Heterogeneous para-phenylamino sulfonic acid ligand functionalizedon MCM-41 derived from rice husk ash: Selective mono-alkylatedproducts of tert-butylation of phenol

Article abstract of DOI:10.1016/j.apcata.2014.09.047

A new organo-inorganic hybrid material was prepared by immobilizing 3-(4-aminophenylamino)propane-1-sulfonic acid onto functionalized mesoporous MCM-41 via simplepost-synthesis method. The hybrid organo MCM-41 preserved its hexagonal honey-comb configurationafter both surface chemical modification and immobilization of sulfonic acid ligand. XRD analysisexhibited three well-resolved diffraction peaks corresponding to the highly ordered mesostructure. Thefive intense carbon peaks of solid-state CP-MAS ¹³CNMR spectroscopy confirmed the grafting of sulfonicacid ligand onto the well-structured MCM-41. Surface properties of the material revealed a pore size of 1.98 nm and surface area of 468 m²g^-1. The catalytic performance of this hybrid material was tested inthe alkylation of phenol with tert-butanol (TBA) and showed a high catalytic activity leading to 99.5%conversion of tert-butyl alcohol and high selectivity to monoalkylated products.

Full text of DOI:10.1016/j.apcata.2014.09.047

Applied Catalysis A: General 489 (2015) 162–170
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Heterogeneous para-phenylamino sulfonic acid ligand functionalized
on MCM-41 derived from rice husk ash: Selective mono-alkylated
products of tert-butylation of phenol
∗
Farook Adam , Chien-Wen Kueh
School of Chemical Sciences, University Sains Malaysia, 11800 Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2014
Received in revised form
A
new
organo-inorganic
hybrid
material
was
prepared
by
immobilizing
3-(4-
aminophenylamino)propane-1-sulfonic acid onto functionalized mesoporous MCM-41 via simple
post-synthesis method. The hybrid organo MCM-41 preserved its hexagonal honey-comb configuration
after both surface chemical modification and immobilization of sulfonic acid ligand. XRD analysis
exhibited three well-resolved diffraction peaks corresponding to the highly ordered mesostructure. The
five intense carbon peaks of solid-state CP-MAS CNMR spectroscopy confirmed the grafting of sulfonic
acid ligand onto the well-structured MCM-41. Surface properties of the material revealed a pore size of
2
1 September 2014
Accepted 28 September 2014
Available online 7 October 2014
1
3
Keywords:
Organic–inorgnic hybrid
MCM-41
Immobilization
tert-Butylation of phenol.
2
−1
1
.98 nm and surface area of 468 m g . The catalytic performance of this hybrid material was tested in
the alkylation of phenol with tert-butanol (TBA) and showed a high catalytic activity leading to 99.5%
conversion of tert-butyl alcohol and high selectivity to monoalkylated products.
© 2014 Elsevier B.V. All rights reserved.
◦
1
. Introduction
Alkylation of phenol with tertiary butyl alcohol is a typical
phenol conversion of 86.3% at 150 C [9]. Other related materials
which have been tested by gas-phase phenol alkylation include
H PO /MCM-41 [10], Ga-HMS-30 [7] and Al-MCM-41 [3]. It was
3
4
Friedel–Crafts reaction that is important in industry due to the
wide application of butylated products. 2-tert-Butylphenol (2-
TBP) is an intermediate for frangrances and pesticides, whereas
found that a cost-effective liquid-phase phenol alkylation with
tert-butyl alcohol over a hybrid heterogeneous catalyst is very
limited in the literature.
4
-tert-butylphenol (4-TBP) is used to make oils and phosphate
In the current industrial advancement which emphasizes a
benign environment, mesoporous molecular sieves with their dis-
tinctive textural properties (high surface area, high thermal and
chemical stability) [11–13] has stimulated a tantalizing prospect
of merging both organic and inorganic compounds to form new
hybrid materials. The practical organic modification on silica is an
excellent transformation of homogeneous catalyst into heteroge-
neous catalyst to overcome difficulty in product separation [9],
non-reusability and corrosive nature [14].
Heterogeneous hybrid material provide pathways for gener-
ation of active sites on molecular sieves. This has opened up a
wide application in catalysis and adsorption. In these few years,
researchers have reported many attempts at tethering organic lig-
ands onto mesoporous molecular sieves. Some related examples
are Cyclam on SBA-15 for aerial oxidation of ethylbenzene [15], l-
tryptophane on MCM-41 as a drug carrier system [16], imidazolium
derivatives on MCM-41 for conversion of CO2 to cyclic carbonate
[17], Schiff base thiopene-2-carbaldehye on MCM-41 applied in
olefin epoxidation [18]. 3-Mercaptomethoxysilane supported onto
esters [1]. The other commercial uses of butylated phenols include
the essential feedstock for antioxidants, phenolic resins, ultravio-
let absorbers, varnishes and heat stabilizers in polyolefins [2–6].
Despite the literature reporting phenol alkylation catalyzed by
homogeneous Bronsted acids, i.e. HCIO , H PO , H SO , HF, and
4
3
4
2
4
Lewis acids such as BF3 and AlCl3 [7,8], the use of heterogeneous
catalysts is favorable due to many desirable advantages.
In the past years, alkylation of phenol by tertiary butyl alcohol
has been extensively studied by different types of heterogeneous
materials. Till now, many gas-phase reactions which involve
costly method due to high pressure and high temperature have
been reported. For example, Song et al. reported a high phenol
conversion by M-MCM-22 at 418 K [3]. Vinu et al. have studied
the vapor-phase phenol alkylation over AlSBA-15 and reported a
∗ Corresponding author.
E-mail addresses: farook@usm.my, farookdr@gmail.com (F. Adam).
http://dx.doi.org/10.1016/j.apcata.2014.09.047
0
926-860X/© 2014 Elsevier B.V. All rights reserved.

F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
163
SBA-15, Amberlyst 15 and Nafion, MCM-41 and MCM-48 were
oxidized with H O to convert it into sulfonic acid groups. These
2.2. Characterization of the acid catalyst
2
2
sulfonic acid catalysts were used in the benzylation of toluene using
benzyl alcohol [19,20].
The TEM images were obtained from a Philips CM12 instrument
(Eindhoven, the Netherlands) equipped with an analyzer, Docu Ver-
sion 3.2 image processing software (Munster, Germany). The SEM
images were recorded using Leo Supra 50 VP FESEM, equipped
with Oxford INCA 400 energy-dispersive X-ray microanalysis sys-
tem (Carl–Ziess SMT, Oberkochen, Germany; Oxford Instruments
Analytical, Bucks, UK). The X-ray patterns were recorded on a
Siemens Diffractometer D5000, Kristalloflex (voltage of 40 kV and
current 30 mA) using Cu K␣ (ꢀ = 0.154 nm) radiation. The diffrac-
In this paper, we have synthesized a sulfonic acid ligand, 3-
(
4-aminophenylamino)propane-1-sulfonic acid (4-NHPhSO H), by
3
the reaction of 1,4-phenylene diamine and 1,3-propane sultone
using a simple reflux method [21]. We report on the synthesis
of new organo-inorganic hybrid hexagonal mesoporous material
in which 4-NHPhSO H was covalently bonded to the framework
3
of MCM-41 via direct post-synthesis method. The hybrid organo-
MCM-41 was characterized by several physiochemical methods
and the catalyst was used in Friedel–Craft reaction between tert-
butanol with phenol. Various reaction conditions such as reaction
time, reaction temperature, mass of catalysts and mole ratios of
phenol to tert-butanol were studied are herein reported.
◦
tion angle was scanned in the 2Â range, 1.5–10 for 1/2 h, at a rate
◦
−1
of 0.050 s . The thermogravimetric analysis (TGA) was performed
e
using a TGA/SDTA 851 instrument: 10.0 mg of the sample was
heated from 30 to 900 C under nitrogen flow. The elemental anal-
◦
ysis was carried out using Perkin Elmer Series II, 2400 instrument.
13
29
The C and Si CP/MAS NMR were recorded on a Bruker AV 400
WB Solid State NMR machine, equipped with a magic angle spin-
2
. Experimental
13
1
ning (MAS) unit. The C and H liquid NMR were obtained with a
Bruker Avance 111 500 MHz NMR.
2.1. The synthesis of solid acid catalyst using rice husk as the
source of silica
2.3. Catalytic reaction
The synthesis of silica was carried out according to literature
22,23]. Rice husk was washed with copious amount of water and
The liquid-phase alkylation experiments were carried out
[
under argon gas in a small two-neck round-bottom flask (25 mL),
equipped with a magnetic stirrer, a thermometer and a condenser.
In order to prevent TBA from evaporating, ice water was used to
circulate the condenser by liquid filter pump to maintain the tem-
rinsed with distilled water. After drying at room temperature, the
rice husk was stirred with 1.0 M nitric acid at room temperature for
2
◦
4 h. The rice husk was calcined in a furnace at 600 C for 6 h to get
high-purity silica. To prepare MCM-41, the required sodium silicate
Na SiO ) was prepared by combining rice husk ash (6.0 g) with
◦
perature at 2 C. In a typical run, 100 mmol of each phenol and
(
2
3
TBA were placed in the round bottom flask containing 200 mg cat-
NaOH pellet (2.0 g) and H O (40.0 mL). The resulting gel mixture
was heated and stirred for 2 h at 80 C. This was labeled as solution
2
◦
◦
alyst pre-dried for 24 h at 110 C. The reaction mixture was stirred
at 1000 rpm for 7 h. The samples of the reaction mixture were
withdrawn periodically and analyzed by GC, whereby a qualitative
product analysis was conducted using GC-MS. The gas chromato-
graph instrument was equipped with a capillary wax column (30 m
length and 0.25 mm inner diameter). The temperature program was
A.
Another solution B was prepared by mixing CTAB (6.0 g) with
◦
H O (35.0 mL) by stirring at 80 C until a clear solution was
2
obtained. Solutions A and B were mixed together in a polypropyl-
ene bottle and stirred for 15 min. The mixture was then placed in an
oven for crystallization at 100 C for 24 h. The gel mixture was then
cooled to room temperature. The pH of the reaction mixture was
adjusted to 10.2 by drop-wise addition of 25 wt% acetic acid with
vigorous stirring. The mixture was then placed in an oven for 48 h
to crystallize the material. The final product was filtered, washed,
◦ ◦ −1 ◦
set from 40 to 46 C at a rate of 2 C min , followed by 46–230 C at
◦
◦
−1
a rate of 30 C min . Acetonitrile was used as the internal standard,
which was added to the aliquots taken for GC and GC-MS analysis.
The amount of acetonitrile added was 20 ␮L.
◦
dried and calcined at 550 C in air for 10 h to obtain pure siliceous
MCM-41 [23].
3. Results and discussions
To modify the MCM-41, 1.0 g of MCM-41 was refluxed with
-chloropropyltriethoxysilane (CPTES) (12.5 mmol) in toluene for
4 h [24]. The resulting solid was washed in a soxhlet appara-
tus with diethyl ether-dichloromethane mixture (1:1) for 12 h to
remove excess reactant [25]. The resulting solid was labeled as
MCM-PrCl. The yield of MCM-PrCl was 1.94 g.
3
3
.1. The characterization of
-(4-aminophenylamino)propane-1-sulfonic acid
3
2
(
4-NH PhSO H)
2 3
3
.1.1. The 1H and 13C NMR spectra of 4-NH PhSO H
2 3
1
The H NMR spectrum (Fig. S1a) of 4-NH PhSO H confirmed the
2
3
The ligand, 3-(4-aminophenylamino)propane-1-sulfonic acid
proton resonance of the –CH CH CH – species indicated by Hb, Ha
2
2
2
(
(
4-NHPhSO H), was prepared by reacting 1,3-propane sultone
3
and Hc at 1.88, 2.60 and 3.14 ppm. The aromatic protons, Hd and
He appeared at 6.76 and 6.94 ppm, respectively. The sulfonic acid
proton, Hf appeared at 8.56 ppm.
0.01 mol) with 1,4-phenylene diamine (0.01 mol) under reflux in
◦
acetonitrile at 80 C. The solid product obtained was filtered by suc-
tion pump and was washed thoroughly using acetonitrile to remove
the unreacted reactants. The organic ligand obtained was charac-
The 13C NMR spectrum (Fig. S1b) had chemical shifts for the
aliphatic carbons at Ca, Cb and Cc at 24.33, 44.37 and 49.38 ppm,
1
13
terized by H and C NMR spectroscopy and elemental analysis
CHN).
Immobilization of 4-NHPhSO H on MCM-PrCl was carried out
respectively. The aromatic carbons were recorded at 114.75,
1
and C NMR spectra are very consistent with the structure of
4
(
1
19.05, 121.19 ppm for Cd, Ce, Cf and Cg, respectively. The
H
3
13
by adding 1.0 g of MCM-PrCl (12.5 mmol), with 12.5 mmol 4-
NHPhSO H and triethylamine (Et N) as deprotonating agent and
-NH PhSO H.
2 3
3
3
◦
refluxed in toluene at 110 C for 24 h. The solid obtained was
rinsed thoroughly with toluene, distilled water, dichloromethane
and finally with acidified ethanol. The product was dried at 110 C
3.1.2. Elemental analysis of 4-NH PhSO H
2 3
◦
The carbon, hydrogen and nitrogen contents of 4-NH PhSO H
2
3
for 24 h and was labeled as MCM-4-NHPhSO H. The synthesis of
3
are shown in Table 1. The deviation of the experimental value
from theoretical is negligible with carbon, hydrogen and nitrogen
the catalyst is shown in Scheme 1.

1
64
F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
Si OH
Si OH
Si OH
Si OH
O
SO H
3
O
O
OH
(
CH CH ) Si(CH ) Cl
Si
O
2
3 3
2 3
MCM-41
MCM-41
O
O
Si
Cl
+
Toluene, 110 o
C
NH
Si
O
O
H N
2
Si OH
Si OH
o
Toluene, Et 3N, 110 C
Si OH
O
O
OH
Si
Si
O
O
MCM-41
Si
NH
O
NH
SO H
3
Si OH
Scheme 1. The schematic representation of the synthesis of MCM-4-NHPhSO3H prepared from MCM-41 derived from rice husk ash.
Table 1
The chemical analysis of 4-NHPhSO3H.
MCM-41
MCM-PrCl
(100)
MCM-4-NHPhSO H
Theoretical (%)
46.9
Experimental (%)
3
Carbon
47.0
6.0
12.2
Hydrogen
Nitrogen
6.1
12.2
recording 46.96, 5.99 and 12.15%, respectively. The CHN analysis is
consistent with the formula of 4-NH PhSO H.
2
3
(110)
200)
(
3
.2. The characterization of MCM-4-NHPhSO H
(210)
3
(
(
(
a)
b)
c)
3
.2.1. The X-ray diffraction pattern of MCM-4-NHPhSO H
3
Fig.
1 shows the powder X-ray diffraction (XRD) pat-
terns of the calcined MCM-41, functionalized MCM-PrCl and
MCM-4-NHPhSO H. The X-ray diffraction pattern of calcined MCM-
3
6
9
3
◦
o
4
1 consists of a strong reflection at 2Â = 2.3 assigned to the (100)
2
Theta ( )
reflection and three weaker reflections at higher angles corre-
sponds to (110), (2 00) and (210) reflections of a hexagonal unit cell
Fig. 1. The XRD patterns of (a) calcined MCM-41, (b) functionalized MCM-PrCl and
c) MCM-4-NHPhSO3H.
(
[
26–28]. These reflections were maintained after the immobiliza-
tion in MCM-PrCl and MCM-4-NHPhSO H. The shifting of reflection
3
peaks (100), (110) and (200) to higher 2Â angle was observed.
However, the mesostructure was retained after incorporating the
organic groups.
mesoporosity in MCM-41, as well as the evaporation of N2 via
narrow constriction for ink-bottle cage-type mesopore [15]. The
sharp step from 0.01 to 0.2 P/P0 shows the uniform pore filling
in the lattice and the capillary condensation occurs between 0.20
3.2.2. Nitrogen sorption analysis
The nitrogen adsorption–desorption isotherms were measured
and 0.98 P/P . The specific surface areas and total pore volume
0
at liquid nitrogen temperature for all three samples. As shown
in Fig. 2, the resulting sorption isotherms were of type IV. The
isotherm, which has a percolation phenomenon in the desorption
branch was found to be similar to Ru-based cyclohexadiamine
supported on MCM-41 reported by Soundiressane et al. [26]
and chloropropyl functionalized mesoporous silica by Sujandi
et al. [15]. This phenomenon could be due to the decrease in
were calculated by Barrett–Joyner–Halenda (BJH) method and is
tabulated in Table 2. The modification resulted in the successive
reduction in the respective specific surface area and pore volume
2
−1
in MCM-4-NHPhSO H. A
from 796 in MCM-41 to 468 m g
3
similar reduction in the total pore volume can also be observed.
The pore diameter of MCM-41 was calculated from the desorption
isotherm. The pore diameter has been reduced from 28.7 to 19.8 A˚

F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
165
MCM-41
MCM-PrCl
MCM-4-NHPhSO H
3
(
a)
MCM-4-NHPhSO H
3
(
b)
(
c)
0
20
40
60
80
100
120
0.0
0.2
0.4
0.6
0.8
1.0
Pore Radius (A)
Relative Pressure, P/Po
Fig. 2. N2 adsorption and desorption isotherms at 77 K of (a) calcined MCM-41, (b) functionalized MCM-PrCl and (c) MCM-4-NHPhSO3H and pore size distribution profiles
inset) of MCM-4-NHPhSO3H.
(
Table 2
The surface properties of MCM-41 and modified samples.
Samples
d100 spacing (Å)a
Unit cell
parameter, a0 (Å)
BET surface area
Pore volume, Vp
Pore wall thickness
(Å)
Pore diameter, Wd
(Å)
b
2
−1
c
3
−1
c
b
b
(m
g
)
(cm
g
)
MCM-41
MCM-PrCl
MCM-4-NHPhSO3H
37.9
37.2
36.9
43.8
43.0
42.6
796
673
468
0.29
0.23
0.11
15.1
16.8
22.8
28.7
26.2
19.8
a
The values obtained from the XRD studies.
b
The values were calculated from the formulae [27].
The values obtained from N2 sorption studies.
c
Table 3
after every step of modification due to the accommodation of
CPTES and 4-NH PhSO H inside the mesopores.
Elemental analysis of MCM-PrCl and MCM-4-NHPhSO3H.
2
3
MCM-PrCl
MCM-4-NHPhSO3H
3
.2.3. FT-IR spectra analysis
The FT-IR spectra of the as-synthesized MCM-41, calcined MCM-
1, MCM-PrCl and MCM-4-NHPhSO H is shown in supplementary
Carbon
Hydrogen
Nitrogen
2.7
3.5
0.0
18.0
3.1
2.2
4
3
figure. The difference between the as-synthesized and the calcined
MCM-41 can be seen from Fig. S2a and b, which shows the disap-
−
1
pearance of the CH2 vibration bands at 2924 and 2845 cm [29].
This showed the complete removal of the template, i.e. CTAB. The
carbon percentage from 2.7 to 18.0 is consistent with the immobi-
lization of 4-NH2PhSO3H onto MCM-PrCl.
spectrum in Fig. S2c shows the CH vibration of the propyl groups
2
−1
at 2928 and 2861 cm , which proved to be due to the successful
functionalization of CPTES on MCM-41. For the spectrum in Fig. S2d,
the vibration band at 3228 cm was attributed to the secondary
3.2.5. Thermogravimetric analysis (TGA)
−1
The thermogravimetric analysis of MCM-4-NHPhSO H showed
3
◦
N–H bond which confirms the immobilization of 4-NHPhSO H. The
the weight loss before 120 C is due to the removal of physisorbed
3
−
1
vibration band at 3004 cm was assigned to the C–H aromatic sys-
tem, whereas the symmetrical and asymmetrical CH units were
centered at 2962 and 2804 cm . The C=C of the benzene ring was
centered at 1612 and 1452 cm , whereas the band at 1635 cm
was attributed to O–H bending mode [30]. A strong absorption band
at 1517 cm was due to the formation of new C–N bond between
MCM-PrCl and ligand, 4-NH PhSO H by the removal of HCl. The S=O
water. The mass loss is larger than the usual physisorbed water
2
on silica as the presence of SO H functional group on MCM-4-
3
−
−
1
NHPhSO H has a tendency to adsorb water through the formation
3
1
−1
of hydrogen bonds [32]. The second mass loss which is from 146 to
◦
509 C was due to the decomposition of CPTES and organic groups,
−
1
◦
while the mass loss between 500 and 893 C was due to the con-
2
3
densation of Si–OH groups to form a siloxane bond, loosing H O in
2
bond and –SO3 stretching band of sulfonic group was assigned to
the process.
−1
the vibration at 1311, 1162 and 1045 cm [30]. All spectra show
−1
bands at 1224, 1080 and 785 cm , which were attributed to the
stretching vibrations of the mesoporous silica framework (Si–O–Si)
.2.6. The 13C and 29Si CP/MAS NMR analysis of
3
MCM-4-NHPhSO H
3
[
31].
13
The C CP MAS NMR spectrum of MCM-4-NHPhSO H is shown
3
in Fig. 3a. The strong resonance at 12.27, 28.52, 49.00 and 52.75 ppm
is due to the carbons of –CH CH CH - moiety [26,28]. The CPTES
3.2.4. Elemental analysis (CHN)
2
2
2
The elemental analysis of MCM-PrCl and MCM-4-NHPhSO H are
shown in Table 3. The presence of 2.2% nitrogen and an increase in
linker has three distinct carbons labeled as C10, C11 and C12, while
the sulfonic acid ligand’s aliphatic carbons –CH CH CH – are
3
2
2
2

1
66
F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
Fig. 3. The NMR spectrum of (a) the 13C CP/MAS NMR and (b) 29Si CP/MAS NMR of MCM-4-NHPhSO3H.
indicated by C1, C2 and C3. The chemical shifts overlapped due to
distinct resonances can be clearly observed for the siloxane
network with organic fragments covalently bonded to silica: the
similar chemical environment. The immobilization of 4-NHPhSO H
3
3
onto MCM-PrCl was further confirmed by the appearance of aro-
matic peaks at 115.64 and 124.39 ppm as indicated in Fig. 3a.
chemical shift at –104.05 ppm for the Q silicon atom of the silica
4
solid, a chemical shift at –112.31 ppm for the Q silicon atom in
1
3
n
n
4−n
3
2
The solid-state C CP/MAS NMR spectra of MCM-4-NHPhSO H
the silica solid [Q = Si(OSi) (OH)
of the organosilicon atoms are seen at –68.50 and –59.51 ppm,
, n = 2–4]; the T and T signals
3
confirmed the presence of organic moieties as part of the silica.
2
9
m
m
3−m
Fig. 3b shows the Si CP/MAS NMR of MCM-4-NHPhSO H. The
respectively [T = RSi(OSi) (OH) , m = 1–3] [33].
3

F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
167
Fig. 4. The scanning electron micrographs: (a) The SEM morphology of (i) MCM-PrCl and (ii) MCM-4-NHPhSO3H and (b) the TEM image of (iii) MCM-PrCl and (iv) MCM-4-
NHPhSO3H.
3
.2.7. The transmission electron microscopy (TEM) and scanning
1
00
100
80
60
40
20
0
Conversion of TBA
Selectivity IBE
electron microscopy (SEM)
Selectivity TBPE
Selectivity 2-TBP
Selectivity 4-TBP
Fig. 4a(i) and a(ii) show the surface morphology of MCM-PrCl
8
6
4
2
0
0
0
0
0
and MCM-4-NHPhSO H with the presence of large orifices and
overlapping cylindrical worm-like structure at 30 k and 50 k mag-
nification. The TEM images of MCM-PrCl and MCM-4-NHPhSO H
show the well structured honey-comb design after immobilization
of the organic moiety as shown in Fig. 4b(iii) and (iv).
3
3
3.3. Catalytic alkylation
The Friedel–Craft alkylation of phenol by t-butyl alcohol
0
2
4
6
8
10
(
1
Scheme 2) was carried out over MCM-4-NHPhSO H from 100 to
Reaction Time (h)
3
◦
20 C, with various catalyst amount and molar ratio. The obtained
Fig. 5. The effect of reaction time on t-butylation of phenol by MCM-4-
NHPhSO3H. Reaction conditions: molar ratio of TBA (100 mmol):phenol = 1:1, cata-
lyst amount = 200 mg, reaction temperature 120 C, run time = 9 h.
products were 2-(tert-butyl)phenol (2-TBP), 4-(tert-butyl)phenol
4-TBP) and some minor tert-butylphenol ether (TBPE) and
isobutene (IBE). The reaction scheme may be depicted as follows.
(
◦
with 56.0 and 37.0% selectivity to 2-TBP and 4-TBP, respectively.
Zhang et al. [5] reported only 68.0% conversion of TBA, with 26.0%
selectivity to 2-TBP. This shows that the organo hybrid catalyst in
this study performs better than the HY zeolite reported by Zhang
et al.
3
.3.1. Effect of time on TBA conversion
Fig. 5 shows the relative activity and product selectivity of MCM-
4
1
-NHPhSO H as a function of time for alkylation of phenol by TBA at
3
◦
20 C and 1:1 molar ratio of phenol to TBA using 20 mg of catalyst.
Initially, the conversion of TBA was 25.0% in 1 h, with the main
product selective to TBPE and then it decreased with time as the
selectivity towards 2-TBP and 4-TBP increased. The conversion of
TBA increased with reaction time until it reached an equilibrium
level at 7 h. The final conversion at 7 h is 96.0% with the selectivity
towards monoalkylated products, 2-TBP (56.0%) and 4-TBP (37.0%).
3.3.3. Effect of catalyst amount
Fig. 7 shows the effect of catalyst amount on TBA conversion
studied within the range of 30–200 mg. All the different masses of
catalysts used gave approximately 98.0% conversion when the reac-
tions were carried out for 7 h. However, in order for a meaningful
comparison, the reaction time of 4 h was selected. The increase in
amount of catalyst from 30 to 50 mg had significantly increased
the conversion of TBA to 98.4% in 4 h with a selectivity of 62.0 and
33.0% for 2-TBP and 4-TBP, respectively. This result was an improve-
ment from the previous work by Adam et al. [30] which reported
a 95.0% TBA conversion in 9 h instead of 4 h reported herein. When
the catalyst amount was increased beyond 50 mg, gradual decrease
in overall conversion could be observed, with increasing selectivity
3
.3.2. Effect of reaction temperature
The effect of reaction temperature on the conversion of TBA was
◦
performed in the range of 100–120 C as shown in Fig. 6. At a lower
temperature of 100 C, the conversion of TBA was only 28.0% with a
very high selectivity of 95.0% to TBPE. This could be due to the likeli-
hood of o-alkylation occurring at the lower activation energy, which
prompted the high TBPE selectivity [10,34]. As the reaction temper-
◦
◦
ature increased to 120 C, 96.0% conversion of TBA was obtained,

1
68
F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
OH
CH3
HO
CH3
+
CH3
MCM-4-NHPhSO H
3
o
1
20 C, argon gas
H C
3
CH3
H C
3
OH
CH3
CH3
O
CH3
H C
OH
3
CH
3
H C
3
tert-butylphenol ether (1. 2 %)
4
-(tert-butyl)phenol (30. 8 %)
2
-(tert-butyl)phenol (67. 8 %)
CH3
H C
CH2
3
isobutene (0. 2 %)
Scheme 2. The reaction scheme for tert-butylation of phenol.
Conversion of TBA
Selectivity IBE
Selectivity TBPE
Selectivity 2-TBP
Selectivity 4-TBP
1
00
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
30
50
100
150
200
Zoom In
Amount of catalyst (mg)
0
0
30
50
100
150
200
Amount of catalyst (mg)
Fig. 7. The effect of catalyst amount on t-butylation of phenol by MCM-4-
Fig. 6. The effect of reaction temperature on t-butylation of phenol by MCM-4-
NHPhSO3H. Reaction conditions: molar ratio of phenol (100 mmol):TBA = 1:1, mass
of catalyst = 20 mg, 7 h.
NHPhSO3H. Reaction conditions: molar ratio of phenol (100 mmol):TBA = 1:1,
◦
1
20 C, 4 h.
to TBPE from 4.0 to 41.0%. The selectivity to the main products of
mono-alkylated 2-TBP and 4-TBP was found to gradually decrease
with increasing catalyst mass. This could be explained by the large
amount of catalyst which gives rise to agglomeration and cause
pore blocking of the active sites when the catalyst amount was
increased above 50 mg.
3
.3.4. Effect of mole ratio on TBA conversion
The effect of reactant mole ratio of TBA to phenol was conducted
in the range of 1:1, 1:2 and 1:3. From Fig. 8, it can be observed that
as the TBA:phenol feed mole ratio increased from 1:1 to 1:3, the
optimum mole ratio of 1:2 of TBA to phenol was found to have the
highest selectivity for 2-TBP (67.8%). A total of 99.5% conversion of

F. Adam, C.-W. Kueh / Applied Catalysis A: General 489 (2015) 162–170
169
Conversion of TBA
Reusability
1
00
100
80
60
40
20
0
Selectivity IBE
Selectivity TBPE
Selectivity 2-TBP
Selectivity 4-TBP
1
00
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
1
:1
1:2
1:3
TBA: Phenol
Zoom In
Conversion of TBA
Selectivity IBE
Selectivity TBPE
Selectivity 2-TBP
Selectivity 4-TBP
Fresh
Reuse 1
Reuse 2
Reuse 3
3
0
3
0
Fig. 9. The reusability of MCM-4-NHPhSO3H in the t-butylation of phenol. Reaction
conditions: molar ratio of phenol (100 mmol):TBA = 2: , mass of catalyst = 50 mg,
◦
1
20 C, 4 h.
This shows that the catalytic activity depends on the presence of
the sulfonic acid group on the catalyst surface. It should be high-
lighted here that if one desires to obtain TBPE in high yield, then
MCM-PrCl could be used as the catalyst. It is believed that this reac-
tion is worthwhile investigating in the future, despite the fact the
conversion was only 15.4%.
1
:1
1:2
1:3
TBA: Phenol
Fig. 8. The effect of reactant mole ratio on t-butylation of phenol by MCM-4-
NHPhSO3H. Reaction conditions: mass of catalyst = 50 mg, 120 C, 4 h.
◦
4. Conclusions
TBA was recorded in a short 4 h reaction time. The higher affinity of
phenol adsorbing on the active sites allows the primary generation
of carbenium ion to react readily with sufficient phenol adsorbed
in close proximity [35]. Furthermore, the higher ratio of phenol to
TBA is able to prevent formation of dialkylated products [35]. The
reported catalytic activity was two times faster from the work by
Adam et al. which reported a 95.0% conversion of TBA within a
longer reaction time of 9 h [30].
A novel organo-inorganic hybrid material was successfully syn-
thesized via a simple post-synthesis method. The organic species
bearing the sulfonic acid group was able to tether onto the MCM-
4
1 mesoporous silica and maintained the honey-comb structure of
the original MCM-41. The catalyst was tested in the solvent-free
liquid-phase tert-butylation of phenol and gave a high 99.5% TBA
conversion in 4 h with good selectivity of 67.8% 2-TBP and 30.8%
4
-TBP. The catalyst was selective to only mono-alkylated products.
3
.3.5. Reusability studies on the catalyst
In order to study the recoverability and recyclability of MCM-4-
Acknowledgements
NHPhSO H, this organo-hybrid catalyst was regenerated by simple
washing with dichloromethane, acidified ethanol and dried at
3
The authors would like to thank Universiti Sains Malaysia
for the Postgraduate Research Grant Scheme (PRGS)
◦
1
10 C for 24 h. Fig. 9 shows only a slight decrease in the catalytic
(1001/PKIMIA/844073 and 1001/PKIMIA/811092) and RU research
◦
activity after several reuse under the optimum conditions of 120 C,
with 50 mg of catalyst and 1:2 mole ratio of TBA:phenol for 4 h. This
could be due to the loss of active catalytic sites after several consec-
utive reused. Some of the organic ligands anchored on the external
surface and accessible pores of MCM-41 could be washed away by
the solvents. This can be further correlated with the XRD analysis
grant (No. PKIMIA/814019) which partly supported this work.
C.W.K. would also like to thank the National Science Fellowship
(NSF) of Malaysia for the scholarship provided.
Appendix A. Supplementary data
of the reused MCM-4-NHPhSO H. The used catalyst was charac-
3
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
terized once again using the XRD and TEM analyses. The image in
Fig. S3 shows that the catalyst’s morphology was not altered upon
being used as a catalyst.
2
014.09.047.
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