Cobalt Nanoparticles Embedded in N-Doped Porous Carbon Derived from Bimetallic Zeolitic Imidazolate Frameworks for One-Pot Selective Oxidative Depolymerization of Lignin

Article abstract of DOI:10.1002/cctc.201801752

Cobalt nanoparticles embedded in N-doped porous carbon (Co@CN) were prepared by the pyrolysis of bimetallic zeolitic imidazolate frameworks (BMZIFs) based on ZIF-8 and ZIF-67. The catalyst shows excellent catalytic efficiency in one-pot selective oxidative cleavage of different linkages like β-O-4, a-O-4 and β-1 in organosolv lignin and lignin model compounds in the presence of oxygen (ambient pressure) under mild conditions (383 K). Compared with traditional supported catalyst, the catalyst gives a highly hollow structure, which favored the adsorption of substrates and oxygen. The uniform cobalt nanoparticles surrounded by N-doped graphitic structures and the strong electron transfer from graphitic nitrogen to Co NPs make it hard to be oxidized prior to use and higher catalytic reactivity. Moreover, the catalyst can be easily recovered by magnetic force after the reaction, and reused after reduction for five times without an obvious change in yields.

Full text of DOI:10.1002/cctc.201801752

Accepted Article
Title: Cobalt Nanoparticles Embedded in N-Doped Porous Carbon
Derived from Bimetallic Zeolitic Imidazolate Frameworks for One-
pot Selective Oxidative Depolymerization of Lignin
Authors: Kangkang Sun, Shujie Chen, Jiawei Zhang, Guo-ping Lu, and
Chun Cai
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To be cited as: ChemCatChem 10.1002/cctc.201801752
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ChemCatChem
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Cobalt Nanoparticles Embedded in N-Doped Porous Carbon
Derived from Bimetallic Zeolitic Imidazolate Frameworks for One-
pot Selective Oxidative Depolymerization of Lignin
Kangkang Sun,[a] Shujie Chen,[b] Jiawei Zhang,[a] Guo-Ping Lu*[a] and Chun Cai*[a]
Abstract: Cobalt nanoparticles embedded in N-doped porous carbon
(Co@CN) were prepared by the pyrolysis of bimetallic zeolitic
imidazolate frameworks (BMZIFs) based on ZIF-8 and ZIF-67. The
catalyst shows excellent catalytic efficiency in one-pot selective
oxidative cleavage of different linkages like β-O-4, a-O-4 and β-1 in
organosolv lignin and lignin model compounds in the presence of
oxygen (ambient pressure) under mild conditions (383 K). Compared
with traditional supported catalyst, the catalyst gives a highly hollow
structure, which favored the adsorption of substrates and oxygen. The
uniform cobalt nanoparticles surrounded by N-doped graphitic
structures and the strong electron transfer from graphitic nitrogen to
Co NPs make it hard to be oxidized prior to use and higher catalytic
reactivity. Moreover, the catalyst can be easily recovered by magnetic
force after the reaction, and reused after reduction for five times
without an obvious change in yields.
metallosalen catalysts,[10] polyoxometalate-based catalysts[11] or
simple metal salt-based catalysts.[12] However, there are several
problems with these strategies such as the requirement of some
specific conditions in the biocatalysis processes, the
decomposition of metallosalen catalysts and lack of selectivity for
depolymerization of lignin using metal salt-based catalysts.
Besides, homogeneous catalysts are difficult to be reused and
contaminate the products. To overcome these issues, various
heterogeneous noble catalysts are designed for the
transformation, which are more efficient than earth-abundant
metals, but are unfavorable to industrial applications.[13] Therefore,
seeking efficient and recyclable earth-abundant metal catalysts to
achieve this goal is an appealing, yet difficult, task.
Meanwhile, a two-step strategy as a novel method for
depolymeriation of lignin and lignin compounds has been
investigated in recent years,[7a, 14] in which the oxidation of β-O-4
alcohol to β-O-4 ketone in the first step can lower the Cβ-O bond
energy from 247.9 to 161.1 kJ mol−1,[2a] then another catalytic
system was used to creak β-O-4 ketone in the second step.
Inspired by the encouraging results of these catalytic systems, we
envisage to develop a highly efficient, recyclable earth-abundant
metal heterogeneous catalyst, by which the oxidation of β-O-4
alcohol to β-O-4 ketone and the oxidation abruption of β-O-4
linkage can be realized in one-pot process.
On the other hand, N-doped carbon supported Co
nanoparticles derived from ZIF-67 have been widely applied in
catalysis (especially for oxidation),[15] electrochemistry,[16] and gas
adsorption.[17] Nevertheless, compared with ZIF-67, the BET
surface areas of Co/CN prepared by pyrolysis is greatly reduced
and the metal nanoparticles are agglomerated. To solve these
issues, Jiang and co-works have been successfully synthesized
a Co/Zn bimetallic ZIFs as templates/precursors to afford Co NPs
embedded in nitrogen-doped porous carbon (Co@CN) with high
surface area and high graphitization degree.[18] During the
pyrolysis process, Zn would be evaporated away at high
temperature (> 900 oC). The obtained Co@CN has been
exploited as an electro-catalyst that exhibits excellent ORR
activity approaching the value of Pt/C. If this is the case, it can be
expected that the catalyst may be also work well in the oxidative
depolymerization of lignin.
Introduction
Lignin as the second richest biomass polymer on the earth, is
regarded as the most promising biofuel and biochemical resource
owing to its potential to produce functionalized aromatic fine
chemicals.[1] Different linkages like β-O-4, α-O-4, 4-O-5 and β-1
are prevalent in lignin,[2] so breaking down these linkages under
mild conditions is extremely important for the utilization of lignin.
In recent years, various approaches have been proposed for
lignin transformation such as acidolysis,[3] alkaline hydrolysis,[4]
transfer hydrogenation[5] oxidation,[6] hydrogenolysis[7] and so on.
Among these, the oxidative depolymerization of lignin is one of
the most attractive strategies because it overcomes graphite
stacking energy and molecular aggregation, and leads to highly
functionalised monomeric or oligomeric products, which can be
used directly as fine chemicals or as platform chemicals.[8]
Oxidative cleavage of lignin and its associated model
compounds has been extensively investigated in the past few
decades. At the initial stage, a great deal of researches have been
done on homogeneity strategies including biomimetic catalysts,[9]
With our interest in the exploring nano metal catalysts for the
depolymerization of lignin,[19] herein we report an one-pot Co@CN
catalyzed selective oxidative dissociation of lignin and lignin
model compounds with different linkages like β-O-4, α-O-4 and β-
1 in methanol in the presence of ambient pressure O2 under mild
conditions (383 K) without the assistance of any acid, base, ligand
or noble metal.
[a]
[b]
K. Sun, J. Zhang, G. Lu, Prof. C. Cai
Chemical Engineering College
Nanjing University of Science&Technology
Xiaolingwei 200
Nanjing 210094 (P. R. China)
E-mail: glu@njust.edu.cn, c.cai@njust.edu.cn
S. Chen
School of Chemistry and Chemical Engineering
Guangzhou University
Guangzhou 510006 (P. R. China)
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201801752
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Results and Discussion
particles (Figure 2b). However, the Co/CN resulted by the
calcination of ZIF-67 was severely deformed and disordered
(Figure 2c). From TEM images (Figure 2d), it is clear that Co
nanoparticles with an average size of 24 nm were better
dispersed in Co@CN than in Co/CN (Figure 2d vs 2e). In addition,
it can be observed from the elemental mapping that Co@CN has
a more uniform element distribution than Co/CN, which is
consistent with the results of SEM, TEM analysis (Figure 3).
The XRD patterns of as-synthesized ZIF-8, ZIF-67 and BMZIF
(Figure 1a) match well with the simulated and also the published
XRD patterns in the literature,[18] confirming the as-synthesized
MOF structure in this work. The XRD pattern of Co@CN (Figure
1b) shows that the C (002) diffraction peak shifts from 23 to 26°
compare with CN (ZIF-8). This result indicates that the
graphitization degree in Co@CN is increased, which is beneficial
to the improvement of the electron transfer from graphitic nitrogen
to Co NPs. The Raman spectra (Figure S1) show that CN (ZIF-8)
gives a relatively high value of ID/IG compared with Co@CN, which
further confirms the result.[20] There are three diffraction peaks at
around 44, 51 and 76°, respectively, corresponding to the
characteristic diffractions of (110), (200), and (220) lattice planes
of metallic Co (JCPDS No. 15-0806),[15a] indicating that the ligand
carbon has been successfully reduced CoII in Co-MOF to Co0 at
high temperature.[21]
Figure 2. SEM images of (a) BMZIFs; (b) Co@CN; (c) Co/CN; and TEM images
of (d) Co@CN; (e) Co/CN.
Figure 1. XRD patterns of (a) as-synthesized ZIF-8, ZIF-67 and BMZIFs,
simulated ZIF-8 and ZIF-67; (b) Co@CN and CN (ZIF-8) catalysts.
The surface morphology of BMZIFs, Co@CN and Co/CN was
investigated by SEM. It can be observed that the BMZIFs has a
uniform polyhedron shape, with an average size of 85 nm (Figure
2a). After calcination at 900 ℃, the morphology of the particles
remains largely unchanged except for the partial shrinkage of the
Figure 3. SEM image and the elemental mapping of (a) Co@CN; (b) Co/CN
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The contents of Co and Zn in the catalysts were measured by
ICP-MS. The results indicated that the total Co contents of
Co@CN were around 4.96 wt% (Table S1 in SI) while the Zn
residue was almost negligible (0.06 wt%), which is due to Zn
would be evaporated away during the pyrolysis process at 900 °C .
The chemical states of catalyst Co@CN was further studied by
XPS spectra (Figure S2). The XPS spectra of Co 2p and N 1s in
Co@CN are shown in Figure 4. The N 1s spectra of the Co@CN
composites can be fitted into two peaks at 398.3 and 400.9 eV
respectively, which are consistent with the pyridinic N and
graphitic N in the carbon matrix.[22] These N sites may give the
catalyst a rich Lewis base site, which may promote the interaction
between lignin and catalyst by hydrogen bonds. Two peaks were
observed at around 795.06 eV and 779.68 eV, indicating that Co
species in Co@CN existed as Co0 in the Co cluster, which was
also in accordance with the XRD results (Figure 1b). However,
there are some differences between these two peaks and those
reported in the literature,[23] presumably due to the strong electron
transfer from graphitic nitrogen to metallic Co NPs.[24] This
electron transfer can inhibit the oxidation of cobalt nanoparticles
and improve the catalytic activity effectively. Therefore, the
catalysts should be stable under air atmosphere at room
temperature.
Nitrogen gas sorption measurements were performed to
estimate the Brunner-Emmet-Teller (BET) specific surface area
(m2/g) and the porous texture of the obtained Co@CN. As shown
in Figure 5, it was observed that the Co@CN exhibits a BET
surface area of 686 m2 g-1, which exhibited type IV isotherms with
medium-pressure and high-pressure region hysteresis loops,
demonstrating that the coexistence of micropore and mesopore
in the structure of the Co@CN.[25] The total pore volumes of
Co@CN are 0.51 m3 g-1. The high pore volume of the catalysts
can provide more surface area to enhance the accessibility of the
reaction substrates to the Co NPs. While the Co/CN exhibits only
the surface area of 80 m2 g-1 and the total pore volumes of 0.21
m3 g-1, much smaller than Co@CN.
Figure 5. Nitrogen adsorption/desorption isotherms for Co@CN and Co/CN
and the corresponding BJH pore-size distribution curves.
To investigate the absorptivity of the catalysts to substrate, the
FT-IR experiments were performed. The signals of 1a (Figure
S3a) disappeared after Co@CN was added (Figure S3c), leaving
only the absorption peak of the catalyst. However, if we replaced
Co@CN with Co/ZrO2 or Co/MgO (Figure S3d, S3e), the infrared
absorption singles still existed. These results suggest that highly
porous structure of Co@CN can absorb the lignin models
efficiently, which shortens diffusion pathway and provides
sufficient interface area accessible to lignin models compared
with the traditional solid carriers, thereby making the reactants
fully contact with the catalysts, thus playing a better catalytic role.
Furthermore, the porous structure of Co@CN may also have a
strong absorption ability for oxygen,[17] which is also beneficial to
the oxidative cleavage of lignin.
The catalytic activities of the prepared materials were tested
using the oxidative conversion of β-O-4 lignin model 1a as a
model reaction (Table 1). The catalytic reaction was carried out
under atmospheric pressure using O2 as oxidant at 110 °C in
methanol. The blank run (without any catalysts) gave essentially
no activity in this system after 12 h (Table 1, entry 12). When CN
Figure 4. XPS spectra of Co@CN: (a) Co 2p; (b) N 1s
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material (derived from ZIF-8) was used as the catalyst, only a
trace of products can be detected (Table 1, entry 11). To our
delight, in the case of Co@CN, 2a, 3a and 4a could be obtained
at the yields of 65 %, 31 % and 32 %, respectively. These results
indicated that the Co NPs in Co@CN was the active sites for the
oxidative conversion of β-O-4 lignin models. Then, we tried to
perform the reaction in the air, and after 12 h of stirring, 21 % of
phenol was detected, which was lower than that reaction in
oxygen (Table 1, entry 13). When the reaction time was prolonged
to 24 h, the yields of phenol and methyl benzoate was enhanced
(Table 1, entry 14). We next investigated the catalytic behaviors
of several typical supporters such as AC (active carbon), Nb2O5,
MgO, ZrO2 and SiO2 (Table 1, entries 6-10) for the oxidative
conversion of 1a. However, conversions of 1a were quite low
owing to the fact that the zero valence cobalt was attached to the
surface of the support, which is particularly vulnerable to oxidation
without protection.[26]
nitrogen in carbon nitrogen matrix keeps cobalt in zero valence
state. In addition, the ratio of Zn and Co in the bimetallic ZIF
precursor plays a crucial role in the catalytic activity of the
obtained materials. When ZIF-67 was calcined directly, the
catalytic reaction of the derived material was only 5% conversion
(Table 1, entry 5). When the ratio of Zn and Co in bimetallic ZIF
precursors was increased to 5:1, the yield was slightly better
(Table 1, entry 1). When the ratio of Zn and Co in bimetallic ZIF
precursors was increased to 20:1 (Table 1, entry 4), the
conversion rate is 70 % that slightly better than the use of Co@CN,
because the smaller the Co ratio is, the more dispersed Co NPs
and higher specific surface area it is found in the material.
However, considering the material loss after calcination, we
chose Zn/Co at 10:1 as the catalyst for the reaction. Complete
transformation was detected after 12 h using 8 mol% Co@CN
(catalyst amount measured based on Co) as the catalyst (Table
1, entry 3).
Oxidative conversion of different lignin model compounds was
investigated to further demonstrate the versatility of Co@CN in
Table 2. A series of substituted β-O-4 linkage models were high
selectively converted to phenol in moderate to excellent yields
(Table 2, entries 1-6), while previous studies on the oxidative
cracking of lignin showed that the yield of phenol was low since
phenol was easily oxidized.[8b,27] The α-O-4 is another common
type of linkage in lignin that has a higher bond energy than the β-
O-4 linkage,[28] so breaking α-O-4 linkage has been always a
difficult challenge. To our delight, the 8% conversion rate of α-O-
4 linkage could be achieved in the presence of Co@CN (Table 2,
entry 7). When a nitro was connected to the benzene ring, 51%
conversion of α-O-4 lignin model was achieved under identical
conditions (Table 2, entry 8). β-1 linkage is prevalent in hardwood,
but few researches have been explored for the cleavage of this
linkage.[29] As expected, the Co@CN was also active for breaking
β-1 linkage with excellent yields and selectivity (Table 2, entries
9,10).
Table 1． Optimization of the conditions for oxidation of lignin model compound
1a.[a]
Yield(%)
Entry
catalyst
2a
9
3a
2
4a
5
1
Co@CN[d]
Co@CN
Co@CN
Co@CN[e]
Co/CN
2
65
98
70
5
31
66
56
0
32
33
13
0
3[c]
4
5
6
Co/AC
5
0
0
7
Co/Nb2O5
Co/MgO
Co/ZrO2
Co/SiO2
CN(ZIF-8)
-
4
0
0
8
5
0
0
9
3
0
0
10
11
12
13
14
4
0
0
6
3
0
0
0
0
Co@CN[f]
Co@CN[g]
21
54
14
36
6
15
[a]
Reaction conditions: 1a (0.2 mmol), catalyst (20 mg, 4 mol% of Co), MeOH
[b]
(1.5 mL), 0.1 MPa O2, 110 °C, 12 h.
anisole as an internal standard. [c] Catalyst 40 mg (8 mol% of Co). [d] The ratio
of Zn and Co in the bimetallic ZIF was 5:1.
bimetallic ZIF was 20:1. [f] The reaction was proceed under air. [g] The reaction
mixture was stirred under air for 24 h.
Yields were determined by GC using
Figure 6. Partial 2D HSQC NMR spectra of organosolv lignin (a) before and (b)
after oxidation.
[e]
The ratio of Zn and Co in the
To further demonstrate the potential of Co@CN, it was also
tested on an organosolv lignin extracted from birch sawdust under
similar conditions, which provides lignin with a structure similar to
On the contrary, the zero valence cobalt of Co@CN protected
by carbon nitrogen matrix, and the electronic supply of graphite
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Table 2． Substrate scope of various oxidized lignin models.[a]
entry
substrate
product（%）
1
98
60
66
29
33
30
2
3
4
5
83
97
95
41
74
58
41
24
33
6
73
39
34
7
8
8
8
28
39
51
41
9
10
43
47
[a] Reaction conditions: Substrate (0.2 mmol), Co@CN (40 mg, 8 mol% Co), MeOH (1.5 mL), 0.1 MPa O2, stirred in a sealed tube at 110 °C for 12 h. b The yields of
all products were determined by GC using anisole as an internal standard.
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the native lignin.[30] To better understand the change of the lignin
structure before and after reaction, 2D-HSQC NMR spectroscopy
was performed. The disappearance of the β-O-4 peak (A) could
be readily identified in the 2D HSQC NMR spectrum (Figure 6).
The result was also analyzed by GC-MS (Figure S4), and a
mixture of aromatics was obtained in 15 wt% yields.
Finally, the stability and reusability of Co@CN catalyst was also
investigated by selecting the oxidative cleavage of 1a as the
model reaction (1 mmol scale). After reaction completed, the
catalyst was easily separated by an external magnet due to the
strong magnetism of Co@CN (Figure 7b). Then, it was washed
with ethanol to remove the absorbed organic chemicals, and dried
in a vacuum oven at 50 °C . It can be observed from figure 7a that
the efficiency of Co@CN was decreased due to the Co0 in
Co@CN could be oxidized at high temperature. To restore the
activity of Co@CN, the spent catalyst was reduced by H2 flow at
400 °C for 1 h before the next run.[15a] The results shown in Figure
7a reveal that Co@CN could be regenerated and reused at least
five times in subsequent reactions without a significant loss of
catalytic activity.
[31]
To explore the reaction mechanism, several mechanism
verification experiments were conducted (Scheme 1). According
to previous reports,[32] lignin β-O-4 alcohol will be oxidized to β-O-
4 ketone in the first step. If β-O-4 ketone was used as the
substrate, under the same reaction conditions, the yields of these
compounds were 86 %, 58 wt% and 28 wt%, respectively. (eqn
1). According to the experimental results, we can find that the
products contain methyl benzoylformate, and the content of
methyl benzoylformat decreased with the increase of reaction
time. When the methyl benzoylformate was used as the substrate,
93 % of methyl benzoate was found in methanol after the reaction
(eqn 2). This indicates that methyl benzoylformate is one of the
intermediates. Previous studies have shown that the oxidation
process may take place via the OOH free radical pathway.[2d,32,33]
In this work, the reaction was carried out by adding the of free
radical quenching agent 2,2,6,6-tetramethylpiperidinyloxy
(TEMPO) into the reactor to study whether the reaction proceeded
by a free-radical pathway. When 1.2 eq TEMPO was added, the
reaction was almost impossible (eqn 3). These results indicated
that free radicals may be formed in the oxidation process. Finally,
no reaction occurred when benzoic acid was applied as the
substrate, which indicated that benzoic acid was not a reaction
intermediate (eqn 4).
On the basis of the above experiments and previous works, a
plausible reaction mechanism for the oxidative cleavage of lignin
is presented in Scheme S1. Firstly, 2-phenoxy-1-phenylethanol
was oxidized into 2-phenoxyacetophenone with the help of
Co@CN in oxygen atmosphere. Whose β-O-4 bond becomes
weakened because of the presence of Cα=O. In this process,
dioxygen will be activated to the superoxide species with the
assistance of Co@CN. Then the 2-phenoxyacetophenone can be
oxidized into ROOH transition state. The subsequent cleavage of
Cβ-O and O−O bond to form phenol and methyl benzoylformat.
Finally, methyl benzoate was formed by oxidative cleavage of the
C-C bond of methyl benzoyoformate.
Figure 7 (a) Recyclability of Co@CN in the oxidation of lignin (Blue: The
Co@CN was treated by H2 flow 400 °C for 1 h before the next run. Red: There
is no other treatment after Co@CN cycling). (b) The photographs showing the
facile separation of the catalyst via an external magnet.
Conclusions
In summary, we have developed a highly efficient, low-cost and
magnetically recyclable Co@CN nanocatalyst for the selective
oxidative depolymerization of lignin via a pyrolysis of a bimetallic
ZIF based on ZIF-8 and ZIF-67. The catalytic system features a
broad substrate scope for lignin model compounds with different
linkages like β-O-4, a-O-4 and β-1 as well as organosolv lignin
extracted from birch sawdust, giving their corresponding phenol
and esters in good to excellent yields under mild conditions
without the assistance of any other additives. The small Co NPs
in Co@CN are better dispersed inside the porous carbon and
nitrogen matrix than Co/CN, which effectively limits the
aggregation and oxidation of the Co NPs. Compared with
Scheme 1 Control experiments to illustrate the reaction mechanism.
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separated by magnetic force, the organic solution was collected and
concentrated in vacuum. Then, the obtained residue was analyzed by
GC/MS. The conversion and the product yields were determined by GC
with anisole as an internal standard.
traditional supported catalyst, the catalyst gives a higher hollow
structure that is favor to the adsorption of substrates and oxygen,
thus improving the catalytic efficiency of the catalyst. The
nanocatalyst can be readily recycled with an external magnet and
reused after reduction at least five times without any loss of
activity. Excellent catalytic performance, simple preparation
technology and retrievability endow Co@CN great potential for
industrial application in the production of phenol and methyl
benzoate from direct aerobic oxidation of lignin.
The procedure for the oxidative dissociation of organosolv lignin.
Organosolv lignin (50 mg), Co@CN (40 mg), CH3OH (2 mL), and a
magnetic stirrer was placed into a 25 mL sealed tube. The sealed tube was
degassed and replaced several times with O2. Then the sealed tube was
transferred into an oil bath that was preheated to 110 °C for 12 h. After the
reaction completed, the mixtures were cooled to ambient temperature and
EtOAc (5 mL) was added to the sealed tube. After the solid was separated
by centrifugation, the organic solution was collected and concentrated in
vacuum. Then, the obtained residue was analyzed by GC/MS and 2D
HSQC NMR.
Experimental Section
Catalyst Preparation.
The synthesis of BMZIFs was carried out following a literature procedure
with a minor modification.[18] Typically, 0.13 g of Co(NO3)2·6H2O and 1.33
g of Zn(NO3)2·6H2O were dissolved in 100 mL of methanol, forming a
homogeneous solution. Then, 3.244 g of 2-methylimidazole was dissolved
in 100 mL of methanol. The two solutions were mixed at room temperature,
stirred for 30 min, and then allowed to stand for 24 h. The final product
were obtained by centrifugation and washed three times with methanol
followed by vacuum drying at 150 ℃ for 12 h. Different BMZIFs could be
prepared by changing the mole ratio of Co(NO3)2·6H2O and
Zn(NO3)2·6H2O (1/5 or 1/20).
Acknowledgements
We gratefully acknowledge Chinese Postdoctoral Science
Foundation (2015M571761, 2016T90465) for financial support.
This work was a project funded by the Priority Academic Program
development of Jiangsu Higher Education Institution. We also
thank Wan-yin Tang at Analysis and Test Center Nanjing
University & Technology for the help in obtaining the FT-IR data.
Keywords: Bimetallic zeolitic imidazolate frameworks • Cobalt
nanoparticles • Heterogeneous catalysis • Lignin • Oxidation
depolymerization
The as-prepared BMZIFs were carbonized at 900 ℃ for two hours under
an argon atmosphere at a heating rate of 5 ℃/min, followed by cooling to
ambient temperature to afford Co@CN. The Co/CN was also prepared by
the similar process except that ZIF-67 instead of BMZIFs was used.
[1]
[2]
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a) J. Luo, X. Zhang, J. Lu, J. Zhang, ACS Catal., 2017, 7, 5062-5070; b)
J. M. Fraile, J. I. García, Z. Hormigón, J. A. Mayoral, C. J. Saavedra, L.
Salvatella, ACS Sustainable Chem. Eng., 2017, 6, 1837-1847; c) R. M.
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Luo, F. Wang, Green Chem. 2017, 19, 702-706.
GC-MS was performed on an ISQ Trace 1300 in the electron ionization
(EI) mode. GC analyses are performed on an Agilent 7890A instrument
(Column: Agilent 19091J-413: 30 m × 320 μm × 0.25 μm, carrier gas: H2,
FID detection. XRD analysis was performed on Shimadzu X-ray
diffractometer (XRD-6000) with Cu Kα irradiation. Transmission electron
microscopy (TEM) images were taken using a PHILIPS Tecnai 12
microscope operating at 120 kv. Scanning electron microscopy (SEM)
images and energy dispersive spectroscopy (EDS) was performed using
a Hitachi S-4800 apparatus on a sample powder previously dried and
sputter-coated with a thin layer of gold. X-ray photoelectron spectroscopy
(XPS) were performed on a ESCALAB 250Xi spectrometer, using a Al Kα
X-ray source (1350 eV of photons) and calibrated by setting the C 1s peak
to 284.80 eV. Inductively coupled plasma mass spectrometry (ICP-MS)
was analyzed on Optima 7300 DV. Infrared (IR) spectra were collected on
a Nicolet NEXUS670 Fourier transform IR spectrophotometer at room
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Entry for the Table of Contents (Please choose one layout)
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Kangkang Sun, Shujie Chen, Jiawei
Zhang, Guo-Ping Lu* and Chun Cai*
Page 1 – Page 8
Cobalt Nanoparticles Embedded in
N-Doped Porous Carbon Derived
from Bimetallic Zeolitic Imidazolate
Frameworks for One-pot Selective
Oxidative Depolymerization of Lignin
One-pot Co@CN catalyzed selective oxidative dissociation of lignin and lignin model
compounds with different linkages like β-O-4, α-O-4 and β-1 under mild conditions
without the assistance of any acid, base, ligand or noble metal has been reported.
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[a]
K. Sun, J. Zhang, G. Lu, Prof. C. Cai
Chemical Engineering College