Nitrogen-Doped Carbon Composites with Ordered Macropores and Hollow Walls

Article abstract of DOI:10.1002/anie.202108396

Metal-organic frameworks provide versatile templates for the fabrication of various metal/carbon materials, but most of the derived composites possess only microspores, limiting the accessibility of embedded active sites. Herein, we report the construction of cobalt/nitrogen-doped carbon composites with a three-dimensional (3D) ordered macroporous and hollow-wall structure (H-3DOM-Co/NC) using a single-crystal ordered macropore (SOM)-ZIF-8@ZIF-67 as precursor. During the pyrolysis, the interconnected macroporous structure of SOM-ZIF-8@ZIF-67 is mostly preserved, whereas the pore wall achieves a solid-to-hollow transformation with Co nanoparticles formed in the hollow walls. The 3D-ordered macroporous carbon skeleton may effectively promote long-range mass transfer and the hollow wall can facilitate local accessibility of active sites. This unique structure can greatly boost its catalytic activity in the selective hydrogenation of biomass-derived furfural to cyclopentanol, much superior to its counterparts without this well-designed hierarchically porous structure.

Full text of DOI:10.1002/anie.202108396

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Nitrogen-Doped Carbon Composites with Ordered Macropores
and Hollow Walls
Authors: Yingwei Li, Wen Yao, Jianmin Chen, Yajing Wang, Ruiqi
Fang, Ze Qin, Xianfeng Yang, and Liyu Chen
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: Angew. Chem. Int. Ed. 10.1002/anie.202108396
Link to VoR: https://doi.org/10.1002/anie.202108396

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
Nitrogen-Doped Carbon Composites with Ordered Macropores
and Hollow Walls
Wen Yao,[a] Jianmin Chen,[a] Yajing Wang,[a] Ruiqi Fang,[a] Ze Qin,[a] Xianfeng Yang,[b] Liyu Chen,[a]*
Yingwei Li[a]*
[a]
W. Yao, Dr. J. Chen, Dr. Y. Wang, Dr. R. Fang, Z. Qin, Prof. L. Chen, Prof. Y. Li
State Key Laboratory of Pulp and Paper Engineering, School of Chemistry and Chemical Engineering, South China University of Technology
Guangzhou 510640 (P.R. China)
E-mail: liyuchen@scut.edu.cn; liyw@scut.edu.cn
Prof. X. Yang
[b]
Analytical and Testing Centre, South China University of Technology
Guangzhou 510640 (P.R. China)
Supporting information for this article is given via a link at the end of the document.
Abstract: Metal–organic frameworks provide versatile templates for
the fabrication of various metal/carbon materials, but most of the
derived composites possess only microspores, limiting the
accessibility of embedded active sites. Herein, we report the
construction of cobalt/nitrogen-doped carbon composites with a three-
dimensional- (3D-) ordered macroporous and hollow-wall structure
(H-3DOM-Co/NC) using a single-crystal ordered macropore- (SOM-)
ZIF-8@ZIF-67 as precursor. During the pyrolysis, the interconnected
macroporous structure of SOM-ZIF-8@ZIF-67 is mostly preserved,
while the pore wall achieves a solid-to-hollow transformation with Co
nanoparticles formed in the hollow walls. The 3D-ordered
macroporous carbon skeleton may effectively promote long-range
mass transfer and the hollow wall can facilitate local accessibility of
active sites. This unique structure can greatly boost its catalytic
activity in the selective hydrogenation of biomass-derived furfural to
cyclopentanol, much superior to its counterparts without this well-
designed hierarchically porous structure.
ZIF-derived M/NC catalysts with mesopores and/or macropores,[6]
their pore structures show a random distribution and low
connectivity of mesopores and/or macropores. Recently, we
reported a single-crystal ordered macroporous- (SOM-) ZIF-8,[7]
which can be modified with transition metal ions (e.g., Ni, and Fe)
as versatile precursors for the synthesis of various hierarchically
porous M/NC materials with improved mass transfer.[8]
Nevertheless, in these hierarchically porous M/NC materials,
most of the active sites are buried in thick microporous walls,
which still suffer from the restricted accessibility to reaction
substrates. Here, we reasonably conceive that the creation of
hollow walls in the hierarchically porous carbon skeleton can
further decrease the diffusion resistance to enhance the
accessibility of active sites and in turn greatly boost the catalytic
performance.
In this work, we report the fabrication of Co/NC catalysts with
three-dimensional ordered macropores and hollow walls (denoted
as H-3DOM-Co/NC) by employing a SOM-ZIF-8@ZIF-67 crystal
as precursor, which is synthesized through epitaxial growth of
ZIF-67 nanolayers on SOM-ZIF-8. During the thermal
transformation, the interconnected macroporous structure of
SOM-ZIF-8@ZIF-67 crystals can be inherited to the yielded
carbon composites, while the pore walls achieve a solid-to-hollow
transformation accompanied by the formation of Co NPs. The 3D-
ordered macroporous skeleton of H-3DOM-Co/NC can promote
long-range mass transfer meanwhile the hollow walls can
facilitate local accessibility of active sites, allowing maximum
exposure of active Co sites to reaction substrates. The H-3DOM-
Co/NC catalyst exhibited significantly enhanced catalytic activity
and selectivity in the hydrogenation of furfural (FFA) to
cyclopentanol (CPL), as compared to conventional- (C-), hollow-
(H-), and 3DOM-Co/NC catalysts derived from C-ZIF-67, C-ZIF-
8@ZIF-67, and SOM-ZIF-67, respectively.
Introduction
Porous carbon-supported metal nanoparticles (NPs), a major
category of functional materials, are critically important for a
variety of applications including catalysis.[1] Among them,
transition metals embedded in nitrogen-doped carbon (M/NC)
materials have attracted great attention as promising
heterogeneous catalysts due to their catalytically active centers.[2]
For heterogeneous catalysts, their performance is determined by
not only their intrinsic activity but also the number of accessible
active sites.[3] Therefore, it is desirable to develop M/NC catalysts
with hierarchical pore and/or hollow structures to enhance the
accessibility of active sites.
Metal–organic frameworks (MOFs), with controllable pore
structure and tunable composition, have provided a good platform
for fabricating various functional nanomaterials.[4] In particular, N-
rich zeolitic imidazolate frameworks (ZIFs) have been
demonstrated to be ideal precursors to design M/NC catalysts.[5]
However, most of these ZIF-derived M/NC catalysts only possess
microspores, limiting the accessibility of active sites. Although
some templated methods have been applied for the synthesis of
Results and Discussion
Scheme 1 illustrates the synthetic route of H-3DOM-Co/NC,
consisting of four main steps. First, a mixed ammonia-methanol
solution was employed to induce the formation of the ZIF-8
1
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
crystalline phase in 3D-ordered polystyrene spheres (PS)
template voids filled with 2-methylimidazole and zinc nitrate
hexahydrate to yield ZIF-8@PS. Thermogravimetric analysis
(TGA) of the PS template showed a complete weight loss at ca.
400 °C (Figure S1). Thus, the PS template was removed by
calcination at 400 °C for 5 h to obtain SOM-ZIF-8. Subsequently,
the SOM-ZIF-8 served as seeds for the epitaxial growth of thin
ZIF-67 nanolayers in the solution of 2-methylimidazole and cobalt
nitrate hexahydrate to produce SOM-ZIF-8@ZIF-67. Finally, the
SOM-ZIF-8@ZIF-67 was employed as the precursor for the
synthesis of H-3DOM-Co/NC by pyrolysis in an argon atmosphere.
SOM-ZIF-8@ZIF-67
characteristics, implying their microporous structures (Figure S7).
showed
similar
type-I
isotherm
a
b
c
f
i
410 nm
2 μm
1 μm
200 nm
d
e
Hollow
Solid
340 nm
Pyrolysis
Epitaxial growth
PS removal
2 μm
1 μm
200 nm
g
ZIF-8@3D-PS
SOM-ZIF-8
h
[100]
SOM-ZIF-8@ZIF-67
H-3DOM-Co/NC
[110]
002
-
011
002
110
Scheme 1. Schematic illustration of the synthesis process of H-3DOM-Co/NC.
1 nm-1
1 nm-1
1 μm
Co+Zn
The SOM-ZIF-8 was synthesized using a PS template with a
diameter size of 500 nm (Figure S2). Field-emission scanning
electron microscopy (SEM) and transmission electron microscopy
(TEM) images of SOM-ZIF-8 displayed a uniform size distribution
and a cubic morphology with 3D-ordered macroporous structure
(Figures 1a–c and S3). The highly ordered macropore
arrangement in {100} and {111} planes of SOM-ZIF-8 was clearly
evidenced from SEM images (Figure S4). The macropore
diameter of SOM-ZIF-8 was measured to be ~410 nm.
1 μm
1 μm
Co
Zn
Figure 1. FESEM images of (a–c) SOM-ZIF-8 and (d–f) SOM-ZIF-8@ZIF-67.
(g and h) TEM images of SOM-ZIF-8@ZIF-67 in the [100] and [110] zone axis,
respectively (inset shows corresponding SAED patterns). (i) HAADF-STEM
image and the corresponding EDX elemental mappings of SOM-ZIF-8@ZIF-67.
SOM-ZIF-8 functioned as the crystal seeds for subsequent
epitaxial growth of ZIF-67 (Co) with isoreticular structure, leading
to the corresponding change in color from light yellow to light
purple (Figure S5). Low-magnification SEM images of SOM-ZIF-
8@ZIF-67 showed that ZIF-67 exclusively grew along with the
surface of SOM-ZIF-8 without self-nucleation (Figure 1d). High-
magnification SEM and TEM images revealed a similar ordered
macroporous skeleton but a smaller pore size (~340 nm) and a
thicker wall of SOM-ZIF-8@ZIF-67 compared with those of SOM-
ZIF-8 due to the epitaxial growth of ZIF-67 layers (with a thickness
of ~35 nm) (Figures 1e–h and S4). High-angle annular dark-field
scanning transmission electron microscopy images (HAADF-
STEM) and the corresponding energy-dispersive X-ray
spectroscopy (EDX) mapping images of SOM-ZIF-8@ZIF-67
verified the outer layers of ZIF-67 on SOM-ZIF-8 (Figure 1i).
Selected-area electron diffraction (SAED) patterns taken from an
entire crystal in the direction of [100] and [110] zone axes
revealed the single-crystalline nature of SOM-ZIF-8@ZIF-67
(Figures 1g and h, insets).
Powder X-ray diffraction (XRD) patterns of both SOM-ZIF-8
and SOM-ZIF-8@ZIF-67 exhibited characteristic peaks ascribed
to C-ZIF-8 and C-ZIF-67,[9] indicating the formation of phase-pure
ZIF-8 and ZIF-8@ZIF-67, respectively (Figure S6). The peak
intensity of SOM-ZIF-8@ZIF-67 was weaker than that of SOM-
ZIF-8, implying the reduced crystallinity of SOM-ZIF-8@ZIF-67
after the epitaxial growth process, which is similar to previous
reports.[10] Nitrogen (N2) sorption isotherms of SOM-ZIF-8 and
After pyrolysis, the obtained H-3DOM-Co/NC preserved the
cubic morphology and interconnected macroporous structure of
SOM-ZIF-8@ZIF-67 but showed relatively rough surfaces due to
the carbonization of the framework and formation of small Co NPs
(Figures 2a–c). The pore size of H-3DOM-Co/NC (~400 nm) was
larger than that of SOM-ZIF-8@ZIF-67, indicating shrinkage of
the MOF during pyrolysis. Importantly, the pore walls of H-3DOM-
Co/NC exhibited a solid-to-hollow transformation and were
decorated with small Co NPs (Figures 2d and e). High-
magnification TEM image of H-3DOM-Co/NC clearly showed
macropores surrounded by hollow walls (Figure 2f). The hollow
walls of H-3DOM-Co/NC were further evidenced from elemental
line scan profiles of H-3DOM-Co/NC (Figure 2h, inset). SAED
patterns showed two obvious diffraction rings, assigned to the
(111) plane of metallic Co and the (002) plane of graphite carbon
(Figure 2e, inset). A high-resolution TEM (HRTEM) image of the
embedded NPs exhibited
a lattice spacing of 0.21 nm,
corresponding to the (111) plane of face-centered cubic (fcc)
metallic Co (Figure 2g). HAADF-STEM images and the
corresponding EDX elemental mappings revealed the uniform
distribution of Co NPs with an average size of ~4.9 nm on the
support consisted of C and N (Figures 2h, 2i, and S8). The content
of Co in the H-3DOM-Co/NC was determined to be 24.6 wt% by
atomic absorption spectroscopy (AAS). The formation of the
hollow wall may be governed by a surface-stabilized contraction
process due to the different thermal stabilities between ZIF-67
and ZIF-8, as demonstrated by TGA (Figure S9). During the
2
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
thermal transformation, the outer ZIF-67 layers first decomposed
into a rigid Co/NC shell, which then provided a driving force to pull
ZIF-8 precursors outward during carbonization, resulting in the
formation of hollow walls.[11]
3d). The high-resolution N 1s spectrum of H-3DOM-Co/NC could
be deconvoluted into four main peaks centered at 398.3, 398.9,
399.5, and 400.6 eV, assigned to pyridinic-N, Co-coordinated N,
pyrrolic-N, and graphitic-N, respectively (Figure 3e). The strong
coordination interaction between the Co and N can contribute to
the electron modulation and stabilization of active Co sites,
potentially benefitting for catalytic activity and stability.
a
b
c
FFA is a key platform molecule industrially produced from
cellulosic biomass. The conversion of FFA to value-added
products (e.g., CPL, cyclopentanone (CPO), furfural alcohol (FA),
and tetrahydrofurfuralalcohol (THFFA)) is of great importance in
both academic research and industrial application (Figure 4a).[12]
Among them, CPL is widely employed in the production of
pharmaceuticals, dyes, and fragrances. Many catalytic systems
have been developed for the selective hydrogenation of FFA to
CPL. However, it remains a big challenge to simultaneously
achieve both high activity and excellent selectivity under mild
conditions.
400 nm
1 μm
500 nm
100 nm
e
f
d
(111)
(002)
Hollow
5 nm-1
a
b
c
100 nm
50 nm
500 nm
C-Co/NC
H-Co/NC
3DOM-Co/NC
H-3DOM-Co/NC
C-Co/NC
H-Co/NC
3DOM-Co/NC
H-3DOM-Co/NC
350
300
250
200
150
100
50
2.04
1.36
0.68
0.00
0.93
0.62
0.31
0.00
0.81
0.54
0.27
0.00
0.93
0.62
0.31
0.00
g
h
i
H-3DOM-Co/NC
Co: JCPDS Card No. 15-0806
Co
C
N
0
Co
C
3DOM-Co/NC
20
30
40
50
60
80
90
2q (degree) 70
0.0
0.2
0.4
0.8
1.0
Relative press0u.6re (P/P0)
d
e
Co0
Co-Nx
N 1s
Co 2p3/2
Satellite
Pyrrolic N
CoOx
CoNx
Line scan
Pyridinic N
Graphitic-N
H-3DOM-Co/NC
H-3DOM-Co/NC
2 nm
200 nm
H-Co/NC
Co+C+N
N
3DOM-Co/NC
H-Co/NC
3DOM-Co/NC
H-Co/NC
Figure 2. (a–c) FESEM and (d–f) TEM images of H-3DOM-Co/NC. (g) HRTEM
image of H-3DOM-Co/NC. (h and i) HAADF-STEM image and the
corresponding EDX elemental mappings of H-3DOM-Co/NC. The insets of (e)
and (h) are the corresponding SAED patterns and elemental line scan profiles,
respectively.
C-Co/NC
C-Co/NC
C-Co/NC
788 786 784 782 780 778 776
Binding energy (eV)
404
402
400
398
396
1
10
100
Binding energy (eV)
Pore size (nm)
Figure 3. (a) XRD patterns, (b) N2 adsorption-desorption isotherms, (c) pore
size distribution calculated from the non-local density functional theory model,
(d) Co 2p and (e) N 1s XPS spectra of C-Co/NC, H-Co/NC, 3DOM-Co/NC, and
H-3DOM-Co/NC.
The XRD patterns of H-3DOM-Co/NC showed two diffraction
peaks at around 44.4 and 51.6°, which could be indexed to the
(111) and (200) planes of fcc metallic Co, respectively, indicating
the carbonization of the MOF and formation of Co0 during
pyrolysis (Figure 3a). Raman spectra of H-3DOM-Co/NC
presented obvious D band (~1327 cm−1) and G band (~1587
cm−1), corresponding to defective carbon and graphitic carbon,
respectively (Figure S10). The N2 sorption isotherm of H-3DOM-
Co/NC showed a steep increase at relatively low pressures (P/P0
< 0.05) and a hysteresis loop at high pressures, representing the
features of microporous and mesoporous structures, respectively
(Figure 3b). The pore size distribution revealed that the micropore
and mesopore diameters mainly centered at around 0.64 nm and
27.3 nm, respectively (Figure 3c). The Brunauer-Emmett-Teller
(BET) surface area of H-3DOM-Co/NC was calculated to be 299
m2/g (Table S1). H-3DOM-Co/NC with the interconnected
microporous-mesoporous-macroporous structure can effectively
improve the accessibility of the active sites to reactants.
Herein, H-3DOM-Co/NC with highly dispersed ultrafine Co NPs
on N-doped carbon support featuring 3D-ordered macroporous
and hollow-wall structure was supposed to be an effective catalyst
for this hydrogenation reaction. The reaction parameters were
first screened and pointed to optimized reaction conditions of H2
pressure of 2.0 MPa and temperature of 180 °C (Figures S12 and
S13). The time profiles showed that CPL selectivity steadily
increased when the reaction time increased from 1 to 8 h,
demonstrating that FFA could be continuously converted into the
final CPL product (Figure 4c). H-3DOM-Co/NC achieved a 97.2%
yield of CPL within 8 h (Figure 4b). For comparison, Co-free
3DOM-NC with residual Zn derived from SOM-ZIF-8 was
prepared (Figure S14), which showed no catalytic activity,
suggesting the critical role of Co sites and the negligible role of Zn
in the hydrogenation reaction (Table S2).
Moreover, the influence of basicity and acidity of the catalysts
on the reaction was studied. CO2-temperature-programmed
desorption (CO2-TPD) spectra of H-3DOM-Co/NC showed a
strong CO2 desorption peak at ca. 166 °C, suggesting the
existence of Lewis basic sites originated from abundant N
dopants in the support (Figure S15). To verify the role of N in the
The electronic structure of H-3DOM-Co/NC was examined by
X-ray photoelectron spectroscopy (XPS). The survey spectra
revealed that Co, C, and N were the predominant elements in H-
3DOM-Co/NC with residual Zn (Figure S11). The high-resolution
Co 2p3/2 spectrum exhibited the characteristic peaks of Co0, Co-
Ox, and Co-Nx at 778.4, 780.1, and 781.4 eV, respectively (Figure
3
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
catalysis, Co NPs supported on N-free active carbon (Co/AC) with
similar Co loading were prepared. Co/AC exhibited much larger
sizes of Co NPs compared with H-3DOM-Co/NC (Figure S14),
suggesting the important role of N in preventing the aggregation
of Co NPs in the calcination process. Co/AC showed a lower
activity (17.8% conversion) compared with that of H-3DOM-
Co/NC (Table S2). But it exhibited a similar selectivity of CPL
mass transfer and mesopores in hollow walls can facilitate the
local accessibility of active Co sites, thus cooperatively boosting
the catalytic activity.
These findings inspired us to further evaluate the effect of the
sizes of macropores in the skeletons and hollow space in the walls
of 3DOM-Co/NC on the accessibility of Co sites. We prepared a
series of H-3DOM-Co/NC-X materials with various macropore
(67.4%) to that of H-3DOM-Co/NC at a similar conversion (17.8%). sizes using PS templates with different diameters. PS templates
These results demonstrated that the effect of N doping on tuning
the catalytic selectivity was negligible and the distinct activities
should be attributed to the different sizes of Co NPs. We further
studied the influence of acidity of catalysts on the reaction.
Fourier-transform infrared spectra of pyridine adsorbed on H-
3DOM-Co/NC displayed two strong peaks at 1442 and 1596 cm−1,
confirming the Lewis acidic sites originated from Co species
(Figure S16). In the hydrogenation of FFA, the Co acidic sites can
promote the formation of carbocation intermediates for
subsequent cyclization rearrangement (Figure 4d), allowing the
stepwise hydrogenation of FFA to CPO/CPL.[13]
with diameters of X (X = 210, 320, 410, and 600 nm) were used
for the first synthesis of SOM-ZIF-8-X with macropore sizes
ranging from ca. 182 to 512 nm and the subsequent SOM-ZIF-
8@ZIF-67-X with reduced macropore sizes ranging from ca. 160
to 405 nm (Figures S23–S32). The thickness of the ZIF-67 layers
in SOM-ZIF-8@ZIF-67-X increased from ca. 11.0 to 53.5 nm with
enlarged macropore sizes (Figure S33).
a
To demonstrate the advantage of the 3D-ordered
macroporous and hollow-wall structures for boosting the reaction,
we prepared three counterpart materials, including C-Co/NC, H-
Co/NC, and 3DOM-Co/NC derived from C-ZIF-67, C-ZIF-8@ZIF-
67, and SOM-ZIF-67, respectively (Figures S5, S17–S22). XRD
patterns of these materials all exhibited characteristic peaks
assigned to fcc metallic Co with high purity (Figure 3a). XPS
measurements demonstrated the similar electronic structures of
these Co-based materials (Figures 3d and 3e). The main
difference between these materials is their distinct pore structures.
c
100
b
H-3DOM-Co/NC
3DOM-Co/NC
H-Co/NC
100
FA
80
60
40
20
0
80
60
40
20
0
C-Co/NC
CPO
CPL
FFA
0
2
4
6
8
10
0
2
4
6
8
10
Time (h)
Time (h)
Solid C-Co/NC possessed
a micropore-dominant support
e
d
100
80
60
40
20
0
embedded with Co NPs (Figure 3c and Figure S20). H-Co/NC
showed a hollow structure with Co NPs dispersed in the micro-
mesoporous shells but without interconnected macropores
(Figure 3c and Figure S21). 3DOM-Co/NC showed an
interconnected macroporous carbon skeleton similar to H-3DOM-
Co/NC but a microporous wall (Figure 3c and Figure S22).
H2O
[H]
Acidic sites
FFA
CPL
The catalytic activity of C-Co/NC, H-Co/NC, and 3DOM-
Co/NC were examined with the same amount of Co under the
same reaction conditions (Table S2). All of the materials showed
similar selectivities to CPL but distinct activities (yields of CPL in
8 h) in the order of H-3DOM-Co/NC (97.2%) > 3DOM-Co/NC
(62.3%) > H-Co/NC (41.7%) > C-Co/NC (21.3%). Since these Co-
based catalysts possessed similar electronic structures, their
different activities should be attributed to their distinct pore
structures. The activity trend implies the important role of
mesopores and macropores in facilitating the catalytic reaction.
For a detailed analysis of the effect of the porous structure, the
accessible Co sites in these materials were determined by H2-
TPD measurement (Table S3). These materials showed the
dispersion of Co in the order of H-3DOM-Co/NC (20.3%) > H-
Co/NC (14.2%) > 3DOM-Co/NC (11.6%) > C-Co/NC (8.7%),
implying the contribution of mesopores in improving the
accessibility of Co sites. However, considering of the higher
activity of mesopore-free 3DOM-Co/NC than macropore-free H-
Co/NC, the accessbility of Co sites alone can not explain the
activity improvement. Mass trasport should be another factor that
could greatly affect the catalytic efficiency. The interconected
macropores can greatly contribute to long-range mass transfer
improvement, as demonstrated in our previous study.7 Therefore,
the interconnected macropores can enhance the long-range
C
O
N
H
Co
1
2
3
4
5
6
7
Cycle
Figure 4. (a) The possible reaction pathway for the hydrogenation of FFA to
CPL. (b) The yield of CPL as a function of reaction time over C-Co/NC, H-Co/NC,
3DOM-Co/NC, and H-3DOM-Co/NC. (c) Plots of the product distribution for the
conversion of FFA at different reaction times. (d) Plausible mechanism for the
hydrogenation of FFA to CPL over the H-3DOM-Co/NC catalyst. (e) Reusability
tests of H-3DOM-Co/NC for the FFA hydrogenation at reaction times: 8 h (pink
bars), and 4 h (purple stars).
After pyrolysis, SOM-ZIF-8@ZIF-67-X was transformed to the
corresponding H-3DOM-Co/NC-X with slightly increased
macropore sizes (Figure S34). Interestingly, the void sizes of the
walls increased along with the increase of macropore sizes
(Figure S34). The hysteresis loop in the N2 sorption isotherms of
H-3DOM-Co/NC-X also became more and more evident with the
enhancement of macropore sizes, indicating the enlarged
mesopore sizes of the walls (Figures S35 and S36). This finding
is similar to previous reports that a thicker rigid layer on ZIF-8
would result in a larger hollow space in the derived carbon
composites.[6e] HRTEM images (Figure S34) and XRD patterns
(Figure S37) of H-3DOM-Co/NC-X confirmed the successful
formation of fcc metallic Co. XPS measurements revealed similar
chemical environments of Co among the H-3DOM-Co/NC-X
4
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
samples (Figures S38–41). In the catalytic reactions, the activity
of H-3DOM-Co/NC-X increased with the enhancement of
macropore and void sizes, which may be attributed to the
improved substrate diffusion and increased number of available
active sites. Among the synthesized H-3DOM-Co/NC-X materials,
H-3DOM-Co/NC-600 showed the highest activity, achieving a
97.8% yield of CPL in 8 h with a turnover frequency of 1.8 h-1,
making it one of the most active non-noble-metal catalysts
reported thus far for this hydrogenation reaction (Tables S2 and
S4).
The hot filtration experiment demonstrated no further
conversion of FFA after catalyst removal from the system and the
Co content of the reaction mixture measured by AAS was below
the detecting limit (< 5 ppb), suggesting the heterogeneous nature
of the catalytic system (Figure S42). Furthermore, H-3DOM-
Co/NC could be reused at least seven times without significant
loss of activity (Figure 4e). The CPL yields were also similar at an
incomplete reaction time (4 h) in the recycling experiments (purple
stars suit in Figure 4e), revealing the high durability of this catalyst.
The XRD patterns of the used H-3DOM-Co/NC matched well with
those of the fresh one with almost unchanged intensity (Figure
S43). The HAADF-STEM images also confirmed that the 3D-
ordered macropores and hollow walls of the reused catalyst were
well preserved and no obvious aggregation of Co NPs was
observed (Figure S44). These results demonstrate that the
hierarchically porous N-doped carbon support can protect the
aggregation and leaching of Co NPs during the reaction, thus
allowing the active H-3DOM-Co/NC catalyst to show high stability
and reusability under the investigated conditions.
Dongguan City (2020607263005), and the Natural Science
Foundation of Guangdong Province (2016A050502004,
2017A030312005).
Competing interests
The authors declare no competing interest.
Keywords: hierarchical pore • hollow structure • heterogeneous
catalysis • metal-organic frameworks • selective hydrogenation
[1]
a) R. J. White, R. Luque, V. L. Budarin, J. H. Clark, D. J. Macquarrie,
Chem. Soc. Rev. 2009, 38, 481–494; b) A. Dhakshinamoorthy, H. Garcia,
Chem. Soc. Rev. 2012, 41, 5262–5284; c) X. Zhang, H. Liu, Y. Shi, J.
Han, Z. Yang, Y. Zhang, C. Long, J. Guo, Y. Zhu, X. Qiu, G. Xue, L.
Zhang, B. Zhang, L. Chang, Z. Tang, Matter 2020, 3, 558–570.
a) C.-X. Zhao, B.-Q. Li, J.-N. Liu, Q. Zhang, Angew. Chem. Int. Ed. 2021,
60, 4448–4463; Angew. Chem. 2021, 133, 4496–4512; b) C. Tang, L.
Chen, H. Li, L. Li, Y. Jiao, Y. Zheng, H. Xu, K. Davey, S.-Z. Qiao, J. Am.
Chem. Soc. 2021, 143, 7819–7827; c) R. V. Jagadeesh, K. Murugesan,
A. S. Alshammari, H. Neumann, M.-M. Pohl, J. Radnik, M. Beller,
Science 2017, 358, 326–332; d) S. Wang, J. Wang, M. Zhu, X. Bao, B.
Xiao, D. Su, H. Li, Y. Wang, J. Am. Chem. Soc. 2015, 137, 15753–15759;
e) L. Chen, L. Zhang, Z. Chen, H. Liu, R. Luque, Y. Li, Chem. Sci. 2016,
7, 6015–6020.
[2]
[3]
[4]
a) J. Shan, C. Ye, S. Chen, T. Sun, Y. Jiao, L. Liu, C. Zhu, L. Song, Y.
Han, M. Jaroniec, Y. Zhu, Y. Zheng, S.-Z. Qiao, J. Am. Chem. Soc. 2021,
143, 5201–5211; b) W. Zhu, L. Zhang, P. Yang, C. Hu, Z. Luo, X. Chang,
Z.-J. Zhao, J. Gong, Angew. Chem. Int. Ed. 2018, 57, 11544–11548;
Angew. Chem. 2018, 130, 11718–11722; c) J. Nai, X. W. Lou, Adv. Mater.
2019, 31, 1706825; (d) H.-F. Wang, L. Chen, M. Wang, Z. Liu, Q. Xu,
Nano Lett. 2021, 21, 3640–3648.
a) H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi, Science 2013,
341, 1230444; b) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int.
Ed. 2004, 43, 2334–2375; Angew. Chem. 2004, 116, 2388–2430; c) B.
Li, H.-M. Wen, Y. Cui, W. Zhou, G. Qian, B. Chen, Adv. Mater. 2016, 28,
8819–8860; d) S. Dang, Q.-L. Zhu, Q. Xu, Nat. Rev. Mater. 2017, 3,
17075; e) K. Shen, X. Chen, J. Chen, Y. Li, ACS Catal. 2016, 6, 5887–
5903; f) H.-F. Wang, L. Chen, H. Pang, S. Kaskel, Q. Xu, Chem. Soc.
Rev. 2020, 49, 1414–1448; g) L. Chen, R. Luque, Y. Li, Chem. Soc. Rev.,
2017, 46, 4614–4630.
Conclusion
In summary, we have successfully fabricated 3D-ordered
macroporous H-3DOM-Co/NC with hollow walls, through epitaxial
growth of ZIF-67 nanolayers on SOM-ZIF-8 followed by a simple
thermal transformation process. The 3D-ordered macroporous
carbon framework can effectively promote long-range mass
transfer, and the hollow walls can facilitate the local accessibility
of active sites, which can cooperatively maximize the exposure of
embedded Co NPs to reaction substrates, thus boosting the
catalytic activity in the hydrogenation of FFA. Further tuning the
sizes of macropores in the skeleton and hollow space in the walls
demonstrated the positive correlation between macropore/void
sizes and mass transfer efficiency/accessibility of active sites.
Moreover, the porous N-doped carbon support could well protect
the embedded Co NPs from aggregation during the catalytic
reaction to achieve good stability and reusability in the reaction.
This study might provide insights into the rational design and
synthesis of hierarchical and hollow structures with enhanced
activity and stability for various applications.
[5]
a) H.-L. Jiang, B. Liu, Y.-Q. Lan, K. Kuratani, T. Akita, H. Shioyama, F.
Zong, Q. Xu, J. Am. Chem. Soc. 2011, 133, 11854–11857; b) W. Zhong,
H. Liu, C. Bai, S. Liao, Y. Li, ACS Catal. 2015, 5, 1850–1856; c) X. Wang,
Z. Chen, X. Zhao, T. Yao, W. Chen, R. You, C. Zhao, G. Wu, J. Wang,
W. Huang, J. Yang, X. Hong, S. Wei, Y. Wu, Y. Li, Angew. Chem. Int. Ed.
2018, 57, 1944–1948; Angew. Chem. 2018, 130, 1962–1966; d) X. F. Lu,
L. Yu, J. Zhang, X. W. Lou, Adv. Mater. 2019, 31, 1900699; e) Z. Qi, Y.
Pei, T. W. Goh, Z. Wang, X. Li, M. Lowe, R. V. Maligal-Ganesh, W.
Huang, Nano Res. 2018, 11, 3469-3479.
[6]
a) C. Wang, J. Kim, J. Tang, M. Kim, H. Lim, V. Malgras, J. You, Q. Xu,
J. Li, Y. Yamauchi, Chem 2019, 6, 19–40; b) A. I. Douka, Y. Xu, H. Yang,
S. Zaman, Y. Yan, H. Liu, M. A. Salam, B. Y. Xia, Adv. Mater. 2020, 32,
2002170; c) L. Shang, H. Yu, X. Huang, T. Bian, R. Shi, Y. Zhao, G. I. N.
Waterhouse, L.-Z. Wu, C.-H. Tung, T. Zhang, Adv. Mater. 2016, 28,
1668–1674; d) Y. Qian, Q. Liu, E. Sarnello, C. Tang, M. Chng, J. Shui, T.
Li, S. J. Pennycook, M. Han, D. Zhao, ACS Mater. Lett. 2019, 1, 37–43;
e) C. Liu, X. Huang, J. Wang, H. Song, Y. Yang, Y. Liu, J. Li, L. Wang,
C. Yu, Adv. Funct. Mater. 2018, 28, 1705253; f) J. Niu, J. Albero, P.
Atienzar, H. García, Adv. Funct. Mater. 2020, 30, 1908984.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21825802, 22136003, 22108083), the
Fundamental Research Funds for the Central Universities
(2019PY11), Introduced Innovative R&D Team Leadership of
[7]
[8]
K. Shen, L. Zhang, X. Chen, L. Liu, D. Zhang, Y. Han, J. Chen, J. Long,
R. Luque, Y. Li, B. Chen, Science 2018, 359, 206–210.
a) M. Qiao, Y. Wang, Q. Wang, G. Hu, X. Mamat, S. Zhang, S. Wang,
Angew. Chem. Int. Ed. 2020, 59, 2688–2694; Angew. Chem. 2020, 132,
2710–2716; b) Z. Zhu, H. Yin, Y. Wang, C.-H. Chuang, L. Xing, M. Dong,
5
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
Y.-R. Lu, G. Casillas-Garcia, Y. Zheng, S. Chen, Y. Dou, P. Liu, Q. Cheng,
H. Zhao, Adv. Mater. 2020, 32, 2004670. c) C. Zhao, G.-L. Xuꢀ, Z. Yu, L.
Zhang, I. Hwang, Y.-X. Mo, Y. Ren, L. Chengꢀ, C.-J. Sun, Y. Renꢀ, X. Zuoꢀ,
J.-T. Li, S.-G. Sun, K. Amine, T. Zhao, Nat. Nanotechnol. 2021, 16, 166–
173; d) Y. Guo, L. Feng, C. Wu, X. Wang, X. Zhang, J. Catal. 2020, 390,
213–223; e) X. Zhang, X. Han, Z. Jiang, J. Xu, L. Chen, Y. Xue, A. Nie,
Z. Xie, Q. Kuang, L. Zheng, Nano Energy 2020, 71, 104547; f) Y.-L. Wu,
X. Li, Y.-S. Wei, Z. Fu, W. Wei, X.-T. Wu, Q.-L. Zhu, Q. Xu, Adv. Mater.
2021, 33, 2006965.
[9]
a) X.-C. Huang, Y.-Y. Lin, J.-P. Zhang, X.-M. Chen, Angew. Chem. Int.
Ed. 2006, 45, 1557–1559; Angew. Chem. 2006, 118, 1587–1589; b) K.
S. Park, Z. Ni, A. P. Côté, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K.
Chae, M. O’Keeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. U.S.A. 2006, 103,
10186–10191.
[10] a) J. Tang, R. R. Salunkhe, J. Liu, N. L. Torad, M. Imura, S. Furukawa,
Y. Yamauchi, J. Am. Chem. Soc. 2015, 137, 1572–1580; b) H. Chen, K.
Shen, Y. Tan, Y. Li, ACS Nano 2019, 13, 7800–7810.
[11] S. Liu, Z. Wang, S. Zhou, F. Yu, M. Yu, C.-Y. Chiang, W. Zhou, J. Zhao,
J. Qiu, Adv. Mater. 2017, 29, 1700874.
[12] a) P. Sudarsanam, E. Peeters, E. V. Makshina, V. I. Parvulescub, B. F.
Sels, Chem. Soc. Rev. 2019, 48, 2366–2421; b) D. M. Alonso, S. G.
Wettstein, J. A. Dumesic, Chem. Soc. Rev. 2012, 41, 8075–8098; c) R.
Fang, A. Dhakshinamoorthy, Y. Li, H. Garcia, Chem. Soc. Rev. 2020, 49,
3638–3687; d) D. Sun, S. Sato, W. Ueda, A. Primo, H. Garcia, A. Corma,
Green Chem. 2016, 18, 2579–2597.
[13] a) Y. Yang, Z. Du, Y. Huang, F. Lu, F. Wang, J. Gao, J. Xu, Green Chem.
2013, 15, 1932–1940; b) N. Pino, G. Hincapié, D. López, Energy Fuels
2018, 32, 561–573; c) Q. Deng, R. Gao, X. Li, J. Wang, Z. Zeng, J.-J.
Zou, S. Deng, ACS Catal. 2020, 10, 7355–7366; d) M.-M. Zhu, X.-L. Du,
Y. Zhao, B.-B. Mei, Q. Zhang, F.-F. Sun, Z. Jiang, Y.-M. Liu, H.-Y. He, Y.
Cao, ACS Catal. 2019, 9, 6212–6222.
6
This article is protected by copyright. All rights reserved.

10.1002/anie.202108396
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
Cobalt/nitrogen-doped carbon catalysts with 3D-ordered macroporous and hollow-wall structures were successfully fabricated by
using ordered macroporous ZIF-8@ZIF-67 single crystals as precursors. This unique porous structure can greatly enhance mass
transfer and boost catalytic activity in the selective hydrogenation of furfural.
7
This article is protected by copyright. All rights reserved.