Bicontinuous mesoporous Co, N co-doped carbon catalysts with high catalytic performance for ethylbenzene oxidation

Article abstract of DOI:10.1039/c9nj00453j

A series of bicontinuous mesoporous Co, N co-doped carbon catalysts (Co-N-C), which have large pore sizes and high specific surface areas with remarkable catalytic activity, were prepared through a method using KIT-6 silica as a hard template, and cobalt porphyrin and sucrose as precursors. And morphological and structural characterizations were performed using N₂ adsorption-desorption isotherm, XRD, Raman, TEM and XPS techniques. The results showed that the ethylbenzene oxidation with TBHP as an oxidant over the bicontinuous mesoporous Co, N co-doped carbon catalysts achieved 93% of ethylbenzene conversion with about 99% of selectivity to acetophenone. The superior catalytic performance of the catalysts was attributed to the synergistic effect of factors such as high surface area and well-dispersed metal active sites.

Full text of DOI:10.1039/c9nj00453j

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Bicontinuous mesoporous Co, N co-doped carbon
catalysts with high catalytic performance for
ethylbenzene oxidation†
Cite this:DOI: 10.1039/c9nj00453j
Lushuang Zhang, Shanshan Jie and Zhigang Liu
*
A series of bicontinuous mesoporous Co, N co-doped carbon catalysts (Co–N–C), which have large
pore sizes and high specific surface areas with remarkable catalytic activity, were prepared through a
method using KIT-6 silica as a hard template, and cobalt porphyrin and sucrose as precursors. And
morphological and structural characterizations were performed using N2 adsorption–desorption iso-
therm, XRD, Raman, TEM and XPS techniques. The results showed that the ethylbenzene oxidation with
TBHP as an oxidant over the bicontinuous mesoporous Co, N co-doped carbon catalysts achieved 93%
of ethylbenzene conversion with about 99% of selectivity to acetophenone. The superior catalytic
performance of the catalysts was attributed to the synergistic effect of factors such as high surface area
and well-dispersed metal active sites.
Received 25th January 2019,
Accepted 8th April 2019
DOI: 10.1039/c9nj00453j
rsc.li/njc
donor ability, and increasing active sites.5 Additionally, the use
of doped metal nanoparticles, such as Pt, Pd, Rh, Ru and Au,
1. Introduction
Recently, diverse types of carbon-based materials have been emerges as an innovative tool in catalysis.6 Similar to
actively pursued due to their sustainability and remarkable molecularly-defined complexes, the activity and selectivity of
physiochemical properties, such as ultrahigh surface areas, such nanoparticles can be fine-tuned by means of their chemical
large pore volumes and tunable pore sizes.1 Common strategies surrounding. It has been shown that carbonizing organometallic
used for the synthesis of ordered mesoporous carbon are the complexes enables strong metal–support interactions, thereby
hard-templating method and the soft-templating method. The influencing the electron density and the steric environment of
hard-templating method usually employs mesoporous silica as the active sites.7 Metalloporphyrins, with a unique carbon-rich
a template and carbon materials with controllable structure macrocycle and inherent metal–nitrogen coordination, especially
and good shape can be obtained through a simple acid/base transition metalloporphyrins (Co, Fe, and Mn), are attractive
etching process.2 Nanoporous silica materials (KIT-6) with precursors for synthesis of M–N–C catalysts.8 Following this
three-dimensional (3D) ordered porous structures are widely concept, earth-abundant-metal porphyrins embedded in nitrogen-
used as hard templates. Hereafter, the mesoporous carbon doped carbon materials have been employed in catalytic reactions.9
materials derived from KIT-6 by a hard-template method have Recently, Wu Li et al. have manufactured catalysts for highly
received great attention in recent years due to their advantages of selective hydrogenation of nitroarenes with Co nanoparticles
easy mass transfer and avoiding the pore blockage, compared to supported on ordered mesoporous carbon CMK-3.10
materials with one-dimensional or layered nanostructures.3
Herein, as illustrated in Scheme 1, we prepared a series of Co/N
Previous research studies have shown that the incorporation co-doped ordered mesoporous carbon catalysts (Co–N–C), which
of heteroatoms (B, N, P, and S) into many carbon materials can have large specific surface areas, well-dispersed metal active sites
enhance their catalytic activity by modulating the physicochemical and high catalytic activity. Briefly, KIT-6 silica, cobalt porphyrin and
properties.4 Among the doping atoms, nitrogen (N) has been used sucrose were employed as a structural model, a metal precursor and
most frequently so far due to the fact that N-doping will enhance a carbon source, respectively. Metalloporphyrins contain alternating
p-bonding networks in carbon materials, improving electron N-containing ligands and Co ions, which could efficiently control
the dispersion of active sites at the atomic level.11 The selective
oxidation of ethylbenzene under mild conditions with TBHP as an
oxidant was carried out to investigate the catalytic performance of
the as-prepared catalysts. And a series of morphological and
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry
and Chemical Engineering, Hunan University, Changsha, Hunan 410082, China.
E-mail: liuzhigang@hnu.edu.cn
structural characterizations were performed using N2 adsorption–
desorption isotherm, XRD, Raman, TEM and XPS techniques.
† Electronic supplementary information (ESI) available: Experimental details,
graphics (Fig. S1–S4) and tables (Tables S1–S3). See DOI: 10.1039/c9nj00453j
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before CoTPP (60 mg) was dissolved in CH2Cl2 (10 mL), and
then, refluxed at 40 1C for 24 h with constant magnetic stirring.
After removing the solvent, the samples were transferred into a
quartz boat, and then heated to 900 1C at a rate of 5 1C per
minute and kept for 4 h under N2. The product was denoted as
Co–N/C.
2.2. Catalyst characterization
Using a NOVA 1000e from Quantachrome Instruments, N2
adsorption–desorption analysis of the samples were outgassed
at 200 1C for 3 h was conducted at 77 K and a relative pressure
range of 0.05 to 0.98. The specific surface areas were calculated
using the BET method. The pore size distribution plot was
recorded from the desorption branch of the isotherm based on
the DFT model. The surface morphology of the samples was
investigated and high angle annular dark field scanning TEM
images (HAADF-STEM) were obtained using an FEI Talos F200x
with an image corrector operating at 300 kV. X-ray powder
diffraction (XRD) was performed using a Japan XRD-6100
analyser with Ni-filtered Cu Ka radiation (50 kV, 10 mA). Raman
spectroscopy was performed using a Mono Vista 2560 Spectro-
meter with a laser at 532 nm (2.33 eV). X-ray photoelectron
spectra (XPS) measurements were obtained using an Escalab
520Xi system and Al Ka radiation (1486.6 eV).
Scheme 1 Schematic illustration of the synthesis process of the repre-
sentative Co–N–C-X catalysts and the catalytic reaction for ethylbenzene.
2. Experimental section
2.1. Catalyst preparation
2.1.1 Synthesis of Co–N–C-X catalysts. KIT-6, sucrose and
cobalt porphyrin (CoTPP) were used to synthesize Co–N–C-X
catalysts, which acted as a template, a carbon source and a
metal precursor, respectively. Briefly, 0.58 g of sucrose was
dissolved in 2.4 g of H2O containing 0.07 g of H2SO4, and then,
0.06 g of CoTPP and 0.6 g of KIT-6 were added successively into
the solution to form a transparent mixture. Subsequently, the
mixture was transferred to a drying oven at 100 1C for 6 h and
160 1C for 6 h. After cooling to room temperature, 1.9 g of H2O,
0.035 g of H2SO4, 0.31 g of sucrose and 0.03 g of CoTPP were
added. After this, the autoclave was heated again at 100 1C and
160 1C for 6 h respectively. Carbonization was completed in a
quartz boat at a temperature up to 900 1C under a N2 atmo-
sphere for 4 h. The products were finally obtained by etching
the silica templates in 3 M NaOH solution for 4 h, and this
process was repeated 3 times. The catalysts were obtained after
being filtered, washed and dried at 100 1C overnight under
vacuum, namely Co–N–C-10 (0.1 : 1). A series of controllable
Co–N–C-X catalysts were prepared by controlling the mass ratio
of CoTPP/sucrose of 0.02 : 1, 0.05 : 1, 0.15 : 1, and 0.2 : 1, marked
as Co–N–C-2, Co–N–C-5, Co–N–C-15, and Co–N–C-20, respec-
tively. For comparison, CoCl2Á6H2O and tetraphenylporphine as
2.3. Catalyst activity
In an oven-dried reaction tube with 15 mg catalyst, 3 mL H2O,
ethylbenzene (122 mL, 1 mmol) and TBHP (490 mL, 3.5 mmol)
were added successively. After heating to 80 1C, the mixture was
stirred for another 6 h. When the mixture was cooled down to
ambient temperature, ethyl acetate and n-dodecane were added
as an extraction agent and an internal agent, respectively. The
organic layer was extracted and analysed by gas chromatography
(Shimadzu GC-2014 equipped with a capillary column (RTX-5)).
Catalyst recovery experiments were carried out under the same
conditions; the Co–N–C-10 catalyst was extracted from the mixture
using ethyl acetate after the reaction, centrifuged and washed with
alcohol, and then dried at 80 1C in a baking oven overnight before
being used again.
3. Results and discussion
3.1. BET
metal or nitrogen precursors were supported on KIT-6 following The porous texture was characterized by N2 adsorption–
similar processes as the above mentioned impregnation method, desorption measurements. Fig. 1A and B show the resulting
and the final samples were assigned as Co–C and N–C, respectively. isotherms and the pore size distribution of Co–N–C-X and KIT-6.
2.1.2 Synthesis of Co–N/C. Briefly, 0.58 g of sucrose was The isotherm of KIT-6 was type IV with an H4 hysteresis loop in
dissolved in 2.4 g of H2O containing 0.07 g of H2SO4, and then P/P0 = 0.5–0.8, from which the specific surface area is estimated to
0.6 g of KIT-6 was added into the solution to form a transparent be 880 m2 gÀ1 (Fig. 1A). And the pore diameter of KIT-6 derived
mixture. Subsequently, hydrothermal, calcination and etching from the desorption branch of the isotherm is calculated using
processes the same as above were followed. The template-free the DFT mode and it is hierarchically mesoporous with a pore size
carbon product was obtained after being filtered, washed and distribution of 5–6 nm(Fig. 1B). All Co–N–C-X samples were
dried at 100 1C overnight in a vacuum, namely C. Co–N/C different from KIT-6 which showed a typical type IV curve
catalysts were prepared through an impregnation method, according to the IUPAC nomenclature, indicating the presence
and the typical process is as follows: 0.6 g of C was added of micropores and mesopores with a narrow pore size
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surface area, a larger pore volume and an average pore size than
any other samples, which could provide more opportunities for
the substrates to participate in the reaction.
3.2. TEM
The morphologies and structures of the KIT-6 and the carbon
materials were studied by TEM. A typical regular three-
dimensional (3D) ordered porous structure about 5 nm could
be observed in KIT-6 (Fig. S1A and B, ESI†). Significantly, there
was a very big change in the morphological features of KIT-6,
which was clearly observed in Co–N–C-10 (Fig. 2A–C). However,
we hardly observed any metal-containing nanoparticles in the
high resolution transmission electron microscopy (HRTEM)
image because the leaching process removed most of the
unstable cobalt particles and a small amount of cobalt species
might be incorporated into the carbon framework in disor-
dered forms (Fig. 2D). Meanwhile, from the HAADF-STEM
images and the corresponding elemental maps of Co–N–C-10,
it can be seen that the Co species were mostly bound to O
species uniformly covering the entire carbon materials (Fig. 2E
and F), which demonstrated that the cobalt species were
uniformly bound with O and N within the carbon materials.
However, there were large amounts of Co species deposited and
well-distinguished pores as revealed by the TEM analysis of
different regions within Co–N/C (Fig. 2G–I), indicating that the
Co of Co–N/C was not evenly distributed as in Co–N–C-10. In
addition, Co–C was similar to Co–N/C (Fig. S2C and D, ESI†),
which suggested that the use of CoTPP contributed to the
dispersibility of Co species.
Fig. 1 (A) Nitrogen adsorption–desorption isotherms at 77 K, and (B) the
corresponding DFT mesopore size distribution curves of KIT-6, and
Co–N–C-X.
distribution.12 The reported microporous materials showed
that micropores have no facilitation effects on diffusion and
mass transfer due to their small pore sizes. But the mesopores
could improve the performance very well.13 Therefore, the
mesoporous structure had an overwhelming effect on the
excellent performance of the mesoporous catalyst. This could
be attributed to the fact that the mesoporous structure allowed
the reactants to easily enter the active part, which improved the
performance of the mass transport. The porous properties of
the samples are summarized in Table 1. The specific surface
area, average pore sizes and pore volume first increased with
the increase in mass ratio of CoTPP/sucrose from 0.02 : 1 to
0.1 : 1, and then declined with a further increase in mass ratio
from 0.1 : 1 to 0.3 : 1. CoTPP served not only as metal and
nitrogen precursors, but also as partial carbon sources. When
the content of CoTPP was low, the pores of KIT-6 were not fully
filled. In contrast, when the content was high, the pores were
blocked. Co-–N-–C-10 exhibited higher values of 423 m2/ gÀ1
,
3.3. XRD and Raman spectroscopy
0.81 cm3/ gÀ1 and 5.78 nm for the specific surface area, pore
volume and average pore size (Table S1, ESI†), respectively. So
the Co–N–C-2, Co–N–C-5, Co–N–C-15 and Co–N–C-20 samples
had a lower specific surface area, a smaller pore volume, and a
narrower pore size, which might lead to reaction defects enter-
ing into the hole of these catalysts and disable contacts with the
active site. The specific surface area and average pore size of
Co–N/C was 481 m2 gÀ1 and 4.70 nm, respectively (Table S1,
ESI†). Typically, Co–N–C-10 catalysts with a higher surface area
and a uniform distribution of pore size could provide more
active sites and be more efficient for diffusion of substrates.
It was worth noting that the Co–N/C had a higher specific
Fig. 3A shows the XRD diffraction patterns of the as-prepared
samples. All samples showed two broad peaks located at
Table 1 The results of N2 adsorption–desorption measurements
SBET (m2 gÀ1
)
Vp (cm3 gÀ1
)
Sample
Dp (nm) Stotal Smicro Smeso Vtotal Vmicro Vmeso
KIT-6
Co–N–C-2
Co–N–C-5
Co–N–C-10 5.78
Co–N–C-15 5.52
Co–N–C-20 5.14
4.95
4.85
4.93
880
629
765
645
581
458
143
253
347
222
212
188
737
376
418
423
369
270
1.09
0.76
0.96
0.93
0.80
0.59
0.09
0.15
0.18
0.12
0.12
0.11
1.00
0.61
0.78
0.81
0.68
0.48
SBET: BET surface area; Stotal: BET surface area; Smicro: micropore surface
area; Smeso: mesopore surface area; Smeso = Stotal À Smicro; Vp: pore
Fig. 2 (A–D) TEM analysis of different regions within Co–N–C-10, (E and F)
HAADF-STEM and the corresponding elemental maps of the Co–N–C-10
catalyst, (G–I) TEM analysis of different regions within Co–N/C.
volume; Vtotal: total pore volume; Vmicro: micropore volume; Vmeso
mesopore volume; Vmeso = Vtotal À Vmicro; Dp: average pore diameter.
:
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Fig. 3 XRD analysis and Raman spectra analysis of Co–N–C-X.
24.71 and 43.41, which could be assigned to the (002) and (101)
diffraction peaks of graphitic carbon, respectively.14 The XRD
pattern of the Co–N–C-10 composite showed weak peaks at
around 39.51, which were in good agreement with JCPDS card
43-1300 (Fig. 3A), implying the presence of CoO in the Co–N–C-10
composite. No other detectable peaks appeared in the XRD
pattern of Co–N–C-10, which could be due to the cobalt atoms
being incorporated into the carbon framework in disordered
forms, which was consistent with the TEM image. However, with
the increasing amount of CoTPP, the peaks matched Co3O4, CoO
and some remaining cobalt metals, indicating partial oxidization
of the metallic cobalt in Co–N–C-15 and Co–N–C-20. The results
suggested that there was a deposit of cobalt particles in these
composites. The same conclusion applied to Co–C (Fig. S3, ESI†).
The pattern of Co–N/C showed a good matching with the metal
cobalt peaks, which again proves the deposit of cobalt metal in
the TEM image (Fig. S3, ESI†).15 This result was in good
agreement with the TEM observations (Fig. 2G–I).
Raman spectra have been widely used to investigate the
degree of graphitization and defect of catalysts.16 Fig. 3B shows
the Raman spectra of Co–N–C-X. All of them showed a similar
pattern with a D band at 1330 cmÀ1 (related to the defects) and
a G band at 1590 cmÀ1 (related to the crystalline graphite).17
The values of the ID/IG ratio, reflecting the defect and disorder
level in the graphitic carbon layers, for Co–N–C-5, Co–N–C-10,
Co–N–C-15 and Co–N–C-20 were 1.03, 1.07, 1.03 and 1.02,
respectively. A higher ID/IG value for Co–N–C-10 was due to
the incorporation of heterogeneous atoms into the matrix.18
Fig. 4 XPS spectra of the as-prepared catalysts. (A) Survey, (B) C 1s, (C) N
1s, (D) Co 2p spectra of Co–N–C-10 and Co–N/C.
between the binding energies of M–N and pyridinic N.21
Notably, the pyridinic and pyrrolic N sites were the most and
second most abundant ones, which were highly demanded
because they could provide strong N coordination and act as
good anchoring sites for deposition and stabilization of Co.22 At
the same time, there were relatively lower contents of pyridinic
N in the Co–N/C (Table S2, ESI†). Moreover, some previous
studies have reported that a larger amount of pyridinic species
bound to cobalt was considered indispensable for the high
catalytic performance.23 For the Co 2p XPS data, the signals
were relatively weak because most Co species were located
inside the N-doped carbon matrix. The Co 2p3/2 high-resolution
spectra were fitted with three components corresponding to metal
Co (778.5 eV), Co–O (780.0 eV) and Co–N (781.7 eV) (Fig. 4D).24
The ratio of Co, Co–O and Co–N was 6.9%, 40.6% and 52.5%,
respectively (Table S2, ESI†). The dominant existence of Co–O and
Co–N in the XPS analysis indicated that the Co of the Co–N–C-10
composite was partly oxidized and partly combined with N
species. XPS analysis reflected that the N sites can act as
coordination and anchoring sites for Co of the Co–N–C-10
catalyst, which agrees well with the results of XRD, TEM and
STEM-HAADF.
3.4. XPS
The surface compositions and chemical states of Co–N–C-10
were further determined by X-ray photoelectron spectroscopy
3.5. Catalyst performance
(XPS). As shown in Fig. 4A, a set of peaks corresponding to C 1s In order to identify the performance of catalysts, we conducted
(284.8 eV), N 1s (401.0 eV), O 1s (531.6 eV) and Co 2p (780.0 eV) experiments at 80 1C using TBHP as the oxidant and water as
were observed.19 The ratio of C, O, N and Co was 79.24%, the solvent. It was found that the blank experiment gave a very
18.80%, 1.52% and 0.44%, respectively (Table S2, ESI†). The low yield under the reaction conditions (Table 2, entry 1). To
peaks of the C 1s spectrum showed the following types of C our delight, the desired acetophenone was obtained in 93%
species: CQC, C–N, C–O, and CQO, indicating the existence of yield at full conversion with the Co–N–C-10 catalyst (Table 2,
carbon atoms connected to N and O heteroatoms (Fig. 4B). The entry 4). Other samples with different contents of CoTPP
corresponding N 1s XPS spectra could be well-fitted with four exhibited a lower conversion than Co–N–C-10 (Table 2, entries
peaks at E398.5, 400.5, and 401.3 eV, assigned to pyridinic, 2, 3, 5 and 6), because the lower specific surface area, the
pyrrolic and graphitic N species, respectively (Fig. 4C).20 The smaller pore volume, and the narrower pore radius might lead
peak at a binding energy of 398.5 eV could be attributed to to reaction defects entering into the mesopores of these cata-
pyridinic N, which should also include the contribution from lysts and disable contacts with the active site. Meanwhile,
nitrogen bound to the metal (M–N), due to the small difference compared with Co–N–C-10, the Co–N/C was found to exhibit
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Table 2 Results of different catalysts for the oxidation of ethylbenzene
Entry
Catalyst
Conv./%
Yield(Sel.)/%
1
2
3
4
5
6
7
8
9
10
—
o5
82
87
93
91
89
78
55
52
45
o5
Co–N–C-2
Co–N–C-5
Co–N–C-10
Co–N–C-15
Co–N–C-20
Co–N/C
Co–C
77(94)
84(97)
93(100)
90(99)
88(99)
75(96)
42(77)
40(76)
33(73)
N–C
C
Reaction conditions: substrate (1.0 mmol), TBHP (3.5 mmol, 75 wt% in
water), catalyst (0.015 g), H2O (3.0 mL), 353 K, 6 h; the conversion and
yield were determined by GC.
a relatively lower conversion and yield (Table 2, entry 7). The
XRD and TEM images showed that there was aggregation of
cobalt species in the preparation process which resulted in
reactive Co not being well exposed and not being in good
contact with the reactants like Co–N–C-10. Thereafter the key
factors of the catalytic effect were not only specific area, pore
volume and average pore size, but also the dispersion of Co
species. In order to verify the unique catalytic performance,
a series of control experiments were conducted to show that
the high activity for selective oxidation of ethylbenzene took
place only in the presence of Co and N. As shown in Table 2
(entries 8–10), the catalysts N–C, Co–C and C only afforded
ethylbenzene conversion of 55%, 52%, and 45%, respectively.
The catalytic effect of catalysts Co–C and N–C was higher than
Fig. 5 (A) The results of Co–N–C-10 recycling experiments, (B) N2
adsorption–desorption isotherm plot of Co–N–C-10-R. The inset on
top left: BJH pore size distribution of Co–N–C-10-R, (C and D) XRD
patterns and Raman spectra analysis of the reused catalyst, (E and F) high-
resolution XPS spectra of the reused Co–N–C-10-R catalyst.
that of C, so both cobalt and nitrogen could improve the pyridinic N and Co–N changed from 1.52% to 0.94% and
catalytic activity. However, since Co and N existed together in 52.9% to 39.0%, respectively, which were lower than those of
the catalyst Co–N–C-10, its catalytic performance was much the fresh ones. And then the content of Co–N decreased. So the
higher than that of Co–C and N–C. Hence, the presence of Co–N activity of the used catalyst showed a little change after several
could improve the catalytic activity more significantly, which recycling. The results further illustrated that the structure was
confirmed that the Co–N sites also played a vital role in well maintained and the stable Co–N species were indispensa-
providing the conversion and selectivity for ethylbenzene oxida- ble in the reaction. The embedment of the active sites as well as
tion under the investigated conditions.25 In an earlier report, it the bicontinuous structure of carbon materials provided a
has been proven that Co–N sites were typically responsible for stabilizing effect during catalysis and therefore preserves the
the high catalytic activity in ethylbenzene oxidation.9 Hence, nanoparticles from further agglomeration, leaching and sub-
there existed a synergistic effect of three factors affected the sequent deactivation. Using Co–N–C-10 as the catalyst, we
catalytic activity of the catalyst.
further investigated the oxidation of a wide range of substituted
Here, the stability and reusability of the Co–N–C-10 catalyst arylalkanes with TBHP. A good yield was observed for other
were studied for the application of selective oxidation of arylalkanes such as isopropylbenzene, tetrahydronaphthalene,
ethylbenzene catalysts. As depicted in Fig. 5A, after five succes- diphenylmethane, indan and fluorine (Table S3, entries 1–9,
sive cycles the conversion obtained was 89%. It could be seen ESI†), and a moderate yield in the oxidation of toluene to
that the activity was well-retained after five consecutive circles, benzoic acid (Table S3, entry 10, ESI†), indicating that the
demonstrating its excellent stability. Interestingly, as shown in catalyst showed general applicability for the selective oxidation
Table S1 (ESI†), after the Co–N–C-10 was reused 5 times, the of arylalkanes to ketones.
specific surface area and pore volume both decreased, while the
pore diameter increased, about 347 m2 gÀ1, 0.75 cm3 gÀ1 and
8.66 nm, respectively. The reason for this phenomenon could
be that there were collapse and blocking of micropores partly.
4. Conclusion
From the TEM images (Fig. S4, ESI†) and the XPS analysis To sum up, we prepared a highly active Co, N co-doped carbon
(Table S2, ESI†) of the recycled catalyst, there existed partial catalyst via structuring of sucrose and cobalt porphyrin upon
collapse and blocking of pore and partial leaching of cobalt. impregnation into KIT-6 and then removing the template by
Furthermore, from the analysis of XPS, the contents of etching with NaOH. The results revealed that the desired
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active sites. Compared to the two-step method, Co–N/C catalysts
supported on mesoporous carbon, hard-templating enabled the
synthesis of well-structured Co–N–C-10 catalysts significantly
enhancing the activity due to improved dispersibility of the
Co–N active sites. The mass ratio of sucrose to CoTPP influenced
the resulting catalyst performance significantly. In this respect,
the ratio of sucrose to CoTPP is 1 : 0.1 the best result, which was
attributed to the large mesopores derived from improved KIT-6
replication and high surface areas, thus facilitating the dispersi-
bility of the active sites within the catalyst. Applying the optimal
Co–N–C-10 catalyst, a wide range of arylalkane compounds were
oxidized to the corresponding ketone in excellent yields. This
strategy could be extended to immobilize other metal or metal
composite active sites into mesoporous silica structures.
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Conflicts of interest
8 (a) X. J. Cui, J. P. Xiao, Y. H. Wu, P. P. Du, R. Si, H. X. Yang,
H. F. Tian, J. Q. Li, W. H. Zhang, D. H. Deng and X. H. Bao,
Angew. Chem., Int. Ed., 2016, 55, 6708–6712; (b) M. Halma,
There are no conflicts to declare.
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K. A. D. de Freitas Castro, V. Prevot, C. Forano, F. Wypych
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