Low-temperature and highly efficient liquid-phase catalytic nitration of chlorobenzene with NO2: Remarkably improving the para-selectivity in O2-Ac2O-Hβ composite system

Article abstract of DOI:10.1016/j.apcata.2020.117468

In this work, we developed a low-temperature and efficient approach for the highly selective preparation of valuable p-nitrochlorobenzene from the liquid-phase catalytic nitration of chlorobenzene with NO₂ in O₂-Ac₂O-Hβ composite system. The results demonstrated that the introduction of molecular oxygen remarkably enhanced the chlorobenzene conversion and the cooperation catalysis of Hβ zeolite and Ac₂O envidently improved the selectivity to para-nitro product. Under the optimized reaction conditions, 93.6 % of the selectivity to p-nitrochlorobenzene with 84.0 % of chlorobenzene conversion was obtained, and the ratio of p-nitrochlorobenzene to o-nitrochlorobenzene could reach up to 20.3. Furthermore, the selectivity distribution of nitration products was reasonably explained by the density functional theory (DFT) calculation. Finally, the possible nitration reaction pathway of chlorobenzene with NO₂ was suggested in O₂-Ac₂O-Hβ composite catalytic system. The present work affords a new and mild nitration approach for highly selective preparation of valuable para-nitro products, and has potential industrial application prospects.

Full text of DOI:10.1016/j.apcata.2020.117468

Journal Pre-proof
Low-temperature and highly efficient liquid-phase catalytic nitration of
chlorobenzene with NO : Remarkably improving the para-selectivity in
2
O -Ac O-H␤ composite system
2
2
Renjie Deng (Methodology) (Writing - original draft), Kuiyi You
Supervision) (Methodology) (Investigation), Wenjin Ni, Fangfang
Zhao, Pingle Liu, He’an Luo (Supervision) (Methodology)
Investigation)
(
(
PII:
S0926-860X(20)30061-2
DOI:
https://doi.org/10.1016/j.apcata.2020.117468
APCATA 117468
Reference:
To appear in:
Applied Catalysis A, General
Received Date:
Revised Date:
Accepted Date:
24 December 2019
6 February 2020
13 February 2020
Please cite this article as: Deng R, You K, Ni W, Zhao F, Liu P, Luo H, Low-temperature and
highly efficient liquid-phase catalytic nitration of chlorobenzene with NO : Remarkably
2
improving the para-selectivity in O -Ac O-H␤ composite system, Applied Catalysis A,
2
2
General (2020), doi: https://doi.org/10.1016/j.apcata.2020.117468

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Low-temperature and highly efficient liquid-phase catalytic nitration
of chlorobenzene with NO : Remarkably improving the
O-Hβ composite system
2
para-selectivity in O
2
-Ac
2
a,c
a,b,
a
a
a,b
Renjie Deng , Kuiyi You *, Wenjin Ni , Fangfang Zhao , Pingle Liu ,
and He’an Luo a,b,*
a
School of Chemical Engineering, Xiangtan University, Xiangtan 411105,
P.R. China
b
National & Local United Engineering Research Center for Chemical
Process Simulation and Intensification, Xiangtan University, Xiangtan
4
11105, P. R. China
c
College of Material and Chemical Engineering, Hunan Institute of
Engineering, Xiangtan 411105, P.R. China
*Corresponding author
Tel.: +86-731-58293545; Fax: +86-731-58298267.
E-mail address: kuiyiyou@xtu.edu.cn(K.You); hluo@xtu.edu.cn (H. Luo)
1

Graphical abstract:
Cl
Cl
NO2
（
4.6%）
Cl
o
NO2
35 C, 4 h
（
93.6%）
NO2
Cl
Conversion： 84%
Ac O
O2
2
（
1.8%）
NO2
Hβ zeolite
Highlights





A low-temperature and highly efficient nitration approach has been
developed.
The introduction of molecular oxygen remarkably enhanced the
substrate conversion.
Cooperation catalysis of Hβ zeolite and Ac
2
O envidently improved the
para- selectivity.
The selectivity distribution of nitration products was explained by
DFT calculation.
The possible catalytic nitration mechanism was suggested in
O
2
-Ac O-Hβ system.
2
Abstract
In this work, we developed a low-temperature and efficient approach
for the highly selective preparation of valuable p-nitrochlorobenzene
2

from the liquid-phase catalytic nitration of chlorobenzene with NO in
2
O -Ac O-Hβ composite system. The results demonstrated that the
2
2
introduction of molecular oxygen remarkably enhanced the
chlorobenzene conversion and the cooperation catalysis of Hβ zeolite and
Ac O envidently improved the selectivity to para-nitro product. Under
2
the optimized reaction conditions, 93.6% of the selectivity to
p-nitrochlorobenzene with 84.0% of chlorobenzene conversion was
obtained, and the ratio of p-nitrochlorobenzene to o-nitrochlorobenzene
could reach up to 20.3. Furthermore, the selectivity distribution of
nitration products was reasonably explained by the density functional
theory (DFT) calculation. Finally, the possible nitration reaction pathway
of chlorobenzene with NO was suggested in O -Ac O-Hβ composite
2
2
2
catalytic system. The present work affords a new and mild nitration
approach for highly selective preparation of valuable para-nitro products,
and has potential industrial application prospects.
Keywords:
NO2;
acetic
anhydride;
molecular
oxygen;
p-nitrochlorobenzene; Hβ zeolite
3

1
. Introduction
Nitration of aromatic compounds is one of the most important
organic reactions in synthesis field, which provides many important
organic intermediates for manufacturing pharmaceuticals, agrochemicals,
energetic materials and fine chemicals [1]. For example,
para-nitrochlorobenzene (p-NCB), is an important and versatile
intermediate for producing dyes, rubber chemicals, perfumes,
pharmaceuticals, and so on [2]. The industrial production of p-NCB still
employed the conventional mixed-acid (nitric acid and concentrated
sulphuric acid) nitration method. However, the mixed-acid process suffers
from many disadvantages, including poor chemo-selectivity of
destination product (the ratio of p-NCB to ortho-nitrochlorobenzene
(
o-NCB) (p/o) is only close to 2.0), high reaction temperature [3], severe
corrosion of the equipment, and the generation of large quantities of
acidic wastewater resulted in environmental pollution [4] .
Due to the commercial importance and demand of p-NCB, a lot of
studies have focused on improving the para-selectivity. Martyn et al.
investigated the nitration of chlorobenzene (CB) in the presence of the
acidic imidazole-cation ionic liquids, and the p/o ratio was about 3.0 [5].
Gigante et al. reported the copper nitrate gave 98% yield with 6.5 of p/o
ratio (85:13) employing fuming nitric acid as nitration reagent [6].
Choudhary et al. claimed the p/o ratio could reach to 11.5 (92:8) using
4

3
+
Fe exchanged montomorillonite-K10 as catalyst in the nitric acid-acetic
anhydride (HNO -Ac O) system [7]. Masci had reported that the
3
2
para-selectivity was significantly improved by complexing the nitronium
ion with crown ether [8]. Moreover, Mishra et al. reported a high p/o ratio
(15.66) employing the transition metal pillared clay as catalyst in
HNO -Ac O system [9]. However, the above-mentioned these processes
3
2
have more or less disadvantages, such as long reaction time, high reaction
temperature, high catalyst cost, and so on. All these factors maybe
prevent the large-scale industrial applications. Therefore, developing a
highly efficient catalyst to further enhance the para-selectivity under the
mild conditions is becoming an attractive target in the academic and
industrial fields [10].
Recently, solid acid catalysts have been extensively investigated for
the liquid or vapor-phase nitration process, which include zeolite [11],
solid superacid [12] and heteropolyacid [13], etc. Among these solid acid
catalysts, it is well known that zeolites as solid acid catalysts have
well-defined pore structure and adjustable acidity. The shape-selective
catalysis of zeolite has been applied in a large variety of reactions. In
recent years, various zeolite catalysts instead of traditional sulfuric acid
have also been applied to the nitration of aromatic compounds, which
involve zeolite or modified zeolite, such as HZSM-5 [14], H PO /ZSM-5
3
4
[
15], β-zeolite [11], HY zeolite [16] etc. These zeolite catalysts can
5

effectively play the role on the improvement of product selectivity.
In addition, regarding to nitrating agents studied at present mainly
included NO (N O ) [17], N O [18], nitrate salts [19], acetyl nitrate [20]
2
2
4
2
5
and Liquid Ag K Na NO [21] in the nitration process. As is known
0
.51 0.42
0.07
3
to all, the industrial nitric acid commonly used as nitrating agent at
present is manufactured from lower nitrogen oxides via a multi-step
process. Therefore, NO directly acted as a non-acidic nitration reagent
2
instead of the traditional nitric acid for the aromatic nitration has received
wide attentions [22].
In this work, we developed a low-temperature and efficient nitration
approach for the highly selective preparation of p-NCB from the
liquid-phase nitration of chlorobenzene (CB) employing NO as green
2
nitrating agent promoted by molecular oxygen in Ac O-Hβ composite
2
catalytic system. Likewise, for the nitration of other mono-substituted
benzenes (fluorobenzene, bromobenzene, iodobenzene, toluene and
anisole), the selectivities to para-nitro products were also improved in
this composite catalytic system. The obtained results were discussed in
detail in this paper.
2
. Experimental
2
.1. Reagents and instruments
CB (AR) and acetic anhydride (AR) were purchased from Macklin
Reagent Corporation and the trace water was removed by activated 4Å
6

molecular sieve. NO (purity >99.9%) was purchased by Chendu Keyuan
2
Gas Company, China. The other reagents were obtained from Aladdin
Industrial Corporation. Some zeolites (such as Hβ (Si/Al =25, 40 and 60),
HY (Si/Al=5) and HZSM-5 (Si/Al=38)) and molecular sieve MCM-41
were obtained from the Catalysis Centre of Nankai University. The gas
chromatography-mass
spectrometry
(GC-MS)
(Shimadzu,
GCMS-QP2010Plus) was used as the qualitative analysis of products.
The quantitative analysis of products were performed on the GC (Agilent
7
890B) with hydrogen flame ion detector (FID) and a DB-1701 (30
m×0.32 mm×0.25 um) column using an internal standard method.
2
.2. Preparation of Treated Hβ (25) zeolite
In order to further reveal the micro-structure changes of Hβ (25)
zeolite in NO -O -Ac O composite system, the Hβ (25) zeolite was
2
2
2
treated in the NO -O -Ac O composite system without CB. The treatment
2
2
2
process was as follows: Firstly, Hβ (25) zeolite (0.3 g) was added into the
mixed solution of NO (4.2 g) and Ac O (5.0 g) in 100 ml stainless steel
2
2
reactor. Then, the molecular oxygen was introduced into the reactor, and
the pressure was maintained at 0.5 MPa. The sealed reactor was stirred at
o
3
5 C for 6 h. Finally, the resulted solid was separated by filtration and
o
dried at 60 C for 3 h. The obtained sample was marked as “Treated Hβ
(25) zeolite”.
2
.3. Characterization of catalyst
7

The N adsorption-desorption characterization of samples was
2
performed on an ASAP 2020 (Micrometrics, USA) at 77 K. The surface
areas of samples were measured by Brunauer-Emmett-Teller (BET)
method. The micropore areas of samples were accorded to t-plot method,
and the pore size distributions were analyzed by Saito-Foley (SF) method.
The XRD patterns of samples were recorded by a Japan Rigaku
+
D/Max-2550V diffractometer with Cu Kα radiation (λ=1.5418 Å) at 40
kV voltage and 300 mA electric current. Thermogravimetric/derivative
thermogravimetric (TG/DTG) characterizations of samples were
conducted on a Mettler TGA/DSC1/1600HT analyzer under N2
atmospher. The fourier transform infrared spectroscopy (FT-IR) spectra of
samples were recorded using a Nicolet 380 instrument in KBr matrix. The
ammonia temperature-programmed desorption (NH -TPD) curves were
3
obtained at Chembet-3000 instrument with 10 vol% NH in Ar (30 mL
3
-
1)
o
o
-1
min from 100 to 800 C at a rate of 10 C min . The infrared spectra of
pyridine adsorption (Py-FT-IR) of samples were examined using a
-
1
Thermo Nicolet 380 spectrometer in the range of 1400-1650 cm . The
X-ray photoelectron spectroscopies (XPS) spectra of samples were
obtained on a Thermo Scientific ESCALAB 250Xi spectrometer with Mg
Kα radiation, and the binding energy referred to the C 1s peak (284.6 eV).
2
.4. Typical experimental process
The liquid-phase catalytic nitration reaction of mono-substituted
8

benzenes with NO was carried out in a 100 ml stainless steel reactor.
2
Typically, CB (5.0 g), cold liquid NO (4.2 g), acetic anhydride (2.0 g)
2
and catalyst (0.3 g) were added into the reactor. Molecular oxygen was
introduced into the autoclave and the oxygen pressure was maintained at
o
0
.5 MPa. The sealed reactor was stirred at 35 C for 6 h. After the
reaction, the catalyst was filtered and the reaction solution was fully
dissolved in acetonitrile. The resulted solution was analyzed by GC and
GC-MS. For the nitration of CB, the nitration products are o-NCB,
m-nitrochlorobenzne (m-NCB) and p-NCB. The conversion of CB and
selectivity to p (m or o)-NCB was calculated using the following
formulas:
the mole of CB reacted
Conversion of CB (%) =
× 100%
the mole of CB added
the mole of p(m or o)-NCB
Selectivity to p(m or o)-NCB (%) =
× 100%
the mole of CB reacted
2
.5. Theoretical background and computational details
As is well known that the density functional theory (DFT) and Fukui
function [23] are used to describe the chemical reactivity and charge
+
distribution of chemical compounds. The electron gain f (r) is defined as
-
the index for the nucleophilic attack ability, the electron donation f (r) is
0
+
defined as the index for the electrophilic attack ability, and f (r)=(f (r) +
f -(r))/2, represents the radical attack reactivity. The condensed Fukui
9

functions are based on the natural bond orbital (NBO) analysis [24]. For
the atom a in a target molecule, for example, the condensed Fukui
functions f are:
a
+
f = q (N+1)-q (N)
a
a
a
-
f = q (N)-q (N-1)
a
a
a
0
f = (q (N+1)-q (N-1))/2
a
a
a
where q (N+1), q (N), and q (N-1) represent the total NBO charges on
a
a
a
atom a with N+1, N, and N-1 electrons, respectively. The Fukui function
-
value (f (r)) used as the index for electrophilic reactivity of the typical
carbon atoms (ortho-C, meta-C, and para-C) in the molecular structure of
mono-substituted benzenes were calculated. All the geometrical
configurations for mono-substituted benzenes, mono-nitro benzenes and
transition states were calculated by using DFT B3LYP/6-31+G (d) level
with the GAUSSIAN-03 package, version 3.6.
3
. Results and discussion
3
.1. Comparison on the nitration reaction results in different systems
The nitration of CB with NO had been studied in different reaction
2
systems and the results were summarized in Table 1. As can be seen, CB
conversion was remarkably enhanced from 0 to 67.5% in the presence of
molecular oxygen (Entry 1-2). By contrast, the nitrogen was introduced
into the nitration system, the nitration reaction was not occurred (Entry 3).
Likewise, Hβ (25) zeolite did not play a role in the nitration reaction in
10

absence of molecular oxygen (Entry 4). The results demonstrated that the
molecular oxygen played a crucial role on improving the nitration ability
of NO . However, CB conversion and selectivity to p-NCB were slightly
2
improved (Entry 5-7) as the Hβ zeolites with different Si/Al ratio were
added into the reaction system. These results suggested that the Hβ
zeolites exhibited some catalysis on the nitration reaction in the presence
of molecular oxygen. It's worth mentioning that, the selectivity to p-NCB
was significantly enhanced as the acetic anhydride (Ac O) was
2
introduced into the nitration reaction (Entry 8). Moreover, CB conversion
was improved obviously in the presence of molecular oxygen (Entry 9).
In order to further verify the synergistic catalysis between Ac O and Hβ,
2
the NO -Ac O, NO - acetic acid (AC), NO -O -Ac O and NO -Ac O-Hβ
2
2
2
2
2
2
2
2
(25) systems were also studied (Entry 10-13). The results showed that the
molecular oxygen played a crucial role on boosting the nitration ability of
NO , and the synergic catalytic effect of Hβ (25) and Ac O resulted in
2
2
improving the para-selectivity. The possible reasons were as follows. In
this nitration process, the acetyl nitrate (AcONO ) formed from Ac O and
2
2
NO could be chemically bonded in the pore of Hβ zeolite. CB reacted
2
with the bonded AcONO by the electrophilic reaction in the pore of Hβ
2
zeolite, which resulted in the formation of transient Wheland
intermediates (Wheland intermediates: In the case of σ-attracting and
π-donating groups, the ortho- and para-orientation of the second
11

substitution is rationalized through the analysis of the resonance forms
describing the π-system of the different possible cationic intermediates,
also called σ-complex) [25, 26]. Due to the steric hindrance effects, the
ortho-site and meta-site Wheland intermediates were difficult to be
formed, while the para-site Wheland intermediate with the least steric
hindrance was easy to be formed. Therefore, the para-nitro product was
dominant. Under the present reaction conditions, 66.4% of CB conversion
with 92.8% of selectivity to p-NCB was obtained in the
NO -O -Ac O-Hβ (25) system. In addition, the catalytic performances of
2
2
2
other molar sieves (such as HZSM-5, HY and MCM-41) were also tested
in NO -O -Ac O systems, and the reaction results were unsatisfactory
2
2
2
(Entry 14-16). These results demonstrated that the cooperation catalysis
of Hβ (25) zeolite and Ac O evidently improved the selectivity to
2
para-nitro product, and the introduction of molecular oxygen remarkably
enhanced the reaction conversion.
3
.2. Optimization of the nitration reaction conditions
Firstly, the effects of the amounts of Ac O and catalyst Hβ (25) on
2
the nitration reaction were investigated, as shown in Fig. 1A and 1B,
respectively. The results showed that an appropriate amount of Ac O and
2
catalyst can effectively improve CB conversion and selectivity to p-NCB.
Then, the effects of oxygen pressure and molar ratio of CB to NO were
2
also studied, and the obtained results were depicted in Fig. 1C and 1D,
12

respectively. Clearly, CB conversion was remarkably increased with
oxygen pressure, which indicated that the molecular oxygen efficiently
promoted the nitration reaction of CB with NO . Furthermore, the molar
2
ratio of reactants was also a very important factor for the nitration, under
the present reaction conditions, the appropriate molar ratio of CB to NO2
was 1:2. Finally, the effects of reaction temperature and reaction time on
A
100
50
40
30
20
10
0
B
100
90
80
70
60
50
40
30
20
10
0
50
40
30
20
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Conversion of CB
Selectivity to p-NCB
p/o ratio
Conversion of CB
Selectivity to p-NCB
p/o ratio
0
1
2
3
4
5
6
7
8
9
10 11
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Amount of Ac O (g)
2
Amount of catalyst (g)
C 100
40
D100
90
80
70
60
50
40
30
20
10
0
40
35
30
25
20
15
10
5
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
3
3
2
5
0
5
20
1
1
5
0
5
0
Conversion of CB
Selectivity to p-NCB
p/o ratio
Conversion of CB
Selectivity to p-NCB
p/o ratio
0
0
.1
0.2
0.3
0.4
0.5
0.6
0.7
1:0.5
1:1
1:2
1:2.5
1:3
Oxygen pressure (MPa)
Molar ratio of CB to NO
2
E100
40
F 100
90
40
35
30
25
20
15
10
5
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
3
3
2
5
0
5
80
70
60
20
50
40
1
5
Conversion of CB
Selectivity to p-NCB
p/o ratio
30
Conversion of CB
Selectivity to p-NCB
p/o ratio
10
5
20
10
0
0
0
2
5
30
35
40
45
1
2
3
4
5
6
o
Reaction temperature ( C)
Reaction time (h)
Fig. 1 Effects of the amounts of Ac O (A) and Hβ (25) (B), oxygen
2
pressure (C), molar ratio of CB to NO (D), reaction temperature (E) and
2
13

reaction time (F) on CB conversion, selectivity to p-NCB and p/o ratio.
Reaction conditions: (A) the molar ratio of CB to NO is 1:2, reaction
2
o
temperature is 35 C, reaction time is 4 h, the oxygen pressure is 0.5 MPa,
and the amount of Hβ (25) is 0.3 g; (B) the molar ratio of CB to NO is
2
o
1
:2, reaction temperature is 35 C, reaction time is 4 h, the oxygen
pressure is 0.5 MPa and the amount of Ac O is 5.0 g;(C) the molar ratio
2
o
of CB to NO is 1:2, reaction temperature is 35 C, reaction time is 4 h,
2
the amount of Ac O is 5.0 g and the amount of Hβ (25) is 0.2 g; (D) the
2
o
reaction temperature is 35 C, reaction time is 4 h, the oxygen pressure is
0
.5 MPa, the amount of Ac O is 5.0 g and the amount of Hβ (25) is 0.2 g;
2
(
E) the molar ratio of CB to NO is 1:2, reaction time is 4 h, the oxygen
2
pressure is 0.5 MPa, the amount of Ac O is 5.0 g and the amount of Hβ
2
(
25) is 0.2 g; (F) the molar ratio of CB to NO is 1:2, reaction temperature
2
o
is 35 C, the oxygen pressure is 0.5 MPa, the amount of Ac O is 5.0 g and
2
the amount of Hβ (25) is 0.2 g.
the nitration were also studied, as shown in Fig. 1E and 1F. The results
showed that the reaction temperature and time had a litttle influences on
the conversion of CB, and the selectivity to p-NCB and the p/o ratio was
almost unchanged. Therefore, from the considerations of CB conversion
and selectivity to p-NCB, the suitable reaction conditions were as follows:
the amounts of Ac O and catalyst Hβ (25) were 5.0 g and 0.2 g,
2
respectively; the pressure of oxygen was 0.5 MPa, the molar ratio of CB
o
to NO was 1:2, the nitration temperature was 35 C, and the reaction
2
time was 4 h. Under the optimal reaction conditions, 84.0% of CB
conversion with 93.6% of selectivity to p-NCB was achieved, and the p/o
14

ratio was reached up to 20.3 in Ac O-O -Hβ (25) system.
2
2
3
.3. Comparison on the nitration reaction results in the different catalytic
systems
The obtained results from the catalytic nitration reaction of CB in
the different systems reported in previous literatures were compared, as
shown in Table 2. Although some catalytic systems showed relatively
high conversion of CB, most kinds of them had various disadvantages
such as environmentally unfriendly, expensive and complex catalyst, high
reaction temperature, long reaction time, and use of solvent, which
restricted their further applications. In our developed catalytic system,
9
4% of selectivity to p-NCB with 84.0% of CB conversion was achieved,
and the p/o ratio was reached up to 20.3.
3
.4. The nitration of other mono-substituted benzenes with NO2
The nitration reactions of other mono-substituted benzenes (such as
flurobenzene, bromobenzene, idobenzene, toluene and anisole) with NO2
were also investigated in O -Ac O-Hβ (25) system, and the obtained
2
2
results were listed in Table 3. As can be seen, the substrate conversion
was remarkably enhanced as the molecular oxygen was introduced to the
nitration reaction. Especially, the selectivity to para-nitro products was
further improved as Hβ (25) zeolite catalyst and Ac O were together
2
introduced to the nitration reaction. These results indicated that the
15

present O -Ac O-Hβ (25) nitration system could be also applied to the
2
2
nitration of other mono-substituted benzenes with NO2.
.5. DFT calculations on the nitration reaction of mono-substituted
3
benzenes with NO2
In order to further explain the selectivity distribution of nitration
products from the molecular configuration, the DFT computational
methods were employed. All the NBO charges and geometrical
configurations of aromatic compounds and aromatic nitro-compounds
were calculated by using DFT calculations at the B3LYP/6-31G+(d) level.
The obtained results were showed in Table 4-6 and Fig. 2.
The results of NBO charges and condensed Fukui function values of
typical carbon atom (ortho-C, meta-C, and para-C) in the molecular
structures of mono-substituted benzenes were listed in Table 4, and the
energies for the transition states of different nitro-substituted benzenes
+
with NO were showed in Table 5. The condensed Fukui function value
2
f-(r) is used as the index for electrophilic reactivity in Table 4. It is clear
-
that the f (r) value of the para-site is the highest in the halogenated
benzenes (such as CB, flurobenzene, bromobenzene and idobenzene),
which indicates that the para-nitro halogenated bezene is easy to be
formed. This agrees with our experimental results. Furthermore, the
energies of three possible transition states (E(ts_m-), E(ts_o-) and
+
E(ts_p-)) in each mono-substituted benzene with NO are also calculated,
2
16

as shown in Table 5. The energy order of three possible transition states
in the nitration of halogenated benzenes is as follows:
E(ts_m-)>E(ts_o-)>E(ts_p-). As is well-known, the transition state with
lower energy is easy to be formed. Therefore, the selectivity to para-nitro
products should be higher than other nitro-products. Our experimental
results also confirmed that the selectivity to para-nitro products was the
highest in the nitration of halogenated benzenes. However, for the
nitration of toluene and anisole, the energy order of the three possible
transition states is as follows: E(ts_m-)>E(ts_p-)>E(ts_o-), which
demonstrated that the ts_o- is the most stable transition state. Therefore,
the selectivity to ortho-nitro products should be higher than other
nitro-products. This is consistent with our experimental results in the
nitration of toluene and anisole.
Fig. 2 depicts the formation pathway of three transition states (TS-1,
TS-2 and TS-3), and the calculated energies of the transition states and
nitration products are also listed. The calculated results indicate that the
molecular structures of transition states are stereo-structures, and the nitro
group and CB are not in the same plane. However, all atoms of final
nitration products were coplanar. It is also clearly seen that the energy of
the TS-3 (formed by attacking the para-position of CB) and resulted
p-NCB is lowest. Therefore, the selectivity to p-NCB is also highest in
our experimental results.
17

Fig. 2 The energies for transition states and products in the nitration of
+
CB with NO
2
Furthermore, in order to further illustrate the shape-selective effects
of Hβ zeolite on the selectivity distribution of nitration products, the
molecular diameters of mono-substituted benzene substrates and their
nitration products were calculated, as listed in Table 6. The results
showed that the molecular diameters of reactants and para-nitro products
were about 0.43 nm, the molecular diameters of ortho- and meta-nitro
products were between 0.51 to 0.57 nm, and the pore diameter of treated
catalyst is 0.48 nm. Obviously, the molecular diameters of ortho- and
meta-nitro products are larger than the pore size of catalyst, while the
molecular diameters of para-nitro products are less than the pore size of
catalyst. This means that the ortho- and meta-nitro products are difficult
to be generated in the pore channels of catalyst. These results also explain
18

the reason that the selectivities to para-nitro products are remarkably
enhanced after the addition of catalyst.
3
.6. The recycling of Hβ (25) zeolite in the nitration reaction
The stability of Hβ (25) zeolite was examined in present nitration
reaction. The catalyst after the reaction was filtered, washed with
o
acetonitrile, and dried at 100 C for 6 h. The used catalyst after five runs
o
was regenerated by calcination at 550 C for 4 h. The catalytic reaction
results of catalyst in five runs were depicted in Fig. 3. Obviously, Hβ (25)
zeolite showed the acceptable stability in the catalytic nitration reaction,
CB conversion and selectivity to p-NCB were only slightly decreased
after five runs. However, the spent catalyst was easy to be regenerated,
and the catalytic performance could be restored by the simple calcination
method (5a in Fig. 3). Moreover, the chemical composition of used Hβ
(25) zeolite was determined by an inductively coupled-plasma atomic
emission spectroscopy (ICP-AES). The results indicated that the content
of Si and Al was not changed after five runs.
19

Conversion of CB
Selectivity to p-NCB
100
80
60
40
20
0
1
2
3
4
5a
5
Recycling times
Fig. 3 Recycling of catalyst Hβ (25) in the nitration reaction. Reaction
o
conditions: molar ratio of CB to NO is 1:2, reaction temperature is 35 C,
2
reaction time is 4 h, oxygen pressure is 0.5 MPa, Hβ (25) is 0.2 g and
Ac O is 5.0 g. 5a stands for the recycling of regenerated catalyst.
2
3
3
.7. Characterization of catalysts
.7.1. XRD
Fig. S1 in Supported Information (SI) shows the XRD patterns of
Hβ (25) samples. As can be seen, the diffraction peaks of used and
regenerated samples well match with the characteristic peaks of zeolite
beta (JCPDS No. 47-0183). The results indicated that the Hβ (25) zeolite
exhibited good stability, and the crystalline structure was not destroyed
during the reaction [36].
20

3
.7.2. N adsorption-desorption
2
The N adsorption-desorption isotherms and the pore diameter
2
distribution curves of Hβ (25) samples are depicted in Fig. 4. The BET
surface area, micropore area, pore volume and mode pore diameter of
three samples are given in Table 7, respectively. The results showed that
all samples exhibited the type I isotherms, which was the characteristic of
classical microporous materials [37, 38]. Moreover, it can be seen that Hβ
(25) zeolite mainly possesses abundant micropores. However, the BET
surface area, pore volume and mode pore diameter of Hβ (25) sample are
slightly decreased after five runs. However, these textural properties
could be recovered by simple heat treatment. The results indicated that a
small amount of organic substances were adsorbed in the microporous of
Hβ (25) zeolite during the reaction.
21

700
600
500
400
300
200
100
0
0
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
.0
Fresh H
Five runs H
Fresh H zeolite
Used H zeolite
Regenerated H zeolite
Regenerated H
0
.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Pore diameter (nm)
0
.0
0.2
0.4
0.6
0.8
1.0
P/P
0
Fig. 4 N adsorption-desorption isotherms and pore diameter distribution
2
curves of samples
3
.7.3. FT-IR
The FT-IR spectra of Hβ (25) samples are shown in Fig. S2 in SI. It
-
1
-1
can be seen that the peaks at 3440 cm and 1630 cm are ascribed to the
OH stretch and bending vibration on the samples (including the adsorbed
water on the samples) [39], the characteristic peaks at 1220, 1090, 798
-
-
1
and 465 cm , which are assigned to the framework bands of Hβ zeolite
40]. The result demonstrates that the framework of Hβ (25) zeolite is still
remained during the reaction.
.7.4. TG-DTG
The TG-DTG curves of Hβ (25) samples are shown in Fig. S3 in SI.
[
3
22

o
Clearly, all samples exhibited a big mass loss peak below 100 C, which
is ascribed to the loss of adsorbed water. However, for used Hβ zeolite,
two new small mass loss peaks are observed, which shows that a small
quantity of organic species is deposited in the pores of Hβ (25) zeolite
during the reaction. Nonetheless, the deposited organic substances can be
removed from the pores by simple heat treatment, which shows Hβ (25)
zeolite is easy to be regenerated.
3
.7.5. NH -TPD and pyridine adsorbed FT-IR
3
Fig. 5 shows the NH -TPD curves and FT-IR spectra of pyridine
3
adsorption of the fresh, used and regeneratd Hβ zeolites. Evidently, all
o
samples exhibit two NH desorption peaks at 167 and 472 C in Fig. 5A,
3
which are assigned to the desorption of ammonia bonded on weak acid
sites and strong acid sites, respectively [41, 42]. Moreover, the weak acid
sites were still dominant in present Hβ zeolite samples. Although the acid
amount of catalyst was slightly decreased after five reuses, it was easy to
be regenerated by the calcination method. In order to further indentify the
acidic sites of the fresh, used and regenerated Hβ zeolites, the FT-IR
spectra of samples adsorbed pyridine are depicted in Fig. 5B. The peaks
-
1
at around 1445 and 1640 cm are ascribed to the characteristics of
pyridine adsorbed on Lewis acidic sites, the peak appeared at 1545 cm-1
is attributed to the characteristic of pyridine adsorbed on Brønsted acidic
-
1
sites [43]. The characteristic peak at 1490 cm is ascribed to the
23

interaction of pyridine with Lewis and Brønsted acidic sites [44]. The
results indicate that the Hβ zeolites have both the Lewis and Brønsted
acid sites.
1
00
A
B
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
a
Fresh Hzeolite
Used Hzeolite
Regenerated Hzeolite
1
67
b
c
4
72
1450
1628
1
545
1490
-
10
1
00
200
300
400
500
600
1400 1450 1500 1550 1600 1650 1700
o
-1
Temperature ( C)
Wavenumbers (cm )
Fig. 5 NH -TPD curves (A) and pyridine adsorbed FT-IR spectra (B) of
3
samples: (a) fresh Hβ zeolite, (b) used Hβ zeolite and (c) regenerated Hβ
zeolite.
3
.8. Possible nitration reaction mechanism of CB with NO in
2
Ac O-O -Hβ composite catalytic system
2
2
In order to reveal the inherent interaction between Hβ zeolite and the
NO -O -Ac O system, the Hβ (25) zeolite was treated in the
2
2
2
NO -O -Ac O system without CB, and the treated Hβ zeolite was
2
2
2
characterized by N adsorption-desorption, FT-IR, TG/DTG, NH -TPD,
2
3
Py-FT-IR and XPS. The obtained results were showed in Fig. 6-9 and
24

Table 8.
A 700
B
0
.6
0.5
.4
.3
.2
.1
.0
Fresh Hzeolite
6
00
00
00
00
00
00
FreshHzeolite
Fresh H zeolite
Treated H zeolite
0
Treated Hzeolite
0
5
0
0
4
0
1383
Treated Hzeolite
0
.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
3
Pore diameter (nm)
2
1720
3440
1630
1
798
1220
465
0
1090
0.0
0.2
0.4
0.6
0.8
1.0
4000 3500 3000 2500 2000 1500 1000 500
P/P
-1
Wavenumbers (cm )
0
Fig. 6 N adsorption-desorption isotherms (A) and FT-IR spectra (B) of
2
samples
As can be seen in Fig. 6A and Table 8, the BET surface area,
micropore area, pore volume and pore diameter of treated Hβ zeolite were
2
obviously reduced. The micropore area decreased from 457 to 259 m /g,
and the pore diameter decreased from 0.83 to 0.48 nm. The probable
reason for this phenomenon was that the formed acetyl nitrate (AcONO2)
from the reaction of NO with Ac O in the presence of molecular oxygen
2
2
was bonded in the pore of Hβ zeolite, which resulted in the decrease of
pore volume and mode pore diameter. In the subsequent nitration reaction
of the bonded AcONO with CB, the pore diameter and pore volume of
2
catalyst was also recovered.
From the comparison on the FT-IR spectra of treated and fresh Hβ
-
1
-1
zeolites in Fig. 6B, two new peaks appeared at 1383 cm and 1720 cm ,
which are attributed to the symmetric stretching vibration of the nitro
25

group (-NO ) [45, 46] and C=O stretching of the ester [47, 48],
2
respectively, are observed in the FT-IR spectrum of treated Hβ zeolite.
The results verified the formation of AcONO in the pore of Hβ zeolite.
2
Likewise, the formation of AcONO in the pore of Hβ zeolite was also
2
demonstrated from the characterization results of TG/DTG in Fig. S4 in
SI.
The NH -TPD profiles of samples were shown in Fig. 7A. It is
3
clearly seen that the acid amount and acid strength are evidently
increased, and the acid centers were transferred from weak acid centers to
strong acid centers after the Hβ (25) zeolite was treated in the
NO -O -Ac O system. The possible reason for the NH adsorption
2
2
2
3
increases was due to NH reacted with AcONO in the pore of Hβ zeolite.
3
2
Moreover, it was found that the treated Hβ zeolite still remained the
Lewis and Brønsted acid sites from the pyridine adsorbed FT-IR spectra
of samples in Fig. 7B.
In order to further reveal whether the formed acetyl nitrate (AcONO2)
was chemically bonded in the pore of Hβ zeolite, the chemical states for
typical elements (Al, N, O and C) of fresh and treated Hβ zeolites were
characterized by XPS, and the results were shown in Fig. 8. Compared to
the fresh Hβ zeolite, some new peaks at 73.6, 534.2, 532.5, 396.2 and
2
88.8 eV, which were ascribed to the Al-N binding energy [49-51], O-N
binding energy [52], O-C binding energy [53], N-Al binding energy [50]
26

and C-O binding energy [54], respectively, were observed in the XPS
spectra of treated Hβ zeolite. The results further verified that the formed
AcONO was chemically bonded in the pore of Hβ zeolite. Moreover, in
2
order to reveal whether CB was chemically bonded in the pore of Hβ
zeolite, the Hβ zeolite treated with CB was also characterized by XPS,
the obtained results were shown in Fig. 8 A, C and D. As can be seen,
compared to the fresh Hβ zeolite, no new peaks were appeared in XPS
spectra of the Hβ zeolite treated with CB. The result was verified that CB
was not chemically adsorbed on the surface of zeolite.
1
1
1
20
10
00
A
B
Fresh Hzeolite
Treated Hzeolite
Fresh H zeolite
Treated H zeolite
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
1545
1450
1490
1630
1
00 200 300 400 500 600 700 800
1400 1450 1500 1550 1600 1650 1700
o
-1
Temperature ( C)
Wavenumbers (cm )
Fig. 7 NH -TPD (A) and FT-IR pyridine adsorbed curves (B) of samples
3
27

(A)
(B)
7
4.9 eVAl-O
Al 2p
N 1s
4
00.9 eV N-O
Fresh H zeolite
7
3.6 eVAl-N
3
96.2 eV N-Al
Treated H zeolite
Treated H zeolite
H zeolite treated with CB
8
4
82
80
78
76
74
72
70
68
410 408 406 404 402 400 398 396 394
Binding energy (eV)
Binding energy (eV)
(C)
(D)
5
32.9 eV O-Si
284.6 eV C-C
O 1s
C 1s
5
32.2 eV O-H
31.8 eV O-Al
5
Fresh H zeolite
Fresh H zeolite
5
32.5 eV O-C
2
88.8 eV C-O
Treated H zeolite
H treated with CB
5
34.2 eV O-N
Treated H zeolite
H zeolite treated with CB
5
38
536
534
532
530
528
526
290
288
286
284
282
280
Binding energy (eV)
Binding energy (eV)
Fig. 8 XPS spectra of samples: (A) Al 2p spectra of fresh, treated Hβ
zeolites and Hβ zeolite treated with CB, (B) N 1s spectrum of treated Hβ
zeolite, (C) O 1s spectra of fresh, treated Hβ zeolites and Hβ zeolite
treated with CB, and (D) C 1s spectra of fresh, treated Hβ zeolites and Hβ
zeolite treated with CB.
On the basis of the results obtained above and our previous works [4,
1
7, 55], the possible nitration reaction pathway of CB with NO over Hβ
2
zeolite in the Ac O-O composite system was suggested in Scheme 1.
2
2
+
Firstly, the dimeric NO was disproportionated to nitrosyl cation (NO )
2
-
+
and nitrate ion (NO ) [56], and the formed NO was easy to be
3
+
oxygenated to NO in the presence of molecular oxygen. The formed
2
28