Nitrogen and oxygen-doped metal-free carbon catalysts for chemoselective transfer hydrogenation of nitrobenzene, styrene, and 3-nitrostyrene with hydrazine

Article abstract of DOI:10.1016/j.molcata.2014.06.021

An activated carbon (AC) was treated by hydrogen peroxide and ammonia to dope oxygen and nitrogen on its surface. The surface-functionalized AC catalysts were used for the transfer reduction of nitrobenzene, styrene, and 3-nitrostyrene by hydrazine hydrat

Full text of DOI:10.1016/j.molcata.2014.06.021

Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
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Editor’s Choice paper
Nitrogen and oxygen-doped metal-free carbon catalysts for
chemoselective transfer hydrogenation of nitrobenzene,
styrene, and 3-nitrostyrene with hydrazine
Shin-ichiro Fujita, Hiroyuki Watanabe, Ayaka Katagiri, Hiroshi Yoshida, Masahiko Arai∗
Division of Chemical Process Engineering, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
An activated carbon (AC) was treated by hydrogen peroxide and ammonia to dope oxygen and nitrogen on
its surface. The surface-functionalized AC catalysts were used for the transfer reduction of nitrobenzene,
styrene, and 3-nitrostyrene by hydrazine hydrate. The reduction of nitrobenzene and 3-nitrostyrene was
promoted over the oxygen- and nitrogen-doped catalysts compared to the parent AC catalyst. Those were
less active for the reduction of styrene but active for the reduction of vinyl group of 3-nitrostyrene. How-
ever, the nitrogen dopant suppressed the reduction of vinyl group of 3-vinylaniline. The functionalized
AC catalysts are likely to facilitate the adsorption and activation of nitro group of the nitro substrates
through interactions with polarized surface induced by the oxygen and nitrogen hetero dopants. This
should make it possible to reduce the vinyl group of 3-nitrostyrene on the surface. The nitrogen dopant
hindered the reduction of the vinyl group of 3-vinylaniline because the adsorption through its amino
group should become difficult on the surface of basic nature induced by the nitrogen doping. The AC
serves as an electrical conductor and its performance should be enhanced by the surface functionaliza-
tion and this would contribute to the formation of reducing species such as diimide and proton from
hydrazine on the surface. The present results show that oxygen- and/or nitrogen-doped, functionalized
carbon materials could be promising as metal-free multi-task catalysts.
Received 27 March 2014
Received in revised form 16 June 2014
Accepted 17 June 2014
Available online 26 June 2014
Keywords:
Chemoselective hydrogenation
Hydrazine
Carbon catalyst
Nitrogen doping
Oxygen doping
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
reactions can be catalyzed by base catalysts and the latter by
metal or metal oxide catalysts. Those bulk carbon materials are
Carbon materials are known to act as an effective catalyst in
several organic reactions [1]. Nitrogen-doped carbon and carbon
nitride materials may act as interesting and promising metal-free
catalysts in chemical and electrochemical reactions. Several review
articles demonstrate the development of the catalysis of those car-
bon materials including nitrogen species [2–4]. For example, Bitter
et al. prepared nitrogen-doped carbon materials in the form of
nanotube by chemical vapor deposition of acetonitrile and pyri-
dine on supported metal particles [5]. They showed that these
nitrogen-doped carbon materials were active for Knoevenagel reac-
tions. The present authors doped nitrogen to an activated carbon
(AC) and a carbon black by treating in a stream of pure ammonia
and a mixture of ammonia and air at temperatures of 400–800 ◦C
and indicated that these catalyzed Knoevenagel condensation and
transesterification reactions [6]. It is known that the former two
useful for practical preparation and application. Thomas et al. pre-
pared well-designed carbon nitride materials and showed their
catalytic actions in Friedel-Craft reactions and cyclization of func-
tional nitrile and alkynes [3]. Their work is important for discussing
the structure of active sites working on the surface of nitrogen-
doped carbon materials, which may be different depending on the
nature of chemical reactions of interest. Recently, Chizari et al.
reported that nitrogen-doped carbon nanotubes served as metal-
free catalysts for the selective transformation of harmful hydrogen
sulfide into solid sulfur [7].
For considering and judging the potential of nitrogen-doped car-
bon materials as metal-free catalysts, it is desirable and interesting
to further examine their catalytic actions in other reactions. In the
present work, the surface of a parent AC material was modified by
nitrogen doping and wet treatments with hydrogen peroxide and
hydrazine and the catalytic performance of these carbon materials
prepared was tested in liquid-phase reduction with hydrazine for
monofunctional aromatic substrates of nitrobenzene and styrene
and a bifunctional substrate of 3-nitrostyrene. The influence of the
∗
Corresponding author. Fax: +81 11 706 6594.
E-mail address: marai@eng.hokudai.ac.jp (M. Arai).
http://dx.doi.org/10.1016/j.molcata.2014.06.021
1381-1169/© 2014 Elsevier B.V. All rights reserved.

258
S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
surface modifications on the reaction rate and the product selectiv-
ity was examined. The surface properties of the carbon materials
prepared were examined by nitrogen adsorption and X-ray photo-
electron spectroscopy, and the quantity of basic sites on their
surfaces was also measured. The reaction results were discussed by
considering possible interactions of nitro, vinyl, and amino groups
with the surface modified with nitrogen and oxygen species and
possible impact of the surface treatments on the electrical proper-
ties of the AC derived materials.
After separation of the solid AC sample by filtration, a certain
volume of solution (10 cm3) was sampled and titrated by 0.01 M
sodium hydroxide solution (Wako). The amount of basic sites was
calculated from the initial amount of hydrochloric acid used and
the amount of sodium hydroxide added to reach the point of neu-
tralization, which was determined by titration curve measured (pH
value of solution vs. amount of sodium hydroxide added).
2.4. Activity measurement
It is well-known that hydrazine can serve as an effective reduc-
ing agent for various organic synthetic reactions [8]. A few workers
examined the reduction of aromatic nitro compounds to corre-
sponding aniline over activated carbon or graphite in the presence
of iron chloride [9,10]. Good yields of aniline products (>90%)
were obtained for several nitro substrates. Larsen et al. discussed
the reaction mechanisms of carbon-catalyzed transfer hydrogena-
tion of nitrobenzene by hydrazine [11]. In the literature, we could
find only a few works that consider the use of metal-free carbon
materials for the reduction of aromatic mononitro- and dinitro-
compounds by hydrazine. The reduction of aliphatic and aromatic
nitro compounds by hydrazine was studied by Gowda et al. [12,13]
using zinc and magnesium catalysts and by Kappe et al. [14] using
iron oxide nanocrystals.
The catalytic performance of several carbon materials prepared
was tested in liquid-phase reduction of nitrobenzene, styrene, and
3-nitrostyrene by hydrazine. The Teflon-coated reactor was loaded
with carbon catalyst, substrate, and hydrazine hydrate, purged by
0.2 MPa N2, and heated to a reaction temperature of 100 ◦C on a
heating place. The reaction mixture was stirred by a magnetic stir-
rer at 100 ◦C for a certain period of time. The multiphase reaction
mixture was so mixed at a stirring rate of >400 rpm that the influ-
ence of agitation was negligible. Then, the reactor was cooled by ice
water and the liquid phase was separated by filtration. The liquid
mixture was analyzed by gas chromatography (GL Science 390B)
using decane as an internal standard. The conversion was deter-
mined from the amounts of substrate before and after reaction and
the selectivity from the amount of a product divided by the total
amount of all products detected.
2. Experimental
3. Results and discussion
2.1. Sample preparation
3.1. Textural and chemical properties of modified carbon
materials
A commercially available AC (GL Science) was used as a parent
carbon material and it was modified in different manners to change
its surface properties. A weighted AC sample (500 mg) was placed
in a quartz reactor and a stream of either pure NH3 or NH3 90% + air
(10%) was passed at a rate of 100 cm3 min−1 at room temperature
for 30 min [6]. Then, the sample was heated at 10 K min−1 up to
a temperature lower by 100 K than the desired value and then at
5 K min−1 to the desired temperature. The sample was treated at
this temperature for 1 h and then cooled to 300 ◦C, at which the
gas stream was changed to pure N2 and the sample was further
cooled to room temperature. The parent AC was also subjected to
a wet treatment with either hydrazine or hydrogen peroxide. The
AC sample (2.0 g) was placed in a Teflon-coated autoclave (100 cm3)
followed by introduction of hydrazine hydrate (2.0 cm3, Wako) and
distilled water (20 cm3). The mixture was treated at 100 ◦C and at
a stirring speed of 400 rpm for 5 h. The solid sample so treated was
washed with water and ethanol (Wako) and dried under ambient
conditions for 1 day. The hydrogen peroxide treatment was made
by using 0.3 g of the same AC and 15 cm3 of 30% hydrogen peroxide
(Wako) in the same procedures as used in the hydrazine treatment.
The parent AC was treated with hydrogen peroxide, ammonia,
and hydrazine hydrate. Table 1 shows the textural properties of
several carbon materials prepared. The parent AC has a surface area
of 1047 m2 g−1 and its surface contains oxygen in 10% (entry 1).
The content of oxygen was found to decrease to 6% by treatment
with hydrazine (entry 2) while it increased to 15% by treatment
with hydrogen peroxide (entry 3). The treatments of ammonia (90%
in air) at 400 ◦C, 600 ◦C, and 800 ◦C supplied nitrogen in 3–4% to
the surface of AC (entries 4–6). The content of oxygen was slightly
decreased by the treatments at 400, 600, and 800 ◦C. The material
treated with hydrogen peroxide and then ammonia had an oxygen
content of 6.1% and a nitrogen content of 5.3% (entry 7). Compared
to these changes in the chemical nature, the surface area did not
change so much by those surface treatments. The treatments by
hydrogen peroxide and/or ammonia caused the weight of AC to
decrease by 10–40% (entries 3–7).
The basic character of AC catalysts may be important for the
adsorption of reacting species on their surface, as will be discussed
later. The amounts of basic sites were determined by back titra-
tion for a few selected samples at room temperature, in which a
strong acid of hydrochloric acid (pKa = −7.0) [15] was used. The
results obtained are also given in Table 1, indicating that the amount
of basic sites of the parent AC is 0.426 mmol g−1 (entry 1) and
it decreases to 0.163 mmol g−1 on the treatment with hydrogen
peroxide (entry 3). The treatment with ammonia was observed
to produce larger amounts of basic sites (entries 4, 6 and 7). The
amount of basic sites was 0.615 mmol g−1 for the sample treated
at 400 ◦C and 0.758 mmol g−1 for the one treated at a higher tem-
perature of 800 ◦C. The sample treated by hydrogen peroxide and
2.2. Surface area and XPS measurement
The textural properties of those carbon samples so prepared
were measured by nitrogen adsorption/desorption (Quantachrome
NOVA 1000). Total surface area was determined by the Brunauer,
Emmet and Teller’s (BET) equation. Chemical nature of their sur-
faces was examined by X-ray photoelectron spectroscopy (XPS)
on JEOL JPS-9200 with monochromatic Al-K␣ radiation [6]. The
charge-up shift correction of the binding energy was made by using
C1s binding energy at 284.5 eV.
ammonia also had a large amount of basic sites of 0.710 mmol g−1
.
2.3. Measurement of basic sites
The amount of basic sites was determined by back titration at
room temperature. An AC sample (100 mg) was added to 0.01 M
hydrochloric acid solution (15 cm3) (Wako) in a glass bottle with a
cap and the mixture was stirred by a magnetic stirrer overnight.
3.2. Reduction of nitrobenzene and styrene
Those surface-modified carbon materials were applied for
the liquid-phase reduction of either nitrobenzene or styrene by

S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
259
Table 1
Textural properties of different carbon catalysts prepared.
Entry
Surface treatment
Surface areaa (m2 g−1
)
Burn-off
(%)
Surfacecompositionb
Amount of basic sitesc (mmol g−1
)
O (%)
N (%)
1
2
3
4
5
6
7
No treatment
N2H4
1047
–
10
6.1
15
8.1
7.4
8.2
6.1
0
0
0
1.7
2.6
4.1
5.3
0.426
–
0.163
d
d
H2O2
1188
1180
1116
1260
37
10
17
27
55
NH3 90%, 400 ◦
NH3 90%, 600 ◦
NH3 90%, 800 ◦
C
C
C
0.615
d
–
0.758
0.710
H2O2 → NH3 90%, 600 ◦
C
–
d
a
Determined by nitrogen adsorption (BET surface area).
Determined by XPS.
Determined by back titration using hydrochloric acid and sodium hydroxide.
Not measured.
b
c
d
Table 2
Results of reduction of nitrobenzene, styrene, and 3-nitrostyrene by hydrazine using different carbon catalysts.
Entry
Surface treatment
Conversion (%)
Nitrobenzene
Selectivityin3-nitrostyrenereductiona (%)
Styrene
3-Nitrostyrene
1
2
3
1
2
3
4
5
6
7
No catalyst
No treatment
N2H4
26
40
36
80
42
47
67
11
14
–
55
62
–
58
46
16
20
26
34
b
b
H2O2
13
97
56
13
45
29
21
58
34
NH3 90%, 600 ◦
NH3 90%, 800 ◦
C
C
–
b
b
13
18
–
H2O2 → NH3 90%, 600 ◦
C
93
10
54
36
Reaction conditions: catalyst 10 mg, nitrobenzene 8.5 mmol (styrene 8.0 mmol, 3-nitrostyrene 3.8 mmol), hydrazine 4 cm3, temperature 100 ◦C, and time 2 h.
a
1: 3-ethylnitrobenzene; 2: 3-vinylaniline; 3: 3-ethylaniline.
Not measured.
b
hydrazine (Scheme 1), in which aniline and ethylbenzene were
respectively detected to form as products under the conditions
used. Table 2 shows that the reduction of nitrobenzene occurred
in the absence of catalysts and gave a conversion of 26% (entry
1). The parent AC was inherently active with a conversion of
40% (entry 2). The treatment with hydrazine indicated no activity
improvement (entry 3) and that with ammonia increased the con-
version slightly (entries 5 and 6). The conversion was significantly
enhanced to 80% on the treatment with hydrogen peroxide (entry
4). This improvement was somewhat canceled by additional treat-
ment with ammonia at 600 ◦C, the conversion being 67% (entry 7).
In contrast, the reduction of styrene was only a little improved by
the presence of catalysts and the surface treatments had hardly
positive impact on the performance of AC (entries 2, 4 and 6).
But a marginal activity improvement was observed with the treat-
ment with hydrogen peroxide and ammonia, the conversion being
increased to 18% (entry 7).
and/or nitrogen. Fig. 1 gives a plot of nitrobenzene conversion (ani-
line yield) against the total amount of surface oxygen and nitrogen,
which includes the reaction results over the AC-based materials
shown in Table 2 and a few other samples surface-treated under
different conditions. Fig. 1 suggests that both surface oxygen and
nitrogen species contribute to the formation of working active sites.
These active sites should adsorb and activate a polar nitro group of
nitrobenzene but not a less polar vinyl group of styrene, which will
be discussed later. As reported previously [6], there are a few dif-
ferent types of either nitrogen or oxygen on the surface-modified
AC samples. However, these surface nitrogen and oxygen dopants
should almost equally contribute to the production of active sites
for the reduction of nitro compounds by hydrazine under the con-
ditions used.
For comparison, the reduction of nitrobenzene was also exam-
ined by gaseous hydrogen (2 MPa) using an AC catalyst modified by
The results of Tables 1 and 2 imply that the reduction of
nitrobenzene may be improved by the presence of surface oxygen
100
80
60
40
20
0
NO2
NH2
+ 3/2N2H4
- 2H2O, - 3/2N2
Aniline
Nitrobenzene
+ 1/2N2H4
- 1/2N2
0
5
10
15
20
Total amount of surface O and N (%)
Ethylbenzene
Styrene
Fig. 1. Plot of the conversion of nitrobenzene reduction against the total amount of
Scheme 1. Reduction of nitrobenzene and styrene by hydrazine.
surface oxygen and nitrogen for several treated and untreated AC catalysts.

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S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
Table 3
Influence of a small quantity of water on the results of 3-nitrostyrene reduction by
hydrazine over two selected catalysts.
Entry Surface treatment
Watera
Conversion (%) Selectivity (%)b
NO2
NH2
1
2
3
1
2
1
2
3
4
H2O2
H2O2
–
14
19
14
18
53
41
69
46
36 11
48 11
ꢀ
H2O2 → NH3 90%, 600 ◦
C
C
–
24
45
7
9
NH2
NO2
3-Nitrostyrene
H2O2 → NH3 90%, 600 ◦
ꢀ
3
Reaction conditions: catalyst 10 mg, 3-nitrostyrene 3.8 mmol, hydrazine 4 cm3, water
0.02 cm3, temperature 100 ◦C, and time 10 min.
a
Water added (ꢀ); not added (–).
b
1: 3-ethylnitrobenzene; 2: 3-vinylaniline; 3: 3-ethylaniline.
Scheme 2. Reduction of 3-nitrostyrene to 3-ethylnitrobenzene (1), 3-vinylaniline
(2), and 3-ethylaniline (3).
Fig.
3 shows the plot of product selectivity against 3-
nitrostyrene conversion for the two selected catalysts of entries 4
and 7 of Table 2. For the AC catalyst modified by hydrogen per-
oxide, the selectivity to 1 decreased with conversion, that to 2
also decreased but more slightly, and that to the final product of
3 increased; 3 was formed more dominantly through the reduc-
tion of 1 rather than 2. The selectivity at a conversion close to 100%
was 3 > 2 > 1. In contrast, for the catalyst treated by hydrogen per-
oxide and ammonia, the selectivity to 1 decreased more markedly
with conversion while that to either 2 or 3 increased. At a high con-
version of about 90%, the selectivity to 2 was larger than that to
3 and the selectivity to 1 was the smallest. These results indicate
an interesting fact that the presence of surface nitrogen suppresses
the reduction of 2 to 3; namely, the reduction of the vinyl group of
2 becomes more difficult. At an early stage of reaction, 1 is formed
in a large quantity and so the reduction of its vinyl group cannot be
inhibited.
The reduction of a nitro group by hydrazine yields two water
molecules. The influence of water on the conversion and selectiv-
ity was examined by making reaction runs in the presence of a small
quantity of water at the start of reaction. The results obtained are
given in Table 3, indicating that the presence of water did not affect
the total conversion so much for the two AC catalysts (used in the
runs of Fig. 3) but changed the product selectivity. The selectivity to
2 was increased by water while that to 1 was decreased; the selec-
tivity to 3 was similar at similar conversion levels (entries 1 and 2,
entries 3 and 4). The effects of water were not different between
the two catalysts. These results suggest that the difference in the
selectivity pattern observed with the two catalysts is caused by that
in the contents of surface oxygen and nitrogen species (Table 1).
The presence of water does not induce such a negative effect as
catalyst deactivation. The effects of water observed are difficult to
explain at present and further work is needed. We should consider
the interactions of water molecules with the surface of catalyst and
the reacting species of substrate and/or intermediate. It is known
that water will act as a reaction promoter in organic synthetic reac-
tions with homogeneous catalysts in which water could change
the reactivity of reactive functional groups at the aqueous–organic
interface [16]. For those using heterogeneous catalysts, water will
also serve as a promoter in different manners [17]. Infrared spec-
troscopy may be useful to examine the interactions of water with
organic substrates and intermediates [18,19].
ammonia at 800 ◦C while keeping the other conditions unchanged
(Table 2). No reaction was found to occur, indicating that nitroben-
zene was not reduced by gaseous hydrogen under the conditions
used.
3.3. Reduction of 3-nitrostyrene
The results of the reduction of a bifunctional substrate of 3-
nitrostyrene (Scheme 2) are also presented in Table 2. The parent
AC catalyst gave a conversion of 62% (entry 2), slightly larger than
a conversion of 55% in the absence of catalyst (entry 1). The treat-
ment with hydrogen peroxide was effective to enhance its activity,
increasing the conversion to 97% (entry 4). In addition, the treat-
ment caused a significant change in the product selectivity (entries
1, 2 and 4). The untreated AC gave 3-ethylnitrobenzene 1 in the
largest selectivity of 46% (entry 2) while the hydrogen peroxide-
treated AC produced 1 in a selectivity 13% but 3-ethylaniline 3 in
58% (entry 4). These results imply that nitro group of 3-nitrostyrene
becomes more reactive on the surface of AC modified by hydrogen
peroxide, which has a larger content of oxygen (Table 1). The treat-
ment with ammonia gave a catalyst that had a similar catalytic
activity as observed with the parent AC (entries 2 and 5). A larger
conversion of 93% was also obtained with the catalyst treated by
hydrogen peroxide and then ammonia (entry 7). This catalyst gave
a similar smaller selectivity to 1 (10%) but a larger selectivity to 2
(54%) as compared to the catalyst treated with hydrogen peroxide
alone. Similar to nitrobenzene (Fig. 1), the total conversion tends
to increase with the total amount of surface oxygen and nitrogen
species (Fig. 2).
100
80
60
40
20
0
Furthermore, the influence of reaction temperature was exam-
ined using a selected catalyst. Table 4 shows the results of reaction
runs at 60, 80, and 100 ◦C, in which the reaction time was varied to
compare the product selectivity at similar conversion levels. When
the temperature was raised, the selectivity to 1 tended to increase
while that to 2 decrease but not so markedly. Then, one may say that
the reduction temperature does not affect the product selectivity
so much under the conditions used. Table 4 shows again that the
catalyst is selective for the production of 2 through the reduction of
the nitro group in the reduction of 3-nitrostyrene after considering
0
5
10
15
20
Total amount of surface O and N (%)
Fig. 2. Plot of the conversion of 3-nitrostyrene reduction against the total amount
of surface oxygen and nitrogen for several treated and untreated AC catalysts.

S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
261
100
80
60
40
20
100
(a)
(b)
80
60
40
20
3
2
3
1
2
1
0
0
0
20
40
60
80
100
0
20
40
60
80
100
Conversion (%)
Conversion (%)
Fig. 3. Plot of the product selectivity against the total conversion of 3-nitrostyrene reduction by hydrazine over two selected AC catalysts treated by hydrogen peroxide and
by hydrogen peroxide and ammonia. (a) Entry 4 and (b) Entry 7 of Table 2. 1: 3-ethylnitrobenzene; 2: 3-vinylaniline; 3: 3-ethylaniline.
the contribution of non-catalytic reduction in which the product
1 is produced through the reduction of the vinyl group in a larger
selectivity.
that the selectivity to vinylaniline was enhanced in the presence of
basic ionic liquid, which suppressed its further hydrogenation to
ethylaniline [20], similar to the present treated AC surface of basic
nature.
A few previous works assume possible reaction pathways for
the transfer hydrogenation with hydrazine as shown in Scheme 3
[8,12,14]. Ozaki et al. showed the effectiveness of nitrogen- and/or
boron-doped carbon materials as a Pt-free electrode in proton
exchange membrane fuel cells [21–25]. Namely, those surface-
modified carbon materials may act as high-performance electrical
conductors. A similar change in the electrical properties is assumed
to occur for the present AC materials through the surface treat-
ments. This may contribute to facilitate the formation of diimide
N2H2, along with two electrons and two protons H+, from hydrazine
N2H4 on the carbon surface. The diimide and/or proton would then
attack the nitro group of nitrobenzene and 3-nitrostyrene adsorbed
on the surface and the vinyl group of the latter substrate, as dis-
cussed above. Ikeda et al. discussed possible structures of active
sites for oxygen reduction reaction on the surface-modified car-
bon electrode via first-principles molecular dynamics simulation
[25]. Such a model calculation will give an insight into the work-
ing active sites for the present transfer hydrogenation of organic
substrates with hydrazine over the nitrogen- and oxygen-doped
AC catalysts, for which detailed surface characterization is not
easy.
3.4. Implication of surface hetero dopants in the reduction
Carbon can serve as an adsorbent and an electrical conductor
[8,11] and these functions should be taken into account to discuss
the above-mentioned impact of the surface modifications of AC on
its catalytic performance. The present AC-derived materials can be
a catalyst for the reduction of nitrobenzene and 3-nitrostyrene by
hydrazine but not for styrene; the doping of oxygen and nitrogen
species promotes the reduction of nitro groups but the reduction
of vinyl group of vinylaniline is suppressed by the presence of sur-
face nitrogen species, resulting in an increase in its selectivity. It is
difficult at present to discuss the structural features of the surface
modified AC materials in detail. However, the authors consider a
possibility that the doping of either a 5B element of nitrogen or a
6B element of oxygen to produces some polar sites on the surface of
AC composed of a 4B element of carbon. These polar sites are likely
to adsorb polar nitro group of nitrobenzene and 3-nitrostyrene and,
hence, the surface-treated AC materials may act as a catalyst for the
reduction of their nitro group. Less polar vinyl group is difficult to
be adsorbed on those polar sites and so styrene cannot be reduced;
for 3-nitrostyrene, however, it can be adsorbed on the AC catalysts
through its nitro group and there is a chance for its vinyl group to
be reduced to some extent. For vinylaniline, in contrast, the reduc-
tion of its vinyl group is not possible because the adsorption of
the vinylaniline is difficult to occur due to repulsive interactions
of its amino group with basic sites formed on the surface of AC
by the doping of nitrogen. Beier et al. used supported platinum
particles for reduction of 3-nitrostyrene by hydrogen and showed
Probably, those effects on the adsorption of the substrates and
the reactivity of the reducing agent would be responsible for the
catalytic performance of nitrogen- and oxygen-doped AC materi-
als in the chemoselective hydrogenation of nitrobenzene, styrene,
and 3-nitrostyrene. It is interesting that the doping of hetero atoms
to the surface of carbon-based catalysts, which produces polar
sites (C N, C O) on their surface, is an effective way in promoting
2H+
2H+
N2H2
N2
(a)
(b)
N2H4
N2H2
+
2e-
2e-
+
Table 4
Influence of reaction temperature on the reduction of 3-nitrostyrene by hydrazine
over a selected catalyst (entry 4 of Table 2).
+
+
Entry Temperature
(◦C)
Time
(min)
Conversion Selectivitya (%)
(%)
H+
1
2
3
R-NO2
R-C=C
R-NH2
R-C-C
(c)
63 (22)b
67 (24)b
69 (35)b
18 (69)b 45 (21)b 37 (10)b
16 (72)b 43 (17)b 41 (11)b
23 (50)b 37 (25)b 40 (25)b
N2H2
1
2
3
60
80
100
225
90
60
H+
N2H2
(d)
Reaction conditions: catalyst 10 mg, 3-nitrostyrene 3.8 mmol.
a
1: 3-ethylnitrobenzene; 2: 3-vinylaniline; 3: 3-ethylaniline.
Figures in parentheses are conversion and selectivity values obtained in the
b
Scheme 3. Possible pathways for the reduction of nitro and vinyl groups by
absence of catalyst.
hydrazine [8,12,14].

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S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 257–262
organic synthetic reactions and controlling their product distribu-
tion patterns. A similar phenomenon appears with a quadrupole
molecule of CO2, which interacts with nitro and other functional
groups of organic substrates, promoting the rate of liquid-phase
reaction and the product selectivity in selective hydrogenation and
other reactions [26–29].
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Acknowledgement
This work was supported by Japan Society for the Promo-
tion of Science Grant-in-Aid for Challenging Exploratory Research
23656499.