Magnetic Co3O4/reduced graphene oxide nanocomposite as a superior heterogeneous catalyst for one-pot oxidative esterification of aldehydes to methyl esters

Article abstract of DOI:10.1039/c5ra14665h

A magnetically separable hybrid material consisting of Co₃O₄ nanoparticles supported on reduced graphene oxide (Co₃O₄/rGO) was synthesized through a simple co-reduction process of graphene oxide (GO) and cobalt chloride (CoCl₂) using sodium borohydride (NaBH₄). The Co₃O₄/rGO heterogeneous catalyst exhibited a high-performance for the oxidative esterification of aldehydes to the corresponding methyl esters using tert-butyl hydroperoxide (TBHP) as an oxidant. Owing to the synergistic effect of rGO support, the hybrid catalyst exhibited superior catalytic activity to the corresponding cobalt oxide catalyst. Importantly, the synthesized hybrid possesses good magnetic properties, which enable facile recovery of the catalyst by using an external magnet.

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Magnetic Co3O4/reduced graphene oxide nanocomposite as
superior heterogeneous catalyst for one-pot oxidative
esterification of aldehydes to methyl esters
Received 00th January 20xx,
Accepted 00th January 20xx
Vineeta Panwar,a Amer Al-Nafiey,b,c Ahmed Addad,c Brigitte Sieber,c Pascal Rousseld, Rabah
Boukherroubb* and Suman L. Jaina*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A magnetically separable hybrid material consisting of Co3O4 nanoparticles supported on reduced graphene oxide
(Co3O4/rGO) was synthesized through a simple co-reduction process of graphene oxide (GO) and cobalt chloride (CoCl2)
using sodium borohydride (NaBH4). The Co3O4/rGO heterogeneous catalyst exhibited a high-performance for the oxidative
esterification of aldehydes to the corresponding methyl esters using tert-butylhydroperoxide (TBHP) as an oxidant. Owing
to the synergistic effect of rGO support, the hybrid catalyst exhibited superior catalytic activity than the corresponding
cobalt oxide catalyst. Importantly, the synthesized hybrid possesses good magnetic properties, which provide the facile
recovery of the catalyst by using external magnet.
Introduction
graphene provides a better dispersion of the NPs and thus
Graphene oxide (GO), derived from the exfoliation of graphite
oxide possesses several fascinating features such as large
surface area, as well as good electrical, thermal, and
mechanical properties.1,2 Owing to these outstanding
properties, graphene has been considered to be a promising
candidate for the synthesis of composite materials by
combining it with various nanoparticles (NPs).3,4 The
immobilization of nanoparticles, such as Fe3O4, MnO2, TiO2,
Co3O4, and Au onto graphene sheets provided hybrid materials
with special features suitable for use in various applications,
including catalysis,5,6 supercapacitors,7,8 and biotechnology.9
These hybrid materials are well known to show higher stability
as well as improved catalytic activity than the individual
components due to the strong synergistic interaction between
both components. Owing to their low cost and high
electrochemical stability, cobalt and cobalt oxide NPs have
widely been used for various practical applications including
biomedical10 and catalysis.11-14 However, pure Co3O4 NPs have
represents an effective approach to improve the catalytic
activity as well as durability.
The direct synthesis of esters from the oxidation of
aldehydes or alcohols is an important transformation in
organic synthesis as these compounds find extensive
applications in the synthesis of several natural and bioactive
products.16 The conventional approach for the synthesis of
esters involves the reaction of carboxylic acids or their
derivatives (acyl chlorides and anhydrides) with alcohols,17-18
which is a multistep process and often leads to the formation
of large amounts of undesired byproducts. In the recent years,
direct catalytic transformation of aldehydes or alcohols to
esters,19-22 without the use of the corresponding acid or acid-
derivative has gained considerable interest. In this context, a
number of metal free23 and metal based catalysts24 for
oxidative esterification of aldehydes to the corresponding
esters have been reported in the literature. Among the
reported systems heterogeneous catalysts are preferred due
to their facile recovery, less contamination of the product and
efficient recyclability. However, most of the reported
heterogeneous catalysts such as gold nanoparticles supported
on Ce-Zr oxides,24b magnetic gold nanoparticles,24d gold-nickel
nanoparticles,24f alumina supported palladium catalyst24g etc
are based on the expensive metals such as gold and palladium
and involve the tedious multi-step synthetic procedures.
Herein, we report for the first time a highly efficient and
reusable hybrid i.e Co3O4/rGO nanocomposite as catalyst for
direct oxidation of aldehydes to esters using tert-butyl
hydroperoxide (TBHP) as oxidant (Scheme 1). In comparison to
the known methods, the developed methodology has several
a
tendency to aggregate; the aggregation is generally
accompanied by the decrease of their surface area and their
catalytic activity.15 Therefore, the synthesis of hybrid materials
by combining these NPs with carbon materials such as
a.Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun-248005
(India) *Email: suman@iip.res.in; Tel: 91-135-2525788; Fax: 91-135-2660202
b.Institut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN, CNRS-
8520), Cité Scientifique, Avenue Poincaré – B.P. 60069, 59652 Villeneuve d’Ascq,
France, E-mail : rabah.boukherroub@iemn.univ-lille1.fr
c.Unité Matériaux et Transformations, UMR CNRS 8207, Université Lille 1, 59655
Villeneuve d’Ascq, France
d.Unité de Catalyse et Chimie du Solide, UMR CNRS 8181, Université Lille 1, 59655
Villeneuve d’Ascq, France
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advantages such as the use of a low cost metal, shorter General experimental procedure for oxidative esterification
reaction times and excellent product yields. Furthermore, the of aldehydes
synergestic effect of rGO support has been observed in the Aldehyde (1 mmol), K2CO3 (0.1 mmol), methanol (2 mL), TBHP
hybrid Co3O4/rGO catalyst which exhibited superior catalytic (1.8 mmol, 0.25 mL of a 70% aqueous solution) and Co3O4/rGO
activity than the corresponding cobalt oxide. Furthermore, catalyst (25 mg, 2.5 mol % Co) were mixed together in a round
good magnetization of the synthesized hybrid allowed it to be bottomed flask. The reaction mixture was heated in an oil bath
readily separated from the reaction mixture by using external at 60 °C for 6 h with constant stirring. The progress of the
magnet.
reaction was monitored by TLC. After completion of the
reaction, the catalyst was recovered by filtration and the
mixture was extracted with ethyl acetate. Removal of the
solvent under vacuum afforded the crude product, which was
purified by column chromatography using a hexane/ethyl
acetate mixture, and was analyzed by GC and GC-MS. The
recovered catalyst was washed with methanol, dried at 60 °C
and was reused for recycling experiments.
O
O
Co3O4/rGO, 600C
H
OCH3
+
CH3OH
R
R
TBHP, 0.1 mmol K2CO3
Scheme 1: Oxidative esterification of aldehydes
Experimental
Sample characterization
Materials
Transmission electron microscopy (TEM) imaging was
performed with a Philips CM30 microscope operating at 300
kV. It was equipped with a Gatan SS CCD camera and a Digital
Micrograph software for the acquisition of bright-field and
All chemicals were reagent grade or higher and were used as
received unless otherwise specified. Graphite powder (< 20
micron), potassium permanganate (KMnO4), sulphuric acid
(H2SO4), phosphoric acid (H3PO4), hydrogen peroxide (H2O2),
cobalt chloride (CoCl2), sodium borohydride (NaBH4),
potassium carbonate (K2CO3), hexane, ethyl acetate, methanol,
ethanol and tert-butyl hydroperoxide (TBHP) were purchased
from Sigma-Aldrich. Silicon wafers were purchased from
Siltronics. The water used throughout the experiments was
purified with a Milli-Q system from Millipore Co. (resistivity =
18 MΩ.cm).
high-resolution
characterization of the Co3O4/rGO nanocomposite was carried
out on 9kW Rigaku Smartlab rotated anode X-ray
imaging
(HRTEM).
The
structural
a
diffractometer using Cu Kα (1.5406 °A) wavelength, operated
in Bragg-Brentano reflexion geometry. X-ray photoelectron
spectroscopy (XPS) measurements were performed with an
ESCALAB 220 XL spectrometer from Vacuum Generators
featuring a monochromatic Al Kα X-ray source (1486.6 eV) and
a spherical energy analyzer operated in the CAE (constant
analyzer energy) mode (CAE=100eV for survey spectra and
CAE=40eV for high-resolution spectra), using the
electromagnetic lens mode. The detection angle of the
photoelectrons is 30°, as referenced to the sample surface.
After subtraction of the Shirley-type background, the core-
level spectra were decomposed into their components with
mixed Gaussian-Lorentzian (30:70) shape lines using the
CasaXPS software. Quantification calculations were performed
using sensitivity factors supplied by PHI. The sample was
prepared by drop casting a concentrated ethanoic solution of
the nanocomposite onto a silicon wafer followed by oven
drying at 50 °C for 2 h. Thermogravimetric analysis (TGA)
measurements were carried out in Al2O3 crucibles in nitrogen
Preparation of graphene oxide (GO)
GO nanosheets were produced from natural graphite powder
by an improved Hummers and Offeman method. The detailed
experimental conditions are reported in a recently published
work.25 A homogeneous yellow brown suspension (1 mg mL-1)
of GO sheets in deionized water (DI) was achieved by
ultrasonication for 3 h.
Preparation of Co3O4/rGO catalyst
Co3O4/rGO nanocomposite was prepared by simultaneous
chemical reduction of GO and CoCl2 with sodium borohydride
(NaBH4). Typically, to 5 mL of GO (1 mg mL-1) in DI water,
sonicated for about 20 min to form
a homogeneous
dispersion, was added (50 mg) of CoCl2 and the mixture was
sonicated for 30 min. Then 5 mL of NaBH4 (0.1 M) aqueous
solution was added to the mixture at room temperature. A
spontaneous formation of a black precipitate was observed.
The precipitate was washed repeatedly with water and
separated by centrifugation. The percentage of cobalt in the
synthesized catalyst was found to be 26.4 % (1.5 mmol/g) as
determined by ICP-AES analysis.
atmosphere at
a heating rate of 30°C/min using a TA
Instruments Q50 thermogravimetric analyzer.
Results and discussion
Synthesis of Co3O4 nanoparticles
Synthesis and characterization of catalyst
For comparison, we have synthesized Co3O4 nanoparticles by
chemical reduction of CoCl2 with NaBH4. To an aqueous
solution of CoCl2 (50 mg) in 5 mL of DI was added 5 mL of
NaBH4 (0.1 M) aqueous solution at room temperature. The
precipitate was washed repeatedly with water and separated
by centrifugation.
A schematic of the synthesis of Co3O4/rGO nanocomposite
is shown in Scheme 2. For comparison Co3O4 NPs were
synthesized by direct reduction of CoCl2 with NaBH4.
2 | J. Name., 2012, 00, 1-3
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the Scherer formula for the two single peaks located at 59.35°
(511) and 65.23 (440).
4500
(311)
4000
3500
3000
2500
2000
(400)
(440)
(220)
1500
1000
500
0
(511)
25
35
45
55
65
75
2 teta (°)
Scheme 2: Schematic illustration of the synthesis of Co3O4/rGO nanocomposite.
Figure 2: XRD of Co3O4/rGO nanocomposite
The HR-TEM images of the synthesized Co3O4 NPs and
Co3O4/rGO nanocomposite are displayed in Figure 1. In case of
Co3O4 NPs, most of the nanoparticles of about 20 nm were
found to be agglomerated in the form of clusters. Only
nanoparticles located on the surface of the clusters could be
observed and were in the range of 2 to 4 nm. If the
nanoparticles self-agglomerate during the catalysis
experiment, it can be easily understood that their efficiency is
greatly reduced in comparison to that of nanoparticles
dispersed on rGO sheets. On the other hand, the HR-TEM
image of the Co3O4/rGO nanocomposite exhibits well
dispersed and well-textured Co3O4 NPs (Fig. 1b). It can be
clearly seen that small Co3O4 NPs are closely anchored on the
X-ray photoelectron spectroscopy (XPS) analysis also confirms
the formation of Co3O4/rGO nanocomposite. Figure 3a displays
the C1s core level XPS spectrum of GO nanosheets. It can be
deconvoluted into three components with binding energies at
about 284.9, 287.0 and 288.2 eV assigned to C-H/C-C, C-O and
C=O species, respectively. The spectrum is dominated by the
peak at 287.0 eV due to C-O, in accordance with a high
oxidation degree of GO. In contrast, the C1s high resolution XPS
spectrum of Co3O4/rGO nanocomposite showed a significant
decrease in the peak intensities associated with C-H/C-C, C-O
and C=O groups (Figure 3b). The spectrum is dominated by a
band with a binding energy at 283 eV due to sp2 carbon,
suggesting the restoration of the graphene network in the
synthesized hybrid composite.
graphene sheets surface, implying
a strong interaction
between graphene and Co3O4. The inter-planar distance
between adjacent planes is 0.47 nm, corresponding to the
interplanar spacing of (111) plane of Co3O4.26
The high resolution Co2p XPS spectrum of Co3O4/rGO exhibits
two peaks at 780 and 795 eV, corresponding to the Co2p1/2 and
Co2p3/2 spin-orbit peaks of Co3O4. The spectrum displays also
two shake-up satellite peaks of the Co2p3/2 and Co2p1/2 located
at around 784 and 801 eV with deviations from the main peaks
of 4 and 7 eV, respectively. The results suggest that cobalt
exists in the form of Co3O4, in good agreement with the
previously reported data.27-28
Figure 1. HRTEM images of a) Co3O4 NPs, b) Co3O4/rGO and c) SAED of Co3O4/rGO.
The XRD pattern of Co3O4/rGO displays diffraction peaks (2θ)
at 31.27°, 36.84°, 38.56°, 44.8°, 59.35°, 65.23°, 74.11°, 77.34°
and 78.4° which correspond to the (220), (311), (222),
(400),(511), (440), (620), (533) and (622) crystalline planes of
Co3O4 (ICDD file number 043-1003) (Figure 2). The crystallite
size (i.e. coherent domain size) was evaluated at 5 nm using
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104.4
100.8
97.2
93.6
90.0
86.4
82.8
1.0
0.5
0.0
-0.5
-1.0
GO/ C1s
C-O 287 ev
Mass chang : -11,73 %
C-C 284,9 ev
C=O 288 ev
-1.5
880
110
220
330
440
550
660
770
292
290
288
286
284
282
Binding Energy (ev)
Temp. Co
Figure 4: TG-DTA curve of Co3O4/rGO nanocomposite.
rGo-Co / C1s
sp2 283 ev
Figure 5 depicts the Raman spectra of Co3O4 NPs and
Co3O4/rGO hybrid. The Raman spectrum of the Co3O4/rGO
composite shows characteristic peaks of Co3O4 in the region of
500-700 cm-1 and characteristic peaks of the D and G bands
from graphene at around 1335 and 1600 cm-1, respectively.
The presence of these peaks clearly indicates the existence of
both rGO and Co3O4 in the as prepared hybrid. Furthermore,
the higher intensity of D band in the composite showed a
largely disordered structure of the obtained rGO. The loading
of cobalt in the synthesized hybrid was found to be 26.4 wt %
(1.5 mmol/g) as determined by ICP-AES analysis.
C-C 284,3 ev
C-O 286,2 ev
294
292
290
288
286
284
282
280
278
276
Binding energy (ev)
rGO-Co/ Co2p
Co
780 ev
2p1/2
Co
795 ev
2p3/2
Co
801 ev
2p3/2
Co
784 ev
2p1/2
810
805
800
795
790
785
780
775
770
Binding Energy (ev)
Figure 3: XPS analysis of Co3O4/rGO hybrid material C1s spectra of a) GO and b)
Figure 5: Raman spectra of Co3O4 and Co3O4/rGO
Co3O4/rGO; c) Co2p of Co3O4/rGO.
Catalytic activity
The thermal properties of Co3O4/rGO nanocomposite were
investigated using thermogravimetric analysis (TGA). Figure 4
shows a weight loss of ~3% below 100 °C due to the
evaporation of adsorbed water molecules. Then, a weight loss
of ~9% occurred between 100 and 320 °C, which can be
assigned to the removal of the labile oxygen-containing
functional groups such as CO, CO2, and H2O within the
nanocomposite. Correspondingly, the DTG curve displays a
strong exothermal peak centred at 320 °C, and abrupt weight
loss of 11.73%. The weight loss is usually attributed to the loss
of the residual (or adsorbed) solvent and to the decomposition
of residual organic functional groups on the graphene sheets.
From 320 to 900 °C, the Co3O4/rGO nanocomposite exhibits
much higher thermal stability.
The catalytic activity of the synthesized Co3O4/rGO catalyst
was tested for the oxidative esterification of benzaldehyde
with methanol to give methyl benzoate. Typically, the model
reaction was performed at 60 °C using THBP (70 wt % aq.
solution) as an oxidant in the presence of catalytic amount of
K2CO3 as base (0.1 mmol) for 6 h. The results of the
optimization experiments are summarized in Table 1. In the
absence of catalyst under similar conditions, no conversion of
benzaldehyde was observed (Table 1, entry 1). Similarly, no
reaction occurred when reduced graphene oxide (rGO) was
used as a catalyst under similar reaction conditions (Table 1,
entry 2). In order to compare the activity of hybrid Co3O4/rGO
catalyst, the oxidation of benzaldehyde was performed using
bare Co3O4 nanoparticles under otherwise identical reaction
4 | J. Name., 2012, 00, 1-3
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Table 1: Results of the optimization experimentsa
conditions. The reaction was found to be slow and gave poor
yield of the product (Table 1, entry 3). Furthermore, the
reaction was performed with other metal oxides such as Fe3O4,
MnO2, and TiO2 and their rGO composites under described
experimental conditions. The results of these experiments are
summarized in Table 1 (entries 4-9). Among all the metal
oxides and their rGO composites, only Fe3O4 and Fe3O4/rGO
gave corresponding methyl ester in moderate yield (Table 1,
entries 4,7). Other metal oxides such as MnO2 and TiO2 and
their rGO composites yielded the corresponding acid
selectively in moderate yields (Table 1, entries 5,6,8,9). The
reaction of benzaldehyde with TBHP in the presence of
Entry
Catalyst
Oxidant Time
Base
Conv.
(%)b
1
2
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
O2
12
10
6
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0
-
-
rGO
3
56
Co3O4
4
6
62
Fe3O4
5
6
50d
35d
70
MnO2
6
6
TiO2
o
Co3O4/rGO catalyst was very slow at room temperature; 60 C
7
6
Fe3O4/rGO
MnO2/rGO
TiO2/rGO
was found to be the optimum temperature for this organic
transformation. Further increase of temperature to 80 °C
showed only marginal enhancement in the yield of the final
product under similar reaction conditions (Table 1, entry 10).
Furthermore, the same reaction was performed with other
oxidants such as molecular oxygen and hydrogen peroxide
(H2O2) in place of TBHP. The reaction was found to be very
slow with molecular oxygen and afforded poor product yield
(Table 1, entry 11) in longer reaction time (24 h). In the case of
H2O2 under otherwise similar reaction conditions, moderate
yield of the desired product was obtained (Table 1, entry 12).
The presence of a base was of prime importance as in its
absence the reaction gave only 30 % conversion after 72 h
under described reaction conditions (Table 1, entry 13). Finally
to demonstrate the effectiveness of the base, we performed
the reaction using different bases like KOH, K3PO4, Na2CO3 and
K2CO3 (Table 1, entries 14-16). Among the various bases
studied, K2CO3 proved to be optimum and gave the best
results for this reaction (Table 1, entry 10). Furthermore, we
checked the catalytic activity of the GO, physical mixture of GO
and Co3O4 NPs and rGO/Co3O4 under identical experimental
conditions (Table 1, entries 17-19). In case of GO, the
corresponding acid was obtained as the sole product, whereas
mixtures of GO and rGO with Co3O4 NPs yielded poor yield of
the corresponding methyl ester along with the acid as by-
product. These results confirmed the synergistic effect of the
rGO support in enhancing the reaction rate as well as
selectivity for the desired product.
8
6
52d
48d
93, 95c
25
9
6
10
11
12
6
Co3O4/rGO
Co3O4/rGO
24
Co3O4/rGO
H2O2
10
48
72
85
12e
30e
-
13
14
15
16
17
18
19
Co3O4/rGO
Co3O4/rGO
Co3O4/rGO
Co3O4/rGO
GO
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
-
6
6
6
6
6
6
KOH
Na2CO3
K3PO4
K2CO3
K2CO3
K2CO3
70
85
75
72d
GO+Co3O4
rGO+Co3O4
50, 20d
35, 15d
aReaction conditions: benzaldehyde (1 mmol), CH3OH (2 mL), base (0.1 mmol),
catalyst (5 mol % Co, 20 mg) and oxidant (1.5 mmol) at 60 °C; bdetermind by GC-
MS; ctemperature at 80 °C; dacid is the product; ein the absence of base K2CO3
After having demonstrated the excellent activity of Co3O4/rGO
in the model reaction, a wide range of aldehydes containing
electron donating as well as withdrawing groups were oxidized
under described experimental conditions. The results of these
experiments are summarized in Table 2. All the substrates
were smoothly oxidized to give the desired product with good
to excellent yields. In general, aromatic aldehydes substituted
with electron-withdrawing groups were found to be more
reactive and afforded desired products with good to excellent
yields (Table 2, entries 2-8) than those containing electron
donating groups (Table 2, entries 8-12). Under the optimized
experimental conditions, aliphatic aldehydes gave moderate to
high yield of the desired product (Table 2, entries 13-14).
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Table 2: Co3O4/rGO catalyzed oxidative esterification of aldehydes with methanola
shown in Table 3, all the reported methods required
comparatively longer reaction time, higher temperature and
afforded moderate product yield.
Conv.
(%)b
Yield
(%)c
Entry
1
Reactant
Product
O
O
93
85
88
89
87
91
83
85
86
84
Table 3: Comparison of the catalytic activity of Co3O4/rGO with state of the art
H
OCH3
methods
CHO
COOCH3
O
O
Catalyst
H
OCH3
2
3
4
MeOH, TBHP
Br
Br
O
Entry
Catalyst
Time
/h
Temp.
/ oC
80
Yield
Ref.
O
(%)
86
85
78
91
OCH3
H
Cl
1
2
3
4
B(C6F5)3
CuF2
KI
18
23d
29
Cl
24
120
65
O
O
17
30
H
OCH3
Cu(ClO4)2.6H2
O InBr3
16
80
31
O2
N
O2
N
5
6
Ti-superoxide
Co3O4/rGO
10
6
90
60
82
93
32
O
O
This
work
H
OCH3
5
Br
Br
Next, we have checked the recycling of the catalyst by using
benzaldehyde as a model substrate. After completion of the
reaction, the catalyst was easily recovered from reaction
mixture by using external magnet, washed with methanol and
then dried. The recovered catalyst was used for six subsequent
runs under similar reaction conditions. The results of recycling
experiments are summarized in Figure 6. The yield of the
desired product remained in all cases almost similar. This
confirmed that the developed catalyst was quite stable and
could be reused efficiently without any significant loss in
activity. Furthermore, the cobalt content in the recovered
catalyst after six runs was found to be almost similar (26.36
wt.%) as in the fresh catalyst (26.4 wt.%) as determined by ICP-
AES analysis.
O
O
91
87
H
OCH3
6
7
Br
Br
O
O
90
78
72
88
70
75
H
OCH3
NO2
NO2
O
O
H
OCH3
8
HO
HO
O
O
H
OCH3
9
H3C
H3C
O
O
79
80
77
72
H
OCH3
10
11
H3CO
H3CO
O
O
H
OCH3
CH3
CH3
O
O
80
75
H
OCH3
12
OCH3
OCH3
O
O
Figure 6: Results of catalytic recycling experiments.
91
90
88
86
CHO
CHO
OCH3
13
14
Conclusion
OCH3
We have synthesized an efficient, stable and low cost cobalt
metal based hybrid Co3O4/rGO nanocomposite catalyst for the
one-pot oxidative methyl esterification of aldehydes using
aqueous TBHP as oxidant. We have shown the first successful
oxidative esterification methodology using TBHP as oxidant in
significantly shorter reaction times than those usually used.23d,
aReaction conditions: substrate (1.0 mmol), CH3OH (4 mL), K2CO3 (0.1 mmol),
catalyst (5 mol % ); bdetermined by GC-MS; cisolated yield
To establish the superiority of the developed catalyst, we
also compared the potential of Co3O4/rGO catalyst with the
state of the art systems using TBHP as oxidant (Table 3). As
29-32
The synergistic effect of rGO support was observed and
the hybrid catalyst exhibited superior catalytic activity than the
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We acknowledge Director, CSIR-Indian Institute of Petroleum (IIP) for
his kind permission to publish these results. VP thanks Council of
Scientific and Industrial Research (CSIR) for providing fellowship in the
form of Junior Research Fellowship (JRF). The Centre National de la
Recherche Scientifique (CNRS), Lille1 University and Nord Pas de Calais
region are acknowledged for financial support.
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29
Magnetic Co3O4/reduced graphene oxide nanocomposite as
superior heterogeneous catalyst for one-pot oxidative
esterification of aldehydes to methyl esters
O
OCH3
R
CH3OH
+
O
H
R
Co3O4/rGO
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