Eco-friendly nitration of benzenes over zeolite-β-SBA-15 composite catalyst

Article abstract of DOI:10.1016/j.catcom.2014.02.006

Direct synthesis of microporous-mesoporous zeolite-β-SBA-15 (ZBS-15) composite catalyst from the synthetic precursors of SBA-15and zeolite-β seeds under acidic hydrothermal conditions through the simultaneous self-assembly of mesoporous silica SBA-15 and zeolite-β has been accomplished and characterized the ZBS-15 catalyst by XRD, N₂ sorption, FT-IR, TPD of ammonia and SEM techniques. The activity of the ZBS-15 composite catalyst for the nitration of benzenes under solvent-free conditions has been investigated, which revealed that there is a significant synergistic influence of both zeolite-β and SBA-15 materials on the activity of the ZBS-15 catalyst.

Full text of DOI:10.1016/j.catcom.2014.02.006

Catalysis Communications 49 (2014) 82–86
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Eco-friendly nitration of benzenes over zeolite-β-SBA-15
composite catalyst
Venkata Siva Prasad Ganjala a,b,1,2, Chinna Krishna Prasad Neeli a,1, Chodimella Venkata Pramod a,1
,
Mukkanti Khagga b, , Kamaraju Seetha Rama Rao a,1, David Raju Burri
⁎
a,⁎⁎
a
Catalysis Laboratory, Indian Institute of Chemical Technology, Hyderabad-500 607, India
Centre for Chemical Sciences & Technology, Institute of Science and Technology, Jawaharlal Nehru Technological University, Kukatpally, Hyderabad-500085, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Direct synthesis of microporous-mesoporous zeolite-β-SBA-15 (ZBS-15) composite catalyst from the synthetic
precursors of SBA-15and zeolite-β seeds under acidic hydrothermal conditions through the simultaneous self-
assembly of mesoporous silica SBA-15 and zeolite-β has been accomplished and characterized the ZBS-15 cata-
lyst by XRD, N2 sorption, FT-IR, TPD of ammonia and SEM techniques. The activity of the ZBS-15 composite cat-
alyst for the nitration of benzenes under solvent-free conditions has been investigated, which revealed that there
is a significant synergistic influence of both zeolite-β and SBA-15 materials on the activity of the ZBS-15 catalyst.
© 2014 Elsevier B.V. All rights reserved.
Received 5 November 2013
Received in revised form 16 January 2014
Accepted 4 February 2014
Available online 16 February 2014
Keywords:
Zeolite/SBA-15
Nitration
Toluene
Nitrotoluene
1. Introduction
has also been reported as an active catalyst for the nitration of various
aromatic substrates [14,15,22]. However, the main drawback of
Nitration is one of the oldest and the most common industrial pro-
cesses for the production of a variety of chemical intermediates that
are frequently used in dye stuffs, explosives and pharmaceuticals [1].
In these nitration processes, a mixture of nitric acid and sulfuric acid is
being used, which leads to over nitration, oxidized product formation
and generation of environmentally hazardous waste [2]. However,
nitration industries are still largely relying on the early technologies.
At this juncture, the development of eco-friendly catalytic nitration
approaches is initiated and a variety of solid acid catalysts such as mod-
ified silica [3], sulfuric acid on silica [4], modified zirconia [5], clay sup-
ported metal nitrates [6], metal exchanged clays [7], metal pillared
clays [8], mixed catalyst [9] sulfonated polystyrene resin [10], Nafion-
H [11], metal triflates and sulfonates [12] were studied. Simultaneously,
zeolite based solid acid catalysts were investigated in the past decade
[13]. The specific examples are zeolite mordenite, ZSM-5, HY, zeolite-β
[14,15], ZSM-11 [16] and HX [17]. Among the zeolite based solid acid
catalysts, zeolite-β exhibited better activity.
zeolite-β catalyst is its microporous texture, leading to diffusion prob-
lems. At this juncture, a new class of microporous-mesoporous compos-
ite materials is being synthesized from zeolites and mesoporous
materials, where the desired acidic nature derives from zeolite and
diffusion-free porosity from mesoporous material. In this report, aiming
at enhancing the catalytic activity of zeolite-β, its microporous-mesopo-
rous composite material (ZBS-15) has been synthesized via direct syn-
thetic approach by combining the synthesis of zeolite-β and SBA-15.
2. Experimental
2.1. Preparation of the ZBS-15 catalyst
The ZBS-5 composite catalyst has been synthesized following the
reported literature procedure [23]. To 73.62 g of tetraethyl ammonium
hydroxide (TEAOH) aqueous solution (20%), 0.38 g of NaOH, 0.76 g of
NaAlO2, and 42.86 g of tetraethyl orthosilicate (TEOS) were added
(Al2O3/SiO2/Na2O/TEAOH/H2O = 1.0/30/1.4/15/360 M ratio) and
stirred for 4 h at room temperature and transferred to an autoclave and
aged at 140 °C for 24 h. To 7.0 g of this zeolite-β seed solution, 4.3 g of
TEOS and the solution obtained from 2 g of EO20PO70EO20 and 62.5 g
of 2 M hydrochloric acid at 40 °C were added (Al2O3/SiO2/P123/HCl/
H2O = 1.0/60/0.52/188/10400 M ratio). The mixture was stirred at
40 °C for 24 h and then transferred into an autoclave and kept at
100 °C for 24 h. The filtrate was washed, dried at 100 °C for 10 h,
and calcined at 550 °C in air with a ramping rate of 2 °C/min for 6 h
The zeolite-β was first synthesized in 1967 by Smith et al. [18], since
then it has been used as a catalyst for a variety petrochemical processes
such as cracking [19], isomerisation [20] and alkylation [21]. Zeolite-β
⁎
Corresponding author. Tel.: +91 40 23156128, +91 40 2315861; fax: +91 40
23156128.
⁎⁎ Corresponding author. Tel.: +91 40 27191712; fax: +91 40 27160921.
E-mail addresses: kmukkanti@jntuh.ac.in (M. Khagga), david@iict.res.in (D.R. Burri).
1
Tel.: +91 40 27191712; fax: +91 40 27160921.
Tel.: +91 40 23156128, +91 40 2315861; fax: +91 40 23156128.
2
http://dx.doi.org/10.1016/j.catcom.2014.02.006
1566-7367/© 2014 Elsevier B.V. All rights reserved.

V.S.P. Ganjala et al. / Catalysis Communications 49 (2014) 82–86
83
Table 1
Textural properties of SBA-15, β-zeolite and ZBS-15.
a
b
c
d
e
Sample
SBET
Vmeso
Vmicro
Dp
tw
(m2 g−1
)
(cc g−1
)
(cc g−1
)
(nm)
(nm)
SBA-15
β-Zeolite
ZBS-15
654
189
378
0.80
0.09
0.24
0.08
0.15
0.12
7.24
-
4.85
2.31
-
6.34
a
BET surface area.
Mesopore volume.
Micropore volume.
Pore diameter.
b
c
d
e
Pore wall thickness (calculated as: a0 Dp (a0 = 2 × d(100) / √3)).
synthesis, 1 mmol of substrate, 2 mmol of nitric acid (69%), and 20 mg
of catalyst (ZBS-15) were loaded in a 10 ml RB flask containing a
refluxing condenser. The product analysis was made using a gas chro-
matograph (GC-17A, M/s. Shimadzu Instruments, Japan) that consists of
an FID detector and an equity-5 capillary column (0.53 mm 50 × 30 m).
The products were confirmed using a GC-MS (QP-5050 model, M/s.
Shimadzu Instruments, Japan) equipped with a DB-5 capillary column
(0.32 mm in diameter and 25 m in length, M/s. J & W Scientific, USA).
Fig. 1. XRD patterns of (a) wide-angle XRD and (b) low-angle XRD.
to remove the templates. For the purpose of comparison, SBA-15 and
3. Results and discussion
zeolite-β have also been synthesized.
Wide-angle XRD patterns obtained for the ZBS-15 composite cata-
lyst and its parent zeolite-β are displayed in Fig. 1(a). The appearance
of XRD reflections at 2θ = 7.83° and 22.39° is the characteristic feature
of zeolite-β [24]. The XRD pattern of ZBS-15 matches well with the pat-
tern of zeolite-β, which confirms the existence of zeolite-β in the ZBS-
15 composite catalyst. Low angle XRD patterns obtained for the SBA-
15 and ZBS-15 catalysts are depicted as inset in Fig. 1(b), wherein,
three well-resolved XRD reflections for SBA-15, correspond to (100),
(110) and (200) crystal planes, which are associated with p6mm hexag-
onal symmetry [25]. The low-angle XRD pattern of ZBS-15 matches well
with the pattern of SBA-15, revealing the presence of a mesoporous
structure in the ZBS-15 composite catalyst.
The N2 adsorption-desorption isotherms of ZBS-15, the parent SBA-
15 and the zeolite beta are displayed in Fig. 2. Isotherms of SBA-15 are of
type IV with an H1 hysteresis loop and a well defined step due to capil-
lary condensation within the range of 0.6-0.8 p/p0, is a typical nature of
ordered mesoporous materials with cylindrical pores in a narrow pore
size distribution [25]. Isotherms obtained for the ZBS-15 catalyst exhib-
ited type IV and type II characteristics of microporous–mesoporous
materials, whereas the isotherms obtained for zeolite are of type II
2.2. Characterization of catalysts
X-ray diffraction (XRD) patterns were recorded at room tempera-
ture using an X-ray diffractometer (Multiflex, M/s. Rigaku, Japan) with
a nickel filtered CuKα radiation. N2 adsorption–desorption isotherms
were recorded on a N2 adsorption unit (Quadrusorb-SI V 5.06, M/s.
Quantachrome Instruments Corporation, USA) at −196 °C. The samples
were out-gassed at 200 °C for 4 h before the measurement. FT-IR spec-
tra were obtained from a PerkinElmer spectrometer (Spectrum GX).
TPD of NH3 was obtained from AUTOSORB-iQ, automated gas sorption
analyzer (M/S Quantachrome Instruments, USA) using 10% NH3 in a
helium gas mixture. SEM images of the catalysts were taken using a
Hitachi model S-3000N (Japan) scanning electron microscope at an
applied voltage of 15 kV.
2.3. Catalytic activity
The catalytic activity of ZBS-15 was carried out in the liquid phase at
100 °C for a period of 4 h under solvent-free conditions. In a typical
Fig. 2. N2 adsorption-desorption isotherms of (a) SBA-15, zeolite-β and ZBS-15 (b) pore
size distribution of curves of SBA-15, zeolite-β and ZBS-15.
Fig. 3. TPD of NH3 patterns for SBA-15, zeolite-β and ZBS-15.

84
V.S.P. Ganjala et al. / Catalysis Communications 49 (2014) 82–86
Scheme 1. Reaction Scheme for the nitration of benzenes over Zeolite-β-SBA-15 catalyst.
Table 2
Optimization of reaction parameters using ZBS-15 catalysts.
S. no.
Reaction parameter
Conversion, %
Mononitration selectivity, %
Isomer distribution
Ortho
Para
Meta
A
1
2
3
4
Temperature, °C
40
60
80
17
52
71
100
100
100
100
34
37
38
40
66
59
57
55
0
4
5
5
100
100
B
1
2
3
4
Reaction time, h
1
2
3
4
78
86
93
100
100
100
100
37
38
38
40
58
57
57
55
5
5
5
5
100
C
1
2
3
4
Catalyst amount, mg
10
20
30
40
87
100
92
100
100
100
100
37
40
41
41
58
55
54
54
5
5
5
5
88
D
1
2
3
4
Toluene:HNO3
1:0.5
1:1
1:1.5
1:2
37
88
98
100
100
100
100
47
45
39
40
50
55
56
55
3
5
5
5
100
and account for micro porosity [26]. Fig. 2(b) indicates the pore size dis-
tribution in SBA-15, zeolite-β and ZBS-15 catalysts. The distribution of
pores in ZBS-15 is bimodal. The surface area of ZBS-15 is larger than
that of conventional zeolite-β and smaller than that of SBA-15
(Table 1). The pore wall thickness of the ZBS-15 catalyst is much higher
than that of conventional SBA-15. The excess pore wall thickness may
be exerted from the zeolite-β building units that are assembled with
the mesopore wall framework. The surface area of physical mixture
(292 m2/g) is lower than that of ZBS-15 (378 m2/g). This is a clear indi-
cation that a strong interaction exists between zeolite-β and SBA-15. FT-
IR spectra of SBA-15, zeolite-β and ZBS-15 are shown in Fig. S1. In the IR
spectrum of the ZBS-15 catalyst, there are two important regions to
identify the zeolite-β structure, typically at 1000–1250 cm-1and
400–600 cm-1. In the 1000–1250 cm-1 region there are three important
asymmetric stretching bands at 1080, 1175 and 1220 cm-1, which are
responsible for T-O-T (T = Si or Al) of the zeolite-β structure [27]. In
the 400–600 cm-1 region, there is a broad band at 460 cm-1, which is
similar to that of SBA-15 material. However, ZBS-15 exhibited two
sharp bands at 520 and 556 cm-1, which are similar to those of six- or
five membered rings of T-O-T (T = Si or Al) in microporous zeolites
Table 3
Nitration of toluene over SBA-15, zeolite-β and ZBS-15 catalyst.
S. no.
Catalyst
Conversion, %
Selectivity, %
Ortho
Meta
Para
1
2
3
4
SBA-15
Zeolite-β
ZBS-15
33
53
100
13
35
39
39
45
4
4
5
4
61
57
56
51
No catalyst
Catalyst: 20 mg, toluene: 1 mmol, HNO3: 2 mmol, temperature: 100 °C, time: 4h.
Fig. 4. The activity of ZBS-15 catalyst for the nitration of toluene in repeated cycles.

V.S.P. Ganjala et al. / Catalysis Communications 49 (2014) 82–86
85
Table 4
The performance of ZBS-15 catalyst for the nitration of benzenes.
S. no.
Substrate
Conversion, %
Mononitration selectivity, %
Selectivity, %
Ortho
-
Meta
-
Para
1
2
3
4
5
6
7
89
100
82
100
100
95
–
40
41
26
16
-
05
12
-
55
42
34
83
–
88
60
97
99
-
91
76
-
63
100
30
-
70
Catalyst: 20 mg, substrate: 1 mmol, HNO3: 2 mmol, temperature: 100 °C, and reaction time: 4 h.
[25]. These results suggest that ZBS-15 has zeolite building units in its
framework spectrum confirmed by two intense bands at 956 and
796 cm-1, typical for Si\O and Si\O\M bonds respectively in zeo
type frameworks.
The SEM images of ZBS-15 and SBA-15 catalysts are shown in
Fig. S2: (a) SEM of ZBS-15 and (b)SEM of SBA-15. Fig. S2 shows that
the zeolite-β particles of the ZBS-15 catalyst are in a spherical morphol-
ogy. The size and shape of ZBS-15 particles are uniform. SBA-15 support
consists of many vermicular-like domains, which are aggregated into
wheat-like mesostructures.
and chlorobenzene. It is found that all the substrates studied are
smoothly converted into respective mononitration products. Contrarily,
xylenes are converted into oxidized products apart from regular nitra-
tion products under the optimized reaction conditions. The details of
the different substrate conversions under optimized conditions are
displayed in Table 4.
The directly synthesized ZBS-15 composite catalyst is acidic in
nature like zeolite-β and mesoporous like SBA-15; in addition it also
has a bimodal porous behavior and superior acidic nature, which are
clearly reflected in the nitration of benzenes.
The TPD of NH3 patterns are displayed in Fig. 3, which reveals that
the ZBS-15 catalyst possesses a larger number of acidic sites compared
to the parent zeolite-β and SBA-15.
4. Conclusions
Zeolite-β-SBA-15 composite catalyst has been prepared by the
assembly of mesoporous silica SBA-15 and zeolite-β seeds. Compatible
acidic nature and suitable diffusion-free mesoporous architecture of
ZBS-15 may be contributed for the effective nitration of various benzene
derivatives. Furthermore, the process is solvent-free and the catalyst is
recyclable reusable at least for four 4 repeated cycles.
3.1. Catalytic activity
The nitration of benzenes over the ZBS-15 catalyst has been
schematically presented in Scheme 1. To understand the nature of the
ZBS-15 catalyst, the initial experiments were conducted using toluene
as a substrate and 69% HNO3 as a nitrating agent under solvent-free
conditions. Subsequently, the reaction parameters like reaction temper-
ature, reaction time, amount of catalyst and toluene to HNO3 molar ratio
have been optimized. Accordingly, the optimum reaction temperature is
100 °C, reaction time is 4 h, amount of catalyst is 20 mg and toluene to
HNO3 molar ratio is 1: 2 (Table 2). Unless otherwise specified the above
reaction conditions are applicable.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.02.006.
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