Synthesis of N-Doped Mesoporous Carbon Nanorods through Nano-Confined Reaction: High-Performance Catalyst Support for Hydrogenation of Phenol Derivatives

Article abstract of DOI:10.1002/asia.201800112

Traditional hard-template methods for the preparation of mesoporous carbon structures have been well developed, but there are difficulties associated with complete filling of the organic precursors in ordered mesochannels and exact replication of the templates. Herein, mesoporous carbon nanorods (meso-CNRs) were synthesized through thermal condensation of furfuryl alcohol followed by the nano-confined decomposition of polyfurfuryl alcohol in silica nanotubes (SiO₂ NTs) with porous shells. Limited and slow release of gaseous water through the porous shells and finite polyfurfuryl precursor inside silica nanotubes are responsible for the formation of the mesoporous structures. Nitrogen can be doped into the meso-CNRs by adding guanidine hydrochloride to the precursors. The nitrogen dopant not only stabilizes the ultrasmall and active Pd nanocatalyst in the meso-CNRs but also increases the electron density of Pd and accelerates the dissociation of H₂, both of which increase the catalytic activity of the Pd catalyst in hydrogenation reactions.

Full text of DOI:10.1002/asia.201800112

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Synthesis of N-doped Mesoporous Carbon Nanorods through
Nano-confined Reaction: High Performance Catalyst Support for
Hydrogenation of Phenol Derivatives
Authors: Xueteng Liu, Fei Pang, and Jianping Ge
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.201800112
Link to VoR: http://dx.doi.org/10.1002/asia.201800112
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
Synthesis of N-doped Mesoporous Carbon Nanorods through
Nano-confined Reaction: High Performance Catalyst Support for
Hydrogenation of Phenol Derivatives
Xueteng Liu, Fei Pang and Jianping Ge*[a]
Abstract: Traditional hard-template method for the preparation of
mesoporous carbon structures has been well developed, but it may
have difficulty in complete filling of organic precursors in ordered
mesochannels and exact replication of the templates. Here,
mesoporous carbon nanorods (meso-CNRs) are synthesized through
thermal condensation of furfuryl alcohol followed by the nano-confined
decomposition of polyfurfuryl alcohol in silica nanotubes (SiO2 NTs)
with porous shells. Limited and slow releasing of gaseous water
through the porous shells and finite polyfurfuryl precursor inside silica
and soft templates and thereby the supramolecular assembly.[13]
For example, Zhao et al. have synthesized N-doped ordered
mesoporous carbon with a high nitrogen content through an
evaporation-induced self-assembly process, which used a low-
molecular-weight soluble resol as carbon source and
dicyandiamide as nitrogen source.[13d] In addition to the soft-
template strategy, ordered microporous, mesoporous and
macroporous carbon materials can also be obtained by utilizing
zeolite, mesoporous silica or aluminum oxide etc. as hard
nanotubes are responsible for the formation of mesoporous structures. templates[14], which have less requirements for carbon precursors
Nitrogen can be doped to the meso-CNRs by adding guanidine
hydrochloride to the precursors. The nitrogen dopant not only stabilize
the ultrasmall and active Pd nanocatalyst in meso-CNRs but also
increase the electron density of Pd and accelerate the dissociation of
H2, both of which increase the catalytic activity of Pd catalyst in
hydrogenation reactions.
compared to the soft-templating method. For example,
MacLachlan et al. have preserved the chiral nematic structure in
films of nanocrystalline cellulose by filling the cellulose network
with tetraethyl orthosilicate followed by its hydrolysis process. The
as-formed silica served as a hard template for the carbonization
of the cellulose at 900 °C, so that chiral nematic carbon films could
be obtained after removal of the silica by treatment with sodium
hydroxide.[14d] Ding et al. have prepared mesoporous carbon
supported nitrogen-doped carbon by pyrolysis of polyaniline
coated on CMK-3. The obtained N-doped porous carbon is used
as electrocatalyst, which exhibits excellent performance towards
ORR in alkaline media.[14e] Although the hard-template route is a
universal method for various materials including carbon, it may
have difficulty in complete filling of organic precursors in ordered
channels or mesopores of templates, so that the inversed
mesoporous structures are difficult to be reserved exactly and the
yield is sometimes unsatisfactory compared to the templates.[15]
In this work, we reported a “nano-confined reaction” to prepare
mesoporous structures, in which the precursors were confined in
a hollow reactor with porous shells and the gas releasing reaction
inside the nanoreactor produced the disordered mesoporous
structures. Following this idea, mesoporous carbon nanorods
(meso-CNRs) were prepared through thermal polymerization of
furfuryl alcohol (FA) and confined pyrolysis of polyfurfuryl alcohol
(PFA) inside a tubular SiO2 “nanoreactor” followed by the removal
of silica shells. Finite furfuryl precursors inside silica nanotubes
and limited releasing of gaseous water through the porous shells
were responsible for the mesoporous structures. The relevant
experiments and discussions were performed to verify the
mechanism of nano-confined reaction, which exhibited great
potentials to prepare various mesoporous materials for catalysis,
energy storage and electrochemical processes. It is also worth
noting that the nitrogen dopant could be flexibly introduced to the
mesoporous carbon through the addition of guanidine
hydrochloride into the furfuryl alcohol solution in synthesis. The
as-prepared N-doped meso-CNRs (N-meso-CNRs) shall be
proved as a better support than meso-CNRs for Pd nanocatalyst
in hydrogenation of phenol derivatives.
Introduction
The structural design, synthesis and application of porous carbon
materials have received considerable attention in the past
decades due to their extraordinary physicochemical properties,
including high surface area[1], large pore volume[2], adjustable
pore size[3], chemically inert nature[4], mechanical stability[5], good
conductivity[6] and low cost of manufacture. These outstanding
features make porous carbon ideal materials which are widely
used for electrode in fuel cells[7], supercapacitors[8] and energy
storage[9]. It can also be used as sorbents for gas storage[10] and
supports for many important catalytic processes[11]. Among these
applications, carbon materials have a long history serving as
superior supporting materials in heterogeneous catalysis,
particularly as supports of precious metals for organic reactions
including hydrogenation, dehydrogenation, oxidation and
reduction. Because they are usually very stable at different pH
environment in the absence of oxygen, and they also have high
surface area for loading of dispersed metal catalyst.
In the past decades, soft- and hard-template methods have
been proven to be most successful ways for the preparation of
porous carbon structures with well-defined pore structures and
narrow pore-size distributions.[12] Soft-template method using
amphiphilic molecules to fabricate porous carbon materials is
based on the chemical interactions between carbon precursors
[a]
X. Liu, F. Pang, Prof. J. P. Ge
Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, School of Chemistry and Molecular Engineering, East
China Normal University
Shanghai, 200062 (P.R. China)
E-mail: jpge@chem.ecnu.edu.cn
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
Results and Discussion
Different from the traditional hard-templating strategy, the
formation of meso-CNRs can be explained by a gas-releasing
pyrolysis reaction confined in a nanosize “reactor”. (Figure 2) In a
hard-templating process, the products are usually exact replicas
of the templates so that the products in above synthesis should
have retained their tubular morphologies rather than rod-like
structures. The absence of porous templates inside the hollow
cavity of SiO2 NTs cannot explain the large amount of mesopores
in the meso-CNRs either, as shown in the cross-section TEM
images. In addition, the surface area of the product from hard-
templating is generally close to that of the template. However, the
surface area of meso-CNRs (550 m2/g) is actually higher than that
of SiO2 NTs (89 m2/g). (Figure 2c and 2f) All these inconsistencies
suggest that the current synthesis does not follow the traditional
hard-templating mechanism. In fact, meso-CNRs are prepared by
gas-releasing pyrolysis reaction confined in a nanosize “reactor”.
As a direct proof, the external diameters of meso-CNRs are
approximately equal to the inner diameters of SiO2 NTs. (Figure
2g and 2h) The thin porous shells of the SiO2 NT function not as
the template but as a permeable wall, which prevents the
immediate release of the produced gaseous water, so that the
retained tiny gas bubbles lead to the formation of a porous
structure during pyrolysis. The limited furfuryl alcohol precursor
inside the SiO2 NTs is also favorable to the porous structure but
not to the massive bulk structures in large dimensions, as the
gaps and holes are inevitable due to untight packing of carbon
structure. Both reasons are responsible for the formation of meso-
CNRs, where such reaction can be summarized as a nano-
confined gas-releasing reaction. In a parallel decomposition of
polyfurfuryl alcohol without SiO2 NTs, the precursors are
continuously pyrolyzed to form massive bulk products because
the produced water vapor quickly diffuses into the atmosphere,
leaving behind a dense packing of carbon structures.
Mesoporous carbon nanorods (meso-CNRs) are prepared by the
loading of furfuryl alcohol (FA) and oxalic acid catalyzed
polymerization of furfuryl alcohol, followed by nano-confined
pyrolysis of polyfurfuryl alcohol (PFA) in the nanotubes
successively. According to previous research works[16], the SiO2
NTs with hollow cavity and mesoporous shell are first synthesized
by etching ordered mesoporous SiO2 NRs with PEI, which serves
as protective agent and etchant at the same time. Furfuryl alcohol
is loaded via soaking the nanotubes in a concentrated solution of
furfuryl alcohol (40 vol%) and oxalic acid, followed by separation
with centrifugation. Then, furfuryl alcohol filled in the nanotubes is
polymerized under the catalysis of oxalic acid at 100 °C to
produce polyfurfuryl alcohol (PFA/SiO2 NRs). The precursors are
decomposed to carbon through calcination at 550 °C in several
hours to produce the composite of carbon and SiO2 (carbon/SiO2
NRs). Finally, meso-CNRs are obtained by removing the silica
shells using an HF solution. (Figure 1) SEM and TEM images
show that the mesoporous SiO2 NTs prepared by surface-
protected etching have typical tubular structure with disordered
mesopores in the shells. The meso-CNRs are mostly porous
nanorods mixed with few irregular impurities, which might be
produced by the FA residuals left outside the nanotubes during
the precursor loading. Diameters of meso-CNRs are apparently
smaller than that of SiO2 NTs, which suggests that the nanorods
might be produced inside the nanotubes. Apparently, this reaction
does not follow the mechanism of traditional hard-templating,
because no mesoporous carbon nanotubes is produced through
exact replication.
Figure 1. (a) Synthetic process and formation mechanism of meso-CNRs.
Digital photos, SEM and TEM images of (b-d) SiO2 NTs and (e-g) meso-CNRs.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
Figure 2. (a, d) Axial and (b, e) cross-sectional TEM images, (c, f) N2
adsorption-desorption isotherms and (g, h) distribution of the external diameters
of SiO2 NTs and meso-CNRs.
combination of a confined “nano-reactor” and an appropriate gas-
releasing reaction. As the name implies, the confined “nano-
reactor” plays the role of a reaction container in nanoscale where
the reaction is controlled well. Generally, the nano-reactor is
chemically inert to avoid undesirable reaction with the reactants.
A hollow interior cavity and porous shell are necessary so that
there are enough precursors loaded into the reactor, and the
reaction inside each reactor is equally controlled in kinetic aspects
under the same macroscopic condition. The reactor should be
easily removed to obtain the nanostructures of product. Obviously,
the SiO2 NTs obtained through “protective etching” could be an
ideal “nano-reactor”, because the nanotubes have a hollow
interior cavity surrounded by porous shells which provide an ideal
place for the pyrolysis of polyfurfuryl alcohol. In addition, silica has
good thermal stability and is easily removed by HF. On the other
hand, a mild gas-releasing process is also essential to fabricate
the mesoporous structures. For meso-CNRs, the confined
reaction works only when water vapor can be slowly released
through the porous silica shell and the detained gas bubbles can
contribute to the generation of mesoporous structures. Therefore,
the synthesis won’t be successful if the gaseous byproducts (H2O)
are generated asynchronously with the formation of main product
(Meso-CNRs).
According to the reaction mechanism, the prepolymerization of
furfuryl alcohol into polyfurfuryl alcohol is a critical step for the
production of meso-CNRs in the nano-confined reaction. It is
known that furfuryl alcohol will condense to form polyfurfuryl
alcohol in the presence of acidic catalysts at 100 °C.[17] (Scheme
1) The polymerization of furfuryl alcohol can be judged from the
disappearance of IR peaks of O-H stretching at 3300 cm-1 and
those in fingerprint region (1300-400 cm-1). In order to verify the
proposed reaction mechanism, we have made small changes to
the loading and prepolymerization of furfuryl alcohol before
thermal pyrolysis, which are expected to disclose the influence of
“precursors” upon the products. Precursor A is SiO2 NTs loaded
with furfuryl alcohol only while Precursor B is SiO2 NTs loaded
with furfuryl alcohol and oxalic acid. Neither of them was
prepolymerized before thermal pyrolysis. Precursor C and D
correspond to the SiO2 NTs loaded with the mixture of furfuryl
alcohol and oxalic acid, which are prepolymerized at 100 °C for
30 and 120 min. The FTIR spectra show that Precursor A and B
retain the absorption at 3300 cm-1 and the absorptions in
fingerprint region, while those peaks nearly disappear for
Precursor C and D. (Figure 3a) It indicates that both the acidic
catalyst and thermal pretreatment are essential conditions for the
polymerization of furfuryl alcohol. After calcination of the above
four precursors at 550 °C, four kinds of composites (possibly
C/SiO2 NRs) are obtained, which are named as Intermediate
Product A to D. They show 8%, 15%, 33% and 45% weight loss
respectively from 100 °C to 800 °C. (Figure 3b) The higher weight
loss of Intermediate Product C and D indicates that more carbon
is produced during the calcination, compared to that of
Intermediate Product A and B. TEM images also verify the
formation of carbon for Product C and D. (Figure 3c-3f) It suggests
that the effective loading of polyfurfuryl alcohol for Product C and
D prevents evaporation of furfuryl alcohol. But for Product A and
B, the evaporation of furfuryl alcohol results in the loss of carbon
source during the temperature-rise process before calcination.
These results are consistent with the FTIR spectra, which once
again prove the necessity of prepolymerization to the production
of meso-CNRs. In a word, meso-CNRs can be generated only
when furfuryl alcohol loaded in the SiO2 NTs is prepolymerized
into polyfurfuryl alcohol before calcination. Otherwise, furfuryl
alcohol will evaporate before calcination, so that there will be no
carbon source to form mesoporous carbon structures.
Scheme 1. Synthesis of meso-CNRs through polymerization of furfuryl alcohol
and pyrolysis of polyfurfuryl alcohol.
Figure 3. (a) FTIR spectra of 4 kinds of furfuryl alcohol loaded SiO2 NTs, labeled
as Precursor A to D. (b) TGA and (c-f) TEM images of the correspondingly
produced C/SiO2 composites, labeled as Intermediate Product A to D.
Based on the synthesis of meso-CNRs, one can find that the
keys to the nano-confined reactions are the synergetic
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
Due to the similar pyrolysis of guanidine hydrochloride as
furfuryl alcohol, the N-doped meso-CNRs (N-meso-CNRs) are
easily obtained through the addition of guanidine hydrochloride as
nitrogen precursor in the furfuryl alcohol solution. Guanidine
annular dark-field scanning TEM (HAADF-STEM) image shows
that ultrasmall Pd nanoparticles are uniformly dispersed on the N-
meso-CNRs. Energy dispersive spectrometer (EDS) mapping
confirms that nitrogen is successfully introduced into the
mesoporous carbon and Pd nanoparticles are uniformly
dispersed on the obtained carbon materials. (Figure 5) The high
surface area of N-meso-CNRs and the strong interactions
between Pd nanoparticles and the nitrogen species will be
favorable to the deposition of ultrasmall and highly dispersed Pd
nanoparticles. At the same times, the high surface area and
strong interactions would also contribute to the high activity for
most heterogeneous catalysts.
hydrochloride (CH6N3Cl) containing three amidogens in
a
molecule is usually used as precursor for nitrogen doping
because it forms nitrides with many elements at high temperature.
Owing to the high boiling point, guanidine hydrochloride loaded
inside the SiO2 NTs is not volatile during the temperature raising
process and might be reserved until the decomposition. At the
calcination temperature, guanidine hydrochloride is pyrolyzed
accompanied with the elimination of ammonia, and the produced
ammonia diffuses out slowly through the porous silica shells,
which is similar to the pyrolysis of PFA. A series of N-meso-CNRs
with the surface nitrogen contents of 1.5, 2.7 and 4.8 wt% are
prepared by controlling the dosage of guanidine hydrochloride
(0.5, 1 and 2 g) in furfuryl alcohol solution (20 mL). The amounts
of surface nitrogen are determined by XPS, and the samples are
named as N1.5-meso-CNRs, N2.7-meso-CNRs and N4.8-meso-
CNRs respectively. The gradual introduction of nitrogen dopant is
also supported by the Raman spectra, where the ratio of D band
at 1339 cm–1 to G band at 1595 cm–1 (ID/IG) is a sensitive indicator
to the ratio of amorphous carbon toward graphitic carbon, and
thereby an indicator for doping of nitrogen in our case. The
Raman spectra suggest that ID/IG ratios of meso-CNRs, N1.5
-
meso-CNRs, N2.7-meso-CNRs and N4.8-meso-CNRs are 0.51,
0.61, 0.74, and 0.82 respectively. (Figure 4) The higher ID/IG ratio
indicates that a larger amount of graphitic carbon are destroyed
and more nitrogen atoms are successfully embedded into the
framework of graphitic carbon[18], which is consistent with the
nitrogen contents measured by XPS.
Figure 5. (a) HAADF-STEM images and (b-d) EDS mapping of Pd/N-meso-
CNRs.
The as-prepared Pd/N-meso-CNRs are superior nanocatalysts
for the hydrogenation of phenol derivatives due to the good
dispersion of Pd nanoparticles on N-meso-CNRs. (Scheme 2) In
a typical catalytic reaction, the aqueous solution of phenol
derivatives (0.5 mmol) and Pd/N4.8-meso-CNRs catalyst (53 mg)
are loaded to a reaction tube, which is vacuumed and filled by H2
with atmospheric pressure. After catalytic hydrogenation for
several hours at specific temperature, the products are extracted
from the reaction solution by toluene, which is analyzed by GC to
determine the conversion of substrate and selectivity of target
product. The catalytic results show that the conversion for phenol
is 93.2% in 3 hours at 40 °C and the conversions for all phenol
derivatives are above 85% in several hours at 80 °C, which is
relatively higher than the previous work.[19] (Table 1) In addition,
the selectivity is above 95% in all cases, which indicates that
selective production of cyclohexanone could be achieved by the
as-prepared Pd/N-meso-CNRs nanocatalysts. Although the
Pd/N4.8-meso-CNRs shows different activities for hydrogenation
of phenol derivatives, their conversion and selectivity prove that it
Figure 4. Raman spectra of meso-CNRs and N-doped meso-CNRs.
These N-meso-CNRs could be ideal supporting materials for
the deposition of ultrasmall precious-metal nanoparticles. As a
demonstration, Pd/N-meso-CNRs can be prepared by
deposition-precipitation (DP) method of palladium chloride
followed by the reduction of palladium precursor. Its high-angle
a
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
is a universal catalyst for hydrogenation of a broad range of
phenol substrate.
Table 2. Hydrogenation of phenol by 4 Pd catalysts
Cat.
N (wt%)
0
Conv. (%)
52.2
Sel. (%)
98.8
98.4
98
k (h-1)
0.254
0.338
0.485
0.732
Pd/meso-CNRs
Pd/N1.5-meso-CNRs
Pd/N2.7-meso-CNRs
Pd/N4.8-meso-CNRs
1.5
63.6
2.7
78.6
4.8
93.2
97.3
Scheme 2. Hydrogenation of phenol derivatives with Pd/N-meso-CNRs
nanocatalyst.
Reaction conditions: phenol (0.5 mmol), Pd (3.0 mol % relative to phenol), water
(2.0 mL), H2 (0.1 MPa), 40 °C, 3 h.
Table 1. Hydrogenation of phenol derivatives by Pd/N4.8-meso-CNRs
nanocatalyst
Entry
Reactant
T (°C)
t (h)
Conv. (%)
Sel. (%)
1
40
3
93.2
97.3
2
3
4
80
80
80
4
3
4
89.3
95
97.4
96.7
>99
88.2
5
6
80
80
8
4
83.2
94.1
95.6
97.3
Figure 6. Kinetics curves of hydrogenation of phenol catalyzed by Pd/N-meso-
CNRs.
Reaction conditions: substrate (0.5 mmol), Pd (3.0 mol % relative to substrate),
water (2.0 mL), H2 (0.1 MPa).
The aforementioned dependence of catalytic activity upon the
nitrogen contents of supporting materials can be explained by the
stabilization of ultrasmall and highly active Pd nanoparticles by
nitrogen species. It should be noted that the meso-CNRs and the
other three N-meso-CNRs have almost the same structural
characteristics except for the doping amount of nitrogen, and the
Pd nanoparticles deposited on them are well dispersed without
obvious agglomeration. (Figure 7) However, as the nitrogen
content increases, the average diameter of Pd nanoparticles
supported on meso-CNRs, N1.5-meso-CNRs, N2.7-meso-CNRs
and N4.8-meso-CNRs decreases in the sequence of 4.6, 3.6, 3.0
and 2.1 nm, respectively. It is known that the nitrogen dopant in
the meso-CNR will coordinate to Pd atoms during the deposition,
and the N-meso-CNRs with higher nitrogen contents will provide
more coordination sites. In this case, Pd nanoparticles with
smaller size tends to deposit on them since the overall Pd dosage
are kept same. Therefore, the doping of nitrogen in meso-CNRs
will contribute to the stabilization of ultrasmall and well-dispersed
Pd nanocatalysts. Apparently, these smaller Pd nanoparticles will
expose more active cites which effectively increase the activity of
hydrogenation.
The nitrogen content of N-meso-CNRs can be controlled by the
guanidine hydrochloride in synthesis, which shows significant
influence upon the activity of hydrogenation of phenol derivatives.
EDS mapping and ICP-AES results reveal that Pd/meso-CNRs,
Pd/N1.5-meso-CNRs, Pd/N2.7-meso-CNRs and Pd/N4.8-meso-
CNRs have similar Pd contents (2.87, 2.85, 2.83, and 2.92 wt%).
However, when they are used in hydrogenation of phenol, the
conversion reaches 52.2, 63.6, 78.6, and 93.2% respectively in 3
hours at 40 °C. (Table 2) The catalytic activities show a positive
correlation with the nitrogen contents of these catalysts from 0%
to 4.8%. Furthermore, this relationship can also be summarized
from the kinetic curve of phenol hydrogenation. (Figure 6) Since
the hydrogenation of phenol is a first-order reaction based on all
the kinetic curves, its kinetic equation is summarized as ln(C0/Ct)
= kt and the slope is used to determine the rate constant.[20] C0
and Ct are the concentrations of phenol before the reaction and
at a specific reaction time. According to the kinetic curves, the rate
constants of hydrogenation catalyzed by 4 Pd-catalysts are 0.254,
0.338, 0.485 and 0.731 h-1. (Table 2) It suggests that a higher
reaction rate can be achieved with a higher nitrogen content from
0% to 4.8% in the supporting materials of Pd-catalyst, which is
consistent with the overall conversion in Table 2.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
The as-prepared Pd/N-meso-CNRs show good stability in the
hydrogenation of phenol. After 4 cycles of 3-hour reaction, the
conversion of phenol decreases from 93.2% to 88% while the
selectivity maintains above 97%. (Figure 9a) Here, the slight
decrease of activity is probably because of the drop of Pd
nanoparticles in liquid phase reaction, as the Pd content
decreases from 2.92 wt% to 2.67 wt% according to ICP-AES
measurement. TEM images of used catalysts reveal that they still
have a good dispersion of Pd nanoparticles and no aggregation
is induced during the reaction. (Figure 9b, 9c) The good stability
of Pd catalyst can be attributed to the physical confinement from
the mesoporous structures of carbon nanorods and the strong
interactions between catalyst and support, which have been
carefully discussed above.
Figure 7. (a, c, e, g) TEM images of Pd/N-meso-CNRs with different N contents
(0, 1.5, 2.7, 4.8 wt%) and (b, d, f, h) corresponding size distributions of deposited
Pd nanoparticles.
The increasing of catalytic activity of Pd by doping of nitrogen
in supports is also caused by the enrichment of electrons on Pd,
and thereby an accelerated dissociation of H2 to active H species
in hydrogenation of phenol derivatives. In the XPS spectra of Pd-
3d, the peaks at 335.8 eV and 341.1 eV are generally related to
the metallic Pd0 and those at 337.8 eV and 343.4 eV are related
to Pd2+.[21] The XPS spectra of four Pd-catalyst show that all the
peaks shift 0.5 eV towards the lower binding energy, when the
nitrogen contents gradually increase from 0 wt% to 4.8 wt%.
(Figure 8) It is known that the decreasing of binding energy in XPS
spectra is usually caused by the acquiring of extra electrons on
corresponding atomic orbitals. For N-meso-CNRs, the lone pair
electrons from nitrogen will coordinate to Pd, which increases the
electron density of its internal 3d orbital and leads to the
decreasing of binding energy.[21-22] For Pd nanoparticle loaded on
the supports, N-meso-CNRs with higher surface nitrogen
contents will coordinate to it at more positions, so that a higher
electron density and a lower binding energy can be observed.
Since the dissociation of H2 into active H species on Pd catalyst
is positively correlated to the electron density, the nitrogen dopant
in supports will effectively increase the catalytic activity of Pd in
hydrogenation of phenol derivatives.[21]
Figure 9. (a) Conversion and selectivity of 4 continuous phenol hydrogenation
catalyzed by Pd/N4.8-meso-CNRs. (b, c) TEM images of catalyst after 4
reactions.
Conclusions
In summary, mesoporous carbon nanorods are prepared
through thermal condensation of furfuryl alcohol followed by the
nano-confined decomposition of polyfurfuryl alcohol inside the
SiO2 nanotubes with porous shells. The formation of mesoporous
structures is attributed to the controllable releasing of gaseous
water and the limited precursor inside SiO2 nanotubes, which is
summarized as a nano-confined reaction mechanism. Due to the
similar decomposition of guanidine hydrochloride compared to
that of polyfurfuryl alcohol, the N-meso-CNRs with different
nitrogen dopants are obtained by controlling the dosage of
guanidine hydrochloride. With the increase of nitrogen contents,
smaller Pd nanoparticles can be loaded on N-meso-CNRs due to
Figure 8. XPS spectra of Pd-3d for Pd/N-meso-CNRs with different nitrogen
contents.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
under stirring for 1 h. After the addition of H2PdCl4 solution (0.34 mL, 0.1
M) into the above N-meso-CNRs solution, the pH value was regulated to
10.5 with NaOH solution (1 M) and Pd was deposited onto the N-meso-
CNRs through addition of NaBH4 aqueous solution (3.4 mL, 0.1 M). Finally,
the Pd/N-meso-CNRs nanocatalyst (3 wt%) was obtained by centrifugation,
washing with deionized water and drying in vacuum.
the interaction between Pd and N species, and a higher activity
for hydrogenation of phenol can be realized. The nitrogen dopant
can also enrich the electron density of Pd, accelerate the
dissociation of H2 and increase the catalytic activity. Furthermore,
the as-prepared Pd/N-meso-CNRs show good stability and the
highly dispersed Pd nanoparticles remain unchanged after
catalytic reactions.
Catalytic tests were performed in a 50-mL reaction tube. In a typical
process, the Pd/N-meso-CNRs nanocatalyst (53 mg), phenol derivatives
(0.5 mmol) and water (2 mL) were first mixed in the reaction tube under
stirring. Then, the reaction tube was vacuumed and purged with H2 for
three times, and it was attached to a balloon with H2 to ensure the supply
of H2 during the hydrogenation. Subsequently, the reaction mixture was
heated to a specific temperature and maintained for several hours. After
the release of excessive H2 and the cooling till room temperature, toluene
was added to extract the product from the reaction solution, which was
directly injected to the gas chromatography to analyze and calculate the
conversion of phenol derivatives.
Experimental Section
Materials: Tetraethylorthosilicate (TEOS, 98%), hydrochloric acid (HCl,
37%), aqueous ammonia (NH3·H 2O, 28%), ethanol (99.7%), hydrofluoric
acid (HF, 40%), palladium chloride (PdCl2, 99%) and sodium borohydride
(NaBH4, 98%) were obtained from Sinopharm Chemical Reagent Co. Ltd.
Furfuryl alcohol (98%), guanidine hydrochloride (98%) and phenol (99.9%)
were purchased from Aladdin Co. Ltd. Triblock copolymer Pluronic F127,
hexadecyltrimethylammonium bromide (CTAB, 96%), oxalic acid (98%)
and aqueous solution of poly (ethyleneimine) (PEI, Mw=60000, 50 wt%)
were purchased from Sigma-Aldrich. All the chemicals were directly used
without further treatments.
Characterization: Transmission electron microscope (TEM) images were
captured by a FEI Tecnai G2 F30 microscope operated at 300 kV. The
samples were embedded and cut using LEICA EM U27 for the observation
of cross sections. Scanning electron microscope (SEM) images were
captured by a Hitachi S-4800 microscope. Nitrogen adsorption-desorption
isotherms and BET (Brunauer-Emmett-Teller) surface areas were
measured by a Belsorp-Max analyzer at 77 K. X-ray photoelectron
spectroscopy (XPS) measurements were performed on a Perkin-Elmer
PHI 5000C ESCA system. Fourier transformed infrared (FTIR) spectra
were recorded by Nexus 870 FTIR spectrometer. Raman spectroscopy
Synthesis of SiO2 nanotubes (NTs) by protective etching: SiO2 NTs
were prepared based on previous reference.[16] First of all, mesoporous
SiO2 NRs were synthesized by hydrolyzing TEOS in a basic solution at
room temperature with CTAB and F127 as soft templates. Typically, F127
(1.23 g), CTAB (3 g) and NH3·H 2O (28 wt%, 10 mL) were dissolved in
water (300 mL) to form a colorless and transparent solution in an
Erlenmeyer flask. TEOS (10 mL) was then injected to the above solution
under stirring, which gradually transform to mesoporous SiO2 nanorods
within 2 hours. The nanorods were separated by centrifugation at 8000
rpm, washed three times with water and refluxed in the mixture of HCl (10
mL) and ethanol (200 mL) at 75 °C for 2 h to remove the surfactant
molecules in the mesopores. Finally, all the emptied SiO2 nanorods were
dispersed in water as a stock solution with a concentration of 25 mg/mL.
The stock solution (20 mL) was mixed with an aqueous solution of PEI
(400 mL, 5 mg/mL), heated to 90 °C and maintained for 2 h to produce
SiO2 nanotubes. After cooling, the nanotubes were washed three times
with water and dried in vacuum to obtain SiO2 NTs powder (240 mg).
measurements were carried out on
a Thermo Scientific DXR.
Thermogravimetric analysis (TGA) were carried out on a TGA/DSC
3+.Experimental Details.
Acknowledgements
This work is supported by the National Key Research and
Development Program of China (2016YFB0701103), National
Natural Science Foundation of China (21671067, 21471058) and
ShuGuang Program supported by Shanghai Education
Development Foundation and Shanghai Municipal Education
Commission (15SG21).
Synthesis of meso-CNRs and N-meso-CNRs through nano-confined
reaction: The obtained SiO2 NTs (240 mg) were mixed with the ethanol
solution (20mL) of furfuryl alcohol (40 vol%) and oxalic acid (0.8 g) under
stirring for 30 min to ensure the complete loading of precursors in SiO2
NTs. Then, they were separated from the solution by centrifugation to
obtain FA loaded SiO2 NRs. The obtained FA/SiO2 NRs were heated to
100 °C for 2 h so that furfuryl alcohol could be polymerized to form
polyfurfuryl alcohol (PFA) under the catalysis of oxalic acid. The PFA/SiO2
nanorods could be converted to meso-carbon/SiO2 nanorods through
calcination at 550 °C in N2 for 4 h. Finally, pure meso-CNRs (160 mg) were
obtained by removing silica with HF solution (20 mL, 10 wt%). The N-
meso-CNRs were prepared through similar method except for the addition
of a certain amount of guanidine hydrochloride into the furfuryl alcohol
solution.
Keywords: Nano-confined reaction • Mesoporous carbon •
Catalyst support
[1]
[2]
a) Z. J. Li, M. Jaroniec, Y. J. Lee, L. R. Radovic, Chem. Commun. 2002,
1346-1347; b) Z. Ma, H. Zhang, Z. Yang, G. Ji, B. Yu, X. Liu, Z. Liu,
Green Chem. 2016, 18, 1976-1982.
a) X. Wang, Y. Li, J. Mater. Chem. A 2016, 4, 5247-5257; b) J. S. Yu, S.
Kang, S. B. Yoon, G. Chai, J. Am. Chem. Soc. 2002, 124, 9382-9383;
c) A. T. Rodriguez, M. Chen, Z. Chen, C. J. Brinker, H. Fan, J. Am. Chem.
Soc. 2006, 128, 9276-9277; d) J. Wei, Z. Sun, W. Luo, Y. Li, A. A.
Elzatahry, A. M. Al-Enizi, Y. Deng, D. Zhao, J. Am. Chem. Soc. 2017,
139, 1706-1713.
Preparation of Pd/N-meso-CNRs nanocatalyst and catalytic
hydrogenation of phenol derivatives: The Pd/N-meso-CNRs (3 wt%)
were fabricated by a modified deposition-precipitation method. In a typical
process, an aqueous solution of H2PdCl4 (0.1 M) was first prepared by
dissolving PdCl2 (0.177 g) with HCl aqueous solution (10 mL, 10 vol%) at
room temperature. At the same time, an aqueous suspension of N-meso-
CNRs was prepared by mixing the nanorods (120 mg) with water (40 mL)
[3]
a) Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, H. F. Yang, Z. Li, C. Z. Yu, B.
Tu, D. Y. Zhao, Angew. Chem. Int. Ed. 2005, 44, 7053-7059; b) R. Ryoo,
S. H. Joo, S. Jun, J. Phys. Chem. B 1999, 103, 7743-7746; c) Z. Wang,
Y. Zhu, W. Luo, Y. Ren, X. Cheng, P. Xu, X. Li, Y. Deng, D. Zhao, Chem.
of Mater. 2016, 28, 7773-7780.
[4]
[5]
Y. Zhang, A. Wang, T. Zhang, Chem. Commun. 2010, 46, 862-864.
Z. J. Li, W. F. Yan, S. Dai, Carbon 2004, 42, 767-770.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
[6]
H. Xue, T. Wang, J. Zhao, H. Gong, J. Tang, H. Guo, X. Fan, J. He,
Carbon 2016, 104, 10-19.
Coronado, P. Pizarro, D. P. Serrano, Green Chem. 2016, 18, 1938-1951;
c) Y. Meng, D. Gu, F. Zhang, Y. Shi, L. Cheng, D. Feng, Z. Wu, Z. Chen,
Y. Wan, A. Stein, D. Zhao, Chem. Mater. 2006, 18, 4447-4464; d) J. Wei,
D. Zhou, Z. Sun, Y. Deng, Y. Xia, D. Zhao, Adv. Funct. Mater. 2013, 23,
2322-2328.
[7]
a) G. S. Chai, S. B. Yoon, J. S. Yu, J. H. Choi, Y. E. Sung, J. Phys. Chem.
B 2004, 108, 7074-7079; b) Q. Lv, K. Li, C. Liu, J. Ge, W. Xing, Carbon
2016, 98, 126-137.
[8]
[9]
a) B. You, F. Kang, P. Yin, Q. Zhang, Carbon 2016, 103, 9-15; b) H. Jiang,
P. S. Lee, C. Li, Energy Environ. Sci. 2013, 6, 41-53; c) Q. Shi, R. Zhang,
Y. Lu, Y. Deng, A. A. Elzatahrya, D. Zhao, Carbon 2015, 84, 335-346.
H. Nishihara, T. Kyotani, Adv. Mater. 2012, 24, 4473-4498.
[14] a) Z. X. Ma, T. Kyotani, A. Tomita, Chem. Commun. 2000, 2365-2366;
b) M. Kruk, M. Jaroniec, T. W. Kim, R. Ryoo, Chem. Mater. 2003, 15,
2815-2823; c) J. Lee, S. Han, T. Hyeon, J. Mater. Chem. 2004, 14, 478-
486; d) K. E. Shopsowitz, W. Y. Hamad, M. J. MacLachlan, Angew.
Chem. Int. Ed. 2011, 50, 10991-10995; e) J. Xu, S. Lu, X. Chen, J. Wang,
B. Zhang, X. Zhang, C. Xiao, S. Ding, Nanotechnology 2017, 28.
[15] a) S. Schrettl, B. Schulte, H. Frauenrath, Nanoscale 2016, 8, 18828-
18848; b) J. Zhang, F. Guo, X. Wang, Adv. Funct. Mater. 2013, 23, 3008-
3014.
[10] a) J. Tang, J. Liu, R. R. Salunkhe, T. Wang, Y. Yamauchi, Chem.
Commun. 2016, 52, 505-508; b) J. Kong, S. I. S. Shahabadi, X. Lu,
Nanoscale 2016, 8, 1770-1788.
[11] a) T. Sun, L. Xu, S. Li, W. Chai, Y. Huang, Y. Yan, J. Chen, Appl. Catal.
B Environ. 2016, 193, 1-8; b) H. Ba, Y. Liu, T.-P. Lai, D.-V. Cuong, J. M.
Nhut, N. Dinh Lam, O. Ersen, G. Tuci, G. Giambastiani, P.-H. Cuong,
ACS Catal. 2016, 6, 1408-1419; c) V. L. Budarin, J. H. Clark, R. Luque,
D. J. Macquarrie, Chem. Commun. 2007, 634-636; d) B. Chen, S. Shang,
L. Wang, Y. Zhang, S. Gao, Chem. Commun. 2016, 52, 481-484; e) G.
A. Ferrero, K. Preuss, A. B. Fuertes, M. Sevilla, M. M. Titirici, J. Mater.
Chem. A 2016, 4, 2581-2589; f) Q. Yue, J. Li, Y. Zhang, X. Cheng, X.
Chen, P. Pan, J. Su, A. A. Elzatahry, A. Alghamdi, Y. Deng, D. Zhao, J.
Am. Chem. Soc. 2017, 139, 15486-15493; g) M. Wang, X. Wang, Q. Yue,
Y. Zhang, C. Wang, J. Chen, H. Cai, H. Lu, A. A. Elzatahry, D. Zhao, Y.
Deng, Chem. Mater. 2014, 26, 3316-3321.
[16] L. You, T. Wang, J. Ge, Chem. Eur. J. 2013, 19, 2142-2149.
[17] S. Bertarione, F. Bonino, F. Cesano, S. Jain, M. Zanetti, D. Scarano, A.
Zecchina, J. Phys. Chem. B 2009, 113, 10571-10574.
[18] T. C. Mendes, C. Xiao, F. Zhou, H. Li, G. P. Knowles, M. Hilder, A.
Somers, P. C. Howlett, D. R. MacFarlane, ACS Appl. Mater. Interfaces
2016, 8, 35243-35252.
[19] Z. Li, J. Liu, C. Xia, F. Li, ACS Catal. 2013, 3, 2440-2448.
[20] Y. Li, X. Xu, P. Zhang, Y. Gong, H. Li, Y. Wang, RSC Adv. 2013, 3,
10973-10982.
[21] Y. Wang, J. Yao, H. Li, D. Su, M. Antonietti, J. Am. Chem. Soc. 2011,
133, 2362-2365.
[12] a) C. Liang, Z. Li, S. Dai, Angew. Chem. Int. Ed. 2008, 47, 3696-3717; b)
S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature
2001, 412, 169-172; c) C. D. Liang, S. Dai, J. Am. Chem. Soc. 2006, 128,
5316-5317.
[22] Y. Sun, C. Du, G. Han, Y. Qu, L. Du, Y. Wang, G. Chen, Y. Gao, G. Yin,
Electrochim. Acta 2016, 212, 313-321.
[13] a) T.-Y. Ma, L. Liu, Z.-Y. Yuan, Chem. Soc. Rev. 2013, 42, 3977-4003;
b) A. Berenguer, T. M. Sankaranarayanan, G. Gomez, I. Moreno, J. M.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201800112
Chemistry - An Asian Journal
FULL PAPER
Entry for the Table of Contents
FULL PAPER
N-doped mesoporous carbon
nanorods are prepared through the
nano-confined decomposition in
silica nanotubes with porous shells,
in which limited and slow releasing of
gaseous water and finite precursor
inside silica nanotubes are
Xueteng Liu, Fei Pang and Jianping
Ge*[a]
Page No. – Page No.
Synthesis of N-doped Mesoporous
Carbon Nanorods through Nano-
confined Reaction: High
Performance Catalyst Support for
Hydrogenation of Phenol
Derivatives
responsible for the formation of
mesoporous structures.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.