Mesoporous nitrogen-doped carbons with high nitrogen contents and ultrahigh surface areas: Synthesis and applications in catalysis

Article abstract of DOI:10.1039/c5gc01920f

The development of mesoporous nitrogen-doped carbons (NDCs) with high nitrogen contents and high surface areas from biomass is of significance for many applications, such as oxidation reaction catalysts, electrode materials and so on. Herein we report a simple route to prepare mesoporous NDCs via calcinating the mixture of biomass feedstocks (including glucose, cellulose and lignin) and melamine using eutectic salts of KCl and ZnCl₂ as the porogen, and a series of mesoporous NDCs with nitrogen content up to 11.9% and BET specific surface area up to 1800 m² g^-1 were obtained. Served as metal-free catalysts for oxidation of hydrocarbons with tert-butyl hydroperoxide in aqueous phase, the mesoporous NDC with a N content of 11.4% showed the highest efficiency compared to the reported N-doped carbons. Moreover, the as-prepared NDCs were indicated to be an ideal support to immobilize noble nanoparticles (e.g., Pd, Rh, Ru, Pt), producing a series of NDC supported metal nanocatalysts with metal particle size of around 2 nm. This work opens up a new way to prepare mesoporous N-doped carbon materials with tailored properties.

Full text of DOI:10.1039/c5gc01920f

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DOI: 10.1039/C5GC01920F
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ARTICLE
Mesoporous Nitrogen-Doped Carbons with High Nitrogen Content
and Ultrahigh Surface Areas: Synthesis and Applications in
Catalysis
Received 00th January 20xx,
Accepted 00th January 20xx
Zhishuang Ma, Hongye Zhang, Zhenzhen Yang, Guipeng Ji, Bo Yu, Xinwei Liu, Zhimin Liu*
DOI: 10.1039/x0xx00000x
Development of mesoporous nitrogen-doped carbons (NDCs) with high nitrogen content and high surface areas from
biomass is of significance for many applications, such as oxidation reaction catalysts, electrode materials and so on. Herein
we report a simple route to prepare mesoporous NDCs via calcinating the mixture of biomass feedstocks (including
glucose, cellulose and lignin) and melamine using eutectic salts of KCl and ZnCl2 as the porogen, and a series of
mesoporous NDCs with nitrogen content up to 11.9% and BET specific surface area up to 1800 m2·g -1 were obtained.
Served as metal-free catalyst for oxidation of hydrocarbons with tert-butyl hydroperoxide in aqueous phase, the
mesoporous NDC with N content of 11.4% showed the highest efficiency compared to the reported N-doped carbons.
Moreover, the as-prepared NDCs were indicated to be ideal support to immobilize noble nanoparticles (e.g., Pd, Rh, Ru, Pt),
producing a series of NDC supported metal nanocatalysts with metal particle size around 2 nm. This work opens up a new
way to prepare mesoporous N-doped carbon materials with tailored properties.
www.rsc.org/
excellent electrocatalytic activity toward the oxygen reduction
reaction (ORR)11, 13-15. However, it is still challenging to
prepare this kind of NDCs.
Introduction
Nitrogen-doped carbons (NDCs), especially with mesoporous
structures, have received rapidly growing interest in recent
years owing to their remarkable performances in various
applications, such as super-capacitors1, oxygen reduction
catalyst2, catalyst supports3 and gas capture/storage4, etc. The
doped-nitrogen can be regarded as an n-type carbon dopant, and
its lone pair of electrons can interact with the carbon π system,
which causes structural irregularity of the hexagonal carbon
ring and greatly alters the physical and chemical properties of
NDCs can be realized either by direct synthesis using
nitrogen-containing precursors such as melamine16-18
N-
,
heterocycles19-21, benzylamine22, or ionic liquids (ILs)3, 9, 10, 12, 23,
24, or by post-treatment of carbons in the atmospheres of N-
containing compounds (e.g., NH3) at high temperatures25-29. As
for NDCs with high contents of structural nitrogen, their
preparation is usually achieved by using nitrogen-containing
precursors resulting in
a homogeneous incorporation of
nitrogen together with controlled bulk properties. Typical
examples include the use of N-containing ILs as excellent
precursors to produce functional NDCs with controlled pore
architectures9, 30-33. For example, Antonietti and coworkers34
prepared NDCs with specific surface areas up to 1500 m2·g-1
and N content around 12% via carbonization of nucleobases
dissolved in an IL (i.e., 1-ethyl-3-methylimidazolium
dicyanamide) using silica nanoparticles as the hard template,
which showed very high catalytic activity in the oxygen
reduction for fuel cells. Wang et al synthesized a kind of NDCs
with N content of 12 wt% by using a nitrogen-containing IL
(i.e., 3-methyl-1-butylpyridine dicyanamide) as the precursor
and silica nanoparticles as hard template, which could stabilize
Pd nanoparticles, and the supported Pd catalyst showed very
high catalytic activity in hydrodeoxygenation of vanillin4.
the carbon materials, such as the basicity5, catalytic activity6-8
,
oxidative stability9, and so on. The bulk properties of these kind
materials mainly depend on the content as well as mode of the
doped-nitrogen and the structure of the material (e.g., specific
surface areas)9-11. Generally, two major types of the doped-
nitrogen configurations can be distinguished: chemical nitrogen
and structural nitrogen8, 12. The former appears as surface
functionalities (e.g., amine or nitrosyl group), while the latter as
the nitrogen directly bonded into the backbone of the carbon
material (for example, pyridinic, pyrollic or quaternary-type
nitrogen). As reported, NDCs with high nitrogen content,
especially with high quaternary-type nitrogen content, show
From the standpoint of green and sustainable chemistry18, 35,
36, exploring simple strategy using inexpensive, abundant and
renewable resources to produce NDC materials with a large
specific surface area and high nitrogen content is highly
desirable. In a recent work, Wang et al prepared NDCs using
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glucose as the carbon source and a (poly(ionic liquid) as the N NDC samples were termed as M-G (or C and L)-c-T in this
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dopant; however, the N content (~5%) and specific surface work, where M stands for nitrogen resoDuOrcI:e10m.1e0l3a9m/Ci5nGeC, 0G192f0oFr
areas (~400 m2·g -1) of the resultant NDC were relatively low10. glucose (C for cellulose and L for lignin), and c corresponds to
Melamine as
a
nitrogen-enriched, inexpensive and the mass ratio of melamine to carbon source and T to the final
commercially available raw material is a good nitrogen-source calcination temperature.
for the synthesis of the N-doped carbons16, 17, though it is not a
The nitrogen content of the resulting NDCs was examined by
green chemical. Shu and coworkers prepared nitrogen-doped elemental analysis, and the results are listed in Table S1. As
mesoporous graphitic carbon with specific surface area ~200 expected, the nitrogen content of NDCs strongly depended on
m2·g -1 using melamine as a nitrogen source and citric acid as a the ratios of melamine to carbon source in the starting materials,
carbon source without any template17. Cellulose, lignin and and increased from 1.1 wt% for G-800 to 11.9 wt% for M-G-3-
their derivatives (e.g., glucose easily obtained from cellulose 800. The presence of N in G-800 may be originated from the N2
hydrolysis) are abundant and economical feedstocks and have atmosphere during the calcination process. With the
been widely applied in the preparation of carbon materials. melamine/glucose ratio at 1.5, the nitrogen content in the
Moreover, due to the presence of plentiful oxygen in the these resultant NDC reached up to 11.4 wt%, comparable to the
biomass resources, the resultant carbons are generally rich in highest value reported in literature using N-containing IL as the
oxygen-containing groups, which provides the resultant carbons carbon and nitrogen precursors. Further increasing the
with specific functions37, 38
.
melamine amount in the starting mixture did not afford NDCs
In this article, we report a simple route to prepare NDCs with with more nitrogen contents, suggesting that the nitrogen
mesoporous structures based on a “Salt Templating” synthesis content in the nitrogen-doped carbons cannot increase
procedure38 using biomass (including glucose, cellulose, lignin) indefinitely. The solid yield of the resultant samples increased
and melamine as the carbon and nitrogen sources, respectively, with the mass ratios of melamine to glucose increase, reaching
and the KCl/ZnCl2 mixture with the molar ratio of KCl: ZnCl2 the highest value of 27.4% at the melamine/glucose ratio of 1.5,
at 51: 49 (denoted as PZ, melting point at 230 °C )24 as the consistent with the change tendency of nitrogen content.
porogen and solvent. The resultant NDCs were characterized by Further increasing the melamine/glucose ratio resulted in
means of different techniques such as XPS, SEM, TEM, FT-IR, decrease in the sample yields. Thus, taking both of the nitrogen
nitrogen sorption, and so on. It was demonstrated that the as- content and the carbon yield into account, the appropriate ratio
prepared NDCs possessed high nitrogen contents up to 11.9% of melamine to glucose was set at 1.5. In addition, using
with quaternary-N species of 31%, and possessed mesoporous cellulose or lignin instead of glucose as the carbon source,
structures with specific surface area (SSA) up to 1731 m2·g -1, samples M-C-1.5-800 and M-L-1.5-800 were prepared,
which was the largest one among the reported values to the best respectively, both of which possessed high nitrogen contents
of our knowledge. The pore volume reached 1.83 cm3·g -1, around 9.0 wt%, as illustrated in Table S1. This suggests that
dominated with mesopore volume proportion of 77.4%. The as- the method to prepare NDCs in this work is suitable for various
prepared NDC with N content of 11.4% as a metal-free catalyst carbon sources with melamine as the starting materials.
showed high efficiency for the oxidation of alkanes in aqueous
phase with tert-butyl hydroperoxide (TBHP) as the oxidant.
Moreover, as supports NDCs could immobilize noble metal
nanoparticles (e.g., Pd, Pt, Ru and Rh), resulting in a series of
supported metal nanocatalysts.
Results and discussion
The fabrication of NDCs was based on “Salt Templating”
synthesis together with gradient heating carbonization
program38. Typically, carbon source (e.g., glucose), melamine
and PZ with a certain ratio were directly mixed via grinding at
room temperature, and the mixture was subsequently heated
with a gradient temperature program under nitrogen atmosphere.
The mixture was first heated at 240 C for 4 h to make carbon
source and melamine dissolve in PZ uniformly, and form cross-
linked compounds via the reactions between glucose and
melamine catalysed by PZ. Then the temperature was increased
Figure 1 (A) XPS survey spectrum, (B) C1s XPS spectrum, (C) O1s XPS spectrum
to 800 C with a rate of 1 C/min, and kept at 800 C for 6 h,
aiming at getting carbon materials with mesoporous pores. The
NDCs with various nitrogen contents were prepared through
varying mass ratios of melamine to carbon source (e.g.,
glucose). As reference a carbon sample without N was prepared
in the absence of melamine, denoted as G-800. The as-prepared
and (D) N1s XPS spectrum of the sample M-G-1.5-800.
The types of the structural nitrogen species in the resultant
NDCs were analysed by X-ray photoelectron spectroscopy
(XPS). The XPS survey spectrum of sample M-G-1.5-800
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(Figure 1A) showed the presence of the principal C1s, O1s, and surface area (SSA), pore volume and size distribution of the
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N1s core levels. In the C1s spectrum (Figure 1B), the wide resultant NDC samples were obtainedD, OaIn: d10.s10u3m9/mC5aGriCz0e1d920inF
peak ranging from 282 to 290 eV can be resolved into four
individual component peaks at 284.7, 285.5, 286.5 and 289.0
eV, respectively, corresponding to C-C, C-OH, C=O and C-
C=O bonds. Meanwhile, the XPS spectrum of O1s (Figure 1C)
(C-OH at 533.9 eV, C=O at 532.5 eV, and C(O)OH at 531.8 eV)
also confirmed the existence of oxygen-containing groups. The
presence of oxygen-containing groups in the resultant NDCs
may afford them different properties compared to the traditional
carbon materials (e.g., amphiphilicity). In the N1s XPS
spectrum (Figure 1D) three peaks could be deconvoluted with
binding energies (BEs) at 398.4, 399.3, 401.2 eV, assigning to
pyridinic, pyrrolic and quaternary nitrogen, respectively. Based
on the integration areas of the different N species in the XPS
spectrum, the contents of nitrogen species in different form
could be estimated, following the order for sample M-G-1.5-
800: pyridinic nitrogen (36.3%), pyrrolic nitrogen (33.3%) and
quaternary nitrogen (30.4%). As listed in Table S1, the
quaternary nitrogen contents in the resultant NDCs increased
Figure 2 (A) SEM image, (B) TEM image and EDS profile (inset), (C) XRD pattern
with the ratios of melamine to glucose, and reached a maximum
and (D) N2 sorption isotherm and DFT pore size distribution of the M-G-1.5-800
sample (inset).
as the ratio increased to 1.5. However, further increasing the
melamine/glucose ratio to 3, the quaternary N in M-G-3-800
decreased to 25.2%. It was reported that the quaternary N was
Table 1. To our delight, all the samples prepared in this work
the most active specie for catalysing selective oxidation of
showed high SSAs in the range from 1273 to 1834 m2·g -1, with
alkanes and alcohols39. The high content of quaternary N in the
large mesopore volumes from 1.00 to 3.00 cm3·g -1. For
resultant NDCs may result in high performance if the samples
example, M-G-1.5-800 showed a BET SSA of 1731 m2·g -1 and
serve as the catalyst for the oxidation of alkanes. In this work,
a pore volume of 1.83 cm3·g -1 dominated with mesopore
the ratio of melamine to glucose set at 1.5 was appreciate for
volume proportion of 77.4%. These values rank the as-prepared
getting high quaternary nitrogen content in NDCs.
NDCs among the nitrogen-doped porous carbons with the high
SSA together with high pore volumes.
The morphology and structure of the samples were
examined by scanning electron microscopy (SEM) and
transmission electron microscopy (TEM), and Figure 2A and
Table 1 Pore textural properties of the mesoporous nitrogen-doped carbon materials.a
2B show the typical SEM and TEM images of M-G-1.5-800.
Sample name
Stotal
(m2·g -1)
1424
1273
1671
1834
1731
1500
1787
1578
Pore volume (cm3·g -1)
Vmeso/Vtotal (%)
The SEM image (Figure 2A) revealed that M-G-1.5-800
appeared to be composed of uniform rough carbon
nanoparticles, which aggregated to give a porous structure. The
TEM image (Figure 2B) showed that M-G-1.5-800 had an
obvious interconnected mesoporous network with well-
Vtotal
Vmicro
0.19
0.25
0.44
0.45
0.41
0.08
0.45
0.34
Vmeso
G-800
1.64
1.65
1.44
1.45
1.83
3.08
1.47
1.41
1.45
1.40
1.00
1.00
1.42
3.00
1.02
1.08
88.3
85.1
69.3
69.0
77.4
97.5
69.2
76.2
M-G-0.33-800
M-G-0.67-800
M-G-1-800
dispersed spherules. The EDS profile (Figure 2B inset) M-G-1.5-800
M-G-3-800
M-C-1.5-800
M-L-1.5-800
obtained during the TEM observation indicated the existence of
N element together with trace amount of ZnCl2, consistent with
the elemental analysis results, and also suggesting that most of
the porogen salts could be removed by washing. In addition, the
XRD pattern (Figure 2C) of M-G-1.5-800 had two diffraction
peaks at 2θ ≈ 23° and 44° with large width and low intensity,
which may be ascribed to the graphitic carbon, albeit with
disorder. The above analyses indicate that nitrogen-doped
material with mesoporous structures was successfully
synthesized.
N2 sorption analysis was performed to determine the pore
textural properties of the as-prepared NDCs. Typically, M-G-
1.5-800 exhibited type IV sorption isotherm (Figure 2D),
typical feature of mesoporous materials, whose pore diameter
was centred at 3.8 nm according to the DFT model (Figure 2D,
inset). Based on the sorption isotherms, the BET specific
a
Stotal: total BET specific surface area; Vtotal: total pore volume; Vmicro: micropore
volume; Vmeso/Vtotal: mesopore volume proportion.
In order to investigate the NDCs formation process, the
samples prepared with the melamine/glucose ratio of 1.5 at
different calcination temperatures were examined by XPS and
FT-IR. The XPS results (Table S2) showed that only the sample
obtained at 800 C, i.e., M-G-1.5-800, had quaternary nitrogen
specie, suggesting that high temperature (e.g., 800 C) was
required for the formation of quaternary N species. This implies
that the carbon and nitrogen atoms of the NDCs probably
underwent an arrangement or condensation reaction in the
temperature range of 600-800 C to make the pyrrolic N or
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pyridinic N convert to more stable quaternary N. This 6 h. This result is comparable to those obtained over metal or
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phenomenon was also reported by M. Watanabe11.
organometallic complex catalysts40, , and much better than
41
DOI: 10.1039/C5GC01920F
The FT-IR spectrums are shown in Figure 3. Compared to those obtained over nitrogen-doped graphene materials39 (Table
that of melamine, the spectrum of each resultant sample shows 2, entry 3). The good performance of M-G-1.5-800 may be
declined or disappeared corresponding peaks accompanied with originated from its unique features with mesoporous structure,
appearance of new bands around 1623 and 1337 cm-1, assigning high quaternary nitrogen content, and high BET SSA. Further
to C=C and C=N vibration, respectively. This indicates that in prolonging reaction time resulted in the complete conversion of
PZ molten solution the reactions occurred to form C=C and ethylbenzene, however, with slight decline in the product yield,
C=N containing materials. Notably, with increase in which may be caused by the further conversion of the product
carbonization temperature the peak intensity of the band at under the experimental conditions. It was reported that the
1337 cm-1 of the resultant samples increased and shifted to low quaternary-type nitrogen was the most active specie for
wavenumbers, indicating that more C=N bonds formed in the catalyzing selective oxidation of alkanes and alcohols14, 15, 39
.
resultant samples, originated from the reaction of glucose and To verify this, M-G-3-800 with similar nitrogen content and
melamine catalysed by PZ. In the spectrum of M-G-1.5-800, less quaternary-N percentage than M-G-1.5-800 was examined,
there was an obvious wavenumber shift around 1337 cm-1, and it was demonstrated that M-G-1.5-800 was more active
suggesting that from 600 to 800 C the sample may undergo a than M-G-3-800 (Table 2, entries 1 and 4), consistent with the
rearrangement reaction and form quaternary N, consistent with reported results. In addition, the catalyst M-G-1.5-800 showed
the results of XPS analysis (Table S2). In addition, the bands in good reusability, confirmed by the fact that 88.4% yield of
the range of 3470-3135 cm-1 and at 1652 cm-1 were assigned to acetophenone was obtained after the catalyst was reused five
the stretching vibration and bending vibration of the primary times (Table 2, entry 5).
amine N-H bond of melamine, whose intensity became weaker
in the spectra of the samples obtained with the increased
carbonization temperature. This also suggests that the -NH2
groups from melamine may react with glucose and weaken the
hydrogen bond interaction.
Figure 4 Reaction time optimization. Reaction conditions: substrate (1.0 mmol), solvent
(H2O, 3 mL), 80 oC, 3.48 mmol TBHP and 12 mg catalyst.
Based on the above results, the oxidations of other aryl
alkanes with TBHP over M-G-1.5-800 were investigated under
the optimized conditions, and the results are listed in Table 2. It
was indicated that all the tested aryl alkanes could be oxidized
to the corresponding aromatic ketones or aldehydes in high
yields. Notably, even hexane could be oxidized effectively,
affording a product yield of 26.3% (Table 2, entry 13),
demonstrating that our NDCs catalysts were not only active for
benzylic substrates but also potentially active for the linear
hydrocarbons. Furthermore, this catalytic system could also
realize high conversion (85%) of ethylbenzene to acetophenone
(yield of 82.7%) by using O2 as the oxidant with a small
amount of TBHP as the initiator (Table 2, entry 14), which was
superior to the reported nitrogen-doped graphene material39.
More interestingly, benzyl alcohol could be oxidized without
TBHP as the initiator under 0.1 MPa oxygen pressure,
Figure 3 FT-IR spectrums of the resultant NDCs.
As reported, the N-doped carbons could catalyse the
oxidation of alkanes using tert-butyl hydroperoxide (TBHP) as
the oxidant. In this work, M-G-1.5-800 with a nitrogen content
of 11.4% was used to catalyse the oxidation of aryl alkanes
with TBHP in aqueous phase, and the oxidation of
ethylbenzene was first investigated as a model reaction. The
optimization of reaction conditions are shown in Figure S1. It
was indicated that M-G-1.5-800 was very active for catalysing
the ethylbenzene oxidation, and acetophenone was obtained as
the main product accompanied with a trace amount of 1-
phenylethanol. Figure 4 shows the dependences of the
ethylbenzene conversion and product yields on the reaction
time. It is demonstrated that under the experimental conditions
ethylbenzene could convert to acetophenone rapidly with a
conversion of 93.8% and acetophenone yield of 91.2% within
affording
a benzyl alcohol conversion of 12.3% and
acetophenone yield of 9.8% (Table 2, entry 15) under the
experimental conditions. The above results indicate that the as-
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Table 2: Oxidation of arylalkanes with M-G-1.5-800 in the aqueous phase.a
prepared NDCs were good catalyst for oxidation reactions,
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DOI: 10.1039/C5GC01920F
which can realize the oxidations of various alkanes or alcohol
under the metal-free conditions.
Entry
1
Substrate
Productb
Conv./%
Yield/%
O
Mesoporous nitrogen-doped carbons are good catalyst
supports. In this work, M-G-1.5-800 as a representative was
used to immobilize various metal nanoparticles including Pd, Pt,
Rh, Ru via the equal volume impregnation method followed by
hydrogen reduction42, and a series of M-G-1.5-800 supported
metal nanocatalysts were prepared, see Figure S2. Figure 5A
93.8
91.2
O
O
O
O
O
O
O
2c
3d
4e
5f
6
98.5
98.6
93.1
90.0
97.6
>99
97.3
91.3
87.2
88.4
>99
>99
shows
a
TEM image of M-G-1.5-800 supported Pd
nanocatalyst (denoted as Pd/M-G-1.5-800). In the TEM image,
the dark dots were identified as Pd nanoparticles, which were
uniformly distributed on the support with average particle size
around 1.4 nm. XPS analysis (Figure 5B) indicated that the Pd
species in the composite were present in the form of metallic
Pd0 and Pd2+. In addition, the other noble metal (e.g., Rh, Pt,
Ru)/M-G-1.5-800 composites with various metal loadings
showed the similar morphology to Pd/M-G-1.5-800, uniformly
decorated with metal nanoparticles of size around 1.5 nm with
narrow size distribution (Figure S2). These noble metal
nanocatalysts are expected to have promising applications in
catalysis, and the study on their catalytic performances is under
way in our laboratory.
7
O2N
O2N
O
98.7
101.3
8
O2N
OH
5.1: 1
O
89.5
85.4
60.0
82.6
9
O
O
O
O
10
Figure 5 (A) TEM image (Scale bar, 20 nm) and the Pd particle size distribution (inset),
(B) Pd 3d XPS spectrums of the 5% Pd/M-G-1.5-800 composite.
73.9
51.8
11
OH
OH
Conclusions
51.4
-
48.7
26.3
12
13
In summary, mesoporous nitrogen-doped carbons with
nitrogen content up to 11.9% and BET specific surface area up
to 1800 m2·g -1 were prepared with biomass feedstocks
(including glucose, cellulose and lignin) as the carbon precursor
and melamine as the nitrogen resource. The as-prepared NDCs
not only can serve as highly efficient catalyst for the oxidation
of hydrocarbons in aqueous phase under mild conditions (e.g.,
80 C), but also can be used as ideal supports to immobilize
metal nanoparticles. This study opens up a new route for the
development of mesoporous heteroatom-doped carbon
materials with tailored properties.
O
O
O
1.3: 1
14g
15h
85.5
12.3
82.7
9.8
O
OH
H
a Reaction conditions: substrate (1.0 mmol), TBHP (3.48 mmol, 70 wt % in water),
catalyst (12 mg), H2O (3 mL), 80 oC, 6 h; the conversion and yield were
determined by GC; Values listed with product mixtures refer to molar ratios;
b
c
d
12 h; The result from ref. 39 with reaction time 24 h under the same other
conditions to a; e The catalyst was M-G-3-800; f After the catalyst was reused five
times with reaction time 6 h; g Reaction conditions: TBHP (3.48 mmol, 70 wt % in
water) as initiator, ethylbenzene (10.0 mmol), catalyst (10 mg), H2O (10 mL), O2
(4.0 MPa), 100 oC, 48 h; h Reaction conditions: benzylalcohol (1.0 mmol), catalyst
(0.10 g), C2H5OH (5 mL), O2 (0.1 MPa), 120 oC, 5 h.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (no. 21125314, 21321063, 21403252) for financial
support.
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31 X. Wang and S. Dai, Angew. Chem. Int. Ed., 20V1ie0w, A4r9tic,le6O6n6li4ne-
6668.
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2 K. Gong, F. Du, Z. Xia, M. Durstock and L. Dai, Science,
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3 Y. Wang, J. Yao, H. Li, D. Su and M. Antonietti, J. Am. Chem.
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Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C5GC01920F
Graphic Abstract
Mesoporous nitrogen-doped carbons with high nitrogen content and ultrahigh surface areas were prepared using
biomass and melamine as the carbon and nitrogen sources, respectively, together with the eutectic salts KCl/ZnCl2
(PZ) as the porogen agent and solvent through gradient heating program. As a metal-free catalyst, the as-prepared
mesoporous NDCs showed the highest efficiency for the oxidation of alkanes in aqueous phase with tert-butyl
hydroperoxide (TBHP) as the oxidant under mild conditions (80 oC). Moreover, the as-prepared NDCs were
indicated to be ideal support to immobilize noble nanoparticles (e.g., Pd, Rh, Ru, Pt); producing a series of NDCs
supported metal nanocatalysts with metal particle size around 2 nm.