Room-Temperature Methane Conversion by Graphene-Confined Single Iron Atoms

Article abstract of DOI:10.1016/j.chempr.2018.05.006

Direct conversion of methane to high-value-added chemicals is a major challenge in catalysis, which usually requires high-energy input to overcome the reaction barrier. We report that graphene-confined single Fe atoms can be used as an efficient non-precious catalyst to directly convert methane to C1 oxygenated products at room temperature. A series of graphene-confined 3d transition metals (Mn, Fe, Co, Ni, and Cu) were screened, yet only single Fe atoms could catalyze the methane conversion. Combining in operando time-of-flight mass spectrometry, ¹³C nuclear magnetic resonance, and density functional theory calculations, we found that methane conversion proceeds on the O–FeN₄–O active site along a radical pathway to produce CH₃OH and CH₃OOH first, and then the generated CH₃OH can be further catalyzed to form HOCH₂OOH and HCOOH at room temperature. Methane from natural gas and shale gas is one of the most promising feedstocks because of its high reserves and low price. The selective activation and orientable conversion of methane are considered the “holy grail” in catalysis. Because of the highly stable C–H bond, methane conversion usually requires high temperatures to overcome the high reaction barrier. However, the high-temperature reaction is not favorable for industrial application. Despite many efforts to decrease the reaction temperature, it remains a great challenge to promote methane conversion under mild conditions, especially at room temperature. Herein, we report that graphene-confined single Fe atoms can be used as an efficient non-precious catalyst to directly convert methane to high-value-added C1 oxygenated products at room temperature (25°C), which provides a new route to understanding and designing highly efficient non-precious catalysts for methane conversion at room temperature. Graphene-confined single Fe atoms, screened out from a series of 3d transition metals (Mn, Fe, Co, Ni, and Cu), were used as an efficient non-precious catalyst to directly convert methane to C1 oxygenated products at room temperature. The unique O–FeN₄–O structure formed in graphene can readily activate the C–H bond of methane along a radical pathway with a low reaction energy barrier.

Full text of DOI:10.1016/j.chempr.2018.05.006

Article
Room-Temperature Methane Conversion by
Graphene-Confined Single Iron Atoms
Xiaoju Cui, Haobo Li, Yan
Wang, ..., Jianping Xiao, Dehui
Deng, Xinhe Bao
dhdeng@dicp.ac.cn (D.D.)
xhbao@dicp.ac.cn (X.B.)
HIGHLIGHTS
Direct conversion of methane to
C1 oxygenated products at room
temperature
Graphene-confined single Fe
atoms used as an efficient non-
precious catalyst
A radical pathway over
4
O–FeN –O proved by experiment
and theoretical calculations
Graphene-confined single Fe atoms, screened out from a series of 3d transition
metals (Mn, Fe, Co, Ni, and Cu), were used as an efficient non-precious catalyst to
directly convert methane to C1 oxygenated products at room temperature. The
unique O–FeN
4
–O structure formed in graphene can readily activate the C–H
bond of methane along a radical pathway with a low reaction energy barrier.
Cui et al., Chem 4, 1–9
August 9, 2018 ª 2018 Elsevier Inc.
https://doi.org/10.1016/j.chempr.2018.05.006

Please cite this article in press as: Cui et al., Room-Temperature Methane Conversion by Graphene-Confined Single Iron Atoms, Chem (2018),
https://doi.org/10.1016/j.chempr.2018.05.006
Article
Room-Temperature Methane Conversion
by Graphene-Confined Single Iron Atoms
Xiaoju Cui,1,3,4 Haobo Li,1,4 Yan Wang,2,4 Yuanli Hu,1,4 Lei Hua, Haiyang Li, Xiuwen Han,
2
2
1
Qingfei Liu,1,4 Fan Yang, Limin He, Xiaoqi Chen, Qingyun Li, Jianping Xiao, Dehui Deng,1,3,5,*
1
1
1
2
1
1,
and Xinhe Bao *
The Bigger Picture
SUMMARY
Methane from natural gas and
shale gas is one of the most
promising feedstocks because of
its high reserves and low price.
The selective activation and
orientable conversion of methane
are considered the "holy grail" in
catalysis. Because of the highly
stable C–H bond, methane
Direct conversion of methane to high-value-added chemicals is a major
challenge in catalysis, which usually requires high-energy input to overcome
the reaction barrier. We report that graphene-confined single Fe atoms can
be used as an efficient non-precious catalyst to directly convert methane to
C1 oxygenated products at room temperature. A series of graphene-confined
3
d transition metals (Mn, Fe, Co, Ni, and Cu) were screened, yet only single
Fe atoms could catalyze the methane conversion. Combining in operando
1
3
time-of-flight mass spectrometry, C nuclear magnetic resonance, and density
functional theory calculations, we found that methane conversion proceeds on
conversion usually requires high
temperatures to overcome the
high reaction barrier. However,
the high-temperature reaction is
not favorable for industrial
the O–FeN
CH OOH first, and then the generated CH
form HOCH OOH and HCOOH at room temperature.
4
–O active site along a radical pathway to produce CH
3
OH and
3
3
OH can be further catalyzed to
2
INTRODUCTION
application. Despite many efforts
to decrease the reaction
Methane from natural gas, shale gas, coalbed methane, and methane hydrate is a
most promising feedstock because of its high reserves and relatively inexpensive
temperature, it remains a great
challenge to promote methane
conversion under mild conditions,
especially at room temperature.
Herein, we report that graphene-
confined single Fe atoms can be
used as an efficient non-precious
catalyst to directly convert
1
price. Direct conversion of methane without involving the intermediate syngas
2
–4
production step is potentially more economical and environmentally friendly.
ꢀ
1
But, as the most stable and inert hydrocarbon (DHC–H = 104 kcal mol ), methane
conversion is usually operated at high temperatures, such as the oxidative
5
–7
8
coupling of methane
and direct dehydrogenation processes, typically at
ꢁ ꢁ
9–11
6
00 C–1,100 C.
Hence, the development of catalysts for selective conversion
of methane to high-value-added chemicals under mild conditions has become a
challenging task. Nature has demonstrated that methane monooxygenase and cyto-
methane to high-value-added C1
oxygenated products at room
1
2
chrome P450 can directly catalyze methane oxidation under mild conditions, but
the delivery of oxygen involves complex co-enzymes, and the rates are not commer-
cially viable. Recent research indicated that complexes of Hg, Pt, Pd, Au, Ru, Rh,
and V can promote selective oxidation of methane in a strong acid medium,
such as oleum, trifluoroacetic acid, hydrochloric acid, or hydrobromic acid at
ꢁ
temperature (25 C), which
provides a new route to
understanding and designing
highly efficient non-precious
catalysts for methane conversion
at room temperature.
ꢁ
ꢁ
13–17
18–21
8
0 C–500 C.
Also, molecule-sieve-based catalysts, such as ZSM-5
and
2
2–24
MOR,
were successfully developed for the conversion of methane to methanol
ꢁ
ꢁ
25,26
27
at a temperature of 50 C–225 C. In addition, with the aid of electrical
and light
energy, much progress has been made in decreasing the temperature of methane
conversion in the past few years. However, the direct room-temperature conversion
of methane without other energy input and replacement of precious-metal catalysts
remains a big challenge. Herein, we report that graphene-confined single Fe sites
(
FeN
4
/graphene nanosheets [GNs]) can directly convert methane into C1 oxygen-
ꢁ
ated products at room temperature (25 C). We found that the methane is converted
Chem 4, 1–9, August 9, 2018 ª 2018 Elsevier Inc.
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4
by the O–FeN –O structure to first generate methyl radicals, which subsequently
turn into value-added C1 oxygenated products.
RESULTS AND DISCUSSION
The FeN
well-tested procedure. In brief, the highly dispersed single FeN
on graphene was synthesized by high-energy ball milling of iron phthalocyanine
FePc) and GNs. The atomic force microscopy (AFM) image of FeN /GN (Figure S1)
4
moieties embedded in the lattice structure of GNs were prepared by a
2
8
4
center anchored
(
4
shows the typical structure of GNs, and a sub-angstrom resolution high-angle
annular dark-field scanning transmission electron microscopy (HAADF-STEM) image
displays single-atom iron sites distributed homogeneously in GNs (Figure 1A).
2 2
The catalytic oxidation of methane was carried out in an autoclave with H O as the
1
13
oxidant. The liquid and gas products were measured by H and C NMR, time-of-
flight mass spectrometry (TOF-MS), and gas chromatography, respectively.
1
3
13
Combining C NMR (Figure 1B), C DEPT-135 (distortionless enhancement by
1
1
13
polarization transfer) (Figure 1B), H NMR (Figure S2), and 2D H- C heteronuclear
multiple-quantum correlation experiments (Figure S3), we found that methane could
be efficiently oxidized to C1 oxygenated products over a FeN
4
/GN catalyst with a
ꢀ1
turnover frequency (TOF) of 0.47 hr
where TOF = mol of product
ꢀ
1
ꢀ1
(
3 3 2
mol of Fe) hr ; CH OH, CH OOH, HOCH OOH, and HCOOH were the major
products in the liquid phase. TOF-MS in Figure 1C with a vacuum ultraviolet lamp
as the ionization source was used to further confirm the structures of C1 oxygenated
products. The featured peaks match well with CH
3 3 2
OH, CH OOH, HOCH OOH, and
HCOOH from the NMR data. Considering the catalyst itself contains carbon sources,
1
3
we also carried out control experiments by using N
2
, CH
4 4
, and CH as the reactant
1
3
13
gas, where only CH
sults indicate that C1 oxygenated products came from the oxidation of CH
than from the catalyst itself. In addition, the reusability test reveals that the FeN
4
can produce C oxygenated products (Figure 1D). The re-
1
3
4
rather
/GN
4
catalyst almost preserves its initial catalytic activity after six cycles (Figure S4), and
the X-ray adsorption fine-structure spectra indicate that, after the reusability test,
the catalyst almost retains the same chemical state and coordination information
as the original catalyst (Figure S5), demonstrating its good structural stability and
reusability.
Besides the FeN
control catalysts, i.e., graphite, graphene, and different 3d metal-N
phene (MnN /GN, CoN /GN, NiN /GN, and CuN /GN); their structures were
almost the same as the FeN /GN with metal-N centers embedded in the graphene
nanosheets (Figures S6–S9). But none could catalyze methane conversion except the
FeN /GN catalyst (Figure 1E and Table S1). We further evaluated the effect of Fe
content in FeN /GN on the performance of methane oxidation. Figure S10 showed
the yield of C1 oxygenated products increased as the Fe amount increased from 1.5
to 4.0 wt %, where 2.7 wt % Fe in FeN /GN was the optimum according to the calcu-
4
/GN catalyst, we also evaluated the catalytic performance of other
1State Key Laboratory of Catalysis, Collaborative
Innovation Center of Chemistry for Energy
Materials, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023,
China
4
confined in gra-
4
4
4
4
4
4
2Key Laboratory of Separation Science for
Analytical Chemistry, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, Dalian
4
4
116023, China
3State Key Laboratory of Physical Chemistry of
Solid Surfaces, Collaborative Innovation Center
of Chemistry for Energy Materials, College of
Chemistry and Chemical Engineering, Xiamen
University, Xiamen 361005, China
4
lated turnover number (TON) data. That is probably because the increase in Fe con-
tent results in more active sites at low Fe content, whereas the dispersion of active
sites decreases at high Fe content as a result of agglomeration. In addition, the ac-
tivity of FePc on methane oxidation was evaluated, which showed that the TON for
4University of Chinese Academy of Sciences,
Beijing 100039, China
4
FePc was far less than that for FeN /GN catalysts (Figures S10 and S11). That was
5Lead Contact
because FePc had poor ability to activate methane, which is discussed later, and
the corresponding product distribution is also discussed in detail in Figures S11
and S23–S30. Furthermore, the evolution of C1 oxygenated products with the
*
Correspondence: dhdeng@dicp.ac.cn (D.D.),
xhbao@dicp.ac.cn (X.B.)
https://doi.org/10.1016/j.chempr.2018.05.006
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Figure 1. Structural Features and Catalytic Performance of FeN
A) An HAADF-STEM image of FeN /GN-2.7. The red circles show some single iron atoms in the
matrix of graphene nanosheets. The inset shows the model of FeN /GN.
B and C) C NMR and C DEPT-135 spectra (B) and TOF-MS data (C) obtained from typical
reaction products of methane oxidation. The symbol W represents one water molecule.
4
/GN-2.7
(
4
4
1
3
13
(
1
3
13
(
(
D) C NMR spectra obtained from N
2
, CH
4
, and CH
4
as reaction gas.
E) Catalytic performance of graphite, graphene, FeN
4
4 4
/GN, and other metal-N /GN for CH
oxidation.
Reaction conditions in (B)–(E): 50 mg catalyst, 5 mL H
2
O, 5 mL H
2
O
2
(30%), and 2 MPa reaction gas in
ꢁ
a stainless-steel autoclave containing a Teflon liner vessel (working volume, 50 mL) at 25 C for 10 hr.
reaction time is shown in Figure S12. The initial yield of C1 oxygenated products
increased with the reaction time, reaching the highest at 10 hr, and then decayed
with the reaction time. Meanwhile, CO
time, indicating that the liquid C1 oxygenated products can be further oxidized to
CO with longer reaction time, and the reaction time can be controlled to get
maximum C1 oxygenated products. The selectivity of C1 oxygenated products is
2
in gas phase increased with the reaction
2
around 94%, and the CO
with the previous reports,
2
1
selectivity is only 6% for reaction for 10 hr. Compared
8,19,29
the FeN
4
/GN catalyst can promote methane con-
selectivity.
version under milder conditions with lower CO
2
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Figure 2. In Operando Characterizations for the Evolution of Liquid Products over FeN /GN-2.7
(
(
A) A scheme of the designed in operando TOF-MS.
B) The increase in the rate of the products at 0–600 min, which corresponds to the relative intensity
increment.
C–E) The in operando TOF-MS data obtained from 1.0 (C), 1.5 (D), and 1.8 (E) MPa CH
methane oxidation.
1
3
(
4
reaction of
1
3
13
13
(
F) C NMR and C DEPT-135 spectra obtained from reaction products of CH
FeN /GN-2.7 catalyst for 10 hr
G) A possible reaction path for methane oxidation over FeN
3
OH oxidation by
4
(
4
/GN catalyst.
In order to study the reaction mechanism, we designed and developed a set of in
operando TOF-MS, which can track the evolution of liquid products in a high-pres-
sure reaction, as shown in Figures 2A and S13. In brief, the products can be efficiently
extracted by a capillary and analyzed in real time throughout the reaction. Figures
2
C–2E show that, during the reaction, CH
3 3
OH and CH OOH increased gradually
over time. HOCH OOH and HCOOH almost did not change in the first 100 min,
2
4
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which suggests that CH
increasing rate of CH OH in the first 300 min was greater than in the last 300 min
Figures 2B and S14). In the last 300 min, HOCH OOH and HCOOH increased
significantly, which shows that CH OH from CH oxidation is further oxidized to
HOCH OOH and HCOOH. In order to confirm the hypothesis, we used CH
directly as the reactant instead of CH
present three peaks corresponding to CH
Figure 2F), indicating that CH OH can be converted into HOCH
over the catalyst, which agrees well with the results of in operando TOF-MS.
Therefore, we can deduce that CH was first oxidized to CH OH and CH OOH,
and then the CH OH generated was further oxidized to HOCH OOH and HCOOH,
as depicted in Figure 2G.
4 3 3
is first oxidized to CH OH and CH OOH. In addition, the
3
(
2
3
4
1
3
2
3
OH
. Accordingly, C NMR and C DEPT-135
OH, HOCH OOH, and HCOOH
OOH and HCOOH
1
3
13
4
3
2
(
3
2
4
3
3
3
2
To understand the mechanism for the selective oxidation of methane on the
FeN /GN structure, density functional theory (DFT) calculations were used to build
a FeN
Figure S15). Under the reaction conditions, H
on the active Fe sites and decompose into H O and an adsorbed O atom (Figure 3A).
Each active Fe site can absorb two O atoms at each side with a total energy decrease
of 2.63 eV. Figure 3B shows that the electronic states of O–FeN –O around the Fermi
level increase significantly in comparison with those of FeN and FeN –O, suggest-
ing that the O–FeN –O structure is more active than others.
4
2
8
4
structure embedded in the matrix of graphene as the calculation model
molecules can be easily absorbed
(
2 2
O
2
4
4
4
4
The reaction pathway of methane conversion was then calculated on the O–FeN
structure. Previous work reported that there were two possible pathways in the
hydroxylation reactions catalyzed by the O–FeN –SH site of P450, i.e., a concerted
mechanism and a radical pathway. For the O–FeN –O structure, the energy barrier
4
–O
4
3
0
4
of the concerted mechanism is as high as 1.91 eV (Figure S16), more than twice
higher than the formation of a methyl radical, which is only 0.79 eV (Figures
4
S16 and S17). Therefore, methane activation over the O–FeN –O structure
should proceed along the radical mechanism, and the rate-determining step is
C–H bond cleavage (0.79 eV). After the first C–H bond of methane is activated,
the O–FeN
series of oxidation products. Figures 3C and S18 show that the methyl radical gener-
ated can combine with hydroxyl and hydroperoxide groups easily to form CH OH
and CH OOH, and the CH OH can be further converted to HOCH OOH and
4
–O active site can continue to activate other C–H bonds, generating a
3
3
3
2
HCOOH via the hydroxymethyl radical, which was confirmed by the analysis in elec-
tron paramagnetic resonance experiments (Figures 2G, S19, and S20). The energy
required for each step is very low, no more than 0.2 eV, thus enabling the selective
oxidation of methane at room temperature.
In addition, we also employed DFT calculations to study the process of methane acti-
vation on the FePc molecule and other MN
Figures 3D and S21–S23). We found that methane oxidation on O–FeN
easier than that on the O–FePc–O structure (Figure S23 and Table S2), suggesting
that the graphene network can improve the catalytic activity of the FeN center for
methane activation. For other MN /GN structures, the formation energies of
O–MN –O structures (Figure S22) indicated that only Cr, Mn, Fe, and Co can form
their corresponding O–MN –O structures. Furthermore, according to the kinetic
equation of methane activation (see Supplemental Information for details), the for-
mation energy of the O–MN –O active site (G ) can be used as a descriptor for
methane oxidation for a broad range of catalytic materials. A good catalyst should
have a moderate G , resulting in a volcano curve between the methane activation rate
4
/GN (M = Cr, Mn, Co, Ni, Cu) catalysts
(
4
–O was
4
4
4
4
4
f
3
1
f
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Figure 3. Investigation of the Reaction Mechanism over FeN
4
/GN
(
A) Transformation process of a FeN
model for each step.
B) DOS of the three corresponding structures: FeN
Fermi level is shown by the black dashed line.
C) Reaction pathway of methane conversion to CH
4
center in H
2
O
2
solution. The inset was the atomic structure
(
4
4 4
, FeN -O, and O-FeN -O. The position of the
(
3
OH, CH
3
OOH, HOCH
2
OOH, and HCOOH (the
energy of reaction initiation was set as 0 eV) as well as reactants (black), intermediates (blue),
products (green and red), and the activation energy of each step (unit, eV).
(
D) The relationship between the methane activation rate (log[rate]) and the formation energy of
the O–MN –O active site (G ) presents a volcano curve. The G and activation rate of the calculated
O–CrN –O, O–MnN –O, O–FeN –O, and O–CoN –O structures are shown on the volcano marked
by black stars.
4
f
f
4
4
4
4
(
log[rate]) and G
different O–MN
O–MN
mise all barriers in the reaction pathways. Therefore, the FeN
the best activity for CH conversion, confirming the experimental results (Figure 1E).
f
(Figure 3D). As shown in Figure 3D, the corresponding activity of
4
–O structures are plotted on the volcano curve. Among all
4
–O structures (Cr, Mn, Fe, and Co), O–FeN
4
–O has the best ability to compro-
/GN catalyst possesses
4
4
In summary, we have demonstrated that methane can be directly converted to
C1 oxygenated products at room temperature over graphene-confined single
iron atoms. The unique O–FeN
bond of methane to form the methyl radical with a low reaction energy barrier
0.79 eV). The methyl radical is first converted into CH OH and CH OOH,
and CH OH can be further converted to HOCH OOH and HCOOH on the
O–FeN –O structure, as illustrated by TOF-MS, C NMR, and DFT calculations.
The moderate formation energy of O–FeN –O results in its unique activity for
4
–O structure formed is able to active the C–H
(
3
3
3
2
1
3
4
4
methane conversion at room temperature in comparison with that of other gra-
phene-confined first transition metals. These findings provide a new route to
6
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understanding and designing highly efficient non-precious catalysts for methane
conversion in mild conditions.
EXPERIMENTAL PROCEDURES
Raw Materials
Graphite flake (99.8%, metal basis) was purchased from Alfa Aesar. Iron(II) phthalo-
cyanine (FePc), copper(II) phthalocyanine (CuPc), cobalt(II) phthalocyanine (CoPc),
manganese(II) phthalocyanine (MnPc), and nickel(II) phthalocyanine (NiPc) were
purchased from Alfa Aesar. They were commercial materials of analytical grade
and were used as received without further purification.
Synthesis of Catalysts
4
FeN /GN samples with different Fe content were prepared by a well-tested proced-
2
8
ure. In a typical experiment, first, 2.0 g graphite flake and 60 g steel balls (1–1.3 cm
in diameter) were put into hardened steel under Ar (99.999%). The ball milling
process was carried out at 450 rpm for 20 hr to obtain GNs. Then 0.6 g FePc,
1
4
.4 g GN, and 60 g steel balls (1–1.3 cm in diameter) were further ball milled at
50 rpm for 20 hr to obtain FeN /GN-2.7. MnN /GN, CoN /GN, NiN /GN, and
/GN were synthesized in the same way as the preparation of FeN /GN-2.7
4
4
4
4
CuN
4
4
with MnPc, CoPc, NiPc, and CuPc in place of FePc, respectively.
Characterization
STEM was performed on a JEOLARM200F equipped with double aberration correc-
tors and a cold field emission gun operated at 80 kV. STEM images were recorded
with an HAADF detector with a convergence angle of 30 mrad and a collection angle
between 90 and 370 mrad. Tapping-mode AFM measurements were conducted
with a Bruker Metrology Nanoscope III-D atomic force microscope operated under
ambient conditions. Commercial tapping-mode tips made of phosphorus (n)-doped
Si were supplied from Veeco with 115–135-mm-long cantilevers with resonance
frequencies of 293–387 kHz and spring constants of 20–80 N/m.
Catalytic Methane Oxidation Evaluation
The methane oxidation reaction was carried out in a stainless-steel autoclave con-
taining a Teflon liner vessel (working volume, 50 mL). First, the vessel was charged
with 50 mg catalyst, 5 mL deionized water, and 5 mL H
2
O
2
(30%); then the autoclave
(89.9%, N as
was flushed with methane three times and pressurized to 2 MPa CH
4
2
balance gas). The reaction mixture was heated to the desired temperature (typically
ꢁ
2
5 C). The products were cooled down in ice-water for 30 min before analysis before
being filtered and analyzed.
DFT Calculations
DFT calculations were performed with the Vienna ab initio simulation package
3
2
33
(
VASP) according to the projector-augmented wave method. All calculations
were based on the same generalized gradient approximation method with the
3
4
Perdew-Burke-Ernzerhof
plane-wave cutoff was set to 400 eV. The Brillouin zone was sampled by a
functional for the exchange-correlation term. The
6
3 6 3 1 k-point grid for the calculations of charge density and a 2 3 2 3 1
3
5
Monkhorst-Pack
k-point grid for structure optimizations. During geometry
ꢀ4
optimization, the convergence of energy and forces were set to 1 3 10 eV and
˚
0
.05 eV/A, respectively. The transition states of chemical reactions were located
3
6
through the climbing image nudged elastic band method, in which the conver-
˚
gence forces were set to 0.1 eV/A. A periodically repeated single-layer graphene
˚
model was built with a unit cell size of 5 3 5 and a vacuum slab height of 17 A.
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Kinetic analysis details for the volcano curve in Figure 3D are as follows:
B
k T
ꢀ
DGa=kBT
rate = n$
$e
;
h
where
cðH
cðH
cðH
2
O
2
Þ$eꢀGf =kBT
2
OÞ
n =
:
2
O
2
Þ$eꢀGf =kBT
1
+
cðH OÞ
2
The scaling relationship between the activation free energy difference (DG
a
) and the
formation energies of the active sites (G ) was cited from Nørskov et al. According
2
to our reaction conditions, c(H )/c(H O) = 1, T = 298 K.
3
1
f
2
O
2
For the formation energies of MN
= GðO -- MN
SUPPLEMENTAL INFORMATION
4
to O–MN
4
–O active sites,
Þ-- GðO
G
f
4
-- O Þ-- GðMN
4
2
Þ
Supplemental Information includes Supplemental Experimental Procedures, 30
figures, and 3 tables and can be found with this article online at https://doi.org/
1
0.1016/j.chempr.2018.05.006.
ACKNOWLEDGMENTS
We gratefully acknowledge the financial support from the Ministry of Science and
Technology of China (nos. 2016YFA0204100 and 2016YFA0200200), the National
Natural Science Foundation of China (nos. 21573220 and 21621063), the Key
Research Program of Frontier Sciences of the Chinese Academy of Sciences (no.
QYZDB-SSW-JSC020), the strategic Priority Research Program of the Chinese
Academy of Sciences (no. XDA09030100), and the National Postdoctoral Program
for Innovative Talents (BX201700140). We also acknowledge the staff of the
BL14W1 beamline at the Shanghai Synchrotron Radiation Facility for assistance
with the X-ray absorption spectroscopy measurements and the computational
resources from the National Supercomputing Center in Shenzhen. We thank
Prof. Zichao Tang and Prof. Dapeng Wu for fruitful discussions.
AUTHOR CONTRIBUTIONS
X.B. and D.D. conceived and designed the experiments. X. Cui performed the experi-
ments. Haobo Li and J.X. performed the DFT calculations. Y.W., L. Hua, Q. Li, and
Haiyang Li contributed to the TOF-MS experiments. Y.H. and X.H. contributed to the
NMR experiments. Q. Liu and F.Y. performed the AFM tests. L. He and X. Chen contrib-
uted to the catalytic performance tests. D.D., X.B., X. Cui, Haobo Li, Y.W., and Y.H.
analyzed the data and wrote the manuscript. All authors discussed the results and com-
mented on the manuscript.
DECLARATION OF INTERESTS
The authors declare no competing interests.
Received: January 11, 2018
Revised: February 9, 2018
Accepted: May 11, 2018
Published: June 14, 2018
8
Chem 4, 1–9, August 9, 2018

Please cite this article in press as: Cui et al., Room-Temperature Methane Conversion by Graphene-Confined Single Iron Atoms, Chem (2018),
https://doi.org/10.1016/j.chempr.2018.05.006
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