Construction of Dual-Active-Site Copper Catalyst Containing both Cu-N3 and Cu-N4 Sites

Article abstract of DOI:10.1002/smll.202006834

Clear recognition and rational construction of suitable active center for specific reaction is always of great significance in designing highly efficient catalysts. Herein, a dual-active-site copper catalyst (DAS-Cu) containing both Cu-N₃ and Cu-N₄ sites is reported. Such catalysts show extremely high catalytic performance (yield: up to 97%) toward oxyphosphorylation of alkenes, while catalysts with single active site (Cu-N₃ or Cu-N₄) are chemically inert in this reaction. Combined with theoretical and experimental results, the different roles of two different Cu active sites in this reaction are further identified. Cu-N₃ site captures the oxygen and trigger further oxidizing process, while Cu-N₄ site provides moderate adsorption sites for the protection of phosphonyl radicals. This work deeply discloses the significant cooperated role with two single-atomic sites in one catalytic active center and brings up a valuable clue for the rational design of better-performing heterogeneous catalyst.

Full text of DOI:10.1002/smll.202006834

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Construction of Dual-Active-Site Copper Catalyst
Containing both CuN and CuN Sites
3
4
Yu Xiong, Shibin Wang, Wenxing Chen, Jian Zhang, Qiheng Li, Han-Shi Hu,*
Lirong Zheng,* Wensheng Yan, Lin Gu, Dingsheng Wang,* and Yadong Li
Recently, single atom catalysts (SAC)
Clear recognition and rational construction of suitable active center for
specific reaction is always of great significance in designing highly efficient
catalysts. Herein, a dual-active-site copper catalyst (DAS-Cu) containing both
CuN and CuN sites is reported. Such catalysts show extremely high
draw a lot of attentions from researchers,
because such catalysts not only show
excellent catalytic activities but also pos-
sess single atomically active centers which
can be identified by advanced characteri-
zations (aberration-corrected high-angle
annular dark-field scanning transmission
electron microscopy (AC-HAADF-STEM)
images, extended X-ray absorption fine
structure (EXAFS) curve fitting, density
3
4
catalytic performance (yield: up to 97%) toward oxyphosphorylation of alk-
enes, while catalysts with single active site (CuN or CuN ) are chemically
3
4
inert in this reaction. Combined with theoretical and experimental results,
the different roles of two different Cu active sites in this reaction are further
identified. CuN site captures the oxygen and trigger further oxidizing pro-
3
[11–32]
functional theory (DFT) modeling, etc.).
cess, while CuN site provides moderate adsorption sites for the protection
4
However, SACs containing the unitary
active sites are also a hindrance to their fur-
ther applications. On the one hand, some
complex reactions require two or more
active sites to activate substrates, while SACs
are incompetent on these reactions. On the
other hand, the synergistic effect of dual
of phosphonyl radicals. This work deeply discloses the significant cooperated
role with two single-atomic sites in one catalytic active center and brings up
a valuable clue for the rational design of better-performing heterogeneous
catalyst.
or more active sites can also improve the catalytic properties of
1. Introduction
[3,33–41]
simple reactions.
For example, Zbořil and co-workers devel-
Catalytic active centers are known as central characters in
oped a novel strategy to synthesize mixed-valence single atom cat-
alysts by partial reducing the metal atoms (Fe or Cu) coordinated
on nitrile groups functionalized graphene and discovered that the
synergistic effect of Cu(II) and Cu(I) is the essential part in the
catalysis since Taylor introduced this concept for nearly 100
years.[
1–5]
Recognizing active centers clearly in catalysts is crit-
ical to comprehend the reaction mechanism and design new
catalysts with high efficiency. Since a variety of surface sites
[20,40]
oxidative coupling reaction.
Xiao et al. developed FeCoN /C
x
(
including crystal facets, edges, corners, terrace, steps, kinks,
catalysts and discovered that the triangle FeCoN −OH sites show
5
etc.) coexist in traditional nanosized catalysts, the real catalytic
active centers of these catalysts can be hardly identified.
about 20 times the activity of FeN4 sites in oxygen reduc-
[
6–10]
[39]
tion reaction.
However, the novel strategies and potential
Dr. Y. Xiong
Prof. L. Zheng
Department of Chemistry and Chemical Engineering
Central South University
Beijing Synchrotron Radiation Facility
Institute of High Energy Physics
Chinese Academy of Sciences
Beijing 100049, China
Changsha 410083, China
Dr. Y. Xiong, S. Wang, W. Chen, J. Zhang, Q. Li, Prof. H.-S. Hu,
Prof. D. Wang, Prof. Y. Li
Department of Chemistry, Tsinghua University
Beijing 100084, China
E-mail: hshu@mail.tsinghua.edu.cn;
wangdingsheng@mail.tsinghua.edu.cn
E-mail: zhenglr@ihep.ac.cn
Prof. W. Yan
National Synchrotron Radiation Laboratory
University of Science and Technology of China
Hefei 230029, China
Dr. S. Wang
Prof. L. Gu
Institute of Industrial Catalysis
State Key Laboratory Breeding Base of Green-Chemical Synthesis
Technology
Beijing National Laboratory for Condensed Matter Physics
Institute of Physics
Chinese Academy of Sciences
Beijing 100190, China
College of Chemical Engineering
Zhejiang University of Technology
Hangzhou 310032, China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.202006834.
DOI: 10.1002/smll.202006834
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applications of dual-sites catalysts and the cooperation mecha-
nisms of dual or more sites are far from dug out.
in the catalyst (Figure 1a; and Figure S5, Supporting Informa-
tion). In Figure 1b, energy-dispersive X-ray (EDX) mappings of
DAS-Cu denote that Cu, C, and N are homogeneously distri-
buted in the nanosheets. From AC-HAADF-STEM image, we can
identify the atomically dispersed Cu by Z-contrast (Figure 1c).
The metal loading of DAS-Cu is as high as 4.6 wt% (certified by
inductively coupled plasma optical emission spectroscopy (ICP-
OES) analysis), which indicates a short interatomic distance of
neighboring Cu atoms. The further Z-contrast analysis of Cu
atoms (region 1 and region 2 in Figure 1c; more typical adjacent
Cu atoms are cycled by wathet ellipse) shows that the distances
of the adjacent Cu atoms are between 4 and 6 Å (Figure 1d).
In order to identify the atomic local structure of the inde-
pendent Cu species, XAFS spectroscopy was carried out. From
Figure 1e, we can see the Cu K-edge X-ray absorption near-edge
β-ketophosphonates are highly valuable compounds, which
serve as important synthetic intermediates for pharmaceutical
[42–44]
and show interesting biological properties.
Difunction-
alizing alkenes with H-phosphonates in air is the most facile
(
one-pot) and environmental benign (carbon balance and green
[44,46]
oxidant) synthetic strategies.
Three steps (oxidation, cou-
pling, and hydrogen transfer) are involved in this strategy. Both
H-phosphonates and dioxygen should be activated and thus the
division cooperation of two active sites can highly accelerate this
reaction. Therefore, constructing and designing efficient cata-
lysts with dual active sites can help with the completion of the
reaction. Moreover, the further identification of the synergistic
effect for different active sits can deepen the understanding of
reaction mechanisms and pave the way for rational designing
of novel dual-active-site (DAS) catalysts.
structure (XANES) spectra of DAS-Cu with Cu foil, Cu O, and
2
CuO as references. According to the height of white line (H ) at
w
Herein, we prepared DAS-Cu catalysts with both Cu–N and
8996.5 eV and the energy of absorption edge (E ) at 8988.0 eV,
3
0
Cu–N active sites on nitrogen-doped carbon by pyrolyzing Cu
the average oxidation state number of Cu atoms in DAS-Cu is
4
[48,49]
complexes. Atomically dispersed Cu is distinguished by AC-
HAADF-STEM and two different kinds of Cu active sites are
determined by EXAFS analysis combined with Cu 2p and Cu
L-inner level-valence-valence electron transition (LVV) X-ray
photoelectron spectroscopy (XPS) spectra. We surprisingly
discover that such catalysts show great catalytic performance
in oxyphosphorylation reaction (up to 97% yield in only 2 h),
situated between zero and two.
The Fourier-transformed
3
k -weighted EXAFS spectrum of DAS-Cu (Figure 1f) displays
only one main peak at 1.56 Å, which correspond to the first coor-
dination shell of CuN, and no obvious CuCu peaks (2.24 Å)
are observed. Tiny peaks located at ≈2–4 Å can be assigned to
the peaks of the second or higher CuC coordination shell
(Figure S6, Supporting Information). This result further confirms
the sole presence of single atomic Cu species in DAS-Cu catalyst.
We next performed the EXAFS curve fitting analysis to study the
quantitative structural parameters of Cu atoms (Figure S7 and
Table S1, Supporting Information). Cu atoms in DAS-Cu show an
average coordination numbers of 3.3 and an average bond length
of 1.94 Å. The data indicate that two different kinds of Cu atomic
sites coexist in DAS-Cu (the inset of Figure S7 (Supporting Infor-
mation) is the corresponding model of atomic structure), which is
coordinated by three or four N atoms, respectively.
while catalyst possessing Cu–N sites is inert and catalyst con-
3
taining CuN sites only shows trace reactivity under the same
4
condition. The reasonable structure model containing CuN
4
and CuN sites for the DAS-Cu was constructed depending
3
on EXAFS, XPS and near-edge X-ray absorption fine structure
spectra (NEXAFS) spectra. DFT calculations combined with
electron paramagnetic resonance (EPR) studies investigate the
reaction mechanism and the synergistic effect of CuN and
3
CuN . It is believed that this work brings new insights in
4
designing effective catalysts with coherence effects from two
single-atoms based active sites in one catalytic center.
The existence of different Cu sites is also determined by both
Cu 2p and Cu LVV XPS spectra. XPS survey spectrum is shown
in Figure S8 (Supporting Information), suggesting that C, N, O,
and Cu are the major components in DAS-Cu. The XPS spec-
trum of DAS-Cu in Cu 2p region is shown in Figure 2a. Two
main features can be distinguished clearly, which indicates the
coexistence of two different Cu species in DAS-Cu. The feature
located at 932.4 and 952.2 eV can be attributed to Cu species
with the valence state close to +1, while the other feature which
2
. Results and Discussion
The DAS-Cu catalyst was synthesized via pyrolyzing Cu com-
plexes. Creatine is chosen as key ligand of Cu complexes, because
creatine provides two different coordination sites (guanidyl and
carboxylate groups). In the synthetic procedure, Cu(NO ) , NaOH,
[
50]
located at 934.6 and 954.3 eV can be attributed to Cu(II). The
Cu LVV Auger spectrum also shows two deconvoluted peaks,
3
2
and creatine are first mixed in water and the claret powders are
gained by vaporizing the solvent. During this process, Cu atoms
are coordinated with guanidyl or carboxylate groups respectively.
DAS-Cu catalysts with different Cu active sites are obtained after
the calcination of the as-obtained powders and etching of excessive
Cu nanoparticles (see detailed procedure in the Experimental Sec-
tion; Figure S1, Supporting Information). Transmission electron
microscopy (TEM) (Figure S2, Supporting Information) and scan-
ning electron microscopy (Figure S3, Supporting Information)
images show the laminar structure of DAS-Cu. The broad peak
at around 26.5° in powder X-ray diffraction pattern (Figure S4,
Supporting Information) indicates the hexagonal graphitic struc-
[
51]
which can be assigned to two different species (Figure 2b).
On the basis of XPS spectra and EXAFS analysis, we can iden-
tify that CuN and CuN sites coexist in DAS-Cu catalysts.
3
4
C 1s, N 1s, and O 1s XPS spectra combined with NEXAFS
are carried out to further clarify the structure of DAS-Cu. C 1s
XPS spectrum of DAS-Cu deconvolves into four main peaks
(Figure 2c). The major peak at 284.8 eV can be identified as aro-
3
matic CC bonds and weaker peaks can be certified as C-sp
(285.7 eV), C-oxide (286.6 eV) and aromatic NCN (288.1 eV)
respectively, which indicate the 2D structure with some defects
[
52,53]
and vacancies.
In C K-edge NEXAFS spectrum, four reso-
[47]
ture in DAS-Cu. scanning transmission electron microscopy
STEM) image manifests no observable nanoparticles or clusters
nances in π* region are detected (Figure 2d). The resonances
at 284.8, 285.6, and 287.8 eV are associated with 1s→π* (CC),
(
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Figure 1. Characterizations of DAS-Cu. a,b) STEM image and corresponding EDX mappings of DAS-Cu, which show distributions of C (blue), N (red),
Cu (green), respectively. Scale bar: 20 nm. c) AC-HAADF-STEM image of DAS-Cu; the enlarged image of region 1 and region 2 (inset). Scale bar: 5 nm.
d) The corresponding Z-contrast analysis of region 1 and region 2. e,f) XANES spectra and Fourier transform EXAFS spectra of the DAS-Cu catalysts
in comparison with Cu foil; Cu O; CuO at the Cu K-edge.
2
1
s→π* (CCN) and 1s→π* (NCN) transitions respectively,
atomic sites supported on graphene are actually coordinated by
pyridinic/pyrrolic nitrogen atoms, C atoms, or hybrid of C and
indicating the formation of nitrogen containing heteroarenes.
[
14,58–61]
[62]
The weaker resonance at 287.0 eV can be defined as the 1s→π*
N.
According to the research of Gao and co-workers,
(
CO), which suggest the carbonyl or carboxyl group at the
single Cu atoms coordinated to pyridinic N with structures
edge of DAS-Cu. In σ* region, the strong resonance at 292.2 eV
can be assigned to 1s→σ* (CN) transition and the weaker res-
onance at 301.0 eV can be certified as 1s→σ* (CN; CO; and
of CuN site and CuN site both exhibit higher stability in
3
4
contrast to a hybrid coordination with C and N. Moreover, the
experimental results of EXAFS, XPS, and NEXAFS analyses
also strongly suggest that the CuN and CuN sites coexist
[54]
CC) transition. Three deconvoluted peaks can be detected
in N 1s XPS spectrum at 398.2, 399.6, and 400.7 eV, which are
attributed to the pyridinic, graphitic, and pyrrolic nitrogen spe-
cies, respectively (Figure 2e).[ N K-edge NEXAFS spectrum
of DAS-Cu shows three resonances in π* region (399.5 eV for
pyridinic N; 400.1 eV for pyrrolic N; 401.5 eV for graphitic N),
which is coincidence with the N 1s XPS spectrum (Figure 2f).
In σ* region, the resonance at 407.1 eV can be defined as 1s→σ*
3
4
in DAS-Cu. Therefore, these two isolated sites are used in the
subsequent studies.
55]
Though theoretical studies of structure for separate
[
63]
[64]
CuN4
or CuN3
have been reported, the synergistic
catalysis with these two sites working together for highly effi-
cient chemical reactions is rare. Since the distances between
the separate CuN /CuN site are the crucial factor for the
3
4
[56]
(
C-N; CN) transition. Two main components are detected
synergistic effect, the structures with different CuN /CuN
3
4
in O 1s XPS spectrum (Figure S9, Supporting Information),
which can be identified as carbonyl group (533.5 eV) and
absorbed oxygen (531.3 eV).[ In conclusion, we can identify
that CuN and CuN active sites are anchored on the 2D CN
distances are therefore thoroughly investigated. Their stabilities
are measured by relative energies as well as average Cu binding
energies. As shown in Figure 3a, the p−(6 × 6) graphene layer is
57]
employed and vacancy sites with different distances of CuN
3
4
3
sheets with some pendant groups.
and CuN sites are proposed in three directions (a, b, c). Two
4
DFT calculations were performed to further understand
the geometric and electronic structure of DAS-Cu. Previous
experimental and theoretical studies have shown that single-
vacancy sites are constructed along each of the three direc-
tions originated from the CuN site. In total, six inequiva-
4
lent DAS-Cu structures are constructed and the corresponding
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Figure 2. XPS and NEXAFS spectra of DAS-Cu. a,b) Cu 2p XPS spectrum and Cu LVV Auger spectrum of DAS-Cu. c,d) C 1s XPS spectrum and C K-edge
NEXAFS spectrum of DAS-Cu. e,f) N 1s XPS spectrum and N K-edge NEXAFS spectrum of DAS-Cu.
optimized geometries are listed in Figure 3b. Their relative
energies reveal that the energy of the DAS-Cu catalyst increases
when the CuN /CuN distance extends from 5.33 to 9.08 Å
energy is calculated to be highly exothermic of −1.01 to −1.15 eV,
indicating that the isolated CuN and CuN distributions on
the nitrogen doped graphene substrate exhibits high stabilities,
and the single Cu sites are less likely to agglomerate (detailed
calculation methods and results are shown in Table S2, Sup-
porting Information).
4
3
4
3
(
Figure 3c). The result indicates that the dual Cu sites are more
likely to locate close to each other. To further certify the stabili-
ties of the proposed structures, the binding energy per Cu atom
on the graphene substrate is calculated. Among the 6 types of
the CuN and CuN distributions, the average Cu binding
The electronic structure of DAS-Cu is studied using the
model with the CuCu distance of 5.33 Å. Its spin density
4
3
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Figure 3. DFT calculation. a) Schematic of possible single C vacancy sites for further construction of the CuN site. b) The optimized structures of
3
the DAS-Cu surface, with the CuN site located in the corresponding C vacancy sites shown in (a). c) The corresponding relative energies and the
3
average Cu binding energies of the DAS-Cu surfaces with different CuN /CuN dispersion. d) Spin density plot and magnetic moment of the CuN
4
3
4
and CuN site on the DAS-Cu catalyst.
3
plot is shown in Figure 3d. For the CuN site, the Cu atom
CuN distance of 1.93 Å. For the CuN3 site, the Cu atom
is coordinated with three pyridinic N atoms with the average
CuN bond length of 1.95 Å, which is in line with the results
4
is anchored on the double carbon vacancy site in the graphene
layer and coordinated with four N atoms with the average
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in previous report.[56] Spin polarized calculations were per-
formed to further illustrate the oxidation state of Cu atoms in
DAS-Cu. The magnetic moments of the CuN and CuN
this reaction under the same condition. Considering single Cu
atoms and nanosized Cu coexist in DAS-Cu-NPs, we also test
the catalytic performance of nanosized Cu (TEM images are
shown in Figure S29, Supporting Information) and the results
show that nanosized Cu exhibits only moderate activity (14%
yield) toward this reaction under the same condition. These
4
3
sites are 0.614 and 0.004 μB, respectively (Figure 3d), sug-
0
9
0
10
gesting the electronic configurations of 4s 3d and 4s 3d to
Cu(II) in CuN and Cu(I) in CuN , respectively. Additionally,
4
3
the magnetic moment of Cu atoms in CuN site is 0.614 μB,
results strongly certified that the synergistic effect of CuN
4
3
which is close to the value in CuO.[
65,66]
The projected density
and CuN is crucial in this reaction. No desired product is
4
of states of the CuN and CuN site is shown in Figure S10
detected with the absence of NaHCO , which suggests that the
3
4
3
(Supporting Information), which also confirms spin polariza-
weak alkaline environment is also essential in this reaction.
tion of the CuN site.
When the reaction is performed under N atmosphere, no reac-
4
2
The oxyphosphorylation reaction of styrene and diethyl phos-
phite in air is used to evaluate the catalytic activity of DAS-Cu.
To our delight, DAS-Cu shows excellent catalytic performance
toward the desired product 3aa in 90% yield (Figure 4). The
calculated turnover frequency (TOF) value of the catalyst is
tion arises, which gives evidence that air severs as the oxidant
in this reaction system. Moreover, DAS-Cu also shows good
recyclability toward the oxyphosphorylation reaction. The char-
acterizations of DAS-Cu after reaction (DAS-Cu-cycled) indicate
that DAS-Cu nearly unchanged after reaction (TEM, STEM,
XRD, AC-HAADF-STEM, EXAFS, and XPS are shown in Fig-
ures S30–S42 and Table S4, Supporting Information). Further-
more, ICP-OES is used to analyze the liquid phase of reaction
solution. Only a slight amount of dissolved Cu (Cu: 0.6 ppm;
0.3% of the total Cu atoms in DAS-Cu) is detected, which also
demonstrates the good stability of DAS-Cu.
In order to explore the influence of substrate categories, the
substrate scope of the oxyphosphorylation reaction is investi-
gated under the same reaction condition. As shown in Figure S43
(Supporting Information), the aromatic alkenes with electro-
donating substituents (Me and OMe) can react beneficially
with diethylphosphite to produce 3ba and 3ca at the yield of
93% and 97%, respectively. When styrene derivatives bear
electron-withdrawing groups (F, Cl, and AcO), the target
products 3da–3fa are obtained in relatively moderate yields
(82–73%). As for 2-vinylnaphthalene using in the reaction,
the desired product 3ga can also be isolated in a yield of 83%.
Moreover, DAS-Cu also exhibits good catalytic performance for
oxyphosphorylation of internal aryl alkenes (β-methylstyrene),
furnishing the target product 3ha in 80% yield. Besides the dif-
ferent alkenes, different H-phosphonates (diisopropylphosphite
and diisobutylphosphite) can also work well with styrene to
provide products 3ab and 3ac in a good yield of 88% and 77%,
respectively.
−
1
1
86.4 h . In contrast, homogeneous Cu catalysts, such as CuBr,
CuBr , and Cu(II)-phthalocyanine (possess only CuN site)
2
4
are unreacted under the same condition. SAC-Cu (possess
only CuN sites; the detailed synthetic procedures are shown
3
in the Experimental Section; Figures S11–S22 and Table S3,
Supporting Information) and SAC-Cu-2 (possess only CuN
4
sites; synthesized via a reported strategy;[ the detailed syn-
thetic procedures are shown in the Experimental Section;
and Figures S23–S25, Supporting Information) were prepared
to evaluate the synergistic effect of CuN and CuN in this
67]
3
4
reaction. Interestingly, no reaction occurs when SAC-Cu is used
and SAC-Cu-2 only exhibits a low yield of 22%, which indicates
that the synergistic effect of two Cu catalytic sites plays the key
role in the catalytic system. The catalytic properties of DAS-Cu
before teaching (DAS-Cu-NPs; the detailed synthetic proce-
dures and characterizations are shown in the Experimental
Section; Figure S26–S28, Supporting Information) have also
studied, which show the similar activity (86% yield) toward
To investigate the reaction mechanism, EPR technique was
performed with 5,5-dimethyl-1-pyrroline N-oxide as spin trap-
ping agents. When the reaction is heated to 80 °C without
any catalysts, no signals of radicals are detected. Superoxide
radicals can be detected when DAS-Cu added to the reaction
system for 3 min. When prolonging the reaction time, the sig-
nals of superoxide radicals become more obviously (a = 10 G,
H
[
68]
aN = 13 G; Figure S44, Supporting Information). On the con-
trary, SAC-Cu shows no detectable signals after 10 min reaction
(
Figure S45, Supporting Information). These results suggest
that the simultaneous existence of CuN and CuN active
sites promotes the formation of superoxide radicals and thus
accelerates the reaction.
3
4
Previous reports have proposed the reaction mechanisms
for homogeneous catalytic alkene oxyphosphorylation to β-ket
Figure 4. Oxyphosphorylation of styrene to form β-ketophosphonate.
Unless otherwise noted, all reactions were carried out at a 0.22 mmol
scale in DMA (0.5 mL) at 80 °C for 2 h with 2 mg catalysts, a molar ratio
[
44–46]
ophosphonate,
in which the activation of O through the
2
−
Cu(OO∙ ) superoxide formation is the key step, followed by
RO) P(O)H dehydrogenation and radical formation. In this
2
of 1a/2a = 1: 1.1 and 2 mg NaHCO . Yield is determined by gas chroma-
3
(
tography equipped with a flame ionization detector with 20 μL dodecane
as internal standard.
work, our DFT calculations reveal that the CuN site exhibits
3
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Figure 5. Potential energy surfaces for styrene oxyphosphorylation to β-ketophosphonate over DAS-Cu catalyst. The reaction intermediate from each
elementary step is represented by int, and detailed structures for all reaction intermediates are shown in Figure S47 (Supporting Information) (H white,
C gray, blue N, red O, purple P, orange Cu).
high reactivity toward O , with highly exothermic adsorption
0.54 eV, respectively. The above calculations reveal the Cu(I) in
2
energy of −1.18 eV (Figure 5). In contrast, O adsorption on the
the CuN site have higher reducibility and reactivity toward
2
3
CuN site is much less favorable, with the adsorption energy
oxide species (O , diethyl phosphite, and phosphonyl radical).
4
2
calculated to be −0.17 eV. These results suggest that CuN
Spin density plots of phosphonyl species locating at the CuN
3
3
sites in DAS-Cu can capture the gaseous O more effectively
and CuN sites are shown in Figure S48 (Supporting Informa-
2
4
and trigger the subsequent diethyl phosphite dehydrogenation.
tion) with the magnetic moment of the P atom 0.02 μB for the
former and 0.14 μB for the latter, respectively, indicating that
the dehydrogenated diethyl phosphite still remains the feature
To certify this result, O temperature-programmed desorption
2
(
O -TPD) experiments of DAS-Cu with SACs-Cu-2 as references
2
have been carried out. We can see the only peak at ≈160 °C in
of a radical when adsorbing on the CuN site. From the above
4
the plots of SAC-Cu-2, indicating that the O physical adsorp-
data, it can be concluded that the CuN site is mainly respon-
2
3
tion is dominant on the surface of SAC-Cu-2 (Figure S46, Sup-
porting Information). However, the main signal appears at
sible for capturing O in the gas phase, while the CuN is the
2
4
moderate adsorption site for diethyl phosphite and can effec-
tively protect the phosphonyl radical.
above 200 °C, which suggests that O strongly adsorbs on the
2
surface of DAS-Cu. These results are in good consistent with
our previous results and strongly illustrate that CuN3 sites
are regarded to account for O activation. Upon O chemisorp-
After the formation of the phosphonyl radical, the phys-
isorbed styrene can be easily oxidized by the OOH* on the adja-
cent CuN site to form styrene oxide (int 5), which is highly
2
2
3
tion on the CuN site, the Cu atom in the adjacent CuN
exothermic with the reaction energy of −2.03 eV. Meanwhile,
we have also investigated the alternative reaction pathway of
phosphonyl radical direct coupling with the styrene (Figure S49,
Supporting Information, and the reaction energy of this step is
−1.11 eV, which demonstrate that the former reaction pathway
is more favorable. The generated styrene oxide further cou-
ples with the phosphonyl radical (Figure S47, int 6, Supporting
Information), and the reaction energy is −1.02 eV. On the other
hand, the reaction is much less favorable on the SAC-Cu sur-
face exposing two CuN3 sites due to the strong interaction
between PO(OEt) and CuN , in which the radical structure
3
4
further provides the adsorption site for diethyl phosphite and
the POCu bond length is 2.41 Å (Figure S47, int 2, Sup-
porting Information) with the exothermic adsorption energy
of −0.43 eV. The adsorbed diethyl phosphite can further react
with the O * to form the OOH* and the phosphonyl radical
2
(
∙PO(OEt) ) intermediate (Figure S47, int 3, Supporting Infor-
2
mation), with the reaction energy and the energy barrier of 0.60
and 0.64 eV, respectively. Same reaction pathway on SAC-Cu
catalyst with two CuN sites was also calculated for compar-
4
ison (Figure 5). The adsorption energy of diethyl phosphite on
2
3
the CuN site is calculated to be −0.51 eV. CuN O * spe-
is destroyed, and the reaction energy is −0.21 eV (Figure S50,
4
4
2
cies on SAC-Cu surface are less reactive than the CuN O *
Supporting Information). After the coupling of ∙PO(OEt) and
3
2
2
species on DAS-Cu surface, with the diethyl phosphite dehy-
drogenation energy barrier and reaction energy of 0.74 and
styrene oxide, the H atom further transfers to the OH* to gen-
erate the target product (β-ketophosphonate) and H O with
2
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the reaction energy of −1.88 eV. The catalyst can be regener-
vigorous stirring for 10 min, solution B was poured into solution A
and the mixed solution was stirred for 30 min. Subsequently, the
mixture was transferred into 100 mL Teflon-lined autoclave and heated
at 120 °C for 4 h. The products were washed with methanol and N,N-
dimethylformamide, respectively, for three times and dried at 60 °C for
whole night. The obtained powders were pyrolyzed at 1000 °C for 4 h
ated with the desorption of β-ketophosphonate and H O. In
2
conclusion, three key elementary steps are involved in total:
oxidation of styrene, styrene oxide coupling with phosphonyl
radical, and hydrogen transfer to form β-ketophosphonate. All
of these reaction steps are thermodynamically favorable, which
explains the high reactivity of the DAS-Cu catalyst to the target
products.
−
1
under nitrogen atmosphere. The heating rate was set to 5 °C min . The
as-obtained black powder is SAC-Cu-2 (≈45 mg).
The Preparation of Nanosized Cu: At first, Vulcan XC-72
(
100 mg), polyvinyl pyrrolidone (K30, 100 mg), and Cu(NO ) ·3H O
3 3 2
(
38 mg; nominal loading: 10 wt%) was ultrasonically dispersed in
deionized water (20 mL) at room temperature. NaBH (12.8 mg; 4 eq)
4
3
. Conclusion
in 20 mL deionized water was added dropwise to Cu(NO3)2 solution.
After stirred continuously for 2 h, black powders were collected by
centrifugation and washed by deionized water and ethanol twice,
respectively. The as-obtained nanosized Cu catalyst was dried at 70 °C
for 12 h to remove the solvent, then the solid was used for catalytic tests
without further purification.
Catalytic Tests for Oxyphosphorylation Reaction: In a typical procedure,
styrene (or its derivatives; 0.22 mmol), diethyl phosphate (0.24 mmol;
1.1 eq), NaHCO3 (2 mg), DAS-Cu catalysts (2 mg, Cu/substrate =
0.6 mol%) and N,N-dimethylacetamide (DMA) (0.5 mL) were first
added to a Shlenck tube equipped with a stir bar, and the mixture was
stirred at 80 °C for 2 h. After the reaction finished, the reaction mixture
was analyzed by gas chromatography equipped with a flame ionization
detector and gas chromatography-mass spectrometry with dodecane
as the internal standard. The crude reaction mixture was purified by
extraction with saturated NaCl solution and flash chromatography
on silicone gel (eluent: hexane/ethyl acetate, v/v = 3/1) to afford
corresponding products. The overall TOF value was measured upon
completion of reactions and the calculation of it was based on the total
Cu loading in the catalyst.
In conclusion, we report a facile method to prepare DAS-Cu
catalysts by pyrolyzing Cu complexes with Cu atoms in dif-
ferent coordination sphere. DAS-Cu shows robust activity (up
to yields: 97% in 2 h reaction) toward oxyphosphorylation of
styrene and its derivatives. The high activity of atomically dis-
persed CuN and CuN sites are responsible chiefly for the
terrific catalytic properties. DFT calculations revealed the syn-
ergistic effect of two different Cu sites in DAS-Cu toward sty-
3
4
rene oxyphosphorylation: CuN sites capture the oxygen and
3
trigger further oxidizing reactions, CuN sites stabilize the
4
reactant via moderate adsorption and protect the phosphonyl
radical. Overall, this work not only provides a novel strategy to
prepare dual-active sites Cu catalysts but also points out a new
way for potential applications of such catalysts.
Catalyst Recycling Test: After the reaction finished, the reaction
mixture was centrifuged and the liquid layer was siphoned out.
DAS-Cu was washed with ethyl acetate, ethanol, and deionized
water three times, respectively. The black solid was collected by
centrifugation and was dried in a vacuum over 40 °C for 8 h. Finally,
the recovered DAS-Cu was used in the subsequent reaction without
further purification.
4
. Experimental Section
The Preparation of DAS-Cu: In a typical synthetic procedure of DAS-
Cu, creatine (6.00 g; 45.8 mmol) and Cu(NO ) ·2.5 H O (1.331 g;
3
2
2
5
.72 mmol; 0.125 eq) were first added to a flask containing 25 mL
deionized water with vigorously stirring at 80 °C. After stirring for 2 h,
sodium hydroxide (1.83 g; 45.8 mmol) was added to the slight yellow
solution and raise the temperature to 100 °C to evaporate water and
ensure the completion of coordination for 24 h. The collected claret
red solid (≈8.4 g with reasonable losses) was placed in a tube furnace
−
1
and then heated to 600 °C for 2 h at the heating rate of 5 °C min
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
under flowing Ar gas, heated under mixed gas (hydrogen 5% in Ar)
to 400 °C for 2 h and then naturally cooled to room temperature
to obtain the representative samples (2.89 g, pyrolyzed loss rate
6
5.5%). The obtained sample was washed with deionized water for
three times to remove soluble impurities (denoted as DAS-Cu-NPs;
.80 g; nominal loading: 45.4 wt%; actual loading: 40.2 wt%). Cu NPs
0
Acknowledgements
was etched with saturate CuSO in HCl solution (35 wt%) and finally
catalysts were obtained (0.45 g; nominal loading: 2.9 wt%; actual
loading: 4.6 wt%).
4
Y.X. and S.W. contributed equally to this work. This work was supported
by the National Key R&D Program of China (No. 2018YFA0702003),
the National Natural Science Foundation of China (Nos. 21890383 and
21871159), Science and Technology Key Project of Guangdong Province
of China (No. 2020B010188002), and China Postdoctoral Science
Foundation (Nos. 2018M640114 and 2019M650626). The authors thank
the BL14W1 station in Shanghai Synchrotron Radiation Facility (SSRF)
and 1W1B station for XAFS measurement in Beijing Synchrotron
Radiation Facility (BSRF). They also appreciate the BL12B station
of National Synchrotron Radiation Laboratory (NRSL) for NEXAFS
The Preparation of SAC-Cu: Guanidine thiocyanate (6 g; 50.8 mmol)
and Cu(NO ) ·2.5 H O (1.452 g; 6.35 mmol; 0.125 eq) were added to a
3
2
2
flask containing 25 mL deionized water with vigorously stirring at 80 °C.
After stirring for 2 h, raise the temperature to 100 °C to evaporate water
and ensure the completion of coordination for 24 h. The collected brown
solid (≈7 g with reasonable losses) was placed in a tube furnace and
−
1
then heated to 600 °C for 2 h at the heating rate of 5 °C min under
flowing Ar gas, heated under mixed gas (hydrogen 5% in Ar) to 400 °C
for 2 h and then naturally cooled to room temperature to obtain the
representative samples (1.4 g, pyrolyzed loss rate 80%). The obtained
sample was washed with water and ethanol for three times and SAC-Cu
is obtained (≈1.35 g).
measurement. They appreciate Ningqiang Zhang for providing O -TPD
test and Yunhu Han for taking TEM images.
2
The Preparation of SAC-Cu-2: SAC-Cu-2 is prepared via a reported
[
67]
strategy.
2-methylimidazole (2.63 g) was dissolved in methanol
Conflict of Interest
(
40 mL; solution A). Zn(NO ) ·6H O (2.38 g). and Cu(CH COO) ·H O
3
2
2
3
2
2
(0.16 g), were dissolved in methanol (60 mL; solution B). After
The authors declare no conflict of interest.
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[
[
[
[
28] J. Yang, W. Li, D. Wang, Y. Li, Adv. Mater. 2020, 32, 2003300.
29] T. Sun, L. Xu, D. Wang, Y. Li, Nano Res. 2019, 12, 2067.
30] S. H. Ahn, A. Manthiram, Small 2020, 16, 2002511.
31] W. Xiong, H. Li, H. Wang, J. Yi, H. You, S. Zhang, Y. Hou, M. Cao,
T. Zhang, R. Cao, Small 2020, 16, 2003943.
Data Availability Statement
Data sharing is not applicable to this article as no new data were created
or analyzed in this study.
[
32] M. Fan, J. Cui, J. Wu, R. Vajtai, D. Sun, P. M. Ajayan, Small 2020, 16,
1
906782.
Keywords
[
33] Z. Chen, E. Vorobyeva, S. Mitchell, E. Fako, M. A. Ortuño, N. López,
S. M. Collins, P. A. Midgley, S. Richard, G. Vilé, J. Pérez-Ramírez,
Nat. Nanotechnol. 2018, 13, 702.
dual-active-site catalysts, oxyphosphorylation reaction, single atom
catalysts
[
34] Z. Lu, B. Wang, Y. Hu, W. Liu, Y. Zhao, R. Yang, Z. Li, J. Luo, B. Chi,
Z. Jiang, M. Li, S. Mu, S. Liao, J. Zhang, X. Sun, Angew. Chem., Int.
Ed. 2019, 58, 2622.
Received: November 1, 2020
Revised: December 31, 2020
Published online: February 1, 2021
[35] K. Kratzl, T. Kratky, S. Günther, O. Tomanec, R. Zbořil, J. Michalička,
J. M. Macak, M. Cokoja, R. A. Fischer, J. Am. Chem. Soc. 2019, 141,
13962.
[
36] J. Kim, H.-E. Kim, H. Lee, ChemSusChem 2018, 11, 104.
[
[
[
1] H. S. Taylor, Proc. R. Soc. London, Ser. A 1925, 108, 105.
2] M. Boudart, Adv. Catal. 1969, 20, 153.
3] L. Liu, A. Corma, Chem. Rev. 2018, 118, 4981.
[37] R. Zhao, Z. Liang, S. Gao, C. Y., B. Zhu, J. Zhao, C. Qu, R. Zou,
Q. Xu, Angew. Chem., Int. Ed. 2019, 131, 1997 .
[38] E. Vorobyeva, E. Fako, Z. Chen, S. M. Collins, D. Johnstone,
P. A. Midgley, R. Hauert, O. V. Safonova, G. Vil, N. Llpez,
S. Mitchell, J. Pérez-Ramírez, Angew. Chem., Int. Ed. 2019, 58,
8724.
[39] M. Xiao, Y. Chen, J. Zhu, H. Zhang, X. Zhao, L. Gao, X. Wang,
J. Zhao, J. Ge, Z. Jiang, S. Chen, C. Liu, W. Xing, J. Am. Chem. Soc.
2019, 141, 17763.
[
4] L. Ma, G. Zhu, D. Wang, H. Chen, Y. Lv, Y. Zhang, X. He, H. Pang,
Adv. Funct. Mater. 2020, 30, 2003870.
[
[
5] J. Yang, W. Li, D. Wang, Y. Li, Small Struct. 2020, https://doi.
org/10.1002/sstr.202000051.
6] Q. Chen, Y. Jia, S. Xie, Z. Xie, Chem. Soc. Rev. 2016, 45, 3207.
[
7] Y. Yamada, C. Tsung, W. Huang, Nat. Chem. 2011, 3, 372.
[
[
8] Y. Li, W. Shen, Chem. Soc. Rev. 2014, 43, 1543.
9] L. Huang, M. Liu, H. Lin, Y. Xu, J. Wu, V. P. Dravid, C. Wolverton,
C. A. Mirkin, Science 2019, 365, 1159.
[40] M. B. Gawande, P. Fornasiero, R. Zboril, ACS Catal. 2020, 10,
2231.
[41] S. Yuan, L. L. Cui, Z. Dou, X. Ge, X. He, W. Zhang, T. Asefa, Small
2020, 16, 2000742.
[42] W. S. Wadsworth, W. D. Emmons, J. Am. Chem. Soc. 1961, 83, 1733.
[43] J. Boutagy, R. Thomas, Chem. Rev. 1974, 74, 87.
[44] W. Wei, J. X. Ji, Angew. Chem., Int. Ed. 2011, 50, 9097.
[45] J. Gu, C. Cai, Org. Biomol. Chem. 2017, 15, 4226.
[46] X. Chen, X. Chen, X. Li, C. Qu, L. Qu, W. Bi, K. Sun, Y. Zhao, Tetra-
hedron 2017, 73, 2439.
[
[
10] B. H. Lee, S. Park, M. Kim, A. K. Sinha, S. C. Lee, E. Jung,
W. J. Chang, K. S. Lee, J. H. Kim, S. P. Cho, H. Kim, K. T. Nam,
T. Hyeon, Nat. Mater. 2019, 18, 620.
11] K. Murugesan, V. G. Chandrashekhar, T. Senthamarai,
R. V. Jagadeesh, M. Beller, Nat. Protoc. 2020, 15, 1313.
[
12] A. Wang, J. Li, T. Zhang, Nat. Rev. Chem. 2018, 2, 65.
13] B. Q. Li, C. X. Zhao, S. Chen, J. N. Liu, X. Chen, L. Song, Q. Zhang,
[
Adv. Mater. 2019, 31, 1900592.
[47] Y. Cheng, S. Zhao, B. Johannessen, J. P. Veder, M. Saunders,
M. R. Rowles, M. Cheng, C. Liu, M. F. Chisholm, R. D. Marco,
H. M. Cheng, S. Z. Yang, S. P. Jiang, Adv. Mater. 2018, 30,
1706287.
[
[
[
14] H. Xu, D. Cheng, D. Cao, X. C. Zeng, Nat. Catal. 2018, 1, 339.
15] C. Zhu, S. Fu, Q. Shi, D. Du, Y. Lin, Angew. Chem., Int. Ed. 2017, 56, 13944.
16] J. Liu, ACS Catal. 2017, 7, 34.
[
17] E. D. Goodman, A. C. Johnston-Peck, E. M. Dietze, C. J. Wrasman,
A. S. Hoffma, F. Abild-Pedersen, S. R. Bare, P. N. Plessow,
M. Cargnello, Nat. Catal. 2019, 2, 748.
[48] X. Fang, Q. Shang, Y. Wang, L. Jiao, T. Yao, Y. Li, Q. Zhang, Y. Luo,
H. L. Jiang, Adv. Mater. 2018, 30, 1705112.
[49] T. Zhang, D. Zhang, X. Han, T. Dong, X. Guo, C. Song, R. Si, W. Liu,
Y. Liu, Z. Zhao, J. Am. Chem. Soc. 2018, 140, 16936.
[50] S. Carniato, G. Dufour, Y. Luo, H. Ågren, Phys. Rev. B 2002, 66,
045105.
[
[
18] M. D. Marcinkowski, M. T. Darby, J. Liu, J. M. Wimble, F. R. Lucci,
S. Lee, A. Michaelides, M. Flytzani-Stephanopoulos, M. Stamatakis,
E. C. H. Sykes, Nat. Chem. 2018, 10, 325.
19] J. Han, X. Meng, L. Lu, J. Bian, Z. Li, C. Sun, Adv. Funct. Mater.
[51] Y. Bu, C. J. Weststrate, J. W. Niemantsverdriet, O. A. Fredriksson,
ACS Catal. 2016, 6, 7994.
2
019, 10, 1808872.
[
20] A. Bakandritsos, R. G. Kadam, P. Kumar, G. Zoppellaro,
M. Medved’, J. Tuček, T. Montini, O. Tomanec, P. Andrýsková,
B. Drahoš, R. S. Varma, M. Otyepka, M. B., P. F. Gawande, R. Zbořil,
Adv. Mater. 2019, 31, 1900323.
[52] D. Atzei, M. Fantauzzi, A. Rossi, P. Fermo, A. Piazzalunga, G. Valli,
R. Vecchi, Appl. Surf. Sci. 2014, 307, 120.
[53] B. Yan, D. Liu, X. Feng, M. Shao, Y. Zhang, Adv. Funct. Mater. 2020,
30, 2003007.
[
21] H. H. Ou, D. S. Wang, Y. D. Li, Nano Select 2020, https://doi.
org/10.1002/nano.202000239.
[54] K. Mudiyanselage, A. K. Burrell, S. D. Senanayake, H. Idriss, Surf.
Sci. 2019, 680, 107.
[
22] N. Zhang, C. Ye, H. Yan, L. Li, H. He, D. Wang, Y. Li, Nano Res.
[55] J. Zhang, C. Zheng, M. Zhang, Y. Qiu, Q. Xu, W. C. Cheong,
W. Chen, L. Zheng, L. Gu, Z. Hu, D. Wang, Y. Li, Nano Res. 2020, 13,
3082.
[56] K. G. Latham, M. I. Simone, W. M. Dose, J. A. Allen, S. W. Donne,
Carbon 2017, 114, 566.
2
020, 13, 3165.
23] X. Li, H. Rong, J. Zhang, D. Wang, Y. Li, Nano Res. 2020, 13, 1842.
24] J. Liu, Chin. J. Catal. 2017, 38, 1460.
[
[
[
25] S. Tian, M. Hu, Q. Xu, W. Gong, W. Chen, J. Yang, Y. Zhu, C. Chen,
J. He, Q. Liu, H. Zhao, D. Wang, Y. Li, Sci. China Mater. 2020,
https://doi.org/10.1007/s40843-020-1443-8..
[57] R. Bertoncello, M. Bettinelli, M. Casarin, A. Gulino, E. Tondello,
A. Vittadini, Inorg. Chem. 1992, 31, 1558.
[
[
26] Z. Zhuang, Q. Kang, D. Wang, Y. Li, Nano Res. 2020, 13, 1856.
[58] A. Zitolo, V. Goellner, V. Armel, M. T. Sougrati, T. Mineva,
L. Stievano, E. Fonda, F. Jaouen, Nat. Mater. 2015, 14, 937.
[59] H. T. Chung, D. A. Cullen, D. Higgins, B. T. Sneed, E. F. Holby,
K. L. More, P. Zelenay, Science 2017, 357, 479.
27] S. Lin, C. S. Diercks, Y. B. Zhang, N. Kornienko, E. M. Nichols,
Y. Zhao, A. R. Paris, D. Kim, P. Yang, O. M. Yaghi, C. J. Chang, Sci-
ence 2015, 349, 1208.
Small 2021, 17, 2006834
2006834 (9 of 10)
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.small-journal.com
[
60] J. Liu, X. Sun, P. Song, Y. Zhang, W. Xing, W. Xu, Adv. Mater. 2013,
5, 6879.
61] J. Liu, M. Jiao, L. Lu, H. M. Barkholtz, Y. Li, Y. Wang, L. Jiang, Z. Wu,
D. J. Liu, L. Zhuang, C. Ma, J. Zeng, B. Zhang, D. Su, P. Song, W. Xing,
W. Xu, Y. Wang, Z. Jiang, G. Sun, Nat. Commun. 2017, 8, 15938.
62] W. Yang, S. Xu, K. Ma, C. Wu, I. D. Gates, X. Ding, W. Meng,
Z. Gao, Nano Mater. Sci. 2020, 2, 120.
[64] Z. Yang, B. Chen, W. Chen, Y. Qu, F. Zhou, C. Zhao, Q. Xu,
Q. Zhang, X. Duan, Y. Wu, Nat. Commun. 2019, 10, 3734.
[65] A. K. Mishra, A. Roldan, N. H. de Leeuw, J. Phys. Chem. C 2016, 120,
2198.
[66] B. X. Yang, T. R. Thurston, J. M. Tranquada, G. Shirane, Phys. Rev. B:
Condens. Matter Mater. Phys. 1989, 39, 4343.
[67] K. Zhao, X. Nie, H. Wang, S. Chen, X. Quan, H. Yu, W. Choi,
G. Zhang, B. Kim, J. G. Chen, Nat. Commun. 2020, 11, 2455.
[68] G. M. Rosen, E. J. Rauckman, Mol. Pharmacol. 1980, 17, 233.
2
[
[
[
63] W. Li, C. Min, F. Tan, Z. Li, B. Zhang, R. Si, M. Xu, W. Liu, L. Zhou,
Q. Wei, Y. Zhang, X. Yang, ACS Nano 2019, 13, 3177.
Small 2021, 17, 2006834
2006834 (10 of 10)
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