Co?MOF-74@Cu?MOF-74 Derived Bifunctional Co?C@Cu?C for One-Pot Production of 1, 4-Diphenyl-1, 3-Butadiene from Phenylacetylene

Article abstract of DOI:10.1002/cctc.202001140

Carbon-supported metal nanoparticles (NPs) play important roles in heterogeneous catalysis. In particular, supported bimetallic catalytic systems can be promising multifunctional catalysts for one-pot tandem/cascade reactions, in which two or more successive independent reactions are realized in one pot. In this manuscript, we report the preparation of a carbon-supported bimetallic CoCu catalytic system (Co?C@Cu?C), with Co NPs wrapped by carbon-supported Cu NPs, from the pyrolysis of a core-shell structured Co?MOF-74@Cu?MOF-74. The as-obtained Co?C@Cu?C acts as a bifunctional catalyst for the transformation of phenylacetylene to 1, 4-diphenyl-1, 3-butadiene in one pot, in which supported metallic Cu NPs and Co NPs are active for the coupling and hydrogenation reaction respectively. By tuning the reaction rates of the coupling and the hydrogenation in this tandem reaction over the Co?C@Cu?C via changing the reaction medium and the reducing agent, an efficient direct transformation of phenylacetylene to 1, 4-diphenyl-1, 3-butadiene was realized. This work not only highlights the important role of MOFs in the preparation of multifunctional carbon supported metal NPs for heterogeneous catalysis, but also demonstrates the possibility of tuning the reaction rates of different catalytic steps in a tandem reaction to realize an efficient overall reaction.

Full text of DOI:10.1002/cctc.202001140

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Co-MOF-74@Cu-MOF-74 Derived Bifunctional Co-C@Cu-C
for One-Pot Production of 1, 4-Diphenyl-1, 3-Butadiene from
Phenylacetylene
Authors: Jingyu Cai, Yuzheng Zhuang, Yi Chen, Longqiang Xiao, Yulai
Zhao, Xiancai Jiang, Linxi Hou, and Zhaohui Li
This manuscript has been accepted after peer review and appears as an
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content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.202001140
Link to VoR: https://doi.org/10.1002/cctc.202001140
01/2020

10.1002/cctc.202001140
ChemCatChem
FULL PAPER
Co-MOF-74@Cu-MOF-74 Derived Bifunctional Co-C@Cu-C for
One-Pot Production of 1, 4-Diphenyl-1, 3-Butadiene from
Phenylacetylene
Jingyu Cai,[a],[b] Yuzheng Zhuang,[b] Yi Chen,[a] Longqiang Xiao,[b] Yulai Zhao,[b] Xiancai Jiang,[b] Linxi
Hou,*[b] and Zhaohui Li,*[a]
Abstract: Carbon supported metal nanoparticles (NPs) play
important roles in heterogeneous catalysis. In particular, supported
bimetallic catalytic systems can be promising multifunctional catalysts
for one-pot tandem/cascade reactions, in which two or more
successive independent reactions are realized in one pot. In this
manuscript, we reported the preparation of a carbon-supported
bimetallic CoCu catalytic system (Co-C@Cu-C), with Co NPs
wrapped by carbon supported Cu NPs, from the pyrolysis of a core-
shell structured Co-MOF-74@Cu-MOF-74. The as-obtained Co-
C@Cu-C acts as a bifunctional catalyst for the transformation of
phenylacetylene to 1, 4-diphenyl-1, 3-butadiene in one pot, in which
supported metallic Cu NPs and Co NPs are active for the coupling
and hydrogenation reaction respectively. By tuning the reaction rates
of the coupling and the hydrogenation in this tandem reaction over the
Co-C@Cu-C via changing the reaction medium and the reducing
agent, an efficient direct transformation of phenylacetylene to 1, 4-
diphenyl-1, 3-butadiene was realized. This work not only highlights
the important role of MOFs in the preparation of multifunctional carbon
supported metal NPs for heterogeneous catalysis, but also
demonstrates the possibility of tuning the reaction rates of different
catalytic steps in a tandem reaction to realize an efficient overall
reaction.
carbon supported metal NPs with regular size and their even
dispersion on the supports is the pyrolysis of the metal containing
inorganic-organic polymeric complexes.[5] In particular, metal-
organic frameworks (MOFs), a class of porous inorganic-organic
hybrid materials, have been found to be an extremely appealing
type of precursors for fabricating various carbon supported metal
NPs, which have been applied in many fields.[6] Since the metal
cations in the MOFs are reduced by the in-situ generated carbon
matrix from the decomposition of the organic ligands, strong
interactions between the metal NPs and the carbon support exist
in the thus-obtained carbon supported metal NPs. In addition, the
advantages of using MOFs as a precursor lies in that isolated and
uniform distributed metal NPs in the carbon support can be
obtained due to the regular arrangement of the metal cations and
the organic components within the crystalline MOF structures.[7]
Recently, with an aim of developing green and atom-
economic catalytic processes, researchers are paying increasing
attention to the tandem/cascade reactions, in which two or more
successive independent reactions are realized in one pot. As
compared with traditional catalysis, one-pot tandem/cascade
reactions offer enormous economic advantages since the
separation of the reaction intermediates can be avoided, and
therefore can save the processing time and minimize the waste
production.[8] In contrast to the traditional one-catalyst/one-
reaction approach, multifunctional catalyst, which contains
different spatially separated catalytic active sites to maintain their
independent function, is usually required for the one pot
tandem/cascade reaction.[9] Bimetallic catalytic systems, if well
designed and fabricated, can be promising multifunctional
catalysts for one-pot tandem/cascade reactions since metal-
based catalytic activities in these systems can be combined and
cooperated. However, synchronizing the reaction rates of the
different catalytic steps in a tandem/cascade reaction to realize
an efficient overall reaction, which theoretically can be realized
via a delicate tuning of the bimetallic catalytic system, is still a
great challenge. [10]
Introduction
Metal nanoparticles (NPs) play important roles in heterogeneous
catalysis.[1] Catalytic active metal NPs are usually loaded on
different supports for their applications in heterogeneous catalysis,
not only to reduce the amount of their usage but also to improve
their stability during the reactions since the metal NPs have high
surface energy and are prone to sintering at high temperature.[2]
Due to the high surface area and excellent thermal and
mechanical properties, different allotropes of carbon have been
used as supports for catalytic active metal NPs.[3] In addition, the
carbon support can also endow the catalysts with additional
adsorption sites for the reactants.[4] An efficient strategy to obtain
M-MOF-74 (M = divalent cations) is a MOF material
constructed from divalent cations and 2, 5-dihydroxyterephthalic
acid (H4DOBDC).[11] Our previous study revealed that Cu-MOF-
74 derived carbon supported Cu-based catalyst can activate
terminal alkynes to form the copper(I) acetylides and as a result,
can catalyze the C-C coupling of the terminal alkynes.[12] In
addition, Co-MOF-74 derived carbon coated metallic Co NPs
acted as an excellent catalyst for selective semi-hydrogenation of
aromatic alkynes to alkenes with NaBH4.[13] Therefore, in this
manuscript, we rationally combined these two catalysts to afford
a carbon-supported bimetallic CoCu catalytic system, with Co
NPs wrapped by carbon supported Cu NPs (Co-C@Cu-C), from
[a]
Dr. J. Cai, Y. Chen, Pro. Dr. Z. Li
Research Institute of Photocatalysis
State Key Laboratory of Photocatalysis on Energy and Environment
College of Chemistry
Fuzhou University, Fuzhou 350116, P. R. China
E-mail: zhaohuili1969@yahoo.com
[b]
Y. Zhuang, Dr. L. Xiao, Dr. Y. Zhao, Dr. X. Jiang, Pro. Dr. L. Hou
College of Chemical Engineering
Fuzhou University
Xueyuan Road No. 2, Fuzhou 350116, China
E-mail: lxhou@fzu.edu.cn
Supporting information for this article is given via a link at the end of the
document.
1
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10.1002/cctc.202001140
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the pyrolysis of a core-shell structured Co-MOF-74@Cu-MOF-74.
The as-obtained Co-C@Cu-C acts as a bi-functional catalyst for
the one pot tandem reaction to transform phenylacetylene to 1, 4-
diphenyl-1, 3-butadiene, in which supported metallic Cu NPs and
Co NPs are active for the coupling and hydrogenation reaction
respectively. By tuning the reaction rates of the coupling and the
hydrogenation in this tandem reaction over the Co-C@Cu-C via
changing the reaction medium and the reducing agent, an efficient
direct transformation of phenylacetylene to 1, 4-diphenyl-1, 3-
butadiene was realized. This work not only highlights the
important role of MOFs in the preparation of multifunctional
carbon supported metal NPs for fheterogeneous catalysis, but
also demonstrates the possibility of tuning the reaction rates of
different catalytic steps in a tandem reaction to realize an efficient
overall reaction.
the surface of Co-MOF-74 to form the core-shell structured Co-
MOF-74@Cu-MOF-74, as shown in Scheme 1 (Step 2). The ICP-
OES analysis revealed that the amount of Co and Cu in Co-MOF-
74@Cu-MOF-74 was 9.87% and 27.06% respectively, with a
Co/Cu ratio to be 0.36.
Although the pyrolysis of M-MOF-74 to obtain different
carbon supported metal NPs have been demonstrated, the
products obtained via calcinating the MOFs depend not only on
the metal ions in the MOFs, but also on the calcination
conditions.[14] To obtain carbon supported metallic Co and Cu
from Co-MOF-74@Cu-MOF-74, TGA was carried out over Co-
MOF-74@Cu-MOF-74 to provide guidance for its pyrolysis. The
TGA result showed three apparent weight loss regions in 50-210,
210-560 and 560-1100 °C (Supporting Fig. S1). The weight loss
at 210-560 °C can be attributed to the decomposition of the
organic ligands. Different from Co-MOF-74, Co-MOF-74@Cu-
MOF-74 has a faster weight loss rate at the second region, which
may be caused by the decomposition of the outer shell of Cu-
MOF-74 with lower crystallinity. The weight loss region at 560-
1100 °C can be attributed to the reduction of Cu2+ and Co2+ to
form metallic Cu and Co NPs, which was similar to our previous
work.
Therefore, to obtain carbon supported metallic Co and Cu
NPs, Co-MOF-74@Cu-MOF-74 was calcinated at 1000 °C (Step
3 in Scheme 1). The XRD patterns of the product obtained from
Co-MOF-74@Cu-MOF-74 shows six peaks at 43.4°, 44.1°, 50.3°,
51.6°, 74.1° and 75.9° (Figure 2a). The peaks at 44.1°, 51.6° and
75.9° are corresponding to (111), (200) and (220) crystallographic
planes of cubic Co (JCPDS 01-089-7093), while the other three
peaks at 43.4°, 50.3° and 74.1° can be indexed to (111), (200)
and (220) crystallographic planes of cubic Cu (JCPDS 01-070-
3038), respectively. Besides the peaks attributable to metallic Co
and Cu, a broad yet weak diffraction peak at 24.6° assignable to
graphitic carbon is also observed. The XRD result clearly
indicated that the pyrolysis of Co-MOF-74@Cu-MOF-74 at
1000 °C led to the formation of graphitic carbon supported metallic
Cu and Co NPs (denoted as Co-C@Cu-C). Accordingly, the FT-
IR spectrum of Co-C@Cu-C showed that the intensity of the
peaks in the region from 1000 cm-1 to 1600 cm-1 observed in the
Results and Discussion
The core-shell structured Co-MOF-74@Cu-MOF-74 was
fabricated by a two-step microwave method. First, Co-MOF-74
was synthesized via a modified microwave-assisted method from
Co(NO3)2ꞏ6H2O and H4DOBDC, with its XRD shown in Figure 1a
(Step 1 in Scheme 1). To prepare Co-MOF-74@Cu-MOF-74,
Cu(CH3COO)2 and H4DOBDC was introduced into a DMF solution
containing the preformed Co-MOF-74 and the resultant
suspension was heated with the assistance of microwave at
130 °C. The XRD pattern of the as-obtained Co-MOF-74@Cu-
MOF-74 correlated well with that of Co-MOF-74 (Figure 1a),
indicating that the framework of MOF-74 was retained after the
introduction of Cu. The TEM image shows that the morphology of
the as-obtained Co-MOF-74@Cu-MOF-74 is rod-shaped, with a
diameter of ca. 100 nm and a length of ca. 650 nm (Figure 1b).
The HADDF-STEM image (Figure 1c), with the EDX line-scan
along the cross section (inset in Figure 1c), revealed a clear
boundary between Co and Cu segment. It is therefore proposed
that Cu2+ ion coordinated with H4DOBDC on the surface of the
Co-MOF-74 and led to a layer by layer growth of Cu-MOF-74 on
Scheme 1. Schematic illustration of the formation process of Co-C@Cu-C.
Figure 1. Co-MOF-74@Cu-MOF-74 (a) XRD; (b) TEM image; (c) HAADF-STEM image and EDX line-scan of the enlarged area (inset).
2
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10.1002/cctc.202001140
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original Co-MOF-74@Cu-MOF-74 dramatically decreases,
confirming the successful decomposition of organic framework
during the calcination (Supporting Fig. S2).
(111)
The TEM image of the as-obtained Co-C@Cu-C shows rod
with a diameter of ca. 100 nm, indicating that the morphology of
the Co-MOF-74@Cu-MOF-74 was maintained after the pyrolysis
(inset in Figure 2b). However, unlike Co-MOF-74@Cu-MOF-74
which has a smooth surface, the TEM image of Co-C@Cu-C
clearly shows that its surface is rough, with spherical
nanoparticles of ca. 3-4 nm evenly distributed on the outside of
the rod (Figure 2b). These nanoparticles are confirmed to be
metallic Cu NPs since lattice fringes of d = 0.208 nm, which
matches well with (111) crystallographic plane of cubic Cu, are
observed in the HRTEM image (inset in Figure 2b). Apart from Cu
NPs, lattice fringes of d = 0.204 nm, attributed to cubic Co, can
also be observed (inset in Figure 2b). As compared with metallic
Cu NPs, the size of metallic Co NPs is much bigger, which shows
a diameter of ca. 18 nm. The TEM image also confirms that Co
NPs are enwrapped by supported Cu NPs. Since metallic Cu and
Co NPs were formed via the reduction of cationic metal ions in the
MOFs by the in-situ produced carbon, the regular arrangement of
the metals and the organic components in MOF-74 led to a
uniform distribution of the metal NPs on the carbon matrix.
(111)
(200)
(220)
(220)
(200)
Figure 2. Co-C@Cu-C (a) XRD patterns; (b) TEM and HRTEM images; XPS
spectrum in (c) Co region and (d) Cu region.
Table 1. The conversion of phenylacetylene over Co-C@Cu-C and other catalysts under different conditions.
Selectivity (%)
Reducing Conv.
Entry
Solvent
Catalyst
agent
(%)
[a]
1
2
THF
CH2Cl2
EtOH
Co-C@Cu-C NaBH4
Co-C@Cu-C NaBH4
Co-C@Cu-C NaBH4
Co-C@Cu-C NaBH4
13
2
25
-
-
51
>99
5
24
-
-
3
>99
>99
87
52
95
74
-
80
54
52
-
12
39
-
-
4
i-PrOH
7
-
5
THF:i-PrOH=3:1 Co-C@Cu-C NaBH4
4
41
-
6
THF:i-PrOH=3:1 Co-C@Cu-C
-
-
>99
-
7
THF:i-PrOH=3:1
THF:i-PrOH=3:1
Co-C
Cu-C
NaBH4
NaBH4
98
3
-
-
8
-
95
-
-
9[b]
10[c]
11
12[d]
13
14
15
16[e]
THF:i-PrOH=3:1 Co-C@Cu-C NaBH4
THF:i-PrOH=3:1 Co-C@Cu-C NaBH4
THF:i-PrOH=3:1 Co-C@Cu-C NH3BH3
THF:i-PrOH=3:1 Co-C@Cu-C NH3BH3
-
-
-
-
-
-
-
-
77
>99
56
93
>99
75
24
28
37
74
65
25
-
13
12
21
8
63
57
13
16
3
3
25
-
THF:i-PrOH=3:1
Co-Cu-C
NH3BH3
THF:i-PrOH=3:1 Co-C&Cu-C NH3BH3
THF:i-PrOH=3:1 Cu-C@Co-C NH3BH3
THF:i-PrOH=3:1 Co-C@Cu-C NH3BH3
9
-
22
14
61
Reaction conditions: catalyst (5 mg), solvent (4 ml) and phenylacetylene (5.5 µL, 0.05 mmol), reducing agent (0.05 mmol), K2CO3 (20 mg), 323 K, 10 h.
[a] “-” refers to no products were detected. [b] styrene as substrate. [c] 1, 4-diphenylbutadiyne as substrate. [d] 13 h. [e] recycle stability test.
3
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In consistence with the results from the XRD and TEM
occurs over Co NPs to generate H- for the hydrogenation of
alkynes.[15] It is therefore proposed that over the as-obtained Co-
C@Cu-C, the conversion of phenylacetylene to 1, 4-diphenyl-1,
3-butadiene has undergone a tandem hydrogenation and C-C
coupling, as shown in Scheme 2. The first step in this process is
the activation of phenylacetylene by metallic Cu NPs. Due to a
lower work function of Cu (4.65 eV) compared to carbon (4.81 eV)
as well as the existence of the strong interactions between the
carbon support and metallic Cu, electrons transfer from metallic
Cu to carbon matrix when heated and Cu+-phenylacetylide
complex was formed on the surface of Cu NPs (step 1 in Scheme
2).[16] The involvement of the formation of Cu+-phenylacetylide
complex in the first step was confirmed by the result obtained from
the controlled experiment carried out using styrene as the
substrate, which shows almost no 1, 4-diphenyl-1, 3-butadiene
was obtained (Table 1, entry 9). In the meantime, the dissociation
of NaBH4 occurs on the surface of metallic Co NPs in Co-C@Cu-
C to form Co-BH3- and Co-H, which acts as the active species for
the hydrogenation of phenylacetylene (step 2 in Scheme 2). The
hydrides on Co NPs can spillover to Cu NPs through carbon
matrix, and react with the adsorbed Cu+-phenylacetylide complex
to form complex (A) (step 3 and 4 in Scheme 2). The spillover of
the hydrides from the metal NPs to the carbon materials has
already been demonstrated.[17] The hydrogenation of 1, 4-
diphenylbutadiyne over Co-C@Cu-C showed that no target
product was formed (Table 1, entry 10). The participation of
isopropanol in this reaction was confirmed since almost no
hydrogenation products were detected when isopropanol was
replaced by CH2Cl2 (Table 1, entry 2). The remaining hydrides in
BH3(i-PrO)- can also be dissociated sequentially over metallic Co
NPs, and spillover through the carbon matrix to react with the
adsorbed Cu+-phenylacetylide complex to form anothor complex
(A), with BH2(i-PrO)- left in the reaction system (steps 5 in Scheme
2). The in-situ formed complex (A) can dimerize to form 1, 4-
diphenyl-1, 3-butadiene (steps 6 in Scheme 2). Surely, side
reactions including the direct hydrogenation of phenylacetylene to
produce styrene and the direct dimerization of Cu+-
phenylacetylide complex to form 1, 4-diphenylbutadiyne also exist.
Therefore, suppressing the side reactions is important for
improving the selectivity to the target 1, 4-diphenyl-1, 3-butadiene
in this tandem reaction.
results, the XPS of Co-C@Cu-C shows two wide peaks in Co 2p
region, which can be deconvoluted into two sets of peaks (Figure
2c). The peaks with binding energy at 779.66 eV and 795.13 eV
can be attributed to 2p3/2 and 2p1/2 of metallic Co0, while the other
two small peaks at 781.88 eV and 797.10 eV can be assigned to
those from Co2+. Since no diffraction peaks corresponding to CoO
was observed in the XRD pattern of Co-C@Cu-C, the presence
of Co2+ is probably ascribed to the partial oxidation of the surface
of metallic Co. The XPS of Co-C@Cu-C in the Cu region shows
two peaks with binding energy at 932.36 eV (2p3/2) and 952.22 eV
(2p1/2), corresponding to Cu0 (Figure 2d). In addition to these, two
small peaks at 934.10 eV and 954.10 eV are also observed,
indicating the coexistence of Cu2+, probably ascribed to the partial
oxidation of the surface of Cu NPs. The amount of Co and Cu in
Co-C@Cu-C was determined to be 11.52% and 30.12%, with a
Co/Cu ratio (0.38) comparable to that in Co-MOF-74@Cu-MOF-
74 (0.36). Therefore, morphology-maintained transformation of
rod-shape Co-MOF-74@Cu-MOF-74 to carbon supported Co and
Cu NPs has been successfully realized by pyrolysis of Co-MOF-
74@Cu-MOF-74 at 1000 °C.
The catalytic performance of the as-obtained Co-C@Cu-C
for the transformation of phenylacetylene to 1, 4-diphenyl-1, 3-
butadiene was first investigated in THF using NaBH4 as the
reducing agent. As shown in entry 1 (Table 1), 13% of
phenylacetylene was converted, with a selectivity of only 24% to
1, 4-diphenyl-1, 3-butadiene after 10 h. In addition, a selectivity of
51% to 1, 4-diphenylbutadiyne was also detected. This indicated
that although one pot transformation of phenylacetylene to
produce 1, 4-diphenyl-1, 3-butadiene was possible, the
performance over the current system was still too low due to the
existence of the side reactions. To investigate the possibility of
tuning the rates of the coupling and the hydrogenation by
changing the reaction medium, the reactions were carried out in
different solvents. The performance of the reaction was
influenced by the reaction medium. For example, when aprotic
solvents like CH2Cl2 was used, the main product was 1, 4-
diphenylbutadiyne (Table 1, entry 2), while hydrogenated product
like styrene and ethylbenzene were mainly obtained when
protonic solvents such as EtOH or i-PrOH was used as the solvent
(Table 1, entry 3 and 4). The above results clearly indicated that
proton solvents can facilitate the hydrogenation reaction, probably
due to its higher capability for proton transfer. Among the solvents
investigated, a mixed solvent containing THF/i-PrOH (v/v =3:1)
gave the best performance by showing the highest
phenylacetylene conversion ratio of 87%, with a selectivity of 41%
to 1, 4-diphenyl-1, 3-butadiene (Table 1, entry 5). Only 1, 4-
diphenylbutadiyne was detected when the reaction was carried
out in absence of NaBH4 under otherwise similar conditions,
indicating that the formation of 1, 4-diphenyl-1, 3-butadiene is truly
promoted by Co-C@Cu-C through the transfer hydrogenation
(Table 1, entry 6). When Co-MOF-74 derived Co-C was used as
the catalyst, only styrene, the hydrogenation product was
detected, indicating that the hydrogenation occurs over metallic
Co NPs (Table 1, entry 7). On the contrary, only 1, 4-
diphenylbutadiyne, the coupling product, was obtained over Cu-
MOF-74 derived Cu-C, suggesting that metallic Cu is involved in
the coupling of phenylacetylene (Table 1, entry 8).
The above results were consistent with previous studies,
which showed that Cu-based catalyst can catalyze the C-C
coupling of the terminal alkynes, while the disscociation of BH4
Scheme 2. Proposed mechanism for the one pot tandem reaction of
phenylacetylene to produce 1, 4-diphenyl-1, 3-butadiene over Co-C@Cu-C
using NaBH4 as the reducing agent.
-
4
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The regulation of the kinetics of the hydrogenation and the
mechanical mixture of Cu-MOF-74 and Co-MOF-74 led to Co-
C&Cu-C, which was also used for the reaction. Although 93% of
phenylacetylene was converted after 10 h, the main product
obtained was styrene, with a selectivity of only 16% to the
desirable 1, 4-diphenyl-1, 3-butadiene (Table 1, entry 14). The
poor performance observed over both Co-Cu-C and Co-C&Cu-C
clearly highlights the important role of the core-shell structure of
Co-MOF-74@Cu-MOF-74 to the catalytic performance of the
derived bi-metallic catalytic systems. Cu-MOF-74@Co-MOF-74,
with Cu-MOF-74 as a core and Co-MOF-74 as the shell, was also
prepared via a similar strategy, which upon pyrolysis gave Cu-
C@Co-C. Although phenylacetylene was also totally converted
over Cu-C@Co-C after reacted for 10h, the main product
obtained was styrene (65%), with a selectivity of only 3% to the
desirable 1, 4-diphenyl-1, 3-butadiene (Table 1, entry 15). The
exposure of the Co NPs to the substrate would make the rate of
the hydrogenation too fast as compared with that of the coupling
and resulted in the formation of more hydrogenated byproducts.
The cover of metallic Co NPs with Cu NPs with a higher chemical
stability not only helps to inhibit the oxidation of Co NPs, but also
plays a vital role in regulating the reaction rate in a tandem
reaction.
Co-C@Cu-C derived from Co-MOF-74@Cu-MOF-74 also
showed high stability during the one pot transformation of
phenylacetylene to produce 1, 4-diphenyl-1, 3-butadiene, which
is highly important for its practical application. A cycling reaction
revealed that no obvious loss of the activity, with 75% of
phenylacetylene converted and a selectivity of 61% to 1, 4-
diphenyl-1, 3-butadiene (Table 1, entry 16). In addition, the
recovered catalyst shows almost unchanged XRD and TEM
image (Supporting Figure S4a and 4b)
C-C coupling is important to ensure an efficient formation of 1, 4-
diphenyl-1, 3-butadiene. Since the reaction over Co-C@Cu-C
using NaBH4 as the reducing agent gave a high selectivity of 52%
to styrene, the byproduct due to the side reaction of the direct
hydrogenation of phenylacetylene, it is anticipated that the using
of NH3BH3, a milder reducing agent than NaBH4, would decrease
the rate of the hydrogenation and optimize the desired reaction to
yield 1, 4-diphenyl-1, 3-butadiene. Therefore, the reaction using
NH3BH3 as the reducing agent was investigated under otherwise
conditions. As expected, the reaction between NH3BH3 and
phenylacetylene over Co-C@Cu-C gave 1, 4-diphenyl-1, 3-
butadiene as the main product, with
a
conversion of
phenylacetylene to be 77% and a selectivity of 63% to desired 1,
4-diphenyl-1, 3-butadiene after 10 h, confirming that the well-
matched reaction kinetics resulted in a superior performance for
tandem hydrogenation/coupling of phenylacetylene to produce 1,
4-diphenyl-1, 3-butadiene (Table 1, entry 11). An almost total
conversion of phenylacetylene was achieved after reacting for 13
h, at the expense of a slightly decreased selectivity to 1, 4-
diphenyl-1, 3-butadiene (57%). (Table 1, entry 12). The reaction
can also be applied to different phenylacetylene derivatives to
produce corresponding diphenyl-1, 3-butadienes, although with
varied activities (Supporting Table S1).
(111)
(111)
(200)
(200)
(220)
(220)
(220)
(200)
(111)
Conclusion
Figure 3. Co-Cu-C (a) XRD patterns; (b) TEM and (c, d) HRTEM images.
In summary, supported Co NPs wrapped by carbon supported Cu
NPs (Co-C@Cu-C) was successfully obtained from the pyrolysis
of a core-shell structured Co-MOF-74@Cu-MOF-74, which acted
as a bi-functional catalyst for the one pot tandem reaction to
transform phenylacetylene to produce 1, 4-diphenyl-1, 3-
butadiene. By changing the reaction medium and reducing agent,
an optimized performance which show a phenylacetylene
conversion of 77% and a selectivity of 63% to 1, 4-diphenyl-1, 3-
butadiene was realized over Co-C@Cu-C when NH3BH3 was
used as a reducing agent in THF/i-PrOH (v/v =3:1). This work
highlights the important role of MOFs for the preparations of
multifunctional carbon supported metal NPs for heterogeneous
catalysis.
The above observations clearly demonstrated that Co-
C@Cu-C derived from a well-designed core-shell structured Co-
MOF-74@Cu-MOF-74 can act as a successful bi-functional
catalyst for one pot transformation of phenylacetylene to 1, 4-
diphenyl-1, 3-butadiene via tandem hydrogenation/coupling. To
demonstrate the effect of the structure of the precursor on the
performance of the derived catalyst, Co-Cu-MOF-74, a bimetallic
Co-Cu-based MOF-74 (denoted as Co-Cu-MOF-74), fabricated
similarly
to
Co-MOF-74
by
reacting
Cu(CH3COO)2,
Co(NO3)2ꞏ6H2O and H4DOBDC in one-pot, was used as the
precursor to obtain carbon supported bimetallic Co-Cu catalyst
(denoted as Co-Cu-C, Supporting Scheme S1). The formation of
MOF-74 framework was evidenced from the XRD pattern of Co-
Cu-MOF-74 (Supporting Figure S3a). The pyrolysis of Co-Cu-
MOF-74 led to the formation of Co-Cu-C (Figure 3a，Supporting
Fig. S3b) Unlike that in Co-C@Cu-C, the TEM image of Co-Cu-C
shows that metallic Cu and Co NPs are randomly distributed on
the carbon matrix (Figure 3b-d). The reaction carried out over Co-
Cu-C under otherwise similar conditions revealed that 56% of
phenylacetylene was converted, with a selectivity of only 13% to
1, 4-diphenyl-1, 3-butadiene (Table 1, entry 13). By-products
including styrene and ethylbenzene (62%), the hydrogenation
products, as well as 1, 4-diphenylbutadiyne (21%), the coupling
product, were also detected. In addition, the pyrolysis of a
Experimental Section
Syntheses
MOFs precursors. M-MOF-74 (M = Co and Cu) were synthesized based
on previously reported procedures.[18] Co-MOF-74@Cu-MOF-74 was
obtained by reacting Cu(CH3COO)2 and H4DHBDC under microwave
heating in the presence of pre-obtained Co-MOF-74. Co-Cu-MOF-74 was
synthesized similarly to Co-MOF-74, except that equimolar of
Cu(CH3COO)2 and Co(NO3)2ꞏ6H2O was used as the metal precursors.
5
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10.1002/cctc.202001140
ChemCatChem
FULL PAPER
MOF-derived carbon supported metal NPs. Co-C@Cu-C was prepared
by the pyrolysis of Co-MOF-74@Cu-MOF-74 at 1000 °C similar to our
previous work. Typically, the activated Co-MOF-74@Cu-MOF-74 was
transferred into a ceramic boat and placed in a temperature-programmed
furnace under a nitrogen flow. After that, Co-MOF-74@Cu-MOF-74 was
heated slowly at a rate of 2 °C/min to 1000 °C and kept for 1 h. The product
was collected after cooling to room temperature.
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The reactions were carried out in a 10 ml quartz schlenk tube. Catalyst (5
mg) was treated under vacuum at 200 °C to remove any adsorbed species
and purged with N2. After NaBH4 (2 mg, 0.05 mmol) and K2CO3 (20 mg)
was added, ethanol (4 mL) and alkynes (5.5 µL, 0.05 mmol), pre-degassed
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This work was supported by NSFC (21872031, U1705251). Z. Li
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Entry for the Table of Contents
Bimetallic CoCu catalytic system (Co-C@Cu-C), with Co NPs wrapped by carbon supported Cu NPs, were obtained by pyrolysis of a
core-shell structured Co-MOF-74@Cu-MOF-74, which shows an efficient one pot transformation of phenylacetylene to produce 1, 4-
diphenyl-1, 3-butadiene, due to the synergistic roles played by supported metallic Cu NPs and Co NPs.
7
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