Atomically Dispersed Copper Sites in a Metal-Organic Framework for Reduction of Nitrogen Dioxide

Article abstract of DOI:10.1021/jacs.1c03036

Metal-organic framework (MOF) materials provide an excellent platform to fabricate single-atom catalysts due to their structural diversity, intrinsic porosity, and designable functionality. However, the unambiguous identification of atomically dispersed metal sites and the elucidation of their role in catalysis are challenging due to limited methods of characterization and lack of direct structural information. Here, we report a comprehensive investigation of the structure and the role of atomically dispersed copper sites in UiO-66 for the catalytic reduction of NO2 at ambient temperature. The atomic dispersion of copper sites on UiO-66 is confirmed by high-angle annular dark-field scanning transmission electron microscopy, electron paramagnetic resonance spectroscopy, and inelastic neutron scattering, and their location is identified by neutron powder diffraction and solid-state nuclear magnetic resonance spectroscopy. The Cu/UiO-66 catalyst exhibits superior catalytic performance for the reduction of NO2 at 25 °C without the use of reductants. A selectivity of 88% for the formation of N2 at a 97% conversion of NO2 with a lifetime of >50 h and an unprecedented turnover frequency of 6.1 h-1 is achieved under nonthermal plasma activation. In situ and operando infrared, solid-state NMR, and EPR spectroscopy reveal the critical role of copper sites in the adsorption and activation of NO2 molecules, with the formation of {Cu(I)···NO} and {Cu···NO2} adducts promoting the conversion of NO2 to N2. This study will inspire the further design and study of new efficient single-atom catalysts for NO2 abatement via detailed unravelling of their role in catalysis.

Full text of DOI:10.1021/jacs.1c03036

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Article
Atomically Dispersed Copper Sites in a Metal−Organic Framework
for Reduction of Nitrogen Dioxide
Yujie Ma, Xue Han, Shaojun Xu, Zi Wang, Weiyao Li, Ivan da Silva, Sarayute Chansai, Daniel Lee,*
Yichao Zou, Marek Nikiel, Pascal Manuel, Alena M. Sheveleva, Floriana Tuna, Eric J. L. McInnes,
́
Yongqiang Cheng, Svemir Rudic, Anibal J. Ramirez-Cuesta, Sarah J. Haigh, Christopher Hardacre,
Martin Schröder,* and Sihai Yang*
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ABSTRACT: Metal−organic framework (MOF) materials provide
an excellent platform to fabricate single-atom catalysts due to their
structural diversity, intrinsic porosity, and designable functionality.
However, the unambiguous identification of atomically dispersed
metal sites and the elucidation of their role in catalysis are
challenging due to limited methods of characterization and lack of
direct structural information. Here, we report a comprehensive
investigation of the structure and the role of atomically dispersed
copper sites in UiO-66 for the catalytic reduction of NO2 at
ambient temperature. The atomic dispersion of copper sites on
UiO-66 is confirmed by high-angle annular dark-field scanning
transmission electron microscopy, electron paramagnetic resonance
spectroscopy, and inelastic neutron scattering, and their location is
identified by neutron powder diffraction and solid-state nuclear magnetic resonance spectroscopy. The Cu/UiO-66 catalyst exhibits
superior catalytic performance for the reduction of NO2 at 25 °C without the use of reductants. A selectivity of 88% for the
formation of N2 at a 97% conversion of NO2 with a lifetime of >50 h and an unprecedented turnover frequency of 6.1 h−1 is achieved
under nonthermal plasma activation. In situ and operando infrared, solid-state NMR, and EPR spectroscopy reveal the critical role of
copper sites in the adsorption and activation of NO2 molecules, with the formation of {Cu(I)···NO} and {Cu···NO2} adducts
promoting the conversion of NO2 to N2. This study will inspire the further design and study of new efficient single-atom catalysts for
NO2 abatement via detailed unravelling of their role in catalysis.
MOF-based single-atom catalyst, Cu/UiO-66, has been
prepared by anchoring single-atom Cu sites to the defect
sites of UiO-66 and used for catalytic CO oxidation and
removal.16 Herein, we conclusively identify the location of the
Cu sites in Cu/UiO-66, as well as their role in the catalytic
reduction of NO2 to N2, an important process for NOx
abatement. The local structure of structural defects and
atomically dispersed Cu sites within the framework and their
role in promoting the activation of substrates are elucidated by
in situ electron paramagnetic resonance (EPR) spectroscopy,
neutron powder diffraction (NPD), inelastic neutron scattering
(INS), solid-state nuclear magnetic resonance (NMR) spec-
INTRODUCTION
■
Emerging single-atom catalysts show superior selectivity and
activity in a variety of catalytic systems due to their unique
electronic properties, low-coordination (or unsaturated) metal
sites, and high atom efficiency.1−4 Metal−organic framework
(MOF) materials are a class of crystalline porous materials that
are ideal platforms for the fabrication of single-atom catalysts
due to their uniform and well-defined structure, ultrahigh
porosity, and designable functionality and pore sizes.5−8
Functional groups, such as hydroxyl bridges, and intrinsic
defect sites in MOFs can enable the immobilization of
atomically dispersed metal sites on the pore interior.
MOF-based single-atom catalysts have shown great promise
in a number of catalytic reactions, yet the precise identification
of these single-atom metal sites and their roles in catalysis
remain elusive.9−15 As a result, there is a strong motivation to
develop and apply cutting-edge experimental techniques to the
investigation of local structures of the single metal sites, as well
as the elucidation of their roles in catalytic process, thus
unravelling the catalytic pathway and mechanism. Recently, a
Received: March 21, 2021
Published: July 19, 2021
© 2021 The Authors. Published by
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Figure 1. (a) Crystal structure of UiO-66 with a defect site. Yellow and pink spheres represent the cages without and with defect sites, respectively.
(b) View of the {Zr6} cluster in UiO-66 with a defect site and (c) Cu/UiO-66 with a single-atom Cu site coordinated to −OH/−OH2 defect sites.
These structures were derived from Rietveld refinements of the NPD data at 7 K (C, gray; O, red; Zr, blue; Cu, orange; H atoms are omitted for
clarity). The bond distance of Cu−O is 1.88(3) Å, and the bond angle of O−Cu−O is 152.2(1)°. (d) Comparison of the experimental and DFT
calculated INS spectra of UiO-66 and Cu/UiO-66 (inset: magnification of the experimental INS features at around 130 meV). (e) X-band (9.4
GHz) EPR spectra of Cu/UiO-66 before (black) and after H2 reduction (red), at 6.4 K (inset: expansion of low-field region confirming the absence
of characteristic signals for binuclear or aggregated Cu species with S ≥ 1). (f) HAADF-STEM image of Cu/UiO-66 after H2 reduction.
troscopy, diffuse reflectance infrared Fourier transform spec-
troscopy (DRIFTS), high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM), and
density functional theory (DFT) calculations. In addition to
Cu/UiO-66, the catalytic performance of the −NH2 function-
alized analogue of UiO-66 (UiO-66-NH2) has also been
studied to gain insight into the potential activity of −NH2
groups in the reduction of NO2. Of all the catalysts studied
herein, Cu/UiO-66 exhibits superior catalytic performance for
the reduction of NO2 to N2 at room temperature without using
any reducing agent under the activation of nonthermal plasma
(NTP). Cu/UiO-66 shows a superior catalytic stability of >50
h in a continuous flow reaction, affording a N2 selectivity of
88% at a 97% conversion of NO2 with an unprecedented
turnover frequency (TOF) of 6.1 h−1.
tion of UiO-66 and UiO-66-NH2. The presence of structural
defects (missing ligand) in desolvated UiO-66 was confirmed
by NPD (Figure 1a,b), which revealed approximately one
missing ligand per {Zr6} cluster, giving a formula of
[Zr6O4(OH)4(BDC)5.35(OH)1.30(OH2)1.30] (H2BDC ligand =
benzene-1,4-dicarboxylic acid), in good agreement with
previous reports.16−18
Cu/UiO-66 was prepared through the attachment of Cu(II)
ions to the defect sites of UiO-66, followed by reduction by 5%
H2 in Ar at 250 °C for 2 h.16 The PXRD pattern (Figure S1),
N2 adsorption isotherms (Figure S2), and SEM images (Figure
S3) of Cu/UiO-66 confirm the retention of crystallinity,
porosity, and crystal morphology upon the attachment of Cu
to UiO-66. Elemental analysis suggested a ratio of Cu/{Zr6} of
∼1.0, i.e., all defect sites have been filled by Cu sites.
Studies of the Atomically Dispersed Cu Sites. The
location of Cu sites within Cu/UiO-66 has been determined
by the Rietveld refinement of NPD data collected at 7 K
(Figure 1c). Cu is coordinated to the −OH/−OH2 defect sites
of UiO-66 with the ratio of Cu/{Zr6} cluster being ∼1.0. The
Cu−O distance [1.88(3) Å] is in excellent agreement with that
(1.89−1.95 Å) obtained from DFT calculations.16 The binding
of Cu to the −OH/−OH2 defect sites was confirmed further
by a combination of inelastic neutron scattering (INS) and
DFT calculations (Figure 1d). Upon the binding of Cu, the
INS features at 57 and 130 meV, assigned to O−H bending
modes, show notable reductions in intensity, confirming the
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Catalysts. UiO-66
was synthesized according to a reported method (Section
S1.1).16 UiO-66-NH2 was prepared using the amine-function-
alized ligand (2-aminoterephthalic acid) following the same
procedure used for synthesizing UiO-66 (Section S1.1).
Powder X-ray diffraction (PXRD) patterns (Figure S1), N2
adsorption isotherms (Figure S2), scanning electron micros-
copy (SEM, Figure S3) images, and thermal gravimetric
analysis (TGA, Figure S4) confirmed the successful prepara-
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Figure 2. (a) 1H DEPTH (top) and {1H-}13C CP (bottom) MAS NMR spectra of H2-reduced UiO-66 (black) and Cu/UiO-66 (red). The spectra
were recorded at 9.4 T using a MAS frequency of 10 kHz. The arrows and asterisks denote trace adsorbed DMF molecules and the spinning side
bands, respectively. The dashed vertical gray line highlights the defect sites. 1H DEPTH MAS NMR spectra of (b) UiO-66 and (c) Cu/UiO-66. 2D
1H MAS NMR DQ-SQ homonuclear dipolar correlation spectra of (d) UiO-66 and (e) Cu/UiO-66, recorded using the S3 recoupling sequence;
black and gray lines represent positive and negative contours, respectively, and the dashed red line highlights the DQ diagonal. The blue square in
(e) represents an area where the minimum displayed contour level has been decreased by a factor of 2 (equivalent to doubled magnification). The
spectra were recorded at 20 T using a MAS frequency of 60 kHz.
coordination of Cu to these defect sites, and this was validated
by DFT simulations of the INS spectra. The simulations tend
to slightly underestimate the magnitude of the reduction in
intensities of the small features at 100−160 meV, likely due to
the overall complexity of the system. This represents the first
study of the location of Cu sites within Cu/UiO-66 by
diffraction techniques.
Analysis of Structural Defects and the Environment
of Cu by Solid-State NMR. To gain further insights into the
local environment of defects and Cu sites, solid-state NMR
spectroscopy was employed as this has proven extremely
valuable in the study of UiO-66 materials.24,25 Here, a
1
quantitative H magic angle spinning (MAS) NMR spectrum
of reduced UiO-66, obtained following the same treatment as
Cu/UiO-66 (i.e., heating in 5% H2 in Ar at 250 °C for 2 h),
shows that this treatment removes the H center from the μ3−
OH species of the {Zr6} cluster (Figure 2a, top), which was
previously observed by variable-temperature FTIR studies.26
1H NMR signals from low-shifted species (δ{1H} < 2.5 ppm)
Following the determination of the location of the Cu sites,
it was established that these were primarily atomically
dispersed. Thus, the continuous-wave EPR spectra of Cu/
UiO-66 before and after reduction under H2 both show the
characteristics of monomeric Cu(II) sites (Figure 1e).19 No
binuclear (S = 1) or aggregated (long-range magnetically
coupled) Cu(II) species was observed by the X-band EPR
spectra collected at low and room temperatures (Figure 1e and
Figure S7),20 consistent with the presence of atomically
dispersed Cu(II) sites in the framework. The EPR spectra of
reduced Cu/UiO-66 show that the majority of the Cu(II) sites
are reduced to diamagnetic Cu(I) (Figure S8), which is
consistent with X-ray photoelectron spectroscopic (XPS)
analysis (Figure S17). The high-angle annular dark-field
scanning transmission electron microscopy (HAADF-STEM)
of Cu/UiO-66 shows many bright dots, representing Cu and
Zr sites (Figure 1f and Figure S9a).21 Although it is challenging
to distinguish between Cu and Zr centers,22 the HAADF-
STEM image confirms the absence of Cu/CuOx nanoparticles.
Energy dispersive X-ray spectroscopy (EDX) mapping also
shows a uniform distribution of the Cu sites (Figure S9c,d).
This was further validated by the ultraviolet−visible (UV−vis)
absorption spectrum of Cu/UiO-66, where the characteristic
absorption peak of Cu nanoparticles [surface plasmon
resonance (SPR) band] in the region of 550−600 nm23 was
not observed (Figure S10).
1
account for ∼1/10th of the integral intensity compared to H
from the ligands (δ {1H} ∼ 8 ppm) (Figure S11 and Table
S3), whereas this intensity is expected to be 4 times larger for
fully hydroxylated UiO-66. Therefore, these low-shifted species
1
were assigned as −OH/−OH2 centers at defect sites. The H
MAS NMR spectrum of Cu/UiO-66 (Figure 2a, top) is similar
to that of reduced UiO-66, indicating that the majority of
Cu(II) sites were reduced to Cu(I); a close proximity to
paramagnetic Cu(II) ions would cause a substantial broad-
ening and/or shifts of the NMR signals,27 and this was not
observed. The similarity between the 13C MAS NMR spectra
of reduced UiO-66 and Cu/UiO-66 (Figure 2a, bottom)
demonstrates that the incorporation of Cu sites does not
perturb the local ligand structure.
High-field (20 T) 1H NMR spectroscopy with ultrafast MAS
was also employed as this provides superior resolution. The
two-dimensional (2D) double-quantum single-quantum (DQ-
SQ) 1H homonuclear dipolar correlation NMR spectrum
(Figure 2d) for pristine UiO-66 shows the μ3−OH species at δ
{1H} ∼ 0.4 ppm (Figure 2b and Figure S11). The remaining
low-shifted protons at δ {1H} < 2.5 ppm display both diagonal
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(δSQ{1H} ∼ 1.1 ppm) will be correlated to these (off-
diagonal).
The high-resolution 1H MAS NMR spectrum of Cu/UiO-66
confirms the absence of μ3−OH species for this sample (Figure
2c). It is also evident that there are at least three distinct defect
−OH/−OH2 environments at δ {1H} ∼ 2.4, 2.2, and 1.5 ppm.
1
The 2D DQ-SQ H homonuclear dipolar correlation NMR
spectrum of Cu/UiO-66 (Figure 2e) displays clear and intense
autocorrelation peaks for two of the defect sites (at δSQ {1H} ∼
2.4 and 2.2 ppm), indicating that they arise from OH2
environments. Furthermore, these species also give a strong
correlation with protons from the linker (at δDQ {1H} ∼ 10.3
ppm), suggesting that they are somewhat removed from the
defect site. The remaining defect proton environments are thus
likely to be −OH sites (at δSQ {1H} ∼ 1.5 ppm), and cross-
correlations with OH2 environments suggest that these sites
are all in close proximity and remain protonated upon the
attachment of Cu sites. A quantitative comparison (Figure S11
and Table S3) between the defect sites of UiO-66 and Cu/
UiO-66 suggests that displacement of adsorbed water and/or
dehydroxylation of the {Zr6} clusters during Cu attachment
and subsequent H2-reduction leads to a ∼4-fold increase in the
relative amount of protons at the defect sites (δ {1H} < 2.5
ppm). The autocorrelation peak of the lowest-shifted 1H
species of Cu/UiO-66 (at δSQ {1H} ∼ 1.5 ppm) and its cross-
correlation to OH2 environments indicates that Cu is
coordinated at defect sites as {Zr−O(H)−Cu(OH2)−
O(H)−Zr}. Quantitatively, this coordination mode appears
approximately once every two {Zr6} clusters. The other
coordination modes of Cu sites are {Zr−O−Cu(OH2)−O−
Zr} and {Zr−O−Cu−O−Zr}. These coordination modes were
1
confirmed by H hyperfine sublevel correlation (HYSCORE)
EPR spectra (Figure S12 and Table S4), which reveal a
coordinated H2O molecule in the plane perpendicular to the z
axis of the electronic g matrix (the latter being perpendicular to
the coordination plane) with a Cu···H distance of ∼2.3 Å.
Studies of Catalytic Performance. To investigate the
catalytic performance of UiO-66, UiO-66-NH2, and Cu/UiO-
66 for NTP-assisted decomposition of NO2, a simulated gas
flow containing 500 ppm of NO2 diluted in helium at a total
flow rate of 100 mL min−1 was used as the feed gas for a proof-
of-concept study. Without a catalyst, the gas phase NTP alone
Figure 3. (a) Catalytic performance (NO2 conversion and product
selectivities) over different catalysts under steady-state NTP
conditions. (b) Time-on-stream plots of NO2 conversion and N2
selectivity over MOF-based catalysts (UiO-66, UiO-66-NH2, and Cu/
UiO-66) under NTP conditions (0.4 kJ L−1, 10 kHz, 500 ppm of NO2
diluted in He, 25 °C, and atmospheric pressure).
exhibited a conversion of NO2 (CNO ) of 73% with a low
2
selectivity of N2 (SN ) of 18%, with the majority of NO2 being
2
autocorrelation peaks (between equivalent proton sites at δDQ
{1H} ∼ 2.7 ppm) and off-diagonal correlation peaks (between
inequivalent proton sites at δDQ {1H} ∼ 2.4 ppm). Accordingly,
these proton environments can be assigned to defect sites
(Figure 1b), where μ1−OH2 species (δSQ {1H} ∼ 1.3 ppm) will
give an autocorrelation peak and nearby μ1−OH species
converted to NO, which is another major air pollutant that can
be oxidized to NO2 in air (Figure 3, Table 1, Entry 1). All
three MOF catalysts can improve the CNO and SN (Figure 3,
2
2
Table 1, Entries 2−5). UiO-66 showed a steady CNO of 83%
2
with a SN of 47% over 240 min (Figure 3b).
2
a
Table 1. Summary of the NO2 Conversion and Product Selectivities over Different Catalysts
catalyst
empty tube
UiO-66
UiO-66 (H2-reduced)
UiO-66-NH2
Cu/UiO-66
ZrO2
NO2 conversion (%)
N2 selectivity (%)
NO selectivity (%)
N2O selectivity (%)
73
83
85
96
97
88
90
18
47
50
75
88
19
26
77
42
40
20
3
5
11
10
5
9
11
11
70
63
Cu/ZrO2
a
Reaction conditions: 0.4 kJ L−1, 10 kHz, 500 ppm of NO2 diluted in He, 25 °C, and atmospheric pressure.
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assigned to a diazonium salt28 and a decrease in intensity of the
bands at 3514 and 3398 cm−1 assigned to asymmetric and
symmetric N−H stretches. These observations suggest that the
−NH2 group acts as a sacrificial agent in this reaction, with the
deactivation of the catalyst being driven by the formation and
dissociation of the diazonium ions upon irreversible reaction
between NO2 and the −NH2 groups of UiO-66-NH2. Despite
the −NH2 sites being consumed during the reaction, the
overall structure of the framework in UiO-66-NH2 was
retained, as confirmed by PXRD (Figure S14).
Of the three catalysts, Cu/UiO-66 exhibits the highest
catalytic efficiency, with the CNO and SN reaching 97% and
2
2
88%, respectively (Figure 3 and Table 1, Entry 5). Time-on-
stream (ToS) tests further demonstrated the excellent catalytic
stability of Cu/UiO-66 with high values for CNO and SN
2
2
retained for over 50 h (Figure 4a). Importantly, Cu/UiO-66
exhibited a superior TOF of 6.1 h−1 compared with state-of-
the-art Cu-based SCR catalysts, including those using NH3 as
reductant and operating at elevated temperatures (Table 2).
For example, a Cu-exchanged SSZ-13 zeolite29 shows a TOF
value of 1.9−2.2 h−1 at 250−550 °C and Cu-MOF-7430
demonstrates a TOF of 0.28 h−1 at 230 °C. Significantly, the
excellent catalytic activity of Cu/UiO-66 was achieved without
the use of NH3 or heating. In contrast, Cu/ZrO2, prepared
through a similar method as for Cu/UiO-66 (Section S1.1),
showed a much lower catalytic efficiency, with values of 90%
and 26% for CNO and SN , respectively( Figure 3a and Table 1,
2
2
Entry 7), indicating that the nature of atomically dispersed Cu
sites within Cu/UiO-66 plays a crucial role in its observed
activity. Although NTP-activated deNOx systems have been
reported,31−33 they generally suffer from poor catalytic
efficiency, low TOF, and/or stability.
To explore possible sample degradation, the used Cu/UiO-
66 catalyst was characterized by EPR, XPS, PXRD, DRIFTS,
and N2 adsorption isotherms. The X-band EPR spectrum of
the used catalyst confirms (Figure S16) the retention of
atomically dispersed Cu sites, with no evidence of aggregated
species. The EPR spectrum also shows a small increase in the
intensity of Cu(II) signal after reaction (Figure S8). XPS
spectra indicate that the ratio of Cu(II)/Cu(I) increases after
reaction, but with the majority of Cu sites still remaining as
Cu(I) in the used catalyst (Figure S17). Little difference was
observed in the PXRD patterns or DRIFTS spectra of fresh
and used catalysts (Figures S15 and S18). N2 adsorption
isotherms at 77 K indicate a small reduction (∼10%) in the
surface area of Cu/UiO-66 after reaction (Figure S19).
Studies of the Reaction Mechanism. The adsorption of
NO2 onto the catalyst is widely considered as the rate-
determining step for the reduction of NO2,34 and dynamic
breakthrough experiments were therefore carried out with
UiO-66 and Cu/UiO-66 at 25 °C (Figure 4b). Notably, the
dynamic adsorption capacity of NO2 in UiO-66 increases from
2.02 to 3.96 mmol g−1 on incorporation of Cu sites, and the
temperature-programmed desorption (TPD) profiles of NO2-
adsorbed onto UiO-66 and Cu/UiO-66 show the presence of
stronger binding sites for NO2 in the latter with an additional
desorption peak at 235 °C (Figure 4c). Thus, both
breakthrough and TPD experiments confirm the stronger
adsorption of NO2 in Cu/UiO-66 than in UiO-66, presumably
contributing to the observed superior catalytic performance.
In situ DRIFTS spectroscopy confirmed the adsorption of
NO2, resulting in several new bands at ∼1541, 1487, 1415,
Figure 4. (a) Time-on-stream test of Cu/UiO-66 under NTP
conditions. The catalytic efficiency remained constant for 50 h of
reaction under continuous flow. (b) Dynamic breakthrough experi-
ments of UiO-66 and Cu/UiO-66 using the same NO2/He gas feed at
25 °C. (c) NO2-TPD plots of UiO-66 and Cu/UiO-66.
The NH2-functionalized UiO-66-NH2 showed improve-
ments to the catalytic activity observed for UiO-66, with the
CNO and SN reaching 96% and 75%, respectively. However, a
2
2
notable deactivation of UiO-66-NH2 occurred after 170 min,
where the CNO and SN dropped gradually to 88% and 59%,
2
2
respectively, after 240 min (Figure 3b). The operando DRIFTS
spectrum of UiO-66-NH2 exposed to NO2 under plasma
activation (Figure S20) shows a new band at 2280 cm−1
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Table 2. Summary of Values of Turnover Frequency (TOF) Reported for Cu-Based Catalysts for NOx Conversion under NTP
a
Conditions and Thermal Conditions with Reducing Agents
catalyst
temperature (°C)
GHSV (103h−1
)
NOx concentration (ppm)
NOx conversion (%)
TOF (h−1
)
ToS (h)
Cu/UiO-66@NTP [this work]
HKUST-1@NTP31
25
25
25
180
25
250
550
230
210
360
150
300
280
270
150
75
60
60
150
30
30
50
36
36
500
500
500
500
500
350
350
1000
500
500
500
500
1000
1000
97.0
97.9
21.0
60.0
96
95.0
83.0
97.8
90.0
100
48.0
100
95.5
97.2
6.1
50
0.50
0.27
0.62
1.8
2.9
2.2
1.9
0.28
1.0
1.1
2.4
32
Cu/ZSM-5@NTP-NH3
Cu/ZSM-5@NTP-NH3
Cu/MFM-300(Al)@NTP33
Cu-SSZ-13@thermal-NH3
Cu-SSZ-13@thermal-NH3
Cu-MOF-74@thermal-NH3
Cu/SAPO-34@thermal-NH3
Cu/SAPO-34@thermal-NH3
Cu-ZSM-5@thermal-NH3
Cu-ZSM-5@thermal-NH3
32
3.8
24
29
29
30
46
46
47
100
100
50
47
4.9
0.26
0.12
48
HKUST-1@thermal-NH3
49
CuO@thermal-NH3
50
25
a
Note: GHSV = gas hourly space velocity. ToS = time-on-stream. TOF = turnover frequency.
Figure 5. (a) In situ DRIFTS spectra of adsorbed NO2 on Cu/UiO-66 (red) and UiO-66 (black). (b) Operando DRIFTS spectra over Cu/UiO-66
with plasma on (black) and off (red); 500 ppm of NO2 in He was used as a feed gas. All the DRIFTS spectra were recorded at a resolution of 4
1
1
cm−1; the spectra of bare MOF samples were subtracted as the background. (c) H DEPTH and (d) H-Hahn-echo MAS NMR spectra of Cu/
UiO-66 dosed with NO2 for 15 min (black) and the same sample after NO2 desorption (red). A further desorption study can be found in the
Supporting Information.
1394, 1262, and 1230 cm−1 (Figure 5a) assigned to various
monodentate, bidentate, and bridging nitro/nitrate spe-
cies35−37 adsorbed on catalyst surfaces with partially over-
lapping vibrational bands. The band at 1712 cm−1 is associated
with adsorbed NO on the −OH defect sites in both UiO-66
and Cu/UiO-66, and the notable broadening and increase of
intensity of this band in Cu/UiO-66 is due to the additional
contribution from the formation of {Cu(I)···NO} species.38,39
The adsorption of NO onto the −OH defect sites was further
confirmed by the depletion of the O−H stretching vibration
band at 3675 cm−1 (Figure S21). Interestingly, an additional
band was observed at 1625 cm−1 for NO2-loaded Cu/UiO-66,
which could originate from adsorbed NO2 or NO species on
Cu sites.35,40,41 Thus, the formation of {Cu···NO2} adducts on
Cu/UiO-66 greatly accelerates the adsorption and reduction of
NO2. The EPR spectroscopic studies of Cu/UiO-66 and NO2-
loaded Cu/UiO-66 also show differences in both the g- and Cu
hyperfine A-tensors (Figure S22), consistent with binding of
NOx at Cu sites. Operando DRIFTS experiments were carried
out as a function of plasma on−off and reaction time (Figure
5b). Apparent reductions of FTIR bands of various adsorbed
nitro/nitrate species, {Cu(I)···NO}, and {Cu···NO2} adducts
were observed upon the ignition of plasma, indicating the rapid
conversion of these intermediates over Cu/UiO-66. It is worth
noting that, in the present system, the activation effects of NTP
coupled to the adsorption of NO2 by the catalyst appear to
work synergistically.
In situ 1H MAS NMR spectra were recorded for Cu/UiO-66
upon the adsorption of NO2 to investigate the adsorbates as
well as the local structural changes of the catalyst. The
adsorption of NO2 has substantial effects (cf. Figures 2a and
1
5c) with the broadening of the H NMR signals from the
ligand (at δ {1H} ∼ 8 ppm) and a decrease in the intensity of
signals due to the defect sites (at δ {1H} < 2.5 ppm). To
42
1
investigate the broadening, a H Hahn-echo experiment was
employed with a relatively long total echo duration (Figure 5d)
as this will remove homogeneously broadened signals [e.g.,
1
from H centers near Cu(II) sites or with strong dipolar
couplings]. Subsequently, the adsorbed NO2 was removed
using vacuum/heating treatment (Figure 5c and Figure S23),
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1
which resulted in reduced line width of the H resonance for
Auger and DRIFTS spectra, Figures S1−S25 and Tables
S1−S6 (PDF)
the ligand and an increased intensity for the −OH species.
Both NMR spectroscopic experiments indicate that Cu(II) is
not responsible for the line broadening observed upon the
adsorption of NO2 but is a result of increased structural
heterogeneity that facilitates the adsorption of NO2 onto the
MOF interior and, in addition, NO2 binds to −OH and Cu
sites, as revealed by the DRIFTS experiments. Interestingly,
Accession Codes
CCDC 2054313 and 2054314 contain the supplementary
crystallographic data for this paper.
AUTHOR INFORMATION
Corresponding Authors
■
1
the increased resolution in the H Hahn-echo MAS NMR
Daniel Lee − Department of Chemical Engineering and
Analytical Science, University of Manchester, Manchester
M13 9PL, United Kingdom; orcid.org/0000-0002-1015-
0980; Email: daniel.lee@manchester.ac.uk
Martin Schröder − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom;
orcid.org/0000-0001-6992-0700; Email: M.Schroder@
manchester.ac.uk
Sihai Yang − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom;
orcid.org/0000-0002-1111-9272; Email: Sihai.Yang@
manchester.ac.uk
spectrum of NO2-adsorbed Cu/UiO-66 (Figure 5d, bottom)
reveals a high-shifted H signal at δ {1H} ∼ 9.6 ppm, along
1
with adsorbed bulk water at δ {1H} ∼ 5.3 ppm; it should be
noted that this experiment is not quantitative. Upon the
1
removal of NO2, the high-shifted H signal and that of bulk
water mostly disappear, while low-shifted −OH/OH2 signals
1
emerge (Figure 5d, top). The high-shifted H signals (at δ
{1H} ∼ 9.6 ppm) can be ascribed to nitric/nitrous acid
species.43,44 The 2D 1H homonuclear dipolar correlation
spectrum of Cu/UiO-66 with NO2 (Figure S24) displays
correlations between these acidic protons and protons of the
ligand but not with water or defect protons. Notably, this
indicates that an intermediate in the reduction of NO2 by Cu/
UiO-66 could be nitric/nitrous acid and that it adsorbs, most
likely through hydrogen-bonding, to the ligand. This is
corroborated with data from 13C MAS NMR (Figure S25),
which shows a shift in the carboxylate 13C signal upon
adsorption of NO2.45
Authors
Yujie Ma − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom
Xue Han − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom
Shaojun Xu − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom; UK
Catalysis Hub, Research Complex at Harwell, Rutherford
Appleton Laboratory, Harwell OX11 0FA, United Kingdom;
School of Chemistry, Cardiff University, Cardiff CF10 3AT,
United Kingdom; orcid.org/0000-0002-8026-8714
Zi Wang − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom
Weiyao Li − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom
Ivan da Silva − ISIS Facility, STFC Rutherford Appleton
Laboratory, Chilton, Oxfordshire OX11 0QX, United
Kingdom; orcid.org/0000-0002-4472-9675
Sarayute Chansai − Department of Chemical Engineering and
Analytical Science, University of Manchester, Manchester
M13 9PL, United Kingdom
Yichao Zou − Department of Materials, University of
Manchester, Manchester M13 9PL, United Kingdom
Marek Nikiel − Department of Materials, University of
Manchester, Manchester M13 9PL, United Kingdom
Pascal Manuel − ISIS Facility, STFC Rutherford Appleton
Laboratory, Chilton, Oxfordshire OX11 0QX, United
Kingdom
CONCLUSIONS
■
The development and application of new efficient technologies
to enable the precise identification of single metal sites and
their roles in catalysis are important targets. We have
undertaken a comprehensive study of the local structure of
the single-atom Cu sites in Cu/UiO-66, thus enabling
elucidation of their critical role in the reduction of NO2. The
combination of the single-atom catalyst Cu/UiO-66 and NTP
leads to the direct decomposition of NO2 to N2 at room
temperature. Cu/UiO-66 exhibits unprecedented catalytic
efficiency and excellent stability. Atomically dispersed Cu
sites anchored at the defect sites of the UiO-66 scaffold
prevents the Cu atoms from migrating and sintering during
reaction and are responsible for the superior catalytic
performance. In Cu/UiO-66, the adsorption of NO2 occurs
at the Cu and hydroxyl sites, forming nitro/nitrate and related
intermediates, which readily transform on activation with NTP
to regenerate accessible active sites on the catalyst surface. The
excellent catalytic performance of Cu/UiO-66 originates from
the synergistic effects between atomically dispersed Cu sites
and the framework porosity, providing multiple binding sites to
promote the adsorption and conversion of NO2. New
controllable deNOx processes integrating single-atom catalysts
with a NTP technique could provide an efficient solution to
the mitigation of NOx emissions.
Alena M. Sheveleva − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom; Photon
Science Institute, University of Manchester, Manchester M13
9PL, United Kingdom
Floriana Tuna − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom; Photon
Science Institute, University of Manchester, Manchester M13
9PL, United Kingdom
ASSOCIATED CONTENT
■
sı
* Supporting Information
Eric J. L. McInnes − Department of Chemistry, University of
Manchester, Manchester M13 9PL, United Kingdom; Photon
Science Institute, University of Manchester, Manchester M13
9PL, United Kingdom; orcid.org/0000-0002-4090-7040
Yongqiang Cheng − Neutron Scattering Division, Neutron
Sciences Directorate, Oak Ridge National Laboratory, Oak
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c03036.
Additional experimental details, PXRD and NPD data,
N2 adsorption isotherms, TGA plots, SEM and HAADF-
STEM images, EPR, UV−Vis, solid-state NMR, XPS,
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(4) Zhang, T.; Walsh, A. G.; Yu, J.; Zhang, P. Single-atom alloy
catalysts: structural analysis, electronic properties and catalytic
activities. Chem. Soc. Rev. 2021, 50, 569−588.
Ridge, Tennessee 37831, United States; orcid.org/0000-
0002-3263-4812
́
Svemir Rudic − ISIS Facility, STFC Rutherford Appleton
(5) Wei, Y.-S.; Zhang, M.; Zou, R.; Xu, Q. Metal−Organic
Framework-Based Catalysts with Single Metal Sites. Chem. Rev.
2020, 120, 12089−12174.
Laboratory, Chilton, Oxfordshire OX11 0QX, United
Kingdom; orcid.org/0000-0003-3023-8565
Anibal J. Ramirez-Cuesta − Neutron Scattering Division,
Neutron Sciences Directorate, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
Sarah J. Haigh − Department of Materials, University of
Manchester, Manchester M13 9PL, United Kingdom;
orcid.org/0000-0001-5509-6706
(6) Bavykina, A.; Kolobov, N.; Khan, I. S.; Bau, J. A.; Ramirez, A.;
Gascon, J. Metal−Organic Frameworks in Heterogeneous Catalysis:
Recent Progress, New Trends, and Future Perspectives. Chem. Rev.
2020, 120, 8468−8535.
(7) Babucci, M.; Guntida, A.; Gates, B. C. Atomically Dispersed
Metals on Well-Defined Supports including Zeolites and Metal−
Organic Frameworks: Structure, Bonding, Reactivity, and Catalysis.
Chem. Rev. 2020, 120, 11956−11985.
(8) Han, A.; Wang, B.; Kumar, A.; Qin, Y.; Jin, J.; Wang, X.; Yang,
C.; Dong, B.; Jia, Y.; Liu, J.; Sun, X. Recent Advances for MOF-
Derived Carbon-Supported Single-Atom Catalysts. Small Methods
2019, 3, 1800471.
(9) Zhang, E.; Wang, T.; Yu, K.; Liu, J.; Chen, W.; Li, A.; Rong, H.;
Lin, R.; Ji, S.; Zheng, X.; Wang, Y.; Zheng, L.; Chen, C.; Wang, D.;
Zhang, J.; Li, Y. Bismuth Single Atoms Resulting from Transformation
of Metal-Organic Frameworks and Their Use as Electrocatalysts for
CO2 Reduction. J. Am. Chem. Soc. 2019, 141, 16569−16573.
(10) Ji, P.; Song, Y.; Drake, T.; Veroneau, S. S.; Lin, Z.; Pan, X.; Lin,
W. Titanium(III)-Oxo Clusters in a Metal-Organic Framework
Support Single-Site Co(II)-Hydride Catalysts for Arene Hydro-
genation. J. Am. Chem. Soc. 2018, 140, 433−440.
Christopher Hardacre − Department of Chemical Engineering
and Analytical Science, University of Manchester, Manchester
M13 9PL, United Kingdom; orcid.org/0000-0001-7256-
6765
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c03036
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors would like to thank the EPSRC (EP/I011870),
the Royal Society and the University of Manchester for
funding, and the EPSRC for funding of the EPSRC National
EPR Facility at Manchester. This project has received funding
from the European Research Council (ERC) under the
European Union’s Horizon 2020 research and innovation
programme (grant agreement No 742401, NANOCHEM).
This work was supported by the Henry Royce Institute for
Advanced Materials, funded through EPSRC grants EP/
R00661X/1, EP/S019367/1, EP/P025021/1, and EP/
P025498/1. The authors are grateful to the STFC/ISIS
Facility for access to Beamlines TOSCA and WISH. The UK
850 MHz solid-state NMR Facility used in this research was
funded by the EPSRC and BBSRC (contract reference EP/
T015063/1), as well as the University of Warwick including via
part funding through Birmingham Science City Advanced
Materials Projects 1 and 2 supported by Advantage West
Midlands (AWM) and the European Regional Development
Fund (ERDF). Collaborative assistance from the 850 MHz
Facility Manager (Dinu Iuga, University of Warwick) is
acknowledged. A.M.S. was supported by the Royal Society
Newton International Fellowship. Y.M. acknowledges financial
support from the China Scholarship Council. Computing
resources for neutron data analysis were made available
through the VirtuES and the ICE-MAN projects, funded by
Laboratory Directed Research and Development program and
Compute and Data Environment for Science (CADES) at
ORNL.
(11) Li, Z.; Schweitzer, N. M.; League, A. B.; Bernales, V.; Peters, A.
W.; Getsoian, A. B.; Wang, T. C.; Miller, J. T.; Vjunov, A.; Fulton, J.
L.; Lercher, J. A.; Cramer, C. J.; Gagliardi, L.; Hupp, J. T.; Farha, O.
K. Sintering-Resistant Single-Site Nickel Catalyst Supported by
Metal−Organic Framework. J. Am. Chem. Soc. 2016, 138, 1977−1982.
(12) Zhang, Y.; Jiao, L.; Yang, W.; Xie, C.; Jiang, H.-L. Rational
Fabrication of Low-Coordinate Single-Atom Ni Electrocatalysts by
MOFs for Highly Selective CO2 Reduction. Angew. Chem., Int. Ed.
2021, 60, 7607−7611.
(13) He, X.; Looker, B. G.; Dinh, K. T.; Stubbs, A. W.; Chen, T.;
̆
Meyer, R. J.; Serna, P.; Román-Leshkov, Y.; Lancaster, K. M.; Dinca,
M. Cerium(IV) Enhances the Catalytic Oxidation Activity of Singl-
Site Cu Active Sites in MOFs. ACS Catal. 2020, 10, 7820−7825.
(14) Gong, Y. N.; Jiao, L.; Qian, Y.; Pan, C. Y.; Zheng, L.; Cai, X.;
Liu, B.; Yu, S. H.; Jiang, H. L. Regulating the Coordination
Environment of MOF-Templated SingleAtom Nickel Electrocatalysts
for Boosting CO2 Reduction. Angew. Chem., Int. Ed. 2020, 59, 2705−
2709.
(15) He, T.; Chen, S.; Ni, B.; Gong, Y.; Wu, Z.; Song, L.; Gu, L.; Hu,
W.; Wang, X. Zirconium-Porphyrin-Based Metal-Organic Framework
Hollow Nanotubes for Immobilization of Noble-Metal Single Atoms.
Angew. Chem., Int. Ed. 2018, 57, 3493−3498.
(16) Abdel-Mageed, A. M.; Rungtaweevoranit, B.; Parlinska-Wojtan,
M.; Pei, X.; Yaghi, O. M.; Behm, R. J. Highly active and stable single
atom Cu catalysts supported by a metal-organic framework. J. Am.
Chem. Soc. 2019, 141, 5201−5210.
(17) Trickett, C. A.; Gagnon, K. J.; Lee, S.; Gándara, F.; Burgi, H.;
̈
Yaghi, O. M. Definitive molecular level characterization of defects in
UiO-66 crystals. Angew. Chem., Int. Ed. 2015, 54, 11162−11167.
(18) Wu, H.; Chua, Y. S.; Krungleviciute, V.; Tyagi, M.; Chen, P.;
Yildirim, T.; Zhou, W. Unusual and Highly Tunable Missing-Linker
Defects in Zirconium Metal-Organic Framework UiO-66 and Their
Important Effects on Gas Adsorption. J. Am. Chem. Soc. 2013, 135,
10525−10532.
REFERENCES
■
(1) Qiao, B.; Wang, A.; Yang, X.; Allard, L. F.; Jiang, Z.; Cui, Y.; Liu,
J.; Li, J.; Zhang, T. Single-atom catalysis of CO oxidation using Pt1/
FeOx. Nat. Chem. 2011, 3, 634−641.
(2) Wang, A.; Li, J.; Zhang, T. Heterogeneous single-atom catalysis.
Nat. Rev. Chem. 2018, 2, 65−81.
(3) Li, Z.; Ji, S.; Liu, Y.; Cao, X.; Tian, S.; Chen, Y.; Niu, Z.; Li, Y.
Well-Defined Materials for Heterogeneous Catalysis: From Nano-
particles to Isolated Single-Atom Sites. Chem. Rev. 2020, 120, 623−
682.
(19) Garribba, E.; Micera, G. The determination of the geometry of
Cu(II) complexes: An EPR spectroscopy experiment. J. Chem. Educ.
2006, 83, 1229−1232.
(20) Roessler, M. M.; Salvadori, E. Principles and applications of
EPR spectroscopy in the chemical sciences. Chem. Soc. Rev. 2018, 47,
2534−2553.
(21) Ji, S.; Chen, Y.; Zhao, S.; Chen, W.; Shi, L.; Wang, Y.; Dong, J.;
Li, Z.; Li, F.; Chen, C.; Peng, Q.; Li, J.; Wang, D.; Li, Y. Atomically
10984
https://doi.org/10.1021/jacs.1c03036
J. Am. Chem. Soc. 2021, 143, 10977−10985

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Dispersed Ruthenium Species inside Metal-Organic Frameworks:
Combining the High Activity of Atomic Sites and the Molecular
Sieving Effect of MOFs. Angew. Chem., Int. Ed. 2019, 58, 4271−4275.
(22) Tang, Y.; Wei, Y.; Wang, Z.; Zhang, S.; Li, Y.; Nguyen, L.; Li,
Y.; Zhou, Y.; Shen, W.; Tao, F. F.; Hu, P. Synergy of Single-Atom Ni1
and Ru1 Sites on CeO2 for Dry Reforming of CH4. J. Am. Chem. Soc.
2019, 141, 7283−7293.
(23) Ben Aissa, M. A.; Tremblay, B.; Andrieux-Ledier, A.;
Maisonhaute, E.; Raouafi, N.; Courty, A. Copper Nanoparticles of
Well-Controlled Size and Shape: A New Advance in Synthesis and
Self-Organization. Nanoscale 2015, 7, 3189−3195.
(24) Devautour-Vinot, S.; Maurin, G.; Serre, C.; Horcajada, P.;
Paula da Cunha, D.; Guillerm, V.; de Souza Costa, E.; Taulelle, F.;
Martineau, C. Structure and Dynamics of the Functionalized MOF
Type UiO-66 (Zr): NMR and Dielectric Relaxation Spectroscopies
Coupled with DFT Calculations. Chem. Mater. 2012, 24, 2168−2177.
(25) Fu, Y.; Kang, Z.; Yin, J.; Cao, W.; Tu, Y.; Wang, Q.; Kong, X.
Duet of acetate and water at the defects of metal-organic frameworks.
Nano Lett. 2019, 19, 1618−1624.
(26) Valenzano, L.; Civalleri, B.; Chavan, S.; Bordiga, S.; Nilsen, M.
H.; Jakobsen, S.; Lillerud, K. P.; Lamberti, C. Disclosing the Complex
Structure of UiO-66 Metal Organic Framework: A Synergic
Combination of Experiment and Theory. Chem. Mater. 2011, 23,
1700−1718.
(27) Parigi, G.; Luchinat, C. NMR Consequences of the Nucleus−
Electron Spin Interactions. In Paramagnetism in experimental
biomolecular NMR; Luchinat, C., Parigi, G., Ravera, E., Eds.; Royal
Society of Chemistry: London, UK, 2018; pp 1−41.
(28) Peterson, G. W.; Mahle, J. J.; DeCoste, J. B.; Gordon, W. O.;
Rossin, J. A. Extraordinary NO2 removal by the metal-organic
framework UiO-66-NH2. Angew. Chem., Int. Ed. 2016, 55, 6235−
6238.
(29) Kwak, J. H.; Tonkyn, R. G.; Kim, D. H.; Szanyi, J.; Peden, C. H.
Excellent Activity and Selectivity of Cu-SSZ-13 in the Selective
Catalytic Reduction of NOx with NH3. J. Catal. 2010, 275, 187−190.
(30) Jiang, H.; Zhou, J.; Wang, C.; Li, Y.; Chen, Y.; Zhang, M. Effect
of Cosolvent and Temperature on the Structures and Properties of
Cu-MOF-74 in Low-temperature NH3-SCR. Ind. Eng. Chem. Res.
2017, 56, 3542−3550.
(31) Gong, X.; Zhao, R.; Qin, J.; Wang, H.; Wang, D. Ultra-efficient
Removal of NO in a MOFs-NTP Synergistic Process at Ambient
Temperature. Chem. Eng. J. 2019, 358, 291−298.
Spectroscopic Properties and Disproportionation Reactivity of
Copper-Nitrosyl Complexes. J. Am. Chem. Soc. 1998, 120, 11408−
11418.
(40) Moreno-González, M.; Millán, R.; Concepción, P.; Blasco, T.;
Boronat, M. Spectroscopic Evidence and Density Functional Theory
(DFT) Analysis of Low-Temperature Oxidation of Cu+ to Cu2+ NOx
in Cu-CHA Catalysts: Implications for the SCR-NOx Reaction
Mechanism. ACS Catal. 2019, 9, 2725−2738.
(41) Kalita, A.; Kumar, P.; Mondal, B. Reaction of a copper(II)−
nitrosyl complex with hydrogen peroxide: putative formation of a
copper(I)−peroxynitrite intermediate. Chem. Commun. 2012, 48,
4636−4638.
(42) Hahn, E. L. Spin echoes. Phys. Rev. 1950, 80, 580−594.
(43) Steinbeck, C.; Krause, S.; Kuhn, S. NMRShiftDB - constructing
a free chemical information system with open-source components. J.
Chem. Inf. Comput. Sci. 2003, 43, 1733−1739.
(44) Banfi, D.; Patiny, L. Resurrecting and processing NMR spectra
on-line. Chimia 2008, 62, 280−281.
(45) Bignami, G. P. M.; Davis, Z. H.; Dawson, D. M.; Morris, S. A.;
Russell, S. E.; McKay, D.; Parke, R. E.; Iuga, D.; Morris, R. E.;
Ashbrook, S. E. Cost-effective 17O enrichment and NMR spectros-
copy of mixed-metal terephthalate metal−organic frameworks. Chem.
Sci. 2018, 9, 850−859.
(46) Yu, L.; Zhong, Q.; Zhang, S. Research of Copper Contained
SAPO-34 Zeolite for NH3-SCR DeNOx by Solvent-Free Synthesis
with Cu-TEPA. Microporous Mesoporous Mater. 2016, 234, 303−309.
(47) Park, J. H.; Park, H. J.; Baik, J. H.; Nam, I. S.; Shin, C. H.; Lee,
J. H.; Cho, B. K.; Oh, S. H. Hydrothermal Stability of Cu-ZSM-5
Catalyst in Reducing NO by NH3 for the Urea Selective Catalytic
Reduction Process. J. Catal. 2006, 240, 47−57.
(48) Jiang, H.; Wang, S.; Wang, C.; Chen, Y.; Zhang, M. Selective
Catalytic Reduction of NOx with NH3 on Cu-BTC-derived catalysts:
influence of modulation and thermal treatment. Catal. Surv. Asia
2018, 22, 95−104.
(49) Peng, B.; Feng, C.; Liu, S.; Zhang, R. Synthesis of CuO Catalyst
Derived from HKUST-1 Temple for The Low-Temperature NH3-
SCR Process. Catal. Today 2018, 314, 122−128.
(32) Wang, T.; Liu, H.; Zhang, X.; Guo, Y.; Zhang, Y.; Wang, Y.;
Sun, B. A plasma-assisted catalytic system for NO removal over
CuCe/ZSM-5 catalysts at ambient temperature. Fuel Process. Technol.
2017, 158, 199−205.
(33) Xu, S.; Han, X.; Ma, Y.; Duong, T. D.; Lin, L.; Gibson, E. K.;
Sheveleva, A.; Chansai, S.; Walton, A.; Ngo, D.; Frogley, M. D.; Tang,
C. C.; Tuna, F.; McInnes, E. J. L.; Catlow, C. R. A.; Hardacre, C.;
Yang, S.; Schröder, M. Catalytic decomposition of NO2 over a copper-
decorated metal−organic framework by non-thermal plasma. Cell Rep.
Phys. Sci. 2021, 2, 100349.
(34) Wikstrom, L. L.; Nobe, K. Catalytic dissociation of nitrogen
dioxide. Ind. Eng. Chem. Process Des. Dev. 1965, 4, 191−195.
(35) Wang, D.; Zhang, L.; Kamasamudram, K.; Epling, W. S. In Situ-
DRIFTS Study of Selective Catalytic Reduction of NOx by NH3 over
Cu-Exchanged SAPO-34. ACS Catal. 2013, 3, 871−881.
(36) Zhang, Y.; Peng, Y.; Li, K.; Liu, S.; Chen, J.; Li, J.; Gao, F.;
Peden, C. H. F. Using Transient FTIR Spectroscopy to Probe Active
Sites and Reaction Intermediates for Selective Catalytic Reduction of
NO on Cu/SSZ-13 Catalysts. ACS Catal. 2019, 9, 6137−6145.
(37) Sjövall, H.; Fridell, E.; Blint, R. J.; Olsson, L. Identification of
adsorbed species on Cu-ZSM-5 under NH3-SCR conditions. Top.
Catal. 2007, 42, 113−117.
̆
(38) Wright, A. M.; Sun, C.Y.; Dinca, M. Thermal cycling of a MOF-
based NO disproportionation catalyst. J. Am. Chem. Soc. 2021, 143,
681−686.
(39) Schneider, J. L.; Carrier, S. M.; Ruggiero, C. E.; Young, V. G.;
Tolman, W. B. Influences of Ligand Environment on the
10985
https://doi.org/10.1021/jacs.1c03036
J. Am. Chem. Soc. 2021, 143, 10977−10985