Vanadium-oxo immobilized onto Schiff base modified graphene oxide for efficient catalytic oxidation of 5-hydroxymethylfurfural and furfural into maleic anhydride

Article abstract of DOI:10.1039/c6ra21795h

Graphene oxide (GO) sheets are emerging as a new class of carbocatalyst, and also a perfect platform for molecular engineering. The hydroxyl groups on either side of GO sheets can function as anchors by employing them as scaffolds linking organometallic nodes and vanadium-oxo was homogeneously immobilized on a Schiff base modified GO support via covalent bonding. The developed VO-NH₂-GO was shown to be an efficient and recyclable heterogeneous catalyst for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) into maleic anhydride. Up to 95.3% yield of maleic anhydride from HMF and 62.4% from furfural were achieved under optimized reaction conditions. The immobilized vanadium oxo was identified as the active sites, while the residual oxygen-containing groups worked synergistically to adsorb HMF to maintain a high reactant concentration around the catalyst. The STY value was enhanced significantly over VO-NH₂-GO, compared with homogeneous or heterogeneous traditional supported V based catalyst.

Full text of DOI:10.1039/c6ra21795h

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Vanadium-oxo immobilized onto Schiff base modified graphene
oxide for efficient catalytic oxidation of 5-hydroxymethyfurfural
and furfural into maleic anhydride
Received 00th January 20xx,
Accepted 00th January 20xx
Guangqiang Lv,a,b Chunyan Chen,a,c Boqiong Lu,a,b Jinlong Li,a,b Yongxing Yang,a Chengmeng, Chen,d
Tiansheng Deng,a Yulei Zhue and Xianglin Hou*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
Graphene oxide (GO) sheets are emerging as a new class of carbocatalyst, and also a perfect platform for molecular
engineering. The hydroxyl groups on either side of GO sheets can be functioned as the anchor by employing them as
scaffolds linking organometallic nodes and vanadium-oxo was homogeneously immobilized on a Schiff base modified GO
support via covalent bonding. The developed VO-NH2-GO was shown to be an efficient and recyclable heterogeneous
catalyst for aerobic oxidation of 5-hydroxymethyfurfural (HMF) into maleic anhydride. Up to 95.3% yield of maleic
anhydride from HMF and 62.4% from furfural were achieved and under optimized reaction conditions. The immobilized
vanadium oxo was identified as the active sites, while the residual oxygen-containing groups worked synergistically to
adsorb HMF to maintain a high reactant concentration around the catalyst. The STY value was enhanced significantly over
VO-NH2-GO, compared with homogeneous or heterogeneous traditional supported V based catalyst.
generate several kinds of oxidation products such as 2,5-
diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid
(HMFCA), 5-formyl-2-furancarboxylic acid (FFCA), and 2,5-
Introduction
With declining fossil resources, significant effort has been
devoted into convert renewable biomass into fuels,1-3 and
valuable chemicals.4-6 Replacement of petroleum-derived
furandicarboxylic acid (FDCA),16-21 as depicted in Scheme 1.
Besides, C5-based furfural is an analog of HMF and comes
from rich agricultural materials like corncobs, oat, wheat bran,
and sawdust, and they are not competitive with food of
human beings. Particularly, unlike HMF, which is currently
synthesized on a lab scale, furfural production is an on-going
industrial process; therefore, it is considered that furfural is a
better starting material than HMF for MA synthesis from
biomass.22, 23
chemicals with those from biomass will play a key role in
7-11
sustaining the growth of the chemical industry.
5-
Hydroxymethylfrufural (HMF), derived from C6-based
carbohydrates and owned an aldehyde group,
a
hydroxymethyl group and a furan ring, has been regarded as
one of the most promising platform chemicals and used as a
versatile precursor for the production of fine chemical,
plastics, pharmaceuticals, polymer and liquid fuels.10,
12-15
Maleic anhydride (MA) and its derivatives are manufactured
with a large capacity, which are widely employed to synthesize
unsaturated polyester resins, agricultural chemicals, food
additives, lubricating oil additives, pharmaceuticals, and so
forth.24 In industry, MA is mainly produced via oxidation of
petroleum-derived chemicals such as n-butane and benzene.24
Regarding the diminishing of the fossil resources, developing
new chemical process to transform biomass into MA other
than fossil feedstock is greatly attractive. MA can be produced
from HMF in an entirely different route with DFF, HMFCA,
FFCA and FDCA. Yin et al.24 and Xu et al.25 have demonstrated
experimentally and theoretically that HMF can be oxidized into
MA over vanadium-based catalyst by the C-C bond (adjacent to
the hydroxymethyl group) cleavage. The results indicate that
only HMF and HMFCA containing hydroxymethyl group can
convert into MA easily over vanadium-based catalyst, as
depicted in Scheme 1.
Selective oxidation of HMF is one of the most pivotal
transformation in biorefinery. The oxidation of HMF can
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Scheme 1. Schematic illustration of the potential oxidation products during the oxidation of HMF.
Graphene oxide and its derivatives (GO) have attracted low MA selectivity (50%-80%) was often obtained under harsh
significant attention for their outstanding electrical, optical, reaction condition. Furthermore, the aggregation or leaching
electrochemical and mechanical properties.26, 27 The generally of VOx component on traditional support (such as SiO2, Al2O3)
accepted models of GO structure depict hydroxyl and epoxide leads to low catalytic efficiency in reaction. In this paper, the
groups as dominant functionalities residing mainly on the basal ultrasonic exfoliated and freeze-dried GO was chosen as the
plane. Hole defects are found through of the scaffold, which high hydroxyl containing support for immobilizing the
accommodate groups like carboxylic acids, ketones, phenols, vanadium-oxo. The as-prepared composite exhibited superior
lactols, and lactones.28 The Hummers method made GO also activity and selectivity in aerobic oxidation of HMF and furfural
have some sulfonic groups linked on the edge of graphene into MA. The grafted vanadium-oxo worked as the active site,
plane. The oxygen containing functionalities imparted GO the while the residual oxygen-containing groups in GO worked
function as an acid catalyst,29, 30 redox catalyst31, 32 et al. in synergistically to adsorb HMF to maintain a high reactant
chemical synthesis reaction. Beside, using GO as a building concentration around the catalyst.
block in supramolecular chemistry, the scope of functionalities
in GO hybrids can be extended. The presence of epoxy and
Catalyst Characterization
hydroxyl functional groups on either side of the GO sheet
imparts bifunctional properties that allow it to act as a
The detailed procedure for preparing the vanadium-oxo
structural node within metal-organic frameworks. For
immobilized and Schiff base modified graphene oxide (VO-
example, homogeneous molecular catalyst can be anchored on
NH2-GO) is described in the supporting information. The fresh
the GO surfaces by employing them as scaffolds linking
catalyst and recycled catalyst for 5 times in reaction are
organometallic nodes.28, 33 Rhenium-oxo34, vanadium-oxo35, 36
characterized and compared. BET analysis (Table S1) shows
and Fe2+, Co2+, Cu2+,37 have been immobilized onto graphene
379.0 m2/g with an average pore diameter of 14.4 nm. After
oxide via covalent bonding and the composites can be used as
that the obtained graphene oxide has a BET surface area of
efficient and recyclable catalyst in various oxidation reactions.
immobilization of vanadium oxo onto the Schiff base modified
graphene oxide, the oxygen-containing functionalities in GO
Previously, many vanadium-based catalysts, such as
VO(acac)2,25 V-Mo containing heteropolyacid,24, 38, 39 supported
reacted with the introduced APTES and VO(acac)2. After re-
construction, the surface area decrease to 148.8 m2/g with a
41
or unsupported VOx,40,
Mo-V metal oxide,23 have been
little enlarged pore diameter of 14.6 nm. Figure S1 shows the
XRD patterns of the as-prepared materials. The interlayer
reported to catalyze the oxidation of HMF into MA. However, a
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distance obtained from the (002) peak was 3.38 Å (a, 2θ = 26.4
o) in graphite. This was markedly expanded to 8.27 Å (b, 2θ =
10.8o) with oxidation to form GO. The large interlayer distance
has been attributed to the formation of hydroxyl, epoxy, and
the carboxyl groups. After amino functionalization (c) and
immobilization of the vanadium-oxo procedure (d), the peak of
the large interlayer distance in GO (10.8o) decreased radically
and another broad diffraction at ca. 22o appeared, which is
closer to the reduced graphene,42 indicating that the major
oxygen-containing groups of GO have been successfully
reduced or functionalized under hydro-thermal conditions.35, 36
The recycled catalyst (e) shows a similar XRD pattern to the
fresh catalyst (d). Elemental analysis of the fresh and recycled
VO-NH2-GO is shown in the supporting information Table S2.
The prepared GO has a 46.5 wt% of oxygen. After amino
functionalization and immobilization of vanadium-oxo, the
oxygen content decreased to 24.9 wt%, the graphene oxide
was partially reduced and these results are corresponding with
the XRD analysis. The loading of the amino propyl groups onto
the GO support was found to be 2.4 mmol g-1, as determined
by the nitrogen content (3.4 wt% N). Elemental analysis shows
0.32 mmol g-1 V was immobilized onto GO. The V/N atom ratio
in as-prepared VO-NH2-GO was ca. 0.13, much smaller than 1,
indicating most of the introduced APTES did not participated
into the further chemical functionalization with VO(acac)2. It is
deduced that the formation of VO-Schiff base complex is
Results and Discussion
Oxidation of HMF into maleic anhydride
In a typical experiment, 2 mmol HMF dissolved in 10 mL pure
o
acetic acid was heated to 90 C for 4 h under 20 bar oxygen
pressure without any catalyst in a 100 mL Teflon-lined
autoclave. Analysis of the products showed that 48.5% HMF
disappeared, and only 6.7% MA yield was obtained, with DFF
yield of 1.2% observed (Table 1, entry 1). (The detailed
experimental procedure and analytical methods are provided
in the supporting information). Traditionally, vanadium oxide,
such as V2O5 and VO(acac)2 are applied as heterogeneous or
homogeneous catalyst in aerobic oxidation of HMF into MA.25,
40
In this work, V2O5 (entry 2) and VO(acac)2 (entry 3) are also
tested under same reaction conditions above mentioned, and
HMF conversion increased to 98.1% and 99.8%, with MA yield
up to 44.0% and 59.0% achieved, implying the effectiveness of
the vanadium oxide in catalytic oxidation of HMF into MA.
Traditional catalyst support (such Al2O3, SiO2) are often
selected to immobilize and disperse the noble or transition
metal component, enhancing the efficiency and recyclable of
the metal catalyst. For comparison, 100 mg 10 wt% V2O5/SiO2
prepared by incipient wetness impregnation method was
tested, nearly full HMF conversion and an increased MA yield
of 64.5% was observed (entry 3). It is reported that it is the
high dispersion of V2O5 on SiO2 at low V2O5 loading, and the
interaction between V2O5 and SiO2 induced the distortion of
the V2O5 crystals as well as the changes in the valence and
coordination states of surface V atoms that are responsible for
the enhanced activity of SiO2 supported V2O5.40 When VO-NH2-
GO was applied into this reaction under the same reaction
conditions, nearly full HMF conversion and up to 95.3% yield of
MA was obtained. The site-time-yield (STY; expressed as the
amount of MA (mmol) that converted from HMF catalyzed by
V (mmol) in various catalyst per hour) was calculated and
applied to compare the effectiveness of various V-based
catalyst. V2O5 and VO(acac)2 showed a lower STY values (entry
2, 3), while STY increased from 2.0 h-1 to 2.9 h-1 after the V2O5
was supported on SiO2. Remarkably, the STY for VO-NH2-GO
increased to a high value of 148.9 h-1, demonstrating VO-NH2-
GO is a high effective catalyst for the aerobic oxidation of HMF
into MA.
restricted on GO surface due to the steric hindrance, similar
results were reported in literature.35,
36
FT-IR spectrum
presented in Figure S2 show the vibrational assessments of GO
(a), NH2-GO (b), VO-NH2-GO (c), and recycled VO-NH2-GO (d).
The strong bands at 1717, 1254 and 1060 cm-1 are attributed
to the stretching modes of C=O, C-OH and C-O-C, respectively,
revealing the presence of carboxyl, hydroxyl, and epoxy groups
in pure GO. In addition, a broad peak at 3432 cm-1 is attributed
to the stretching mode of O-H bonds, revealing the presence
of many hydroxyl groups. However, the O-H can be derived
from GO material and also adsorbed water. Considering the
XRD results and oxygen content in GO, functionalized NH2-GO
and VO-NH2-GO, it is deduced that the peak at 3432 cm-1 in GO
(a) involves the hydroxyl groups in GO plane, while the peaks
at 3432 cm-1 in NH2-GO(b) and VO-NH2-GO (c) mainly was
caused by adsorbed water from atmosphere during
characterization. The peak at 1600 cm-1 is attributed to the
C=C stretching of sp2-bonded carbons in the GO.36 The FTIR
spectrum of NH2-GO (b) exhibit an enhanced doublet at 2850
cm-1 and 2917 cm-1, corresponding to the symmetric and
asymmetric CH2 of the alkyl chains assigned to the silane
moieties of APTES, and confirm the successful grafting of the
aminosilane moieties onto the GO support. Moreover, the
appearance of the bands at 1127 cm-1 , 1033 cm-1 , and 1577
cm-1 due to Si-O-Si, Si-O-C, and C-N vibration respectively,36
provide more evidence for the successful chemical
functionalization.
To determine whether the residual oxygen groups in VO-NH2-
GO was directly oxidizing the HMF or functioning just as a
catalyst with pressured oxygen as the terminal oxidant,32, 43
the aforementioned oxidant reaction was performed under an
continually decreased pressure of oxygen. After 4 hours at 90
oC, analysis found that the HMF conversion and MA yield
decreased continually with the oxygen pressure (entry 5-9)
When the reaction was conducted under N2 atmosphere at 90
oC for 4 h, analysis of the reaction mixture found the HMF
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Table 1 HMF oxidation over homogeneous or heterogeneous vanadium-based catalysta
Entry
Cat.
PO2 (bar)
Conv. (%)
Yield
(MA+HMA)b
STYc
DFF
1.2
0
1
2
------
20
20
20
20
20
15
10
5
48.5
99.1
99.8
99.8
99.8
89.5
75.1
60.3
41.8
17.9
46.2
48.9
6.7
48.3 (1:5.8)
55.2 (1:3.8)
64.5 (1:4.2)
95.3 (1:2.5)
71.5
---
2.2
7.3
2.9
148.9
---
V2O5
3
VO(acac)2
(10%) V2O5/SiO2
VO-NH2-GO
VO-NH2-GO
VO-NH2-GO
VO-NH2-GO
VO-NH2-GO
VO-NH2-GO
GO
2.3
1.6
2.4
2.6
5.0
2.1
3.8
0
4d
5
6
7
52.9
---
8
45.3
---
9
1
16.2
---
10
11
12
N2
20
20
0
---
9.5
2.0
1.8
---
NH2-GO
8.9
---
a Reaction conditions: HMF 252.2 mg (2.0 mmol); acetic acid 10.0 mL; catalyst 10.0 mg; 90 oC; 4 h.
b The yield includes maleic anhydride (MA) and hydrolyzed maleic anhydride (HMA) in reaction mixture. The data in the bracket
indicates the ratio of maleic anhydride to maleic acid determined by NMR analysis.
c
The site-time-yield was calculated as the amount of MA (mmol) that converted from HMF catalyzed by V (mmol) in various
catalyst per hour (h-1, excluding the amount of MA produced without catalyst).
d 100 mg 10% V2O5/SiO2 was used.
conversion decreased to 17.9%, and no MA or DFF was was the dominant product. The ratio of maleic anhydride and
observed (entry 10). For underscoring the importance of maleic acid was around 1:2~1:6, due to the inevitable
vanadium-oxo, the aforementioned reaction was conducted in produced water in reaction or absorbed water from
o
the presence of GO or NH2-GO, after 4 hours at 90 C, the GO atmosphere during experiment (Table 1, entry 2-5, supporting
or NH2-GO provide HMF conversion of 46.2% and 48.9%, information 1.4).
respectively (entry 11, 12), similar to the results without any
Above experiments demonstrate the grafted vanadium-oxo
catalyst (entry 1), and the MA yield also had no obvious
was the active sites in the aerobic oxidation of HMF. In our
increase compared with entry 1. During the catalyst tests, DFF
previous work, it is found the oxygen-containing groups in
was observed as the main by-products in a yield range from ca.
graphene oxide had an obvious affinity to polar reactant, such
0-5%, and no HMFCA, FFCA or FDCA was observed. Formic acid
as fructose, HMF29, furfural alcohol and levulinic acid30, and
was detected as the accompanied product by NMR while the
thus facilitated the catalytic reaction by maintaining a high
cleavage of the C-C bond between the hydroxymethyl group
reactant concentration around the catalyst. It can be deduced
and furan sketch of HMF over V-based catalyst (supporting
that the residual oxygen-containing groups in VO-NH2-GO are
information 1.4).24 On another side, the analysis of the gas
responsible for the high efficiency of the catalytic oxidation. To
mixture after reaction by GC found about 0.5% CO and 2.0%
verify this hypothesis, affinities of different catalyst to HMF
CO2 existed (not shown in Table 1), indicating the
were evaluated by adsorption experiments (supporting
decarbonylation of the intermediates during the reaction.22, 24
information Table S3). It is found that the adsorption of HMF
Over different V-based catalyst, the distribution of maleic
on GO was the highest, the HMF concentration in acetic acid
anhydride and maleic acid in reaction mixture was determined
by NMR right after the reaction, and results found maleic acid
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Table 2 HMF oxidation over VO-NH2-GO in different solventsa
Entry
Solvent
Conv.
(%)
Yield (%)
MAb
95.3
1.4
DFF
4.4
0.2
0
1
2
3
4
5
6
7
8
AcOH
CH3CN
EtOH
99.8
5.0
7.8
3.8
DMSO
Formic acid
H2O
9.9
2.0
0
100
99.8
96.4
97.7
0.4
0
29.2
35.3
23.8
4.2
2.8
7.3
MIBK
Toluene
a Reaction conditions: HMF 252.2 mg (2.0 mmol); acetic acid 10.0 mL; catalyst 10.0 mg; 90 oC; 4 h; O2, 20 bar.
b The yield includes un-hydrolyzed maleic anhydride and hydrolyzed maleic anhydride in reaction mixture.
decreased about 18.0% (R=18%, Table S3, entry 1-2), the Schiff entry 5). The solvents, such as water, MIBK, and toluene gave
base modification and vanadium-oxo immobilization make the nearly full HMF conversion and moderate MA yield around 25-
GO partially reduced and the adsorption of HMF on the VO- 35% with DFF yield around 3-7% (Table 2, entry 6-8). Above all,
NH2-GO had a slight decrease (R=14.5%, Table S3, entry 2-3). acetic acid showed significant different behavior in HMF
However, the adsorption of HMF on graphene (thermal aerobic oxidation over VO-NH2-GO.
reduced graphene oxide, ca. 2 wt% oxygen content) decreased
sharply (R=6.2% Table S3, entry 4), indicating the oxygen-
Kinetic analysis of catalytic oxidation of HMF over V-based catalyst
containing groups in GO should account for the adsorption of
To explore the kinetic behavior of HMF oxidation, the product
yield as a function of reaction time over VO-NH2-GO is
displayed in Figure 1.
HMF on the graphene based material. The V2O5/SiO2 and V2O5
showed a relative low adsorption of HMF (R= 3.8% and 7.5%
respectively, Table S3, entry 4-5), compared with GO and VO-
NH2-GO. Clearly, it was reasonable to infer that the superior
performance of VO-NH2-GO in HMF catalytic oxidation could
be ascribed to the synergistic effect of the grafted vanadium-
oxo and residual oxygen-containing groups in modified GO
material.
100
80
CHMF
YMA
60
YDFF
Effect of reaction solvents on HMF oxidation reaction
40
The reaction solvents affect the oxidation significantly, various
solvents were tested and the results are summarized in Table 2.
The highest MA yield was obtained in acetic acid (Table 2,
entry 1). Acetonitrile gave a relative high HMF conversion and
20
0
25
MA yield over homogeneous V-containing catalyst,24,
0
1
2
3
4
5
6
however, rather low HMF conversion and MA yield were
achieved over current catalytic system (Table 2, entry 2).
Similar results were obtained in ethanol and DMSO (Table 2,
entry 3-4). Due to the strong acid properties of formic acid,
HMF was fully decomposed, negligible MA or DFF was
observed under current conditions in formic acid. (Table 2,
Reaction time (h)
Figure 1. Reaction kinetics of HMF oxidation over VO-NH2-GO.
Reaction condition: HMF 252.2 mg (2.0 mmol); acetic acid 10.0
o
mL; VO-NH2-GO, 10 mg; 90 C; O2 20 bar. The yield of MA in
graph involves maleic anhydride and maleic acid.
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Recyclability of VO-NH2-GO in catalytic oxidation of HMF and
furfural
The HMF converted quickly increased to above 90% after only
30 min. The MA yield also increased quickly to 80.6% in 30 min
and DFF was observed as the only by-product during reaction.
With reaction time prolonged, the HMF conversion increased
to nearly 100% and the highest MA yield of 95.3% was
obtained in 4 h. The DFF yield showed a relative low yield
around 0-3% during the reaction. The kinetic analysis of HMF
oxidation over V2O5 and VO(acac)2 was provided in Figure S4
and Figure S5 in supporting information. In the presence of
V2O5 (Figure S4), the HMF conversion and MA yield increased
with reaction time prolonged, nearly full HMF conversion was
achieved in 2 h and the highest MA yield of 48.3% was
achieved in 6 h. No DFF was observed in V2O5 catalytic system.
VO(acac)2 provided the full HMF conversion in 2.5 h, and
highest MA yield of 55.2% was achieved in 4 h. In VO(acac)2
catalytic system, DFF was observed as the main by-products in
a yield range of ca. 1.5%~2.5%.
The recyclability of VO-NH2-GO in aerobic oxidation of HMF
and furfural was tested (Figure S6, Figure S7, supporting
information). Considering the high catalytic efficiency of the
catalyst in oxidation of HMF, that, nearly full HMF conversion
and 95% MA yield were achieved in 1.5 h, the reaction time in
each cycle in recyclability test was fixed at 2 h and 5 mg VO-
NH2-GO was used to avoid the excess of catalyst in long
reaction time. Similarly, the reaction time was fixed at 2 h in
catalyst cycle test in oxidation of furfural, with 10 mg VO-NH2-
GO was used.
As shown in Figure S6, 62.1% HMF conversion with 48.8% MA
yield was achieved under the selected reaction conditions. In
Figure S7, 54.4% furfural conversion with 35.2% MA yield was
achieved in first cycle. Slight decrease was observed in first
three cycles in catalyst recyclability test in catalytic oxidation
of both HMF and furfural, however, the catalytic activity
showed an obvious decrease in the fourth and fifth cycles.
Elemental analysis shows 0.32 mmol g-1 V was immobilized
onto GO in fresh catalyst and the V content dropped to 0.30
mmol g-1 V after 5 cycles in HMF oxidation, and 0.27 mmol g-1
V after 5 cycles in furfural oxidation (Table S2). Besides,
catalyst deactivation from coking can not be excluded,
especially in aerobic oxidation of furfural, which is not very
stable because of its polymerization when exposed to
oxygen.22
Oxidation of Furfural into maleic anhydride over VO-NH2-GO
Compared with unsupported or traditional supported V based
catalysts, the prepared VO-NH2-GO shows remarkable
improvement in catalytic transformation of HMF into MA. To
explore the catalytic activity of VO-NH2-GO, synthesis of MA
with furfural as substrate under above mentioned reaction
conditions was operated. As shown in Figure 2, both of furfural
conversion and MA yield increased with the extending of the
reaction time. 82.1% furfural conversion with the highest MA
yield of 62.4% was achieved at a reaction time of 8 h. Furfural
shows lower reactivity than HMF in oxidation reaction into MA,
much longer reaction time (18 h) is needed for the full furfural
conversion. However, the MA yield decreased beyond 8 h and
decreased to 60.9% when furfural transformed completely. No
other by-products was detected, it is speculated that the
furfural polymerization under oxygen atmosphere decreased
the MA selectivity.22
Conclusions
Vanadium oxo has been homogeneously immobilized on a
Schiff base modified graphene oxide support via covalent
bonding. The developed heterogeneous catalyst is found to be
efficient for the aerobic oxidation of HMF and furfural into MA,
with high MA selectivity obtained. The high efficiency of VO-
NH2-GO was attributed to the synergistic effect of active sites
of vanadium-oxo and residual oxygen-containing group
adsorption of reactant onto the catalyst surface. Acetic acid
was demonstrated to be an outstanding solvent for the
preparation of MA from HMF and furfural oxidation reaction
100
CFurfural
YMA
80
60
40
20
0
over VO-NH2-GO. As
a new developed and remarkable
material, graphene oxide is showing more potential in catalyst
utilization.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (NNSFC) (Grant 21403273), the
National Key Basic Research Program of China (No.
2012CB215305), and Science Foundation of Shanxi Province
(2013011010-6).
0
4
8
12
16
20
Reaction time (h)
Figure 2. Reaction kinetics of furfural oxidation over VO-NH2-
GO. Reaction condition: furfural 192.2 mg (2.0 mmol); acetic
acid 10.0 mL; VO-NH2-GO, 10 mg; 90 oC; O2 20 bar. The yield of
MA in graph involves maleic anhydride and maleic acid.
References
6 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
1. O. O. James, S. Maity, L. A. Usman, K. O. Ajanaku, O. O. Ajani, T.
21. X. Wan, C. Zhou, J. Chen, W. Deng, Q. Zhang, Y. Yang and Y.
O. Siyanbola, S. Sahu and R. Chaubey, Energ. Environ. Sci., 2010, 3,
Wang, ACS Catal., 2014, 4, 2175-2185.
22. J. Lan, Z. Chen, J. Lin and G. Yin, Green Chem., 2014, 16, 4351-
4358.
1833-1850.
2. G. W. Huber, S. Iborra and A. Corma, Chem.Rev., 2006, 106, 4044-
4098.
23. X. Li, B. Ho and Y. Zhang, Green Chem., 2016, 18, 2976-2980.
3.J. Q. Bond, A. A. Upadhye, H. Olcay, G. A. Tompsett, J. Jae, R. Xing, 24. J. Lan, J. Lin, Z. Chen and G. Yin, ACS Catal., 2015, 5, 2035-2041.
D. M. Alonso, D. Wang, T. Zhang, R. Kumar, A. Foster, S. M. Sen, C. 25. Z. Du, J. Ma, F. Wang, J. Liu and J. Xu, Green Chem., 2011, 13,
T. Maravelias, R. Malina, S. R. H. Barrett, R. Lobo, C. E. Wyman, J.
A. Dumesic and G. W. Huber, Energ. Environ. Sci., 2014, 7, 1500-
1523.
554-557.
26. J. Pyun, Angew. Chem. Int. Ed., 2011, 50, 46-48.
27. C. Huang, C. Li and G. Shi, Energ. Environ. Sci., 2012, 5, 8848-
8868.
4. M. Besson, P. Gallezot and C. Pinel, Chem. Rev., 2014, 114, 1827-
1870.
28.S. Chenliang and K. P. Loh, Acc. Chem. Res., 2013, 46, 2275-2285.
29. W. Sun and Y. Wang, Nanoscale, 2014, 6, 11528-11552.
30. S. Zhu, C. Chen, Y. Xue, J. Wu, J. Wang and W. Fan,
ChemCatChem, 2014, 6, 3080-3083.
5. B. R. Caes, M. J. Palte and R. T. Raines, Chem. Sci., 2013, 4, 196-
199.
6. A. Corma, S. Iborra and A. Velty, Chem.Rev., 2007, 107, 2411-
2502.
31. C. Su, M. Acik, K. Takai, J. Lu, S. J. Hao, Y. Zheng, P. Wu, Q. Bao, T.
Enoki, Y. J. Chabal and K. P. Loh, Nat. Commun., 2012, 3, 1298-
1307.
7. D. R. Dodds and R. A. Gross, science, 2007, 318, 150-1251.
8. C. M. Cai, T. Zhang, R. Kumar and C. E. Wyman, J. Chem. Technol.
Biotechnol., 2014, 89, 2-10.
32.D. R. Dreyer, H. P. Jia and C. W. Bielawski, Angew. Chem. Int. Ed.,
2010, 49, 6813-6816.
9. J. Carlos Serrano-Ruiz and J. A. Dumesic, Green Chem., 2009, 11,
1101-1104.
33. D. Deng, K. S. Novoselov, Q. Fu, N. Zheng, Z. Tian and X. Bao,
Nat. Nanotechnol., 2016, 11, 218-230.
10. P. Gallezot, Chem. Soc. Rev., 2012, 41, 1538-1558.
11. F. Jin and H. Enomoto, Energ. Environ. Sci., 2011, 4, 382-397.
12.M. M. Antunes, P. A. Russo, P. V. Wiper, J. M. Veiga, M. Pillinger,
L. Mafra, D. V. Evtuguin, N. Pinna and A. A. Valente,
ChemSusChem, 2014, 7, 804-812.
34. P. K. Khatri, S. Choudhary, R. Singh, S. L. Jain and O. P. Khatri,
Dalton Trans., 2014, 43, 8054-8061.
35. H. P. Mungse, S. Verma, N. Kumar, B. Sain and O. P. Khatri, J.
Mater. Chem., 2012, 22, 5427-5433.
36. S. Verma, M. Aila, S. Kaul and S. L. Jain, RSC Adv., 2014, 4,
30598-30604.
13. M. Balakrishnan, E. R. Sacia and A. T. Bell, Green Chem., 2012,
14, 1626-1634.
37. H. Su, Z. Li, Q. Huo, J. Guan and Q. Kan, RSC Adv., 2014, 4, 9990-
9996.
14. J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem. Int.
Ed., 2007, 46, 7164-7183.
38. H. Guo and G. Yin, J. Phys. Chem. C, 2011, 115, 17516-17522.
39. S. Shi, H. Guo and G. Yin, Catal. Commun., 2011, 12, 731-733.
40. X. Li and Y. Zhang, Green Chem., 2016, 18, 643-647.
41. N. Alonso-Fagundez, M. L. Granados, R. Mariscal and M. Ojeda,
ChemSusChem, 2012, 5, 1984-1990.
15. J. P. Lange, E. van der Heide, J. van Buijtenen and R. Price,
ChemSusChem, 2012, 5, 150-166.
16. T. S. Hansen, I. Sádaba, E. J. García-Suárez and A. Riisager, Appl.
Catal., A, 2013, 456, 44-50.
17. J. Nie, J. Xie and H. Liu, J. Catal., 2013, 301, 83-91.
18. A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and C. A. M.
Afonso, Green Chem., 2011, 13, 754-793.
42. H.-J. Shin, K. K. Kim, A. Benayad, S.-M. Yoon, H. K. Park, I.-S. Jung,
M. H. Jin, H.-K. Jeong, J. M. Kim, J.-Y. Choi and Y. H. Lee, Adv.
Funct. Mater., 2009, 19, 1987-1992.
19. B. Saha, D. Gupta, M. M. Abu-Omar, A. Modak and A. Bhaumik,
J. Catal, 2013, 299, 316-320.
43. G. Lv, H. Wang, Y. Yang, T. Deng, C. Chen, Y. Zhu and X. Hou, ACS
Catalysis, 2015, 5, 5636-5646.
20. A. Takagaki, M. Takahashi, S. Nishimura and K. Ebitani, ACS
Catal., 2011, 1, 1562-1565.
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