has three weight loss stages appearing at 200–300 °C,
300–370 °C and 370–440 °C, respectively. The frst loss
stage at temperatures lower than 300 °C is due to the loss of
absorbed water. In the second stage, the decomposition into
V2O5 begins with the loss of around 5% of mass at tempera-
tures higher than 300 °C. Finally, a fat mass loss is observed
at temperatures higher than 400 °C. These results indicate
that NH4·V3O8 was successfully supported on the magnetic
Fe3O4 nanoparticles.
The magnetic performance of NH4·V3O8/Fe3O4 catalyst
was also investigated using vibrating sample magnetometry
(VSM). The obtained curves are depicted in Fig. 5. The Hcb
of NH4·V3O8/Fe3O4 is 120.0 G/s, and the saturation magneti-
zation (Ms) is 18.8 emu/g. It shows that the sample behaves
good magnetic properties at room temperature.
3.3 Catalytic Oxidation of HMF Using Various
Oxidants
The prepared NH4·V3O8 catalyst was used for the selec-
tive oxidation of HMF into DFF using various oxidants in
DMSO and the results are given in Table 2. It is found that
1 3

Efcient and Selective Oxidation of 5‑Hydroxymethylfurfural into 2, 5‑Diformylfuran…
Table 1 Efects of diferent
Entry
Solvent
Conversion/(%)
Selectivity/(%)
Yield
of DFF/
(%)
solvents on the oxidation of
HMF
FDCA
HFCA
FFCA
DFF
Othersa
1
2
3
4
K2COb3(aq)
DMSO
Acetonitrile
MIBK
73.1
59.6
77.9
98.9
0.9
13.6
0
2.5
1.2
7.5
0.5
0.8
31.3
7.2
–
95.7
30.6
84.7
78.1
0
51.8
0.6
7.5
13.9
0.4
7.4
2.9
11.0
Reaction conditions: 0.1 mmol HMF, 20 mg NH4·V3O8, 5 mL solvent, 120 °C, 6 h, 0.5 mmol TBHP
aOthers are mainly acetalized products and ring-opening products, e.g. ethyl levulinate and ethyl formate
b0.05 g/5 mL
Table 2 Efects of diferent
oxidants on the oxidation of
HMF
Entry
Oxidant
Conversion/(%)
Selectivity/(%)
Yield of
DFF/(%)
FDCA
FFCA
HFCA
DFF
Othersa
1
2
3
4
Air
74.9
76.6
75.4
91.4
14.7
13.2
13.0
11.6
6.0
6.3
8.0
7.7
–
–
–
–
64.8
68.5
78.0
57.6
14.5
11.9
1.0
48.5
52.5
58.8
52.6
TBHPb
H2Ob2
O2
23.2
Reaction conditions: 0.1 mmol HMF, 10 mg NH4·V3O8, 5 mL DMSO, 120 °C, 6 h
aOthers are mainly acetalized products and ring-opening products, e.g. ethyl levulinate and ethyl formate
b0.5 mmol
molecular oxygen showed the highest conversion of 91.4%
with 57.6% DFF selectivity (Table 2, Entry 4). This was
consistent with our previous conclusion that O2 was a reli-
able oxidant for the oxidant of HMF into DFF. On the other
hand, high conversion of 75.4% with high DFF selectivity
of 78.0% was obtained in the presence of TBHP and H2O2
(Table 2, Entry 2 and 3). Interestingly, air aforded 74.9%
conversion of HMF with 64.8% selectivity (Table 2, Entry
1), which is close to the results of other oxidants. Therefore,
in terms of the economic and green viewpoint, the use of
air as an oxidant for the selective oxidation of HMF into
DFF should be advantageous and will be used in the next
step (Table 2).
80
60
40
20
HMF Conversion
DFF Selectivity
20
40
60
80
100
Catalyst dosage (wt %)
3.4 Efects of Catalyst Dosage on the Oxidation
of HMF
Fig. 6 Efects of catalyst dosage on the oxidation of HMF. Reaction
conditions: 0.1 mmol HMF, 5 mL DMSO, 120 °C 6 h, in the air
The efects of catalyst dosage was also studied. As shown
in Fig. 6, the conversion of HMF keeps increasing with the
amount of catalyst, while the selectivity of DFF is almost
constant. The results indicate that the dosage of NH4·V3O8
showed a remarkable efect on the selective oxidation of
HMF into DFF due to an increase in the availability and
number of catalytically active sites. The results also sug-
gested that the selectivity of DFF had no relationship with
the catalyst loading when the reaction was carried out in the
same conditions, such as reaction time and reaction tem-
perature. The yield of DFF is up to 54.4% with the equal
amount of catalyst, however, the DFF selectivity begins to
decline due the generation of a new by-product as detected
by HPLC.
1 3

J. Lai et al.
3.5 Time Course of the Oxidation of HMF
100
80
60
40
20
0
The catalytic performances of NH4·V3O8 were investigated
in diferent reaction time, and the results are shown in Fig. 7.
The reaction products, DFF, FDCA, FFCA, and FMF, were
detected by HPLC. It is found that the conversion of HMF
increased with the reaction time and reached 76.2% con-
version with DFF selectivity of 72.7% by 6 h. In the ini-
tial stage, the fast reaction rate should be due to the high
concentration of HMF. FDCA showed a highest selectivity
of 17.0% at 3 h, while the yield of FFCA and FMF keeps
increasing with the reaction time.
HMF Conversion
DFF Selectivity
DFF Yield
FDCA Selectivity
FFCA Selectivity
FMF Selectivity
0
10
20
30
3.6 Efects of Reaction Temperature
Reaction time (h)
on the Oxidation of HMF
Fig. 7 Efects of reaction time on the oxidation of HMF. Reac-
tion conditions: 0.1 mmol HMF, 12.6 mg NH4·V3O8, 5 mL DMSO,
120 °C, in the air
The efects of the reaction temperature was also studied and
the results are shown in Fig. 8. It is seen that both the HMF
conversion and the DFF yield were greatly afected by the
reaction temperature. At the reaction temperature of 110 °C,
the HMF conversion obtained was 49.2%, while it increased
to 99.5% when further elevating the temperature to 150 °C.
The yield of DFF also increased with the reaction tempera-
ture. The highest yield of DFF obtained was 67.5% at 140 °C
and it slightly decreased to 65.0% at 150 °C. These results
indicated that high reaction temperature promoted the selec-
tive oxidation of HMF into DFF, allowing the achievement
of quantitative HMF conversion when the reaction was car-
ried out at 140 °C and 150 °C.
3.7 Catalytic Activities of NH4·V3O8/Fe3O4 Catalyst
with Diferent V/Fe Molar Ratios
The catalytic performance of NH4·V3O8/Fe3O4 catalysts with
diferent V/Fe molar ratios was tested under atmospheric air
and the results are listed in Fig. 9. As expected, no catalytic
activity is observed in the presence of only Fe3O4. In the
presence of NH4·V3O8/Fe3O4 which the V/Fe molar ratio
was 0.2, 25.8% of HMF conversion and 11.8% of DFF yield
implies that the selective oxidation of HMF into DFF takes
place. As the V/Fe ratio of NH4·V3O8/Fe3O4 increases to
100
80
60
50
40
30
60
20
HMF Conversion
DFF Yield
40
20
HMF Conversion
10
0
DFF Yield
110
120
130
140
150
0.0
0.2
0.4
0.6
0.8
1.0
Reaction temperature (°C)
V/Fe molar ratios
Fig. 8 Efects of reaction temperature on the oxidation of HMF.
Reaction conditions: 0.1 mmol HMF, 12.6 mg NH4·V3O8, 5 mL
DMSO, 6 h, in the air
Fig. 9 Efects of V/Fe molar ratios of NH4·V3O8/Fe3O4 on the oxida-
tion of HMF. Reaction conditions: 0.1 mmol HMF, 10 mg NH4·V3O8/
Fe3O4, 5 mL DMSO, 120 °C, 6 h, in the air
1 3

Efcient and Selective Oxidation of 5‑Hydroxymethylfurfural into 2, 5‑Diformylfuran…
0.4, the HMF conversion and DFF yield increase to 35.1%
HMF Conversion
DFF Selectivity
and 15.3%, respectively. However, increasing the V/Fe ratio
to 0.8 and 1.0, only slightly improved catalytic activities are
observed, suggesting that further increase of the V/Fe ratio
couldn’t provide quantitative active sites. These observations
reveal that an appropriate V/Fe ratio of NH4·V3O8/Fe3O4 is
essential to achieving an optimized catalytic performance
for the oxidization of HMF into DFF. Amount of loading
have determined using ICP, the results showed that the V/
Fe ratio of NH4·V3O8/Fe3O4 catalysts were 0.20, 0.36, 0.60,
0.80 and 0.87, respectively.
80
60
40
20
0
The possible reaction mechanism of HMF to DFF cata-
lyzed by the catalyst was illustrated in Scheme 2. The reduc-
tion of V5+ to V4+ by HMF, and the further reoxidation of
V4+ to V5+ by oxygen in the air through a Mars-Van Krev-
elen mechanism.
1
2
3
4
5
6
7
8
Run (No.)
Fig. 10 Recycle experiments of the catalyst NH4·V3O8/Fe3O4 on the
oxidation of HMF. Reaction conditions: 0.1 mmol HMF, 50 mg cata-
lyst (V/Fe ratio: 0.87), 5 mL DMSO, 120 °C, 6 h, in the air
3.8 Recycle Experiments of the Catalyst
Developing a convenient and economical method to reuse
the catalyst and the solvent is very crucial in terms of the
green chemistry. The main advantage of magnetic catalysts
is that they can be readily separated from the reaction mix-
ture by an external magnet. For this purpose, the used cata-
lyst was washed by ethanol to remove the adsorbed products
and dried under vacuum at 80 °C overnight. Then the cata-
lyst was reused for the next cycle under otherwise identical
reaction conditions. As shown in Fig. 10, the conversion of
HMF and the selectivity of DFF were quite stable, indicating
that the catalyst could be reused without signifcant decrease
of the catalytic activity. To confrm the stability of the cat-
alysts after the oxidation of HMF, ICP of the recovered
NH4·V3O8/Fe3O4 was measured. The result confrmed that
the V/Fe ratio of NH4·V3O8/Fe3O4 catalysts was no obvious
change around 0.85, suggesting that the NH4·V3O8 groups
were essentially preserved. Although nonmagnetic hetero-
geneous catalysts could also be reused, some heterogeneous
catalysts lost their catalytic activity due to the inevitable
loss of catalyst mass in the recycling experiments by the
conventional fltration method. In comparison, the recovery
of the catalyst by a permanent magnet obviously avoids the
catalyst loss during the recycling experiments, and thereby is
promising for practical applications comparison with some
others latest catalysts (Table 3).
4 Conclusions
In summary, a new method was developed for the synthesis
of DFF from the selective oxidation of HMF. The magnetic
NH4·V3O8/Fe3O4 was prepared by NH4VO3, NH3·H2O and
FeCl2·4H2O, and showed an excellent catalyst performance
with the achievement of 95.5% HMF conversion as well as
82.9% DFF selectivity in a 6-h reaction time at 140 °C. The
catalyst could be easily separated from the reaction mixture,
and could be reused multiple times without losing catalytic
activity. Such high activity, stability and magnetic recovery,
combined with the simple preparation of catalysts, make it
a promising application in conversion of biomass-derived
platform chemicals into valuable bulk chemicals.
Scheme 2 Possible mechanism
OH
V4+
O
[O]
for the formation of DFF on the
NH4·V3O8
V5+
O
HO
O
O
HO
O
O
V5+
O
O
O
H
1 3

J. Lai et al.
Table 3 Catalytic oxidation
of HMF into DFF
Entry
Catalyst
Oxidation
Solvent
HMF conver- DFF selec-
Ref.
sion/%
tivity/%
over diferent catalysts
1
2
3
4
5
MnOx/P25
VOx-ms
Au–Pd/MnO2
SBA-NH2-VO2+
NH4·V3O8/Fe3O4
Air
O2
O2
O2
Air
Ethanol
H2O
H2O
Toluene
DMSO
33.2
93.7
76.0
98.8
95.5
97.0
95.4
98.0
29.3
82.9
[2]
[5]
[16]
[26]
This work
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Acknowledgements The authors gratefully acknowledge the fnancial
support of the National Natural Science Foundation of China (Grant
Nos. 21606082, 21776068), Hunan Provincial Natural Science Founda-
tion of China (2018JJ3334), the China Postdoctoral Science Founda-
tion (2019M662787), the Opening Fund of CAS Key Laboratory of
Renewable Energy (Y807kc1001), and Hunan Provincial Innovation
Foundation for Postgraduate (CX2018B295).
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