Co embedded within biomass-derived mesoporous N-doped carbon as an acid-resistant and chemoselective catalyst for transfer hydrodeoxygenation of biomass with formic acid

Article abstract of DOI:10.1039/c7gc02648j

An N-doped Co@C catalyst (Co@NC) is synthesized by a one-pot carbonization of biomass-derived glucose and harmless melamine with CoCl₂ as the catalyst, where C and N resources could be transformed into highly graphitic N-doped carbon, while the coordinated Co²⁺ ions are reduced to uniform Co nanoparticles (NPs), which are embedded in N-doped graphitic structures. Under base-free conditions with formic acid (FA) as a hydrogen donor, the optimized Co@NC-700 (pyrolyzed at 700 °C) shows a highly efficient H₂ generation from FA and the best activity for vanillin hydrodeoxygenation (HDO) with FA. For example, Co@NC-700 exhibits 15.4 times higher activity in comparison with uncovered Co on AC (Co/AC), and affords >95% vanillin conversion with 2-methoxy-4-methylphenol (MMP) as the sole product at 180 °C for 4 h. Compared with molecular hydrogen, Co@NC-700 gives a much higher activity and MMP selectivity for vanillin HDO with FA. The Co@NC-700 demonstrates enhanced acid resistance in acidic medium and adsorption of vanillin, and is recyclable and versatile for hydrogenating various unsaturated compounds. The superior performance of Co@NC-700 could be ascribed to N-derived defective sites on Co@NC, which could play multiple roles as base additives in FA dehydrogenation and as a metal-like active center in vanillin HDO.

Full text of DOI:10.1039/c7gc02648j

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Heterogeneous catalytic oxidation for lignin valorization into valuable
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PAPER
Co embedded within biomass-derived mesoporous N-
doped carbon as an acid-resistant and chemoselective
catalyst for transfer hydrodeoxygenation of biomass with
formic acid†
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Huanhuan Yang,a Renfeng Nie,*a Wang Xia,a Xiaolong Yu,a Dingfeng Jin,b Xinhuan Lu,a Dan Zhou,a
Qinghua Xia*a
N-doped Co@C catalyst (Co@NC) is synthesized by one-pot carbonization of biomass-derived glucose and harmless
melamine with CoCl2 as catalyst, where C and N resources could be transformed into highly graphitic N-doped carbon,
while the coordinated Co2+ ions are reduced to uniform Co nanoparticles (NPs), which are embedded in N-doped graphitic
structures. Under base-free conditions with formic acid (FA) as hydrogen-donor, the optimized Co@NC-700 (pyrolyzed at
700 °C) shows a highly efficient H2 generation from FA and the best activity for vanillin hydrodeoxygenation (HDO) with FA.
For example, Co@NC-700 exhibits 15.4 times higher activity in comparison to uncovered Co on AC (Co/AC), and affords
>95% vanillin conversion with 2-methoxy-4-methylphenol (MMP) as sole product at 180 oC for 4 h. Compared with
molecular hydrogen, Co@NC-700 gives a much higher activity and MMP selectivity for vanillin HDO with FA. The Co@NC-
700 demonstrates enhanced acid-resistance in acid medium and adsorption for vanillin, and is recyclable and versatile for
hydrogenating various unsaturated compounds. The superior performance of Co@NC-700 could be ascribed to N-derived
defective sites on Co@NC, which could play multiple roles as the base additives for FA dehydrogenation and as metal-like
active center for vanillin HDO.
intermediate products) and reduce the selectivity of desired
products, and the separation of dehydrogenized byproducts makes
CTH process complicated.7-9
Introduction
The use of renewable biomass to replace the limited fossil fuels
has been recognized as a potential solution for the sustainable
production of liquid fuels and valuable chemicals.1 For instance,
sustainable fuels obtained by the hydrodeoxygenation (HDO) of
phenolic bio-oils derived from pyrolysis of lignin or cellulose offer
good prospects for industrial applications.2 Most of the methods
reported in the literature require the use of a stoichiometric
amount of sensitive reagents or dangerous hydrogen gas under high
pressure.3, 4 Catalytic transfer hydrogenation (CTH) has become the
Formic acid (FA), a byproduct from the acidic hydrolysis of
biomass,10 has attracted a great deal of attention as a suitable liquid
for hydrogen production and as an energy source for hydrogenation
reactions. Hydrogen stored in FA can be released via a catalytic
dehydrogenation reaction (HCOOH→H2+CO2). However, the basic
process is accompanied by undesired dehydration pathway
(HCOOH→H2O+CO), which would reduce the stability of catalyst
due to the intrinsically weak CO tolerance of metal.11 Many
homogeneous and heterogeneous catalytic systems have shown
efficiency for H2 evolution by FA decomposition.12-14 However, in
order to achieve a high efficiency, CTH with FA is always carried out
over noble metals (such as Au, Ru, Pd) with the help of excess bases
(NaOH, triethylamine).15-18 As for non-noble metals, these catalysts
center of attraction because the hydrogen donors,5, such as
6
alcohols and organic acids, are readily available, inexpensive, easy
to handle, and do not require elaborate experimental setups, such
as high pressure reactors. However, the use of various alcohols can
lead to side reactions (esterification or condensation with the
Co+Base-free
This study
H+
Deoxy-products
Lignocellulose
HCOOH
+
Pd, Ru+Base
Previous studies
Scheme 1 Earth-abundant Co catalyzed CTH of biomass with FA under base-
free condition.
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Results and discussion
80 o
▬ Water
Glucose+Melamine
C
700 o
N2
C
HCl
Characterizations of nanostructured Co@NC materials
Co@NC-700
Brown colloid
Co/NC-700
+CoCl2+Water
Scheme 2 Schematic illustration of synthesis of Co@NC-x catalyst.
require high temperature, long reaction time, high catalytic loading,
and a tedious procedure, and are easily deactivated in the present
of FA due to bad tolerance to acidic environment and CO
impurities.7, 19-22 So far, there are still few reports on the use of a
versatile catalytic system that enables selective HDO of biomass
with FA with an excellent switch in selectivity just by adjusting the
reaction conditions. Therefore, the rational design of acid- and CO-
tolerated catalysts based on earth-abundant metals for CTH of
biomass with FA is challenging and attractive (Scheme 1).
Nitrogen-doped carbon has been proven to be a fascinating
catalytic material.23 Doping with electron-rich nitrogen modifies the
surface structure of carbons, endows enhanced π-binding ability
and improved basicity,24 which enables the applications of carbon
with improved performance in catalysis. In traditional CTH process,
FA-triethylamine system is frequently used for improving
dehydrogenation of FA.15-17 Here, similar chemical environment of
nitrogen in triethylamine and nitrogen-doped carbon may make N-
doped carbon as ‘heterogeneous N-type species’ for N-mediated FA
dehydrogenation, affording some attractive characters (high
stability, recyclability, etc.). As expected, carbon nitrides have been
reported as efficient supports for Pd-involved CTH process.12, 25 The
role of N-doping in modifing the electron density of the supported
metals (Mott-Schottky effect) and the catalytic activity has been
recently highlighted.12 It is reported that the CN’s electronic state is
very sensitive to the materials contacted, which induces CN as
metal-like active site for hydrogen activation.26 For example, novel
N-doped graphene encapsulating metal NP catalysts, including Co,
Fe, Ni, Mo multi-metallic catalysts have been developed for
hydrogenation under high H2 pressure.27-35 The inner metal core
and N species on the carbon shell can significantly decrease the
dissociation energies of H2,29, 34 proving the ability of carbon shell in
the hybrids to H2 activation.
Fig. 1 SEM images of (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-700 and
(d) Co@NC-800.
The surface morphology of Co@NC-x is imaged by SEM. As shown
in Fig. 1, Co@NC-x samples show significantly different
morphologies under different pyrolysis temperature. Compared
with Co@NC-500 and Co@NC-600, Co@NC-700 exhibits clear
sponge-like structure. Further increasing temperature to 800 oC,
however, leads to Co@NC-800 with slight agglomeration and pore
shrink.
240
200
160
120
80
40
0
0.03
0.02
0.01
0.00
Stotal=380.9 m2/g
Dv=0.254 cm3/g
Dp= 4.3 nm
1
10
Pore width (nm)
Based on above considerations, mesoporous N-doped carbon
encapsulating Co catalysts (Co@NC) are prepared through one-pot
carbonization of biomass-derived glucose, melamine and CoCl2
(Scheme 2). The unique structure of Co@NC plays multiple roles for
CTH of biomass with FA, including 1) N-doped carbon shell strictly
controls the aggregation of NPs, 2) the strong interaction between
Co core and N-doped carbon shell influences the electronic
structure that induces CN as metal-like active site for
dehydrogenation of FA and hydrogenation of substrate, 3) N-doped
carbon shell physically isolates Co from the acid environment and
protects metal from poisoning or leaching. This catalyst exhibits
high yield and excellent chemoselectivity (typically 100%) for HDO
of vanillin to MMP using FA as reductant. The whole reaction
system does not generate byproducts or harmful products.
Moreover, the Co@NC catalyst exhibits superior recyclability and
excellent stability after being reused at least five times. This work
may promote the investigation of low-cost Co-based catalysts for
highly chemoselective HDO of biomass in the chemical industry.
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Fig. 2 Nitrogen sorption isotherms and pore size distribution of Co@NC-700.
The N2 adsorption/desorption isotherm (Fig. 2 and Fig. S1
shows that Co@NC-x derived from higher pyrolysis temperature
exhibits a typical Type IV one with an apparent hysteresis loop in
the p/p0 range of 0.4−1.0, indicaꢀng the presence of a large number
of mesopores in Co@NC-x, as confirmed by the corresponding pore
distribution curve (Fig. S1). Meanwhile, high pyrolysis temperature
leads to large pore volume but narrow mean pore size (Table S1).
For example, the surface area and average pore size of Co@NC-700
are calculated to be 380.9 m2 g-1 and 4.3 nm, respectively. This
result is also consistent with the reported experimental regularity
that chlorates can be used as porogen in the preparation of porous
carbon materials with high surface area.36
)
XRD patterns (Fig. 3) show that C(002) diffraction peak is
gradually strengthened with increasing pyrolysis temperature,
indicating the increased graphitization of carbon skeleton.37 The
2 | J. Name., 2012, 00, 1-3
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metallic Co diffraction peak is strengthened only at higher pyrolysis 600, but decrease sharply to 64.8% in OMNC-700 and 57.75% in
temperature (> 700 oC). Raman spectra in Fig. 4 show that both D OMNC-800. Noticeably, with the increase of temperature from 500
and G peaks sharpen evidently. Comparatively, Co@NC-700 gives to 800 oC, the proportion of graphitic nitrogen shows an increase
relatively high value of ID/IG (1.35, Table S2), indicating that the from 0 to 42.24%, indicating that graphitic nitrogen tends to
crystalline carbon tends to be disordered.38 Another peak detected generate induced by transition metal under high temperatures.
at ~670 cm-1 can be assigned to the Raman-active mode of Co- Meanwhile, the Co 2p spectra of Co@NC-x (Fig. 6) show obvious
O/Co-N, in which Co@NC-700 and Co@NC-600 show stronger peak, negative-shift as increasing the pyrolysis temperature from 500 to
implying a higher crystallinity of Co-O/Co-N species.39 Further 800oC, implying that the Co-O/Co-N species in Co@NC-x are
increasing pyrolysis temperature to 800 oC weakens the intensity of reduced in situ to metallic Co during thermal decomposition (Table
the peak again, indicating that CoOx and Co-N form firstly, followed S3). For example, Co@NC-500 possesses nearly 12.37% Co0, and
by reacting with carbon elements released from precursor to this value increases to 19.94 and 26.02 % for Co@NC-700 and
generate Co0 during the carbonization.21
Co@NC-800, respectively. It was reported that if the reduction
potential of metal ions were -0.27 volts or higher (such as Co2+, Ni2+,
Cu2+), they would be reduced to metal NPs by the direct pyrolysis in
inert atmosphere.21
C(002)
Co(111)
(f)
N1
N3
N2
(d)
(c)
N4
(e)
(d)
(c)
(b)
(a)
(b)
10
20
30
40
50
60
70
80
2 Theta / o
(a)
Fig. 3 XRD patterns of (a) Co@C-700, (b) Co@N-700, (c) Co@NC-500, (d)
Co@NC-600, (e) Co@NC-700 and (f) Co@NC-800.
394
396
398
400
402
404
406
408
Binding Energy (eV)
Fig. 5 The N1s spectra of (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-700
~670, Co-O/Co-N
and (d) Co@NC-800.
D
G
200
300
400
500
600
700
800
(d)
Co-O
Co0
Co-N
Shake up
(d)
(c)
(b)
(a)
(c)
(b)
(a)
200 400 600 800 1000 1200 1400 1600 1800 2000
Raman shift (cm-1
)
Fig. 4 The Raman spectra of (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-
700 and (d) Co@NC-800.
774 776 778 780 782 784 786 788 790 792
Binding Energy (eV)
FT-IR spectra (Fig. S2) show that the bands at ~3400, 1580 Fig. 6 The Co2p spectra of (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-700
and 1210 cm–1 weaken obviously with increasing the
and (d) Co@NC-800.
temperature, implying the emission of polar species (such as N
The detailed morphology of the Co@NC-x catalyst is disclosed by
TEM (Figs. 7, S4 and S5). It can be seen that the particle size of NPs
is in the range of 5-60 nm, and higher pyrolysis temperature affords
wide particle size distribution as well as large mean particle size (Fig.
S4). It is found that the average particle size in Co@NC-500,
Co@NC-600, Co@NC-700 and Co@NC-800 is 15.3, 16.1, 24.4 and
31.4 nm, respectively. It can be observed that, after being etched
with HCl, rich cavities appear in Co@NC-700 (Fig. 7a and b), and the
particle sizes of Co have
or O) under heat treatment. The N1s spectra of Co@NC-x (Fig. 5
)
can be separated into pyridinic nitrogen (N-1), pyrrolic nitrogen (N-
2), graphitic nitrogen (N-3), and pyridine oxide-N (N-4) at 398.5,
400.1, 401.1, and 403.3 eV, respectively. Apart from obvious
decrease of N content (from 10.0 to 2.7 %, Table S2), Co@NC-x
undergoes significant rearrangement of N species compared to
that of Co@NC-500 (Table S3).40 It is found that the N-1 and N-2
atoms account for >85% of the content in OMNC-500 and OMNC-
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Catalytic property of Co@NC for transfer HDO of vanillin with
FA
The prepared catalysts are studied for selective HDO of vanillin to
MMP with FA as hydrogen source (Table 1). Blank test shows that
no vanillin is transformed when no catalyst is used (entry 1). In a
preliminary catalyst screening, the catalytic performance of
catalysts based on iron, cobalt, nickel and copper pyrolysed with N-
doped carbon is investigated at 180 oC in water. Among the
different metals used (entries 2-5), Fe@NC-700, Ni@NC-700 and
Cu@NC-700 give conversions of 9.7, 37.2 and 3.7 %, with all 100 %
MMP selectivity. In contrast, the excellent conversion reaches up to
95.7 % over Co@NC-700 catalyst.
Next, the optimization of the pyrolysis temperature is carried out
(entries 3, 6-8). The results show that the temperature significantly
affects the activity of Co@NC-x catalyst and Co@NC obtained at
700 oC affords the best activity and 100 % MMP selectivity.
However, other catalysts do not afford the desired catalytic effect.
This is probably because the active sites Co@NC has almost not
been formed when pyrolysed at 500 oC.37 While annealing at the
temperature higher than 800 oC, the CoOx or CoNx NPs tend to
aggregate and to be further reduced to Co NPs. The Co-based
Table 1 Transfer HDO of vanillin with FA over different catalysts.a
Entry
Catalysts
-
Conversion / % MMP selectivity / %
1
2
3
4
5
6
7
8
1.1
9.7
-
Fe@NC-700
Co@NC-700
Ni@NC-700
Cu@NC-700
Co@NC-500
Co@NC-600
Co@NC-800
100
100
100
100
100
100
95.7
37.2
3.7
C-K
Co-K
Co-L
O-K
N-K
(g)
Metal core
35 nm
9.3
CN shell
25 nm
71.1
88.9
67.2
33.4
100
98.8
92.0
9
Co@N-700
Co@C-700
10
0
50
100
150
Position (nm)
200
250
a Reaction conditions: vanillin (0.5 mmol), catalyst (7.9 mol% metal), FA (200
mg), H2O (10 mL), 0.5 MPa N2, 180 oC, 4 h.
Fig. 7 TEM images (a-e), (f) STEM and (g) line scanning EDS elemental
analysis of Co@NC-700.
100
Selectivity
80
a wide size distribution with a fraction of 10-40 nm particles.
HRTEM (Fig. 7b-e) shows that the Co NPs are encapsulated by
graphene layers and the well-defined core/shell structured Co@NC
NPs form in mesoporous carbon framework. Fig. 7c highlights a
typical metallic Co nanoparticle with crystal lattices of 0.215 nm,
assigned to the (111) interplanar spacing of metallic Co, in which
the Co NPs are encapsulated by well-ordered graphitic layers with a
typical distance value of graphite (0.341 nm). Line scanning
elemental analysis of Co@NC (Fig. 7f and g) has also confirmed that
Co is well encapsulated in N-doped graphene shell in Co@NC-700.
The formation of graphitic structure could efficiently facilitate the
electron transfer, and prevent the leaching of acidity or the
poisoning of Co NPs, thereby improving the catalytic activity.
60
Co@NC-700
40
20
Co/AC
0
120
140
160
180
Temperature (oC)
Fig. 8 Transfer HDO of vanillin under different temperatures.
Reaction conditions: vanillin (0.5 mmol), FA (200 mg), catalyst (7.9 mol%
Co), H2O (10 mL), 0.5 MPa N2, and 2h.
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catalyst prepared without melamine (Co@C) shows relatively low
vanillin conversion (33.4 %) and MMP selectivity, while melamine-
to 9.6 %. Further increasing the FA amount to 200 mg, however,
leads to an obvious decrease of conversion to 6.2 %. In comparison,
derived Co@N affords significantly increased catalytic activity Co@NC-700 possesses good activities in the whole acid range.
Increased FA amount causes significant increase of conversion. Even
at a pH value of 1.2 (200 mg FA), the catalyst still shows fairly good
catalytic performance for transfer HDO of vanillin. Considering the
metal leaching might occur, both the filtrate of Co@NC-700 and
Co/AC after reaction is checked by UV-vis spectra (Fig. S11). It is
found that nearly no absorption peak can be observed from the
filtrate of Co@NC-700, while the filtrate of Co/AC gives significant
signal at 518 nm, indicating that obvious Co leaching occurs in
water medium under acidic environment in the presence of FA. XRD
pattern of the spent Co/AC (Fig. S12) shows that the Co or Co3O4
reflections sharply weaken. ICP-AES analysis of the filtrate of
Co@NC-700 further confirms that the Co content in the solution is
below the detection limit, while 77.1% Co leaches into water for
Co/AC during the reaction. These observations appear to be
manifest that the CN shell plays a positive role in our system. On
one hand, the novel CN shell physically isolates Co from the acidic
environment and protects it from corrosion or poisoning. On the
other hand, the intimate interaction between CN and inner Co
induces CN to be activated by Co for CTH of vanillin with FA.
(67.2 %), which might be ascribed to the basicity derived from N-
doping of carbon skeleton (Fig. S6). In comparison with Co@NC-700,
the relatively low activity of Co@N-700 could be ascribed to high
metal loading (Fig. S7) and generation of large-sized NPs (Fig. S8).
Furthermore, the reaction temperature effect on the activity of
Co@NC-700 and Co/AC derived from common impregnation is
studied (Fig. 8). The hydrogenation rate of vanillin catalyzed by
Co/AC increases slowly, and only 6.2 % of conversion is achieved at
180 oC; however, the conversion over Co@NC-700 increases sharply
from 10.7 to 95.7% as increasing temperature from 120 to 180 oC,
which is 15.4 times that of Co/AC. Catalyst loading has a large
impact on catalytic activity (Table S4), and decreasing catalyst usage
leads to obvious decrease of vanillin conversion.
The effect of FA amount on catalytic activity is also studied (Table
2). It can be found that almost no conversion of vanillin occurs
when no FA is used. Once FA is added gradually from 0 to 200 mg,
the pH value of reaction system decreases sharply from
∼7 to 1.2,
for which a highly acidic environment is formed to aggravate the
etching, leaching and inactivation of Co NPs. It has to be noted that
Co/AC catalyst prepared by impregnation possesses nice Co
dispersion (~15 nm, Fig. S10) but exhibits a poor catalytic activity.
For example, as the FA amount increases from 0 to 100 mg, the
vanillin conversion over Co/AC is low and increases slowly from 0.5
Fig. 9 shows the dependencies of vanillin conversion and MMP
selectivity in the HDO of vanillin with FA and molecular hydrogen
over Co@NC-700. Using FA as hydrogen donor, vanillin is
transformed gradually to MMP with a relatively constant rate and
nearly converted fully to MMP as the sole product. In contrast,
using molecular hydrogen as hydrogen donor, the hydrogenation
rate seems to slow down after 2 h and only 34.8 % conversion and
84.8 % MMP selectivity can be achieved at 4 h. The transformation
proceeds efficiently without any decrease in the performance in
comparison with the small-scale transformation in Fig. S13, and
MMP is produced in 100% selectivity and 92.7 % yield. This result
indicates a different hydrogenation route in comparison to the
earlier observation using molecular hydrogen as the hydrogen
source, in which HMP was firstly generated and then hydrogenated
into MMP under high concentration of HMP.41 It could be
concluded that FA plays an important role in the HDO of vanillin to
MMP as the sole product via the interaction with vanillin or
intermediates that suppresses the generation of HMP (Scheme 3).42
To further demonstrate the versatility of Co@NC-700, transfer
hydrogenation of different unsaturated hydrocarbons is
investigated in Table 3. As a common biomass-derived product,
selective hydrogenation of benzaldehyde is carried out. It can be
Table 2 Effect of FA amount on transfer HDO of vanillin over Co@NC-700
and Co/AC.
Co@NC-700
Co/AC
FA/
mg
MMP
MMP
Entry
pH
Conversion
/ %
Conversion
/ %
selectivity
/ %
selectivity
/ %
1
2
3
4
0
25
50
~7.0
1.79
1.56
2.1
-
0.5
4.7
8.1
9.6
6.2
-
11.2
24.5
36.4
95.7
100
100
100
58.3
100
100
100 1.41
200 1.21
5
100
100
a
Reaction conditions: vanillin (0.5 mmol), catalyst (7.9 mol% Co), H2O (10
mL), 0.5 MPa N2, 180 oC, 4 h.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
MMP
o
found that 98.6 % conversion is obtained at 180 C in 4 h with 100
FA
H2
% benzyl alcohol selectivity (entry 2). In the case of phenylpropyl
HMP
0.0
0.5
1.0
1.5
2.0
t/h
2.5
3.0
3.5
4.0
Fig. 9 Effect of hydrogen donor on the HDO of vanillin.
Reaction conditions: vanillin (0.5mmol), Co@NC-700 (7.9 mol% Co), H2O (10
mL), 0.5 MPa N2 or H2, 180 oC.
Scheme 3 Possible reaction mechanism of transfer HDO of vanillin over
Co@NC.
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Table 3 Transfer DHO or hydrogenation of unsaturated hydrocarbons over
50
40
30
20
10
0
44.5
Co@NC-700.
40.9
Conversion
/%
Selectivity /
%
Entry
1
Substrate
Product
CHO
CH3
95.7
100
24.2
O
O
OH
OH
12.8
2
3
4
98.6
97.1
91.0
100
100
100
Co@NC-500 Co@NC-600 Co@NC-700 Co@NC-800
Fig. 11 The saturated adsorption amount of Co@NC-x towards vanillin.
5
91.4
92.7
N
H
6 b
7 b
98.9
99.5
100
boosts high catalytic activity, in which Co@NC-700 affords a full FA
conversion at 140 oC for 2 h. In can be found the order of FA
dehydrogenation is similar to the hydrogenation activity, indicating
that the FA dehydrogenation could be the crucial step in the
transfer HDO of vanillin over Co@NC-x catalysts.
93.0
a
Reaction conditions: Substrate (0.5mmol), Co@NC-700 (7.9 mol% Co), FA
(200 mg), H2O (10 mL), 0.5 MPa N2, 180 oC, 4h.
b 200 oC
The rich surface N dopants can serve as defect sites for increasing
the hydrophilicity of carbons and wettability of the substrate on
carbons.43 It is reported that the more hydrophilic the catalyst, the
more active it is for the HDO of vanillin in water. The adsorption
test (Fig. S14 and 11) shows that the adsorption capacity of vanillin
over Co@NC-x increases in the order of Co@NC-500< Co@NC-600<
Co@NC-700 <Co@NC-800, and the adsorption capacity on Co@NC-
700 and Co@NC-800 can reach > 40 mg/g. This result indicates a
favourable interaction between vanillin and Co@NC-700 that leads
to an increased vanillin concentration and accelerated reaction rate
on surface of Co@NC-700.21
aldehyde (entry 3), the reaction gives 97.1 % of conversion and 100
% of alcohol selectivity. Other α, β-unsaturated aldehyde, such as
cinnamyl aldehyde (entry 4), affords the corresponding
hydrocinnamyl alcohol with 91 % conversion without other side
products. Next, a more challenging hydrogenation of quinoline
toward 1,2,3,4-tetrahydroquinoline (THQ), due to the competitive
hydrogenation of benzene ring, is demonstrated in entry 5. The
result shows that Co@NC-700 affords 91.4 % quinoline conversion
with THQ as the sole product in water, which exhibits obvious
advantage over those noble metals using molecular hydrogen as
reductant. Other substituted benzaldehydes (entries 6-7), such as
hydroxyl benzaldehyde, methoxy benzaldehyde, afford the
corresponding deoxy-products in relatively good yields.
Considering the acidic environment due to the presence of FA,
the recycle of catalyst is an important issue for the development of
sustainable chemicals. Co@NC-700 can be easily recovered and
reused five times without significant loss of efficiency (Fig. 12). The
In order to explore the mechanism of transfer HDO of vanillin
over Co@NC-x, the dehydrogenation of FA is investigated. Fig. 10
shows that Co@NC-500 sample is less active for FA
dehydrogenation (21.1 %). While higher pyrolysis temperature
Conversion
MMP selectivity
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
1
2
3
4
5
Reuse
Fig. 12 Re-uses of Co@NC-700 for transfer HDO of vanillin
.
Reaction conditions: vanillin (0.5 mmol), FA (200 mg), catalyst (7.9 mol% Co),
H2O (10 mL), 0.5 MPa N2, 180 oC, 3h.
0
Co@NC-500 Co@NC-600 Co@NC-700 Co@NC-800
Fig. 10 FA dehydrogenation test over Co@NC-x.
Reaction conditions: FA (200 mg), catalyst (0.91 mol% Co vs. FA), H2O (2 mL),
1 bar N2, 140 oC, 2 h.
6 | J. Name., 2012, 00, 1-3
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temperature at a heating rate of 5 oC/min under a flow of nitrogen
and kept for 4 h. The sample was treated in HCl (5 wt.%) at RT for
24 h to remove soluble cobalt species. The acid treated solid sample
was recovered by filtration and washed with DI water until free of
Cl−. Finally, the sample was dried and denoted as Co@NC-x, where x
corresponds to the treatment temperature. For the synthesis of
Co@C-x or Co@N-x, no melamine or no glucose was added.
Replacing cobalt chloride with nickel chloride, ferric chloride or
copper chloride synthesized Ni@NC-x, Fe@NC-x or Cu@NC-x,
respectively.
C(002)
Co(111)
Fresh
Co(002)
5 times reused
Characterizations
10
20
30
40
50
60
70
80
Powder X-ray diffraction (XRD) was performed on a Bruker D8A25
2 Theta / o
diffractometer with CuK
kV and 25 mA. Fourier transform infrared (FTIR) spectra were
analyzed on an OPUS Fourier Transform Infrared
α radiation (λ=1.54184 Å) operating at 30
Fig. 13 XRD patterns of fresh Co@NC-700 and Co@NC-700 reused 5 times.
Spectrophotometer in the range of 400-4000 cm-1. Raman spectra
were collected at room temperature from 100 to 4000 cm-1 with
514.5-nm argon ion laser (Rhenishaw Instruments, England). N2
adsorption was carried out at -196 oC using an auto-adsorption
analyzer (Micromeritics, TriStar II). Scanning electron images (SEM)
were collected on JEOL (JSM6700F)) at an accelerating voltage of 15
kV. Transmission electron microscope (TEM) images were obtained
using an accelerating voltage of 200 kV on a JEOL-135 2010F
Transmission Electron Microscope. Thermal gravimetric analysis
(TGA) was carried out with a Perkin Elmer thermoanalyzer under
nitrogen atmosphere. X-ray photoelectron spectra (XPS) were
recorded on a Perkin-Elmer PHI ESCA system.
XRD pattern (Fig. 13) of Co@NC-700 reused 5 times shows that only
diffraction peaks of Co0 are recorded and the crystalline state of Co
NPs do not change significantly, which indicates the retention of the
catalytic activity after being recycled. No Co metal is detected in the
reaction solvent after completion of the reaction, showing much
higher stability than that of Co/AC. This confirms the fact that CN
shell holds the cobalt metal very tightly, thus prohibiting metal from
leaching, and facilitating efficient catalyst recycling.
Conclusion
We have demonstrated an efficient method to synthesize a low-
cost and eco-friendly Co@NC catalyst that can utilize FA, a cheap
and readily available hydrogen donor, for highly efficient CTH of
vanillin without adding any base additives. The catalysts are
prepared by an accurate annealing procedure of the mixture of
glucose, melamine and CoCl2. The Co NPs are uniformly
encapsulated in porous N-doped carbon structure, which exhibits
dramatically enhanced acid-resistance in present of FA and high
catalytic activity as well as specific selectivity for transfer HDO of
vanillin with MMP as sole product. Control experiments suggest
that N-derived basic sites on Co@NC, which could play crucial roles
as the base additives for FA dehydrogenation and N-doped carbon
shell is tuned by embedded Co as metal-like active center for
vanillin HDO. Moreover, this catalyst is stable and active for transfer
hydrogenation of various unsaturated compounds. This study offers
a simple way to prepare N-doped carbons from biomass as
‘heterogeneous N-type ligands’ for the non-noble metal-mediated
transfer hydrogenation of biomass.
Vanillin adsorption
50 mg of Co@NC was added into a 5 mL of vanillin aqueous
solution with an initial concentration of 500 ppm and stirred at 30
oC. At a given interval, 0.1 mL of the suspension was diluted with
water. The supernatant was then obtained by centrifugation and
analyzed by a Shimadzu UV-visible UV-2550 spectrometer. The
amount of adsorbed vanillin was calculated according to the
ꢅ
equation: the amount of adsorbed vanillin = ꢀꢁꢂꢃꢁꢄ ×ꢆꢂ. Here C0 is
ꢇꢈ
the initial concentration of vanillin, Cr is the residual vanillin
concentration after adsorption, V0 is the volume of aqueous
solution, and mc is the mass of sample.
Catalytic reactions
The hydrogenation reactions were performed in a 50 mL stainless
autoclave with a Teflon liner. In a typical run, a certain amount of
catalyst, 200 mg FA and 0.5 mmol vanillin were dispersed in 10 mL
DI water. The autoclave was then sealed, purged and pressurized
with N2 to 0.5 MPa, and heated to 180 oC under magnetic stirring
(1000 rpm). After the completion of reaction, the autoclave was
quickly cooled down within cold water. The organic compounds was
extracted by ethyl acetate, the catalyst was recovered from
aqueous phase by centrifugation and then washed several times
with ethanol for next use. The products and substrate were
analyzed by gas chromatograph (Shimadzu 2010) with a 30 m
capillary column (Rtx®-1) using a flame ionization detector (FID).
Interpolated calibration was employed for product quantification
using standard solutions of substrate and product. All the products
were confirmed by GC-MS (Agilent 6890).
Experimental
Materials
The chemicals used included glucose (AR, Sigma-Aldrich), cobalt
chloride (AR, Sinopharm), melamine (AR, Sinopharm). All other
chemicals were of analytical purity if not otherwise noted.
Catalysts preparation
In a typical experiment, glucose, melamine and cobalt chloride
were added to deionized water under stirring ((mass ratio of
glucose/melamine/cobalt chloride=1:1:1)) (Scheme 2). The solution
was then evaporated in air at 80 oC for removing the water. The
powder was transferred into
a crucible, heated to a given
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Journal Name
23. X. Wang, G. Sun, P. Routh, D.-H. Kim, W. Huang and P. Chen,
Chem. Soc. Rev., 2014, 43, 7067-7098.
Acknowledgements
This work was supported by National Natural Science Foundation of
China (21603066, 21673069, 21503074, 21571055), Natural Science
Fund for Creative Research Groups of Hubei Province
(2014CFA015), Natural Science Fund of Hubei Province
(2015CFB232), Hubei Provincial Outstanding Youth Foundation
(2016CFA040) and Natural Science Fund of the Education
Department of Hubei Province (Q2015009). The authors thank Dr.
Xiaoqing Liu of Wuhan University of Technology for TEM assistance.
24. Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier and H. Dai,
Nat. mater., 2011, 10, 780-786.
25. L.-H. Gong, Y.-Y. Cai, X.-H. Li, Y.-N. Zhang, J. Su and J.-S. Chen,
Green Chem., 2014, 16, 3746-3751.
26. T. Fu, M. Wang, W. Cai, Y. Cui, F. Gao, L. Peng, W. Chen and W.
Ding, ACS Catal., 2014, 4, 2536-2543.
27. Y. Feng, X.-Y. Yu and U. Paik, Sci. Rep., 2016, 6, 34004-34012.
28. J. A. Varnell, E. C. M. Tse, C. E. Schulz, T. T. Fister, R. T. Haasch, J.
Timoshenko, A. I. Frenkel and A. A. Gewirth, Nat. Commun.,
2016, 7, 12582-12591.
Notes and references
29. Z. Wei, Y. Chen, J. Wang, D. Su, M. Tang, S. Mao and Y. Wang,
ACS Catal., 2016, 6, 5816-5822.
1. P. Gallezot, Chem. Soc. Rev., 2012, 41, 1538-1558.
2. A. Singh, D. Pant, N. Korres, A. Nizami, S. Prasad and J. Murphy,
Bioresour. Technol., 2010, 101, 5003-5012.
30. J. Shi, Y. Wang, W. Du and Z. Hou, Carbon, 2016, 99, 330-337.
31. T. Wang, Z. Dong, W. Cai, Y. Wang, T. Fu, B. Zhao, L. Peng, W.
Ding and Y. Chen, Chem. Commun., 2016, 52, 10672-10675.
32. J. Y. Park, M. A. Kim, S. J. Lee, J. Jung, H. M. Jang, P. P. Upare, Y.
K. Hwang, J.-S. Chang and J. K. Park, J. Mater. Sci., 2014, 50, 334-
343.
3. R. A. W. Johnstone, A. H. Wilby and I. D. Entwistle, Chem. Rev.,
1985, 85, 129-170.
4. X.-L. Du, L. He, S. Zhao, Y.-M. Liu, Y. Cao, H.-Y. He and K.-N. Fan,
Angew. Chem. Int. Ed., 2011, 50, 7815-7819.
5. H. Mehdi, V. Fabos, R. Tuba, A. Bodor, L. T. Mika and I. T.
Horvath, Top. Catal., 2008, 48, 49-54.
33. G. Lu, S. Li, Z. Guo, O. K. Farha, B. G. Hauser, X. Qi, Y. Wang, X.
Wang, S. Han, X. Liu, J. S. DuChene, H. Zhang, Q. Zhang, X. Chen,
J. Ma, S. C. J. Loo, W. D. Wei, Y. Yang, J. T. Hupp and F. Huo, Nat.
Chem., 2012, 4, 310-316.
6. W. Hao, W. Li, X. Tang, X. Zeng, Y. Sun, S. Liu and L. Lin, Green
Chem., 2016, 18, 1080-1088.
7. M. Chia and J. A. Dumesic, Chem. Commun., 2011, 47, 12233-
12235.
34. J. Long, K. Shen, L. Chen and Y. Li, J. Mater. Chem. A, 2016, 4,
10254-10262.
8. D. Scholz, C. Aellig and I. Hermans, ChemSusChem, 2014, 7, 268-
275.
35. Z.-Y. Wu, B.-C. Hu, P. Wu, H.-W. Liang, Z.-L. Yu, Y. Lin, Y.-R.
Zheng, Z. Li and S.-H. Yu, NPG Asia Mater., 2016, 8, e288.
36. Z. Ma, H. Zhang, Z. Yang, Y. Zhang, B. Yu and Z. Liu, J. Mater.
Chem. A, 2014, 2, 19324–19329.
9. Z. Yang, Y.-B. Huang, Q.-X. Guo and Y. Fu, Chem. Commun., 2013,
49, 5328-5330.
10. X. Liu, S. Li, Y. Liu and Y. Cao, Chin. J. Catal., 2015, 36, 1461-
1475.
37. M. Tian, X. Cui, M. Yuan, J. Yang, J. Ma and Z. Dong, Green
Chem., 2017, 19, 1548-1554.
11. A. M. Ruppert, M. Jędrzejczyk, O. Sneka-Płatek, N. Keller, A. S.
Dumon, C. Michel, P. Sautet and J. Grams, Green Chem., 2016,
18, 2014-2028.
38. R. Nie, J. Wang, L. Wang, Y. Qin, P. Chen and Z. Hou, Carbon,
2012, 50, 586-596.
39. X. Liu, L. Xu, G. Xu, W. Jia, Y. Ma and Y. Zhang, ACS Catal., 2016,
6, 7611-7620.
12. Q.-Y. Bi, J.-D. Lin, Y.-M. Liu, H.-Y. He, F.-Q. Huang and Y. Cao,
Angew. Chem. Int. Ed., 2016, 55, 11849-11853.
13. J. F. Hull, Y. Himeda, W. Wang, B. G. Hashiguchi, R. A. Periana, D.
J. Szalda, J. T. Muckerman and E. Fujita, Nat. Chem., 2012, 4,
383-388.
40. L. F. Chen, X. D. Zhang, H. W. Liang, M. Kong, Q. F. Guan, P.
Chen, Z. Y. Wu and S. H. Yu, ACS Nano, 2012, 6, 7092-7102.
41. R. Nie, H. Yang, H. Zhang, X. Yu, X. Lu, D. Zhou and Q. Xia, Green
Chem., 2017, 19, 3126-3134.
14. L. Deng, Y. Zhao, J. Li, Y. Fu, B. Liao and Q. Guo, ChemSusChem,
2010, 3, 1172-1175.
42. R. Nie, X. Peng, H. Zhang, X. Yu, X. Lu, D. Zhou and Q. Xia, Catal.
Sci. Technol., 2017, 7, 627-634.
15. M. Vilches-Herrera, S. Werkmeister, K. Junge, A. Börner and M.
Beller, Catal. Sci. Technol., 2014, 4, 629-632.
16. L. Tao, Q. Zhang, S.-S. Li, X. Liu, Y.-M. Liu and Y. Cao, Adv. Synth.
Catal., 2015, 357, 753-760.
43. Z. Zhu, H. Tan, J. Wang, S. Yu and K. Zhou, Green Chem., 2014,
16, 2636-2643.
17. Y. Wei, C. Wang, X. Jiang, D. Xue, Z.-T. Liu and J. Xiao, Green
Chem., 2014, 16, 1093-1096.
18. D. Talwar, H. Y. Li, E. Durham and J. Xiao, Chem. Eur. J., 2015, 21,
5370-5379.
19. P. P. Upare, M.-G. Jeong, Y. K. Hwang, D. H. Kim, Y. D. Kim, D. W.
Hwang, U. H. Lee and J.-S. Chang, Appl. Catal. A, 2015, 491, 127-
135.
20. J. Yuan, S. Li, L. Yu, Y. Liu and Y. Cao, Chin. J. Catal., 2013, 34,
2066-2074.
21. J. Long, K. Shen and Y. Li, ACS Catal., 2017, 7, 275-284.
22. J. Long, Y. Zhou and Y. Li, Chem. Commun., 2015, 51, 2331-2334.
8 | J. Name., 2012, 00, 1-3
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