Fe-O Clusters Anchored on Nodes of Metal–Organic Frameworks for Direct Methane Oxidation

Article abstract of DOI:10.1002/anie.202013807

Direct methane oxidation into value-added organic oxygenates with high productivity under mild condition remains a great challenge. We show Fe-O clusters on nodes of metal–organic frameworks (MOFs) with tunable electronic state for direct methane oxidation into C1 organic oxygenates at 50 °C. The Fe-O clusters are grafted onto inorganic Zr₆ nodes of UiO-66, while the organic terephthalic acid (H₂BDC) ligands of UiO-66 are partially substituted with monocarboxylic modulators of acetic acid (AA) or trifluoroacetic acid (TFA). Experiments and theoretical calculation disclose that the TFA group coordinated with Zr₆ node of UiO-66 enhances the oxidation state of adjacent Fe-O cluster due to its electron-withdrawing ability, promotes the activation of C?H bond of methane, and increases its selective conversion, thus leading to the extraordinarily high C1 oxygenate yield of 4799 μmol g_cat^?1 h^?1 with 97.9 % selectivity, circa 8 times higher than those modulated with AA.

Full text of DOI:10.1002/anie.202013807

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Accepted Article
Title: Fe-O Clusters Anchored on Nodes of Metal-Organic Frameworks
for Direct Methane Oxidation
Authors: Wenshi Zhao, Yanan Shi, Yuheng Jiang, Xiaofei Zhang,
Chang Long, Pengfei An, Yanfei Zhu, Shengxian Shao,
Zhuang Yan, Guodong Li, and Zhiyong Tang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202013807
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10.1002/anie.202013807
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Fe-O Clusters Anchored on Nodes of Metal-Organic Frameworks
for Direct Methane Oxidation
Wenshi Zhao, Yanan Shi, Yuheng Jiang, Xiaofei Zhang, Chang Long, Pengfei An, Yanfei Zhu,
Shengxian Shao, Zhuang Yan, Guodong Li* and Zhiyong Tang*
[a]
W. Zhao, Y. Shi, Y. Jiang, Dr. X. Zhang, C. Long, Dr. Y. Zhu, S. Shao, Z. Yan, Prof. G. Li and Prof. Z. Tang
CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and
Technology
Beijing 100190, P. R. China
E-mail: liguodong@nanoctr.cn, zytang@nanoctr.cn
W. Zhao, S. Shao, Z. Yan, Prof. G. Li and Prof. Z. Tang
School of Nanoscience and Technology, University of Chinese Academy of Sciences
Beijing 100049, P. R. China
[b]
[c]
Dr. P. An
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences
Beijing 100049, P. R. China
Supporting information for this article is given via a link at the end of the document.
Abstract: Direct methane oxidation into value-added organic
oxygenates with high productivity under mild condition remains a
great challenge. In this work, we show Fe-O clusters on nodes of
metal-organic frameworks (MOFs) with tunable electronic state for
direct methane oxidation into C1 organic oxygenates at 50C. The Fe-
O clusters are grafted onto inorganic Zr6 nodes of UiO-66 (UiO stands
for University of Oslo), while the organic terephthalic acid (H2BDC)
ligands of UiO-66 are partially substituted with monocarboxylic
modulators of acetic acid (AA) or trifluoroacetic acid (TFA).
Experiments and theoretical calculation disclose that the TFA group
coordinated with Zr6 node of UiO-66 enhances the oxidation state of
adjacent Fe-O cluster due to its electron-withdrawing ability, promotes
the activation of C-H bond of methane and increases its selective
conversion, thus leading to the extraordinarily high C1 oxygenate yield
of 4799 μmol gcat-1 h-1 with 97.9% selectivity, ~8 times higher than
those modulated with AA.
intriguing features including large surface area, tunable pore
dimensions, well-defined metal nodes, adjustable chemical
composition and rich functionality.[5] To be specific, the metal
nodes of MOFs are often coordinated with -OH and -OH2 groups
that could further act as the anchoring sites for active components,
offering many opportunities for precise design of the catalyst at
the molecular level.[6] In this work, we demonstrate that Fe-O
clusters on Zr6 nodes of UiO-66 modulated with TFA are able to
effectively activate the inert C-H bond of methane and
simultaneously catalyze methane oxidation with H2O2 as the
oxidant. The C1 organic oxygenates are acquired with high yield
and good selectivity under mild condition.
In brief, grafting of Fe-O clusters onto Zr6 nodes of UiO-66
involves three steps: (1) competitive coordination of Zr4+ ion with
monocarboxylic modulator over bicarboxylic H2BDC ligand to
form the variant UiO-66,[7] (2) abstracting hydrogen atoms from -
OH/-OH2 groups in UiO-66,[8] (3) anchoring Fe-O clusters to
obtain the catalysts (Figure 1a). In detail, dissolution of ZrCl4 and
H2BDC in N, N’-dimethylformamide (DMF) solution was carried
out, followed by addition of TFA and solvothermal treatment to
Direct conversion of methane into the value-added oxygenated
chemicals, which is considered as the “holy grail” in catalysis, is
economical and environmentally friendly but hardly implemented,
because methane is characteristic of strong C-H bond (439
kJ/mol), negligible electron affinity, large ionization energy, and
low polarizability.[1] It always remains difficult to cleave the C-H
bonds of methane and make it amenable for further chemical
conversion. To date, many types of heterogeneous catalysts,
such as the supported Fe or Cu catalysts, have come to the
forefront of direct catalytic methane oxidation with various
oxidants of N2O, H2O2 and O2.[2] Unfortunately, the obtained target
products are more active than methane and fully oxidized product
of CO2, usually giving rise to the low yield of organic oxygenates.[3]
Therefore, it is highly desirable to rationally design and synthesize
the heterogeneous catalysts that can selectively activate the C-H
bonds of methane while suppressing complete dehydrogenation
and avoiding overoxidation.[4]
acheive
the
UiO-66
with
composition
of
Zr6O4.17(OH)3.83(BDC)4.29(HCOO)0.75(TFA)2.50 (Figure S1), named
as UiO-66(2.5TFA). After that, the hydrogen atoms of -OH and -
OH2 groups in UiO-66(2.5TFA) were removed.[8] Finally, the
obtained solid was transferred into FeCl2 tetrahydrofuran (THF)
solution to get the brown solid products, denoted as UiO-
66(2.5TFA)-Fe. Furthermore, nuclear magnetic resonance (NMR)
spectra show that after grafting Fe sites, the TFA groups are still
well coordinated with Zr6 nodes (Figure S2). As the contrast
sample, another UiO-66 was synthesized by reacting Zr4+ ion and
H2BDC with AA, and its composition was determined as
Zr6O4.33(OH)3.67(BDC)5.34(HCOO)0.62(AA)0.37
,
called as UiO-
66(0.37AA) (Figure S3). Similarly, it was subjected to abstracting
hydrogen and anchoring Fe-O clusters to obtain the UiO-
66(0.37AA)-Fe sample.
Among various heterogeneous catalysts, MOFs, which are
formed by self-assembly of metal ions or clusters with ditopic or
polytopic organic linkers, are ideal candidates, due to their
1
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structure (EXAFS) spectra in R-space demonstrate that Fe sites
in UiO-66(2.5TFA)-Fe and UiO-66(0.37AA)-Fe possess the
similar local structure (Figure 1e), which is close to that of FeO
and Fe2O3 standards based on comparison of the peaks at 1.46
Å (the first oxygen neighbor around Fe) and at 2.66 Å (Fe-Fe from
the second neighbor correlation). The quantitative fitting further
discloses that the Fe-Fe coordination number is low with an
average Fe-Fe distance of 3.07 Å and an average Fe-O
separation of 1.96 Å (Table S1). N2 adsorption-desorption
isotherms manifest that the specific surface areas are 945 m2 g-1
for UiO-66(2.5TFA)-Fe and 1193 m2 g-1 for UiO-66(2.5TFA), as
well as 686 m2 g-1 for UiO-66(0.37AA)-Fe and 971 m2 g-1 for UiO-
66(0.37AA) (Figure S8 and Table S2).
Figure 1. (a) Scheme of synthesizing Zr6 nodes coordinated with TFA or AA
and then anchoring Fe sites on Zr6 nodes. (b) SEM image of UiO-66(2.5TFA)-
Fe. (c) Transmission electron microscopy energy-dispersive X-ray spectroscopy
(TEM-EDX) mapping images of UiO-66(2.5TFA)-Fe. (d) Powder XRD patterns
of UiO-66(2.5TFA)-Fe, UiO-66(0.37AA)-Fe and simulated UiO-66. (e) Fourier
transformed Fe K-edge EXAFS spectra in R-space collected on UiO-
66(2.5TFA)-Fe, UiO-66(0.37AA)-Fe, FeCl2, Fe2O3, FeO and Fe foil under
ambient condition (not corrected for phase shift).
The morphology and structure of as-prepared UiO-66(2.5TFA)-
Fe and UiO-66(0.37AA)-Fe samples are investigated. Scanning
electron microscopy (SEM) observation shows that both
nanoparticles have rather uniform sizes of 340  46 nm for UiO-
66(2.5TFA)-Fe and 165  17 nm for UiO-66(0.37AA)-Fe (Figures
1b, S4 and S5). The element mapping images indicate that the Fe
element is uniformly distributed inside UiO-66(2.5TFA)-Fe and
UiO-66(0.37AA)-Fe samples (Figures 1c, S4 and S5), and the
quantitative measurement reveals 2.2 wt% and 3.0 wt% Fe inside,
respectively. Powder X-ray diffraction (XRD) patterns display that
crystal structure of UiO-66(2.5TFA)-Fe and UiO-66(0.37AA)-Fe is
in good agreement with that of typical UiO-66, validating well
maintenance of the cubic close packed structure of UiO-66; in
addition, no obvious XRD peaks of Fe sites are discerned likely
due to their extremely small size and low loading (Figure 1d). As
shown in Fourier transform infrared (FTIR) spectra (Figure S6),
after anchoring Fe-O clusters, the intensity of O-H peaks become
weaker for both UiO-66(2.5TFA)-Fe and UiO-66(0.37AA)-Fe,[6b]
suggesting successful formation of Fe-O clusters on the Zr6 nodes.
The local structure of the attached Fe-O clusters is elucidated by
X-ray photoelectron spectroscopy (XPS) and X-ray absorption
spectroscopy (XAS). XPS spectra imply that the Cl from FeCl2
precursor is not incorporated in UiO-66(2.5TFA)-Fe (Figure S7).
Fourier transformed Fe K-edge extended X-ray absorption fine
Figure 2. Characterization of oxidation state of Fe sites in different samples. (a)
Fe 2p level profiles of UiO-66(2.5TFA)-Fe and UiO-66(0.37AA)-Fe samples. (b)
Fe K-edge XANES spectra of UiO-66(2.5TFA)-Fe, UiO-66(0.37AA)-Fe, Fe2O3,
FeO, FeCl2 and Fe foil.
XPS measurement was performed on UiO-66(2.5TFA)-Fe
along with UiO-66(0.37AA)-Fe (Figures 2a and S9). The Fe 2p3/2
binding energy is located at 711.10 eV for UiO-66(2.5TFA)-Fe,
higher than 710.86 eV for UiO-66(0.37AA)-Fe (Figure 2a). This
difference is further confirmed by X-ray absorption near-edge
structure (XANES) spectroscopy. The Fe K-edge XANES of UiO-
66(2.5TFA)-Fe shifts toward higher energy compared with UiO-
66(0.37AA)-Fe (inset in Figure 2b), highlighting the higher
oxidation state of Fe sites in UiO-66(2.5TFA)-Fe. This is attributed
to the electronegativity of F element (4.1) higher than H element
(2.1),[9] thus leading to the stronger electron-withdrawing effect of
TFA on Fe-O clusters than AA. Besides, the position of the pre-
edge peaks of both UiO-66(2.5TFA)-Fe and UiO-66(0.37AA)-Fe
is located in the middle between FeO and Fe2O3 reference
compounds (Figure 2b), suggesting that the valent state of the Fe
sites is between + 2 and + 3 with a distorted octahedral
symmetry.[10]
2
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Table 1. Direct methane oxidation catalyzed by different catalysts.[a]
C1 organic products (μmol gcat-1 h-1) [c]
Metal [b]
CO2
(μmol gcat-1 h-1) [c]
Entry
Catalysts
(wt%)
CH3OH
CH3OOH
HOCH2OOH
HCOOH
Total amount
1
UiO-66(2.5TFA)-Fe
UiO-66(1TFA)-Fe
UiO-66(1.24AA)-Fe
UiO-66(0.37AA)-Fe
UiO-66-Fe
2.2
2.2
3.3
3.0
2.1
-
258.7
221.6
79.6
37.0
52.6
0
401.0
260.0
154.4
44.8
60.5
0
1029.8
423.2
148.0
33.6
35.3
0
3109.7
1043.2
226.8
483.8
367.9
0
4799.2
1948.0
608.8
599.2
516.3
0
105
72
2
3
33
4
104
22
5
6
Without catalyst[d]
UiO-66(0.37AA)-Fe[e]
Fe2O3
0.5
240
92
7
3.0
36.8
46.7
1.3
2.4
50.4
51.6
0
86.2
59.2
0
63.8
162.8
0
398.2
0
598.6
273.6
0
8
9
FeO
0
16
10
11
UiO-66(2.5TFA)-Cu
UiO-66(2.5TFA)-Co
5.6
21.2
57.2
0
0
26.8
72
14.4
11.8
0
83.4
0
[a] Reaction condition: catalyst (25 mg), 3 MPa CH4, 0.3 mL 30wt% H2O2 in 9.7 mL D2O, 50oC, 1 h. [b] Metal contents including Fe, Cu
or Co were detected by ICP-MS. [c] The yield of the obtained products was calculated based on the weight of whole catalyst. [d] The
yield of CO2 is 0.5 μmol h-1. [e] 5.26 mg sodium trifluoroacetate was added to the reaction solution.
The catalytic performance of UiO-66(2.5TFA)-Fe was
evaluated on direct methane oxidation in water using H2O2 as the
oxidant at 3 MPa CH4 and 50oC for 1 h. A series of contrast
samples including UiO-66(1TFA)-Fe, UiO-66(1.24AA)-Fe, UiO-
66(0.37AA)-Fe, UiO-66-Fe, UiO-66(2.5TFA), UiO-66(1TFA), UiO-
66(1.24AA) and UiO-66(0.37AA) were also synthesized and
tested (Figures S10-S16). Without Fe-O clusters anchored on Zr6
nodes, almost no activity is found (Table 1, entry 6, and Figure
S17). On the contrary, Fe-O clusters on Zr6 nodes of UiO-66 with
or without modulators could catalyze methane oxidation into C1
products including CH3OH, CH3OOH, HOCH2OOH and HCOOH,
which are confirmed by 13C-NMR spectrum of the obtained
products from 13CH4 substrate as well as 1H-NMR spectrum
without adding substrate (Figure S18). When UiO-66-Fe is used
higher than that over UiO-66(0.37AA)-Fe. It deserves to be
pointed out that after the catalytic reaction, both shape and crystal
structure of UiO-66(2.5TFA)-Fe are well kept and no aggregation
of Fe-O clusters is found (Figure S23). Notably, in comparison
with the state-of-the-art reported heterogeneous catalysts, UiO-
66(2.5TFA)-Fe displays the superior activity and high selectivity
towards C1 organic oxygenates (Table S3).
In addition, FeO and Fe2O3 are used as the contrast catalysts for
methane oxidation. No C1 organic oxygenates is discerned for
FeO (Table 1, entry 9, Figure S24a), while Fe2O3 exhibits very low
activity and the yield of C1 organic oxygenates is only 273.6 μmol
gcat-1 h-1 (Table 1, entry 8, Figure S24b). The major disadvantage
of Fe2O3 is its small specific surface area of 36.8 m2 g-1 (Figure
S25), which offers much less active sites for catalytic reactions
as catalyst, the C1 organic products are 52.6 μmol gcat-1 h-1 CH3OH, compared with porous MOFs. Another reason is that the TFA
60.5 μmol gcat-1 h-1 CH3OOH, 35.3 μmol gcat-1 h-1 HOCH2OOH and
367.9 μmol gcat-1 h-1 HCOOH, and the total amount of C1 organic
oxygenates is 516.3 μmol gcat-1 h-1 (Table 1, entry 5, Figure S19).
Gas product CO2 is observed with a value of 22 μmol gcat-1 h-1.
When UiO-66(0.37AA)-Fe is used as catalyst, the organic
products are achieved with 37.0 μmol gcat-1 h-1 CH3OH, 44.8 μmol
gcat-1 h-1 CH3OOH, 33.6 μmol gcat-1 h-1 HOCH2OOH and 483.8 μmol
gcat-1 h-1 HCOOH (Figure S20a), so the total amount of C1 organic
oxygenates is 599.2 μmol gcat-1 h-1 (Table 1, entry 4). Meanwhile,
the yield of CO2 is 104 μmol gcat-1 h-1, and thus the selectivity of
C1 organic oxygenates is around 85.2%. Notably, when TFA is
coordinated with Zr6 node of UiO-66-Fe, the catalytic performance
is significantly enhanced. UiO-66(1TFA)-Fe exhibits the
productivity of 1948 μmol gcat-1 h-1 for C1 organic oxygenates with
the selectivity of 96.4% (Table 1, entry 2 and Figure S20b). More
impressively, UiO-66(2.5TFA)-Fe shows the much higher yield of
4799.2 μmol gcat-1 h-1 for C1 organic oxygenates with a remarkable
selectivity of 97.9%, and the productivity of CO2 is only 105 μmol
gcat-1 h-1 (Table 1, entry 1, Figures S21 and S22). In detail, the C1
organic oxygenate products include 258.7 μmol/gcat·h CH3OH,
401.0 μmol gcat-1 h-1 CH3OOH, 1029.8 μmol gcat-1 h-1 HOCH2OOH
group coordinated with Zr6 nodes of UiO-66 contributes to the
significantly enhanced catalytic activity of the adjacent Fe-O
clusters for generating C1 organic oxygenate products. To
evidence above, TFA anions were added into the reaction solution
when UiO-66(0.37AA)-Fe was used as catalyst. The yield of C1
-1
organic oxygenate products is 598.6 μmol gcat h-1, and no
considerable improvement is discerned with respect to UiO-
66(0.37AA)-Fe (Table 1, entry 7 vs. 4, Figure S26). This result
suggests that the direct incorporation of TFA modulator in UiO-66
is necessary to increase the catalytic performance of Fe-O
clusters.
Alternatively, more AA modulators are coordinated with Zr6
nodes of UiO-66 to obtain the contrast sample, UiO-66(1.24AA)-
Fe, for catalytic methane oxidation (Figures S12 and S13). XPS
spectra also indicate that Fe 2p3/2 binding energy in UiO-
66(1.24AA)-Fe is almost the same with UiO-66(0.37AA)-Fe
(Figure S27). When UiO-66(1.24AA)-Fe is used as the catalysts,
the yield of C1 organic oxygenate products is 608.8 μmol gcat-1 h-
1, very close to 599.2 μmol gcat-1 h-1 obtained with UiO-66(0.37AA)-
Fe (Table 1, entry 3 vs. 4, Figure S28).
Except for Fe sites, other metal sites anchored on Zr6 nodes of
UiO-66(2.5TFA) are fabricated, such as UiO-66(2.5TFA)-Cu and
UiO-66(2.5TFA)-Co (Figures S29 and S30). UiO-66(2.5TFA)-Cu
-1
and 3109.7 μmol gcat h-1 HCOOH. Evidently, the yield of C1
organic oxygenates over UiO-66(2.5TFA)-Fe is nearly 8 times
3
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10.1002/anie.202013807
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-1
gives rise to the yield of 26.8 μmol gcat h-1 for C1 organic
(Figures 4a and S32). Theoretical calculation demonstrates that
UiO-66(TFA)-Fe possesses the reduced energy of -3.259 eV for
H2O2 activation compared with -2.586 eV over UiO-66-Fe, mainly
due to the higher oxidation state of Fe sites in the UiO-66(TFA)-
Fe (Figure 4b). As manifested in Figure 4c, the activation of first
C-H bond of methane is the rate-determining step, consistent with
the reported work.[4] Noteworthily, in regard of the transit state [Fe-
O…H…CH3] in the first C-H bond activation, the energy barrier of
0.372 eV over UiO-66(TFA)-Fe is lower than 0.603 eV over UiO-
66-Fe, highlighting that UiO-66(TFA)-Fe is more active than UiO-
66-Fe. Moreover, the reaction energy for each step over UiO-
66(TFA)-Fe is lower than that over UiO-66-Fe, again indicating
that UiO-66(TFA)-Fe is more active for methane oxidation
towards C1 organic oxygenates (Figure 4c). To further
differentiate the capability of both samples on first C-H bond
activation, control experiments at a low temperture of 4oC are
performed. No activity is found over UiO-66-Fe, but C1 organic
products are obtained over UiO-66(2.5TFA)-Fe (Figure S33),
indicating that it is easier to activate the first C-H bond by UiO-
66(2.5TFA)-Fe than UiO-66-Fe.
oxygenates (Table 1, entry 10), while the productivity of 83.4 μmol
gcat h-1 for C1 organic oxygenates is obtained with UiO-
-1
66(2.5TFA)-Co (Table 1, entry 11).
It needs to be stressed that small amount of formic species is
likely formed on Zr6 nodes in the original catalyst, due to
decomposition of DMF into formic acid during synthesis of UiO-
66 samples (Figure S1).[7] To exclude its influence on final
products, contrast experiment was performed. No C1 organic
products is detected over UiO-66(2.5TFA)-Fe without adding
methane, indicating that coordinated HCOO- group would not leak
from the Zr6 nodes (Figure S18b).
To investigate the mechanism of direct methane oxidation into
C1 oxygenated products, electron paramagnetic resonance
(EPR) experiments with 5,5’-dimethyl-1-pyrroline-N-oxide
(DMPO) as a radical trapping agent were performed. Without
adding methane, strong •OH signals are distinguished, indicating
that H2O2 is activated by UiO-66(2.5TFA)-Fe (Figure 3a). After
adding methane into the reaction solution, the strong •OH signals
remain but in absence of •CH3 peaks , implying that as-generated
•CH3 reacts with the rich •OH quickly.[2c] When methanol is added
into the reaction solution instead of methane, •OH and •CH2OH
are detected in the solution (Figure 3b); meanwhile, HOCH2OOH
and HCOOH are also produced, similar as those obtained from
direct catalytic methane oxidation (Figure 3c). This result
suggests that CH3OH and CH3OOH are produced from methane
firstly and then further oxidized into HOCH2OOH and HCOOH.
Altogether, EPR and NMR characterizations reveal a radical
reaction process for direct methane oxidation into C1 oxygenates
with H2O2 as the oxidant.[11]
Figure 4. Reaction pathway of direct methane oxidation and theoretical
calculation. (a) Scheme of reaction pathway for direct methane oxidation
catalyzed by UiO-66(TFA)-Fe. (b) Relative energy for H2O2 activation over UiO-
66(TFA)-Fe and UiO-66-Fe. (c) Relative energy for each step of direct methane
oxidation into C1 products over UiO-66(TFA)-Fe and UiO-66-Fe. Color scheme:
light gray for hydrogen, dark gray for carbon, green for fluorine, red for oxygen,
blue for zirconium and brown for iron.
Figure 3. (a) EPR spectra of methane oxidation reaction catalyzed by UiO-
66(2.5TFA)-Fe with H2O2 as oxidant. (b) EPR spectra of the CH3OH oxidation
reaction catalyzed by UiO-66(2.5TFA)-Fe with H2O2 as oxidant, and (c) NMR
spectra of the resultant solution.
In summary, the efficient and selective oxidation of methane is
successfully realized by Fe-O clusters on Zr6 nodes of UiO-66
modulated with TFA. The increased oxidation state of Fe-O
clusters coupled with TFA groups synergistically endows their
higher activity towards activating both methane and H2O2, thus
resulting in high yield of C1 organic oxygenates. This work will
open the avenues for molecular design of diverse coordination
architectures in heterogeneous catalysts for important but
challengeable reactions.
Based on above and the reported works,[2c, 12] it is generally
accepted that H2O2 is firstly decomposed into active oxygen
species and H2O catalyzed by Fe-O clusters (Figure S31).
Subsequently, methane is activated into •CH3 by active oxygen
species on Fe-O clusters, and then •CH3 reacts with •OH and
•OOH to produce CH3OH and CH3OOH, respectively. The C-H
bond of as-formed CH3OH might be further activated to generate
•CH2OH that combines •OOH to form HOCH2OOH. Finally
HOCH2OOH is converted to HCOOH catalyzed by Fe-O clusters
Acknowledgements
4
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COMMUNICATION
[8]
[9]
K. Manna, P. Ji, Z. Lin, F. X. Greene, A. Urban, N. C. Thacker, W. Lin,
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The authors acknowledge financial support from the Strategic
Priority Research Program of Chinese Academy of Sciences
(XDB36000000, Z.Y.T. and G.D.L.), National Key Basic Research
Program of China (2016YFA0200700, Z.Y.T.), National Natural
Science Foundation of China (92056204, 21890381 and
21721002, Z.Y.T.; 21722102 and 51672053, G.D.L.), Beijing
Natural Science Foundation (2182087, G.D.L.), Frontier Science
Key Project of Chinese Academy of Sciences (QYZDJ-SSW-
SLH038, Z.Y.T.), and K. C. Wong Education Foundation (Z.Y.T.),
and Youth Innovation Promotion Association CAS (2016036,
G.D.L.).
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Keywords: iron • methane • metal-organic frameworks •
trifluoroacetic acid • C1 oxygenate
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10.1002/anie.202013807
Angewandte Chemie International Edition
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We successfully synthesize Fe-O clusters on nodes of UiO-66 simultaneously coordinated with trifluoroacetic acid (TFA) or acetic acid
(AA) for direct methane oxidation. The TFA group coordinated with Zr6 node of UiO-66 enhances the oxidation state of adjacent Fe-O
cluster, promotes the activation of C-H bond of methane and increases its selective conversion into the extraordinarily high C1
oxygenates with respect to those coordinated with AA.
6
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