Schiff-based Pd(II)/Fe(III) bimetallic self-assembly monolayer—preparation, structure, catalytic dynamic and synergistic

Article abstract of DOI:10.1016/j.mcat.2019.03.004

Graphene oxide supported Pd (II)/Fe (III) bimetallic catalytic monolayer (denoted as GO@H-Pd/Fe) was prepared and characterized. Its catalytic performances for Suzuki coupling reaction, synergetic effect and catalytic mechanism were systematic investigated. Results showed that orientation, composition and distribution of catalyst had efficient effect on catalytic activity. Catalytic activity of GO@H-Pd_0.10/Fe_0.90 was 475 times more than that of GO@H-Pd due to the ordered catalytic monolayer immobilized on GO, proper ratio of Pd/Fe and the synergetic effect between Pd(II) and Fe(III) which could form active cluster containing Pd and Fe. The Pd(II) could be made more negative by transferring electron from GO to Fe(III) via ligand and then to Pd, improving its catalytic activity since it was easy for oxide addition. It also exhibited better stability and recyclability at least 8 times due to proper functional ligand and support. Deactivation mechanism was confirmed to be the aggregation of active centre during the recycling. Heterogeneous catalytic mechanism was also proved by poison test, hot filtration and ReactIR. The results of ReactIR presented different dynamic catalytic process for GO@H-Pd_0.10Fe_0.90 and homogeneous catalyst (Li₂PdCl₄/FeCl₃·6H₂O).The activation energies were 9.7 KJ/mol and 3.7 KJ/mol obtained for heterogeneous and homogeneous catalyst, respectively. Considering the diffusion effect, the factor of supports on the activity was also investigated by ReactIR, with which that GO@H-Pd_0.10Fe_0.90 catalytic activity was higher than that of homogeneous catalyst could be confirmed.

Full text of DOI:10.1016/j.mcat.2019.03.004

Molecular Catalysis 469 (2019) 75–86
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Schiff-based Pd(II)/Fe(III) bimetallic self-assembly monolayer—preparation,
structure, catalytic dynamic and synergistic
a
a
a
a,⁎
a
b
Pingping Huang , Erran Song , Yimeng Sun , Tiesheng Li , Donghui Wei , Minghua Liu ,
Yangjie Wu
a
a
College of Chemistry and Molecular Engineering, Zhengzhou University, Kexuedadao 100, Zhengzhou, 450001, PR China
b
Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun North First Street 2, Beijing, 100190, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Graphene oxide supported Pd (II)/Fe (III) bimetallic catalytic monolayer (denoted as GO@H-Pd/Fe) was pre-
pared and characterized. Its catalytic performances for Suzuki coupling reaction, synergetic effect and catalytic
mechanism were systematic investigated. Results showed that orientation, composition and distribution of
catalyst had efficient effect on catalytic activity. Catalytic activity of GO@H-Pd0.10/Fe0.90 was 475 times more
than that of GO@H-Pd due to the ordered catalytic monolayer immobilized on GO, proper ratio of Pd/Fe and the
synergetic effect between Pd(II) and Fe(III) which could form active cluster containing Pd and Fe. The Pd(II)
could be made more negative by transferring electron from GO to Fe(III) via ligand and then to Pd, improving its
catalytic activity since it was easy for oxide addition. It also exhibited better stability and recyclability at least 8
times due to proper functional ligand and support. Deactivation mechanism was confirmed to be the aggregation
of active centre during the recycling. Heterogeneous catalytic mechanism was also proved by poison test, hot
filtration and ReactIR. The results of ReactIR presented different dynamic catalytic process for GO@H-
Bimetallic catalyst
Self-assembly
Monolayer
Suzuki coupling reaction
Synergistic effect
ReactIR
2 4 3 2
Pd0.10Fe0.90 and homogeneous catalyst (Li PdCl /FeCl ·6H O).The activation energies were 9.7 KJ/mol and 3.7
KJ/mol obtained for heterogeneous and homogeneous catalyst, respectively. Considering the diffusion effect, the
factor of supports on the activity was also investigated by ReactIR, with which that GO@H-Pd0.10Fe0.90 catalytic
activity was higher than that of homogeneous catalyst could be confirmed.
1. Introduction
states in catalysis. Therefore, designing and preparing novel iron cat-
alysts with high catalytic activity will be great significance.
Precious metal catalysis show important ways in the bond formation
As we know, although homogeneous catalysts with high efficiency
and practical applications, they are significantly restricted to the se-
paration of soluble catalysts from the reaction systems and recycling
[20]. Application of heterogeneous catalysts has received tremendous
scientific and industrial attention because of their high activity and
recyclability [21–26]. Among heterogeneous catalysts, hetero-bime-
tallic catalysts which doped with non-precious metals have attracted
extensive attentions due to greatly reduced the amount of palladium,
and the cost to some extent. Especially, the second metal could induce
the special properties [27–32].
Among various supporting materials used in heterogeneous cata-
lysis, carbon nanomaterials, such as grapheme oxide (GO) has attracted
enormous attention due to its unique chemical, physical properties [33]
used in some application [34,35]. Especially, graphene oxide rich with
hydroxyls, carboxyls and epoxides on the planar surfaces which is
readily available functionalized [36,37], such as suitable textural
in organic synthesis, modern medicine and materials science, in which
palladium-catalyzed Suzuki-Miyaura, Heck, and Negishi couplings are
indispensable [1,2]. Palladium as a precious metal is uneconomical in
using and has limited reserves [3]. To solve this problem, other non-
precious metals such as iron [4,5], copper [6,7], cobalt [8–10] and
nickel [11,12] have been systematic studied [13,14].
Among of them, iron is a non-precious and tremendous amount,
which has various valences and critical function in bio-systems. It is
also an ideal green catalyst and become one of the most active research
fields in recent years [15–19]. The reactions catalyzed by iron are also
spring up, including oxidation, reduction, coupling, substitution, addi-
tion, ring addition and ring expansion, multi-component reaction and
so on. The coupling reactions catalyzed by iron catalyst have achieved
many results, but meet many problems, such as strict reaction condi-
tion, the large dosage of catalyst, the rule of the transform of valence
⁎
Corresponding author.
E-mail address: lts34@zzu.edu.cn (T. Li).
https://doi.org/10.1016/j.mcat.2019.03.004
Received 28 November 2018; Received in revised form 17 January 2019; Accepted 4 March 2019
2468-8231/ © 2019 The Authors. Published by Elsevier B.V. All rights reserved.

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
2.3. Suzuki coupling reaction catalyzed by GO@H-Pd/Fe
It was performed in Supporting information section [49].
3. Results and discussion
3.1. Preparation and characterization of GO@H-Pd/Fe
GO@H-Pd/Fe catalytic monolayer was prepared as depicted in
Scheme 1. Preparation of GO@H-Pd/Fe monolayer.
Scheme 1
XRD of GO@H-Pd/Fe in fabrication process were measured (Figure
design [38], doping (N-doping, P-doping, S-doping and B-doping) [39]
and noble metal loading [40].
S1). The diffraction peaks at 11.27° and 42.40° designed to the planes of
GO [50,51]slightly shift towards a higher angle compared with that of
GO after modified with nitrogen group, followed by loading of Pd and
Fe due to molecular intercalation and also sonication. Characteristic
diffraction peaks at 21.09° was the plane of rGO. The reason is that the
modifying with nitrogen group and load of Pd and Fe covered oxygen
on the surface of GO. Furthermore, the ordered catalytic monolayer was
confirmed by the XRD analysis of Si@H-Pd/Fe at different grafting
processes (Figure S2). The characteristic sharp small angle diffraction
peaks at about 1.4°, and the peak strength and peak width were slightly
changed with the self-assembling. It could be seen that the monolayer
of ordered self-assembled catalyst were grafted on silicon. The catalytic
monolayer also could also be certificated by the water contact angle’s
According to the complexing ability, numerous studies showed that
carbon nano-structure modified by ligands having amino and imine
groups had more surface binding sites of the meal, stability and utility
compare to nitrogen-free. In previous studies, we have reported that
functional groups on surface of support materials had significant impact
to the activity of catalyst [41]. On the one hand, it allowed for an-
choring and better dispersion for the catalytic nano-particles on the
support surface [42] due to the electron effect of nitrogen and the
modified process improved the stability of the produced catalysts be-
cause of enhanced of π binding. Therefore, combining the advantages of
proper supports, ligands, different metals, self-assembly way [43–45]
and measuring methods will made it easy for constructing new catalyst
with special properties and deeply investigating the mechanism for
improving the catalytic activity. The control of chemical processes
through online technology attracted much more attention, such as IR,
NIR, Raman, ReactIR [46,47]. They have the advantages over offline
analysis for avoiding hazardous substances. Suzuki-Miyaura reaction
process also could be detected by ReactIR, with which the reaction
activation energy of homogeneous and heterogeneous catalysts was
calculated based on ReactIR data.
(
WCA) analysis, in which the different properties of monolayer surface
at different grafting processes were observed. (Figure S3)
FTIR of preparation process for GO@H-Pd/Fe were measured as
−
1
−1
−1
shown in Figure S4. Peaks at 3430 cm , 1729 cm , 1622 cm
,
−1
−1
1221 cm
and 1053 cm
were corresponded to stretching of OeH
and C]O, vibration of C–O, stretching of CeOH and epoxy on GO.
−1
After ligand modification, characteristic peaks at 1105, 1042 cm for
−
1
SieO and 1636 cm for free C]N in H-GO could be observed. In the
case of GO@H-Pd/Fe, the peak of C]N red shifted which depended on
coordination with the Fe and Pd ions [52].
In this paper, a ligand having Schiff-base group was chemically
grafted to the surface of graphene oxide, and the ligation site of metal
ions was formed by further modification. The palladium and iron were
immobilized by coordination bond toward synthesis of a reusable and
recoverable Pd/Fe bimetallic heterogeneous catalytic monolayer.
Mechanism of Pd/Fe catalyst during catalyzing reaction, deactivation
during the recycle and synergetic effect were detailed investigated.
Raman spectra of GO, H-GO, and GO@H-Pd/Fe exhibited the dis-
−1
order. The characteristic peak of GO at about 1336 and 1586 cm
D
were D band and G band, respectively in Figure S5 [53]. The ratio of I /
G
I showed a general trend of decrease from 1.05 to 1.01 and 0.99 which
2
reflected the number of Csp atoms increased during fabricating pro-
cesses of GO@H-Pd/Fe [54,55]. There were two possible reasons, one
reason was the change of C sp2 atoms caused by anchoring ligand, re-
sulting in the low ratio of oxygen. Another reason was that ligand graft
2. Experimental
−
1
and metal coordination. The
1
G
band at 1584 cm
shifted to
−1
−1
576 cm as ligand was anchored and then to 1585 cm when GO@
2.1. Regents and equipments
H-Pd/Fe was formed. The peak shifting could be explained by that the
gradually change of local stress was changed by the modifying [56,57].
The elements of GO@H-Pd/Fe monolayer was measured with XPS
as shown in Figure S6. Peaks for N 1s, Cl 2p, C 1s, Si 2s, O 1s, Pd 3d and
Fe 2p could be clearly observed (Figure S6a). Two bands at 338.0 and
Regents were obtained from commercial. Characterization equip-
ments were presented in supporting information section.
3
2
43.2 eV were the character binding energy of Pd (II) (Figure S6b). Fe
p presented two bands at 711.9 and 725.0 eV ascribed to the binding
2.2. Preparation of the amino modified graphene oxide and GO@H-Pd/Fe
energy of iron (III) (Figure S6c).
SEM pictures of graphene oxide (GO), H-GO, GO@H-Pd/Fe were
measured (Figure S7). Layer-like structure could be observed (Figure
It was presented in Supporting information section [48].
Table 1
Influences of the ratio of Pd/Fe on catalytic performance.
Catalyst
Pd
(
Fe
Time
(h)
Isolated yield
(%)
TON(mol molPd−1)
TOF
(h
mol· g−1)
(mol· g−1)
−1
)
−
4
GO@H-Pd
GO@H-Fe
GO@H-Pd0.01Fe0.99
GO@H-Pd0.05Fe0.95
GO@H-Pd0.10Fe0.90
2.49 × 10
–
1.93 × 10
4.28 × 10
5.33 × 10
–
12
12
12
12
12
99
trace
71
87
95
199
–
18394
1016
892
17
–
1533
85
74
−
4
2.42 × 10
2.19 × 10
2.14 × 10
1.93 × 10
−6
−5
−5
−4
−4
−4
a
2 2 3
Reaction condition: PhB(OH) (0.25 mmol), 4-bromotoluene (0.25 mmol), K CO (0.5 mmol), catalyst 5 mg, solvent (50% aqueous alcohol 4 mL) at 70 °C.
76

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Table 2
Optimization of Suzuki-Miyaura reaction conditions using GO@H-Pd0.10Fe0.90
.
TOF(h 1)f
−
Entry
Base
Solvent
Time
h)
T (°C)
Isolated yield (%)
(
1
2
3
4
5
6
7
8
9
K
K
K
K
K
K
K
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
H
EtOH
DMF
MeOH
H
H
2
O
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
1
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
60
50
30
70
70
70
8
6
31
6.3
4.7
–
77
77
–
77
77
73
trace
99
99
trace
99
99
93
39
92
95
2
O:EtOH(2:1)
O:EtOH(3:1)
2
3
Toluene
Na
K
NaOH
NaOAc
NaHCO
2
CO
3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
2
O:EtOH(3:1)
3
PO
4
10
11
12
13
14
15
16
17
18
19
20
21
22
31
72
74
3
Et
3
N
b
Na
Na
Na
Na
Na
Na
Na
Na
Na
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
99
129
383
4318
2324
368
344
137
4412
8074
c
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
98
b
92
b
2
99
b
12
12
12
2
94
b
88
b
35
d
94
e
2
86
a
b
Reaction condition: PhB(OH)
2
(0.25 mmol), 4-bromotoluene (0.25 mmol), Base (0.5 mmol), GO@H-Pd0.10Fe0.90 5 mg, solvent (4 mL) at 70 °C. GO@H-
c
d
(0.55 mmol), 4-bromotoluene (0.5 mmol), Base (1 mmol), GO@H-Pd0.10Fe0.90 1 mg, e PhB(OH)
Pd0.10Fe0.90 3 mg, GO@H-Pd0.10Fe0.90 1 mg. PhB(OH)
2
2
f
(1 mmol), 4-bromotoluene (1 mmol), Base (2 mmol), GO@H-Pd0.10Fe0.90 1 mg. 1 mg GO@H-Pd0.10Fe0.90 containing 0.0000533 mmol Pd.
Table 3
which demonstrated that imine palladium and iron complexes were
orderly modified to graphene oxide sheet (Figure S7c).
Influences of support and the functioned structure on catalytic performance.
Pd loading(mmol· mg−1)
SEM-EDS of GO@H-Pd/Fe were measured (Figure S8), in which
palladium and iron were presented on the surface of the catalyst. It was
clear that relative amount of palladium and iron with different electron
layers from the distribution diagram.
Entry
Catalyst
Yield (%)
b
1
2
3
4
5
6
7
8
9
GO
H-GO
–
–
0
c
0
d
Li
H + Li
GO + Li
H-GO + Li
GO-Pd0.10Fe0.90
2
PdCl
4
/FeCl
PdCl /FeCl
PdCl /FeCl
PdCl /FeCl
3
·6H
2
O
0.0000533
0.0000533
0.0000533
0.0000533
0.0000254
0.0000533
0.000741
76
TEM images of GO, H-GO, GO@H-Pd/Fe were also obtained
2
4
3
·6H
·6H
·6H
2
O
35
53
50
(
Figure S9), in which the clear sheet like structure was obtained (Figure
2
4
3
2
O
2
4
3
2
O
S9a). After modification with nitrogen group and metals, similar sheet
like structures could be seen (Figure S9b and Figure S9c), suggesting
that the morphology of GO maintained during the modification. The
results obtained above exhibited that ordered GO@H-Pd/Fe catalytic
monolayer on GO was fabricated.
To further characterize the SBET (Specific surface area) of corre-
2
sponding pore size distribution about GO@H-Pd/Fe, N adsorption-
desorption isotherms were actualized. As depicted in Figure S10a, it
e
15
GO@H-Pd0.10Fe0.90
Silica@H-Pd0.10 Fe0.90
99f
g
70
a
Reaction condition: PhB(OH)
Na CO (0.5 mmol), catalyst 5 mg, solvent (25% aqueous alcohol 4 mL) at 70 °C
for 2 h. GO 1 mg. H-GO 1 mg. Li
2
(0.25 mmol), 4-bromotoluene (0.25 mmol),
2
3
b
c
d
e
2
PdCl
GO-Pd0.10Fe0.90 1 mg. GO@H-Pd0.10Fe0.90 1 mg. Silica@H-Pd0.10 Fe0.90
mg.
4
0.000053 mmol and FeCl
3
·6H
2
O.
f
g
1
could be clearly observed that the GO and H-GO isotherms were as-
2
−1
cribed as type
4
Ⅳ
with
.2302 m g , respectively).The GO@H-Pd/Fe isotherm as shown in
Figure S10b was ascribed as type Ⅳ with a H3 hysteresis loop
a
H4 hysteresis loop (12.0295 m g
,
S7a). After being grafted with nitrogen group, more crumpling ap-
peared because of the chemical modifications (Figure S7b). Neat sheet
like structure were also obtained after complexed with Pd and Fe,
2 −1
2
−1
(
4.2507 m g
) [58,59], proving the existence of mesoporous
Table 4
Comparison of the results for Suzuki reaction catalyst by GO@H-Pd0.10Fe0.90 catalyst with that by Pd and Fe catalysts reported.
Entry
Catalyst
Reaction conditions
X
Yield (%)
TOFpd (h−1)
Ref
–
This work
GO@H-Pd0.10Fe0.90(0.0106 mol%Pd)
Pd complex 3(0.06 mol% Pd)
Na
2
2
CO
h, 70℃
CO , iPrOH:H
3
, EtOH:H
2
O,
Br
Br
Br
Br
Cl
Br
Br
86
94
70
84
42
97
76
8074
26
2
3
4
5
6
7
K
2
3
2
O,
59
60
61
62
63
64
3
0 h, RT
Na CO , DEM:H
4 h, 100℃
CO , solvent-free,
1 h, 120℃
Pd-Fe
3
O
4
/NCs (1 mol%Pd)
2
3
2
O,
3
2
BIO-IM-Pd
0.5 mol%)
PdCl /P-Fe-C(ax) (1.5 mol% Pd)
K
2
3
84
(
2
K
8
K
2
CO
h, 90℃
CO , EtOH:H
3
, DMF
350
1293
11.5
Pd/Fe
0.15 mol% Pd)
HMMS-salpr-Pd (1 mol%)
3
O
4
/s-G
2
3
2
O,
O,
(
30 min, 80℃
K
7
2
CO , EtOH:H
3
2
h, 70℃
77

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Table 5
Suzuki-Miyaura reaction of aryl halides with different aryl-boronic acids.
Entry
1
Ar–X
Ar’–B(OH)
2
Product
Yield(%)
99
2
3
99
99
4
5
6
7
8
9
99
99
96
99
99
99
1
0
94
1
1
1
2
99
92
1
1
3
4
80
11
1
1
1
5
6
7
21
15
99
1
8
95
1
2
9
0
80
85
2
2
1
2
trace
10
2
3
5
(
continued on next page)
78

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Table 5 (continued)
Entry
Ar–X
Ar’–B(OH)
2
Product
Yield(%)
10
2
4
a
2
Reaction condition: Ar’-B(OH) (0.25 mmol), Ar-X (0.25 mmol), Base (0.5 mmol), GO@H-Pd0.10Fe0.90 1 mg, solvent (25% aqueous alcohol 4 mL) at 70 °C for 2 h.
3
3
.2. Catalytic properties for Suzuki coupling reactions
.2.1. Influences of the ratio of Pd/Fe on catalytic performance
As shown in Table 1, only trace amounts of products were produced
with GO@H-Fe under the reaction condition (at 70 °C, 12 h, 2 mmol
CO in aqueous ethanol (1:1). However, using GO@H-Pd0.10Fe0.90 as
K
2
3
a catalyst 95% isolated yield could be obtained. Considering the cost
and green requirement, GO@H-Pd0.10Fe0.90 was chosen for next cata-
lytic research.
3.2.2. Catalytic properties of GO@H-Pd0.10Fe0.90
The catalytic performance of GO@H-Pd0.10Fe0.90 for Suzuki cou-
pling reaction was carried out with different solvents and bases
Table 2, entries 1–13). 99% yield of 4-phenyltoluene was obtained
under optimization condition (70 °C, 12 h, 2 mmol Na CO , aqueous
(
Fig. 1. The recycle experiments of GO@H-Pd0.10Fe0.90
.
2
3
ethanol (3:1) (entry 8). Furthermore, even though the dosage of catalyst
and reaction time were reduced (1 mg, 2 h), 99% yield could be ob-
tained (entry 17). When temperature was decreased, the yield slightly
decreased (Table 2, entries 18–20). There was still a high isolated yield
of expanded substrate (Table 2, entries 21, 22).
Comparison tests were designed for understanding the effects of
support and ligand on the catalytic properties (Table 3). No targets
were obtained by GO or H-GO (entries 1, 2). The inference of GO added
into catalytic system was studied (entries 3–6). 76% yield was obtained
materials (from 2 to 50 nm) [60]. It was the evident that SBET of GO@H-
Pd/Fe was smaller than that of GO due to modification with catalyst.
EIS (electrochemical impedance spectroscopy) spectra are widely
used to understand the transfer efficiency of electrons. Figure S11
showed exhibits the EIS Nynquist plots of GO, H-GO and GO@H-Pd/Fe
sample. In principle, the arc in EIS spectra implies the electrochemical
reaction impedance of catalysts loaded on the Ni foam electrodes. The
smaller arc implies the faster transfer efficiency of electrons and lower
transfer resistance with low recombination probability of electrons.
Notably, the catalyst GO@H-Pd/Fe has the smallest diameter than GO
and H-GO, suggesting that GO@H-Pd/Fe shows superior charge
transfer ability.
by Li
FeCl ·6H
yield by GO/Ligand/Li
2
PdCl
O (entry 4), 53% yield by GO/Li
PdCl /FeCl ·6H O, 15% yield by GO-
4
/ FeCl
3
·6H
2
O (entry 3), 35% yield by Ligand/Li
2 4
PdCl /
3
2
2
PdCl /FeCl ·6H O, 50%
4
3
2
2
4
3
2
Pd0.10Fe0.90, indicating that ligands and its orientation played a crucial
role for forming regular catalytic monolayer. On the other word, the
coordination between self-assembly ligands and metallic atoms was
efficient. GO@H-Pd0.10Fe0.90 monolayer linked with GO by self-as-
sembly way presented higher catalytic properties (entry 8). The reason
was that the catalytic active site could be isolated on the surface of
Fig. 2. SEM images of the process of catalyst and reused catalyst (a) at 0 min, (b) at 60 min, (c) at 120 min, (d) after 4th run, (e) after 8th run.
79

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Fig. 3. TEM images of the process of catalyst and reused catalyst (a) at 0 min, (b) at 60 min, (c) at 120 min, (d) after 4th run, (e) after 8th run.
Fig. 4. HRTEM of GO@H-Pd0.10Fe0.90 catalysts at different catalytic time: (a) at 60 min; (b) at 120 min; (c) after 4th run; (d) after 8th run. Histogram of the Pd0
nano-cluster diameters at 60 min: 3.36 nm in (a), from a sample population of 140; 120 min: 3.49. nm in (b), from 70; after 4th run 3.77 nm in (c), from 29; after 8th
run 3.87 nm in (d), from 29 particles.
Fig. 5. XPS of the process of catalyst and reused catalyst (a) Pd 3d, (b) Fe 2p, (c) Pd 3d, B 1 s, Br 3p.
80

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
ortho-substituted aryl bromides was lower than that of para-substituted
or meta-substituted due to steric effect (Table 5, entries 8–13). How-
ever, the results for chlorobenzene derivatives were not satisfactory
(
Table 5, entries 14–16). Further, coupling phenylboronic derivatives
and heterocyclic borate with 4-bromotoluene (Table 5, entries 17–24),
comparing to phenylboronic derivatives, heterocyclic borate with 4-
bromotoluene showed lower reactivity. This might be that the catalyst
has poor applicability to heterocyclic substrate. On the other hand, in
Table 5, compare Entry 1 with 3, aryl iodides react faster than bromides
or chlorides, in order to investigate the catalytic activity deeply we
optimize the reaction for iodo (Table S1). 1H and CNMR spectra of
biaryl products have provided in supporting information (Figure S12,
Figure S13, Figure S14, Figure S15, Figure S16 and Figure S17).
For recycle experiments, the performance of GO@H-Pd0.10Fe0.90
reusability was investigated, in which it showed better stability upon
reuse (Fig. 1). Although the isolated yield dropped slightly at the sixth
time, the cycle could reach nine times by extending reaction time
13
Scheme 2. Proposed formation of Pd/Fe active centre.
monolayer and prevented from aggregating by the ligand [61,62].
Compared with Silica@H-Pd/Fe, isolated yield of GO@H-Pd0.10Fe0.90
was not only high yield, but also high TOF value. It was attributed to
GO@H-Pd0.10Fe0.90 could easily disperse in solution (Table 3). These
results could be interpreted that not only good dispersivity of GO@H-
Pd0.10Fe0.90, but also the efficiently electronic transferring between
Pd/Fe complex and GO. What is more, GO could promotes mass
transfer and made the substrates contact with the supported catalytic
active centre easily [63]. At mean time, the function of GO in GO@H-
Pd0.10Fe0.90 for improving catalytic performance was its electron rich,
(
Fig. 1). The reason was the loss of the catalytic active centre during
recycling was studied according to ICP-AES and the remaining amount
−
6
-5
was Pd: 8.79 × 10 mmol/mg, Fe: 6.35 × 10 mmol/mg at sixth re-
cycle.
3.3. Deactivation mechanism of the GO@H-Pd0.10Fe0.90 catalysts
Deactivation of catalysts means a loss of catalytic activity when
recycled in several times [64]. To illuminate the deactivation me-
chanism was of great significance for improving the catalytic activity
and stability.
The SEM images of the catalyst recycled at 8th run exhibited almost
no changes in the morphology shown in Fig. 2. TEM images of GO@H-
Pd0.10Fe0.90 catalysts were also obtained after 1 h, 2 h, the 4th and the
not its bigger SBET according to the data of GO@H-Pd0.10Fe0.90
.
The catalytic activities of GO@H-Pd0.10Fe0.90 compared with other
Pd and Fe complex reported were listed in Table 4. Impressively, a low
amount of GO@H-Pd0.10Fe0.90 (0.0106 mol%) with higher TOF was
presented compared with other catalyst, indicating that ordered GO@
H-Pd0.10Fe0.90 self-assembly monolayer presented some advantage
over other catalysts reported.
Suzuki coupling reaction catalyzed by GO@H-Pd0.10/Fe0.90 was
carried out for screening the scope of substrates. Quantitative yield of 4-
phenyltoluene (> 99%) with aryl iodide was obtained (Table 5, entry 1,
8th run (Fig. 3), in which it could be seen that slight agglomeration
appeared at 4th and 8th run. The morphology and arrangements of
GO@H-Pd0.10Fe0.90 were the similar lattice fringes (Fig. 4a-d) at dif-
ferent catalytic time. The presence of polydisperse, regular-shaped Pd
(
1 1 1) nano-clusters was 0.225 nm. The particle size of metal changed a
2
). Higher yields were obtained for aryl bromides having electron-re-
leasing or electron-withdrawing groups (Table 5, entry 3–13). Mean-
while, different substituting position of aryl bromides, the yield of
little into large size, which implied that deactivation had relation to the
aggregation of active centre and the loss of catalyst during recycling.
Fig. 6. ReactIR plots with time for the resultant of Suzuki reaction at 70 °C (a) 3D map catalyzed by GO@H-Pd0.10Fe0.90, (b) 3D map catalyzed by
−
1
Li
2
PdCl
4
+FeCl
3
·6H
2
O, (c) Kinetic analysis of catalytic reaction of GO@H-Pd0.10Fe0.90 and Li
2
4
PdCl +FeCl
3
·6H
2
O using the band of 754 cm , (d) catalyzed by GO@
H-Pd0.10Fe0.90; ReactIR plots with time for the resultant of Suzuki reaction at 55 °C, (a*) 3D map catalyzed by GO@H-Pd0.10Fe0.90, (b*) 3D map catalyzed by
−
1
Li
2
PdCl
4
+FeCl
3
·6H
2
O, (c*) Kinetic analysis of catalytic reaction of GO@H-Pd0.10Fe0.90 and Li
2
PdCl
4
+FeCl ·6H O using the band of 754 cm , (d*) catalyzed by
3
2
GO@H-Pd0.10Fe0.90
.
81

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Fig. 7. ReactIR plots with time for the resultant of Suzuki reaction (a) 3D map catalyzed by Li
2
PdCl
4
+FeCl
3
·6H
PdCl
+FeCl
2
O at 70 °C, (b) Kinetic analysis of catalytic reaction of
−
1
GO@H-Pd0.10Fe0.90 and Li
Li PdCl +FeCl ·6H O at 55 °C, (b*) Kinetic analysis of catalytic reaction of GO@H-Pd0.10Fe0.90 and Li
catalyzed by Li PdCl +FeCl ·6H O at 55 °C.
2
PdCl
4
+FeCl
3
·6H
2
O using the band of 754 cm
at 70 °C, (c) catalyzed by Li
2
4
+FeCl ·6H
3
2
O at 70 °C (a*) 3D map catalyzed by
−
1
2
4
3
2
2
PdCl
4
3
·6H O using the band of 754 cm at 55 °C (c*)
2
2
4
3
2
3
3
.4. Investigation on the catalytic mechanism
capability of electrical conductivity was declined. The reason was that
as the reaction time increases, the amount of Pd0 increases and there
was a small amount of aggregation, and wasn’t conducive to conduction
.4.1. Hot filtration and poison test
How to distinguish homo- or heterogeneous catalyst is an important
0
and charge transfer. The results showed that appropriate number of Pd
research [54]. The yield went up rapidly before 40 min, then increased
slowly and completed with 95% yield after 90 min (Figure S18). The
high efficiency of GO@H-Pd0.10Fe0.90 catalyst could be attributed to
the favorable dispersibility in solution with the help of GO. To confirm
whether there were metals leaching during catalytic process, GO@H-
Pd0.10Fe0.90 catalyst was removed after 30 min and then the kinetics
was detected till 90 min. The yield did not increase and remain the
constant (57–59%) (Figure S18 (red line)). It was the evident that few
leaching of catalyst occurred during the catalytic process [54].
To further ensure whether or not catalysis was heterogeneous and
where the catalytic reaction occurred, poison experiment was carried
out (Table S2). When a little mercury was put into the mixture before
starting, catalytic activity could not efficient be inhibited as mercury
could not completely cover the active centre on the surface due to its
poor dispersibility. The activity of the catalyst was obviously decreased
with the addition of 2′2-Dipyridyl. So, 2′2-Dipyridyl was an effective
poisoning additive even at less 1.0 equiv than metal atom, indicating
that catalytic active centre was on the surface of GO@H-Pd0.10Fe0.90
monolayer which was characteristic property of heterogeneous catalyst
was conducive to the catalysis.
3.4.3. Studies on the formation of catalytic active centre
The delivery of various elements at different time and recycled
catalysts were obtained by XPS in order to investigate what the real
active centre was during catalytic process. For GO@H-Pd0.10Fe0.90 in
which the palladium was a major Pd (II) species, a pair of Pd 3d peaks
0
at 340.59 and 335.25 eV corresponded to Pd were observed in 1 h
0
(
Fig. 5a), suggesting that Pd might be the real active centre. However,
3+
the binding energy of Fe
shifted to high binding energy during cat-
alysis and recycling process compared with that of fresh catalyst
Fig. 5b), indicating that electron might transfer from Fe to Pd occurred
(
due to the cooperation between Pd and Fe. It was proposed that GO
transferred electron to Fe via ligand, then to Pd via Fe, which made
active Pd more negative which was easy for oxide addition. It also gave
an evident that the catalytic activity could be promoted by not only
single metal, but Pd/Fe system in proper manner. Impressively, B 1 s
and Br 3p were detected at 1 h, 2 h and cycle 4th runs of the reaction
(
Fig. 5c).
Another fascinating question is how Fe interacts with Pd in GO@H-
[
65].
3+
Pd0.10/Fe0.90 to yield higher activity. It can be proposed that Fe can
2+
3.4.2. Electrochemical impedance spectra (EIS) tests
increased the valence of Pd by injecting electrons into Pd . According
to the result of DFT, Pd0 was easily to form the oxidation insertion
intermediate. The bond length of Pd-C, Pd-Br, and C-Br are 2.77, 2.61,
and 2.02 Å in TS, and the oxidative insertion EB is 5.6 kcal/mol (Figure
S20). In addition, there were no results were calculated using Fe and Pd
(II) as active centre. We also obtained the oxidation potential E of
complexes (Figure S21), and the results showed that electrons were
found to be penetrating from Fe to Pd when the R1 as the ligand. As
Furthermore, by means of EIS, the impedance’s variation of the
process of reaction was studied (Figure S19). In high frequency area,
the change of diameter of the EIS showed firstly decreases, and then
increases trend during the reaction process. It was predicted that the
0
decreases in 1 h was due to Pd (II) were reduced to Pd , and the metal
particles could enhance electrical conductivity and facilitate the
transfer of charge. Subsequently, the increases in 2 h indicated that the
82

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Fig. 8. ReactIR plots with time for the resultant of Suzuki reaction (a) 3D map catalyzed by Li
2
PdCl
4
+FeCl
3
·6H
2
O+GO at 70 °C (b) catalyzed by
Li
2
PdCl
4
+FeCl
3
·6H
2
O+GO at 70 °C, (a*) 3D map catalyzed by Li
2
PdCl
4
+FeCl
3
·6H
2
O+GO at 55 °C, (b*) catalyzed by Li
2
4 3 2
PdCl +FeCl ·6H O+GO at 55 °C.
mentioned above, with which electrons might be penetrating into Pd
via Fe. As mentioned above, we thought the active system containing
2 4 3 2
Although Li PdCl /FeCl ·6H O could be evenly dispersed in solution, it
doesn’t catalyze very well at the limited amount. It was also an im-
portant evident that ordered GO@H-Pd0.10/Fe0.90 had higher activity
2
+
0
3+
Pd , Pd and Fe
would be the real catalytic active centre It was
speculated that this might be due to the formation of intermediates
between substrate and metal within or on the surface of the catalyst
during the reaction. Speculated electron transfer in the catalytic process
was shown in Fig. 5c based on the experimental data (Scheme 2).
ReactIR was usually used for investigating on the catalytic process
than that of Li
result was also obtained even at lower temperature as shown in
Fig. 6a*-c*. The rate constants (70 °C, k = 0.0325; 55 °C, k = 0.0278)
and apparent activation energy (Ea Hetero = 9.7 KJ/mol) were obtained
according to the kinetic curves under different reaction conditions
(Fig. 6d and Fig. 6d*).
2 4 3 2
PdCl /FeCl ·6H O under the same condition. The similar
1
2
[
66,67]. While in the prophase of heterogeneous catalysis, there was
adsorption between substrate and catalyst, which was similar to the
induction period described above [68,69]. So the existence of “induc-
tion period” and the sigmoidal shaped curve can be used as a way to
distinguish heterogeneous from homogeneous the catalytic process.
In order to investigate the dynamics of homogeneous and hetero-
geneous catalyst, experiments were designed with different tempera-
ture, with which the activation energy of two catalysts according to the
kinetic curves were calculated (Fig. 7). The catalytic activity of
homogeneous catalysts with the same amount of GO@H-Pd0.10Fe0.90
was very low. Thus, the amount of homogeneous catalysts used was as
40 times as more as that of heterogeneous catalyst. The experimental
data showed that the catalytic rate was higher than that of hetero-
geneous catalysts (Fig. 7b and Fig. 7b*). The reaction rate constants
2 4 3 2
ReactIR catalyzed by GO@H-Pd0.10Fe0.90 and Li PdCl /FeCl ·6H O
showed marked difference catalytic process (Fig. 6). For GO@H-
Pd0.10Fe0.90, the peak intensity presented an increasing trend with in-
creasing time. First, there was an “induction period” with almost no
product, then the peak intensity increased with increasing time (Fig. 6c,
red line). Its phenomenon was the characteristic of heterogeneous
(70 °C, k
1
2
= 0.00615; 55 °C, k = 0.0058) and apparent activation en-
catalytic process. However, Li
2
PdCl
4
/FeCl
3
·6H
2
O (Fig. 6b) showed
ergy (E
a
Homo = 3.7 KJ/mol) were obtained according to the kinetic
completely different phenomena that the intensity of peak did not
change during the recording time. The marked difference changes in-
dicated different catalytic mechanism catalyzed by GO@H-Pd0.10Fe0.90
curves under different reaction conditions. Different catalytic me-
chanism could be confirmed by the dynamic data obtained above.
It was contrary since that the Ea Hetreo was larger than that of Ea Homo
presented. Considering surface catalytic mechanism for GO@H-
Pd0.10Fe0.90, effect of solid particles on the heterogeneous reaction
system must be investigated. In order to eliminate this effect, the same
amount of GO or carbon powder (CP) was added into the homogeneous
catalytic system. The results were as follow: the reaction rate constants
−
1
and Li
Li PdCl
sults of GO@H-Pd0.10Fe0.90 and the presence of sigmoidal kinetics
70], the heterogeneous surface catalytic mechanism could be con-
2
PdCl
4
/FeCl
3
·6H
2
O. The results of the plots at 754 cm
for
2
4
/FeCl
3
·6H
2
O showed different in Fig. 6c. According to the re-
[
firmed, including surface absorption, intermediates forming by reacting
with active centre, diffusion, yielding product, desorption and recovery.
1 2
(70 °C, k = 0.0018; 55 °C, k = 0.00132) and apparent activation
83

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Fig. 9. ReactIR plots with time for the resultant of Suzuki reaction (a) 3D map catalyzed by Li
2
PdCl
4
+FeCl
3
·6H
2
O+CP at 70 °C (b) catalyzed by
Li
2
PdCl
4
+FeCl
3
·6H
2
O+CP at 70 °C, (a*) 3D map catalyzed by Li
2
PdCl
4
+FeCl
3
·6H
2
O+CP at 55 °C, (b*) catalyzed by Li
PdCl +FeCl ·6H O+CP at 55 °C.
2 4 3 2
transferred into products through metal transition and reductive elim-
ination. Finally, the product diffused into the solution.
4. Conclusions
Pd (II)/Fe (III) bimetallic catalytic monolayer supported on GO
(
denoted as GO@H-Pd/Fe) was fabricated and its catalytic properties,
synergetic effect and catalytic mechanism were systematic investigated.
Results showed that composition and orientation of catalyst had effect
on enhancing catalytic activity. Catalytic activity of GO@H-Pd0.10
/
Fe0.90 was 475 times more than that of GO@H-Pd due to the synergetic
effect between Pd and Fe, from which GO transferred electron to Fe (III)
via ligand, then to Pd, which made active Pd more negative. It played a
great role for promoting catalytic activity since it was easy for oxide
addition. GO@H-Pd/Fe exhibited better stability and recyclability at
least 8 times due to proper functional ligand and support. Deactivation
mechanism was confirmed to be the aggregation of active centre and
the loss of catalyst during the recycling. Heterogeneous catalysis was
also proved, in which the catalytic reaction occurred on the surface.
Dynamic studies were deeply investigated by ReactIR. The results
presented different catalytic process for GO@H-Pd0.10Fe0.90 and
homogeneous catalyst. The activation energies were 9.7 KJ/mol and
3.7 KJ/mol for heterogeneous and homogeneous catalyst, respectively.
The inference factor of supports on the results in ReactIR for calculating
activation energy was also investigated, with which that GO@H-
Pd0.10Fe0.90 catalytic activity was higher than that of homogeneous
catalyst could be confirmed.
Scheme 3. Supposed plausible catalytic pathway.
energy (Ea Homo = 19.3 KJ/mol) were obtained according to the kinetic
curves under the addition of GO (Fig. 8). The reaction rate constants
70 °C, k = 0.00218; 55 °C, k = 0.00146) and apparent activation
1 2
(
energy (Ea Homo = 25.0 KJ/mol) were obtained according to the kinetic
curves under the addition of CP (Fig. 9). Experimental results showed
that the solid support had effect on the catalytic activity of catalyst, and
revealed that heterogeneous catalysts have high catalytic activity and
could greatly reduce the activation energy required for the reaction.
From the results above, heterogeneous catalytic process could be
proposed, in which active centre formation, absorption of substrate,
forming intermediates via active centre, target molecular formation and
desorption of product from the surface occurred (Scheme 3). The pro-
cess could be described as that: At the beginning of the reaction, under
the action of a base, the conversion of bivalent palladium to zero valent
palladium through electron transfer between ligand, support and me-
tals. The substrate was first absorbed on the surface, then contact to the
catalytic activity site to form intermediates through oxidative addition.
Subsequently, the intermediate reacted with phenyl boron acid and
Acknowledgements
This work was supported by the CAS [XDA09030203] and the NSFC
[
20973157, 21172200].
84

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
Appendix A. Supplementary data
(2010) 2548–2550 https://pubs.rsc.org/en/content/articlehtml/2010/cc/
b922212j.
[
[
[
23] Z. Li, S. Wu, D. Zheng, J. Liu, H. Liu, H. Lu, Q. Huo, J. Guan, Q. Kan,
Dioxomolybdenum (VI) complex covalently attached to amino-modified graphene
oxide: heterogeneous catalyst for the epoxidation of alkenes, Appl. Organomet.
Chem. 28 (2014) 317–323, https://doi.org/10.1002/aoc.3127.
24] Z.H. Fu, T.S. Li, X.H. He, J. Liu, W.J. Xu, Y.J. Wu, Cyclopalladated ferrocenylimine
functionalized polymer brushes film and its mechanism investigation of hetero-
geneous catalysis, J. Mol. Catal. A Chem. 395 (2014) 293–299, https://doi.org/10.
1016/j.molcata.2014.08.038.
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.03.004.
References
[
1] C.C.Carin. J. Seechurn, M.O. Kitching, T.J. Colacot, V. Snieckus, Palladium-cata-
lyzed cross-coupling: a historical contextual perspective to the 2010 Nobel Prize,
Angew. Chem. Int. Ed. 51 (2012) 5062–5085, https://doi.org/10.1002/anie.
25] Q. Zhao, C. Bai, W. Zhang, Y. Li, G. Zhang, F. Zhang, X. Fan, Catalytic epoxidation
of olefins with graphene oxide supported copper (Salen) complex, Ind. Eng. Chem.
Res. 53 (2014) 4232–4238, https://doi.org/10.1021/ie500017z.
2
01107017.
[
[
[
[
2] H. Li, C.C.Carin J. Seechurn, T.J. Colacot, H. Li, Development of preformed Pd
[26] L. Wang, P. Huang, J. Yang, T. Li, L. Mao, M. Liu, Y. Wu, Fabrication and catalytic
properties of ordered cyclopalladated diimine monolayer: investigation on catalytic
mechanism, RSC Adv. 8 (2018) 31860–31867 https://pubs.rsc.org/en/content/
articlehtml/2018/ra/c8ra06365f.
catalysts for cross-coupling reactions, beyond the 2010 Nobel Prize, ACS Catal. 2
(2012) 1147–1164, https://doi.org/10.1021/cs300082f.
3] D.S. Su, J. Zhang, B. Frank, A. Thomas, X. Wang, J. Paraknowitsch, R. Schlögl,
[
27] (a) R. Ferrando, J. Jellinek, R.L. Johnston, Nanoalloys: from theory to applications
of alloy clusters and nanoparticles, Chem. Rev. 108 (2008) 845–910 https://pubs.
acs.org/doi/abs/10.1021/cr040090g;
Metal-free heterogeneous catalysis for sustainable chemistry, ChemSusChem 3
(2010) 169–180, https://doi.org/10.1002/cssc.200900180.
4] W. Tang, J. Li, X. Jin, J. Sun, J. Huang, R. Li, Magnetically recyclable Fe@Pd/C as a
highly active catalyst for Suzuki coupling reaction in aqueous solution, Catal.
Commun. 43 (2014) 75–78, https://doi.org/10.1016/j.catcom.2013.09.001.
5] Z. Yinghuai, S.C. Peng, A. Emi, S. Zhenshun, Monalisa, R.A. Kemp, Supported ultra
small palladium on magnetic nanoparticles used as catalysts for suzuki cross-cou-
pling and heck reactions, Adv. Syn. Catal. 349 (2007) 1917–1922, https://doi.org/
For selected reviews on bimetallic nanoparticle catalysts see:.
(b) P.P. Huang, Z.Q. Xue, T.S. Li, Z.Y. Liu, D.H. Wei, M.H. Liu, Y.J. Wu,
Investigation on Electron distribution and synergetic to enhance catalytic activity in
bimetallic Ni(II)/Pd(II) molecular monolayer, ChemCatChem 10 (2018) 1–14,
https://doi.org/10.1002/cctc.201801350
1
0.1002/adsc.200700021.
[28] K. Sasaki, H. Naohara, Y. Cai, Y.M. Choi, P. Liu, M.B. Vukmirovic, J.X. Wang,
R.R. Adzic, Core-protected platinum monolayer shell high-stability electrocatalysts
for fuel-cell cathodes, Angew. Chem. Int. Ed. 49 (2010) 8602–8607, https://doi.
org/10.1002/anie.201004287.
[
6] D. Saha, S. Gayen, S. Koner, Cu (II)/Cu (II)-Mg (II) containing pyridine-2, 5-di-
carboxylate frameworks: synthesis, structural diversity, inter-conversion and het-
erogeneous catalytic epoxidation, Polyhedron 146 (2018) 93–98, https://doi.org/
[
29] H. Kobayashi, M. Yamauchi, H. Kitagawa, Y. Kubota, K. Kato, M. Takata, Atomic-
level Pd-Pt alloying and largely enhanced hydrogen-storage capacity in bimetallic
nanoparticles reconstructed from core/shell structure by a process of hydrogen
absorption/desorption, J. Am. Chem. Soc. 132 (2010) 5576–5577, https://doi.org/
10.1021/ja1013163.
1
0.1016/j.poly.2018.02.023.
[
7] X. Gu, S. Bi, L.N. Guo, Y.Q. Zhao, T.S. Li, M.H. Liu, P.L. Chen, Y.J. Wu, Facile
fabrication of ordered component-tunable heterobimetallic self-assembly nanosheet
for catalyzing “Click” reaction, ACS Omega 2 (2017) 5415–5433, https://doi.org/
1
0.1021/acsomega.7b00364.
[
30] P. Phukan, P.R. Boruah, P.S. Gehlot, A. Kumar, A. Bordoloi, D. Sarma, A. Quick,
Efficient and simple protocol for synthesis of bimetallic nickel‐palladium nano-
particles: effective catalyst for biaryl synthesis, ChemistrySelect 2 (2017)
[
8] Y. Li, P. Zhou, Z. Dai, Z. Hu, P. Sun, J. Bao, A facile synthesis of PdCo bimetallic
hollow nanospheres and their application to Sonogashira reaction in aqueous
media, New J. Chem. 30 (2006) 832–837 https://pubs.rsc.org/2006/nj/b604581m.
9] A. Shaabani, M. Mahyari, A. Shaabani, M. Mahyari, PdCo bimetallic nanoparticles
supported on PPI-grafted graphene as an efficient catalyst for Sonogashira reac-
tions, J. Mater. Chem. A Mater. Energy Sustain. 1 (2013) 9303–9311 https://pubs.
rsc.org/en/content/articlehtml/2013/ta/c3ta11706e.
10] Y.S. Feng, X.Y. Lin, J. Hao, H.J. Xu, Pd-Co bimetallic nanoparticles supported on
graphene as a highly active catalyst for Suzuki-Miyaura and Sonogashira cross-
coupling reactions, Tetrahedron 70 (2014) 5249–5253, https://doi.org/10.1016/j.
tet.2014.05.083.
1
1795–11800, https://doi.org/10.1002/slct.201702347.
[
[31] P. Phukan, P.R. Boruah, P.S. Gehlot, A. Kumar, D. Sarma, A simple, quick and novel
protocol for biaryl synthesis using LiCl-promoted in situ-generated Pd nano-
particles, Appl. Organomet. Chem. 32 (2018) e4009, https://doi.org/10.1002/aoc.
4009.
[
[32] P.R. Boruah, P.S. Gehlot, A. Kumar, D. Sarma, Palladium immobilized on the sur-
4
face of MMT K 10 with the aid of [BMIM][BF ]: an efficient catalyst for Suzuki-
Miyaura cross-coupling reactions, Mol. Catal. 461 (2018) 54–59, https://doi.org/
10.1016/j.mcat.2018.10.004.
[
11] F.S. Han, Transition-metal-catalyzed Suzuki-Miyaura cross-coupling reactions: a
[
33] K.S. Novoselov, A.K. Geim, S.V. Morozov, D.A. Jiang, Y. Zhang, S.V. Dubonos,
A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306 (2004)
666–669 http://science.sciencemag.org/content/306/5696/666.
remarkable advance from palladium to nickel catalysts, Chem. Soc. Rev. 42 (2013)
5
270–5298 https://pubs.rsc.org/en/content/articlehtml/2013/cs/c3cs35521g.
[
12] O. Gutierrez, J.C. Tellis, D.N. Primer, G.A. Molander, Nickel-catalyzed cross-cou-
pling of photoredox-generated radicals: uncovering a general manifold for stereo-
convergence in nickel-catalyzed cross-couplings, J. Am. Chem. Soc. 137 (2015)
[
34] S. Stankovich, D.A. Dikin, G.H.B. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach,
R.D. Piner, S.T. Nguyen, R.S. Ruoff, Graphene-based composite materials, Nature
4
42 (2006) 282–286 https://www.nature.com/articles/nature04969.
4
896–4899, https://doi.org/10.1021/ja513079r.
[
[
[
[
13] M.R. Netherton, G.C. Fu, Nickel-catalyzed cross-couplings of unactivated alkyl ha-
[35] (a) C.H. Lu, H.H. Yang, C.L. Zhu, X. Chen, G.N. Chen, A graphene platform for
sensing biomolecules, Angew. Chem. Int. Ed 121 (2009) 4879–4881, https://doi.
org/10.1002/ange.200901479;
lides and pseudohalides with organometallic compounds, Adv. Syn. Catal. 346
(2004) 1525–1532, https://doi.org/10.1002/adsc.200404223.
14] G.D. Allred, L.S. Liebeskind, Copper-mediated cross-coupling of organostannanes
(b) M.B. Avinash, K.S. Subrahmanyam, Y. Sundarayya, T. Govindaraju, Covalent
modification and exfoliation of graphene oxide using ferrocene, Nanoscale, (2010),
pp. 1762–1766 https://pubs.rsc.org/en/content/articlehtml/2010/nr/c0nr00024h;
with organic iodides at or below room temperature, J. Am. Chem. Soc. 118 (1996)
2
748–2749, https://doi.org/10.1021/ja9541239.
(c) W. Gao, The Chemistry of Graphene Oxide[M]//Graphene Oxide, Springer,
15] T. Hatakeyama, T. Hashimoto, K.K. Kathriarachchi, T. Zenmyo, H. Seike,
M. Nakamura, Iron-catalyzed alkyl-Alkyl suzuki-miyaura coupling, Angew. Chem.
Int. Ed. 51 (2012) 8834–8837, https://doi.org/10.1002/anie.201202797.
16] B. Mu, T.S. Li, C.H. Li, P.P. Liu, W. Shang, Y.J. Wu, Langmuir-Blodgett films of
cyclopalladated ferrocenylimine: preparation, characterization, and application in
Suzuki coupling reaction, Tetrahedron 65 (2009) 2599–2604, https://doi.org/10.
Cham, 2015, pp. 61–95 https://link.springer.com/chapter/10.1007/978-3-319-
15500-5-3.
[
x y
36] N.A. Barakat, M. Motlak, Co Ni -decorated graphene as novel, stable and super
effective non-precious electro-catalyst for methanol oxidation, Appl. Catal. B
Environ. 154 (2014) 221–231, https://doi.org/10.1016/j.apcatb.2014.02.019.
[37] S.W. Liu, J.G. Yu, M. Jaroniec, Tunable photocatalytic selectivity of hollow TiO
2
microspheres composed of anatase polyhedra with exposed {001} facets, J. Am.
Chem. Soc. 132 (2010) 11914–11916, https://doi.org/10.1021/ja105283s.
[38] S.W. Liu, J.G. Yu, W.G. Wang, Effects of annealing on the microstructures and
1
016/j.tet.2008.12.075.
[
17] K. Satoh, H. Aoshima, M. Kamigaito, Iron (III) chloride/R-Cl/tributylphosphine for
metal-catalyzed living radical polymerization: a unique system with a higher oxi-
dation state iron complex, J. Polym. Sci.: Polym. Chem. Ed. 46 (2008) 6358–6363,
https://doi.org/10.1002/pola.22941.
18] T. Hatakeyama, T. Hashimoto, Y. Kondo, Y. Fujiwara, H. Seike, H. Takaya,
M. Nakamura, Iron-catalyzed Suzuki-miyaura coupling of alkyl halides, J. Am.
Chem. Soc. 132 (2010) 10674–10676, https://doi.org/10.1021/ja103973a.
19] K.K. Zou, H. Liu, T.S. Li, P.L. Chen, M.H. Liu, Y.J. Wu, An electrochemically poly-
merized and assembled cyclopalladated bi-thiophene imine for catalyzing coupling
reactions: a modern strategy to enhance catalytic activity, RSC Adv. 5 (2015)
2
photoactivity of fluorinated N-doped TiO , Phys. Chem. Chem. Phys. 12 (2010)
12308–12315 https://pubs.rsc.org/en/content/articlehtml/2010/cp/c0cp00036a.
[
[
39] Q.J. Xiang, J.G. Yu, B. Cheng, H.C. Ong, Microwave-hydrothermal preparation and
visible-light photoactivity of plasmonic photocatalyst Ag-TiO
hollow spheres, Chem. Asian J. 5 (2010) 1466–1474, https://doi.org/10.1002/asia.
00900695.
[40] H. Liu, T.S. Li, X.X. Xue, W.J. Xu, Y.J. Wu, The mechanism of a self-assembled Pd
ferrocenylimine)-Si compound-catalysed Suzuki coupling reaction, Catal. Sci.
2
nanocomposite
[
2
(
1
6654–16663 https://pubs.rsc.org/en/content/articlehtml/2015/ra/c4ra14974b.
[
20] M. Pagliaro, V. Pandarus, R. Ciriminna, F. B´eland, P. Demma Car`a, Heterogeneous
Technol. 6 (2016) 1667–1676 https://pubs.rsc.org/en/content/articlehtml/2016/
cy/c5cy01341k.
versus homogeneous palladium catalysts for cross-coupling reactions,
ChemCatChem 4 (2012) 432–445, https://doi.org/10.1002/cctc.201100422.
21] B. Mu, T.S. Li, J.Y. Li, Y.J. Wu, The highly efficient Suzuki-Miyaura cross-coupling
reaction using cyclopalladated N-alkylferrocenylimine as a catalyst in aqueous
medium at room temperature under ambient atmosphere, J. Organomet. Chem. 693
[41] Y. Xin, J.G. Liu, X. Jie, W. Liu, F. Liu, Y. Yin, Z. Zou, Preparation and electro-
chemical characterization of nitrogen doped graphene by microwave as supporting
materials for fuel cell catalysts, Electrochim. Acta 60 (2012) 354–358, https://doi.
org/10.1016/j.electacta.2011.11.062.
[
[
42] Z.H. Fu, J. Liu, X.H. He, T.S. Li, J. Liu, Y.J. Wu, The recyclable cyclopalladated
ferrocenylimine self-assembly catalytic film and investigation of its role in the
mechanism of heterogeneous catalysis, RSC Adv. 4 (2014) 26413–26420 https://
pubs.rsc.org/en/content/articlehtml/2014/ra/c4ra02540g.
(2008) 1243–1251, https://doi.org/10.1016/j.jorganchem.2008.01.012.
[
22] J.A. Elemans, S.J. Wezenberg, M.J. Coenen, E.C. Escudero-Adan, J. Benet-Buchholz,
D. den Boer, S. De Feyter, Axial ligand control over monolayer and bilayer for-
mation of metal-salophens at the liquid-solid interface, Chem. Commun. (Camb.) 46
85

P. Huang, et al.
Molecular Catalysis 469 (2019) 75–86
[
[
[
43] Y. Shao, G. Yin, Y. Gao, P. Shi, Durability study of Pt/C and Pt/CNTs catalysts under
simulated PEM fuel cell conditions, J. Electrochem. Soc. 153 (2006) 1093–1097
http://jes.ecsdl.org/content/153/6/A1093.short.
jz9004174.
[57] A.K. Ladavos, A.P. Katsoulidis, A. Iosifidis, K.S. Triantafyllidis, T.J. Pinnavaia,
P.J. Pomonis, The BET equation, the inflection points of N adsorption isotherms
2
44] N. Zhao, T.S. Li, Z. Zhai, J.J. Qiu, W.J. Xu, H. Liu, Y.J. Wu, Cyclopalladated ar-
and the estimation of specific surface area of porous solids, Microporous
Mesoporous Mater. 151 (2012) 126–133, https://doi.org/10.1016/j.micromeso.
2011.11.005.
ylimine self-assembly films for suzuki reaction, ChemCatChem 5 (2013)
1
481–1489, https://doi.org/10.1002/cctc.201200730.
45] H. Hao, M. Barrett, Y. Hu, W. Su, S. Ferguson, B. Wood, B. Glennon, The use of in
situ tools to monitor the enantiotropic transformation of p-aminobenzoic acid
polymorphs, Org. Process Res. Dev. 16 (2011) 35–41, https://doi.org/10.1021/
op200141z.
46] N.M. Do, M.A. Olivier, J.J. Salisbury, C.B. Wager, Application of quantitative 19F
and 1H NMR for reaction monitoring and in situ yield determinations for an early
stage pharmaceutical candidate, Anal. Chem. 83 (2011) 8766–8771, https://doi.
org/10.1021/ac202287y.
47] H.P. Mungse, S. Verma, N. Kumar, B. Sain, O.P. Khatri, Grafting of oxo-vanadium
Schiff base on graphene nanosheets and its catalytic activity for the oxidation of
alcohols, J. Mater. Chem. 22 (2012) 5427–5433 https://pubs.rsc.org/en/content/
articlehtml/2012/jm/c2jm15644j.
48] Z.Q. Xue, P.P. Huang, T.S. Li, P.X. Qin, D. Xiao, M.H. Liu, P.L. Chen, Y.J. Wu, A
novel “tunnel-like” cyclopalladated arylimine catalyst immobilized on graphene
oxide nano-sheet, Nanoscale 9 (2017) 781–791 https://pubs.rsc.org/en/content/
articlehtml/2017/nr/c6nr07521e.
[58] M.S. Mel’gunov, A.B. Ayupov, Direct method for evaluation of BET adsorbed
monolayer capacity, Microporous Mesoporous Mater. 243 (2017) 147–153, https://
doi.org/10.1016/j.micromeso.2017.02.019.
[59] M.F. De Lange, T.J. Vlugt, J. Gascon, F. Kapteijn, Adsorptive characterization of
porous solids: error analysis guides the way, Microporous Mesoporous Mater. 200
(2014) 199–215, https://doi.org/10.1016/j.micromeso.2014.08.048.
[60] S.L. Wegener, T.J. Marks, P.C. Stair, Design strategies for the molecular level
synthesis of supported catalysts, Acc. Chem. Res. 45 (2011) 206–214, https://doi.
org/10.1021/ar2001342.
[61] J. Nakazawa, B.J. Smith, T.D.P. Stack, Discrete complexes immobilized onto click-
SBA-15 silica: controllable loadings and the impact of surface coverage on catalysis,
J. Am. Chem. Soc. 134 (2012) 2750–2759, https://doi.org/10.1021/ja210400u.
[62] X. Fan, G. Zhang, F. Zhang, Multiple roles of graphene in heterogeneous catalysis,
Chem. Soc. Rev. 44 (2015) 3023–3035 https://pubs.rsc.org/en/content/
articlehtml/2015/cs/c5cs00094g.
[63] S. Paul, M.M. Islam, S.M. Islam, Suzuki-Miyaura reaction by heterogeneously sup-
ported Pd in water: recent studies, RSC Adv. 5 (2015) 42193–42221 https://pubs.
rsc.org/en/content/articlehtml/2015/ra/c4ra17308b.
[
[
[
[
49] Y.J. Li, W. Gao, L.J. Ci, C.M. Wang, P.M. Ajayan, Catalytic performance of Pt na-
noparticles on reduced graphene oxide for methanol electro-oxidation, Carbon 48
(
2010) 1124–1130, https://doi.org/10.1016/j.carbon.2009.11.034.
[64] J.A. Widegren, R.G. Finke, A review of the problem of distinguishing true homo-
geneous catalysis from soluble or other metal-particle heterogeneous catalysis
under reducing conditions, J. Mol. Catal. A Chem. 198 (02) (2003) 317–341,
https://doi.org/10.1016/S1381-1169 00728-8.
[
50] H.K. Jeong, Y.P. Lee, R.J.W.E. Lahaye, M.H. Park, K.H. An, I.J. Kim, C.W. Yang,
C.Y. Park, R.S. Ruoff, Y.H. Lee, Evidence of graphitic AB stacking order of graphite
oxides, J. Am. Chem. Soc. 130 (2008) 1362–1366, https://doi.org/10.1021/
ja076473o.
[65] A.D.J. Calow, A.S. Batsanov, E. Fernandez, C. Sole , A. Whiting, Novel transfor-
́
[
51] M.M. Bhadbhade, D. Srinivas, Effects on molecular association, chelate conforma-
mation of α, β-unsaturated aldehydes and ketones into γ-amino alcohols or 1, 3-
oxazines via a 4 or 5 step, one-pot sequence, Chem. Commun. (Camb.) 48 (2012)
11401–11403 https://pubs.rsc.org/en/content/articlehtml/2012/cc/c2cc36129a.
[66] D.A. Foley, C.W. Doecke, J.Y. Buser, J.M. Merritt, L. Murphy, M. Kissane,
S.G. Collins, A.R. Maguire, A. Kaerner, ReactNMR and ReactIR as reaction mon-
itoring and mechanistic elucidation tools: the NCS mediated cascade reaction of α-
thioamides to α-thio-β-chloroacrylamides, J. Org. Chem. 76 (2011) 9630–9640,
https://doi.org/10.1021/jo201212p.
tion, and reactivity toward substitution in copper Cu (5-X-salen) complexes, salen2-
=
N, N’-ethylenebis (salicylidenaminato), X=H, CH
structures, and EPR investigations. [Erratum to document cited in CA119 (26):
85036b], Inorg. Chem. 32 (1993) 6122–6130, https://doi.org/10.1021/
3
O, and Cl: synthesis, x-ray
2
ic00078a037.
[
52] T.N. Lambert, C.A. Chavez, B. Hernandez-Sanchez, P. Lu, N.S. Bell, A. Ambrosini,
T. Friedman, T.J. Boyle, D.R. Wheelerand, D.L. Huber, Synthesis and character-
ization of titania-graphene nanocomposites, J. Phys. Chem. C 113 (2009)
[67] K.S. Weddle, J.D. Aiken, R.G. Finke, Rh (0) nanoclusters in benzene hydrogenation
1
9812–19823, https://doi.org/10.1021/jp905456f.
catalysis: kinetic and mechanistic evidence that a putative [(C
8
H
17) 3NCH
3
]
[
53] T. Wu, X. Cai, S. Tan, H. Li, J. Liu, W. Yang, Adsorption characteristics of acrylo-
nitrile, p-toluenesulfonic acid, 1-naphthalenesulfonic acid and methyl blue on
graphene in aqueous solutions, Chem. Eng. J. 173 (2011) 144–149, https://doi.org/
+[RhCl ]-Ion-Pair catalyst is actually a distribution of Cl-and [(C
stabilized Rh (0) nanoclusters, J. Am. Chem. Soc. 120 (1998) 5653–5666, https://
doi.org/10.1021/ja973045h.
4
8
H
17) 3NCH ]+
3
1
0.1016/j.cej.2011.07.050.
[68] J.A. Widegren, M.A. Bennett, R.G. Finke, Is it homogeneous or heterogeneous
[54] G. Srinivas, Y. Zhu, R. Piner, N. Skipper, M. Ellerby, R. Ruoff, Synthesis of graphene-
catalysis? Identification of bulk ruthenium metal as the true catalyst in benzene
like nanosheets and their hydrogen adsorption capacity, Carbon 48 (2010)
hydrogenations starting with the monometallic precursor, Ru (II)(η6-C
6 6 2
Me )(OAc) ,
6
30–635, https://doi.org/10.1016/j.carbon.2009.10.003.
plus kinetic characterization of the heterogeneous nucleation, then autocatalytic
[
55] M. Fang, K. Wang, H. Lu, Y. Yang, S. Nutt, Covalent polymer functionalization of
surface-growth mechanism of metal film formation, J. Am. Chem. Soc. 125 (2003)
10301–10310, https://doi.org/10.1021/ja021436c.
graphene nanosheets and mechanical properties of composites, J. Mater. Chem. 19
(
2009) 7098–7105 https://pubs.rsc.org/en/content/articlehtml/2009/jm/
[69] S.K. Movahed, R. Esmatpoursalmani, A. Bazgir, N-Heterocyclic carbene palladium
complex supported on ionic liquid-modified graphene oxide as an efficient and
recyclable catalyst for Suzuki reaction, RSC Adv. 4 (2014) 14586–14591 https://
pubs.rsc.org/en/content/articlehtml/2014/ra/c3ra46056h.
b908220d.
[
56] C.N.R. Rao, A.K. Sood, R. Voggu, K.S. Subrahmanyam, Some novel attributes of
graphene, J. Phys. Chem. Lett. 1 (2010) 572–580, https://doi.org/10.1021/
86