Cooperative transformation of nitroarenes and biomass-based alcohols catalyzed by CuNiAlOx

Article abstract of DOI:10.1039/c4ra16081a

A simple CuNiAlO_x catalyst was prepared for the cooperative transformation of nitrobenzene derivatives and biomass-based alcohols. Under the optimized reaction conditions, a range of nitrobenzene derivatives can be smoothly converted into the corresponding amines and glycerol was directly transformed into 1,3-dihydroxypropan-2-one.

Full text of DOI:10.1039/c4ra16081a

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Cooperative transformation of nitroarenes and
biomass-based alcohols catalyzed by CuNiAlOx†
Cite this: RSC Adv., 2015, 5, 7970
a
a
a
a
Xingchao Dai,ab Xinjiang Cui, Hangkong Yuan, Youquan Deng and Feng Shi
*
Received 10th December 2014
Accepted 22nd December 2014
DOI: 10.1039/c4ra16081a
www.rsc.org/advances
A simple CuNiAlOx catalyst was prepared for the cooperative trans-
Aromatic amines are widely used as important intermediates in
formation of nitrobenzene derivatives and biomass-based alcohols. the synthesis of chemicals such as dyes, antioxidants, pharma-
Under the optimized reaction conditions, a range of nitrobenzene ceuticals and agricultural chemicals.10 A number of processes have
derivatives can be smoothly converted into the corresponding amines been made for the synthesis of aromatic amines. Traditional
and glycerol was directly transformed into 1,3-dihydroxypropan-2- methods for the synthesis of aromatic amines generally make use
11
one.
of H2 or stoichiometric reducing agents such as hydrazine
hydrate,12 silanes,13 sodium hydrosulphite,14 formates15 and deca-
borane16 as hydrogen sources, and possessed denite risk or/and
lead to a certain degree of environmental pollution. Compared
with these traditional hydrogenation reactions, catalytic transfer
hydrogenation using cheap and easily available alcohols17 as the
hydrogen source under moderate conditions, has obvious advan-
tages with respect to selectivity, economy, safety, and pro-
environment, and has been a potential process for the synthesis
of aromatic amines. Despite the rapid progress in catalytic transfer
hydrogenation, a lot of reports have focused on biomass-based
alcohols, because alcohols with diverse structures can be effi-
ciently produced from biomass. Thus, it would be ideal if biomass-
based alcohols could be directly used as the hydrogen source. As a
successful example, recently, nitroarenes could be reduced using
biomass-based glycerol as hydrogen source.18 In this process,
however, a large excess of glycerol was needed. It would be of atom
economy if the synthesis of aromatic amines and the biomass
directional transformation could be accomplished in one-pot
reaction with equivalent amount of nitroarenes and biomass-
based alcohols according to its nal oxidation product. On the
basis of our foregoing efforts about the discovery of nal oxidation
product of glycerol in the reductive coupling of nitrobenzene and
alcohols using glycerol as the hydrogen source,19,20 here, we tried to
develop one-pot synthesis of aromatic amines and high added-
value oxidation products of biomass-based alcohol over a non-
noble metal heterogeneous CuNiAlOx catalyst, and only with
equivalent amount of nitroarenes and glycerol.
Concerns about global warming and energy security have led to
the exploration of alternatives for fossil resources to supply
chemicals and energy.1 Biomass has gained extensive attention
because of its renewability, eco-friendly nature, compatibility
with biological systems, cheapness, high energy storage and
wide availability.2 In the last few years, people have spent much
effort to achieve the conversion of biomass to high-added value
chemical products.3–6 Glycerol from biomass, as a by-product of
the transesterication of triglycerides, is an abundant renew-
able resource and a highly functionalized molecule with three
reactive hydroxyl groups.
A large number of valuable
compounds can be obtained via its oxidation, hydrogenolysis,
dehydration, etherication, esterication or reforming.7 Inter-
estingly, very recently, glycerol has also been used in catalytic
amination reactions via hydrogen transfer mechanism,8 and
hydrogen generation was achieved from glycerol through
pyrolysis reaction. The results suggested that it's possible to use
bio-based feedstock as a hydrogen source. It would be of great
signicance if bio-based feedstock could be regarded as a
reducing agent for the synthesis of ne chemicals without
cracking. However, until now, it is a pity that reports about
synthesis of ne chemicals using bio-based feedstock directly as
the hydrogen source have been few.9
aState Key Laboratory for Oxo Synthesis and Selective Oxidation, Center for Green
Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy
of Sciences, Lanzhou, 730000, China. E-mail: fshi@licp.cas.cn; Fax: +86-931-
8277088; Tel: +86-931-4968142
bGraduate School of the Chinese Academy of Sciences, Beijing, 100049, China
† Electronic supplementary information (ESI) available: Catalyst preparation
procedure and characterization details. See DOI: 10.1039/c4ra16081a
A series of CuNiAlOx catalysts were prepared with simple co-
precipitation method by varying the molar ratios of metal
species and calcination temperatures, and recorded as Cu1Ni4-
Ox-450, Cu1Ni4Al1Ox-450, Cu2Ni4Al0.5Ox-450, Cu1Ni4Al0.5Ox-350,
Cu1Ni4Al0.5Ox-450, Cu1Ni4Al0.5Ox-600 and Cu1Ni4Al0.5Ox-650. To
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explore the correlation of structure and activity, these catalysts
were characterized by inductively coupled plasma-atomic emission
spectroscopy (ICP-AES), BET surface-area analysis, X-ray diffraction
(XRD), transmission electron microscopy (TEM), and X-ray
photoelectron spectroscopy (XPS). The contents of Cu and Ni in
these catalysts were rstly tested by ICP-AES, and the results were
showed in Table 1. According to the results obtained, the molar
ratio of Cu and Ni in each of the catalysts was calculated. The
calculated results suggested that the content of Ni in all the cata-
lysts was a little bit higher than the theoretical calibrations. That
means that a small number of Cu might be loss in the preparation
procedure of the catalysts.
Fig. 1 XRD diffraction patterns of (a) Cu1Ni4Ox-450, (b) Cu1Ni4Al1Ox-
450, (c) Cu2Ni4Al0.5Ox-450, (d) Cu1Ni4Al0.5Ox-350, (e) Cu1Ni4Al0.5Ox-
450, (f) Cu1Ni4Al0.5Ox-600 and (g) Cu1Ni4Al0.5Ox-650 catalysts.
Then, the specic surface areas and pore size distributions of
these catalysts were investigated by BET surface-area analysis
and the results were given in Table 1. The results indicated that
the two-component catalyst Cu1Ni4Ox possessed the smallest
BET surface area, i.e. 1.1 m2 gꢀ1, and the biggest average pore
size, i.e. 17.6 nm (Entry 1). Compared with Cu1Ni4Ox-450, the
BET surface areas of the three-component catalysts were remark-
ably enlarged when Al was introduced. The Cu1Ni4Al1Ox-450
owned the largest BET surface area, i.e. 93.7 m2 gꢀ1, and the
smallest pore size, i.e. 11.0 nm (Entry 2). Moreover, the BET surface
of the Cu1Ni4Al0.5Ox catalysts gradually decreased with the
increasing of the calcination temperature (Entriꢁes 4–7). For catalyst
Cu1Ni4Al0.5Ox-650, which was calcined at 650 C, its BET surface
area was 40.6 m2 gꢀ1 with an average pore size of 12.7 nm.
The XRD diffraction patterns revealed that the major crystal
structure of all the catalysts might be consisted by Ni (111), Ni
(200), Ni (220), Ni (311) and Ni (222) lattices, Fig. 1. The intro-
duction of aluminium didn't change the crystal structure of Ni
but leading to the formation of a small amount of NiO (111) and
NiO (220) peaks. The changes of molar ratio and calcination
temperature could not generate new crystal structure, and only
causing the change of peak intensity. Moreover, there were no
observable peaks for Cu and Al species, which implied that the
copper and aluminium species might exist as amorphous state.
CuNiAlOx catalysts with different molar ratios were further
characterized by TEM and HR-TEM, Fig. 2 and S1.† The HR-
TEM image shown in Fig. S1† conrmed the observations
from the XRD diffraction patterns in Fig. 1. The crystal lattices
of Ni (200) and Ni (111) can be observed clearly. Moreover, there
was still no observable crystal lattice of Cu in the HR-TEM
image, which supported the inference about the amorphous
state. The effects of calcination temperature on the structures
were also explored. Thus, a series of catalysts were prepared by
calcining the catalyst precursors at different temperatures and
were characterized by TEM and HR-TEM, Fig. 2 and S2.† The
TEM image in Fig. S2† indicated that a slight aggregation
happened and some biggish particles were observed on the
surface of catalyst Cu1Ni4Al0.5Ox-350. When the calcination
ꢁ
temperature increased to 600 C, the catalyst was composed of
relatively uniform nano-particles but in the case of 650 ꢁC,
slightly sintering occurred. The crystal lattice of Ni (111), Ni
(200) and NiO (111) could be observed clearly in the HR-TEM in
Fig. 2b, which supported the results from the XRD diffraction
patterns in Fig. 1.
The results of XPS about Cu2p and Ni2p given in Fig. S3†
revealed that Cu and Ni in all catalysts existed in same form
with similar spectra and the typical binding energies of Cu
(932.4 eV) and NiO (854.8 eV) in all CuNiAlOx catalysts were
observable. It means that Cu and Ni on the surface of all the
catalysts were Cu0 and NiO. It was not in accordance with the
results of XRD and HR-TEM. Thus, an inference could be
obtained that NiO was formed by reason of the oxidation of Ni
exposed in the air and mainly existed on the surface of the
catalyst. Moreover, the changes of molar ratios and calcination
temperatures neither inuenced the existence form of Cu and
nor did Ni.
The catalytic activity of different CuNiAlOx catalysts was
initially tested by the reduction of p-Me-nitrobenzene as model
reaction with KOH as the co-catalyst and one equivalent of
glycerol as the hydrogen source (Table 2, Entries 1–7). Clearly,
Table 1 The properties of CuNiAlOx catalysts
Entry
Catalyst
Cua wt%
Nia wt%
Cu/Ni mol/mol
SAb m2/g
APZc nm
1
2
3
4
5
6
7
Cu1Ni4Ox-450
19.4
14.3
27.7
16.8
16.9
16.9
17.2
80.7
61.8
55.8
66.8
66.1
68.3
68.0
1 : 4.5
1 : 4.7
2 : 4.4
1 : 4.3
1 : 4.3
1 : 4.4
1 : 4.3
1.1
93.7
55.8
71.2
60.8
51.9
40.6
17.6
11.0
14.1
11.4
11.4
12.1
12.7
Cu1Ni4Al1Ox-450
Cu2Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-350
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-600
Cu1Ni4Al0.5Ox-650
a
Determined by ICP-AES. b BET surface area. c Average pore size.
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conversions or/and selectivities (Entries 12–14). Then, the
inuence of solvents on the catalytic activity of Cu1Ni4Al0.5Ox-
450 was explored with KOH as the co-catalyst. Good conversions
and selectivities were achieved if using heptane, octane or
cyclohexane as solvent (Entries 1, 16 and 17). If other solvents
such as acetonitrile, 1,4-dioxane and toluene were used, rela-
tively poor results were obtained (Entries 18–20). In addition,
only 2% p-Me-nitrobenzene was converted if using water as
solvent but the reason for the lower activity was still not clear at
this stage (Entry 21).
Commonly, the calcination temperature is an important factor
on the catalytic activity in the preparation of heterogeneous cata-
lyst. Whereupon, a series of catalysts were prepared under
different calcination temperatures and their catalytic activity for
the model reaction were tested and compared (Fig. 3). As a result,
the calcination temperature was optimized between 350 ꢁC and
ꢁ
650 C. The catalytic activity of Cu1Ni4Al0.5Ox took on non-linear
rising tendency with the calcination temperature. From 350 ꢁC
to 400 ꢁC, the catalytic activity was obviously improved, while it did
not change much if the calcination temperature continued to rise
to 600ꢁ C. Interestingly, the catalytic activity declined sharply when
the calcination temperature surpassed 600 ꢁC, which might be
derived from the smaller surface area of Cu1Ni4Al0.5Ox-650 (Table
1, Entry 7).
Aer optimizing the reaction conditions, the catalytic
reduction of diverse nitroarenes with glycerol as reducing agent
was carried out to investigate the scope and limitations of the
methodology. First, nitrobenzene was effectively converted into
the corresponding aniline with an excellent yield (Table 3, Entry
1). Then, a series of aromatic nitro substrates containing
different functional groups such as –CH3, –NH2, –OCH3, –Cl
and –Br were explored (Entries 2–12). Clearly, the structure of
the functional groups did not affect the catalytic activity
signicantly and a good to excellent yields of desired anilines
were obtained.
Next, we attempted to explore the hydrogen source scope of
this catalyst system. Different hydrogen sources such as glyc-
erol, glucose and fructose were studied (Table 4). The results
demonstrated that the polyhydric alcohol, i.e. glycerol, and the
monosaccharide, i.e. glucose and fructose were good and
effective reducing agents in our catalytic system. The yield of the
desired product was 85% when glycerol was used as the
hydrogen source (Entry 1). Meanwhile, glycerol was trans-
formed into 1,3-dihydroxypropan-2-one selectively with 84%
yield. To our delight, 95% aniline was generated with shorter
reaction time when using water as the solvent and glucose as
the reducing agent (Entry 2). Similar result was gotten if the
fructose was used as the hydrogen source (Entry 3). However,
the oxidation products of glucose and fructose were not
observable, which might be attributed to the decomposition
during reaction.21 Moreover, we speculated that the similar
activity of glucose and fructose might be explained by the
interconversion of glucose and fructose in the alkaline solu-
tion.22,23 Namely, fructose was rst converted into glucose via
isomerization during the reaction, and then glucose might be
the real hydrogen source for the reduction reaction. That might
be the reason for the longer reaction time when fructose was
Fig. 2 TEM and HR-TEM images of Cu1Ni4Al0.5Ox-600 (a, b).
Cu1Ni4Al0.5Ox-450 showed the highest activity for the reduction
of p-Me-nitrobenzene, affording p-toluidine in 90% conversion
and 84% selectivity (Entry 1). When decreasing the content of
Cu, the selectivity remained unchanged but lower conversions
were obtained (Entry 2). Conversely, when increasing the
content of Cu, the conversion and selectivity both became lower
(Entry 3). Likewise, the contents of Ni and Al were changed to
regulate the activity of the catalyst. Notably, the change of the
content of Ni had good effect on the selectivity, though the
conversion was unsatisfactory (Entries 4 and 5). Moreover, the
content of Al seems to have been ideal in catalyst Cu1Ni4Al0.5Ox-
450, because the addition of more or less Al results in lower
conversion and selectivity (Entries 6 and 7). In order to clarify
the catalytic performance of AlOx in the absence of Cu and Ni,
an AlOx sample was prepared with the same procedure as
CuNiAlOx. The results suggested that almost no reaction
occurred when applying AlOx as catalyst with or without the
addition of KOH (Entries 8 and 9). Thus AlOx itself is inactive
but it is a nice component for gaining the active Cu–Ni catalyst.
As it was well known, the property of base has a strong inuence
on the catalytic efficiency. The conversion was <5% in the
absence of base (Entry 10). Hence, we explored the catalytic
activity of Cu1Ni4Al0.5Ox-450 with different bases as the co-
catalysts. The results suggested that KOH and tert-BuOK were
the efficient bases for the reduction of p-Me-nitrobenzene in our
catalytic system (Entries 1 and 15). The application of other
bases such as NaOH, Na2CO3 and K2CO3 resulted in much lower
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Table 2 Catalyst screening and reaction conditions optimizationa
Entry
Catalyst
Base
Solvent
Con.b (%)
Sel.b (%)
1
2
3
4
5
6
7
8
Cu1Ni4Al0.5Ox-450
Cu0.5Ni4Al0.5Ox-450
Cu2Ni4Al0.5Ox-450
Cu1Ni2Al0.5Ox-450
Cu1Ni6Al0.5Ox-450
Cu1Ni4Ox-450
Cu1Ni4Al1Ox-450
AlOx
AlOx
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
—
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Heptane
Octane
90
72
37
50
24
19
28
<1
1
84
85
70
92
92
32
46
<1
<1
33
15
85
25
20
71
83
92
99
75
84
99
9
10
11
12
13
14
15
16
17
18
19
20
21
Cu1Ni4Al0.5Ox-450
—
—
3
KOH
NaOH
K2CO3
Na2CO3
ButOK
KOH
KOH
KOH
KOH
KOH
KOH
13
33
4
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
Cu1Ni4Al0.5Ox-450
2
98
86
76
67
65
43
2
Cyclohexane
Acetonitrile
1,4-Dioxane
Toluene
Water
a
b
1 mmol p-Me-nitrobenzene, 3 mmol glycerol, 50 mg catalyst, 2 mmol KOH, 2 mL solvent, Ar, 80 ꢁC, 12 h. Conversions and selectivities were
determined by GC-FID with biphenyl as an external standard material.
and LC-MS. The results suggested that no 1,3-
dihydroxypropan-2-one was generated although ꢂ60% (average
number of three parallel reactions) conversion of glycerol was
obtained. The observed products were 3,30-oxybis (propane-1,2-
diol), glyceraldehyde and some unknown compounds. That
means the addition of nitrobenzene which was regarded as a
hydrogen acceptor might alter the route of glycerol dehydroge-
nation and induce the oriented conversion of glycerol to 1,3-
dihydroxypropan-2-one.
In order to explore the reaction mechanism and reveal the
nal oxidation product of glycerol, the reaction of nitrobenzene
with glycerol was traced by GC-MS, and only a small number of
etherication products of glycerol were observed without
oxidation products. So, the high performance liquid chroma-
tography (HPLC) was used to analyze the nal reaction mixture.
As expected, the oxidation product of glycerol, that is, 1,3-
dihydroxypropan-2-one, was observed. Therefore the oxidation
Fig. 3 The catalytic activity of Cu1Ni4Al0.5Ox with different calcination
temperatures for the reduction of p-Me-nitrobenzene.
of glycerol occurred on the secondary hydroxyl group. According
to the amount of 1,3-dihydroxypropan-2-one obtained, i.e. 84%,
we proposed that nal oxidation product of glycerol in our
system was 1,3-dihydroxypropan-2-one. Clearly, the reduction of
used as the hydrogen source than that using glucose. As an
nitrobenzene derivatives in our system is based on a borrowing
important bio-mass based compound, it would be interesting to
hydrogen mechanism. The base (KOH) in our system is a
promoter for the deprotonation of alcohol.24,25 Moreover, based
on the results of XRD and XPS characterization, metallic Cu and
Ni formed in catalyst CuNiAlOx, which can behave as a nice
check the possible reactions with glycerol itself as starting
material without the addition of nitrobenzene. Aer reacting
under the same reaction conditions as given in Table 4, Entry 1,
the reaction mixture was analyzed by GC-FID, GC-MS, HP-LC
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Table 3 Catalytic reduction of nitrobenzene derivativesa
Entry
Substrates
Products
T/ꢁC
t/h
12
24
Yieldb/%
1
2
80
85
78
80
Scheme 1 A possible reaction mechanism for the reduction reaction
of nitrobenzene derivatives with glycerol catalyzed by Cu1Ni4Al0.5Ox-
600.
3
4
80
80
12
12
80
88
catalyst in borrowing hydrogen reactions.26–28 Thus, a possible
mechanism was presented (Scheme 1). However, the synergistic
effect among Cu, Ni and AlOx was still unclear.
5c
6c
7c
100
100
100
12
24
24
62d
86
Conclusions
72
In summary, here, we have introduced a method for the coop-
erative transformation of nitrobenzene derivatives and
biomass-based alcohols. The synthesis of aromatic amines and
value-added oxidation product of glycerol could be achieved by
one pot method in the presence of non-noble metal CuNiAlOx
catalyst. In this transformation, only an equivalent amount of
glycerol is required and the glycerol can be converted to 1,3-
dihydroxypropan-2-one selectively. It offers a new method for
the conversion of biomass and its derivative to high added-value
product.
8
80
12
81
9
80
80
80
12
12
12
70
71
75
10
11
12
100
24
71
Experiment section
Typical procedure for CuNiAlOx catalyst preparation: Cu
(NO3)2$3H2O (5.1–10.4 mmol), Ni (NO3)2$6H2O (20.7–30.9
mmol) and Al (NO3)3$9H2O (0–5.3 mmol) were added to 150 mL
deionized water and agitated until complete dissolution. Then,
1.25 equivalent amount of Na2CO3 was added to 50 mL deion-
ized water and added dropwise. The mixture was stirred for a
further 3 h at RT. The reaction mixture was centrifuged and
washed with deionized water to remove the base until the pH
value of the aqueous solution was z7. Subsequently, the
precipitate was dried at 100 ꢁC for 5 h, calcinated in air at 350–
650 ꢁC for 5 h, and reduced under a hydrogen ow for 3 h.
Finally, a black solid sample was obtained and denoted as
CuNiAlOx. All the catalysts were reduced by hydrogen before
use.
a
1 mmol nitrobenzene derivatives, 3 mmol glycerol, 50 mg catalyst, 2
b
mmol KOH, 2 mL heptane, Ar. The yields were determined by GC-
FID with biphenyl as an external standard material. The main by-
products were azobenzene and azoxybenzene compounds based on
GC-MS measurement. 1,4-dioxane was used as solvent. The main
by-products were quinoxaline and 2-methylquinoxaline.
c
d
Table 4 The results of reduction of nitrobenzene with different
hydrogen sources
Entry
Hydrogen source
Base
t/h
Yielda/%
Yieldb/%
1c
2d
3e
Glycerol
Glucose
Fructose
KOH
NaOH
NaOH
12
4
12
85
92
89
84
—
—
Typical procedure for the reduction of p-Me-nitrobenzene
using glycerol as the hydrogen source:
1 mmol p-Me-
a
Yield of aniline determined by GC-FID with biphenyl as an external
b
nitrobenzene, 3 mmol glycerol, 50 mg catalyst, 2 mmol KOH,
and 2 mL heptane were added to a 25 mL pressure tube
equipped with a magnetic stirrer. Then tꢁhe pressure tube was
exchanged with argon and reacted at 80 C for 12 h. Aer the
reaction, the reaction mixture was cooled to RT, and then 20 mg
biphenyl and 10 mL EtOH were added for quantitative analysis
by GC-FID.
standard. Yield of 1,3-dihydroxypropan-2-one determined by HP-LC
c
with biphenyl as an external standard. 1 mmol nitrobenzene, 3
mmol glycerol, 50 mg catalyst, 2 mmol KOH, 2 mL heptane, Ar, 80 ꢁC,
d
12 h. 0.5 mmol nitrobenzene, 1 mmol glucose, 25 mg catalyst, 2
e
mmol NaOH, 2 mL water, Ar, 80 ꢁC, 4 h. 0.5 mmol nitrobenzene, 1
mmol fructose, 50 mg catalyst, 2 mmol NaOH, 2 mL water, Ar, 80 ꢁC,
12 h.
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