Ultra stable multinuclear metal complexes as homogeneous catalysts for visible-light driven syngas production from pure and diluted CO2

Article abstract of DOI:10.1016/j.jcat.2020.03.005

For high reactivity but poor stability of homogeneous metal complexes in CO₂ photoreduction, development of durable systems is still a big challenge. Herein, pentanuclear Co(II) complex [Co₅(btz)₆(NO₃)₄(H₂O)₄] (1, btz = benzotriazolate) is explored for converting CO₂ to syngas which shows high stability and reactivity in both pure and diluted CO₂. Compared with mononuclear structure, multinuclear complex exhibits 212-fold enhancement in reactivity, up to ~2748 TONs, with wide adjustability of H₂/CO ratio from 16:1 to 2:1. This reactivity could be maintained over 200 h which is an order of magnitude higher than the durability of mononuclear complex and exceeds most reported homogeneous molecular catalysts. High reactivity is also achieved in extreme low CO₂ content (5%). Structural analysis and density functional theory (DFT) calculations support that multinuclear structure and the low energy barrier for photocatalytic intermediate may account for the durable and efficient performance of complex 1. The multinuclear strategy is also adopted to nickel complex. This work probes origin of metal-node-dependent performance for CO₂ photoreduction, providing new insights in design of durable and efficient metal complexes for photocatalysis and other applications.

Full text of DOI:10.1016/j.jcat.2020.03.005

Journal of Catalysis 385 (2020) 70–75
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Ultra stable multinuclear metal complexes as homogeneous catalysts for
visible-light driven syngas production from pure and diluted CO2
a
a,
b
Min Sun a, Cong Wang a, Chun-Yi Sun a, , Min Zhang , Xin-Long Wang , Zhong-Min Su
⇑
⇑
a National & Local United Engineering Laboratory for Power Battery, Department of Chemistry, Northeast Normal University, Changchun 130024, PR China
b School of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun 130022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
For high reactivity but poor stability of homogeneous metal complexes in CO2 photoreduction, develop-
Received 1 February 2020
Revised 21 February 2020
Accepted 2 March 2020
ment of durable systems is still
a
big challenge. Herein, pentanuclear Co(II) complex
[Co5(btz)6(NO3)4(H2O)4] (1, btz = benzotriazolate) is explored for converting CO2 to syngas which shows
high stability and reactivity in both pure and diluted CO2. Compared with mononuclear structure, mult-
inuclear complex exhibits 212-fold enhancement in reactivity, up to ~2748 TONs, with wide adjustability
of H2/CO ratio from 16:1 to 2:1. This reactivity could be maintained over 200 h which is an order of mag-
nitude higher than the durability of mononuclear complex and exceeds most reported homogeneous
molecular catalysts. High reactivity is also achieved in extreme low CO2 content (5%). Structural analysis
and density functional theory (DFT) calculations support that multinuclear structure and the low energy
barrier for photocatalytic intermediate may account for the durable and efficient performance of complex
1. The multinuclear strategy is also adopted to nickel complex. This work probes origin of metal-node-
dependent performance for CO2 photoreduction, providing new insights in design of durable and efficient
metal complexes for photocatalysis and other applications.
Keywords:
CO2 reduction
Multinuclear metal complex
Photocatalysis
Syngas production
Transition-metal complex
Ó 2020 Elsevier Inc. All rights reserved.
1. Introduction
intermediate adjustments during syngas production is more
valuable.
Solar-driven CO2 reduction to chemical feedstocks or fuels, such
as syngas, has become a viable way to transform sustainable
energy and simultaneously cuts down the atmospheric CO2 level
[1–6]. Direct use of CO2 from gas mixtures without concentration
is of significance from energy-saving perspective [7,8]. In compar-
ison with one-electron or multi-electron reduction reactions under
visible light, two-electron reduction of CO2 to CO is a kinetically
favorable pathway due to the lower reaction barrier [9,10]. Mean-
while, CO, together with H2, is important component of syngas
which is the feedstock for petrochemicals production [11–13]
and the H2/CO ratio is a pivotal factor in synthesizing downstream
chemicals: 1:1 ratio is for the yield of aldehyde by hydroformyla-
tion [13] and 2:1 ratio is for methanol production as well as
Fischer-Tropsch hydrocarbon synthesis [14]. Although the genera-
tion of H2 and CO in CO2 photoreduction is well-known, rare has
been investigated for modulating syngas composition under visible
light which accounts around a half of solar energy [15–18]. There-
fore, controllable H2/CO ratios eliminating the requirement of
Due to the pioneering researches by Lehn and Sauvage
[14,15,19,20], metal complexes serving as homogeneous molecular
catalysts for CO2 photoreduction have attracted more and more
attention with the following reasons: (i) metal complex catalysts
generally exhibit high activity and selectivity; (ii) definite struc-
tures of them make the studies of catalytic mechanisms through
crystallography and theoretical simulation practical and feasible
[10,16,21,22]. In recent years, numerous metal complex catalysts,
particularly mononuclear catalysts have been applied to photocat-
alytic CO2 reduction, including Mn, Fe, Co, and Ni, and tremendous
progresses have been made in efficiency and selectivity [23–36].
However, the poor durability of the reported mononuclear homo-
geneous catalysts greatly restricts their industrial applications
[11]. One reason might be the abscission of coordinated ligand dur-
ing illumination [27–40]. Moreover, the limited active sites sup-
plied by mononuclear metal complexes, extremely affect the
enhancement of reactivity [41]. Thus, exploiting metal complexes
with ultra-stable structures and multiple active sites is of great
significance.
Herein, the strategy of using multinuclear transition-metal
complex as homogeneous catalyst for CO2 photo-reduction is put
forward based on the following considerations [42–45], (i) fas-
⇑
Corresponding authors.
E-mail addresses: suncy009@nenu.edu.cn (C.-Y. Sun), wangxl824@nenu.edu.cn
(X.-L. Wang).
https://doi.org/10.1016/j.jcat.2020.03.005
0021-9517/Ó 2020 Elsevier Inc. All rights reserved.

M. Sun et al. / Journal of Catalysis 385 (2020) 70–75
71
tened structure might bring about the desirable stability; (ii)
multi-metal centers could provide sufficient catalytic sites; (iii)
multiple structure may reduce the energy barrier of reaction inter-
mediate. Given the admired activity of cobalt-based complex in
CO2 reduction, pentanuclear complex, [Co5(btz)6(NO3)4(H2O)4] (1,
btz = benzotriazolate), was employed as the homogeneous catalyst
for visible-light-induced CO2 reduction by cooperating with photo-
sensitizer [Ru(bpy)3]Cl2 (bpy = 2,20-bipyridine) and electron donors
plex (0.08
l
mol of complex 1 or 0.4
l
mol of complex 2), [Ru(bpy)3]
Cl2 (0.01 mmol), MeCN (5 mL) and TEOA (1 mL). After bubbling CO2
gas for 15 min in dark, the reaction tube was fixed in a water bath
at 20 °C and beamed by a 300 W xenon lamp at k ꢁ 420 nm under
continuous stirring. The detection of CO was used a GC with a FID
detector and the detection of H2 was used a GC with a TCD detec-
tor, together with argon as the carrier gas and reference gas.
The isotopic labelling experiment was carried out under the
same experimental condition except using 13CO2 (99% purity,
1 bar) to replace CO2 as the carbon source. The CO product was
detected by Agilent 8860GC-5977BMSD gas chromatography-
mass spectrometer (GC-MS), equipped with DB-624 Columns.
TEOA. Under visible-light irradiation in pure CO2, ~219.8
lmol
(~2748 TONs) syngas was generated within 70 h which is 212-
fold than that of mononuclear cobalt complex with similar struc-
ture. This reactivity could be maintained up to 200 h which far sur-
passes the stability of most reported homogeneous molecular
catalysts. The H2/CO ratio can be wildly tuned, varying from 16:1
to 2:1. In diluted CO2 of 20% content, the yield of syngas was 779
TONs and it was kept even in 5% CO2. A clear understanding of
mechanism was revealed by the density functional theory (DFT)
calculations. Besides, this multinuclear strategy is also applied to
the nickel complex and similar enhancement in reactivity and sta-
bility is achieved by pentanuclear nickel complex.
3. Results and discussion
3.1. Crystal structure
Complex 1 was synthesized by btz and Co(NO3)2ꢀ6H2O in ace-
tone solution. In complex 1, four six-coordinate Co2+ ions together
with the fifth central one construct a pentanuclear cluster and six
btz ligands linking to five Co2+ ions develop a tetrahedral structure
(Fig. 1a). Each vertex Co2+ ion, which connects with the other three
Co2+ ions via the 1,3-bridge pattern of the btz ligands, is coordi-
nated by the three nitrogen atoms of three btz ligands as well as
two oxygen atoms of the chelating nitrate group; the remaining
position is taken up by a water molecule. The central Co2+ ion is
completely coordinated by six nitrogen atoms of six btz ligands.
Complex 1 possesses the advantage of excellent solubility in most
common organic solvents, such as acetonitrile, acetone, methanol
and ethanol. This property makes complex 1 be homogeneous cat-
alysts for CO2 reduction. Moreover, the sites of water molecules in
the structure could be possible the centers for CO2 adsorption.
2. Experimental section
2.1. Chemicals and instrumentation
Co(NO3)2ꢀ6H2O, Ni(NO3)2ꢀ6H2O and btz were used for the syn-
thesis. All other chemicals of analytical grade were purchased from
Alfa and used as received. Single-crystal X-ray diffraction data for
complexes 1–4 were recorded by using a Bruker Apex-II CCD
diffractometer with graphite-monochromated Mo K
a radiation
(k = 0.71069 Å) at 293 K. The C, H and N elemental analyses were
tested on a PerkinElmer 2400 CHN elemental analyzer. Powder X-
ray diffraction (PXRD) patterns were collected by using a Siemens
D5005 diffractometer with Cu K
a (k = 1.5418 Å) radiation in the
3.2. Characterizations
range of 5–30° at a rate of 5 °/min. X-ray photoelectron spec-
troscopy (XPS) was recorded through a Multilab 2000 (Thermo)
spectrometer. The UV-vis absorption spectrum was measured on
a Shimadzu UV-2550 spectrophotometer in the wavelength range
of 200–800 nm.
The purity of complex 1 was investigated by powder X-ray
diffraction (PXRD) patterns. The experimental PXRD pattern is
extremely similar to the simulated one, demonstrating the satisfy-
ing purity of complex 1 (Fig. 1b). The UV-vis absorption of complex
1 displays absorption in the visible light region and the maximum
molar absorption coefficient (
e
= 1614 Mꢂ1 cmꢂ1) at 420 nm
2.2. Synthesis
(Fig. 1c). XPS survey spectra suggest that there are C, N, O, Co ele-
ments in complex 1 (Fig. 1d). The C 1s spectrum (Fig. S2ay) displays
two distinct peaks at 284.7 eV and 288.7 eV. The former peak can
be ascribed to the sp2 hybridized CAC bonds in benzoic ring of btz.
The later peak is consistent with the CANH species on the triazole
of btz. For N 1s (Fig. S2by), the peak located at 399.6 eV is assigned
to CoAN and the peak located at 400.2 eV is corresponded to
pyrrolic-N. The third peak at 401.3 eV is attributed to the nitrogen
atoms from the triazole structure. The peak at 532.4 eV is ascribed
to an OH group which can be assigned to the absorbed H2O
(Fig. S2cy). The deconvolution of XPS spectrum gives two main
peaks at 796.9 eV and 781.4 eV with concomitant broad satellite
structures (Fig. S2dy), related to Co 2p1/2 and Co 2p3/2, respectively
[48–50]. Under CO2, the cyclic voltammogram (CV) of [Ru(bpy)3]
Cl2 shows three reduction peaks at E1/2 = -1.42, ꢂ1.61 and
ꢂ1.79 V vs. Fc+/Fc, respectively, all of which are more negative than
that of complex 1 (ꢂ1.14 V) (Fig. S3y). Therefore, visible-light dri-
ven CO2 reduction is thermodynamically feasible with complex 1
as the catalyst and Ru(bpy)3Cl2 as the photosensitizer [41,51–52].
2.2.1. Synthesis of [Co5(btz)6(NO3)4(H2O)4] (1)
Complex 1 was synthesized according to a reported study [46].
Co(NO3)2ꢀ6H2O (0.4 mmol, 0.117 g) and btz (0.2 mmol, 0.030 g)
were added into 8 mL acetone solution. Then, the mixture was stir-
red for 30 min under ambient condition. Sequentially, the solution
was filtered and the red filtrate was left for slow evaporation. Red
block crystals were collected after 12 h and dried in air. Yield:
25 mg (57% based on btz). Calcd for C36H32N22O16Co5 (found): C,
32.67 (32.69); H, 2.44 (2.46); N, 23.28 (23.25).
2.2.2. Synthesis of [Co(btz)2(H2O)4]∙6H2O (2)
Complex 2 was synthesized according to a reported study [47].
Co(NO3)2ꢀ6H2O (0.5 mmol, 0.146 g), btz (1.0 mmol, 0.136 g) and
NaOH (1.0 mmol, 0.04 g) were added into 10 mL H2O. The resultant
solution was heated at 160 °C for ten days. The autoclave was then
allowed to cool naturally to room temperature and pale-yellow
crystals were obtained. Yield: 68% (based on Co). Calcd for C8H28
N6O10Co (found): C, 22.49 (22.46); H, 6.61 (6.63); N, 19.67 (19.68).
-
2.3. Photocatalytic test
3.3. Photochemical CO2 reduction
Photocatalytic CO2 reduction was carried out in a quartz tube
(total volume of 50.0 mL) sealed with a cap containing metal com-
CO and H2 were detected as the main gas products in the system
containing complex 1, [Ru(bpy)3]Cl2 and TEOA. Time-course curve

72
M. Sun et al. / Journal of Catalysis 385 (2020) 70–75
Fig. 1. (a) The molecular structure of complex 1. Color code: C, gray; O, red; N, blue; Co, pink. (b) PXRD patterns of simulated and as-synthesized complex 1. (c) UV-vis
spectrum of complex 1 in MeCN (0.05 mM) from 200 nm to 800 nm at 25 °C. (d) XPS spectrum of complex 1.
of this system in pure CO2 after visible-light irradiation showed
that in the first 10 h, more than 1000 and 300 TONs of H2 and
CO were produced, corresponding to 103 and 32 hꢂ1 turnover fre-
quency (TOF) (Fig. 2a). Such reactivity outperforms most of com-
plexes based on metal-oxygen clusters under similar condition
[53]. The decrease of catalytic reactivity might be ascribed to the
photo-degradation of [Ru(bpy)3]Cl2 [41]. Owing to the different
generation speed of H2 and CO within 70 h catalysis, the H2/CO
ratio was changed from ~3:1 to ~1.5:1 (Fig. 2b). In addition, the
H2/CO ratio had close relationship with solvent component
(Fig. 2c and S4y), the amount of TEOA (Fig. 2d and S5y) but was
hardly affected by the amount of catalyst (Fig. S6y). The apparent
quantum yields (AQY) at 480 nm for H2 and CO are shown in
Table S1y. Control experiment without complex 1 exhibited negli-
gible CO and H2 (entry 2, Table 1), which may come from the
decomposed species of [Ru(bpy)3]Cl2 and also indicates the impor-
tant role of complex 1 [51,54]. Using Ar to replace CO2, only H2 was
detected, implying the generated CO is not from any other organic
Fig. 2. Time-dependent generation plots of (a) CO and H2
(0.08
mol), [Ru(bpy)3]Cl2 (0.01 mmol) and TEOA (1 mL) at 20 °C and irradiated by k ꢁ 420 nm. (c) Plots of H2/CO generation with the tuning of H2O/MeCN ratio under similar
condition for 70 h reaction. (d) Plots of H2/CO generation with different TEOA amounts under similar condition for 70 h reaction.
(lmol and TON), and (b) H2/CO ratio under the CO2-saturated MeCN solution (5 mL) containing complex 1
l

M. Sun et al. / Journal of Catalysis 385 (2020) 70–75
73
Table 1
The control experiments of complex 1 for visible-driven CO2 reduction.
k
l
Entry
CO [mmol]
H2 [mmol]
H2/COj
TONCAT
TONPS
1a
2b
3c
4d
5e
6f
79.2
0.3
n.d.
n.d.
n.d.
0.3
n.d.
20
17.5
17.5
17.5
140.6
2.6
n.d.
n.d.
n.d.
0.4
62.3
42
42.4
42.4
42.4
1.8
8.7
–
–
–
1.3
–
2.1
2748
–
–
–
–
22
0.3
–
–
–
0.1
6
6
7
7g
8h
9j
9i
779
779
749.1
749
749.1
2.4
6
9j
a
b
c
d
e
f
Reaction conditions: [Ru(bpy)3]Cl2 (0.01 mmol), complex 1 (0.08 mmol), MeCN (5 mL), TEOA (1 mL), CO2 (1 atm), k ꢁ 420 nm, 20 °C, 70 h.
Without complex 1.
Without [Ru(bpy)3]Cl2.
Without TEOA.
In dark.
Using btz, and Co(NO3)2ꢀ6H2O to replace complex 1.
g
h
i
100% Ar.
20% CO2 (CO2/Ar = 20/80).
5% CO2 (CO2/Ar = 5/95).
j
The H2/CO ratio: (mol amount of H2)/(mol amount of CO).
Turnover number based on amount of catalyst: (mol amount of CO and H2)/(mol amount of complex 1).
Turnover number based on amount of photosensitizer: (mol amount of CO and H2)/(mol amount of [Ru(bpy)3]Cl2).
k
l
species in this system (entry 7, Table 1). The isotope labelling
experiment using 13CO2 was also confirmed the source of CO
(Fig. S7y). When conducting the experiment in dark, no gas product
was generated, suggesting the reaction is photo-induced (entry 3
and 5, Table 1). In the absence of TEOA, no product was recorded,
declaring TEOA is the important proton source and electron donors
(entry 4, Table 1).
Directly performing the conversion under low CO2 content
without concentration from gas mixtures, such as flue gas from
coal-fired power stations (5–20% CO2), is significant from the
energy-saving viewpoint [7,8]. The reductive reactivity of complex
1 toward diluted CO2 was investigated. In CO2 content of 20%, the
TONs of H2 and CO was 525 and 254, corresponding to 8 and 4 hꢂ1
TOF (entry 8, Table 1, Fig. 3a). Compared with the yield in pure CO2,
this reactivity only declined 2.5 fold. More significantly, in extre-
mely low content of 5%, the catalytic activity is nearly the same
as that in the concentration of 20% (entry 9, Table 1 and Fig. 3b).
The attractive performance of complex 1 may result from its
multi-potential CO2 adsorption sites. This reactivity of complex 1
in 5% CO2 outperforms most of reported homogeneous systems
in similar condition (Table S2y). In order to demonstrate the cat-
alytic persistence of catalyst, recycling experiments were per-
formed. Owing to the instability of [Ru(bpy)3]Cl2, during the
recycle, equal amount of RuII complex was added. The nearly
Fig. 4. Generation of CO and H2 for complex 1 with 4 cycles under the CO2-
saturated MeCN solution (5 mL) containing complex 1 (0.08 mol), [Ru(bpy)3]Cl2
(0.01 mmol) and TEOA (1 mL) at 20 °C and irradiated by k ꢁ 420 nm.
l
200 h (Fig. 4), illustrates the super stability of complex 1. Such
durability is hard to
achieve by reported metal complexes (Table S3y). To get a clear
understanding of the reason about the high activity and stability of
Fig. 3. Time-dependent generation plots of CO and H2
(lmol and TON) under the CO2-saturated MeCN solution (5 mL) containing complex 1 (0.08 lmol), [Ru(bpy)3]Cl2
(0.01 mmol) and TEOA (1 mL) at 20 °C and irradiated by k ꢁ 420 nm with (a) 20% CO2 and 80% Ar, (b) 5% CO2 and 95% Ar.

74
M. Sun et al. / Journal of Catalysis 385 (2020) 70–75
this complex, control experiment was performed using a mononu-
clear isostructural Co-based complex, [Co(btz)2(H2O)4]∙6H2O (2), to
replace complex 1. In complex 2, the only central Co2+ ion is six-
coordinated by two nitrogen atoms of two disparate btz ligands
and four oxygen atoms of four water molecules, constructing a
bit distorted octahedral structure (Fig. S8y). Under similar catalytic
condition in pure CO2, except the dosage, the photocatalytic effi-
ciency of complex 2 was rather lower than that of complex 1, with
total TONs just of 9 (Fig. S9y). Moreover, complex 2 could only be
active within 10 h (Fig.S10y), even with the addition of fresh [Ru
(bpy)3]Cl2, the reduction activity still cannot recover. We conjec-
ture the super stability of complex 1 may root in the fastened
structure of five Co2+ ions linking to btz ligands, whereas the
enhanced reactivity may be relative to multiple catalytic sites.
tron injection, two coordinated water molecules deviate from the
Co center in the meantime (Fig. 5b and c), indicating the
instability of complex 2 during photocatalytic reactions. With a
decreased coordination number, the reduced Co center with large
spin density (Fig. S12y) attract CO2 molecule effectively forming a
carbonate-bridged structure. The strong interaction between Co
and CO2 induces an energy decrease for the first protonation step,
while the second protonation process with energy barrier of
0.27 eV turns into the potential determining step (Fig. S13y). In
addition, the competitive reaction, i.e. H2 production, readily
occurs for both complex 1 and 2 with free energy of 0.28 eV and
0.17 eV, respectively (Fig. S14y).
The universality of the preponderance in stability and activity of
multinuclear complex is further extended to Ni(II) complex
(Fig. S15ay). TONs of H2 and CO are up to 1195 and 629 with [Ni5(-
btz)6(NO3)4(H2O)4] (3) as catalyst within 70 h visible-light irradia-
tion (Fig. S17ay), corresponding to 17 and 9 hꢂ1 TOF. The ratio of
H2/CO could be tuned from ~2.5:1 to ~1.9:1 via regulating the reac-
tion time (Fig. S17by). Control experiments, including without cat-
alyst, [Ru(bpy)3]Cl2 or CO2, light irradiation, demonstrated that the
produced CO originated from CO2 reduction (Table S4y). Recycling
experiments demonstrated the catalytic activity could be main-
tained up to four cycles of 200 h (Fig. S20y). Whereas the yield of
the mononuclear Ni2+ complex, [Ni(btz)2(H2O)4]∙6H2O (4) is just
5 TONs keeping only dozens of hours, which support the structural
advantages of multinuclear transition-metal complexes as cata-
lysts for CO2 photo-reduction (Fig. S21y).
3.4. Mechanism investigation
DFT calculations are perfermed to illuminate the mechanism.
Following the generally accepted viewpoint, CO generation princi-
pally occurs during the carboxyl process in the following steps: (i)
the activation of CO2 (CO2 + H+ + eꢂ ? COOH*); (ii) the cleavage of
AOH (COOH* + H+ + eꢂ ? CO* + H2O) and (iii) the desorption of CO
(CO* ? CO) [55–57], where * stands for the related adsorption
state on the catalyst, the catalytic route and energy barrier were
studied by DFT calculations (Fig. 5). To simulate a photo-catalysis
process, the catalyst models are firstly negatively charged with
one electron. For complex 1, the reduced Co centers do not incline
to form Co-C bond with CO2 with adsorption energy of ꢂ0.50 eV
(Fig. 5a). The first proton-coupled electron transfer (PCET) that
forming COOH*, which consumes energy of 0.40 eV, serves as the
potential determining step for the whole CO2 reduction reaction
process. The second protonation process requires a slight energy
barrier of 0.08 eV, leading to CO and H2O. For complex 2, the plan-
ner structure in a neutral state can be largely distorted by an elec-
4. Conclusions
In summary, a strategy of constructing multinuclear transition-
metal complex to promote the durability and activity in CO2 reduc-
tion is put forward. Compared with the stability and reactivity of
the mononuclear cobalt complex (2), those of multinuclear com-
plex (1) shows 1 and 2 orders of magnitude improvement in pure
CO2. The yield of syngas generation achieved by complex 1 is up to
~219.8 lmol (~2748 TONs) with wide adjustability of H2/CO ratio
from 16:1 to 2:1. This reactivity could be maintained more than
200 h, outperforming the stability of most reported homogeneous
molecular catalysts. High reactivity is also achieved in diluted CO2
with 20% and 5% content, both up to ~60 lmol. Structural analysis
and DFT studies support that multinuclear structure and the low
energy barrier for photocatalytic intermediate may account for
the durable and efficient performance of complex 1. Moreover, this
strategy is also adopted to nickel complex. This work sheds light on
the rational construction of high efficient homogeneous metal
complexes catalysts for robust solar-driven CO2 conversion
performances.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
This work was supported by NSFC of China (grant numbers
21971032, 21801038, 21771035, 21671034); Jilin Provincial
Department of Science and Technology (grant number
20190103018JH); Foundation of Jilin Educational Committee
(grant number JJKH20190278KJ).
Fig. 5. (a) Schematic of the calculated energy profile for complex 1 during the CO2
reduction process towards to CO production, insert presents the partial structures
of three intermediates and all the full structures are shown in Fig. S11 in supporting
information. Optimized structures of complex 2 in a neutral state (b) and in a
charged state (c), the units for the bond lengths are in Å.

M. Sun et al. / Journal of Catalysis 385 (2020) 70–75
75
[28] P.G. Alsabeh, A. Rosas-Hernandez, E. Barsch, H. Junge, R. Ludwig, M. Beller,
Catal. Sci. Technol. 6 (2016) 3623–3630.
Appendix A. Supplementary material
[29] H. Takeda, K. Ohashi, A. Sekine, O. Ishitani, J. Am. Chem. Soc. 138 (2016) 4354–
4357.
[30] J. Bonin, M. Robert, M. Routier, J. Am. Chem. Soc. 136 (2014) 16768–16771.
[31] T. Jin, C. Liu, G. Li, Chem. Commun. 50 (2014) 6221–6224.
[32] S. Wang, W. Yao, J. Lin, Z. Ding, X. Wang, Angew. Chem., Int. Ed. 53 (2014)
1034–1038.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2020.03.005.
References
[33] S.L.F. Chan, T.L. Lam, C. Yang, S.C. Yan, N.M. Cheng, Chem. Commun. 51 (2015)
7799–7801.
[34] P. Kumar, A. Kumar, B. Sreedhar, B. Sain, S.S. Ray, S.L. Jain, Chem. 20 (2014)
6154–6161.
[1] M. Aresta, A. Dibenedetto, A. Angelini, Chem. Rev. 114 (2014) 1709–1742.
[2] S. Gao, Y. Lin, X. Jiao, Y. Sun, Q. Luo, W. Zhang, D. Li, J. Yang, Y. Xie, Nature 529
(2016) 68–71.
[35] L. Chen, Z. Guo, X.G. Wei, C. Gallenkamp, J. Bonin, E. Anxolabehere-Mallart, K.C.
Lau, T.C. Lau, M. Robert, J. Am. Chem. Soc. 137 (2015) 10918–10921.
[36] V.S. Thoi, N. Kornienko, C.G. Margarit, P. Yang, C.J. Chang, J. Am. Chem. Soc. 135
(2013) 14413–14424.
[3] B.A. Rosen, A. Salehi-Khojin, M.R. Thorson, W. Zhu, D.T. Whipple, P.J. Kenis, R.I.
Masel, Science 334 (2011) 643–644.
[4] M. Aresta, In carbon dioxide as chemical feedstock, WileyVCH Verlag GmbH &
Co KGaA, 2010, pp. 1–13.
[37] R.S. Khnayzer, V.S. Thoi, M. Nippe, A.E. King, J.W. Jurss, K.A. ElRoz, J.R. Long, C.J.
Chang, F.N. Castellano, Energy Environ. Sci. 7 (2014) 1477–1488.
[38] C.F. Leung, S.M. Ng, C.C. Ko, W.L. Man, J. Wu, L. Chen, T.C. Lau, Energy Environ.
Sci. 5 (2012) 7903–7907.
[39] A.B. Tossi, H. Gorner, J. Photochem. Photobiol. B 17 (1993) 115–125.
[40] Y.J. Yuan, Z.T. Yu, X.J. Liu, J.G. Cai, Z.J. Guan, Z.G. Zou, Sci. Rep. 4 (2014) 4045.
[41] T.O. Yang, H.H. Huang, J.W. Wang, D.C. Zhong, T.B. Lu, Angew. Chem., Int. Ed. 56
(2017) 738–743.
[42] V. Balzani, G. Bergamini, F. Marchioni, P. Ceroni, Coord. Chem. Rev. 250 (2006)
1254.
[43] K.L. Wouters, N.R. de Tacconi, R. Konduri, R.O. Lezna, F.M. MacDonnell,
Photosynth. Res. 87 (2006) 41–45.
[44] Z.Y. Bian, K. Sumi, M. Furue, S. Sato, K. Koike, O. Ishitani, Inorg. Chem. 47 (2008)
10801–10803.
[45] Y. Yamazaki, O. Ishitani, Dalton Trans. 46 (2017) 4816–4823.
[46] Y.L. Bai, J. Tao, R.B. Huang, L.S. Zheng, Angew. Chem. Int. Ed. 47 (2008) 5344–
5347.
[47] J.H. Wang, G.M. Tang, Y.T. Wang, T.X. Qin, S.W. Ng, CrystEngComm 16 (2014)
2660–2683.
[48] A. Morozan, P. Jegou, B. Jousselme, S. Palacin, Phys. Chem. Chem. Phys. 13
(2011) 21600–21607.
[49] M.M. Chen, L. Han, J. Zhou, C.Y. Sun, C.Y. Hu, X.L. Wang, Z.M. Su,
Nanotechnology 29 (2018) 284003.
[50] S.S. Yan, S.X. Ouyang, H. Xu, M. Zhao, X.L. Zhang, J.H. Ye, J. Mater. Chem. A 4
(2016) 15126–15133.
[51] Z. Guo, S. Cheng, C. Cometto, E. Anxolabéhère-Mallart, S.M. Ng, C.C. Ko, G. Liu,
L. Chen, M. Robert, T.C. Lau, J. Am. Chem. Soc. 138 (2016) 9413–9416.
[52] Y.N. Yao, Y. Gao, L. Ye, C. Hu, L.C. Sun, J. Energy Chem. 27 (2018) 502–506.
[53] Y.H. Luo, L.Z. Dong, J. Liu, S.L. Li, Y.Q. Lan, Coord. Chem. Rev. 390 (2019) 86–
126.
[5] J. Qiao, Y. Liu, F. Hong, J. Zhang, Chem. Soc. Rev. 43 (2014) 631–675.
[6] A.M. Appel, J.E. Bercaw, A.B. Bocarsly, H. Dobbek, D.L. DuBois, M. Dupuis, J.G.
Ferry, E. Fujita, R. Hille, P.J.A. Kenis, C.A. Kerfeld, R.H. Morris, C.H.F. Peden, A.R.
Portis, S.W. Ragsdale, T.B. Rauchfuss, J.N.H. Reek, L.C. Seefeldt, R.K. Thauer, G.L.
Waldrop, Chem. Rev. 113 (2013) 6621–6658.
[7] T. Kajiwara, M. Fujii, M. Tsujimoto, K. Kobayashi, M. Higuchi, K. Tanaka, S.
Kitagawa, Angew. Chem. Int. Ed. 55 (2016) 2697–2700.
[8] T. Nakajima, Y. Tamaki, K. Ueno, E. Kato, T. Nishikawa, K. Ohkubo, Y. Yamazaki,
T. Morimoto, O. Ishitani, J. Am. Chem. Soc. 138 (2016) 13818–13821.
[9] L. Alibabaei, H. Luo, R.L. House, P.G. Hoeltz, T.J. Meyer, J. Mater. Chem. A 1
(2013) 4133–4145.
[10] Y. Yamazaki, H. Takeda, O. Ishitani, J. Photochem. Photobiol. C 25 (2015) 106–
137.
[11] S.C. Tsang, J.B. Claridge, M.L.H. Green, Catal. Today 23 (1995) 3–15.
[12] I. Wender, Fuel Process. Technol. 48 (1996) 189–297.
[13] M.E. Dry, Catal. Today 71 (2002) 227–241.
[14] R. Franke, D. Selent, A. Borner, Chem. Rev. 112 (2012) 5675–5732.
[15] J.M. Lehn, R. Ziessel, Proc. Natl. Acad. Sci. U. S. A. 79 (1982) 701–704.
[16] M. Beley, J.P. Collin, R. Ruppert, J.P. Sauvage, J. Chem. Soc., Chem. Commun. 19
(1984) 1315–1316.
[17] B. Kumar, J.M. Smieja, A.F. Sasayama, C.P. Kubiak, Chem. Commun. 48 (2012)
272–274.
[18] J.S. Lee, D. Won, W.J. Jung, H.J. Son, C. Pac, S.O. Kan, Angew. Chem. Int. Ed. 56
(2017) 976–980.
[19] J. Hawecker, J.M. Lehn, R. Ziessel, J. Chem. Soc., Chem. Commun. 9 (1983) 536–
538.
[20] J.M. Lehn, R. Ziessel, J. Organomet. Chem. 382 (1990) 157–173.
[21] H. Takeda, C. Cometto, O. Ishitani, M. Robert, ACS Catal. 7 (2017) 70–88.
[22] J.W. Wang, W.J. Liu, D.C. Zhong, T.B. Lu, Coord. Chem. Rev. 378 (2017) 237–
261.
[54] Y. Kuramochi, J. Itabashi, K. Fukaya, A. Enomoto, M. Yoshida, H. Ishida, Chem.
Sci. 6 (2015) 3063–3074.
[55] S. Kattel, W. Yu, X. Yang, B. Yan, Y. Huang, W. Wan, P. Liu, J.G. Chen, Angew.
Chem. Int. Ed. 55 (2016) 7968–7973.
[56] X.C. Jiao, X.D. Li, X.Y. Jin, Y.F. Sun, J.Q. Xu, L. Liang, H.X. Ju, J.F. Zhu, Y. Pan, W.S.
Yan, Y. Lin, Y. Xie, J. Am. Chem. Soc. 139 (2017) 18044–18051.
[57] A. Li, T. Wang, X.X. Chang, Z.J. Zhao, C.C. Li, Z.Q. Huang, P.P. Yang, G.Y. Zhou, J.L.
Gong, Chem. Sci. 9 (2018) 5334–5340.
[23] M.D. Sampson, C.P. Kubiak, J. Am. Chem. Soc. 138 (2016) 1386–1393.
[24] H. Takeda, H. Koizumi, K. Okamoto, O. Ishitani, Chem. Commun. 50 (2014)
1491–1493.
[25] E. Torralba-Peñalver, Y. Luo, J.D. Compain, S. Chardon-Noblat, B. Fabre, ACS
Catal. 5 (2015) 6138–6147.
[26] H. Fei, M.D. Sampson, Y. Lee, C.P. Kubiak, S.M. Cohen, Inorg. Chem. 54 (2015)
6821–6828.
[27] P.L. Cheung, C.W. Machan, A.Y.S. Malkhasian, J. Agarwal, C.P. Kubiak, Inorg.
Chem. 55 (2016) 3192–3198.