Al-containing mesoporous carbon as effective catalysts for the chemoselective reduction of carbon-carbon double bonds in nitrostilbene derivatives

Article abstract of DOI:10.1016/j.apcata.2013.01.040

A series of Al, Mn, Cu and Fe metal-containing mesoporous carbon catalysts were synthesized for catalyzing selective reduction of carbon-carbon double bond in 4-nitrostilbene analogs bearing nitro group with hydrazine hydrate. The results indicated that the reduction reaction was able to be achieved successfully between carbon-carbon double bond and nitro group. The efficient method has been developed for the reduction of CC double bonds with diimide, catalytically generated in situ from hydrazine hydrate by the synthesized catalysts. The 0.15Al-MC1 as heterogeneous catalyst exhibited the highest catalysis activity and chemoselectivity in all synthesized catalysts. In the presence of 0.15Al-MC1, the reduction of carbon-carbon double bond in 4-nitrostilbene derivatives was up to 99% yield and >99% chemoselectivity at 70 °C in ethanol. On the other hand, the high selective reduction of nitro group in 4-nitrostilbenes was also facile to be achieved with hydrazine hydrate, active carbon and FeCl₃·6H₂O under inert atmosphere.

Full text of DOI:10.1016/j.apcata.2013.01.040

Applied Catalysis A: General 456 (2013) 23–29
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Al-containing mesoporous carbon as effective catalysts for the
chemoselective reduction of carbon–carbon double bonds in
nitrostilbene derivatives
Liuchang Wanga, Yanjun Zhenga, Xiquan Zhangb, Hongmei Gub, Jiang Lia, Wei Wanga,
Baolin Lia,∗
a Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, and School of Chemistry & Chemical
Engineering, Shaanxi Normal University, Xi’an 710062, PR China
b Jiangsu Chia Tai Tianqing Pharmaceutical Co. Ltd., Nanjing 210042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Al, Mn, Cu and Fe metal-containing mesoporous carbon catalysts were synthesized for cat-
alyzing selective reduction of carbon–carbon double bond in 4-nitrostilbene analogs bearing nitro group
with hydrazine hydrate. The results indicated that the reduction reaction was able to be achieved success-
fully between carbon–carbon double bond and nitro group. The efficient method has been developed for
the reduction of C C double bonds with diimide, catalytically generated in situ from hydrazine hydrate
by the synthesized catalysts. The 0.15Al–MC1 as heterogeneous catalyst exhibited the highest catalysis
activity and chemoselectivity in all synthesized catalysts. In the presence of 0.15Al–MC1, the reduction of
carbon–carbon double bond in 4-nitrostilbene derivatives was up to 99% yield and >99% chemoselectivity
at 70 ◦C in ethanol. On the other hand, the high selective reduction of nitro group in 4-nitrostilbenes was
also facile to be achieved with hydrazine hydrate, active carbon and FeCl3·6H2O under inert atmosphere.
Received 3 December 2012
Received in revised form 28 January 2013
Accepted 31 January 2013
Available online xxx
Keywords:
Al-containing mesoporous carbon
Selective reduction
Carbon–carbon double bond
Hydrazine
Heterogeneous catalysis
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Experimentally, the use of diimide as reducing agent has the advan-
tage of avoiding flammable gases and that no noble metal catalysts
The reduction of carbon–carbon double bonds is a very impor-
tant process in organic synthesis, which is normally accomplished
by hydrogen gas in the presence of nobler transition metal cata-
lysts. These catalysts can be in either a hetero [1] or a homogeneous
fashion [2], such as Rh/C, Pd/C, Nickel Raney, PtO2, hetero rhodium
complex [3,4], or Wilkinson’s catalyst, homogeneous rhodium
complex. Although these hydrogenations with metal catalysts
often proceed efficiently, there are important limitations for high
pressures, expensive catalysts, toxicity and heavy metal pollution.
Carreira and co-workers reported a new catalyst system for the
enantioselective reduction of nitroalkenes utilizing Cu species and
bis-phosphine ligand JOSIPHOS [5,6]. However, these hydrogenat-
ions are problematic when several functional groups such as nitro
group, benzylic ketone, aryl halide and other unsaturated bond
exist in the same molecule because they are rapidly reduced or
isomerized.
are needed. This reduction process of using diimide is environ-
mentally benign since nitrogen gas is the sole waste product. It
is generally accepted that diimide reduce nonpolarized double
bonds via a cycloaddition mechanism [8]. Therefore hydrogenol-
ysis, reduction of polarized bonds, or isomerization does not take
place. However, diimide itself is unstable and facile to produce
nitrogen and hydrazine. Therefore a large number of methods
for its in situ generation have been reported including the base-
induced elimination of substituted hydrazines [9] and the oxidation
of hydrazine hydrate [10]. The catalytic oxidation of hydrazine
using oxygen or air, which would be the ideal method for gener-
ating diimide [11,12], also remains problematic from the point of
view of green chemistry since a great excess of hydrazine (10 to
>400 equiv.) is required to achieve this [13–15]. Recently, Imada’s
group and Minnaard’s group reported the generation of diimide
from hydrazine hydrate and oxygen/air using flavin-type com-
pounds as organocatalysts, respectively [7,10]. Remarkably, a large
excess of hydrazine hydrate was not needed. These systems do
not give double bond isomerization, and it is a valuable alterna-
tive when metal-catalyzed hydrogenations are problematic. Very
recently, Imada’s group further extended the potential of flavin
catalysts with the development of a two-phase system allowing
One of the few alternatives is the use of diimide (diazene,
HN NH), generated in situ from hydrazine or its derivatives [7].
∗
Corresponding author. Tel.: +86 29 81530726.
E-mail address: baolinli@snnu.edu.cn (B. Li).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.01.040

24
L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
H2N NH2
was naturally cooled to room temperature under N2 atmosphere.
O2
NO2
NO2
Rn
X-ray photoelectron spectra (XPS) was recorded on a Kratos Ana-
lytical Ltd. AXIS ULTRA X-ray photoelectron spectrometer using
monochromatized Al K␣ X-ray (1486.6 eV) as the excitation source.
The binding energy (BE) of the spectra was calibrated by referring
to carbon 1s peak located at 284.8 eV. The resulting catalysts are
designated as xAl–MC1, x denotes the molar ratio of Al ion to R at
the beginning of polymerization (e.g. 0.15Al–MC1 show that the
Al-containing mesoporous carbon was prepared from 0.15 molar
ratio of Al ion to R at the beginning of polymerization mixture).
The same procedures were carried out for the preparation
of 0.25Al(NO3)3–MC1, 0.4Al(NO3)3–MC1 and 0.6Al(NO3)3–MC1,
except that the different amount of Al(NO3)3 was used as aluminum
source. Pure mesoporous carbon MC1 was prepared by the similar
method except for adding aluminum salt.
Metal-MC
hybrids
Rn
H2O
N2
HN NH
Scheme 1. The reduction of C C in stilbene derivatives with hydrazine hydrate in
the presence of metal–MC hybrids.
the recycling of their catalysts [16]. Although their catalysis sys-
tem could afford a high yields in the reduction of terminal and
disubstituted alkenes, tetra-substituted double bonds and stilbene
were not reduced at all. Thus, introduction of new efficient method-
ologies for the reduction of various carbon–carbon double bonds is
still in strong demand. In our efforts to develop mesoporous carbon
(MC) materials for clean heterogenous catalysts, we have success-
fully prepared MC materials with high specific surface area and
uniform mesoporous structure [17–19], and introduced organic
functional groups on the surface of pore channels of synthesized
MC material to yield a surface modified MC materials for catalyzing
some organic reactions [20]. Considering the generation of diimide
in situ from hydrazine hydrate and oxygen/air needs the presence
of appropriate catalysts, and MC and its metal-containing hybrids
with high specific surface area and uniform mesoporous structure
have attracted considerable attention in catalysis area [21,22], we
attempt to support some cheap metal species, possessing an ability
for the activation of molecular oxygen, on MC materials as catalysts
in the generation of diimide in situ. With this strategy, the selec-
tive reduction of C C bond in stilbene analogs bearing nitro group
was carried out (Scheme 1). Herein, we report the highly chemos-
elective catalytic reduction of carbon–carbon double bond or nitro
group in nitrostilbene derivatives with hydrazine hydrate.
2.3. Preparation of Cu, Mn and Fe-containing MC1
The same procedures were carried out for the preparation
of 0.15Cu–MC1, 0.15Mn–MC1, 0.15Cu–Mn–MC1 and 0.15Fe–MC1,
except that the corresponding metal salts Cu(NO3)2·3H2O, 50%
solution of Mn(NO3)2, and Fe(NO3)3·9H2O were used, respectively.
2.4. Preparation of 0.25Cu–MC2 and 0.25Mn–MC2
2.4.1. Preparation of resol precursor
The resol precursor was prepared by using phenol and formalde-
hyde in a base-catalyzed process according to the reported method
[24]. 20.0 g (212.5 mmol) of phenol was melted at 40–42 ◦C and
4.26 g of 20 wt% NaOH (21.3 mmol) aqueous solution was added
slowly under stirring. After 10 min, 35.4 g (436.2 mmol) of forma-
lin (37 wt% formaldehyde) was added dropwise, and the mixture
was then heated up to 70–75 ◦C and stirred for another 60 min at
this temperature. Upon cooling down to room temperature, the
pH value was adjusted to about 6.0 by 2.0 M HCl solution. Sub-
sequently, the solution was evaporated at 50 ◦C under reduced
pressure to remove water. The resultant product was re-dissolved
in ethanol to form a 20 wt% ethanolic solution; thereby separating
sodium chloride as a precipitate at the same time.
2. Experimental
2.1. Materials and chemicals
All reagents materials were obtained from commercial sources
and used without any further purification. 50% aqueous solution
of Mn(NO3)2 was used of commercially available reagent. The 4-
nitrostilbene derivatives were prepared from aromatic aldehyde
and 4-nitrotoluene using our published procedure [23].
2.4.2. Preparation of 0.25Cu–MC2 and 0.25Mn–MC2
0.25Cu–MC2 was synthesized from prepared resol, tetraethyl
orthosilicate and F127, followed by carbonization and silica
removal with NaOH solution. In
a typical preparation, 3.2 g
2.2. Preparation of Al-containing MC1 and MC1
(0.26 mmol) of block copolymer F127 and 0.50 g of Cu(NO3)2·3H2O
(2.07 mmol) were dissolved in 16.0 g of ethanol with 2.0 g of 0.2 M
HCl. Then, 4.16 g (19.9 mmol) of TEOS and 10.0 g 20 wt% ethanol
solution of resol were mixed in sequence. After stirring for 2 h
at 40 ◦C, the solution was transferred into dishes and kept at
room temperature for 5–8 h to remove ethanol. After ethanol was
evaporated, the dishes were put into an oven at 100 ◦C for ther-
mopolymerization for 24 h. The product was scraped from the
dishes, pyrolyzed at 700 ◦C for 2 h with a ramping rate of 2 ◦C/min
under nitrogen flow. The silica component was removed by stirring
the resulted mixture in 60 g of 1.0 M NaOH solution at 80 ◦C for 24 h.
The obtained product was designated as 0.25Cu–MC2, 0.25 denotes
that 0.25 g of Cu(NO3)2·3H2O was applied to per 1.0 g of resol.
The same procedures were carried out for the preparation of
sample 0.25Mn–MC2, except using 1.0 g of 50% Mn(NO3)2 aqueous
solution instead of Cu(NO3)2·3H2O.
Al-containing MC1 and MC1 were synthesized by multi-
component co-assembly strategy associated with a direct car-
bonization process. In a typical synthesis, 25.0 g F127 was dissolved
absolutely in 140.0 g of ethanol/water (1/1 vol.) solution under stir-
ring at room temperature. And 16.5 g resorcinol (R) was added
into the solution (signed A). An appropriate amount of hydrated
AlCl3 corresponding to Al/R (molar ratio) equal to 0.15, 0.25,
0.60 was dissolved in 70.0 g of ethanol/water (1/1, v/v) solution
(signed B). Solution B was dropped into solution A when the
color of solution A turned to be a light brown. The pH value
was adjusted to 2 with 37% HCl. After stirring for 2 h, 23.0 mL of
formaldehyde (F) (37%) was subsequently dropped into the above
solution. The mixture was kept stirring until it turned cloudy
and began to separate into two layers. The upper layer was dis-
carded, after this two phase mixture was further kept aging for
60 h. The lower polymer-rich phase was formed to a stick mono-
lith. The monolith was dried at 85 ◦C for 24 h and carbonized under
N2 atmosphere. The carbonized process was programmed with
heating ramps of 1 ◦C/min from 25 to 400 ◦C and 5 ◦C/min from
400 to 800 ◦C and kept at 800 ◦C for 2 h. After that, the furnace
2.5. Preparation of 0.62Al–MC1–I and 0.62Mn–MC1–I
0.62Al–MC1–I and 0.62Mn–MC1–I were prepared by a con-
ventional wet impregnation method. In a typical preparation of
0.62Al–MC1–I, 2.5 g of MC1 was added to a beaker containing 8 mL

L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
25
Table 1
of deionized water. 0.58 g (1.56 mmol) Al(NO3)3·9H2O was added to
the above-mentioned solution under vigorous stirring. The mixture
was further stirred for 3 h, and allowed to stand for 8 h under ambi-
ent condition. The 0.62Al–MC1–I was obtained by heating at 100 ◦C
overnight to evaporate water and incubating in a N2 atmosphere at
600 ◦C for 6 h. 0.62 denotes that 0.62 mmol of Al(NO3)3·9H2O was
applied to per 1.0 g of MC1.
The same procedures were carried out for the preparation of
sample 0.62Mn–MC1–I, except using 0.56 g (1.56 mmol) of 50%
Mn(NO3)2 aqueous solution instead of Al(NO3)3·9H2O.
Screening the catalyst for the reduction of C C double bonds of 4-nitrostibene.a
.
catalyst, N2H4 H2O, air
ethanol, 70oC, 3 h
NO2
NO2
.
Entry
Catalyst
–
0.15Mn–MC1
0.15Cu–MC1
0.15Cu–0.15Mn–MC1
0.15Fe–MC1
0.15Al–MC1
Yieldb (%)
Selectivity (%)
1
2
3
4
5
6
7
8
9
34
64
46
62
58
80
6
72
91
71
90
61
95
6
0.25Cu–MC2
2.6. Characterization methods
0.25Mn–MC2
0.62Mn–MC1–I
23
62
47
84
N2 adsorption isotherms were measured using a Micromeritics
ASAP 2020 nitrogen adsorption apparatus (USA). All the samples
were degassed at 260 ◦C for 6 h prior to Brunauer–Emmett–Teller
(BET) measurements. The BET surface area was calculated using the
BET method based on adsorption data in the relative pressure (P/P0)
range 0.05–0.3, the total pore volume (Vtot) was determined based
on the amount of the N2 adsorbed at a relative pressure of 0.992
(P/P0). The pore size distribution (Dpore) was derived from desorp-
tion isotherm by using the Barrett–Joyner–Halenda (BJH) model.
The powder XRD patterns were recorded on a Rigaku D/Max-3c
diffractometer equipped with a Cu K␣ radiation (ꢀ = 0.154 nm)
beam operating at 40 kV and 40 mA. Data were obtained in the 2ꢁ
range of 0–80◦ at a scanning rate of 8◦/min. SEM image and EDX
were recorded using a Quanta 200 environmental scanning elec-
tron microscope. Sample was mounted using conductive carbon
double-sided sticky tape. TEM experiment was conducted on a JEM
2100 electron microscope operating at 200 kV. 1H NMR, 13C NMR
spectra were recorded using CDCl3 as a solvent on a Bruker Avance
400 MHz spectrometer. Chemical shifts (ı) are reported in parts
per million, and coupling constants (J) are in hertz, using TMS as
an internal standard. Data are presented as follows: chemical shift
(ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet). Elemental analyses were performed on a Vario EL III
elemental analyzer. GC and GCMS analyses were performed on Shi-
madzu GCMS-QP2010 apparatus with RTX-1MS capillary column
(30 m × 0.25 mm × 0.25 ␮m).
a
The reaction conditions: 4-nitrostilbene (0.22 g, 1.0 mmol), catalyst (100 mg),
80% hydrazine hydrate (0.60 g, 4 equiv.), ethanol (7 mL), 70 ◦C, 3 h under air.
b
Determined by GC using diphenylmethanol as internal standard.
triconstituent co-assembly of prepared resol, tetraethyl orthosili-
cate (TEOS) and F127, followed by carbonization and silica removal
[24]. Meanwhile pure mesoporous carbon MC1 was prepared by
the similar method with that of to 0.15Al–MC1 method except for
adding metal salt, and Mn-containing mesoporous carbon hybrid
0.62Mn–MC1–I was prepared with impregnating method [33] from
MC1 and Mn(NO3)2. With these catalysts, we used 4-nitrostilbene
as a model substrate to investigate the chemoselective reduction
of carbon–carbon double bonds with hydrazine hydrate in ethanol
under air atmosphere. As shown in Table 1, in the control exper-
iment the desired product was obtained in low yield (34%) and
selectivity (72%) in the absence of catalyst (entry 1 in Table 1). Mn,
Cu, Fe and Al supported on MC exhibited certain catalytic activ-
ity to the reduction of C C double bonds (entries 2–6 in Table 1).
0.25Mn–MC2 presented negative activity (entry 8 in Table 1)
compared with the control experiment (Fig. 1 in S1), although
Mn-containing catalysts 0.15Mn–MC1 and 0.62Mn–MC1–I exhib-
ited moderate activity (entries 2 and 9 in Table 1). It was worthy
to note that 0.15Cu–MC1 exhibited low catalytic activity in the
reaction (entry 3 in Table 1), in contrast, 0.25Cu–MC2 possessed
obvious inhibition effect on the reaction (entry 7 in Table 1 and
Fig. 2A in S1). The constituents of reaction mixtures in the pres-
ence of 0.15Cu–MC1 and 0.25Cu–MC2 were determined by GC
analysis when reactions were prolonged to 7 h (see Fig. 2B in S1).
Although the higher conversions of 4-nitrostilbene were obtained
at 7 h in the presence of 0.15Cu–MC1 and 0.25Cu–MC2, (88% and
99%) respectively, 1-nitro-4-phenethylbenzene (1), 4-styrylaniline
(2) and 4-phenethylaniline (3) were found in these two reaction
mixtures. The results suggested that three different reduction reac-
tions as Scheme 2 occurred competitively at the same time, and
the Cu-containing MC showed lower chemoselective reductions
especially in the presence of 0.25Cu–MC2. These results indicated
that the chemoselective reduction of C C double bond or nitro
group in 4-nitrostilbene is a key problem, and Cu-containing MC
2.7. Catalytic reductions
To a 10 mL two neck flask were added 100 mg of catalyst, 7 mL of
ethanol, 1.0 mmol of the corresponding substrate and the 4 equiv.
of 80% hydrazine hydrate. The reaction mixture was stirred at 70 ◦C
under air environment for required time. Samples were taken at
regular intervals to analyze by GC using diphenylmethanol as inter-
nal standard for calculation the yields of target products and the
conversions of substrates. The final mixture was filtered and the
filtrate was concentrated under reduced pressure to afford crude
product which was purified by recrystallization with the mixture
solvent of ethanol and water.
3. Results and discussion
NO2
Considering that Cu [25,26], Mn [27,28], Fe [29,30] and Al
[31] complexes, metal nanoparticle, alloys and metal–organic
frameworks (MOFs) have been used as catalysts to activate
molecular oxygen for the oxidation of organic substrates or
the reduction of carbon–carbon double bonds with hydrazine
hydrate, we used multi-component co-assembly strategy asso-
1
NO2
NH2
NH2
2
3
ciated with
a direct carbonization process to yield several
metal-containing MC catalysts, such as 0.15Mn–MC1, 0.15Cu–MC1,
0.15Cu–0.15Mn–MC1, 0.15Fe–MC1 and 0.15Al–MC1 in modified
method [32]. 0.25Cu–MC2 and 0.25Mn–MC2 were synthesized by
Scheme 2. Various reduction of 4-nitrostilbene.

26
L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
70 o
70 oC Control
50 o
50 oC Control
25 o
25 oC Control
C
100
90
80
70
60
50
40
30
20
10
100
C
80
60
C
0.15Al-MC1
0.25Al-MC1
0.6Al-MC1
40
0.25Al(NO
0.4Al(NO
)
-MC1
3 3
)
-MC1
-MC1
3 3
0.6Al(NO
)
3 3
MC1
Control
0.62Al-MC1-I
20
0
AlCl
6H O
3
2
0
1
2
3
4
5
6
7
0
5
10
15
20
25
30
35
Time (h)
Time (h)
Fig. 1. The catalytic effects of Al-containing MCs on the chemoselective reduction of
Fig. 2. The yields of 1-nitro-4-phenethylbenzene from 4-nitrostilbene in the pres-
ence of 0.15Al–MC1 at different temperatures.
C
C bond in 4-nitrostilbene. Reaction condition: 4-nitrostilbene (0.22 g, 1.0 mmol),
catalyst (100 mg), 80% hydrazine hydrate (0.60 g, 4 equiv.), ethanol (7 mL), 70 ◦
under air atmosphere.
C
acetonitrile, the selectivity of reduction on C C bond became lower,
and 4-phenethylaniline was detected in the reaction system. The
result indicated that higher reaction temperature does not fit to the
selective reduction of C C bond. In fact, higher temperature such as
100 ◦C will result in the decomposition of hydrazine hydrate to N2,
NH3 and H2. Therefore considering the selectivity of reaction and
toxicity of acetonitrile, ethanol was selected as the ultimate solvent.
On the basis of above results, the optimized catalyst and reaction
condition were obtained as 4-nitrostilbene (0.22 g, 1.0 mmol), 80%
hydrazine hydrate (0.60 g, 4 equiv.) in ethanol (7 mL), at 70 ◦C under
air in the presence of 0.15Al–MC1 (100 mg) for 5 h.
is not suitable to chemoselectively reduce C C double bonds. The
reaction in the presence of 0.15Fe–MC1 has middle chemoselec-
tivity (61%) with 96% conversion of 4-nitrostilbene at 3 h. To our
delight, 80% yield and 95% selectivity was achieved in the presence
of 0.15Al–MC1 (entry 6 in Table 1). It might imply that Al supported
on MC1 as catalyst prefer to the selective catalytic reduction of
C
C double bond in 4-nitrostilbene. All the results indicated that
the activity of these materials depend closely on metal species, the
amount of metal loading and the synthesis procedure of catalyst.
To further investigate the catalytic effect of Al-containing MCs,
other six Al-containing MCs were evaluated in the reduction of C
C
In order to investigate the key role of oxygen in the reduc-
tion, an oxygen-free experiment was investigated in the presence
of 0.15Al–MC1 in optimized reaction condition under N2 atmo-
sphere. A few of target product (<10% yield) was found under
N2 atmosphere despite in the presence of 0.15Al–MC1 (Fig. 4 in
S1) after 5 h. In contrast, the certain 4-styrylaniline was found in
the reaction mixture. These results further suggest the oxygen is
essential in the formation of diimide from hydrazine with catalyst
(Scheme 1). To the best of our knowledge, the hydrazine produces
H2 at higher temperature in the presence of Fe3+ and active car-
bon to reduce nitro group in organic compounds [34]. Thus, the
chemoselectivity reduction of nitro group in 4-nitrostilbene was
also investigated using hydrazine hydrate with FeCl3 and active
carbon in ethanol at 70 ◦C under the protection-free from inert
gases. 77% of yield of 4-styrylaniline from 4-nitrostilbene and 98%
of conversion were obtained after 10 min, while about 17% of 4-
phenethylaniline was determined in this reaction. The generation
of 4-phenethylaniline should attribute to the presence of air. Thus
as the expectation, an improved yield (93%) of 4-styrylaniline was
obtained after 10 min under N2 atmosphere (Fig. 5 in S1). These
experiment facts obviously indicated that when hydrazine hydrate
was used as reducing agent, diimide was generated for the reduc-
tion of C C double bonds in the presence of oxygen, while in
air-free condition it preferred to the reduction of nitro group. So
far, an excellent method has been achieved successfully for the
chemoselective reduction of C C double bond or nitro group in
4-nitrostilbene.
bond under the same condition. As shown in Fig. 1, 0.15Al–MC1
exhibited the highest activity in all tested catalysts. With pro-
longation of reaction time from 10 min to 5 h, the yield of target
product 1-nitro-4-phenethylbenzene increased rapidly from 25%
to 94% with 98% selectivity. Subsequently from 5 h to 7 h, the
yield increased slowly to 98%. Apparently an excellent result was
achieved at 5 h under the catalysis of 0.15Al–MC1. Fig. 1 also
showed that support MC1 itself presented catalytic activity com-
paring with control experiment, but its activity is lower clearly
than that of 0.15Al–MC1. It is obvious that this excellent result
contribute to the synergetic effect of Al specie with MC, and the
technological process of catalyst preparation. This result inspirited
us to further optimize the reaction conditions using 0.15Al–MC1 as
catalyst.
The reaction temperature was investigated in the presence of
0.15Al–MC1 at 25, 50, 70 ◦C, respectively. The yields of target prod-
uct were increased with the extension of reaction time and increase
of temperature (Fig. 2). At 25 ◦C, the reduction reaction occurred
very slowly, and gave low yields whatever in the presence or absent
of catalyst. Only 16% yield of product was obtained in the presence
of catalyst, even if prolonging reaction time to 30 h. The results indi-
cate that the reduction of C C double bonds is hard to carry out at
lower temperature. Increasing reaction temperature to 50 ◦C, the
yield of target product sharply increased to 79% at 14 h in the pres-
ence of 0.15Al–MC1. But little increase in yield was only observed
when reaction was prolonged from 14 to 24 h at 50 ◦C. However,
further increasing temperature to 70 ◦C, an excellence yield (95%)
could be obtained at 6 h. These results indicated the 70 ◦C is opti-
mum temperature. To further investigate the temperature effect
on the catalytic reaction, acetonitrile with higher boiling point was
selected as solvent to replace of ethanol. At 70 ◦C, the slightly dif-
ferent result was observed under the same reaction condition (Fig.
3 in S1). When the reaction temperature was increased to 80 ◦C in
The catalyst 0.15Al–MC1 should also be able to chemoselec-
tively catalyze the reduction of C C double bonds in other stilbene
analogs. We expanded reaction to the reduction of various sub-
stituted stilbenes under the optimized condition. It can be seen
from Table 2 that all the nitrostilbenes with electron-withdrawing
or electron-donating groups afford high yields and chemoselec-
tivity of C C double bond reduction except for 3ꢀ,5ꢀ-dimethoxyl

L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
27
Table 2
The selective reduction of C C double bonds in stilbenes bearing nitro group with hydrazine hydrate in the presence of 0.15Al–MC1 catalyst in ethanol.a
Entry
Substrate
Product
Yieldb (%)
Selectivityb (%)
Time (h)
1
98
98
7
2
3
4
92
96
94
97
97
95
10
8
11
5
6
7
92
99
94
>99
9
11
7
>99
99
8
9
91
73
96
96
7
10
10
89
53
92
65
14
7
11
12
68
89
93
92
10
14
13
a
The reaction conditions: substrate (1.0 mmol), 0.15Al–MC1 (100 mg), 80% hydrazine hydrate (4 equiv.), ethanol (7 mL), 70 ◦C under air.
Determined by GC. Yields were calculated using diphenylmethanol as internal standard.
b
-4-nitrostilbene and 3ꢀ,4ꢀ-dimethoxyl-4-nitrostilbene (entries 11
microscopy (TEM) imaging techniques. The nitrogen adsorption
isotherms of the four catalysts, MC1, 0.15Al–MC1, 0.25Al–MC1 and
0.6Al–MC1 and their corresponding BJH (Barrett–Joyner–Halenda)
pore size distribution are shown in Fig. 3. These samples show type
IV isotherms with a quite obvious H2-type hysteresis loop at rel-
ative pressure, which is a characteristic of mesoporous structure
[35]. As presented in Table 3, their specific surface areas closely
depend on the molar ratio of Al ion to resorcinol in their preparation
process. Their catalysis activities for the reduction of C C double
bond (Fig. 1) are consistent with their specific surface areas. Except
MC1, catalyst 0.15Al–MC1 possesses the highest specific surface
area (493 m2/g) in three catalysts prepared from AlCl3 as aluminum
source and it also exhibits the best catalytic activity with TOF
and 12 in Table 2). The electron-withdrawing groups in nitros-
tilbene derivatives did not affect the yield of the C C double
bond reduction, and the reactions exhibit high selectivity (>91%).
Compounds with electron-donating groups such as methoxyl gave
lower yields than compounds with electron-withdrawing groups.
An excellent catalyst 0.15Al–MC1 has been obtained for the
chemoselective catalytic reduction of C C double bond in nitros-
tilbene analogs with hydrazine hydrate. In order to further explore
the relationship between catalyst structure and catalytic activ-
ity, the structures of some prepared catalysts were characterized
by N2 adsorption, powder wide-angle X-ray diffraction (WAXD),
scanning electron microscopy (SEM) and transmission electron

28
L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
of 5.372 × 10−3 mmol/m2 h−1. Meanwhile 0.25Al–MC1 presents
600
500
400
300
200
100
(a)
slight lower catalysis activity (TOF: 5.188 × 10−3 mmol/m2 h−1
)
MC1
than 0.15Al–MC1, consenting with that 0.25Al–MC1 possessing
slight lower specific surface area than 0.15Al–MC1. These facts indi-
cated that in our established containing Al–MCs catalysis system
the specific surface area of these mesoporous catalysts is an impor-
tant factor for their catalytic activity, and the ratio of Al ion to R in
the preparing process of catalysts affected obviously on the specific
surface area of catalysts. On the other hand, the pure mesoporous
carbon material MC1 with the biggest surface area exhibited the
lowest TOF value. It suggests that the Al play a key role in the
catalyst.
0.15Al-MC1
0.25Al-MC1
0.6Al-MC1
Nevertheless, it is difficult to characterize the structure only
with the N2 sorption measurement. To further obtain structure
evidence of the porous catalyst 0.15Al–MC1 with the best catal-
ysis activity, we observed its optical impression by TEM. Fig. 4a
reveals the existence of the evidently disordered but uniform-size
wormlike pore channels in 0.15Al–MC1. The surface morphology of
catalyst 0.15Al–MC1 was shown by the SEM image in Fig. 4b. Since
the samples were crushed for SEM analysis, 0.15Al–MC1 demon-
strates largely smooth granular carpolite-like morphology with
particle size up to the micrometer scale. The aluminum including
in catalyst 0.15Al–MC1 is affirmed by energy dispersive X-ray spec-
troscopy (EDX) (Fig. 6 in S2). Approximately 0.4 wt% of aluminum
species is enchased in the mesoporous frame of carbon. The Al state
in Al–MC1 catalysts is major in Al2O3 form deduced from the peak
at 73.8 eV [36] in the XPS of 0.6 Al–MC1 (Fig. 7 in S2). In the Al 2p
spectrum, another littler peak at 76.5 eV could be assigned to Al3+
in AlCl3 and imply small amount AlCl3 also exist in the catalyst.
In the O 1s spectrum, the peak at 531.6 eV assigned to oxygen in
Al2O3 [37], consistent with the observation in the Al 2p spectrum.
However, no diffraction peak of any Al species was observed in XRD
spectrum of 0.15Al–MC1 (Fig. 8b in S2), and two broad diffraction
peaks of all the tested samples centered at 23◦ and 44◦ of 2ꢁ in wide
angle region (Fig. 8 in S2), which can be generally indexed to (0 0 2),
(1 0 1) diffraction for glass-like carbons bearing graphitic character-
istic [38]. These imply that Al species is very equably disperse and
not to form crystal in carbon matrix.
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure P/P0
0.012
0.010
0.008
0.006
0.004
0.002
0.000
(b)
MC1
0.15Al-MC1
0.25Al-MC1
0.6Al-MC1
0
10
20
30
40
Pore width (nm)
Fig. 3. N2 adsorption isotherms (a) and corresponding pore size distribution curves
(b) of MC1; 0.15Al–MC1; 0.25Al–MC1; 0.6Al–MC1. Pore size distributions were eval-
uated from desorption branches of N2 isotherms using the BJH model.
Table 3
Textual parameters of several catalysts.a
Sample
SBET (m2/g)
Vtot (cm3/g)
Dpore (nm)
TOFb
MC1
518
493
470
370
0.94
0.72
0.81
0.71
10.5
8.6
10.3
9.4
2.653
5.372
5.188
4.085
4. Conclusion
0.15Al–MC1
0.25Al–MC1
0.6Al–MC1
We reported a simple method to prepare Al-containing meso-
porous carbon catalysts by multi-component co-assembly strategy
associated with a direct carbonization process from resorcinol,
formaldehyde, triblock copolymer F127 and corresponding metal
salt. When these heterogeneous catalysts were used to the chemos-
elective reduction of C C double bond in nitrostilbene derivatives
a
SBET, apparent surface area calculated by BET method; Vtot, total pore volume at
P/P0 = 0.99; Dpore, pore sizes calculated from desorption branches of N2 isotherms
using the BJH model.
b
TOF = mmol product formed per unit specific surface area per hour
(×10−3 mmol/m2 h−1).
Fig. 4. TEM (a) and SEM (b) images of 0.15Al–MC1.

L. Wang et al. / Applied Catalysis A: General 456 (2013) 23–29
29
with hydrazine hydrate as reducing agent under air atmosphere,
0.15Al–MC1 exhibited the best catalysis activity (up to 99% yield
and >99% selectivity) in all the tested catalysts. Meanwhile the nitro
group in nitrostilbene derivatives can also chemoselective reduced
with hydrazine hydrate under inert atmosphere. These protocols
were preformed under relatively mild reaction conditions, and will
attract considerable attention because of low cost, high efficiency
and low environmental impact.
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Appendix A. Supplementary data
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