Aerobic oxidation of the C-H bond under ambient conditions using highly dispersed Co over highly porous N-doped carbon

Article abstract of DOI:10.1039/c8gc03653e

Highly dispersed Co sites in highly porous N-doped carbon (Co-NC) were synthesized by high-temperature pyrolysis of Zn/Co bimetallic zeolitic imidazolate framework-8 (Co_xZn_100-x-ZIF). Wide characterization indicated that the pyrolysis atmosphere and temperature play crucial roles in the metal dispersion and pore structure of the resulting materials. A hydrogen treatment at elevated temperatures is found to favour the Zn volatilization and restrict the pore shrinkage of the ZIF precursor, thus yielding efficient catalysts with highly dispersed Co, a high surface area (1090 m² g^-1) and pore volume (0.89 cm³ g^-1). When used as a catalyst for aerobic oxidation of ethylbenzene (EB), Co₁Zn₉₉-ZIF-800-H₂ contributes to 98.9% EB conversion and 93.1% ketone selectivity under mild conditions (60 °C, 1 atm O₂), which is 41.3 times more active in comparison to the ZIF-67-derived Co catalyst. Co-NC is stable and could be reused four times without obvious deactivation. This catalyst displays good chemoselectivity to the corresponding ketones when using a broad scope of hydrocarbon compounds.

Full text of DOI:10.1039/c8gc03653e

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Nie, J. Chen, M.
Chen, Z. Qi, T. W. Goh, T. Ma, L. Zhou, Y. Pei and W. Huang, Green Chem., 2019, DOI:
1
0.1039/C8GC03653E.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Page 1 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C8GC03653E
Graphic abstract
R
O
R
-
1
Up to 424.7 h
1
0 examples
O
n
Water solvent
n
o
6
0 C
Up to 100% conversion
0-95% selectivity
1
atm O
2
6
Highly dispersed Co
Higly dispersed Co sites in highly porous N-doped carbon are highly active for
o
aerobic oxidation of C-H bond to corrosponding ketones under 60 C and 1 atm O ,
2
which is 41.3 times more active in comparison to ZIF-67-derived Co catalyst.

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 2 of 7
View Article Online
DOI: 10.1039/C8GC03653E
Green Chemistry
PAPER
Aerobic oxidation of C-H bond under ambient conditions
using highly dispersed Co over highly porous N-doped
carbon†
Received 00th January 20xx,
Accepted 00th January 20xx
,
a, b
b
b
b
b
c
c
Renfeng Nie,*
Jingwen Chen, Minda Chen, Zhiyuan Qi, Tian-Wei Goh, Tao Ma, Lin Zhou,
DOI: 10.1039/x0xx00000x
b
, b, c
Yuchen Pei, Wenyu Huang*
www.rsc.org/
Highly dispersed Co sites in highly porous N-doped carbon (Co-NC) were synthesized by high-temperature pyrolysis of Zn/Co
bimetallic zeolitic imidazolate framework-8 (Co Zn100-x-ZIF). Wide characterizations indicated that the pyrolysis atmosphere
x
and temperature play crucial roles in the metal dispersion and pore structure of the resulting materials. A hydrogen
treatment at elevated temperatures is found to favour the Zn volatilization and restriction the pore-shrink of the ZIF
precursor, thus yielding efficient catalysts with highly dispersed Co, high surface area (1090 m²/g) and pore volume (0.89
1 2
cm³/g). When using as a catalyst for aerobic oxidation of ethylbenzene (EB), Co Zn99-ZIF-800-H contributes to 98.9 % EB
o
conversion and 93.1 % ketone selectivity at mild conditions (60 C, 1 atm O
2
), which is 41.3 times more active in comparison
to ZIF-67-derived Co catalyst. Co-NC is stable and could be reused for four times without obvious deactivation. This catalyst
displays good chemoselectivity to the corresponding ketones when using a broad scope of hydrocarbon compounds.
activity of metal NPs for specific catalytic reactions.21 Nevertheless,
the traditional methods typically do not endow much manipulation
over the dispersion of the metal and often results in its severe
aggregation, which deteriorates the catalytic efficiency and stability
of catalysts. Consequently, these catalysts are required to be
operated in organic solvents under high temperatures, a large excess
Introduction
The selective oxidation of hydrocarbons is of great importance in
the production of valuable building blocks such as alcohols, ketones,
1, 2
aldehydes and epoxides.
Compared with traditional oxidants,
undoubtedly, molecular oxygen is the most atom-economical and
environmentally benign oxidant. A large number of noble metals,
such as Pd, Au, and Ru, are active for aerobic oxidation.3 However,
the scarcity and high cost of noble metals hinder their large-scale
practical applications. Searching for earth-abundant yet efficient
catalysts to replace noble metals has, therefore, become one of the
most exciting topics in the aerobic oxidation chemistry.
2
of base additives or high O partial pressures (0.5-3 MPa) in order to
achieve a high yield of desired products. These harsh conditions
often lead to the over-oxidation of products, environmental
-8
2
4, 25, 29
pollution, and the risk of explosion.
Therefore, designing highly
dispersed active centres that are easily reachable by reactants is
highly desirable to solve the above problems and thereby improve
their catalytic performance.
N-doped carbon materials have attracted much attention due to
their feasibility for the selective oxidation with oxygen as the
Zeolitic imidazolate frameworks (ZIFs), composed of tetrahedrally-
coordinated transition metal ions (e.g., Fe, Co, Cu, Zn) connected by
N-containing imidazolate linkers, have received a lot of attention
since they possess permanent porosity, three-dimensional (3D)
9
-13
oxidant. The combination with early transition metals (Co, Fe, Mn,
etc.) is believed to be the promising non-noble catalysts owing to
1
4-28
their low price and large availability.
N-doped carbon support is similar to the function of a ligand in
homogeneous catalysts, in which the electron density of metal
centres can be adjusted by special N species. This electronic effect
can be much stronger than any ligand effect and finally promotes the
The way of activation of the
3
0
structure and diversity of metals and organic linkers. Pyrolysis of
ZIFs serves as an important route to metal-supported N-doped
carbon materials, in which metal species were confined in a CN
2
3
1
7, 19, 31
matrix for recycling.
However, several important issues are still
unresolved, such as pore shrinkage and metal aggregation during the
pyrolysis, which unfavour the molecular diffusion and
a
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, trasformation. Herein, the bimetal-organic frameworks (Co
32
Zn100-x
-
x
&
Ministry-of-Education Key Laboratory for the Synthesis and Application of
Organic Functional Molecules, School of Chemistry and Chemical Engineering,
Hubei University, Wuhan 430062, P.R. China.
ZIF) were used to tune the spatial distribution of Co in the precursor,
thereby realizing the control in dispersion of Co atoms for the final
pyrolyzed catalysts (Co-CN). Compared with pyrolization in an Ar
atmosphere, the hydrogen-pyrolytic approach leads to a high specific
surface area and generates mesoporosity in the N-doped carbon
matrix. These Co sites in the mesoporous N-doped carbon matrix
b
Department of Chemistry, Iowa State University, Ames, Iowa 50011, United
States.
c
Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States.
E-mail: refinenie@163.com (N. Nie); whuang@iastate.edu (W. Huang)
†
Electronic Supplementary Information (ESI) available: Additional experimental
results. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Page 3 of 7
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
Journal Name
exhibit superior activity for aerobic oxidation of C-H bond under very
mild conditions. The catalysts also displayed abroad versatility and
good stability.
View Article Online
(
b) DOI: 10.1039/C8GC03653E
Results and discussion
Characterization of Co-based materials
Co Zn99-ZIF-800-Ar
Co Zn99-ZIF
1
1
700
600
500
(
a)
Co Zn99-ZIF-900-H2
1
(b)
(d)
Co Zn99-ZIF-800-H2
1
Co Zn99-ZIF-800-H2
Co Zn99-ZIF-800-Ar
1
1
Co Zn99-ZIF-700-H2
ZIF-67-800-Ar
Co10Zn90-ZIF-800-Ar
1
·
C
Co Zn99-ZIF-600-H2
1
4
3
2
1
00
00
00
00
0
¨
Co
¨
Co
(c)
(d)
1
0
20 30 40 50 60 70 80 90
0.0
0.2
0.4
0.6
0.8
1.0
o
Relatvie pressure (p/p0)
2
theta ( )
6
6
.5
Co Zn99-ZIF
1.4
1.2
1.0
0.8
1
Co Zn99-ZIF-800-H2
1
(
c)
Co Zn99-ZIF-800-H
1
2
.0
Co Zn99-ZIF-800-Ar
1
Co Zn99-ZIF-800-Ar
1
Co10Zn90-ZIF-800-Ar
ZIF-67-800-Ar
ZIF-67-800-Ar
Co10Zn90-ZIF-800-Ar
1
0
0
.0
.5
.0
0
.6
0.4
.2
0.0
200 nm
100 nm
0
Fig. 2 (a and b) Aberration-corrected TEM images of Co
c and d) TEM images of Co10Zn90-ZIF-800-Ar.
1 2
Zn99-ZIF-800-H and
1
10
100
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
(
Pore size (nm)
Pore size (nm)
Fig. 1 (a) XRD patterns, (b) nitrogen sorption isotherms, (c) pore size
distribution and (d) micropore size distribution of Co Zn100-x-ZIF materials.
The micropore size distribution is calculated using the Horvath-Kawazoe
method.
not observed. According to the STEM Z-contrast, those white dots
are likely heavier than the support, and hence could be the highly
dispersed Co atoms. In contrast, considerable Co NPs could be
observed in Co10Zn90-ZIF-800-Ar (Fig. 2c and d).
x
o
When temperature was raised to 900 C, the crystallized metallic
Co/Zn bimetallic ZIF was prepared by mixing of Co(NO
Zn(NO in methanol, denoted as Co Zn100-x-ZIF. The powder X-ray
diffraction (XRD) pattern (Fig. S1) of the bimetallic Co Zn100-x-ZIF
matches well with ZIF-8 and ZIF-67, confirming the successful
3 2
) and
Co phase was emerged, as confirmed by the appearance of
diffraction peaks from metallic Co (Fig. 1a). The presence of Zn plays
a pivotal role in the formation of highly dispersed Co species, for
which the spatial interval between two Co atoms can be finely
3
)
2
x
x
3
3
synthesis of Co, Zn co-doped ZIF structure. Moreover, Both ZIF-8
and Co Zn100-x-ZIF showed similar type I isotherms with a high
nitrogen adsorption capacity at very low relative pressures (Fig. S2),
Table S1 shows that Co Zn99-ZIF processes high surface area (1450
m²/g), similar as ZIF-8 (1410 m²/g) and ZIF-67 (1560 m²/g).
3
5
controlled. For example, Fig. S4 shows that decreasing the Co
content would significantly weaken the Co diffractions of Co Zn100-x-
x
x
3
4
ZIF-800-Ar, indicating the improved dispersion of Co species in the
final N-doped carbon framework when x < 1.0. The low boiling point
1
o
and high vapor pressure of Zn (bp 907 C, 1 atm) can be evaporated
2
+
2+
The addition of Co can replace a certain proportion of Zn sites
2
+
away at high temperatures, and the removing of Zn sites generates
free N sites during pyrolysis, which could be beneficial for the
2
+
in ZIF-8. Meanwhile, the Zn sites serve as a “fence” to isolate the
3
4
1
adjacent Co atoms. The XRD patterns show that, utilizing Co Zn99-
3
6
formation of highly porous structure. As shown in Fig. 1b, under the
ZIF as a precursor, no peaks characteristic of Co crystals emerged
H
2
atmosphere, although the surface area of Co
1
Zn99-ZIF-800-H
2
o
even when the pyrolysis temperature was raised to 800 C under a
2
(1090 m /g) declines after pyrolysis in comparison to ZIF-8
hydrogen atmosphere (Fig. 1a). The detected Co contents in the
Co
measured by ICP-MS due to the loss of C and N from the support
Table S2). The measured Co content of Co Zn99-ZIF-800-H is 0.93 %.
The aberration-corrected TEM (Fig. 2a and b) and HRTEM (Fig. S3)
images of Co Zn99-ZIF-800-H show amorphous support, on which
x 2
Zn100-x-ZIF-800-H increase with the pyrolysis temperature as
1
.4
7
00
Co Zn99-ZIF-600-H
1
2
2
(b)
Co Zn99-ZIF-600-H
1 2
(
a)
Co
Zn99-ZIF-700-H
1.2
1.0
0.8
0.6
0.4
0.2
Co Zn99-ZIF-700-H2
600
500
1
1
Co Zn99-ZIF-800-H2
Co Zn99-ZIF-800-H2
1
1
(
1
2
Co
1
Zn99-ZIF-900-H
2
Co Zn99-ZIF-900-H2
1
4
3
2
1
00
00
00
00
0
1
2
white dots can somewhat be identified. Big clusters or nanoparticles
were
0
.0
0
.0
0.2
0.4
0.6
0.8
1.0
1
10
D(nm)
100
Relatvie pressure (p/p0)
Fig. 3 (a) Nitrogen absorption isotherms and (b) pore size distribution of
Co
1
Zn99-ZIF-T-H
2
treated under different temperature.
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 4 of 7
Journal Name
ARTICLE
View Article Online
Zn100-x-ZIF catalysts. a
2 x
Table 2 Selectvie oxidation EB with O over Co
DOI: 10.1039/C8GC03653E
OH
O
TOF/h-1
Entry
Catalysts
t/h
Conv./%
1
2
3
4
5
6
7
8
9
No catalyst
4
4
4
4
4
4
4
4
8
4
4
4
4
17
0
-
-
-
0
Co
Co
Co
Co
Co
Co
1
1
1
1
1
1
Zn99-ZIF
0
-
-
Zn99-ZIF-600-H
Zn99-ZIF-700-H
Zn99-ZIF-800-H
Zn99-ZIF-900-H
2
2
2
2
0
-
-
0
11.4
79.7
90.8
44.2
89.5
98.9
0
42.1
31.1
21.8
31.4
23.8
6.9
-
57.9
68.9
78.2
68.6
76.2
93.1
-
10.8
63.1
55.3
50.1
1.6
39.2
-
Zn99-ZIF-800-Ar
ZIF-67-800-Ar
Co
Co
Co
Co
Co
Co
1
Zn99-ZIF-800-H
1
Zn99-ZIF-800-H
1
Zn99-ZIF-800-H
1
Zn99-ZIF-800-H
1
Zn99-ZIF-800-H
1
Zn99-ZIF-800-H
2
2
2
2
2
2
1
1
1
1
1
0 b
1 c
2 d
3 e
4 f
17.1
33.3
9.6
57.0
30.5
34.3
14.3
6.5
69.5
65.7
85.7
93.5
13.5
26.4
7.6
424.7
a
o
(1 atm). b No TBHP was added. Reaction in N
c
atmosphere. d
Reaction condition: EB (0.25mmol), catalyst (5mg), H
2
O (3mL), TBHP (0.28 equiv.), 60 C, O
2
2
e
f
Reaction in air atmosphere. Hydroquinone was added. 10 mmol EB (1.06g) was added.
2
(
1410 m /g), its pore volume keeps almost constant (Table S1), accelerates the evaporation of Zn (Table S2 and S3) and favors the
indicating the reserved pore-structure after hydrogen-mediated mesopore generation (Table S1). These results suggest that
pyrolysis. In control experiment (Fig. 1b), Ar atmosphere gave rise to controlling catalyst morphology with large surface areas is critical to
2
Co
1
Zn99-ZIF-800-Ar with much lower BET surface area (610 m /g) and achieving enhanced catalytic performance.
3
pore volume (0.40 cm /g). Meanwhile, increasing the Co content in
N1s XPS spectra (Fig. S5) show that, after pyrolysis, most N species
ZIF would aggravate the collapse of the pore structure. For example, are removed as indicated by the dramatically decreased peak
Co10Zn90-ZIF-800-Ar and ZIF-67-800-Ar afford low surface area (350 intensity (Table S3). The residual imidazole-N could be deconvoluted
2
3
and 260 m /g) as well as small pore volume (0.51 and 0.44 cm /g). into four types of N species with binding energy around 398.5, 399.8,
The BJH pore-size distribution of Co Zn99-ZIF-800-H shows two 400.8, and 402.3 eV, which can be attributed to pyridinic-N (55.1
peaks at 1.5 and 100 nm, corresponding to micropore and at.%), pyrrolic-N (6.1 at.%), quaternary-N (30.0 at.%) and oxidized-N
1
2
2
0
macropores in the catalyst. On the contrary, both the micropore and (8.9 at.%), respectively. As shown in Fig. 4a, Zn 2p3/2 peaks in the
macropore of Co Zn99- and Co10Zn90-ZIF-800-Ar closed obviously, XPS spectra of Co Zn99-ZIF and Co Zn95-ZIF are located at ~1021.0 eV,
confirmed by the corresponding micropore size distribution curves which could be assigned to Zn that is coordinated with imidazole.
Figs. 1c and d). After pyrolysis, this XPS peak in Co Zn99-ZIF-800-H weakens
1
1
5
2
+
(
1
2
significantly and shifts to 1021.6 eV, which could be ascribed to
δ+
oxidized Zn (Zn ) that is strongly interacted with N-doped carbon. Co
(
a)
Zn2+
Zn
(b)
2p XPS spectrum of Co Zn -ZIF (Fig. 4b) shows that nearly no Co
1
99
1
021.0
1020
2+
signal could be detected, indicating Co ions are mainly embedded


Co Zn95-ZIF
5
2+
1
021.6
in inside the ZIF due to the relatively fast nucleation between Co
and 2-methylimidazole.
2
9,38
1
016
1024
1028
1
After pyrolysis of Co Zn99-ZIF at 800 °C,
Co Zn99-ZIF
1
Co Zn95-ZIF
0.2
5
0
Co Zn99-ZIF-800-H affords a relatively strong Co 2p3/2 signal at ~780
1
2
Co
Co Zn99-ZIF-800-H
1 2
Co Zn99-ZIF
0.2
1
eV. After deconvolution, nearly no metallic Co could be observed at
~778 eV.
Co Zn99-ZIF-800-H2
1
1
015 1020 1025 1030 1035 1040 1045 1050 1055
Binding energy (eV)
772 776 780 784 788 792 796 800 804 808
Bindind Energy (eV)
Fig. 4 (a) Zn 2p and (b) Co 2p XPS spectra of Co
and Co Zn95-ZIF.
1 2 1
Zn99-ZIF-800-H , Co Zn99-ZIF
Catalytic property of Co-based catalysts
5
In a preliminary study, screening of catalysts for EB oxidation using
TBHP as the oxidation agent was studied. As presented in Table S4,
the ZIF-8 exhibited negligible activity for oxidation compared with
the Co-doped catalysts (entry 1), indicating that the activity of Co-
based catalysts could largely be ascribed to Co-N-C sites rather than
The metal contents measured by ICP-MS (Table S2) show that the
total Zn of Co Zn99-ZIF-800-H (6.24 %) is lower than that of Ar-
derived Co Zn99-ZIF-800-Ar (9.53 %), indicating that H is favor the
1
2
1
2
3
7
evaporation of Zn. As showing in Table S1, decreasing the pyrolysis
temperature affords samples with low BET surface area (500-800
2
9
N-C sites (entry 10). Especially, for unpyrolysed sample, the
oxidation activity was much lower than that of Ar-treated catalysts
2
m /g) and high Zn content (10-25 %). When the temperature was
(
entries 1-3). Then, catalysts with different Co-doping demonstrated
a significant difference in activity (entries 4-10). It is noted that the
Co content increased from the Co0.2Zn99.8-ZIF-800-Ar to the Co50Zn50
o
raised to 900 C (Fig. 3), Co
1
Zn99-ZIF-900-H
2
still afforded high surface
2
3
area (1100 m /g) and pore volume (0.88 cm /g) as well as further
-
expanding of pore size. These results indicate that H
2
atmosphere
ZIF-800-Ar sample, the oxidation activity increased from 1.5 to 75.6
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Page 5 of 7
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
Journal Name
%
. However, further increasing Co content (ZIF-67-800-Ar) decreased oxidation rate was dropped significantly, which implied that the EB
View Article Online
DOI: 10.1039/C8GC 400 3653E
the EB conversion obviously to 62.5 %. In order to further oxidation proceeded through a radical chain pathway. The
demonstrate the activity difference, the turnover frequency (TOF) oxidation of EB at a gram scale (1.06 g, entry 14) also preceded
based on total Co atoms were calculated. As the Co content efficiently in comparison with the small-scale transformation and
increased, the catalytic activity increased first and then decreased, acetophenone was produced with 93.5% selectivity and 53.3% yield.
the highest TOF (32.2 h ) was achieved on Co
catalyst (entry 5).
-1
1
Zn99-ZIF-800-Ar In fact, in comparison to reports in the literature (Table S6), our
Co Zn99-ZIF-800-H catalyst has the superior catalytic performance
1
2
In order to further explore the effect of pyrolysis atmosphere and for aerobic oxidation of EB at relatively low temperature.
temperature, H -treated Co Zn99-ZIF catalysts were synthesized and
tested for catalyzing the oxidation of EB. Interestingly, Co
Zn99-ZIF- Table 3 Selectvie oxidation C-H bonds with O
.a
00-H afforded much higher EB conversion (57.4 %) and TOF value
2
1
2 1
over Co Zn99-ZIF-800-
1
8
2
H
2
-1
-1
(90.9 h ) than that of the Ar-treated counterpart (32.2 h , entry 11).
Entry Reactants
t/h
Conv./%
Selectivity/%
O
Co Zn99-ZIF-400-H and Co Zn99-ZIF-600-H had nearly no activity for
1
2
1
2
1
8
98.9
93.1
.9
OH
EB oxidation (entries 12 and 13). Further increasing the temperature
6
o
to 700 C brought a boost for oxidation activity (entry 14). When the
2
3
6
4
95.9
98.4
O
83.0
17.0
o
temperature was raised to 900 C (entry 15), the TOF decreased
OH
-1
o
slightly to 72.2 h . When increasing reaction temperature to 60 C
Table S5), Co Zn99-ZIF-800-H could afford 97.4 % conversion and
4.9 % selectivity at 4h.
The excellent catalytic performance of Co
(
9
1
2
61.4
O
1
7.9
1
Zn99-ZIF-800-H
2
toward
OH
EB oxidation with TBHP inspired us to study the aerobic oxidation of
EB with readily available oxygen molecular (Table 2). A blank test
shows that no EB was transformed when no catalyst was added
10.7
62.9
HO
O
4
5
4
8
100
HO
2
3.9
(
entry 1). Similarly, the Co
samples exhibited negligible activity for aerobic oxidation compared
with other Co-doped catalysts. Among those catalysts, Co Zn99-ZIF-
1
Zn99-ZIF and low-temperature-treated Co
O
7.2
1
81.5
71.8
O
8
00-H
2
and Co
1
Zn99-ZIF-900-H
2
gave conversions of 79.7 and 90.8 %
-1
-1
O
O
27.1
68.8
as well as TOF of 63.1 h and 55.3 h , respectively (entries 5 and 6).
1
Comparatively, Co Zn99-ZIF-800-Ar afforded relatively low
6
7
6
4
94.8
92.6
-1
conversion (44.2 %) and TOF value (50.1 h ). When the reaction time
COOH
O
3
1.2
o
was prolonged at 60 C, Co
1
Zn99-ZIF-800-H
2
afforded 98.9% EB
conversion and 93.1 % ketone selectivity at 8 h (entry 9).
In control experiments, no EB was transformed when no TBHP was
used (entry 10), suggesting that TBHP is functioning as the initiator
58.2
OH
2
3.0
3
9
O
for EB oxidation. When the EB oxidation was carried out in N
atmosphere (entry 11), the conversion was found to be only 17.1%.
When using air (entry 12) as the alternative of pure O , we
2
5.2
O
8
6
83.2
47.0
2
OH
2
1.2
COOH
1
00
OH
9
15
15
27.8
28.3
70.1
29.9
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
conv.
selec.
O
O
OH
1
0
OH
O
48.4
3
6
9.9
.7
O
a
2
Reaction condition: substrate (0.25mmol), catalyst (0.008mol% Co), H O
o
(
3mL), TBHP (0.28 equiv.), 60 C, O
2
(1 atm).
1
2
3
4
Run number
The stability and reusability of the Co Zn -ZIF-800-H catalyst
1
99
2
Fig. 5 Recycle of Co
1
Zn99-ZIF-800-H
2
for selective oxidation of EB with O
2
at were also investigated. Under the studied conditions, the Co
1
Zn99-
low conversion.
ZIF-800-H catalyst exhibits a EB conversion of 79.7 % after 4 h and
2
Reaction condition: EB (0.25mmol), catalyst (5mg), H
2
O (3mL), TBHP (0.28 can be reused at least four times with EB conversion still above 66 %
after the fourth run (Fig. S6). In order to further test the stability of
o
2
equiv.), O (1 atm), 60 C, 15 min.
1 2
the catalyst, the recycling Co Zn99-ZIF-800-H at low conversion
obtained 33.3 % EB conversion. When hydroquinone (entry 13), a (~18%) was carried out. The catalyst shows no significant
free radical scavenger, was added into the reaction system, the deactivation for 4 runs (Fig. 5). XRD pattern (Fig. S7) of the spent
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 6 of 7
Journal Name
ARTICLE
Co
1
Zn99-ZIF-800-H
2
after the fourth run shows that no cobalt a tube furnace. The sample was heated to desired temperatures with
View Article Online
DOI: 10.1039/C8GC03653E
2
diffraction peaks can be observed. The pore structure of the spent a heating rate of 5 °C/min and kept for 2 h under 10% H /Ar and then
1 2
Co Zn99-ZIF-800-H catalyst is still well preserved as revealed by the naturally cooled to room temperature. The catalyst was denoted as
nitrogen sorption in Fig. S8, in which the BET surface area is about Co
x
Zn100-x-ZIF-T-H
2
, where T is the pyrolysis temperature. For
2
9
80 m /g. No Co metal is detected in the reaction solvent after the comparison, pyrolyzation under an Ar atmosphere afforded Co
x
Zn100-
completion of the reaction, showing that Co
active and stable in aerobic oxidation of EB under this mild condition.
To further demonstrate the versatility of Co Zn99-ZIF-800-H , we
investigated aerobic oxidation of C-H bonds of a broad scope of The catalytic reaction was conducted in a flask equipped with a O
1
Zn99-ZIF-800-H
2
is highly
x
-ZIF-T-Ar.
Catalyst evaluation
1
2
2
substrates under the same condition. As shown in Table 3, good to balloon. Before the reaction test, 5 mg catalyst and 0.25 mmol
excellent yields of the corresponding ketones were obtained. It can substrate were added into the flask. Then water (3 mL) and TBHP
be found that 95.9% cyclohexene conversion was obtained at 60 °C (0.28 equiv.) were added. The reaction mixture was stirred under 1
o
in 6 h with 83 % cyclohexenone selectivity (entry 2). In the case of atm O
2
balloon at 60 C. After the reaction, the organic phase was
macromolecule-cyclooctene (entry 5), the reaction gave 81.5 % of extracted with 15 mL ethyl acetate (5 mL each time), the solid
conversion and 71.8 % of cyclooctenone selectivity. Apart from catalyst was recovered by centrifugation. The identification of
simple cycloalkenes, cyclodiolefins and terminal olefins were also products was conducted using an Agilent 6890N/5975 GC-MS
selectively oxidized with relatively high ketone/aldehyde selectivities system. The products were quantitatively analyzed by using gas
(entries 6-8). For example, cyclooctadiene (entry 7) afforded the chromatography (Hewlett Packard 5890 II, FID detector) equipped
corresponding ketone and enol with 92.6 % conversion without over- with a HP-5 capillary column. Dodecane was used as the internal
oxidized products. Other substituted alcohols (entries 9 and 10), such standard.
as benzyl alcohol and phenylpropanol, afforded the corresponding
aldehydes in relatively low yields.
Acknowledgements
This work was supported by National Natural Science Foundation of
China (21603066). This work was also partially supported by Iowa
Conclusion
In summary, we demonstrate an effective approach to construct State University. R.Nie thanks the China Scholarship Council and
highly dispersed Co in highly porous N-doped carbon for the selective Hubei Chenguang Talented Youth Development Foundation for
oxidation C-H bond under mild conditions. It can achieve excellent financial support.
o
product yield in aqueous solution at low temperatures (60 C) and
2
ambient-O -pressure (1 atm), affording 41.3 times higher activity
than those of Ar-treated ZIF-67 catalyst. The catalytic system can also
be adopted for aerobic oxidation of macromolecule hydrocarbons
Notes and references
1
2
3
.
.
.
T. Mallat and A. Baiker, Chem. Rev., 2004, 104, 3037-3058.
J. A. Labinger and J. E. Bercaw, Nature, 2002, 417, 507-514.
C. M. A. Parlett, D. W. Bruce, N. S. Hondow, A. F. Lee and K.
Wilson, ACS Catal., 2011, 1, 636-640.
(e.g. cyclooctene and cyclodiolefin) with high yield of ketones. This
catalyst is stable and easy to catalyze substrate with large scale. The
structure results indicate that, in contrast of Ar, hydrogen-pyrolysis
environment for preparing the Co Zn99-ZIF-800-H is found to favour
1 2
the Zn volatilization and beneficial for restricting the pore-shrink of
the ZIF precursor, thus yielding N-doped carbon matrix with high
surface area and pore volume. The highly porous carbon frame and
highly dispersed Co sites are the two key factors for this catalyst to
show the excellent performance in the aerobic oxidation of C-H
bond.
4
5
6
.
.
.
A. Buonerba, A. Noschese and A. Grassi, Chem. Eur. J., 2014, 20,
5
478-5486.
E. J. García-Suárez, M. Tristany, A. B. García, V. Collière and K.
Philippot, Micro. Meso. Mater., 2012, 153, 155-162.
T. Balcha, J. R. Strobl, C. Fowler, P. Dash and R. W. J. Scott, ACS
Catal., 2011, 425-436.
7
8
9
.
.
.
X. Yang, X. Wang and J. Qiu, Appl. Catal. A, 2010, 382, 131-137.
N. Zheng and G. D. Stucky, Chem. Commun., 2007, 3862-3864.
J. Long, X. Xie, J. Xu, Q. Gu, L. Chen and X. Wang, ACS Catal.,
Experimental
2
012, 2, 622-631.
Catalyst preparation
1
1
1
1
1
0. S.-I. Fujita, K. Yamada, A. Katagiri, H. Watanabe, H. Yoshida and
M. Arai, Appl. Catal. A, 2014, 488, 171-175.
1. Y. Wang, J. Zhang, X. Wang, M. Antonietti and H. Li, Angew.
Chem. Int. Ed., 2010, 49, 3356-3359.
2. X.-H. Li, J.-S. Chen, X. Wang, J. Sun and M. Antonietti, J. Am.
Chem. Soc., 2011, 133, 8074-8077.
3. A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J.-O. Müller,
R. Schlögl and J. M. Carlsson, J. Mater. Chem., 2008, 18, 4893.
4. W. Zhong, H. Liu, C. Bai, S. Liao and Y. Li, ACS Catal., 2015, 5,
Co
Typically, 6.8 mmol mixture of Zn(NO
x
Zn100-x-ZIF was prepared by a modified method from Li’s work.41
·6H O and Co(NO ·6H
)
3 2
2
3
)
2
2
O
was dissolved in 80 mL methanol with stirring. Then 80 mL methanol
containing 36.5 mmol 2-methylimidazole was added with vigorous
stirring for 24 h at room temperature. The obtained product was
separated by centrifugation and washed with methanol and finally
dried at 60 °C under vacuum for overnight, which was marked as
Co
or no Zn(NO
Co Zn100-x-ZIF was then transferred into a ceramic boat and placed in
x
Zn100-x-ZIF. For the synthesis of ZIF-8 or ZIF-67, no Co(NO
3 2 2
) ·6H O
1
850-1856.
3
)
2
·6H O was added, respectively. The powder of
2
x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Page 7 of 7
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
Journal Name
1
1
1
1
5. C. Bai, A. Li, X. Yao, H. Liu and Y. Li, Green Chem., 2016, 18, 1061-
069.
6. J. Zheng, X. Chen, X. Zhong, S. Li, T. Liu, G. Zhuang, X. Li, S. Deng,
D. Mei and J.-G. Wang, Adv. Funct. Mater., 2017, 27, 1704169.
7. Y.-X. Zhou, Y.-Z. Chen, L. Cao, J. Lu and H.-L. Jiang, Chem.
Commun., 2015, 51, 8292-8295.
View Article Online
DOI: 10.1039/C8GC03653E
1
8. J. Deng, H.-J. Song, M.-S. Cui, Y.-P. Du and Y. Fu, ChemSusChem,
2
014, 7, 3334-3340.
1
2
9. R. Fang, R. Luque and Y. Li, Green Chem., 2016, 18, 3152-3157.
0. R. Nie, J. Shi, W. Du, W. Ning, Z. Hou and F.-S. Xiao, J. Mater.
Chem. A, 2013, 1, 9037.
2
2
2
2
2
2
2
2
2
1. H. Su, K.-X. Zhang, B. Zhang, H.-H. Wang, Q.-Y. Yu, X.-H. Li, M.
Antonietti and J.-S. Chen, J. Am. Chem. Soc., 2017, 139, 811-818.
2. R. V. Jagadeesh, H. Junge, M.-M. Pohl, J. Radnik, A. Brückner and
M. Beller, J. Am. Chem. Soc., 2013, 135, 10776-10782.
3. W. Liu, L. Zhang, X. Liu, X. Liu, X. Yang, S. Miao, W. Wang, A.
Wang and T. Zhang, J. Am. Chem. Soc., 2017, 139, 10790-10798.
4. C. Yang, L. Fu, R. Zhu and Z. Liu, Phys. Chem. Chem. Phys., 2016,
1
8, 4635-4642.
5. Y. Chen, S. Zhao and Z. Liu, Phys. Chem. Chem. Phys., 2015, 17,
4012-14020.
6. Y. Cao, S. Mao, M. Li, Y. Chen and Y. Wang, ACS Catalysis, 2017,
, 8090-8112.
1
7
7. D. Su, Z. Wei, S. Mao, J. Wang, Y. Li, H. Li, Z. Chen and Y. Wang,
Catal. Sci. Technol., 2016, 6, 4503-4510.
8. Z. Wei, J. Wang, S. Mao, D. Su, H. Jin, Y. Wang, F. Xu, H. Li and Y.
Wang, ACS Catal., 2015, 5, 4783-4789.
9. J. Xie, J. D. Kammert, N. Kaylor, J. W. Zheng, E. Choi, H. N. Pham,
X. Sang, E. Stavitski, K. Attenkofer, R. R. Unocic, A. K. Datye and
R. J. Davis, ACS Catal., 2018, 8, 3875-3884.
3
3
0. S. Kitagawa, Chem. Soc. Rev., 2014, 43, 5415-5418.
1. K. Shen, X. Chen, J. Chen and Y. Li, ACS Catal., 2016, 6, 5887-
5
903.
3
3
3
2. R. V. Jagadeesh, K. Murugesan, A. S. Alshammari, H. Neumann,
M.-M. Pohl, J. Radnik and M. Beller, Science, 2017, 358, 326-332.
3. K. Zhou, B. Mousavi, Z. Luo, S. Phatanasri, S. Chaemchuen and
F. Verpoort, J. Mater. Chem. A, 2017, 5, 952-957.
4. X. Wang, Z. Chen, X. Zhao, T. Yao, W. Chen, R. You, C. Zhao, G.
Wu, J. Wang and W. Huang, Angew. Chem., 2018, 130, 1962-
1
966.
3
3
3
3
3
4
4
5. C. Yan, H. Li, Y. Ye, H. Wu, F. Cai, R. Si, J. Xiao, S. Miao, S. Xie and
F. Yang, Energ. Environ. Sci., 2018, 11, 1204-1210.
6. X. Dai, Z. Chen, T. Yao, L. Zheng, Y. Lin, W. Liu, H. Ju, J. Zhu, X.
Hong and S. Wei, Chem. Commun., 2017, 53, 11568-11571.
7. Z. Qi, Y. Pei, T. W. Goh, Z. Wang, X. Li, M. Lowe, R. V. Maligal-
Ganesh and W. Huang, Nano Res., 2018, 11, 3469-3479.
8. D. Saliba, M. Ammar, M. Rammal, M. Al-Ghoul and M. Hmadeh,
J. Am. Chem. Soc., 2018, 140, 1812-1823.
9. I. Y. Skobelev, A. B. Sorokin, K. A. Kovalenko, V. P. Fedin and O.
A. Kholdeeva, J. Catal., 2013, 298, 61-69.
0. P. Zhang, Y. Gong, H. Li, Z. Chen and Y. Wang, Nat. Commun.,
2
013, 4, 1593.
1. P. Yin, T. Yao, Y. Wu, L. Zheng, Y. Lin, W. Liu, H. Ju, J. Zhu, X. Hong,
Z. Deng, G. Zhou, S. Wei and Y. Li, Angew. Chem. Int. Ed., 2016,
5
5, 10800-10805.
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins