Synthesis, characterization and catalytic activity of copper incorporated and immobilized mesoporous MCM-41 in the single step amination of benzene

Article abstract of DOI:10.1016/j.molcata.2009.11.011

The paper reports the synthesis, surface and textural characterization of copper and amine modified MCM-41 and its application for the single step amination of benzene to aniline at 70 °C. Varying the amount of Cu different Cu/amine modified MCM-41 samples was synthesized by co-condensation and impregnation method. The samples were characterized by nitrogen adsorption-desorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FT-IR), ²⁹Si magic-angle spinning (MAS) and ¹³C Nuclear Magnetic Resonance (NMR) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. FT-IR and DRS results indicated that Cu and amino groups are incorporated into the Si-O framework and frame wall respectively. NMR showed higher degree of condensation of materials in framework position. Cu-amine-MCM-41 samples showed significant catalytic activity for single step amination of benzene in acetic acid-water medium under mild reaction conditions using hydroxylamine as aminating agent. The Cu-amine-MCM-41 (Si/Cu = 20) showed highest benzene conversion (72.2%) and 100% selectivity for aniline.

Full text of DOI:10.1016/j.molcata.2009.11.011

Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis, characterization and catalytic activity of copper incorporated and
immobilized mesoporous MCM-41 in the single step amination of benzene
∗
K.M. Parida , Dharitri Rath, S.S. Dash
Institute of Minerals & Materials Technology, Bhubaneswar 751013, Orissa, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 October 2009
Received in revised form
The paper reports the synthesis, surface and textural characterization of copper and amine modified
MCM-41 and its application for the single step amination of benzene to aniline at 70 C. Varying the
◦
amount of Cu different Cu/amine modified MCM-41 samples was synthesized by co-condensation and
impregnation method. The samples were characterized by nitrogen adsorption–desorption, X-ray pow-
1
8 November 2009
Accepted 18 November 2009
Available online 24 November 2009
2
9
der diffraction, Fourier-transform infrared spectroscopy (FT-IR), Si magic-angle spinning (MAS) and
1
3
C Nuclear Magnetic Resonance (NMR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). X-ray
diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. FT-IR
and DRS results indicated that Cu and amino groups are incorporated into the Si–O framework and
frame wall respectively. NMR showed higher degree of condensation of materials in framework position.
Cu-amine-MCM-41 samples showed significant catalytic activity for single step amination of benzene
in acetic acid–water medium under mild reaction conditions using hydroxylamine as aminating agent.
The Cu-amine-MCM-41 (Si/Cu = 20) showed highest benzene conversion (72.2%) and 100% selectivity for
aniline.
Keywords:
Co-condensation
Impregnation
Aniline
Benzene
Amination
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
ferent areas, where the organic groups play the role of providing
improved hydrophobicity and the presence of metals provide the
catalytic property [9,10]. Among the transition metals studied cop-
per is particularly interesting due to its special redox properties
and polarizability. So in the improved current state-of-art we can
design a periodic mesoporous silica material having bifunctional
sites of tunable pore size.
Since the discovery of surfactant micelle-templated synthesis of
mesoporous silica materials such as MCM-41/48, SBA-15 [1], MSU-
n [2], KIT-1 [3], FSM-16 [4], many research efforts have been focused
on the synthesis of organic/inorganic hybrid materials. This can
be done by functionalizing the exterior and interior surfaces and
controlling particle morphology. These organic/inorganic hybrid
materials with active groups are unique as they offer potential
advantages than the parent silica for various surface modifica-
tions. These materials are successfully utilized in separation, sensor
design, catalysis and drug delivery.
Among the aromatic amines, aniline is most widely used in
industries. Traditionally aniline was produced through multiple
chemical reactions. These roots have some disadvantages like
unwanted waste production, use of very high temperature and
pressure, time consumption etc. Single-step production of aniline
via the direct amination of benzene, which significantly improves
the atomic efficiency, is an attractive and challenging method from
the viewpoint of both green chemistry and synthetic chemistry. The
direct amination of benzene with ammonia in gas phase was carried
out using Ni/NiO catalo reactant or the group VIII metal catalysts
[11,12]. But these methods suffer from the needs high tempera-
The discovery of periodic, ordered mesoporous molecular sieves
M41s received considerable attention in the heterogeneous cataly-
sis area by applying these materials as support due to their high
2
specific surface area (700–1500 m /g) as well as their uniform
pore size (1.5–10 nm). Many researchers have made their efforts
to adopt the single site functionalization of MCM-41 related mate-
rials but there are very few reports and limited success is obtained
on bifunctional groups [5–8]. Bifunctional mesoporous materials
containing organic groups and transition metals can be used in dif-
◦
◦
ture (from 100 C to 1000 C) and high pressure (from 10 atm to
1000 atm), relatively low aniline yield, and/or relatively low selec-
tivity to aniline. Thus, we need enhancement of both the aniline
yield and the selectivity.
Many attempts have been made to achieve liquid phase ami-
nation of benzene with hydroxylamine over transition metal redox
catalysts [13–16]. The study of the direct amination of benzene with
hydroxylamine will help in providing information for synthesiz-
ing aniline-like molecules with ammonia and hydrogen peroxide
∗ Corresponding author at: C& MC Department, Institute of Minerals & Materials
Technology, (formerly RRL), Bhubaneswar 751013, Orissa, India.
Fax: +91 674 2581637.
E-mail address: paridakulamani@yahoo.com (K.M. Parida).
1
381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.11.011

8
6
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
Fig. 1. (A) Low angle XRD patterns of MCM-41 (a), Cu-MCM-41 (20) (b), Cu-amine-
MCM-41 (20) (c) and 4Cu/amine-MCM-41 (d). (B) High angle XRD patterns of MCM-
4
1 (a), Cu-MCM-41 (20) (b), Cu-amine-MCM-41 (20) (c) and 4Cu/amine-MCM-41
(
d).
in the future. Mantegazza et al. [17] reported the direct synthe-
sis of hydroxylamine by the oxidation of ammonia with hydrogen
peroxide in the presence of Ti–silicalite at low temperature under
atmospheric pressure. With suitable selection of solvent, no poten-
tial deep oxidation of ammonia occurs, and no byproduct forms.
Thus, it provided a potential benign supply of hydroxylamine for
the amination of benzene.
In our previous work [15] we have studied the effect of Mn
towards the single step amination of benzene but herein, we have
made a comparative study between the copper incorporated and
immobilized mesoporous MCM-41 samples towards the reaction
under mild experimental conditions. In the present study amine
is used as the functional group which stabilized the catalyst and
hence increased the catalytic activity. As catalytic properties of the
transition metal modified amine functionalized MCM-41 depend
on the structure, location and nature of the incorporated metal, we
studied the details of the characterization of the material before
Fig. 2. (A) N2 adsorption–desorption isotherms of MCM-41. (B) N2
adsorption–desorption isotherms of Cu-MCM-41 (20). (C) N2 adsorption–
desorption isotherms of Cu-amine-MCM-41 (20).

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
87
Table 1
Surface properties of MCM-41 and modified MCM-41.
BET surface areaa (m /g)
2
Unit cell parameterb (Å)
Pore diameter (Å)
Pore volumea (cm /g)
3
Wall thicknessc (Å)
Sample code
MCM-41
Cu-MCM-41 (20)
1380
960
835
814
796
773
828
805
789
742
723
43.1
46.8
46.2
47.5
48.3
48.5
47.8
48.1
47.9
48.6
48.9
25.5
24.9
24.1
23.9
23.4
22.9
23.6
23.3
22.8
22.1
21.9
1.28
1.04
0.97
0.90
0.89
0.87
0.92
0.88
0.85
0.79
0.76
17.6
21.9
22.1
23.6
24.9
25.6
24.2
24.8
25.1
26.5
27
d
Cu-amine-MCM-41 (40)
Cu-amine-MCM-41 (30)
Cu-amine-MCM-41 (20)
Cu-amine-MCM-41 (10)
d
d
d
e
2
4
6
8
1
Cu/amine-MCM-41
Cu/amine-MCM-41
Cu/amine-MCM-41
Cu/amine-MCM-41
0Cu/amine-MCM-41
e
e
e
e
a
b
c
Values obtained from N2 adsorption results.
√
Unit cell parameter = 2 × d100/ 3 (from XRD).
Wall thickness (t) = unit cell parameter − pore size.
Samples prepared by co-condensation method.
Samples prepared by impregnation method.
d
e
performing the title reaction. The effects of reaction temperature,
time, solvent, and catalyst concentration on conversion and prod-
ucts selectivity were also examined and the results are discussed
thoroughly.
aqueous solution of Cu(NO ) ·3H O (0.076–0.379 g) was added
3
2
2
◦
dropwise. The liquid phase was removed by a 4 h treatment at 50 C
in a rotary evaporator. Further the prepared samples are termed as
xCu/amine-MCM-41 (x varies from 2 wt% to 10 wt%).
2
. Experimental
2.2. Catalytic amination reaction
2
.1. Material synthesis
The catalytic amination reaction is carried out in a thermo-
static two-necked round-bottomed flask at atmosphere pressure.
In a typical experiment, 0.05 g of catalyst and 11.25 mmol of
The Cu incorporated MCM-41 was synthesized as follows:
aqueous solutions of cetyltrimethyl ammonium bromide (CTAB),
NH OH·HCl were loaded into the reaction flask containing 7.5 ml
2
ammonium hydroxide and copper acetate Cu(CH COO)2 are
of 70 vol% acetic acid and stirred for about 20 min at room tem-
perature. Then 1 ml benzene (11.25 mmol) was introduced, and
3
well mixed with tetraethyl orthosilicate (TEOS) to obtain a gel
with a molar composition of 0.l2CTAB:1TEOS:0.6NH :l00H O:
◦
3
2
the mixture was heated at 70 C for 2 h. After the reaction was
0
.05Cu(CH COO) to get the Si/Cu = 20 ratio. After stirring for 1 h,
completed, the resulting mixture was cooled to room temperature
and neutralized by a saturated solution of sodium bicarbonate. The
organic compounds were extracted with ether and analyzed by gas
chromatography (Shimadzu, GC-2010) on FID mode using a cap-
illary column). M-toluidine was used as an internal standard to
quantify the aniline produced (Scheme 1).
3
2
the gel is left at room temperature for 24 h. The products are fil-
tered, washed with distilled water and then heated in a drying oven
◦
◦
at 80 C. The as-synthesized samples are calcined in air at 540 C for
h.
Copper modified amine functionalized MCM-41 can be syn-
6
thesized in two ways, co-condensation method and impregnation
method
Decomposition of hydroxylamine was carried out at atmo-
spheric pressure in argon with a flow rate of 25 ml/min. The gas
product formed during the decomposition was analyzed by GC
(3 mm × 2.3 mm Porapak Q column, TCD detector) after being dried
by CaO.
2.1.1. Co-condensation method
The mixture of cetyltrimethyl ammonium bromide (CTAB,
0
.5 g, 5.49 mmol), 2 M of NaOH (aq) (7 ml, 14 mmol), and H O
2
◦
(
480 g, 26.67 mmol) was heated at 80 C for 30 min at a pH
2.3. Physico-chemical characterizations
of 12.4. To this clear solution, tetraethyl ortho silicate (TEOS,
9
5
.34 g, 44.8 mmol), aminopropyl triethoxy silane (APTES, 1.03 g,
Low angle XRD patterns of powdered samples were taken in
.75 mmol) and Cu(NO ) ·3H O (0.474–0.118 g for Si/Cu = 10–40)
◦
◦
◦
3
2
2
the 2Â range of 1–30 at a rate of 2 /min in steps of 0.01 (Rigaku
Miniflex set at 30 kV and 15 mA) using Cu K␣ radiation. The high
angle XRD patterns of powdered samples were taken in the 2Â range
were added sequentially and rapidly. Following the addition, a light
blue precipitation was observed after 3 min of stirring. The reaction
temperature was maintained at 80 C for 2 h. The products were iso-
lated by a hot filtration, washed with sufficient amount of water and
methanol and dried under vacuum. For each 1 g of as-synthesized
material a mixture of 100 ml of ethanol and 1 ml of concentrated
HCl was used for acid extraction at 80 C for 6 h. Resulting surfac-
tantremovedsolid productswere filtered and washed withethanol,
and then dried at 60 C. With the variation of copper amount we
can get various wt% of Cu modified amine functionalized MCM-
◦
◦
◦
of 20–80 at a rate of 1.2 /min (Philips analytical 3710) using Cu K␣
radiation.
The BET surface area, average pore diameter, mesopore dis-
tribution, total and micropore volume of all the samples were
determined by multipoint N2 adsorption–desorption method at
liquid N2 temperature (77 K) by an ASAP 2020 (Micromeritics).
◦
◦
◦
Prior to analyses, all the samples were degassed at 200 C and
−4
1
0
Torr pressure for 2 h to evacuate the physically adsorbed
4
1. Further the samples are termed: Cu-amine-MCM-41 (x) (where
moisture. The mesopore structure was characterized by the dis-
tribution function of mesopore volume calculated by applying the
Barrett–Joyner–Halenda (BJH) method.
x = Si/Cu = 10–40).
2
.1.2. Impregnation method
The amine functionalized MCM-41 was synthesized by the
The FT-IR spectra of the samples were recorded using JASCO
−
1
FT-IR-5300 in KBr matrix in the range of 4000–400 cm
.
29
13
above method without taking copper source. One gram of acid
treated sample was suspended by 50 ml water in a beaker and then
Si and C MAS NMR spectra of the samples were recorded on
AV300 NMR spectrometer.

8
8
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
UV–visible DRS spectra of the samples were recorded in Varian
Cary 100 Conc UV-visible spectrophotometer.
3
3
3
. Results and discussion
.1. Characterization
.1.1. XRD
PXRD patterns of MCM-41, Cu/MCM-41 and surfactant
extracted copper modified organic amine functionalized meso-
porous silica samples are shown in Fig. 1A. Regardless of
organosilane and copper content all the samples show low
angle peaks characteristics of mesoporous materials. The sam-
ples showed a typical mesoporous structure with three sharp
peaks corresponding to Miller indices (1 0 0), (1 1 0) and (2 0 0). The
◦
◦
prominent peak at 2Â ranging between 2 and 2.5 , corresponds
to (1 0 0) plane, which is indicative of standard mesoporous sil-
ica. There is increase in d-spacing and unit cell parameter with the
introduction of amine in the silica framework. This indicates that
the organic groups get loaded into the frame wall position.
The copper modified MCM-41 sample (without organic amine)
◦
◦
shows high angle XRD (Fig. 1B) peaks at 2Â = 35.5 and 38.7 , corre-
sponding to monoclinic CuO (JCPDS 80-1917). But these high angle
peaks are absent in Cu/amine modified samples. Thus the introduc-
tion of large organo spacers reduces the probability of formation of
CuO.
3.1.2. Nitrogen adsorption–desorption isotherms
N2 adsorption–desorption is a common method to characterize
mesoporous materials, which can provide information about the
specific surface area, average pore diameter and pore volume etc.
BET surface area, pore size and pore volume for the synthesized
materials are presented in Table 1.
As shown in Fig. 2 (A and B) MCM-41 and Cu/amine modified
MCM-41 exhibited characteristic type IV BET isotherms consistent
with the presence of cylindrical meso-scale pores. It is observed
that there are three different well-defined stages in the isotherm.
The initial increase in nitrogen uptake at low P/P0 may be due to
monolayer adsorption on the pore walls, a sharp steep increase at
intermediate P/P0 may indicate the capillary condensation in the
mesopores and a plateau portion at higher P/P0 associated with
multilayer adsorption on the external surface of the materials. Both
the catalysts show a characteristic step around P/P0 ≈ 0.3 indicat-
ing the mesoporous nature of the materials [18]. MCM-41 sample
exhibits isotherm with well-developed step in the relative pressure
range ≈ 0.32, characteristic of capillary condensation into uniform
mesopores. A hysteresis of H3 type was observed for the modi-
fied samples. This is due to N2 condensation and evaporation with
interparticles.
Fig. 3 (A and B) shows the BJH pore size distribution of MCM-41
and Cu/amine modified MCM-41. From the figure one can see that
all the samples possess good mesoporous structural ordering and a
narrow pore size distribution. The surface area of parent MCM-41
2
was 1380 m /g; this value gradually decreased with the increase in
metal and amine loading. The pore diameter and volume decrease
with increase in Cu loading.
3.1.3. FT-IR
The FT-IR spectra of MCM-41, amine modified MCM-41 and
Cu/amine modified MCM-41 samples are shown in Fig. 4. The
−
1
characteristic band at 1080–1090 cm is due to the Si–O stretch-
ing in Si–O–Si structure, which is seen in all the figures. The
absorption band due to H–O–H bending vibration in water is
Fig. 3. (A) BJH pore size distribution curves of MCM-41. (B) BJH pore size distribution
curves of Cu-MCM-41 (20). (C) BJH pore size distribution curves of Cu-amine-MCM-
41 (20).
−1
at 1620–1640 cm . The spectra showed a broad band around
100–3600 cm , which is due to adsorbed water molecules.
−1
3
Cu/amine modified sample shows the N–H bending vibration at

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
89
Fig. 4. FT-IR spectra of MCM-41 (a), amine-MCM-41 (b) and Cu-amine-MCM-41 (c).
−
1
−1
and –NH2 symmetric bending vibration at 1525 cm .
6
82 cm
−1
−1
But these two peaks should be at 690 cm and 1532 cm respec-
tively. The shifting in peak position towards lower wave number is
due to bonding of Cu metal with the amine group. Neat MCM-41
is lacking these two peaks. The characteristic band of asymmetric
Fig. 5. 29Si MAS NMR spectra of MCM-41 (a), amine-MCM-41 (b) and Cu-amine-
MCM-41 (c).
vibration of the –CH – groups of the propyl chain in the silylating
agent is at 2935 cm , which is present in both the amine modified
MCM-41 and the Cu/amine modified MCM-41.
2
1
−
The surface coverage of the mesopores with organic amine
2
3
2
3
2
3
could be estimated as SC = (T + T )/(T + T + Q + Q ). The surface
coverage of Cu-amine-MCM-41 (20) modified sample is calcu-
lated as 39%. These results suggested that the organoalkoxy silanes
with hydrophobic functional groups could better orient themselves
around the water/micelle interface and intercalate these groups
to the hydrophobic regions of the CTAB micelles during the co-
condensation reactions.
.1.4. 29Si MAS NMR
3
The NMR spectra of parent MCM-41, amine modified MCM-41
and Cu/amine modified MCM-41 are shown in Fig. 5. Solid-state 29Si
NMR experiments employing magic-angle spinning (MAS) with
cross polarization (CP) has been shown to be a reliable mean to
characterize various silicate materials. Peaks in the “T” region are
contributed by Si atoms of the trialkoxy silane while those in the
“
tionalities confirmed the existence of the covalent linkage between
the organic groups and the silica surface.
Q” region arise from Si atoms of TEOS. Presence of T and T3 func-
2
13
3.1.5.
C MAS NMR
The 13C NMR spectra of amine modified MCM-41 and Cu/amine
13
modified MCM-41 are shown in Fig. 6. C CP MAS NMR spec-
tra show the presence of functionalized organic groups inside
the MCM-41 pore channels and the absence of surfactant species
after solvent extraction process. Absence of signals at 15 ppm and
58 ppm, assigned to the SiO–CH2–CH3 species, and in the range
50–70 ppm, for surfactant groups, indicates that the hydrolysis of
the organosilane monomers is complete and the surfactant is com-
pletely removed from the MCM-41 pore channels. 13C NMR spectra
show three peaks at 44.18 ppm, 22.45 ppm and 10.86 ppm corre-
sponding to the carbon atom of the propyl chain starting from the
carbon attached to the amine group. There is no much change in
the peak values with the modification of copper.
Resonances around −60.77 ppm and −68.33 ppm represented
silicon atoms in positions [( SiO) Si(OH) R] and [(≡SiO) SiR],
2
3
which are denoted as T2 and T3 respectively. The resonance
4
lines at −110.66, −101.59 and −93.73 representing Q [siloxane,
3
2
(
(
≡SiO) Si], Q [single silanol, (≡SiO) SiOH] and Q [geminal silanol,
4
3
≡SiO ) Si(OH) ] are also observed [19] in case of Cu/amine func-
2
2
2
tionalized MCM-41.
Parent MCM-41 sample shows the presence of resonance peaks
from −95 ppm to −110 ppm, indicating a range of Si–O–Si bond
3
angles. The sample contains a large amount of Q sites indicating
2
3
4
the reduced framework cross-linking. (Q + Q )/Q ratio indicates
the presence of silanol groups residing on the support surface. This
value for amine-modified and Cu/amine modified MCM-41 samples
is less than that of the parent MCM-41. Hence it indicates that the
materials have few residual silanol groups with a greater degree of
condensation and hydrothermal stability than that of parent sam-
3.1.6. UV–vis DRS
UV–vis diffuse reflectance spectra of the Cu-MCM-41 and
Cu/amine modified samples (modified by both co-condensation
and impregnation method) are shown in Fig. 7. The DR spectra of
the samples prepared by co-condensation method show three main
bands; first one is around 270 nm, second one is at 320 nm and
the last one is around 430 nm. The first two bands around 270 nm
and 320 nm corresponding to the ligand to metal (O → Cu2+and
2
3
ple. The decrease in Q and Q signals after organo functionalization
suggests that the condensation proceeds by the simultaneous co-
condensation of the TEOS and the organosilanes at the structure
directing interface.

9
0
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
Fig. 6. 13C MAS NMR of amine-MCM-41.
N → Cu2+ respectively) charge transfer (LMCT) spectra. The band
around 430 nm is due to the d–d transition (t → eg) for the diva-
2
g
2
+
lent Cu ions (Cu ) in octahedral coordination.
2+
The second peak corresponding to N → Cu
Cu/MCM-41 sample. This sample is having another peak at
50 nm which has been assigned to the formation of Cu1+ three-
is absent in
4
dimensional clusters in the CuO matrix [20].
Cu/amine modified samples prepared by impregnation method
shows two sharp bands at 318 nm and 425 nm and a weak band at
Fig. 7. UV–vis DRS figures of Cu-amine-MCM-41 (20) (a), 4Cu/amine-MCM-41 (b)
and Cu-MCM-41 (20) (c).
2
70 nm. This may be due to the fact that in impregnation method
most of the metal is present as a coordinate bonding with the –NH2
group of the functional group and rarely the metal is sited inside
the silica framework.
the influence of Cu/amine in the reaction. The enhanced activity is
due to (i) the wormhole-like channel morphology obtained which
may facilitate an enhanced access for the benzene molecules to the
active copper sites, (ii) the better hydrophobicity relations between
3.2. Catalytic amination reaction
the NH OH and catalyst and (iii) the absence of CuO clusters,
2
All the Cu loaded organic amine functionalized MCM-41 were
which create all the active copper sites available for the substrate
molecules.
testedfor directaminationof benzene toaniline in acidic medium at
◦
7
0 C and atmospheric pressure and the results are summarized in
Further it is observed that Cu/amine samples prepared by co-
condensation method gives higher catalytic activity compared to
samples prepared by impregnation method due to uniform dis-
tribution of Cu in the silica framework. Benzene conversion and
aniline selectively increases with decrease in Si/Cu ratio up to 20
and then decreases with further rise in Cu amount. The highest ben-
Table 2. Conversion of benzene, selectivity for aniline and hydrox-
ylamine are also given in this table. MCM-41 and Cu/MCM-41 (20)
gave 5.6% and 42.5% benzene conversion with 55% and 78% aniline
selectivity respectively. Cu/amine loaded MCM-41 samples shows
higher conversion than parent MCM-41 and Cu/MCM-41 indicating
Table 2
Effect of various catalysts on single step amination of benzene.
Catalyst
Benzene conversion (%)
Selectivity (%)
Hydroxyl amine
Conversion (%)
Aniline
Others
Selectivitya (%)
MCM-41
Cu/MCM-41 (20)
5.6
42.5
11.7
26.1
72.2
53.5
59.3
55.9
54.8
41.2
32.3
79.6
86.3
55
78
68
80
100
82
93
86
96
92
45
22
32
20
–
18
7
14
4
43
13
57.6
51.4
64.1
88.6
71.8
69.2
61.3
74.5
55.8
51.5
89.3
91.7
73.7
22.6
40.6
81.5
74.4
49.5
58.4
80.0
73.8
62.6
89.1
94.0
b
Cu-amine–MCM-41 (40)
Cu-amine-MCM-41 (30)
Cu-amine-MCM-41 (20)
Cu-amine-MCM-41 (10)
b
b
b
c
2
4
6
8
1
Cu/amine-MCM-41
Cu/amine-MCM-41
Cu/amine-MCM-41
Cu/amine-MCM-41
0Cu/amine-MCM-41
c
c
c
c
b
b
8
10
–
90
100
100
Cu-diamine-MCM-41 (20)
Cu-triamine-MCM-41 (20)
–
a
b
c
Selectivity (SE) of NH2OH = NH2OH consumption for aniline formation/total consumption of NH2OH.
Samples prepared by co-condensation method.
◦
Samples prepared by impregnation method: temperature = 70 C, benzene = 11.25 mmol, catalyst amount = 0.05 g, acetic acid = 7.5 ml (70 vol%), NH2OH = 11.25 mmol,
time = 2 h.

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
91
Table 3
Effect of various solvents on single step amination of benzene.
Solvent
Benzene conversion (%)
Selectivity (%)
Aniline
Others
Acetone
5.5
11
19
52
72.2
59
66
69
78
100
41
34
31
22
0
Acetonitrile
Acetic acid
Water
Scheme 1. Schematic presentation of amination of benzene.
70% acetic acid
◦
Temperature = 70 C, benzene = 11.25 mmol, catalyst amount = 0.05 g, NH2OH =
1.25 mmol, time = 2 h.
1
zene conversion of 72.2% and 100% aniline selectivity is observed
using Cu/amine-MCM-41 (20) catalyst. Further increase in copper
content on Cu/amine-MCM-41 may block some pores of MCM-41
which results in decrease in benzene conversion.
of benzene using and results are given in Table 3. Only 5.5%,
11%, 19% and 52% of benzene conversion observed in acetone,
acetonitrile, water and acetic acid medium respectively. Acetic
acid–water medium as solvent gives highest benzene conversion
(72.2%), indicating some influence of acidic medium for generation
Free-radical mechanisms have been proposed for amination
reactions using N-chloroalkylamines, hydroxylamine-o-sulfonic
acid and alkylhydroxylamines as the aminating agents catalyzed
by redox metal ions such as Ti3 , Fe , and Cu+ [21]. Kuznetsova et
+
2+
of NH3+ radicals. The pKa of NH3 is 3.75 [19], which indicates
•
•
+
that in a relatively acidic medium NH3+ rather than the neutral
amino radical predominates. The effect of acetic acid concentra-
tion on amination of benzene and hydroxylamine selectivity is
shown in Fig. 8. With the increase in acetic acid concentration
up to 70 vol%, the percentage of benzene conversion and aniline
selectivity increased but a reverse effect is observed with further
increase in acetic acid concentration. This may be due to 70 vol%
acetic acid exhibits good solubility and favorable acidity for the
highest decomposition of hydroxylamine, thus giving highest con-
version of benzene and 100% selectivity for aniline. The selectivity
of hydroxylamine for aniline formation increases with an increase
in acetic acid concentration up to 70 vol% and decreases thereafter
with further rise in acetic acid concentration. This may be due to
decrease of the reduction of Cu2+ to Cu in strongly acidic medium
[20].
•
al. [22] proposed a free-radical mechanism, considering the proto-
•
+
nated amino radical ( NH3 ) as the active aminating species for the
amination of benzene. The catalyst interacts with hydroxylamine
•
+
in acidic medium and generates protonated amino ( NH3 ) radical
by reduction of hydroxylamine. Then the protonated amino radi-
cals react with benzene to give protonated aminocyclohexadienyl
intermediates. Then the unstable intermediate is oxidized by cata-
lyst to give aniline along with regeneration of catalyst. The detailed
mechanism of amination reaction is given in Scheme 2.
The total amount of hydroxylamine consumed, including cat-
alytic process and disproportionation reaction, is equivalent to the
amount of N O released in the process. Such total consumption of
2
hydroxylamine was analyzed and is included in Table 2.
+
In order to study the effect of various amines the present
reaction is studied using the Cu/diamine-MCM-41 (20) and
Cu/triamine-MCM-41 (20). MCM-41 is modified with Cu and N-
[
3-(trimethoxysilyl)-propyl] ethylene diamine to get Cu/diamine-
3
.2.2. Effect of reaction temperature
The effect of reaction temperature on amination of benzene
MCM-41 (20) and with N-[3-(trimethoxysilyl)-propyl] diethylene
triamine to get Cu/triamine-MCM-41 (20). Cu/diamine-MCM-41
(
conversion respectively. In case of triamine modified samples the
leaching effect of Cu is very much reduced compared to other sam-
ples. So the catalytic activity of Cu is enhanced.
was studied and experimental results are shown in Fig. 9. Neither
hydroxylamine decomposition nor aniline formation was observed
up to 40 C of reaction temperature, suggesting that the amination
20) and Cu/triamine-MCM-41 (20) gave 79.6% and 86.3% benzene
◦
The influences of various reaction parameters such as different
reaction times, temperature, solvents, amount of hydroxylamine
and catalyst loadings have been investigated by taking Cu-amine-
MCM-41 (20) as catalyst to optimize the reaction conditions.
3.2.1. Effect of solvent
Different solvents such as acetone, acetonitrile, acetic acid,
water and acetic acid–water medium were tried for amination
Fig. 8. Influence of acetic acid concentration on amination of benzene. Acetic
acid = 7.5 ml, benzene = 11.25 mmol, catalyst amount = 0.05 g, NH2OH = 11.25 mmol,
time = 2 h.
Scheme 2. Schematic presentation of mechanism for amination of benzene.

9
2
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
Fig. 9. Influence of temperature on amination of benzene. Acetic acid = 7.5 ml
70 vol%), benzene = 11.25 mmol, catalyst amount = 0.05 g, NH2OH = 11.25 mmol,
(
time = 2 h.
process is associated with the decomposition of hydroxylamine.
◦
Fig. 11. Influence of catalyst amount. Temperature = 70 C, benzene = 11.25 mmol,
◦
◦
With the increase in reaction temperature from 50 C to 70 C,
benzene conversion increased from 28% to 72.2%. The selectiv-
ity of hydroxylamine for aniline formation increases from 45% to
acetic acid = 7.5 ml (70 vol%), NH2OH = 11.25 mmol, time = 2 h.
3.2.4. Effect of hydroxylamine amount
◦ ◦
9
5% with the increase in temperature from 50 C to 70 C. With
The variation of percentage of conversion of benzene with the
amount of hydroxylamine was studied and results are shown in
Fig. 11. As the molar ratio of NH OH/benzene increased from 0.5
to 1, the conversion of benzene, selectivity of aniline and selec-
tivity of hydroxylamine increases from 42% to 72.2%, 75% to 100%
and 78% to 95% respectively. On further increase in molar ratio of
further increase in reaction temperature a sharp fall on benzene
conversion as well as selectivity of hydroxylamine is observed.
2
◦
The sharp decrease in conversion of benzene to aniline at 80 C
may be due to vaporization of benzene and accelerated decom-
position of hydroxylamine, resulting in loss of active aminating
species.
NH OH/benzene to 2, the benzene conversion increased slightly
2
from 72.2% to 79% but the selectivity aniline and hydroxylamine
decreases from 100% to 69% and 95% to 77% respectively. This may
be due to formation of more side products i.e. chlorobenzene, phe-
nol and biphenyl etc. A relatively larger initial concentration of
hydroxylamine in the solution led to an accelerated decomposi-
tion of hydroxylamine by amine/Cu catalyst resulting decrease in
aniline selectivity.
3
.2.3. Effect of time
The effect of reaction time on amination reaction is shown in
Fig. 10. As the time increased from 0.5 h to 2 h, benzene conversion
and hydroxylamine selectivity increases from 15% to 72.2% and 40%
to 95% respectively. Further reaction time increases from 2 h to 3 h
selectivity of hydroxylamine increases form 95% to 97% indicat-
ing aniline yield increases marginally. Therefore 2 h is sufficient for
carring out amination of benzene.
◦
◦
Fig. 10. Influence of time on amination of benzene. Temperature = 70 C,
Fig.
12. Influence
of
NH2OH/C6H6
ratio.
Temperature = 70 C,
ben-
benzene = 11.25 mmol, catalyst amount = 0.05 g, acetic acid = 7.5 ml (70 vol%),
NH2OH = 11.25 mmol.
zene = 11.25 mmol, catalyst amount = 0.05 g, acetic acid = 7.5 ml (70 vol%),
NH2OH = 11.25 mmol, time = 2 h.

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 318 (2010) 85–93
93
3
.2.5. Effect of catalyst amount
The effects of catalyst amount on amination of benzene were
ples prepared by co-condensation method shows higher amount
of copper in framework compared to samples prepared by impreg-
nation technique. Cu-amine-MCM-41 samples show good activity
for single step liquid phase amination of benzene to aniline. The
Cu-amine-MCM-41 (20) modified sample shows highest catalytic
activity having 72.2% benzene conversion and 100% aniline selec-
tivity. Samples prepared by co-condensation method shows better
activity than samples prepared by impregnation technique.
studied and the results are shown in Fig. 12. With the increase in
catalyst amount from 0.01 g to 0.05 g, the benzene conversion, ani-
line and hydroxylamine selectivity increased from 23.5% to 72.7%,
9
0% to 100% and 43.3% to 95%, respectively. As the amount of cata-
lyst further increases from 0.05 g to 0.1 g, the benzene conversion
also increased from 72.2% to 83% but aniline and hydroxylamine
selectivity decreased to 70% and 67.5% respectively. This may
be due to the formation of more side products and unselective
decomposition of hydroxylamine resulting decrease in formation
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