Bi-functional catalyst of porous N-doped carbon with bimetallic FeCu for solvent-free resultant imines and hydrogenation of nitroarenes

Article abstract of DOI:10.1016/j.mcat.2018.12.029

The efficient and stable catalyst applied to the transformation of amines into the corresponding imines and hydrogenation of nitroarenes under mild reaction conditions is reported. The catalytic performance of porous N-doped carbon with FeCu (FeCu@NPC) catalyst are tested by aromatic alcohol-based N-alkylated of amines with solvent-free and hydrogenation of nitroarenes via N₂H₄·H₂O. The results proved that the yield of these two reactions are all over 99.9% under optimum condition. Moreover, the synergistic effect of the catalyst for N-alkylated reaction was investigated through the kinetic study. The catalyst can be easily separated from reaction system by an external magnetism, and can be recycled and reutilized for at least 4 runs with conversions are all over 75%. The study of the catalyst indicated that it was suitable for the reactions in industry. Hence, the catalysis process by the inexpensive metals-based catalyst is green and sustainable.

Full text of DOI:10.1016/j.mcat.2018.12.029

MolecularCatalysis465(2019)43–53
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Bi-functional catalyst of porous N-doped carbon with bimetallic FeCu for
solvent-free resultant imines and hydrogenation of nitroarenes
Kaizhi Wanga,b, Wenbing Gaoa,b, Pengbo Jianga,b, Kai Lana,b, Ming Yanga,b, Xiaokang Huanga,b
,
⁎
Lei Maa,b, Fang Niua,b, Rong Lia,b,
a State Key Laboratory of Applied Organic Chemistry (SKLAOC), PR China
b College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
N-alkylated
Hydrogenation of nitroarenes
Inexpensive metals
The efficient and stable catalyst applied to the transformation of amines into the corresponding imines and
hydrogenation of nitroarenes under mild reaction conditions is reported. The catalytic performance of porous N-
doped carbon with FeCu (FeCu@NPC) catalyst are tested by aromatic alcohol-based N-alkylated of amines with
solvent-free and hydrogenation of nitroarenes via N2H4·H2O. The results proved that the yield of these two
reactions are all over 99.9% under optimum condition. Moreover, the synergistic effect of the catalyst for N-
alkylated reaction was investigated through the kinetic study. The catalyst can be easily separated from reaction
system by an external magnetism, and can be recycled and reutilized for at least 4 runs with conversions are all
over 75%. The study of the catalyst indicated that it was suitable for the reactions in industry. Hence, the
catalysis process by the inexpensive metals-based catalyst is green and sustainable.
1. Introduction
catalysts in homogeneous catalyst, such as Co-based, it is hard to in-
vestigate such a homogeneous phase complex catalyst in reaction
With the rapid development of petrochemical industry, the reaction
of alcohol-based N-alkylated of amines is one of the most promising
methods for organic amine synthesis [1]. Amines are important che-
mical products including a variety of functional organic compounds
suchlike herbicides, polymers, dyes, and pharmaceuticals, bioactive
molecules [1,2]. Typically, the N-alkyl amines is synthesized from
aromatic amine and alkyl reagent (ether, halogenated hydrocarbon,
sulfuric acid ester, etc.) [2]. However, the requiring reducing agents
would yield a certain amount of halogen waste [1]. Thusly, more effi-
cient and friendly environmental protocols are required for N-alkyla-
tion of amines. Since alcohol acts as both an alkylating reagent and a
hydrogen source, which can provide high atom efficiency, environ-
mental amity, and easy operation at normal pressures, the alcohol-
based N-alkylated of amines reaction is regarded as the most effective
methods for the synthesis of organic amines. In previous studies, it can
be concluded that the heterogeneous N-alkylated of amines reaction are
usually catalyzed by metals and their ligands, such as Ru [3,4], Ir [5,6],
Pd [1], Au [7], Cu [8,9], Mn [10,11], or Ni [12]. Besides, amines are
more reactive than alcohols, which leads to the frequent occurrence of
undesired side reactions with decreasing the yield of N-alkylated re-
action. Though much effort has been devoted to developing efficient
system [13]. To overcome this challenge, a drastic variation in the
chemical properties of active metals is needed. Recently, Furukawa,
Shinya and his co-worker catalyst has reported the PdZn/Al2O3, while
the noble metal Pd can not be industrialized extensively owning to its
high cost and scarce storage and there has been few reports on the
coupling of fatty amines [1]. Hence, a lower-cost, more universal and
greener industrial catalyst should be explored.
Furthermore, since aromatic amine is an important intermediate of
organic synthesis, it can also be transformed by hydrogenation of ni-
troarenes. Nitroarenes reduction methods of the preparation of aro-
matic amine mainly include the CO selective reduction method [14],
metal reduction method [15–19], alcali of sulphide reduction method
[20], catalytic hydrogenation reduction [18,21], hydrazine reduction
method [22], electrochemical reduction method [23], etc. The two
latter methods are popular among researchers because of its friendly
environment. Universally, for the hydrogenation of nitro groups, the
most used precious metals are platinum, palladium and gold, no matter
it was supported or not [17,21,24,25]. Thereby, a wider possible choice
is considered, that is using base-metals (including copper, iron and
cobalt) for hydrogenation reaction.
As is reported, N-doped carbon materials are considered as potential
⁎ Corrorponding author at: State Key Laboratory of Applied Organic Chemistry (SKLAOC), PR China.
E-mail address: liyirong@lzu.edu.cn (R. Li).
https://doi.org/10.1016/j.mcat.2018.12.029
Received 2 November 2018; Received in revised form 19 December 2018; Accepted 30 December 2018
2468-8231/©2018ElsevierB.V.Allrightsreserved.

K. Wang et al.
MolecularCatalysis465(2019)43–53
Scheme 1. The schematic caption of the synthesis of catalyst.
Fig. 1. (a) The SEM of FeCu@NPC-850, (b) the TEM of FeCu@NPC-850, (c) the HRTEM of Fe, (d) the HRTEM of Cu, (e) the HAADF-STEM of FeCu@NPC-850, (f–i)
the mapping of FeCu@NPC-850.
Fig. 2. (a) XRD pattern of FeCu@NPC-850 and (b) Raman spectra of NPC and FeCu@NPC-850.
support materials for heterogeneous catalysis [26–28]. And metal de-
posited on N-doped carbon materials can be easily obtained by pyr-
olyzing the mixture of inorganic metal salts and most common N-con-
taining organic compounds at high temperatures [25,29]. In the study
presented here, the prepared porous N-doped carbon with bimetallic
FeCu (FeCu@NPC) was synthesized successfully. The results show that
the catalyst has a good catalytic effect in alcohol-based N-alkylation of
various amines and hydrogenation of kinds of nitroarenes. The active
Fe-N, Cu-N sites, and Fe, Cu nanoparticles on porous N-doped carbon
(NPC) of the catalyst are formed upon its designated temperature [29].
The catalytic performance of these active sites can be compared with
those precious metal catalysts. After testing the catalyst, the results
44

K. Wang et al.
MolecularCatalysis465(2019)43–53
Fig. 3. The XPS pattern of FeCu@NPC-850 (a) C 1 s, (b) N 1 s, (c) Fe 2p and (d) Cu 2p.
Table 1
Texture parameters and the element contents of the prepared catalyst.
1
Samples
Surface area (m2 g−1
)
Average pore size (nm)
Pore volume (cm3 g−
)
N
Fe
Cu
(wt. %)
(wt. %)
(wt. %)
FeCu@NPC-850
NPC
58.5
327.79
135.68
5.12
6.35
3.11
0.079
0.19
0.11
2.58
6.79
6.70
13.31
–
–
32.22
–
–
NPC*
Fig. 4. (a) Nitrogen adsorption/desorption isotherms of FeCu@NPC-850, NPC and NPC*, and (b) the corresponding pore-width distribution curves.
show that the yields of two reactions are all over 99.9%, and it can be
easily separated from reaction system by an external magnetism, and
also can be reutilized at least 4 runs with reaction activity lightly de-
creased. Meanwhile, the observed catalytic performances were ratio-
nalized on the basis of kinetic and computational studies. Therefore, a
green and highly efficient catalytic system for solvent-free resultant
imines and hydrogenation nitroarenes reaction is studied.
2. Experimental
2.1. Reagents and chemicals
All reagents and chemicals were of analytical grade and used as
received without any further purification. Detailed description of the
reagents and chemicals are showed in supporting information.
2.2. Synthesis of the catalyst
Methods of synthesizing the NPC are exhibited in supporting
45

K. Wang et al.
MolecularCatalysis465(2019)43–53
Fig. 5. (a) FT-IR spectrogram of catalysts, (b) magnetization curves of FeCu@NPC-850 (Inset is the magnetic separate process of catalyst).
information. For the synthesis of the FeCu@NPC-850 catalyst, 200 mg
NPC, 150 mg FeCl3, 300 mg C10H14CuO4 and 50 mL petroleum ether
were thoroughly stirred in a 100 mL round-bottomed flask at 30 °C until
the petroleum ether completely evaporated. Then, the mixture pre-
cursor particles passed through a heating zone at 450 °C for 60 min and
carbonized at 850 °C for 180 min under an N2 atmosphere at a heating
rate of 2 °C min–1. Eventually, the FeCu@NPC-850 was obtained. The
schematic caption of the synthesis of catalyst was shown in Scheme 1.
Meanwhile, the comparison catalysts were also prepared, they were
called FeCu@C-850, Fe@C-850, Cu@C-850 and FeCu@MWCNTs-850.
And the detail synthesis methods of the FeCu@C, FeCu@MWCNTs,
FeCo@NPC-850, Fe@NPC-850, Cu@NPC-850, CoCu@NPC-850 and
Co@NPC-850 catalysts are displayed in supporting information.
Table 2
The catalytic activities of the different catalysts.a,b
.
Entry
Catalyst
Conversion of 2 [%]
Selectivity
of 3[%]
Yield
of 3 [%]
1d
FeCu@NPC-850
CoCu@NPC-850
FeCo@NPC-850
Co@NPC-850
Cu@NPC-850
Fe@NPC-850
NPC
99.9
90
70
60
40
30
29
–
> 99.9
92
98
94
96
90
99.9
–
–
99.9
94
99.9
55
69
56
38
27
29
–
Trace
68
57
–
82
90
95
26
34
2c,d
3c,d
4c,d
5c,d
6c,d
7
2.3. Catalytic conversion of benzylamine to N-Alkylation
8
9
Graphite Powder
MWCNTs
–
10c
11c
12
13
14
15
16
17
CuFe2O4
CuCo3O5
69
61
–
82
90
95
26
34
The reaction was tested in a 25 mL, a three-necked reactor with a
spherical condenser tube, oil bath, and thermocouple at atmospheric
pressure. Typically, 20 mg of the catalyst, 5 mmol benzylalcohol and
4 mmol benzylamine were mixed with magnetic stirring at 120 °C. The
reaction time is 3 h and air was continuously brought in bottle by the
air pump (15 mL min−1). The sample was analyzed by GC–MS (Agilent
6,890 N/5,937 N). Moreover, the reaction catalyst can be recycled and
collected by the external magnetic force, and then it was washed with
deionized water and absolute ethanol several times, and followed by a
heat treatment in a vacuum oven at 60 °C before the next utilization.
The catalytic activity was calculated as follows: conversion % = 100×
[(C1-C2)/C1], and Yield % = 100× [C3]/[C1], based on the initial [C1]
and the final [C2] concentrations of organic substrate and the reaction
[C3] concentrations of imines.
Non-catalyst
FeCu@NPC-600
FeCu@NPC-700
FeCu@NPC-800
FeCu@C-850
FeCu@MWCNTs-
850
–
99.9
99.9
99.9
99.9
99.9
19
20
Fe@C-850
Cu@C-850
15
18
99.9
97
15
17
a
The reaction was carried out using 20 mg of the catalyst, benzyl alcohol
(5 mmol) and benzylamine (4 mmol), solvent-free and air with 15 mL/min at
120 °C for 3 h.
b
Determined by GC–MS measurement.
Entries 2–7, 10 and 11, the XRD spectrogram in Fig. S.2, with SEM of en-
c
tries 7 and TEM of entries 10 and 11 in Fig. S.4.
3. Result and discussion
d
The FeCu@NPC catalyst is calcined at 600, 700 and 800 °C, respectively.
And the ratio of Fe to Cu in the catalyst is displayed in Table S.1.
3.1. Characterizations catalyst
To characterize the morphology and microstructures of FeCu@NPC-
Fig. 6. Reaction conditions: catalyst (20 mg), solvent-free and air with 15 mL/min and (a) benzylalcohol (5 mmol) and benzylamine (4 mmol), 2.5 h, (b) benzy-
lalcohol (5 mmol) and benzylamine (4 mmol), 120 °C, and (c) reaction at 120 °C for 3 h. Conversion and selectivity were determined by GC–MS.
46

K. Wang et al.
MolecularCatalysis465(2019)43–53
Table 3
N-alkylated reaction of aromatic alcohol and phenylamine.a,b
Entry
Conversion of 2 [%]
Selectivity
of 3[%]
Reaction
(h)
1
2
3
4
5
6
87
89
97
91
92
86
99.9
99.9
99.9
99.9
99.9
99.9
3.5
3.5
3.5
3.5
4
3
7
8
87
93
77
96
4
4
a
The reaction was carried out using the catalyst (20 mg), alcohol (3 mmol), phenylamine (1 mmol), solvent-free and air with 15 mL/min at 120 °C.
Determined by GC–MS measurement.
b
850, the SEM and TEM were carried out. The SEM image of FeCu@NPC-
the ID/IG values of the NPC and FeCu@NPC-850 are 0.98 and 1.04 in
Fig. 2(b).
850 in Fig. 1(a) that indicates the catalyst consists of interrelated na-
nospheres with not much damage to the morphology after roasted,
which was also confirmed by the TEM image in Fig. 1(b). The HRTEM
(Fig. 1(c)) images of the catalyst show that the lattice spacing values
were 0.206 and 0.172 nm corresponding to the (110) and (200) plane of
Fe. The corresponding fast Fourier transform (FFT) image (shown in the
inset of Fig. 1(c)) also demonstrates it. And the included angle around
108.1° of (110) and (200) facets was very close to the theoretical value
of ˜109° [30]. In Fig. 1(d) the two intervals of 0.201 and 0.175 nm
corresponding to the (111) and (200) facets of Cu, which in agreement
with FFT image shown in the inset of Fig. 1(d) [31,32]. Thus, the ob-
served angle between (111) and (200) facets is 53.3°, being in good
agreement with the theoretical value of 54.7° [33]. Meanwhile, the
mapping results of the Fig. 1(e) zone are revealed in Fig. 1(f), (g), (h)
and (i), in which Fig. 1(f)–(i) show that the elements of C and N were
mostly overlapped and the element of the Fe and Cu cluster together
[34,35]. In particular, the relatively black part of Fig. 1(h) may be
caused by uneven distribution of iron. Furthermore, the EDX of the
catalyst was shown in Fig. S1.
Fig. 2 (a) presents the XRD spectrogram of the synthesized metal
catalyst. The peaks of black line at 2-Theta value of 43.55°, 50.40° and
74.00° corresponded to the (111), (200), and (220) planes, respectively,
which was indicated to Cu (JCPDS file no. 4-836). And the 2-Theta
values of 44.66°, 65.04° and 82.36°corresponded to the (110), (200),
and (211) planes was accorded with Fe (JCPDS file no. 65-4899) in
Fig. 2(a). The peaks at 50.40° and 44.66° in XRD pattern, which are also
ensured by the measured lattice fringe. And in Fig. S2, the diffraction
peaks at 24.50° and 43.52° of pure NPC become weaker when the base
metals mingling. The Raman spectrum was showed in Fig. 2(b), there
were two strong peaks at 1367 and 1606 cm−1, and the intensities of
the D- and the G-bands reveal that a significant number of structural
defects exist in carbon framework due to N doping [36]. Furthermore,
XPS was performed to investigate the chemical elements binding
states of Cu, Fe, C and N on the outer surface of FeCu@NPC-850. The
high-resolution spectrum of C 1 s, N 1 s and Fe 2p can be clearly seen
from Fig. 3(a–c). In Fig. 3(a), the C 1 s spectrum can be devided into
two peaks C-C (284.59 eV) and C–N (285.05 eV) [37–39]. In Fig. 3(b),
the N 1 s spectrum can be designated into four peaks, which are pyr-
idiniC–N (398.41 eV), pyrrolic or pyridoniC–N (399.80 eV), graphitic N
(400.95 eV) and oxidized-N (401.83 eV). The former peak might also
include a contribution from metal-bound nitrogen (N-M) because of the
small difference between binding energies of pyridinic N and N-M
[39,40]. Graphitic N may cause non-uniform distribution of electrons in
the π-system, enhancing electron transport throughout the carbon
plane. In Fig. 3(c), the high-resolution spectrum of Fe 2p can be dis-
assembled into three main peaks with the binding energy of 712.40,
724.0 and 710.56 eV, while the binding energy of 710.56 and 724.0 eV
can be assigned to Fe 2p3/2 and Fe 2p1/2, respectively [41–45]. The
high-resolution spectrum of Cu 2p In Fig. 3(d) is spilt into Cu 2p1/2
(952.2 eV) and Cu 2p3/2 (932.59 eV) [43]. Compared with the high-
resolution XPS spectrum of FeCu@C-850 in Fig. S3 ((a)-(b))), it is very
bright that the Fe 2p3/2 peak position of FeCu@C-850 is 1.2 eV lower
than that of FeCu@NPC-850 (710.56 eV). Similarly, the Cu 2p3/2 peak
position of FeCu@C-850 is 0.8 eV lower than that of FeCu@NPC-850
(932.59 eV). Therefore, the XPS spectra of the Cu 2p and Fe 2p are
shifted towards higher binding energy values, indicating that Cu and Fe
both act as electron donors to NPC. And it can also be said these shift
also can be explained by the different charge densities of the Fe atoms
in Fe-N and the Cu atoms in Cu-N. To sum up, the Fe element mainly
exists as coordinate with N atoms (Fe-N) in the surface of NPC, and the
binding energy of 712.40 eV contribution from Fe-Ox. And the Cu ele-
ment mainly exists as coordinate with N atoms (Cu-N) in the supporting
material NPC, and the peak at 933.6 and 953.8 eV contribution from
47

K. Wang et al.
MolecularCatalysis465(2019)43–53
Table 4
N-alkylated reaction of benzylalcohol and amines.a,b
Entry
Conversion of 2 [%]
Selectivity
of 3[%]
Reaction
(h)
1
2
99.9
90
99.9
4
99.9
5
3
4
99.9
76
99.9
99.9
4
4
5
6
88
84
99.9
99.9
4
4
7
8
70
64
99.9
99.9
4
4
9
90
85
50
3
6
10
99.9
11
12
99.9
83
99.9
99.9
3
3.5
13
14
96
90
99.9
78
6
4.5
15
a
32
99.9
5
The reaction was carried out using the catalyst (20 mg), benzylalcohol (5 mmol), amine (1 mmol), solvent-free and air with 15 mL/min at 120 °C.
b
Determined by GC–MS measurement.
Cu-Ox [46,47]. The wide-range XPS spectrum exhibits in Fig. S3 (c), and
indicating that the catalyst mainly contains mesoporous structures,
which can provide higher surface area to increase the accessibilities of
the active sites, as well as partial microporous structures [48–50]. The
texture parameters related the catalyst are listed in Table 1, exhibiting
that FeCu@NPC-850, NPC and the prepared NPC without NaCl was
called NPC* possess the high surface area, average pore size and pore
volume. In Table 1, surface area of NPC is larger than those of FeCu@
the elemental contents of the catalyst can be known from the XPS
spectrum, of which the contents of C, N, Fe and Cu are 96.06 atm. %,
2.05 atm. %, 0.93 atm. % and 0.96 atm. %.
Nitrogen adsorption–desorption isotherms of the FeCu@NPC-850
catalyst were also measured. The catalyst exhibited type IV isotherms
with a medium-pressure and the high-pressure region hysteresis loops,
48

K. Wang et al.
MolecularCatalysis465(2019)43–53
Table 5
Hydrogenation of nitroarenes to amines at optimal conditions.a,b
Entry
1
Conversion [%]
99.9
Selectivity
[%]
Reaction
(min)
99.9
15
2
3
99.9
99.9
99.9
99.9
15
15
4
5
99.9
99.9
99.9
99.9
25
15
6
7
94
89
15
40
99.9
99.9
8
9
99.9
99.9
55
60
15
15
10
99.9
78
15
a
The reaction was carried out using the catalyst (20 mg), nitroarenes (3 mmol)and N2H4·H2O (1.5 mL) at 90 °C.
Determined by GC–MS measurement.
b
Fig. 7. (a) the N-alkylated reaction order of benzylalcohol, (b) order of benzylamine and (c) the N-alkylated reaction of activation energy.
NPC-850 and NPC*, it could be that the Fe and Cu inside the NPC oc-
cupy a certain space, and a large surface area was given by NaCl.
Furthermore, the elemental contents of the catalyst are also listed in
Table 1 according to the element analysis and ICP-OES test results. In
Fig. 4, the pore-width distributions of the prepared samples were not be
changed obviously, demonstrating that the structure of the N-doped
carbon materials did not be distinctly damaged by the introduction of
bimetal [49].
FT-IR spectrogram of NPC, Cu@NPC-850 and FeCu@NPC-850 are
measured to farther elucidate the structures of catalyst. As is described
in Fig. 5(a), 800-400 cm−1 characteristic for the vibration of CN het-
erocycles of triazine ring, and the peaks at 1200–800 cm−1 are attrib-
uted to CeC, CeN, CeO [51,52]. The characteristic bands of
1600–1200 cm−1 are assigned to aromatic carbon and nitrogen
heterocycles [53,54]. Especially for peaks at 1629 and 1598 cm−1 are
matched with C]N stretching [44,55]. Compared black line with red
line and blue line, IR spectroscopic results obviously indicate the co-
existence of NPC and Cu or FeCu because of the disappeared peaks. The
magnetic property is of great importance to evaluate the recoverability
of a heterogeneous catalyst. Fig. 5(b) exhibits the magnetization curves
of FeCu@NPC-850 catalyst at room temperature. The VSM curves show
that the catalyst has magnetization value of approximately 25 emu g-1.
This magnetic property is essential for catalyst to be recycled from the
reaction mixture solution.
3.2. Catalyst performance
In order to expound the application and catalytic activity, Table 2
49

K. Wang et al.
MolecularCatalysis465(2019)43–53
molar ratio of benzylalcohol and benzylamine, is represented as A and
B, respectively. It is obviously seen that the optimized molar ratio is SA
:
SB = 5 : 4 in the N-alkylated reaction. The optimum reaction conditions
of the hydrogenation of nitroarenes reaction were confirmed to be that
the temperature is 90 °C and the dosage of hydrazine is 15 mmol, and
more detailed explanations of screening the reaction conditions are
shown in Fig. S.5.
To study the generalities of the catalyst, other types of aromatic
alcohol, amines and nitroarenes were chosen for N-alkylated reaction
and nitroarenes reduction under the optimal reaction condition, re-
spectively. Different type substrates are converted to relevant products
with well conversion and selectivity in Tables 3–5. It can be clearly seen
from Table 3, the yield of N- alkylation reaction by various aromatic
alcohols and aniline was more than 85% under the optimum reaction
conditions, whether the substituent of alcohols is an electron-absorbing
group or an electron-supplying group. As for Table 4, entries 1–10 and
13–15, imines are produced via benzylalcohol together with different
derivatives of arylamines. Besides entries 7, 8 and 15, the yields of these
reactions are all over 75%. Especially for entries 11 and 12, the re-
actants of amines are fatty amines, these yields are at least 85%.
Meanwhile, in Table 5, it is concluded that the high yield for hydro-
genation of nitroarenes reaction is obtained. Compared entry 7 with
other entries, the electron induction effect reduces the rate of reaction.
However, for entries 8–10, the decrease of selectivity is due to the
demineralization. Herein, the perfectly catalytic performance and. the
incomparably bi-functional property of the catalyst are demonstrated.
Fig. 8. The recycles ability of the catalyst. (Reaction conditions: the catalyst
(20 mg), benzylalcohol (5 mmol) and benzylamine (4 mmol), solvent-free and
air with 15 mL/min at 120 °C for 3 h, conversion and selectivity were de-
termined by GC–MS.).
presents the different metallic catalysts. Obviously, FeCu@NPC-850
catalyst is different with other metal-based catalysts and metal oxide-
based catalysts in the N-alkylated reaction with solvent-free condition
as to the conversion and yield, the yield could reach 99.9%. From
Table 2, comparing with Entry 1–3 with Entry 4–6, it is clearly seen that
bimetallic catalysts are better than single metallic catalysts, there is no
doubt in conversion and selectivity. The results of entries 1–3 indicate
that metallic copper doped in NPC can effectively improve the con-
version rate, and magnetic metal in NPC can be highly selective. And
entries 7 and 8 explained that NeC bonds work in N-alkylated reaction
compared with graphite powder. The CuFe2O4 and CuCo3O5 catalysts
(entries 10 and 11) were obtained via the calcination of FeCu@NPC-
850 and CoCu@NPC-850 catalyst at 400 °C for 60 min in muffle fur-
nace. Obviously, compared entries 1 with 16, 17, 18, 19 and 20, metal-
N activity sites played an important role in the N-alkylated reaction.
Therefore, it is strong evidence prove the main active sites is Fe-N and
Cu-N, which synergistically promote the reaction processing. Mean-
while, it was also found that the optimum catalyst FeCu@NPC-850 can
be used in hydrogenation of nitroarenes. The N-alkylated reaction and
nitroarenes reduction were performed over FeCu@NPC-850 to screen
the optimum reaction conditions [56]. Primarily, benzylalcohol and
benzylamine were regarded as the N-alkylated reaction model sub-
strate, and nitroarenes served as the hydrogenation reaction model
substrate. The optimum reaction time, temperature, and the molar ratio
of these two reaction were tested. As is seen in Fig. 6(a), with the
temperature increasing from 90 to 130 °C, the conversion of reaction
firstly increased remarkably and then decreased sharply. So the opti-
mized temperature was determined to be 120 °C. To investigate the
effect of reaction time, the products existed in the reaction system from
0.5 to 3.5 h were analyzed. The results are presented in Fig. 6(b), the
conversion of the reactants was improved with increasing the reaction
time. Hence, the optimum reaction time was determined as 3 h. The
3.3. Kinetic study
In order to investigate the order of the reaction, one of the reactants
in the reaction system was needed to be far excessive. That is to say the
molar ratio of benzylamine and benzylalcohol are 10:0.1, 10:0.15,
10:0.2, 10:0.25 and 10:0.3 at 100 °C for 15 min with air (15 mL/min).
And the molar ratio of benzylalcohol and benzylamine is 3:0.2, 3:0.25,
3:0.3, 3:0.35 and 3:0.4 at the same reaction condition. The overall ki-
netics equation of the reaction can be defined as:
K
[alcohol] + [amine] + [O2] → [N − alkylated imines]+H2O
(1)
The formulation of the reaction rate is given by Eq. (2). Where the
[SA] and [SB] represents the benzylalcohol and benzylamine, K re-
presents the rate constant, and the a and b are the series of the [SA] and
[SB]. And it is assumed that the excessive reactant was neglected. The
formulation of the reaction rate is given by Eqs. (3) and (4), where the
k1 and k2 also represent the rate constants.
r = KCSa CSb
(2)
A
B
r = k1CSa
(3)
(4)
A
r = k2CSb
B
Then, the value of the reaction velocity and the value of equilibrium
Table 6
Comparative chart of catalytic activity of FeCu@NPC with other reported catalysts.
Entry
Catalyst
Amine dosage
(mmol)
Time (h)
Temp.
(oC)
Ea
Yield of
N-alkylated (%)
Reference
(kJ/mol)
1
2
3
4
5
6
7
8
FeCu@NPC-850
PdZn@Al2O3
CeO2
Cp*Ir(NHC)Cl2
Ni(OTf)2
CoCl2·6H2O/PPh3
Au-TiO2
[Cp*IrCl2]2
/K2CO3
4
1
0.05
1
–
1
–
1
3
120
110
30
110
120
140
25
55.52
56
–
–
–
–
–
–
99.9
99
99
93
99
72
90
88
This work
[1]
[48,63]
[6]
[12]
[64]
0.6
24
16
24
24
4
[7]
[5]
17
110
9
Ru3(CO)12
1
24
110
–
90
[4]
50

K. Wang et al.
MolecularCatalysis465(2019)43–53
better accelerating the reaction. Then, it is found the coupling reaction
of benzaldehyde and benzylamine can easily occur without the catalyst.
Accordingly, the oxidation of benzylalcohol is the rate controlling step.
Meanwhile, in order to explore what the role of oxygen in the reaction
process, nitrogen protection after vacuuming for reaction system is
designed. The result of this reaction is that yield of imines is only 20%.
So we can conclude that oxygen as oxidants are necessary to promote
the occurrence of the reaction.
For further investigating the mechanism of the N-alkylated reaction
and further studying the impact of the catalyst in the reaction, the
adsorption of reactants in the reaction system at optimum reaction
condition are detected by FT-IR in Fig. S.6 [58]. As is well known, the
adsorption of reactants in the reaction system is a prerequisite for
catalytic reaction. In Fig. S6, it can be definitely understood there are
new peaks of the adsorption of benzylamine and benzaldehyde in the
reaction system compared with black line and red line. Hence, a con-
clusion can be obtained that the adsorption of benzylamine and ben-
zaldehyde on the surface of the catalyst enables the reaction pro-
ceeding. And the IR spectrograms of catalyst before and after reaction
are the same from the Fig. S6. Therefore, combined with the previously
reported mechanism and the study of experimental data, the reaction
mechanism could be reasonably proposed in Scheme 2 [13,59–62].
Firstly, the OeH of alcohol was conducted dehydrogenation oxidation
to obtain the carbonyl compound intermediates in the presence of
benzylamine, which can provide an alkaline environment. After cata-
lytic oxidation, benzaldehyde was adsorbed at Fe-N-C or Cu-N-C active
sites of the catalyst. Secondly, amine was simultaneously adsorbed at
the active sites. Then, under the control of the active site, the inter-
mediate and amine contact to obtain the imine, namely the reaction
creates a new N bond.
Scheme 2. Proposed mechanism of the reaction.
concentration in the mixture are linearly fitted and the values of a and b
(in Fig. 7(a), (b)) are 0.16, 3.40, respectively. Hence, the N-alkylated
reaction order is 3.56. Through changing the reaction temperature at
the optimum substrates molar ratio (that is SA: SB = 5: 4), such as 80,
90, 100, 110 and 120 °C for 15 min and calculating the rate of reaction,
the value of Ea can be obtained to be 55.52 kJ/mol from linear fitting
(A = 3.952 × 1010 in Fig. 7(c)), and the formulation of the rate is given
by Eq. (5–7).
r = KCS0.16CS3.40
(5)
A
B
E
a
K = Ae−
RT
(6)
4. Conclusion
Ea
RT
lnK = lnA −
(7)
In this study, a versatile catalyst for alkylation of amines with al-
cohols and hydrogenation of nitroarenes was investigated. FeCu@NPC-
850 was observed as a highly efficient heterogeneous catalyst with
superiorly catalytic performance, a wide substrate scope for various
alcohols and amines with excellent conversion and selectivity with
solvent-free. Notably, the well catalytic characteristic of N-doped
carbon with base metals can be compared with those noble metal cat-
alysts and the work reported here would provide an effective strategy
for sustainable green chemistry.
Simultaneously, in order to verify the total order and apparent ac-
tivation energy of the reaction, the molar ratio of SA and SB are cal-
culated to be 1:1 at 100 and 110 °C for different reaction time with the
Eqs. (8–9). It can be obviously calculated the total order is n = 3.48,
and Ea is 58.46 kJ/mol.
r = KCSn
(8)
/S
B
A
k1
k2
Ea
R
1
T
2
1
T
1
ln
=
(
−
)
(9)
Acknowledgements
3.4. Catalyst recycling
The authors thank for the financial support from the Nation Nature
Science Foundation of China (No: 21773098).
Moreover, the heterogeneous catalyst can be easily collected by an
extra magnetism and washed with alcohol for several times to further
evaluate the reusability of the FeCu@NPC-850 catalyst. The circulating
runs were investigated and reused of the catalyst under the same re-
action conditions for it want be used in industry [56,57]. The results of
the reaction were shown in Fig. 8, which could found that after four
times recycle, the conversions are all over 75% and the selectivities are
slightly decreased after four recycles, which illustrates the excellent
recyclability of the catalyst.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2018.12.029.
References
[1] S. Furukawa, R. Suzuki, T. Komatsu, Selective activation of alcohols in the presence
of reactive amines over intermetallic PdZn: efficient catalysis for alcohol-based N-
alkylation of various amines, ACS Catal. 6 (2016) 5946–5953.
[2] V.V. Patil, E.M. Gayakwad, G.S. Shankarling, M-CPBA mediated metal free, rapid
oxidation of aliphatic amines to oximes, J. Org. Chem. 81 (2016) 781–786.
[3] S. Imm, S. Bähn, L. Neubert, H. Neumann, M. Beller, An efficient and general
synthesis of primary amines by ruthenium-catalyzed amination of secondary alco-
hols with ammonia, Angew. Chem. Int. Ed. 49 (2010) 8126–8129.
[4] A. Tillack, D. Hollmann, D. Michalik, M. Beller, A novel ruthenium-catalyzed
amination of primary and secondary alcohols, Tetrahedron Lett. 47 (2006)
8881–8885.
[5] K.I. Fujita, Z. Li, N. Ozeki, R. Yamaguchi, N-alkylation of amines with alcohols
catalyzed by a Cp*Ir complex, Tetrahedron Lett. 34 (2003) 2687–2690.
[6] A. Fernandes, B. Royo, Water-soluble iridium N-heterocyclic carbene complexes for
3.5. Mechanism consideration
On the basis of previous research in Table 6 and verified experiment
of this work, much benzyl cyanide was formed in the presence of single
benzylamine and a small amount of benzaldehyde was produced in the
presence of single benzylalcohol under the same optimum reaction
conditions. Combining with kinetic study, when a small amount of
benzylamine exists, most of benzylalcohol can be turned into benzal-
dehyde. Distinctly, benzylamine provides the alkaline environment for
51

K. Wang et al.
MolecularCatalysis465(2019)43–53
the alkylation of amines with alcohols, ChemCatChem 9 (2017) 3912–3917.
Catal. 452 (2018) 117–122.
[7] D. Stíbal, J. Sá, J.A.V. Bokhoven, One-pot photo-reductive N-alkylation of aniline
and nitroarene derivatives with primary alcohols over Au–TiO2, Catal. Sci. Technol.
3 (2012) 94–98.
[35] M. Marimuthu, P. Marimuthu, A.K.S.K.S. Palanivelu, V. Rajagopalan, Tuning the
basicity of Cu-based mixed oxide catalysts towards the efficient conversion of gly-
cerol to glycerol carbonate, Mol. Catal. 460 (2018) 53–62.
[8] R. Sakamoto, S. Sakurai, K. Maruoka, Alkylsilyl peroxides as alkylating agents in the
copper-catalyzed selective mono-N-alkylation of primary amides and arylamines,
Chem. Eur. J. 23 (2017) 9030–9033.
[36] Z.S. Wu, W. Ren, L. Xu, F. Li, H.M. Cheng, Doped graphene sheets as anode ma-
terials with superhigh rate and large capacity for lithium ion batteries, ACS Nano 5
(2011) 5463.
[9] G. Anbarasu, M. Malathy, P. Karthikeyan, R. Rajavel, Silica functionalized Cu(II)
acetylacetonate Schiff base complex: an efficient catalyst for the oxidative con-
densation reaction of benzyl alcohol with amines, J. Solid State Chem. 253 (2017)
305–312.
[10] A. Mukherjee, A. Nerush, G. Leitus, L.J.W. Shimon, Y. Ben David, N.A. Espinosa
Jalapa, D. Milstein, Manganese-catalyzed environmentally benign dehydrogenative
coupling of alcohols and amines to form aldimines and H2: a catalytic and me-
chanistic study, J. Am. Chem. Soc. 138 (2016) Journal of the American Chemical
Society4298-4301.
[11] B. Chen, J. Li, W. Dai, L. Wang, S. Gao, Direct imine formation by oxidative cou-
pling of alcohols and amines using supported manganese oxides under an air at-
mosphere, Green. Chem. 16 (2014) 3328–3334.
[12] P. Yang, C. Zhang, Y. Ma, C. Zhang, A. Li, B. Tang, J.S. Zhou, Nickel-catalyzed N-
alkylation of acylhydrazines and arylamines using alcohols and enantioselective
examples, Angew. Chem. 56 (2017) 14702–14706.
[13] Z. Liu, Z. Yang, X. Yu, H. Zhang, B. Yu, Y. Zhao, Z. Liu, Efficient cobalt-catalyzed
methylation of amines using methanol, Adv. Synth. Catal. 359 (2017) 4278–4283.
[14] A.M. Tafesh, J. Weiguny, A review of the selective catalytic reduction of aromatic
nitro compounds into aromatic amines, isocyanates, carbamates, and ureas using
CO, Chem. Rev. 96 (1996) 2035.
[15] R. Mantha, K.E. Taylor, N. Biswas, J.K. Bewtra, A continuous system for fe° re-
duction of nitrobenzene in synthetic wastewater, Environ. Sci. Technol. 35 (2001)
3231–3236.
[37] P. Jiang, X. Li, W. Gao, X. Wang, Y. Tang, K. Lan, B. Wang, R. Li, Highly selective
hydrogenation of α, β-unsaturated carbonyl compounds over supported Co nano-
particles, Catal. Commun. 111 (2018) 6–9.
[38] S. Frindy, A. Primo, H. Ennajih, A. El Kacem, R. Qaiss, M. Bouhfid, E.M. Lahcini,
H. Essassi, A. Garcia, Kadib El, Chitosan-graphene oxide films and CO2-dried porous
aerogel microspheres: interfacial interplay and stability, Carbohydr. Polym. 167
(2017) 297–305.
[39] F. Sun, H. Wu, X. Liu, F. Liu, H. Zhou, J. Gao, Y. Lu, Nitrogen-rich carbon spheres
made by a continuous spraying process for high-performance supercapacitors, Nano
Res. 9 (2016) 3209–3221.
[40] Z. Liu, F. Sun, L. Gu, G. Chen, T. Shang, J. Liu, Z. Le, X. Li, H.B. Wu, Y. Lu, Post iron
decoration of mesoporous nitrogen-doped carbon spheres for efficient electro-
chemical oxygen reduction, Adv. Energy Mater. 7 (2017) 1701154.
[41] J.-Y. Su, G.-P. Jin, T. Chen, X.-D. Liu, C.-N. Chen, J.-J. Tian, The characterization
and application of prussian blue at graphene coated carbon fibers in a separated
adsorption and electrically switched ion exchange desorption processes of cesium,
Electrochim. Acta 230 (2017) 399–406.
[42] T. Liu, X. Niu, L. Shi, X. Zhu, H. Zhao, M. Lana, Electrocatalytic analysis of su-
peroxide anion radical using nitrogen-doped graphene supported Prussian Blue as a
biomimetic superoxide dismutase, Electrochim. Acta 176 (2015) 1280–1287.
[43] W. Gao, S. Li, H. Huo, F. Li, Y. Yang, X. Li, X. Wang, Y. Tang, R. Li, Investigation of
the crystal structure of Cu-Fe bimetal oxide and their catalytic activity for the
Baeyer–Villiger oxidation reaction, Mol. Catal. 439 (2017) 108–117.
[44] S. Ren, C. Chen, Y. Zhou, Q. Dong, H. Ding, The α-Fe2O3/g-C3N4 composite as an
efficient heterogeneous catalyst with combined Fenton and photocatalytic effects,
Res. Chem. Intermediat. 43 (2016) 3307–3323.
[45] X. Lei, Z. Ye, N. Zhao, F. Lei, H. Yang, Magnetic γ′‐Fe4N/Fe3C, χ‐Fe5C2, and θ‐Fe3C
by a simple route for application as electrochemical catalysts, Chem. Eur. J 23
(2017) 17592–17597.
[46] P. Ling, Q. Zhang, T. Cao, F. Gao, Versatile three‐dimensional porous Cu@Cu2O
aerogel networks as electrocatalysts and mimicking peroxidases, Angew. Chem. Int.
Ed. 57 (2018) 6819–6824.
[47] J. Xie, J.D. Kammert, N. Kaylor, J.W. Zheng, E. Choi, H.N. Pham, X. Sang,
E. Stavitski, K. Attenkofer, R.R. Unocic, A.K. Datye, R.J. Davis, Atomically dispersed
Co and Cu on N-doped carbon for reactions involving C-H activation, ACS Catal. 8
(2018) 3875–3884.
[48] J. Zhang, J. Yang, J. Wang, H. Ding, Q. Liu, U. Schubert, Y. Rui, J. Xu, Surface
oxygen vacancies dominated CeO2 as efficient catalyst for imine synthesis: influ-
ences of different cerium precursors, Mol. Catal. 443 (2017) 131–138.
[49] X. Cui, Y. Long, X. Zhou, G. Yu, J. Yang, M. Yuan, J. Ma, Z. Dong, Pd-doped Ni
nanoparticle-modified N-doped carbon nanocatalyst with high Pd atom utilization
for the transfer hydrogenation of nitroarenes, Green. Chem. 20 (2018) 1121–1130.
[50] J. Liang, X. Zhang, L. Jing, H. Yang, N-doped ordered mesoporous carbon as a
multifunctional support of ultrafine Pt nanoparticles for hydrogenation of nitroar-
enes, Chin. J. Catal. 38 (2017) 1252–1260.
[51] I.S. Pieta, A. Rathi, P. Pieta, R. Nowakowski, M. Hołdynski, M. Pisarek,
A. Kaminska, M.B. Gawande, R. Zboril, Electrocatalytic methanol oxidation over
Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride,
Appl. Catal. B Environ. 244 (2019) 272–283.
[52] M.J. Lima, A.M.T. Silva, C.G. Silva, J.L. Faria, Graphitic carbon nitride modified by
thermal, chemical and mechanical processes as metal-free photocatalyst for the
selective synthesis of benzaldehyde from benzyl alcohol, J. Catal. 353 (2017)
44–53.
[16] P. Sarmah, D.K. Dutta, Manganese mediated aqueous reduction of aromatic nitro
compounds to amines, J. Chem. Res. (2003) 236–237.
[17] C.K.P. Neeli, P. Puthiaraj, Y.-R. Lee, Y.-M. Chung, S.-H. Baeck, W.-S. Ahn, Transfer
hydrogenation of nitrobenzene to aniline in water using Pd nanoparticles im-
mobilized on amine-functionalized UiO-66, Catal. Today 303 (2018) 227–234.
[18] M. Takasaki, Y. Motoyama, K. Higashi, S.H. Yoon, A. Isao Mochida, H. Nagashima,
Chemoselective hydrogenation of nitroarenes with carbon nanofiber-supported
platinum and palladium nanoparticles, Org. Lett. 10 (2008) 1601–1604.
[19] Y. Motoyama, M. Taguchi, N. Desmira, S.H. Yoon, I. Mochida, H. Nagashima,
Chemoselective hydrogenation of functionalized nitroarenes and imines by using
carbon nanofiber-supported iridium nanoparticles, Chem. Asian J. 9 (2014) 71.
[20] R.A. Scheuerman, D. Tumelty, The reduction of aromatic nitro groups on solid
supports using sodium hydrosulfite (Na2S2O4), Tetrahedron Lett. 41 (2000)
6531–6535.
[21] C.S. Couto, L.M. Madeira, C.P. Nunes, P. Araújo, Commercial catalysts screening for
liquid phase nitrobenzene hydrogenation, Appl. Catal. A Gen. 522 (2016) 152–164.
[22] J.W. Larsen, M. Freund, K.Y. Kim, M. Sidovar, J.L. Stuart, Mechanism of the carbon
catalyzed reduction of nitrobenzene by hydrazine, Carbon 38 (2000) 655–661.
[23] G. Seshadri, J.A. Kelber, A study of the electrochemical reduction of nitrobenzene at
molybdenum electrodes, J. Electrochem. Soc. 146 (1999) 3762–3764.
[24] B. Dong, Y. Li, X. Ning, H. Wang, H. Yu, F. Peng, Trace iron impurities deactivate
palladium supported on nitrogen-doped carbon nanotubes for nitrobenzene hy-
drogenation, Appl. Catal. A Gen. 545 (2017) 54–63.
[25] X. Gu, Z.H. Lu, H.L. Jiang, T. Akita, Q. Xu, Synergistic catalysis of metal-organic
framework-immobilized Au-Pd nanoparticles in dehydrogenation of formic acid for
chemical hydrogen storage, J. Am. Chem. Soc. 133 (2011) 11822–11825.
[26] Z. Wei, J. Wang, S. Mao, D. Su, H. Jin, Y. Wang, F. Xu, H. Li, Y. Wang, In situ
generated co°-Co3O4/N-doped carbon nanotubes hybrids as efficient and chemo-
selective catalysts for hydrogenation of nitroarenes, ACS Catal. 5 (2015)
4783–4789.
[27] L.G. Bulusheva, A.V. Okotrub, Y.V. Fedoseeva, A.G. Kurenya, I.P. Asanov,
O.Y. Vilkov, A.A. Koos, N. Grobert, Controlling pyridinic, pyrrolic, graphitic, and
molecular nitrogen in multi-wall carbon nanotubes using precursors with different
N/C ratios in aerosol assisted chemical vapor deposition, Phys. Chem. Chem. Phys.
17 (2015) 23741–23747.
[28] S. Cao, J. Jiang, B. Zhu, J. Yu, Shape-dependent photocatalytic hydrogen evolution
activity over a Pt nanoparticle coupled g-C3N4 photocatalyst, Phys. Chem. Chem.
Phys. 18 (2016) 19457–19463.
[29] Y. Tang, H. Chai, W. Chen, X. Cui, Y. Ma, M. Zhao, X. Dai, Theoretical study on
geometric, electronic and catalytic performances of Fe dopant pairs in graphene,
Phys. Chem. Chem. Phys. 19 (2017) 26369–26380.
[30] Y.-X. Chen, S.-P. Chen, Z.-Y. Zhou, N. Tian, Y.-X. Jiang, S.-G. Sun, Y. Ding,
Z.L. Wang, Tuning the shape and catalytic activity of Fe nanocrystals from rhombic
dodecahedra and tetragonal bipyramids to cubes by electrochemistry, J. Am. Chem.
Soc. 131 (2009) 10860–10862.
[31] W. Wang, Y. Wang, G.C. Wang, Ethanol synthesis from syngas over Cu(Pd)-doped
Fe(100): a systematic theoretical investigation, Phys. Chem. Chem. Phys. 20 (2018)
2492–2507.
[32] J.J. Beltran, C.A. Barrero, A. Punnoose, Understanding the role of iron in the
magnetism of Fe doped ZnO nanoparticles, Phys. Chem. Chem. Phys. 17 (2015)
15284–15296.
[33] Y.-n. Wang, X. Duan, J. Zheng, H. Lin, Y. Yuan, H. Ariga, S. Takakusagi, K. Asakura,
Remarkable enhancement of Cu catalyst activity in hydrogenation of dimethyl
oxalate to ethylene glycol using gold, Catal. Sci. Technol. 2 (2012) 1637–1639.
[34] Z. Tang, G.-H. Han, E. Jung, M.-g. Seo, K.-Y. Lee, W.-S. Kim, T. Yu, Synthesis of Cu-
Pd nanoplates and their catalytic performance for H2O2 generation reaction, Mol.
[53] Y. Zheng, L. Lin, X. Ye, F. Guo, X. Wang, Helical graphitic carbon nitrides with
photocatalytic and optical activities, Angew. Chem. Int. Ed. 53 (2014)
11926–11930.
[54] T.S. Miller, A.B. Jorge, T.M. Suter, A. Sella, F. Cora, P.F. McMillan, Carbon nitrides:
synthesis and characterization of a new class of functional materials, Phys. Chem.
Chem. Phys. 19 (2017) 15613–15638.
[55] L. Xu, J. Xia, H. Xu, S. Yin, K. Wang, L. Huang, L. Wang, H. Li, Reactable ionic liquid
assisted solvothermal synthesis of graphite-like C3N4 hybridized α-Fe2O3 hollow
microspheres with enhanced supercapacitive performance, J. Power Sources 245
(2014) 866–874.
[56] H. Huo, L. Wu, J. Ma, H. Yang, L. Zhang, Y. Yang, S. Li, R. Li, Fabrication of Fe3O4-l-
dopa-CuII/SnIV@Micro-mesoporous-SiO2 catalyst applied to Baeyer-Villiger oxi-
dation reaction, ChemCatChem 8 (2016) 779–786.
[57] W. Gao, F. Li, H. Huo, Y. Yang, X. Wang, Y. Tang, P. Jiang, S. Li, R. Li, Investigation
of hollow bimetal oxide nanomaterial and their catalytic activity for selective oxi-
dation of alcohol, Mol. Catal. 448 (2018) 63–70.
[58] S. Zhao, C. Zhao, X. Li, F. Li, L. Jiao, W. Gao, R. Li, Pd nanoparticles supported on
amino-functionalized magnetic mesoporous silica nanotubes: a highly selective
catalyst for the catalytic hydrodechlorination reaction, RSC Adv. 6 (2016)
76582–76589.
[59] G. Zhang, S.K. Hanson, Cobalt-catalyzed acceptorless alcohol dehydrogenation:
synthesis of imines from alcohols and amines, Org. Lett. 15 (2013) 650–653.
[60] P. Liu, C. Li, E.J.M. Hensen, Efficient tandem synthesis of methyl esters and imines
by using versatile hydrotalcite-supported gold nanoparticles, Chem. A Eur. J. 18
(2012) 12122–12129.
[61] L. Jiang, L. Jin, H. Tian, X. Yuan, X. Yu, Q. Xu, Direct and mild palladium-catalyzed
52

K. Wang et al.
MolecularCatalysis465(2019)43–53
[63] H. Zhang, C. Wu, W. Wang, J. Bu, F. Zhou, B. Zhang, Q. Zhang, Effect of Ceria on
redox-catalytic property in mild condition: a solvent-free route for imine synthesis
at low temperature, Appl. Catal. B-Environ. 227 (2018) 209–217.
aerobic oxidative synthesis of imines from alcohols and amines under ambient
conditions, Chem. Commun. 47 (2011) 10833–10835.
[62] Y. Xiang, Q. Meng, X. Li, J. Wang, In situ hydrogen from aqueous-methanol for
nitroarene reduction and imine formation over an Au–Pd/Al2O3 catalyst, Chem.
Commun. 46 (2010) 5918–5920.
[64] E. Balaraman, S. Midya, A. Mondal, A. Begum, A simple cobalt(II) chloride cata-
lyzed N-alkylation of amines with alcohols, Synthesis 49 (2017) 3957–3961.
53