Bioinspired Metal-Organic Framework Catalysts for Selective Methane Oxidation to Methanol

Article abstract of DOI:10.1021/jacs.8b11525

Particulate methane monooxygenase (pMMO) is an enzyme that oxidizes methane to methanol with high activity and selectivity. Limited success has been achieved in incorporating biologically relevant ligands for the formation of such active site in a synthetic system. Here, we report the design and synthesis of metal-organic framework (MOF) catalysts inspired by pMMO for selective methane oxidation to methanol. By judicious selection of a framework with appropriate topology and chemical functionality, MOF-808 was used to postsynthetically install ligands bearing imidazole units for subsequent metalation with Cu(I) in the presence of dioxygen. The catalysts show high selectivity for methane oxidation to methanol under isothermal conditions at 150 °C. Combined spectroscopies and density functional theory calculations suggest bis(μ-oxo) dicopper species as probable active site of the catalysts.

Full text of DOI:10.1021/jacs.8b11525

Subscriber access provided by University of Winnipeg Library
Article
Bioinspired Metal-Organic Framework Catalysts
for Selective Methane Oxidation to Methanol
Jayeon Baek, Bunyarat Rungtaweevoranit, Xiaokun Pei, Myeongkee Park, Sirine C. Fakra, Yi-Sheng Liu, Roc
Matheu, Sultan A. Alshmimri, Saeed Alshihri, Christopher A. Trickett, Gabor A. Somorjai, and Omar M. Yaghi
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 10 Dec 2018
Downloaded from http://pubs.acs.org on December 10, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Bioinspired Metal–Organic Framework Catalysts for Selective Methane
Oxidation to Methanol
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Jayeon Baek,1,2,3,4,# Bunyarat Rungtaweevoranit,1,2,3,5,# Xiaokun Pei,1,2,3,5 Myeongkee Park,7 Sirine C.
Fakra,6 Yi‐Sheng Liu,6 Roc Matheu,1,2,3,5 Sultan A. Alshmimri,8 Saeed Alshehri,8 Christopher A.
Trickett,1,2,3,5 Gabor A. Somorjai,1,4,5,* and Omar M. Yaghi1,2,3,5,*
1Department of Chemistry, 2Kavli Energy NanoSciences Institute at Berkeley, and 3Berkeley Global Science Institute,
University of California—Berkeley, California 94720, United States
4Chemical Sciences Division, 5Materials Sciences Division, and 6Advanced Light Source, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
7Department of Chemistry, College of Natural Science, Dong‐A University, Busan, 49315, Republic of Korea
8King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia
KEYWORDS: Metal–organic framework, Particulate methane monooxygenase (pMMO), Bioinspired catalyst,
Methane oxidation, Heterogeneous catalysis
ABSTRACT: Particulate methane monooxygenase (pMMO) is an enzyme that oxidizes methane to methanol with high activity
and selectivity. Limited success has been achieved in incorporating biologically relevant ligands for the formation of such active
site in a synthetic system. Here, we report the design and synthesis of metal–organic framework (MOF) catalysts inspired by
pMMO for selective methane oxidation to methanol. By judicious selection of a framework with appropriate topology and chemical
functionality, MOF-808 was used to post-synthetically install ligands bearing imidazole units for subsequent metalation with Cu(I)
in the presence of dioxygen. The catalysts show high selectivity for methane oxidation to methanol under isothermal conditions at
150 °C. Combined spectroscopies and density functional theory calculations suggest bis(μ-oxo) dicopper species as probable active
site of the catalysts.
stability.19 At elevated temperatures, these compounds are
INTRODUCTION
susceptible to decomposition via ligand oxidation and thus the
loss of catalytically active copper–oxygen cores.20 Although
there exist synthetic catalysts capable of partial methane
oxidation such as Cu-exchanged zeolites, the diversity of the
active sites are limited to mono(μ-oxo)dicopper and tris(μ-
oxo)tricopper cores.3, 5, 21 In gas phase, these catalysts typically
operate in step-wise treatment for partial methane oxidation:
(1) catalyst oxidation, (2) methane activation, and (3)
methanol extraction, proceeding at different reaction
temperatures, thus presenting a challenge for a streamlined
catalytic process. Comparatively, oxidation of methane in the
liquid phase where H2O2 is used as an oxidant, despite
exhibiting high conversion, suffers from overoxidation of
methanol yielding a mixture of methyl peroxide, formic acid
and carbon dioxide.1-2, 22
Selective methane oxidation to methanol represents an
important challenge in catalysis due to the difficulty in
activating the strong C–H bond of methane (bond dissociation
energy = 104 kcal mol–1), giving rise to selectivity and activity
problems.1-8 Finding a solution to this impediment is a key
toward the direct synthesis of methanol from methane.9-11 In
nature, particulate methane monooxygenase (pMMO) is an
effective catalyst for the oxidation of methane to methanol.12
Extensive studies on the pMMO suggest that the active sites
are composed of copper complexes coordinated to histidines
although the nuclearity and the definitiveness of their
structures remain a subject of debate.12-15
Inspired by pMMO, molecular complexes have utilized the
tunability of ligand design in pursuit of duplicating the
structure and reactivity in a synthetic system. A library of
compounds with various copper–oxygen complexes have been
reported, including but not limited to Cu2O2 [trans-1,2-peroxo,
μ-η2:η2-peroxo and bis(μ-oxo)dicopper cores] and Cu2O
[mono(μ-oxo) dicopper core] along with their spectroscopic
fingerprints.16-18 Despite such vast library of compounds, the
reactivity of this class of catalysts are generally limited to
substrates with weak C–H bonds due to the restricted thermal
The active sites of metalloenzymes are typically enclosed in
a pocket for environmental control, hydrogen bonding, ion
transport or controlling the reaction to prevent self-
destruction.23-27 We envisaged that metal–organic frameworks
(MOFs)28 can serve as a scaffold akin to the polypeptide
chains in enzymes whose arrangement of secondary and
tertiary structures can be achieved by judicious choice of
structure and topology of MOFs.29-32 The metal binding
ligands bearing an imidazole unit in the copper active site of
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 16
pMMO can be mirrored in a synthetic system by post-
Catalysis. The catalytic testing was performed using a
synthetic modification of MOFs.33-35 Once these metal-binding
ligands are in place, metalation with the desired configuration
can be accomplished.36-37
custom-designed continuous flow tubular reactor (Parr
Instrument Co.). Mass flow controllers were calibrated using
ADM 1000 flow meter (Agilent Technologies) and ultrahigh
purity He, CH4 (Research 5.0 Grade, Airgas), and 3% N2O/He
(Primary Standard Grade, Praxair) were flowed into a 30 cm
long quarter inch 316-stainless steel reactor. The catalyst (100
mg) was sieved to 100–250 μm and placed in the middle of the
reactor tube, delimited by a layer of purified glass wool and a
layer of quartz sand (50–70 mesh) at each end. Pretreatment of
the catalyst was conducted under He (30 sccm) at 150 °C
(3 °C/min) for 1 h. The catalyst was then oxidized using 3%
N2O/He flow (30 sccm) at 150 °C for 2 h. After purging with
He (30 sccm) for 30 min, CH4 (30 sccm) was flowed into the
catalyst for 1 h. After purging with He (50 sccm) for 1 h, 3%
steam/He (30 sccm) was flowed into the catalyst. All lines
were heated at 120 °C to prevent condensation. The outlet of
the reactor was analyzed by gas chromatography (Model: GC-
2014, Shimadzu Co.). The measurement started 3 min after
opening the valve to 3% steam/He. The reactants and products
were separated using HayeSep R 80/100 stainless steel packed
column (12 ft, 1/8 in OD, 2mm ID). The water and CO2 were
monitored using a thermal conductivity detector and methanol
was monitored using a flame ionization detector.
1
2
3
4
5
6
7
8
Here, we demonstrate how a MOF can be used as a
backbone for the creation of an enzyme-like active site by
installing biologically relevant imidazole moieties, then
subsequently metalating these ligands to incorporate reactive
copper–oxygen complexes within the framework. From
structural analysis of various MOFs, MOF-808,
Zr6O4(OH)4(BTC)2 (HCOO)5(H2O)1(OH)1,38 was selected as it
possesses the chemical and geometric parameters for post-
synthetic modifications to create the active sites inspired by
pMMO. The resulting catalysts are capable of highly selective
oxidation of methane to methanol under isothermal conditions.
We identified the structure of the active sites using solid-state
UV-Vis, resonance Raman and X-ray absorption
spectroscopies complemented by density functional theory
(DFT) calculations.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EXPERIMENTAL METHODS
Further details are available in the Supporting Information (SI).
Synthesis of MOF-808. MOF-808 was synthesized following
the reported procedure.39 In a 100-mL media bottle, 1,3,5-
benzenetricarboxylic acid (210 mg) and ZrOCl2ꞏ8H2O (970
mg) were dissolved in a solution containing DMF (30 mL) and
formic acid (30 mL). The bottle was sealed and heated in a
100 °C isothermal oven for a day. White powder was collected
by centrifugation (8,000 rpm, 3 min), washed with DMF 3
times (60 mL × 3) over a 24 h period and with acetone 3 times
(60 mL × 3) over a 24 h period. Finally, MOF-808 was dried
under dynamic vacuum overnight at room temperature. EA of
X-ray absorption spectroscopy (XAS). N K-edge X-ray
absorption spectra were collected at beamline 8.0.1, an
undulator beamline with energy range of 80–1200 eV of the
Advanced Light Source (ALS) at Lawrence Berkeley National
Laboratory (LBNL). Its spherical gratings monochromator
delivers 1012 photons/second with linear polarization with a
resolving power up to 6000. The experimental energy
resolution is better than 0.15 eV. Experiments were performed
at room temperature. All the spectra were collected in both
total-electron-yield (TEY) and total-fluorescence-yield (TFY)
modes simultaneously, corresponding to a probe depth of
about 10 nm and 100 nm, respectively. We present spectra of
TFY modes in this work as bulk measurement is preferred for
our samples. The MOF-808-L-Cu samples were cooled down
with a He purge after each gas treatment in a 316-stainless
steel reactor. The reactor containing the sample was sealed
with a Swagelok valve and moved to an argon-filled glovebox
(H2O and O2 levels <1 ppm). The sample was unloaded and
pressed onto an indium foil using a hand press. Thereafter
these samples were transferred into an ultrahigh vacuum XAS
end station (10–9 torr) through our dedicated sample transfer
kit to avoid air exposure. Energies were aligned by
periodically collecting Ti L-edge spectra of a TiO2 (anatase)
reference for N K-edge. The XAS spectra were recorded over
a wide energy range covering energies well below and above
sample absorptions. The normalization was performed
following the established procedure: 1) I0-normalization: the
sample signal is divided by the incident intensity measured
from the sample drain current from a freshly coated gold mesh
inserted into the beam path before the X-rays can impinge on
the sample. 2) A linear, sloping background is removed by
fitting a line to the flat low energy region of the XAS spectrum,
i.e., at energies below any absorption peaks. 3) The spectrum
is normalized by setting the flat low energy region to zero and
the post edge to unity (unit edge jump).
activated
sample:
Calcd
for
Zr6O4(OH)4(C9H3O6)2
(HCOO)5(H2O)(OH)(C3H7NO)0.5: C, 21.17; H, 1.56; N, 0.50%;
Found: C, 21.18; H, 1.37; N, 0.44%.
Synthesis of MOF-808-Bzz.
A
solution of 5-
benzimidazolecarboxylic acid was prepared by dissolving 5-
benzimidazolecarboxylic acid (3 g) in DMSO (100 mL) in a
250 mL bottle in a 100 °C isothermal oven. MOF-808 (0.5 g)
was suspended by sonication in the solution of 5-
benzimidazolecarboxylic acid and the suspension was heated
in a 100 °C isothermal oven overnight. The reaction was
allowed to cool to room temperature. Brown powder was
collected by centrifugation (8,000 rpm, 3 min), washed with
DMSO 5 times (80 mL × 5) over 3 days and with acetone 5
times (80 mL × 5) over 3 days. Finally, MOF-808-Bzz was
dried under dynamic vacuum overnight at room temperature.
EA of activated sample: Calcd for Zr6O4(OH)4(C9H3O6)2
(C8H5N2O2)3.4(HCOO)1.6(OH)1(H2O)1: C, 32.15; H, 1.82; N,
5.45%; Found: C, 31.07; H, 2.61; N, 5.30%.
Synthesis of MOF-808-Bzz-Cu. A solution of CuI (99.999%
metals basis, 81.6 mg) in ACN (12.8 mL) was added to a
suspension of MOF-808-Bzz (75 mg) in ACN (1.9 mL) in a 20
mL vial while stirring (500 rpm) under ambient conditions.
The vial was sealed and the mixture was stirred for 3 days at
room temperature. Brown powder was collected by
centrifugation (8,000 rpm, 3 min) and washed with ACN 5
times (15 mL × 5) over 3 days. Finally, MOF-808-Bzz-Cu was
dried under dynamic vacuum overnight at room temperature.
ICP analysis: Cu/Zr molar ratio = 1.2.
Cu K-edge X-ray absorption spectroscopy data were collected
at the Advanced Light Source (ALS) bending-magnet
beamline 10.3.2 (2.1−17 keV) with the storage ring operating
ACS Paragon Plus Environment

Page 3 of 16
Journal of the American Chemical Society
at 500 mA and 1.9 GeV, using a Si(111) monochromator and of the metal binding ligands were frozen to simulate the
adjustable pre-monochromator slits.40 All data were collected
at room temperature (24 °C) in fluorescence mode at the Cu
K-edge (8980.48 eV). The incoming X-ray intensity (I0) was
measured in an ion chamber and the fluorescence emission
with a seven element LN2 cooled Ge solid state detector
(Canberra) using XIA electronics. A Cu foil was used to
calibrate the monochromator, with 1st derivative maximum set
at 8980.48 eV41 and an internal I0 glitch (present in all spectra)
was used to calibrate the data. The MOF-808-L-Cu samples
were cooled down with a He purge after each gas treatment in
a 316-stainless steel reactor. The reactor containing the sample
was sealed with a Swagelok valve and moved to an argon-
filled glovebox (H2O and O2 levels <1 ppm). The sample was
unloaded and sealed with Kapton tape for ex-situ
measurements. Cu K-edge XANES spectra were recorded in
fluorescence mode by continuously scanning the Si (111)
monochromator (Quick XAS mode) from 8,880 to 9,020 eV,
with 0.3 eV steps in the XANES region. All data were
processed using the LabVIEW custom BL 10.3.2 software to
perform dead time correction, energy calibration, and glitch
removal with detail procedure described elsewhere.42 XANES
spectra were processed with Athena software61 to find first
derivative peak (E0), pre-edge background subtraction and
post-edge normalization, align and merge the spectra. EXAFS
spectra were recorded up to 565 eV above the edge
(8,880−9,545 eV, i.e., up to k ≈ 12 Å−1) and 11 scans were
averaged. EXAFS spectra of samples were reduced with k1-,
k2-, and k3-weighting, out to k = 10 Å−1, and analyzed via
shell-by-shell fitting using the FEFF6l code and the Artemis
software where it yields minima in variances.43-44
rigidity of the framework. Minima of all geometry-optimized
structures were verified by having no imaginary frequency
found from analytical frequency calculation performed at the
same level of theory.
1
2
3
4
5
6
7
8
RESULTS AND DISCUSSION
Synthesis of the catalysts. MOF-808 is composed of 12-
connected cuboctahedron Zr6O4(OH)4(-COO)12 secondary
building units (SBUs) linked to the other SBUs by six
benzenetricarboxylates (BTC) with three above and three
below the ring of formates to form tetrahedral cages (Figure
1a). When linked, these cages form an adamantane-shaped
pore with formate, water and hydroxide molecules completing
the coordination spheres of Zr(IV) and pointing into the
pseudohexagonal pore openings (Figure 1b). Replacement of
these formate, water or hydroxide molecules with imidazole-
based ligands bearing carboxylic acid functionality will result
in imidazole units localizing in the center of the pores. These
ligands are spatially and precisely positioned for stabilizing
copper–oxygen species in the framework (Figure 1c).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Specifically, we synthesized microcrystalline MOF-808 to
allow for a facile diffusion of substrates during post-synthetic
modifications and catalysis.39 We selected three different
metal binding ligands comprising biologically relevant
imidazole units for incorporation into the framework to
demonstrate the modularity of our system and to study the
effects of ligand on the catalytic properties. Metal binding
ligands including L-histidine (His), 4-imidazoleacrylic acid
(Iza) and 5-benzimidazolecarboxylic acid (Bzz) were
incorporated into the framework by heating MOF-808 in
saturated solutions of these metal binding ligands to produce
MOF-808-L with -L being -His, -Iza and -Bzz, respectively.
The successful substitution of formate with these ligands in
Resonance Raman spectroscopy. In an argon-filled glovebox,
a solution of CuI (6.25 mg) dissolved in anhydrous ACN (0.98
mL) was added to a suspension of MOF-808-Bzz (5.77 mg) in
anhydrous ACN (0.14 mL) in a 1.5-mL GC autosampler vial
equipped with a PTFE/rubber septum. The vial was sealed and
removed from the glovebox. Either 16O2 (Praxair, 99.999%) or
18O2 (Aldrich, 99 atom%) was bubbled through the solution
using a needle pierced through the septum at a rate of ca. 30
mL min–1 for 10 min. The suspension was allowed to react at
room temperature for 3 days. The solid was collected by
centrifugation, dried overnight, transferred to an argon-filled
glovebox and washed with anhydrous ACN 5 times (2 mL × 5)
over 3 days. The sample was dried under dynamic vacuum
overnight at room temperature, and the dried solid was
transferred back to the glovebox. The sample was loaded into
a thin-wall quartz capillary tube and sealed with epoxy glue
for the measurements. All spectra were collected using the 407
nm light with the power density of 3.1 W/cm2. The Raman
scattering was collected using a Spex 1401 double grating
spectrograph and liquid nitrogen cooled Roper Scientific
LN/CCD 1100 controlled by ST133 controller. The measured
Raman shifts were calibrated by using Raman peaks of
cyclohexane.
1
the MOF was confirmed by H nuclear magnetic resonance
(NMR) of the digested samples (Section S2.1). Of the six
available sites per chemical formula, approximately half of
these were exchanged with the metal binding ligands to
produce MOF-808-His [Zr6O4(OH)4 (BTC)2(His)3.5(OH)2.5
(H2O)2.5], MOF-808-Iza [Zr6O4(OH)4 (BTC)2(Iza)3.7(HCOO)1.6
(OH)0.7(H2O)0.7] and MOF-808-Bzz [Zr6O4(OH)4(BTC)2
(Bzz)3.4(HCOO)1.6(OH)1(H2O)1]. Similar procedures were
performed on single crystals of MOF-808 for structural
elucidation of these functionalized MOFs. Single crystal X-ray
diffraction (SXRD) analysis reveals that these ligands bind to
the Zr clusters in a bridging fashion with carboxylate group
coordinating to Zr(IV) (Section S4) and thus placing imidazole
units in the center of the pseudohexagonal window. Metalation
of these MOFs with CuI in ACN under air at room
temperature provides the catalysts, namely MOF-808-His-Cu,
MOF-808-Iza-Cu and MOF-808-Bzz-Cu. Inductively coupled
plasma atomic emission spectroscopy (ICP-AES) analysis
performed on these catalysts indicates the Cu/Zr6 molar ratios
of 4.9, 6.0 and 7.1 for MOF-808-His-Cu, MOF-808-Iza-Cu
and MOF-808-Bzz-Cu, respectively (Table 1). A control
experiment was performed by metalation of MOF-808 under
similar condition. Negligible incorporation of copper was
observed (Cu/Zr6 molar ratio = 0.3) suggesting the role of
imidazole ligands in ligating to copper atoms. The phase
purity and crystallinity of the materials after post-synthetic
modifications were preserved as confirmed by powder X-ray
DFT calculations. The clusters were geometrically optimized
at the density functional theory (DFT) in gas phase using spin-
unrestricted B3LYP functional45-46 as implemented in
Gaussian 16 (revision A03) without symmetry constraints.47
The 6-31G basis sets were employed for C and H atoms while
6-311G(d) basis sets were used for Cu, N and O atoms.
Numerical integrations were performed on an ultrafine grid.
During geometry optimization, O atoms of carboxylate groups
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Design and synthesis of the catalysts bearing copper–oxygen complexes in MOF-808 for methane oxidation to methanol. (a)
Structure of MOF-808. (b) Pseudohexagonal pore opening of MOF-808. (c) Synthesis of the catalysts comprising the replacement of
formate with imidazole-containing ligands and metalation with Cu(I). Atom labeling scheme: C, black; O, red; N, green; Cu, orange; Zr,
blue polyhedra. H atoms are omitted for clarity. Orange spheres represent the space in the tetrahedral cages.
Table 1. Summary of catalyst compositions.
starting from room temperature to 150 °C at a ramping rate of
3 °C min–1. After a clean background was achieved by
monitoring the signals from a gas chromatograph, the catalyst
was treated with 3% N2O/He for 2 h at 150 °C followed by
purging the catalyst with He for 30 min. The catalyst was
subsequently exposed to a flow of CH4 for 1 h at 150 °C for
methane activation. After He purge, water was introduced in
the form of 3% steam in He at 150 °C to desorb methanol. As
shown in Figure 2a, the average methanol productivity
corresponds to 31.7 ± 13.0, 61.8 ± 17.5 and 71.8 ± 23.4 µmol
L/Zr6
Cu/Zr6
Cu/L
Catalyst
molar ratio molar ratio molar ratio
MOF-808-His-Cu
MOF-808-Iza-Cu
MOF-808-Bzz-Cu
MOF-808-Cu
3.5
3.7
3.4
-
4.9
6.0
7.1
0.3
1.4
1.6
2.1
-
-1
gMOF-808-L-Cu for MOF-808-His-Cu, MOF-808-Iza-Cu, and
MOF-808-Bzz-Cu, respectively; indicating that the MOF-808-
Bzz-Cu has the highest methanol productivity among three
catalysts. In terms of the turnover numbers (methanol
productivity per mole of copper), MOF-808-His-Cu exhibited
lower activity which is more likely due to lower number of
catalytically active copper–oxygen species (~43% lower
turnover number compared to MOF-808-Bzz-Cu), attributed
to the flexibility of histidine ligand. Another possible reason is
related the electronic properties of the active site which will be
discussed below.
diffraction (PXRD) analysis (Section S2.2). The porosity of
these materials was verified by N2 adsorption-desorption
isotherm measurements at 77 K with BET surface areas of 385,
580, and 580 m2 g–1 for MOF-808-His-Cu, MOF-808-Iza-Cu,
and MOF-808-Bzz-Cu, respectively (Section S2.3).
Methane oxidation. Methane oxidation was conducted with
an isothermal series of treatments at 150 °C. First, 100 mg of
MOF-808-L-Cu catalyst was pretreated in He flow to remove
residual solvents (i.e., ACN and water) at temperatures
ACS Paragon Plus Environment

Page 5 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. (a) Average with standard error of methanol productivity of MOF-808-His-Cu, MOF-808-Iza-Cu and MOF-808-Bzz-Cu. (b) Ex-
situ N K-edge XANES spectra of MOF-808-Bzz, as-synthesized MOF-808-Bzz-Cu and MOF-808-Bzz-Cu after the reactions with He, 3%
N2O/He, CH4 and 3% steam/He. (c) Ex-situ Cu K-edge XANES spectra of MOF-808-Bzz-Cu after the reactions with He, 3% N2O/He,
CH4 and 3% steam/He. (d) Resonance Raman spectra of MOF-808-Bzz-Cu synthesized using 16O2 and 18O2 with 407 nm laser. Note that
18O2 spectrum contain some 16O2 contamination.
Notably, only methanol and water were observed as products
during methanol desorption at temperatures below or equal to
150 °C. This was confirmed by gas chromatographs equipped
with flame ionization and thermal conductivity detectors and a
mass analyzer. Above this temperature, we observed increased
methanol production with temperature, as we expected due to
improved methanol extraction efficiency. However, CO2 was
also observed as a byproduct from the overoxidation of the
methanol generated (Figure S27). For the control experiments,
we did not observe any products in the experiments performed
on MOF-808-L and CuI (Cu(I) precursor in this study).
We performed recyclability test on MOF-808-Bzz-Cu with
an isothermal series of treatment at 150 °C (Figure S28). A
drastic deactivation was observed in the second and third cycle
giving methanol productivities of 7.5 µmol g-1 and 0.1 µmol g-
1, respectively. After the third cycle, MOF-808-Bzz-Cu was
subjected to a flow of He by increasing temperature from
150 °C to 250 °C at a ramping rate of 3 °C min–1 and hold for
10 min. Desorbed water was observed during this He
treatment until the temperature reaches 250 °C. We then
proceeded with the isothermal series of treatments at 150 °C;
the catalyst showed methanol productivity of 5.4 µmol g–1
which is similar to the productivity obtained from the second
cycle. This result indicates that the catalyst deactivation is due
to water molecules strongly bound to the active site. We also
performed the recyclability test of MOF-808-His-Cu. There is
a 77% decrease in methanol productivity from 28 µmol g–1 in
the first cycle to 6.3 µmol g–1 in the second cycle (Figure S29).
Unlike MOF-808-Bzz-Cu, the histidine-derived catalyst still
exhibits methanol productivity in the third and fourth cycle
with 17% and 12% decrease per cycle. Even though there is a
We examined the structural integrity of the catalysts after
the reactions. The crystallinity of the catalysts was maintained
as evidenced by PXRD (Figure S14). Interestingly, unlike
molecular copper–oxygen complexes,19 ligand hydroxylation
was not observed from digested 1H NMR of the catalysts even
at 150 °C, highlighting the significantly enhanced stability
imposed by covalent attachment of the complexes that are
geometrically constrained in the MOF.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 16
recyclability problem in MOF-808-L-Cu catalysts, it is ements of the samples after each step of the series of
1
2
3
4
noteworthy that this catalyst shows the highest reported
methanol productivity at 71.8 µmol g–1 with an isothermal
series of treatments at 150 °C with high selectivity to
methanol.48
treatments show that two absorption bands remain similar.
This indicates that the Cu atoms are coordinated to N atoms
throughout the catalytic process.
Ex-situ Cu K-edge XANES measurements were performed
to probe the oxidation states of copper during catalysis (Figure
2c). Four characteristic peaks located at 8979, 8984, 8989, and
8998 eV are observed. The pre-edge region is shown in the
inset of Figure 2c showing a weak absorption peak around
8979 eV corresponding to a dipole-forbidden Cu(II) 1s  3d
electronic transition.50 The shoulder peak at 8989 eV is
attributable to Cu(II) 1s  4p + L shakedown transition.51-52
Cu(I) 1s  4p + L shakedown feature is observed at 8984
eV.53 This data suggests that the catalysts are composed of a
mixture of Cu(I) and Cu(II) species. The He pretreatment at
150 °C resulted in a decrease in the white line intensity at
8998 eV along with an increase in the absorption peak
intensity at 8984 eV showing that the majority of Cu(II) is
reduced to Cu(I) by autoreduction.54-55 The spectrum recorded
after 3% N2O/He at 150 °C exhibits oxidation of Cu(I) to
Cu(II), indicative of the formation of the active copper–
oxygen species. After the reaction with methane at 150 °C, the
peak intensity of Cu(I) at 8984 eV increased while the white
line intensity decreased suggesting the reduction of Cu(II) to
Cu(I).
Identification of the active site in MOF-808-L-Cu. To
elucidate the identity of the active site of the catalysts, we
synthesized single crystals of MOF-808-L-Cu catalysts
following similar procedures employed for microcrystalline
samples. However, the active sites of the catalysts are
crystallographically disordered prohibiting an unambiguous
structural characterization using SXRD analysis (Section S4).
We therefore employed element- and structure-specific
techniques to determine the structures of the active sites.
Energy-dispersive X-ray spectroscopy (EDS) analysis of the
catalysts shows a uniform distribution of Zr, N and Cu atoms
throughout the crystals, thus precluding the localization of the
active sites on the surface of the MOF crystals (Section S2.5).
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
We carried out N K-edge X-ray absorption near edge
structure (XANES), Cu K-edge X-ray absorption spectroscopy
(XAS), UV-Vis diffuse reflectance spectroscopy (DRS) and
resonance Raman spectroscopy measurements on three MOF-
808-L-Cu catalysts (detailed spectroscopic data can be found
in SI). These catalysts show similar trends in the spectroscopic
features unless otherwise noted. We therefore use MOF-808-
Bzz-Cu as a representative in the following discussion.
Comparison of N K-edge XANES spectra of MOF-808-Bzz
and MOF-808-Bzz-Cu provides insight into the location of
copper in the MOF catalysts (Figure 2b). Two absorption
bands at 398.8 and 400.6 eV are observed, assignable to the 1s
 π* transitions of the nitrogen atoms in C-NH-C and C-N=C
of imidazole ring, respectively.49 After the metalation, two
absorption peaks are shifted and changed in intensity,
indicating that Cu atoms are coordinated to N atoms that are
part of the imidazole units. Ex-situ N K-edge XANES measur-
Figure 3. DFT optimized structure of the proposed active site in
1
MOF-808-Bzz-Cu. From ICP, H NMR, and N K-edge XANES,
each N atoms of the ligands is coordinated to one copper atoms.
However, copper in bis(μ-oxo) dicopper is known to be four-
coordinated.17 We propose that the fourth ligand coordinating to
Figure 4. The series of k2-weighted Cu-EXAFS spectra of MOF-
808-Bzz-Cu (black line) and best fit (red line) in k-space (left) and
R-space (right) without phase correction after the reactions with
(a,b) He; (c,d) 3% N2O/He; (e,f) CH4 and (g,h) 3% steam/He at
150 °C. Fitting was conducted using N scatter. Fit range: 3 < k <
10 Å-1; 1 < R < 4 Å; Fit window: Hanning.
copper is
a
neutral ligand such as water or N,N-
dimethylformamide molecules as we observed the latter molecule
1
in the H NMR spectra of the digested samples after activation
(only the optimized structure of the active site is shown, while the
remaining atoms of the MOF-808 are omitted for clarity). Atom
labeling scheme: C, black; O, red; N, green; H, white; Cu, orange.
ACS Paragon Plus Environment

Page 7 of 16
Journal of the American Chemical Society
Table 2. Cu EXAFS fitting result of MOF-808-Bzz-Cu with a series of treatments.
1
2
Ab-Sc paira
Nb
Rc
DWFd
R-factore
0.019
3
4
5
6
MOF-808-Bzz-Cu, He treated at 150 °C
Cu-N/(O) SSf
Cu∙∙∙Cu SS
2.9
0.6
1.94േ0.02
2.51േ0.04
0.0080േ0.0025
0.0146േ0.0065
MOF-808-Bzz-Cu, N2O treated at 150 °C
7
Cu-N/(O) SS
Cu∙∙∙Cu SS
3.7
0.4
1.94േ0.02
2.49േ0.10
0.0070േ0.0025
0.0156േ0.0149
8
9
0.021
0.020
0.018
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
MOF-808-Bzz-Cu, CH4 treated at 150 °C
Cu-N/(O) SS
Cu∙∙∙Cu SS
3.3
0.5
1.94േ0.02
2.51േ0.07
0.0072േ0.0025
0.0151േ0.0102
MOF-808-Bzz-Cu, Steam treated at 150 °C
Cu-N/(O) SS
3.9
1.95േ0.01
2.53േ0.10
0.0058േ0.0022
0.0169േ0.0151
Cu∙∙∙Cu SS
0.5
aAb = absorber; Sc = scatterer. b Coordination number. c Distance (Å). d Debye-Waller factor (Å2). eA measure of mean square sum
of the misfit at each data point. f SS = single scattering; Fitting was conducted using N scatter. Fit range: 3 < k < 10 Å-1; 1 < R < 4 Å;
Fit window: Hanning.
This reduction could be ascribed to either homolytic cleavage
C–H bond followed by direct radical rebound route56 or Lewis
acid/base pair adsorption of methane where oxygen atoms of
the active copper–oxygen species reacted with methane.7, 57
After methanol desorption was performed by flowing 3%
steam/He at 150 °C into the catalyst, the white line intensity
increased accompanied by decreasing intensity of the peak of
Cu(I) at 8984 eV. This redox behavior of copper observed
from Cu K-edge XANES further proves that the copper active
site in our catalysts participates in methane oxidation to
methanol. MOF-808-Iza-Cu also shows distinctive changes in
the oxidation state of copper following the same trend through
the course of the catalytic process as described for MOF-808-
Bzz-Cu. MOF-808-His-Cu, however, shows minor intensity
changes, consistent with the lower methanol productivity as
previously described (Figure 2a).
vibrational energy from the reported values17 can be ascribed
to the variation in the geometric parameters of the dicopper
species due to the framework constraints.
With the information of the location of the ligands (Section
S4) and the identity of active copper–oxygen sites, we
modeled the active sites using the framework as a constraint
and geometrically optimized the models using density
functional theory (DFT) calculations. Following the digested
1H NMR data where ~3 ligand molecules were incorporated
per chemical formula, these ligands were placed on the Zr
cluster on the pseudohexagonal window in a way such that
these ligands pose a minimal steric hindrance to each other.
Cu atoms were then allowed to coordinate to N atoms of
imidazole units, and the Cu atoms were further coordinated to
O2 to form N-Cu2O2-N species (Section S6). Geometrical
optimization indicates that bis(μ-oxo) dicopper species can
reside in the framework in all MOF-808-L-Cu structures
(Figure 3). Of particular note, the Raman shifts relevant to O2
are in close agreement with the experimental data confirming
the presence of bis(μ-oxo) dicopper species in the catalysts
(Section S6).
Figure 4 depicts the k2-weighted and Fourier transforms
without phase correction of the extended X-ray absorption fine
structure (EXAFS) data measured at the Cu K-edge of the
MOF-808-Bzz-Cu. The spectra were recorded after the
successive treatment with (a) He, (b) 3% N2O/He, (c) CH4 and,
(d) 3% steam/He at 150 °C. We used the DFT-optimized
cluster as a model to fit the experimental Cu EXAFS spectra.
The full EXAFS data were analyzed in k- and R-space using a
combined k1-k2-k3 fitting procedure for reliable analysis.62 The
best fits are presented in Figure 4 and the respective fitted
parameters are reported in Table 2. In the He treated sample,
the first shell is assigned to Cu-N/(O) coordination with the
coordination number of 2.9 at distance of 1.94 Å. It should be
noted that N and O atoms are indistinguishable from EXAFS
analysis as they have similar atomic scattering factors. For the
second shell, we identified the scatterer by fitting the EXAFS
data with Cu, C, N and O and only Cu could be fitted with
reasonable fitting statistics. Copper was found at distance of
2.51 Å with the coordination number of 0.6. This result
To gain more information about the active copper–oxygen
species, UV-Vis DRS was performed. Background subtracted
UV-Vis DRS spectra of the as-synthesized samples show the
absorption band centered at ~400 nm. After 3% N2O/He
treatment at 150 °C, we observed the increase of this
absorption band (Section S5.1) corresponding to oxygen-to-
metal charge-transfer transition.58-61 To definitively
characterize this copper–oxygen species, we turned to
resonance Raman spectroscopy measurement because each
copper–oxygen species have characteristic Raman shifts
(Section S8).16-17 We prepared the samples by synthesizing
MOF-808-L-Cu in an argon-filled glovebox and oxygenating
the samples with either 16O2 or 18O2 gas at room temperature.
Figure 2d shows the isotope-dependent Raman peaks at ~560
and ~640 cm–1 by using an excitation wavelength of 407 nm
which is resonant at the charge-transfer band. These peaks are
assigned to Cu–O bonds vibration in the core breathing mode
of bis(μ-oxo) dicopper species (SI, Section S6). In the 18O2-
labeled samples, these Raman peaks are shifted to ~545 cm–1
and ~630 cm–1. This isotope-dependent trend is verified for all
three MOF-808-L-Cu (Figure 2d and Figures S37 and S39).
Ex-situ resonance Raman spectroscopy of the samples after the
treatments in He and 3% N2O/He display similar Raman peaks,
indicating that bis(μ-oxo) dicopper species are preserved prior
to the methane activation. The deviation (~20 cm–1) in the
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 16
suggests that copper site is present as dinuclear and a short
Author Contributions
1
2
3
4
5
6
7
8
distance of CuꞏꞏꞏCu supports the presence of bis(μ-oxo)
dicopper species. Contrary to a formal Cu(III) oxidation state
typically assigned for bis(μ-oxo) dicopper species,63-64 the
oxidation state of active copper in our catalysts appears to be
close to Cu(II). This discrepancy can be ascribed to the high
electron density provided by the imidazole ligand to the Cu
centers. The bond valence sum analysis (BVS) (Tables S5–S7)
further indicates the actual charge being close to 2-fold.53, 65-66
Oxidation of the catalyst in 3% N2O/He at 150 °C leads to 0.8
increase of the Cu-N/(O) coordination while its distance
remains at 1.94 Å indicating the additional formation of bis(μ-
oxo) dicopper species. BVS analysis further sheds light on the
difference in electronic properties leading to varying catalytic
properties among three catalysts. From this analysis, the
oxidation state of copper in MOF-808-His-Cu is slightly lower
than that in MOF-808-Iza-Cu and in MOF-808-Bzz-Cu which
agrees with the trend of Mulliken charges of these catalysts
determined from DFT calculations (Figures S49–S51). These
results suggest that Cu active sites in MOF-808-His-Cu have
lower oxidizing power compared to the other two. After
methane treatment, there is a slight decrease in Cu-N/(O)
coordination and after methanol extraction, Cu-N/(O)
#These authors (J. Baek and B. Rungtaweevoranit)
contributed equally to this work.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
The research performed in the O.M.Y. laboratory was
supported by BASF SE (Ludwigshafen, Germany) and King
Abdulaziz City for Science and Technology. G.A.S.
acknowledges support from the Director, Office of Basic
Energy Sciences, Division of Chemical Sciences, Geological
and Biosciences of the U.S. Department of Energy under
contract No. DE‐AC02‐05CH11231. Research work at the
Molecular Foundry was supported by the Office of Science,
Office of Basic Energy Sciences, of the DOE under Contract
No. DE‐AC02‐05CH11231. The Advanced Light Source (ALS)
is supported by the Director, Office of Science, Office of
Basic Energy Sciences, of the U.S. Department of Energy
under Contract DE‐AC02‐05CH11231. The Molecular Graphics
and Computation Facility is funded by the NIH
(S10OD023532). The AVB‐400 NMR spectrometer is partially
supported by NSF Grant CHE‐0130862. We thank Drs.
Philipp Urban, Dave Small, Kathleen A. Durkin, Georgios
Katsoukis and Tae Yong Kim for discussions and Drs. Simon
J. Teat and Laura J. McCormick for synchrotron X‐ray
diffraction data acquisition support. B.R. is supported by the
Royal Thai Government Scholarship.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
coordination increases by 0.6.
However, Cu-N/(O)
coordination in MOF-808-His-Cu and MOF-808-Iza-Cu
remains similar after treatment with methane and steam.
CONCLUSION
We show that, by selection of MOF with appropriate structure
and topology, MOF-808 can be utilized as a scaffold to host
and stabilize highly active copper–oxygen complexes, bis(μ-
oxo) dicopper species, ligated to biologically relevant
imidazole moieties including L-histidine (His), 4-
imidazoleacrylic acid (Iza) and 5-benzimidazolecarboxylic
acid (Bzz) inspired by pMMO. The catalysts show high
selectivity for methane oxidation to methanol under isothermal
condition at 150 °C. We anticipate that the strategy reported
here will serve as a blueprint for other bioinspired catalysts in
MOFs for a broad array of catalytic transformations.
REFERENCES
1.
Periana, R. A.; Taube, D. J.; Evitt, E. R.; Löffler, D.
G.; Wentrcek, P. R.; Voss, G.; Masuda, T., A mercury-
catalyzed, high-yield system for the oxidation of methane to
methanol. Science 1993, 259 (5093), 340-343.
2.
Groothaert, M. H.; Smeets, P. J.; Sels, B. F.; Jacobs,
P. A.; Schoonheydt, R. A., Selective oxidation of methane by
the bis(μ-oxo) dicopper core stabilized on ZSM-5 and
mordenite zeolites. J. Am. Chem. Soc. 2005, 127 (5), 1394-
1395.
3.
Woertink, J. S.; Smeets, P. J.; Groothaert, M. H.;
Vance, M. A.; Sels, B. F.; Schoonheydt, R. A.; Solomon, E. I.,
A [Cu2O]2+ core in Cu-ZSM-5, the active site in the oxidation
of methane to methanol. Proc. Natl. Acad. Sci. U.S.A. 2009,
106 (45), 18908-18913.
ASSOCIATED CONTENT
Supporting Information. The Supporting Information is
available free of charge on the ACS Publications website.
4.
Hammond, C.; Forde, M. M.; Rahim, A.; Hasbi, M.;
Detailed
description
of
synthesis,
materials
Thetford, A.; He, Q.; Jenkins, R. L.; Dimitratos, N.; Lopez‐
Sanchez, J. A.; Dummer, N. F., Direct Catalytic Conversion of
Methane to Methanol in an Aqueous Medium by using
Copper‐Promoted Fe‐ZSM‐5. Angew. Chem. Int. Ed. 2012, 51
(21), 5129-5133.
characterization, catalysis, single crystal X‐ray
diffraction analyses, UV‐Vis diffuse reflectance and
resonance Raman spectroscopy, density functional
theory calculations, X‐ray absorption spectroscopy,
charge distribution, and identification of the active site
(PDF)
5.
Grundner, S.; Markovits, M. A.; Li, G.; Tromp, M.;
Pidko, E. A.; Hensen, E. J.; Jentys, A.; Sanchez-Sanchez, M.;
Lercher, J. A., Single-site trinuclear copper oxygen clusters in
mordenite for selective conversion of methane to methanol.
Nat. Commun. 2015, 6, 7546.
X‐ray crystallographic data for MOF‐808‐His, MOF‐
808‐Iza, and MOF‐808‐Bzz structures (CIF)
6.
Narsimhan, K.; Iyoki, K.; Dinh, K.; Román-
AUTHOR INFORMATION
Corresponding Author
*To whom correspondence should be addressed.
Email: yaghi@berkeley.edu, somorjai@berkeley.edu
Leshkov, Y., Catalytic oxidation of methane into methanol
over copper-exchanged zeolites with oxygen at low
temperature. ACS Cent. Sci. 2016, 2 (6), 424-429.
7.
Sushkevich, V. L.; Palagin, D.; Ranocchiari, M.; van
Bokhoven, J. A., Selective anaerobic oxidation of methane
ACS Paragon Plus Environment

Page 9 of 16
Journal of the American Chemical Society
enables direct synthesis of methanol. Science 2017, 356 (6337),
methane to methanol. ACS Catalysis 2018, 8 (6), 5542-5548.
23. Wang, V. C.-C.; Maji, S.; Chen, P. P.-Y.; Lee, H. K.;
Yu, S. S.-F.; Chan, S. I., Alkane oxidation: Methane
monooxygenases, related enzymes, and their biomimetics.
Chem. Rev. 2017, 117 (13), 8574-8621.
1
2
3
4
5
6
7
8
523-527.
8.
Tomkins, P.; Mansouri, A.; Bozbag, S. E.; Krumeich,
F.; Park, M. B.; Alayon, E. M. C.; Ranocchiari, M.; van
Bokhoven, J. A., Isothermal Cyclic Conversion of Methane
into Methanol over Copper‐Exchanged Zeolite at Low
Temperature. Angew. Chem. 2016, 128 (18), 5557-5561.
24.
Lu, Y.; Yeung, N.; Sieracki, N.; Marshall, N. M.,
Design of functional metalloproteins. Nature 2009, 460 (7257),
855.
9.
Lawton, T. J.; Rosenzweig, A. C., Methane-
oxidizing enzymes: an upstream problem in biological gas-to-
liquids conversion. J. Am. Chem. Soc. 2016, 138 (30), 9327-
9340.
25.
Lillerud, K. P.; Olsbye, U.; Tilset, M., Designing
heterogeneous catalysts by incorporating enzyme-like
functionalities into MOFs. Top. Catal. 2010, 53 (13-14), 859-
868.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10.
Ravi, M.; Ranocchiari, M.; van Bokhoven, J. A., A
Critical Assessment of the Direct Catalytic Oxidation of
Methane to Methanol. Angew. Chem. Int. Ed. 2017, 56 (52),
16464-16483.
26.
Xiao, D. J.; Bloch, E. D.; Mason, J. A.; Queen, W.
L.; Hudson, M. R.; Planas, N.; Borycz, J.; Dzubak, A. L.;
Verma, P.; Lee, K., Oxidation of ethane to ethanol by N2O in a
metal–organic framework with coordinatively unsaturated iron
(II) sites. Nat. Chem. 2014, 6 (7), 590.
11.
Schoedel, A.; Ji, Z.; Yaghi, O. M., The role of
metal–organic frameworks in a carbon-neutral energy cycle.
Nature Energy 2016, 1, 16034.
27.
Gu, Z. Y.; Park, J.; Raiff, A.; Wei, Z.; Zhou, H. C.,
12.
Balasubramanian, R.; Smith, S. M.; Rawat, S.;
Metal–organic frameworks as biomimetic catalysts.
ChemCatChem 2014, 6 (1), 67-75.
28.
O. M., The chemistry and applications of metal-organic
frameworks. Science 2013, 341 (6149), 1230444.
29.
J.; Yaghi, O. M., Spiers Memorial Lecture: Progress and
prospects of reticular chemistry. Faraday Discuss. 2017, 201,
9-45.
30.
Dependent Materials. Acc. Chem. Res. 2017, 50 (3), 532-534.
31. Fracaroli, A. M.; Siman, P.; Nagib, D. A.; Suzuki,
M.; Furukawa, H.; Toste, F. D.; Yaghi, O. M., Seven post-
synthetic covalent reactions in tandem leading to enzyme-like
complexity within metal–organic framework crystals. J. Am.
Chem. Soc. 2016, 138 (27), 8352-8355.
Yatsunyk, L. A.; Stemmler, T. L.; Rosenzweig, A. C.,
Oxidation of methane by a biological dicopper centre. Nature
2010, 465 (7294), 115.
Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi,
13.
Culpepper, M. A.; Cutsail III, G. E.; Hoffman, B.
M.; Rosenzweig, A. C., Evidence for oxygen binding at the
active site of particulate methane monooxygenase. J. Am.
Chem. Soc. 2012, 134 (18), 7640-7643.
Rungtaweevoranit, B.; Diercks, C. S.; Kalmutzki, M.
14.
Culpepper, M. A.; Cutsail III, G. E.; Gunderson, W.
A.; Hoffman, B. M.; Rosenzweig, A. C., Identification of the
valence and coordination environment of the particulate
methane monooxygenase copper centers by advanced EPR
characterization. J. Am. Chem. Soc. 2014, 136 (33), 11767-
11775.
Osborn Popp, T. M.; Yaghi, O. M., Sequence-
15.
Cao, L.; Caldararu, O.; Rosenzweig, A. C.; Ryde, U.,
Quantum Refinement Does Not Support Dinuclear Copper
Sites in Crystal Structures of Particulate Methane
Monooxygenase. Angew. Chem. Int. Ed. 2018, 57 (1), 162-166.
32.
O’Keeffe, M.; Yaghi, O. M., Deconstructing the
crystal structures of metal–organic frameworks and related
materials into their underlying nets. Chem. Rev. 2011, 112 (2),
675-702.
16.
Elwell, C. E.; Gagnon, N. L.; Neisen, B. D.; Dhar,
D.; Spaeth, A. D.; Yee, G. M.; Tolman, W. B., Copper–oxygen
complexes revisited: structures, spectroscopy, and reactivity.
Chem. Rev. 2017, 117 (3), 2059-2107.
33.
Lee, S.; Kapustin, E. A.; Yaghi, O. M., Coordinative
alignment of molecules in chiral metal-organic frameworks.
Science 2016, 353 (6301), 808-811.
34.
Bury, W.; Snurr, R. Q.; Hupp, J. T.; Farha, O. K.,
Perfluoroalkane functionalization of NU-1000 via solvent-
assisted ligand incorporation: synthesis and CO2 adsorption
studies. J. Am. Chem. Soc. 2013, 135 (45), 16801-16804.
17.
Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P.,
Structure and spectroscopy of copper−dioxygen complexes.
Chem. Rev. 2004, 104 (2), 1013-1046.
Deria, P.; Mondloch, J. E.; Tylianakis, E.; Ghosh, P.;
18.
Solomon, E. I.; Ginsbach, J. W.; Heppner, D. E.;
Kieber-Emmons, M. T.; Kjaergaard, C. H.; Smeets, P. J.; Tian,
L.; Woertink, J. S., Copper dioxygen (bio) inorganic chemistry.
Faraday Discuss. 2011, 148, 11-39.
35.
Yuan, S.; Lu, W.; Chen, Y.-P.; Zhang, Q.; Liu, T.-F.;
19.
Citek, C.; Herres-Pawlis, S.; Stack, T. D. P., Low
Feng, D.; Wang, X.; Qin, J.; Zhou, H.-C., Sequential linker
installation: precise placement of functional groups in
multivariate metal–organic frameworks. J. Am. Chem. Soc.
2015, 137 (9), 3177-3180.
temperature syntheses and reactivity of Cu2O2 active-site
models. Acc. Chem. Res. 2015, 48 (8), 2424-2433.
20.
Que Jr, L.; Tolman, W. B., Bis(μ‐oxo) dimetal
36.
Manna, K.; Zhang, T.; Lin, W., Postsynthetic
“Diamond” Cores in Copper and Iron Complexes Relevant to
Biocatalysis. Angew. Chem. Int. Ed. 2002, 41 (7), 1114-1137.
metalation of bipyridyl-containing metal–organic frameworks
for highly efficient catalytic organic transformations. J. Am.
Chem. Soc. 2014, 136 (18), 6566-6569.
21.
Pappas, D. K.; Borfecchia, E.; Dyballa, M.; Pankin,
I. A.; Lomachenko, K. A.; Martini, A.; Signorile, M.; Teketel,
S.; Arstad, B.; Berlier, G., Methane to Methanol: Structure–
Activity Relationships for Cu-CHA. J. Am. Chem. Soc. 2017,
139 (42), 14961-14975.
37.
Doonan, C. J.; Morris, W.; Furukawa, H.; Yaghi, O.
M., Isoreticular Metalation of Metal− Organic Frameworks. J.
Am. Chem. Soc. 2009, 131 (27), 9492-9493.
38.
Queen, W. L.; Hudson, M. R.; Yaghi, O. M., Water adsorption
in porous metal–organic frameworks and related materials. J.
Am. Chem. Soc. 2014, 136 (11), 4369-4381.
Furukawa, H.; Gándara, F.; Zhang, Y.-B.; Jiang, J.;
22.
Osadchii, D.; Olivos Suarez, A. I.; Szécsényi, Á.; Li,
G.; Nasalevich, M. A.; Dugulan, A. I.; Serra-Crespo, P.;
Hensen, E. J.; Veber, S. L.; Fedin, M. V., Isolated Fe sites in
Metal Organic Framework catalyze the direct conversion of
39.
Choi, K. M.; Jeong, H. M.; Park, J. H.; Zhang, Y.-B.;
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 16
Kang, J. K.; Yaghi, O. M., Supercapacitors of nanocrystalline
metal–organic frameworks. ACS Nano 2014, 8 (7), 7451-7457.
40. Marcus, M. A.; MacDowell, A. A.; Celestre, R.;
Manceau, A.; Miller, T.; Padmore, H. A.; Sublett, R. E.,
Beamline 10.3. 2 at ALS: a hard X-ray microprobe for
environmental and materials sciences. J. Synchrotron Radiat.
2004, 11 (3), 239-247.
and ligand K-edge studies to probe the origin of the EPR
hyperfine splitting in plastocyanin. J. Am. Chem. Soc. 1993,
115 (2), 767-776.
1
2
3
4
5
6
7
8
52.
Kau, L. S.; Hodgson, K. O.; Solomon, E. I., X-ray
absorption edge and EXAFS study of the copper sites in zinc
oxide methanol synthesis catalysts. J. Am. Chem. Soc. 1989,
111 (18), 7103-7109.
41.
Kraft, S.; Stümpel, J.; Becker, P.; Kuetgens, U.,
53.
Groothaert, M. H.; van Bokhoven, J. A.; Battiston,
High resolution x‐ray absorption spectroscopy with absolute
energy calibration for the determination of absorption edge
energies. Rev. Sci. Instrum. 1996, 67 (3), 681-687.
A. A.; Weckhuysen, B. M.; Schoonheydt, R. A., Bis(μ-oxo)
dicopper in Cu-ZSM-5 and its role in the decomposition of
NO: a combined in situ XAFS, UV− Vis− Near-IR, and kinetic
study. J. Am. Chem. Soc. 2003, 125 (25), 7629-7640.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
42.
Kelly, S.; Hesterberg, D.; Ravel, B., Analysis of
soils and minerals using X-ray absorption spectroscopy.
Methods of soil analysis. Part 5. Mineralogical methods 2008,
5, 387-464.
54.
Trout, B. L.; Chakraborty, A. K.; Bell, A. T., Local
spin density functional theory study of copper ion-exchanged
ZSM-5. J. Phys. Chem. 1996, 100 (10), 4173-4179.
55.
Ranocchiari, M.; van Bokhoven, J. A., Bis(μ-oxo) versus
mono (μ-oxo) dicopper cores in a zeolite for converting
methane to methanol: an in situ XAS and DFT investigation.
PCCP 2015, 17 (12), 7681-7693.
43.
Ravel, B.; Newville, M., ATHENA, ARTEMIS,
Alayon, E. M. C.; Nachtegaal, M.; Bodi, A.;
HEPHAESTUS: data analysis for X-ray absorption
spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12
(4), 537-541.
44.
and FEFF fitting. J. Synchrotron Radiat. 2001, 8 (2), 322-324.
45. Becke, A. D., Density‐functional thermochemistry.
Newville, M., IFEFFIT: interactive XAFS analysis
56.
Li, G.; Vassilev, P.; Sanchez-Sanchez, M.; Lercher, J.
A.; Hensen, E. J.; Pidko, E. A., Stability and reactivity of
copper oxo-clusters in ZSM-5 zeolite for selective methane
oxidation to methanol. J. Catal. 2016, 338, 305-312.
III. The role of exact exchange. J. Chem. Phys. 1993, 98 (7),
5648-5652.
46.
Lee, C.; Yang, W.; Parr, R. G., Development of the
57.
Olivos-Suarez, A. I.; Szécsényi, A. g.; Hensen, E. J.;
Colle-Salvetti correlation-energy formula into a functional of
the electron density. Phys. Rev. B 1988, 37 (2), 785.
Ruiz-Martinez, J.; Pidko, E. A.; Gascon, J., Strategies for the
direct catalytic valorization of methane using heterogeneous
catalysis: challenges and opportunities. ACS Catalysis 2016, 6
(5), 2965-2981.
47.
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;
Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.;
Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato,
M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.;
Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.;
Sonnenberg, J. L.; Williams; Ding, F.; Lipparini, F.; Egidi, F.;
Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe,
D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.;
Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Vreven, T.; Throssell, K.; Montgomery Jr., J. A.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.;
Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.;
Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.;
Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.;
Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J.
Gaussian 16 Rev. A.03, Wallingford, CT, 2016.
58.
Mahadevan, V.; Hou, Z.; Cole, A. P.; Root, D. E.;
Lal, T. K.; Solomon, E. I.; Stack, T., Irreversible Reduction of
Dioxygen by Simple Peralkylated Diamine−Copper (I)
Complexes: Characterization and Thermal Stability of a
[Cu2(μ-O)2]2+ Core. J. Am. Chem. Soc. 1997, 119 (49), 11996-
11997.
59.
Hedman, B.; Solomon, E. I.; Stack, T. D. P., Bis(μ-oxo)
dicopper (III) species of the simplest peralkylated diamine:
enhanced reactivity toward exogenous substrates. Inorg. Chem.
2010, 49 (23), 11030-11038.
Kang, P.; Bobyr, E.; Dustman, J.; Hodgson, K. O.;
60.
Smeets, P. J.; Hadt, R. G.; Woertink, J. S.;
Vanelderen, P.; Schoonheydt, R. A.; Sels, B. F.; Solomon, E. I.,
Oxygen precursor to the reactive intermediate in methanol
synthesis by Cu-ZSM-5. J. Am. Chem. Soc. 2010, 132 (42),
14736-14738.
48.
Ikuno, T.; Zheng, J.; Vjunov, A.; Sanchez-Sanchez,
61.
Kim, Y.; Kim, T. Y.; Lee, H.; Yi, J., Distinct
M.; Ortuño, M. A.; Pahls, D. R.; Fulton, J. L.; Camaioni, D.
M.; Li, Z.; Ray, D., Methane Oxidation to Methanol Catalyzed
by Cu-oxo Clusters Stabilized in NU-1000 Metal–Organic
Framework. J. Am. Chem. Soc. 2017, 139 (30), 10294-10301.
activation of Cu-MOR for direct oxidation of methane to
methanol. Chem. Commun. 2017, 53 (29), 4116-4119.
62.
Bitter, J. H.; van Koten, G.; Koningsberger, D. C., Cu K‐Edge
EXAFS Characterisation of Copper (I) Arenethiolate
Complexes in both the Solid and Liquid State: Detection of
Cu−Cu Coordination. Chem. Eur. J. 2002, 8 (24), 5667-5678.
Tromp, M.; van Bokhoven, J. A.; Arink, A. M.;
49.
Zubavichus, Y.; Shaporenko, A.; Grunze, M.;
Zharnikov, M., Innershell absorption spectroscopy of amino
acids at all relevant absorption edges. J. Phys. Chem. A 2005,
109 (32), 6998-7000.
63.
Herres-Pawlis, S.; Verma, P.; Haase, R.; Kang, P.;
50.
Kau, L. S.; Spira-Solomon, D. J.; Penner-Hahn, J.
Lyons, C. T.; Wasinger, E. C.; Flörke, U.; Henkel, G.; Stack, T.
E.; Hodgson, K. O.; Solomon, E. I., X-ray absorption edge
determination of the oxidation state and coordination number
of copper. Application to the type 3 site in Rhus vernicifera
laccase and its reaction with oxygen. J. Am. Chem. Soc. 1987,
109 (21), 6433-6442.
D. P., Phenolate hydroxylation in a bis(μ-oxo) dicopper (III)
complex: lessons from the guanidine/amine series. J. Am.
Chem. Soc. 2009, 131 (3), 1154-1169.
64.
DuBois, J. L.; Mukherjee, P.; Stack, T.; Hedman, B.;
51.
Shadle, S. E.; Penner-Hahn, J. E.; Schugar, H. J.;
Solomon, E. I.; Hodgson, K. O., A systematic K-edge X-ray
absorption spectroscopic study of Cu (III) sites. J. Am. Chem.
Soc. 2000, 122 (24), 5775-5787.
Hedman, B.; Hodgson, K. O.; Solomon, E. I., X-ray
absorption spectroscopic studies of the blue copper site: metal
ACS Paragon Plus Environment

Page 11 of 16
Journal of the American Chemical Society
65.
Hati, S.; Datta, D., Nature of the active sites in
copper-mediated dioxygen activation. J. Am. Chem. Soc. 1996,
118 (46), 11555-11574.
1
2
3
4
5
6
7
haemocyanin and iron nickel hydrogenases: the bond valence
sum approach. J. Chem. Soc., Dalton Trans. 1995, (7), 1177-
1182.
66.
Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan,
G.; Wang, X.; Young, V. G.; Cramer, C. J.; Que, L.; Tolman, W.
B., Structural, spectroscopic, and theoretical characterization
of bis(μ-oxo) dicopper complexes, novel intermediates in
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 16
1
2
3
Insert Table of Contents artwork here
4
5
CH3OH
6
7
8
CH4
N
O
9
N
Cu
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
N2
Cu
N2O
pMMO-inspired
bis(μ-oxo) dicopper
MOF catalyst
12
ACS Paragon Plus Environment

Page 13 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Design and synthesis of the catalysts bearing copper–oxygen complexes in MOF-808 for methane
oxidation to methanol. (a) Structure of MOF-808. (b) Pseudohexagonal pore opening of MOF-808. (c)
Synthesis of the catalysts comprising the replacement of formate with imidazole-containing ligands and
metalation with Cu(I). Atom labeling scheme: C, black; O, red; N, green; Cu, orange; Zr, blue polyhedra. H
atoms are omitted for clarity. Orange spheres represent the space in the tetrahedral cages.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 14 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. (a) Average with standard error of methanol productivity of MOF-808-His-Cu, MOF-808-Iza-Cu and
MOF-808-Bzz-Cu. (b) Ex-situ N K-edge XANES spectra of MOF-808-Bzz, as-synthesized MOF-808-Bzz-Cu
and MOF-808-Bzz-Cu after the reactions with He, 3% N O/He, CH and 3% steam/He. (c) Ex-situ Cu K-edge
2
4
XANES spectra of MOF-808-Bzz-Cu after the reactions with He, 3% N O/He, CH and 3% steam/He. (d)
2
4
16
18
Resonance Raman spectra of MOF-808-Bzz-Cu synthesized using O and O with 407 nm laser. Note
2
2
18
16
that O spectrum contain some O contamination.
2
2
ACS Paragon Plus Environment

Page 15 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
Figure 3. DFT optimized structure of the proposed active site in MOF-808-Bzz-Cu. From ICP, H NMR, and N
K-edge XANES, each N atoms of the ligands is coordinated to one copper atoms. However, copper in bis(μ-
oxo) dicopper is known to be four-coordinated. We propose that the fourth ligand coordinating to copper is a
neutral ligand such as water or N,N-dimethylformamide molecules as we observed the latter molecule in the
1
H NMR spectra of the digested samples after activation (only the optimized structure of the active site is
shown, while the remaining atoms of the MOF-808 are omitted for clarity). Atom labeling scheme: C, black;
O, red; N, green; H, white; Cu, orange.
169x122mm (300 x 300 DPI)
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 16 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
Figure 4. The series of k -weighted Cu-EXAFS spectra of MOF-808-Bzz-Cu (black line) and best fit (red line)
in k-space (left) and R-space (right) without phase correction after the reactions with (a,b) He; (c,d) 3%
N O/He; (e,f) CH and (g,h) 3% steam/He at 150 °C. Fitting was conducted using N scatter. Fit range: 3 <
2
4
-1
k < 10 Å ; 1 < R < 4 Å; Fit window: Hanning.
169x230mm (300 x 300 DPI)
ACS Paragon Plus Environment