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Radhika et al.
Nanocrystalline Hierarchical ZSM-5: An Efficient Catalyst for the Alkylation of Phenol with Cyclohexene
Further, the activity of the catalyst so synthesized was
assessed in the alkylation of phenol with cyclohexene.
Reaction data was subjected to kinetic studies using regres-
sion analysis.
intervals and were centrifuged. The supernatant was anal-
ysed by gas chromatographic analysis using a 10% OV-17
column and a flame ionisation detector (FID). The prod-
ucts were confirmed by GC-MS (Varian Star 3400 GC,
Column: DB-1 megapore) technique.
The progress of the reaction is expressed as the per-
centage of cyclohexene that was consumed in the reaction.
The effects of reaction conditions on this progress of reac-
tion were investigated. Based on this, the optimised reac-
tion conditions (duration of the reaction, catalyst quantity,
cyclohexene to phenol mole ratio and reaction tempera-
ture) were deduced.
2. EXPERIMENTAL DETAILS
2.1. Synthesis of the Catalyst
Nanocrystalline hierarchical ZSM-5 (Si/Al = 100) was fab-
ricated by a dual template approach, under controlled
steaming at 175 ꢀC. Tetrapropylammonium hydroxide
(TPAOH) was used as the structure-directing agent and
polydiallyldimethylammonium chloride (PDDA) was used
as the macropore directing template. At first, a clear solu-
tion of zeolite was prepared by mixing aluminium iso-
propoxide and TPAOH. To this clear solution, tetraethyl
orthosilicate and deionized water were added, with con-
stant stirring for 2 h. The pH of this solution was found
to be 11.5. To this sample, PDDA was added.
3. RESULTS AND DISCUSSION
3.1. Characterizations of the Catalyst
The DLS curve of the precursor sol after 24 h of aging
ꢀ
(at 80 C) is shown in Figure 1(a). The distribution is
monomodal and indicates the presence of particles below
100 nm. XRD pattern (recorded from 5ꢀ to 30ꢀ at a scan
rate of 2ꢀ/min using a step size of 0.04ꢀ) of the synthe-
sized catalyst (Fig. 1(b)) shows the characteristic peaks of
ZSM-5 around 2ꢁ = 7ꢂ94ꢀ, 9.94ꢀ, 13.9ꢀ, 14.8ꢀ, 20.9ꢀ, 23.1ꢀ
and 23.9ꢀ, which correspond to reflections from planes
(011), (200), (012), (031), (241), (051) and (033) respec-
tively. Broadening of the XRD peaks is due to the small
crystal size. Furthermore, the incorporation of the vacuum-
ꢀ
The mixture was concentrated at 60 C for 30 minutes
under a pressure of 500–700 mmHg. The concentrated sol
was then aged at 80 ꢀC for 24 h. The sample was then sub-
jected to hydrothermal treatment in an autoclave at 175 ꢀC
ꢀ
for 3 h. The solid was dried overnight at 110 C. The
material so procured was then subjected to calcination at
ꢀ
550 C for another 6 h.
concentration step reduced the high-temperature crystalli-
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2.2. Characterization of the Catalyst
sation time, which otherwise takes 4 h–3 days.14–17 FTIR
Copyright: American Scientific Publishers
DLS study was done using Malvern Zetasizer Nano
ZS instrument. Powder X-ray diffraction patterns were
recorded using a Rigaku 2000 diffractometer equipped
with Cu-Kꢀ radiation (1.5418 Å). The FTIR spectrum
of the catalyst was recorded using the KBr wafer tech-
nique (1.2% w/w) on a Perkin Elmer FTIR instrument. The
morphology of the zeolite nanocrystals was determined
with SEM (JEOL JSM-6500f). Nitrogen sorption studies
were done using a Micromeritics ASAP 2020 instrument
at 77.8 K. Before recording the measurements, the cat-
alysts were vacuum-degassed. Perkin Elmer TGA TAC
7/DX instrument was used to get the TGA profiles.
spectra (from 400 to 1400 cm−1) of the as-synthesized
sample of nanocrystalline hierarchical zeolite ZSM-5 is
presented in Figure 1(c). The spectrum shows structure-
sensitive bands at around 1220 cm−1and 572 cm−1, char-
acteristic of the MFI framework type. The bands at
435 cm−1, 795 cm−1 and 1043 cm−1 are respectively due to
the bending, symmetric stretching and asymmetric stretch-
ing of Al/Si–O tetrahedra. The ratio of absorbances of the
bands at 572 cm−1 and 435 cm−1 was calculated to be
0.74, which indicates that the sample is well-crystallised.
From the SEM micrograph of the synthesized nanocrys-
talline hierarchical zeolite ZSM-5 (Fig. 2(a)), it can be
deciphered that the particles possess spherical morphology
and have diameters in the range of 20–70 nm. The syn-
thetic route adopted has thus been successful in producing
nanocrystallites.
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2.3. Catalytic Studies
The nanocrystalline hierarchical ZSM-5 catalysed alkyla-
tion of phenol with cyclohexene was conducted in a mag-
netically stirred glass reactor of 100 cm3 capacity. The
reactor was fitted with a reflux condenser and a thermome-
ter. The temperature was maintained by keeping the reactor
in an oil bath.
Figure 2(b) shows the adsorption–desorption isotherm
of nitrogen on the calcined nanocrystalline hierarchical
ZSM-5. The isotherm is a combination of Type 1 and
Type 2 adsorption isotherms, with H4 hysteresis loop. The
isotherm obtained matches well with that usually obtained
for mesoporous zeolites, as stated in the IUPAC Techni-
cal Report.18 The regions of the isotherm are described
below as per this report. A steep uptake at very low p/p0
is due to filling in narrow micropores, accompanied by
high adsorbent-adsorptive interactions. Point B (Fig. 3(b))
marks the concomitant onset of multilayer adsorption.
Before the reaction,ꢀthe catalyst was activated by heat-
ing it for 10 h at 120 C. A typical reaction mixture con-
sisted of phenol (20.0 mmol), cyclohexene (10.0 mmol)
and 0.300 g of the zeolite catalyst. The contents were
ꢀ
heated to the reaction temperature (for instance, 50 C)
in an oil bath, accompanied by constant magnetic stirring.
Samples of the reaction mixture were withdrawn at regular
J. Nanosci. Nanotechnol. 18, 5404–5413, 2018
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