Sulfuric acid functional zirconium (or aluminum) incorporated mesoporous MCM-48 solid acid catalysts for alkylation of phenol with tert-butyl alcohol

Article abstract of DOI:10.1016/j.jssc.2014.06.021

Several zirconium (or aluminum) incorporated mesoporous MCM-48 solid acid catalysts (SO₄^2-/Zr-MCM-48 and SO₄ ^2-/Al-MCM-48) were prepared by the impregnation method and their physicochemical properties were characterized by means of XRD, FT-IR, TEM, NH₃-TPD and N₂ physical adsorption. Also, the catalytic activities of these solid acid catalysts were evaluated by the alkylation of phenol with tert-butyl alcohol. The effect of weight hour space velocity (WHSV), reaction time and reaction temperature on catalytic properties was also studied. The results show that the SO₄^2-/Zr-MCM-48 and SO₄^2-/Al-MCM-48 still have good mesoporous structure and long range ordering. Compared with the Zr (or Al)-MCM-48 samples, SO ₄^2-/Zr-MCM-48 and SO₄^2-/Al-MCM-48 solid acid catalysts have strong acidity and exhibit high activities in alkylation reaction of phenol with tert-butyl alcohol. The SO₄ ^2-/Zr-MCM-48-25 (molar ratio of Si/Zr=0.04) catalyst was found to be the most promising and gave the highest phenol conversion among all catalysts. A maximum phenol conversion of 91.6% with 4-tert-butyl phenol (4-TBP) selectivity of 81.8% was achieved when the molar ratio of tert-butyl alcohol:phenol is 2:1, reaction time is 2 h, the WHSV is 2 h^-1 and the reaction temperature is 140 °C.

Full text of DOI:10.1016/j.jssc.2014.06.021

Journal of Solid State Chemistry 218 (2014) 71–80
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Sulfuric acid functional zirconium (or aluminum) incorporated
mesoporous MCM-48 solid acid catalysts for alkylation of phenol
with tert-butyl alcohol
n
Tingshun Jiang , Jinlian Cheng, Wangping Liu, Lie Fu, Xuping Zhou, Qian Zhao, Hengbo Yin
School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301#, Zhenjiang 212013, PR China
a r t i c l e i n f o
a b s t r a c t
2
ꢀ
Article history:
Received 3 April 2014
Received in revised form
Several zirconium (or aluminum) incorporated mesoporous MCM-48 solid acid catalysts (SO /Zr-MCM-
4
48 and SO2 /Al-MCM-48) were prepared by the impregnation method and their physicochemical
properties were characterized by means of XRD, FT-IR, TEM, NH -TPD and N physical adsorption. Also,
3 2
the catalytic activities of these solid acid catalysts were evaluated by the alkylation of phenol with tert-
ꢀ
4
12 June 2014
Accepted 15 June 2014
Available online 23 June 2014
butyl alcohol. The effect of weight hour space velocity (WHSV), reaction time and reaction temperature
on catalytic properties was also studied. The results show that the SO2
ꢀ
/Zr-MCM-48 and SO
2ꢀ
4
/Al-MCM-
4
Keywords:
4
8 still have good mesoporous structure and long range ordering. Compared with the Zr (or Al)–MCM-48
2
4
ꢀ
ꢀ
SO
SO
/Zr-MCM-48
/Al-MCM-48
2ꢀ
2ꢀ
4
samples, SO
4
/Zr-MCM-48 and SO
/Al-MCM-48 solid acid catalysts have strong acidity and exhibit
2
4
2ꢀ
high activities in alkylation reaction of phenol with tert-butyl alcohol. The SO
4
/Zr-MCM-48-25 (molar
Solid acid catalyst
Impregnation method
Alkylation
ratio of Si/Zr¼0.04) catalyst was found to be the most promising and gave the highest phenol conversion
among all catalysts. A maximum phenol conversion of 91.6% with 4-tert-butyl phenol (4-TBP) selectivity
of 81.8% was achieved when the molar ratio of tert-butyl alcohol:phenol is 2:1, reaction time is 2 h, the
ꢀ
1
WHSV is 2 h
and the reaction temperature is 140 1C.
&
2014 Elsevier Inc. All rights reserved.
1
. Introduction
Acid catalysts play a vital role in organic synthesis. Many
products, viz. alkylphenols such as 2-t-butyl phenol (2-TBP), 4-t-
butyl phenol (4-TBP) and 2, 4-di-t-butyl phenol (2,4-DTBP) are
widely used as raw materials or important intermediates in some
areas such as phenol resins, petrochemicals, fine chemicals, anti-
oxidants, rubber chemicals, heat stabilizers of polymeric materials,
agrochemical, etc. [9–11]. In consideration of societal, environ-
mental and economic pressures, many efforts for the target
reaction have recently been carried out by environmental friendly
solid acid catalysts including ion-exchanged resins, zeolite, clay-
based catalysts and mesoporous molecular sieves [12–16]. Among
solid acid catalysts, cation-exchanged resins exhibit good perfor-
mance, but they are thermally unstable at high reaction tempera-
ture. Microporous zeolites have high acidity, high thermal stability
and easy separation from reaction products [17,18]; however,
these microporous materials possess small pore size (o2 nm),
which severely limits the formation of butylated products like 2,
4-DTBP.
organic reactions such as alkylation, isomerization, esterification,
cracking, acylation, nitration, condensation, etc., are accomplished
by acid catalysts. Conventionally, these organic reactions were
carried out by homogeneous liquid acid catalysts such as sulfuric
acid, phosphoric acid, hydrofluoric acid, etc. However, the use of
liquid acid catalysts encountered some disadvantages like increas-
ing waste disposal costs, heavy environmental pollution, corro-
siveness and low reaction selectivity [1–4]. This severely limits
their applications in industry. Owing to some advantages of solid
acid catalysts such as high reactivity, no corrosion, environmen-
tally friendliness, easy handling, inexpensive and easy to recover
and reuse [5–7], numerous efforts have been made with novel
heterogeneous solid acid catalysts to replace traditional homo-
geneous liquid acid ones.
Alkylation of phenol with tert-butyl alcohol, an interesting
industrial organic reaction, has received great interest due to the
immense application of the butylated phenol in chemical indus-
tries [4,8]. Alkylation of phenol with tert-butyl alcohol yields
M41S family mesoporous materials, discovered in 1992 [19],
have potential application in some fields of catalysis, adsorption,
materials science and petrochemical industry due to their high
surface areas and tunable pore diameters [20,21]. Recently, much
attention is paid to the study of the sulfonic acid functionalized
mesoporous materials. Li et al. [22] synthesized the mesoporous
2
ꢀ
n
superacid catalysts SO
various technologies characterization results reveal that the
/ZrO –SiO by the one-pot method and
Corresponding author. Tel./fax: þ86 511 88791800.
4 2 2
E-mail address: tshjiang@mail.ujs.edu.cn (T. Jiang).
http://dx.doi.org/10.1016/j.jssc.2014.06.021
0
022-4596/& 2014 Elsevier Inc. All rights reserved.

72
T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
resulting superacid catalyst has some potential applications for
catalytic reactions of large molecules. Bhaumik et al. [23] reported
that the mesoporous ZrO nanomaterial was synthesized by an
2
evaporation-induced self-assembly method and was sulfated by
dilute sulfuric acid. The results show that the resulting sulfated
mesoporous zirconia nanometerial exhibits very high catalytic
activity in the Friedel-Crafts alkylation of aromatics. Ref. [24]
reported the preparation of 3-Propylsulfonic acid-functionalized
SBA-15 solid acid catalyst by post synthesis grafting of
CTAB was added into the mixture with vigorous stirring for 30 min
at 35 1C. After that, 10 ml of TEOS was slowly added into the above
mixture and the reaction mixture was stirred for another 60 min
until a homogeneous gel was obtained. The initial gel (molar)
composition was 1TEOS: x Zr(or Al): 0.65CTAB: 0.5NaOH: 0.1NaF:
62H
2
O (x¼0.02 and 0.04, respectively). The resulting mixture was
transferred into a 100 ml Teflon-lined stainless autoclave and
crystallized at 120 1C for 24 h in an oven. The obtained solid
product was filtered, washed with deionized water, and dried at
60 1C for 24 h. The resulting sample was calcined at 550 1C for 6 h
in air at a heating rate of 2 1C/min. The calcined sample is denoted
as M-MCM-48-x, where M stands for Zr or Al, and x is the molar
ratio of Si/M in synthesis gel.
3
-mercaptopropyl group on highly ordered SBA-15 mesoporous
material and the experimental results demonstrate that a highly
efficient conversion of α, β-substituted nitroethanols to corre-
sponding nitroolefins over this solid acid catalyst can be obtained
under mild reaction conditions. To our knowledge, the catalytic
activities of some mesoporous solid acid catalysts have been
evaluated by t-butylation of phenol [25,26] and the experimental
results reveal that mesoporous solid acid catalysts are the more
ideal ones for t-butylation of phenol as compared with the others
solid acid catalysts like cation-exchange resins and microporous
materials. However, many of the previous reports are focused on
the study of mesoporous MCM-41 solid acid catalysts. Little
attention is paid to investigation on mesoporous MCM-48 solid
acid catalysts. Compared with the one-dimensional channel struc-
ture of MCM-41, MCM-48 was found to be a more potent and
interesting candidate as catalyst or catalyst support due to its
attractive and unique cubic arrangement of three-dimensional
interwoven structure [27], which can effectively avoid pore block
by guest molecules.
2.3. Preparation of solid acid catalysts
2
ꢀ
2ꢀ
4
SO
4
/Zr-MCM-48 and SO
/Al-MCM-48 solid acid catalysts
were prepared by the wet impregnation method. Typically, 2 g of
Zr-MCM-48(or Al-MCM-48) sample was dissolved in 0.4 mol/L of
H SO solution with stirring for 1 h. The obtained suspension was
2 4
statically placed at ambient temperature for 8 h till the suspension
was deposited. After evaporating the solvent, the residual solid
was dried at 100 1C for 12 h in an oven. The dried sample was
calcined at 550 1C for 3 h in air at a heating rate of 2 1C/min, and
2
ꢀ
2ꢀ
2ꢀ
4
denoted as SO
4
/Zr-MCM-48-25, SO
4
/Zr-MCM-48-50, SO
ꢀ
4
/Al-MCM-48-50, correspondingly.
/
2
Al-MCM-48-25 and SO
2.4. Characterization
2
ꢀ
2ꢀ
4
In this present work, several SO
4
/Zr-MCM-48 and SO
/Al-
MCM-48 solid acid catalysts were prepared by the impregnation
method and their catalytic activities were evaluated by the
alkylation of phenol with tert-butyl alcohol. We discussed in detail
the effect of WHVS, reaction time and temperature on the phenol
XRD patterns were recorded on a powder XRD instrument
(Rigaku D/max 2500PC) with Cu Kα radiation (λ¼0.154 18 nm)
operating at 40 kV and 50 mA in a 2θ range of 1–101. FT-IR spectra
were recorded on a Nexus FT-IR 470 spectrometer made by Nicolet
Corporation (USA) with KBr pellet technique. The effective range
2
ꢀ
conversion and product selectivity. It is found that the SO
4
/Zr-
ꢀ
1
MCM-48-25 catalyst exhibits the highest catalytic activity among
the four solid acid catalysts. A maximum phenol conversion of
2
was from 400 to 4000 cm . N adsorption–desorption isotherms
at 77 K were recorded with a NOVA2000e analytical system made
by Quantachrome Corporation (USA). Prior to measurement, all
samples were outgassed at 300 1C for 3 h. The specific surface area
was calculated by the BET method. Pore size distribution was
calculated from the desorption branch using the BJH method.
Transmission electron microscopy (TEM) morphologies of samples
were observed on a Philips TEMCNAI-12 with an acceleration
91.6% with 81.8% selectivity to 4-TBP was attained at the optimum
reaction conditions. In particular, the use of solid acid catalyst
2
ꢀ
(
SO /Zr (or Al)-MCM-48) to replace the conventional liquid acid
4
catalyst in alkylation of phenol with tert-butyl alcohol aimed at
avoiding environmental concerns and converted polluting pro-
2
ꢀ
cesses into greener ones. The SO
4
/Zr-MCM-48 solid acid catalysts
are hopeful to be an ideal catalyst for alkylation of phenol with
tert-butyl alcohol.
voltage of 100–120 kV. NH
(NH -TPD) profiles of the samples were carried out on a TP-5000
adsorption instrument made by Tianjin Xianquan Corporation
China). In a standard procedure, the catalyst (500 mg) was
activated at 400 1C in pure nitrogen flow for 1 h, and then cooled
down to room temperature and began to adsorb ammonia to
saturation following by flushing the samples with helium gas at
3
temperature-programmed desorption
3
(
2
. Experimental
2.1. Starting materials
8
0 1C for 40 min until the integrator baseline was stable. NH
curves were obtained at a heating rate of 10 1C/min from 80 to
00 1C. The TPD was measured with a TCD detector. Si content in
3
-TPD
Tetraethyl orthosilicate (TEOS), zirconium sulfate (Zr(SO
4
)
2
ꢁ
4
H
2
O), aluminum sulfate (Al
2
(SO
4
)
3
2
ꢁ 18H O) and cetyltrimethyl
8
ammonium bromide (CTAB) were used as sources for silicon,
zirconium, aluminum and template, respectively. Phenol and
tert-butyl alcohol were used for phenol alkylation reaction. More-
over, sodium hydroxide (NaOH), sodium fluoride (NaF) and con-
the sample was determined by the gravimetric method. Zr or Al
content in the sample was determined by inductive coupled
plasma (ICP) technique (Vista-MAX, Varian).
2 4
centrated sulfuric acid (H SO ) were also used in the experiment.
2.5. Alkylation reaction
All chemicals were of analytical grade and they are purchased
from Shanghai Chemical Reagent Corporation, PR China.
The alkylation of phenol with tert-butyl alcohol was carried out
in a fixed-bed flow reactor (WFD-3030) with a stainless steel
reaction tube. Before the start of the reaction, the catalysts were
activated at 400 1C in air for 10 h followed by cooling to room
temperature in nitrogen atmosphere. In a typical run, 500 mg of
catalyst was placed in the reaction tube, and the reactant mixture,
i.e., phenol and tert-butyl alcohol, was fed into the preheating
reactor using a liquid injection pump (WMCB102-A) at a flowing
2
.2. Synthesis of Zr (or Al)-MCM-48 mesoporous molecular sieves
A typical synthesis procedure of Zr (or Al)-MCM-48 mesopor-
ous molecular sieves was as follows: a required amount of Zr
SO O (or Al (SO ꢁ 18H O), 0.9 g of NaOH and 0.19 g of
ꢁ 4H
NaF were dissolved in 50 ml distilled water, and then 10.62 g of
(
4
)
2
2
2
4
)
3
2

T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
73
rate of 60 mL/min using N
2
as the carrier gas. In this case, the
sample increased. This may be due to the partial collapse of the
cubic ordered phase aroused by the incorporation content increas-
ing of Zr (or Al) species into the mesoporous framework. On the
preheating temperature was kept at 75 1C. After that, the pre-
heated reactant mixture with a flowing nitrogen entered into the
fixed-bed flow reactor to process alkylation reaction. The effluents
were cooled to room temperature in air and collected at every 2 h
interval. The products were analyzed by SP-2000 gas chromato-
graph fitted with a SE-54 capillary column coupled with FID.
other hand, it is also noticed that after impregnation using H
2
SO
4
2
ꢀ
2ꢀ
4
solution, the resulting SO
4
/Zr-MCM-48 and SO
/Al-MCM-48
samples still have the cubic mesoporous structure. However,
compared with the Zr (or Al)-MCM-48 samples, the intensities of
the main diffraction peak (211) and the shoulder peak (220) of
2
ꢀ
2ꢀ
4
SO
4
/Zr-MCM-48 and SO
/Al-MCM-48 samples decreased, and
3
. Results and discussion
the other planes (420 and 332) weakened obviously, implying that
the crystallinity of the resulting solid acid samples clearly lose and
the mesoporous ordering evidently decreased after impregnation
3.1. XRD analysis
using H
The cubic unit cell parameters a
samples were calculated by formulas
2 4
SO solution.
Fig. 1a–d displays XRD patterns of various samples. From
0
and d211 values of several
Fig. 1a, for the Zr-MCM-48-50 sample, the diffraction peaks at ca.
.401, 2.781, 4.581 and 4.801 are assigned to (211), (220), (420) and
332), which clearly indicates the formation of the Ia3d cubic
a
0
¼ d211 ꢂ √6 and
2
(
2d211 sin θ ¼ nλ, respectively. The results are listed in Table 1.
According to Table 1, the d211 values and cubic unit cell parameters
mesoporous structure with long range ordering [28]. Also, similar
observation can be noted from the XRD patterns of the other
samples (see Fig. 1b–d), indicating that these samples have the
typical Ia3d cubic mesoporous structure. Further, we found that
the intensities of the characteristic peaks weakened with the
increasing of Zr (or Al) content in sample, suggesting that the
mesoporous ordering decreased gradually as Zr (or Al) content in
0
a increased with an increase in Zr (or Al) content. Similar results
are reported in Ref. [29].
3.2. Results of nitrogen physical adsorption
2
The N adsorption–desorption isotherms of all samples are
shown in Fig. 2. As shown in Fig. 2, all isotherms are of typical type
Table 1
Analysis results of XRD and structure properties for various samples.
n
n
2
Samples
Si/Zr or Si/Al
d211 (nm)
a
0
(nm)
S
BET (m /g)
BJH pore size (nm)
Zr-MCM-48-50
Zr-MCM-48-25
Al-MCM-48-50
Al-MCM-48-25
58.25
27.63
61.24
28.51
59.36
38.45
63.31
39.87
3.68
3.82
3.45
3.51
3.65
3.79
3.45
3.49
9.01
9.36
8.45
8.60
8.94
9.38
8.45
8.54
1246.99
1007.08
1247.72
1102.09
975.16
937.33
1090.23
1025.05
2.5
2.5
2.47
2.47
2.46
2.45
2.44
2.46
2
4
2
4
2
4
ꢀ
ꢀ
ꢀ
ꢀ
SO
SO
SO
SO
/Zr-MCM-48-50
/Zr-MCM-48-25
/Al-MCM-48-50
/Al-MCM-48-25
2
4
n
Molar ratio of Si/Zr or Si/Al in sample.
211
211
hkl d(nm)
hkl d(nm)
211 3.82
220 3.25
420 1.93
332 1.86
211 3.68
220 3.18
420 1.92
332 1.84
220
220
420 332
Zr-MCM-48-25
420 332
Zr-MCM-48-50
SO /Zr-MCM-48-25
SO /Zr-MCM-48-50
0
2
4
6
8
10
0
2
4
6
8
10
2
Theta(degree)
2Theta(degree)
211
hkl d(nm)
211
hkl d(nm)
211 3.51
220 3.04
420 1.90
332 1.81
211 3.45
220 2.99
420 1.88
332 1.80
2
20
2
20
420 332 Al-MCM-48-50
4
20332 Al-MCM-48-25
SO /Al-MCM-48-25
SO /Al-MCM-48-50
0
2
4
6
8
10
0
2
4
6
8
10
2
Theta(degree)
Fig. 1. XRD patterns of various samples.
2Theta(degree)

74
T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
Zr-MCM-48-50
Zr-MCM-48-25
5
4
3
2
00
00
00
00
4
3
2
00
00
00
2
.5nm
2.5nm
0
0
0
.16
.08
.00
0
.10
.05
.00
0
0
0
2
4
6
8
10
0
2
4
6
8
10 12
Pore size/nm
Pore size/nm
0
.0
.0
.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure(p/p0)
Relative pressure(p/p0)
4
3
2
1
00
00
00
00
SO42-/Zr-MCM-48-50
SO42-/Zr-MCM-48-25
4
3
2
00
00
00
2.46nm
0.08
2.45nm
0
0
0
0
.12
.08
.04
.00
0.04
0.00
0
4
8
12
16
0
4
8
12
16
Pore size/nm
Pore size/nm
0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure(p/p0)
Relative pressure(p/p0)
5
4
3
2
00
00
00
00
600
Al-MCM-48-50
Al-MCM-48-25
0
.16
2
.47nm
2.47nm
0
0
.16
.12
0.12
0.08
4
2
00
00
0.08
0
0
.04
.00
0
0
.04
.00
0
4
8
12
16
0
4
8
12
16
Pore size/nm
Pore size/nm
0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure(p/p0)
Relative pressure(p/p0)
SO42-/Al-MCM-48-50
400 SO42-/Al-MCM-48-25
5
4
3
2
00
0
0
0
.08 2.46nm
2
.44nm
00
00
00
3
2
1
00
00
00
0
0
0
.08
.04
.00
.04
.00
0
4
8
12
16
0
4
8
12
16
Pore size/nm
Pore size/nm
0
.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure(p/p0)
Relative pressure(p/p0)
Fig. 2. N
2
adsorption–desorption isotherms and pore size distribution curves of various samples.
IV isotherms with hysteresis loop as defined by IUPAC, suggesting
that these samples have typical mesoporous framework [30]. Also,
a sharp inflection owing to capillary condensation within uniform
0
mesopores was observed at the relative pressure (p/p ) between
0.25 and 0.4, which is characteristic of the cubic MCM-48
mesoporous materials. The sharpness and height of the inflection

T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
75
2
ꢀ
reflect the pore size uniformity [31]. On the other hand, the BJH
pore size distribution curves are shown in the graphs in Fig. 2.
From the inset in Fig. 2, the narrow and sharp pore size distribu-
tion peaks can be noted.
samples. On the other hand, for SO
4
/Zr-MCM-48 samples, the
intensity and area of desorption peak corresponding to the strong
2
ꢀ
acid sites for the SO
4
/Zr-MCM-48-25 sample is much larger than
2
ꢀ
2
ꢀ
that of the SO
4
/Zr-MCM-48-50 sample, showing that the SO /
4
The corresponding textural properties including the specific
surface areas and pore sizes calculated by the BET and BJH
methods are summarized in Table 1. From Table 1, all samples
exhibit an average pore size of ca. 2.5 nm, which agrees with the
inserted pore size distribution curves. Moreover, we found that the
BET specific surface area of Zr-MCM-48 (or Al-MCM-48) sample
decreased with Zr (or Al) incorporation content increasing in
synthesis gel, which is probably attributed to the loss of the lattice
ordering of MCM-48 framework aroused by increasing of incor-
porating content of Zr (or Al). Also, the BET specific surface areas of
Zr-MCM-48-25 sample has much strong acid sites and the amount
of the strong acid sites increase with the increase of Zr content.
Thus, it can be concluded that the acid amounts of these catalysts
2
ꢀ
2ꢀ
decreased in the following order: SO
4
/Zr-MCM-48-254SO
4
/Zr-
2
ꢀ 2ꢀ
MCM-48-504SO
/Al-MCM-48-254SO /Al-MCM-48-504Zr-
4 4
MCM-48-254Al-MCM-48-25.
3.4. FT-IR analysis
The FT-IR spectra of various samples are shown in Fig. 4. The
2
ꢀ
2ꢀ
ꢀ1
SO
4
/Zr-MCM-48 (or SO
SO
4
/Al-MCM-48) samples obtained after
solution decreased as compared with
absorption band at 1080 cm
is attributed to anti-symmetric
impregnation using H
2
4
stretching vibration of the silica framework. The band approxi-
ꢀ
1
Zr-MCM-48 (or Al-MCM-48) samples, suggesting that the meso-
porous frameworks of these samples were slightly damaged and
the mesoporous ordering decreased. This is in agreement with the
analysis XRD results.
mately at 795 cm
is aroused by the vibration of Si–O–Si bond.
ꢀ
1
The band at 1649 cm may be attributed to surface silanol groups
and adsorbed water molecules. Additionally, it can be seen that the
four solid acid catalysts all exhibit the absorption band at ca.
380 cm corresponding to SQO, which may be regarded as the
characteristic band of SO
ꢀ
1
1
2
ꢀ
4
in solid acid catalyst [32], suggesting
3
.3. NH
3
-TPD analysis
2ꢀ
that SO
4
has been introduced into the mesoporous framework.
ꢀ
1
The band at 1380 cm
is probably attributed to the interaction
Ammonia adsorption–desorption technique generally was used
2ꢀ
2ꢀ
4
and metallic element [33]. The structure of SO /Zr
between SO
4
to determine the strength and amount of acid sites present on the
surface of catalyst. Usually, the low temperature desorption peak
below 200 1C is due to surface hydroxyl groups from weak acid
sites. The high temperature desorption peak located at above
2ꢀ
4
or Al)-MCM-48 and acid sites on the SO /Zr (or Al)–MCM-48 are
(
presented in Schemes 1 and 2. From Scheme 1, the central metal
ion acts Lewis sites and the inductive effect of SQO in sulfate
complex strongly influenced its acid strength. Brönsted acid sites
may be due to the weakening of the O–H bond by the inductive
effect of neighboring sulfate groups [7,34].
3
00 1C was assigned to the moderate and strong (Brönsted) acid
sites [17], which was aroused by the presence of trivalent alumi-
num (or other metal) in two different framework positions. The
NH
be seen that the Zr-MCM-48-25 and Al-MCM-48-25 samples only
exhibit one NH desorption peak around 180 1C, indicating that the
two catalysts have certain number of weak acid sites and the
strong acid sites are lacking. Also, we can observe that four solid
3
-TPD profiles of all samples are depicted in Fig. 3. Clearly, it can
3
.5. TEM analysis
3
The TEM images of various samples are displayed in Fig. 5.
Clearly, all samples exhibit well-defined ordered mesoporous
structure of MCM-48. However, as shown in Fig. 5e–h, it was
found that the mesoporous framework of four solid acid catalysts
was partial damaged as compared with the Zr (or Al)-MCM-48
samples. This suggests a loss of mesoporous ordering of these
samples obtained after impregnation using H SO solution. More-
2 4
over, selected area electron diffraction (SAED) patterns of the TEM
images of the Zr-MCM-48-25 and SO
are shown in Fig. 5. It is confirmed that pore walls of our prepared
acid catalysts all exhibit one NH
3
desorption peak around ca.
3
50 1C except for the desorption peak located at the same low
temperature, suggesting that the four catalysts have both the weak
acid sites and the strong acid sites. However, the adsorption peaks
of SO2
(
4
ꢀ
/Zr-MCM-48 samples located at the higher temperature
4
2
ꢀ
ca. 350 1C) are observed clearly as compared with SO
8 samples. This indicates that the strong acid sites of SO /Zr-
MCM-48 samples are much more than that of SO
4
/Al-MCM-
2ꢀ
4
/Zr-MCM-48-25 samples
2
ꢀ
4
2
ꢀ
4
/Al-MCM-48
materials belong to amorphous structure.
3
3
.6. Catalytic activity
.6.1. Effect of reaction temperature on phenol conversion and
product selectivity
The effect of reaction temperature on the alkylation of phenol
with tert-butyl alcohol was investigated over various catalysts in
the temperature range of 100–180 1C for 2 h (Fig. 6). Obviously, in
all cases, the phenol conversion increased as the reaction tem-
perature increased in the temperature range of 100–140 1C and a
maximum phenol conversion over six catalysts was achieved at
a
b
c
d
e
140 1C. Further, the phenol conversion decreased with increase in
reaction temperature from 140 to 180 1C. This phenomenon may
be due to the following: the butylation of phenol undergoes
dealkylation at higher temperature and the dealkylation is domi-
nant. Thus, phenol conversion decreased at higher temperature
f
1
00
200
300
400
500
600
700
[
35]. Additionally, from Fig. 6, it can be observed that the max-
2
ꢀ
2ꢀ
4
Temperature /°C
imum phenol conversion of SO
48-50, SO
/Zr-MCM-48-25, SO
/Zr-MCM-
4
2
ꢀ
2ꢀ
4
2
ꢀ
2
ꢀ
4
/Al-MCM-48-25, SO
/Al-MCM-48-50, Zr-MCM-48-
Fig. 3. NH
MCM-48-50; (c) SO
5; (f) Al-MCM-48-25.
3
-TPD profiles of various samples. (a) SO /Zr-MCM-48-25; (b) SO /Zr-
4
4
2
ꢀ
2
ꢀ
25 and Al-MCM-48-25 catalysts at 140 1C is 91.6%, 77.3%, 74.5%,
66.5%, 27.9% and 39.9%, respectively. By comparing with the results
4
/Al-MCM-48-25; (d) SO / Al-MCM-48-50; (e) Zr-MCM-48-
4
2

76
T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
Zr-MCM-48-50
Zr-MCM-48-25
Al-MCM-48-50
Al-MCM-48-25
SO42-/Al-MCM-48-50
SO42-/Zr-MCM-48-50
SO42-/Al-MCM-48-25
SO42-/Zr-MCM-48-25
500
1000
Wavenumber/(cm )
Fig. 4. FT-IR spectra of various samples.
1500
2000
500
1000
1500
2000
-1
Wavenumber/(cm-1)
δ−
H+ δ−
O
O
O
O
O
O
+
H O
S
O
M
2
S
O
O
O
O
O
_
H O
2
Si
Si
Si
M
Si
OH
Lewis acid site
Bronsted acid site
2
ꢀ
2ꢀ
4
Scheme 1. Structure of SO
4
/M-MCM-48 and acid sites on the SO
/M-MCM-48(M¼Zr or Al) .
O
weak acid or
basic sites
TPBE
OH
OH
strong acid sites
moderate
acid sites
and higher temperature
+
OH
2-TBP
moderate
acid sites
isomerization
medium or stong
acid sites
OH
OH
OH
strong
medium or stong
acid sites
acid sites
4-TBP
2,4-DTBP
2,4,6-TTBP
OH
strong acid sites
and higher temperature
3
-TBP
Scheme 2. Effect of acid sites on the alkylation of phenol using tert-butanol (adapted from [17]) .

T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
77
2
ꢀ
Fig. 5. TEM images of various samples and SAED patterns of the TEM images of the Zr-MCM-48-25 and SO
2
4
/Zr-MCM-48-25 samples. (a) Zr-MCM-48-50; (b) Zr-MCM-48-
2
ꢀ 2ꢀ 2ꢀ 2ꢀ
5; (c) Al-MCM-48-50; (d) Al-MCM-48-25; (e) SO /Zr-MCM-48-50; (f) SO /Zr-MCM-48-25; (g) SO /Al-MCM-48-50; (h) SO /Al-MCM-48-25.
4
4
4
4

78
T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
1
00
100
80
100
80
60
40
20
0
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
Phenol
,4DTBP
2
6
4
2
0
0
0
0
Phenol
,4DTBP
2
4
TBP
TBP
2
2
4
TBP
TBP
1
00
120
140
160
180
100
120
140
160
180
Temperature /°C
Temperature /°C
1
00
100
80
60
40
20
0
100
100
Phenol
8
6
4
2
0
0
0
0
0
80
60
40
20
0
80
60
40
20
0
2
,4DTBP
Phenol
2
4
2
TBP
TBP
,4DTBP
2TBP
4TBP
1
00
120
140
160
180
100
120
140
160
180
Temperature /°C
Temperature /°C
1
00
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
Phenol
2TBP
Phenol
2TBP
4TBP
8
6
4
2
0
0
0
0
0
4
2
TBP
,4DTBP
2,4DTBP
1
00
120
140
160
180
100
120
140
160
180
Temperature /°C
Temperature /°C
Fig. 6. Phenol conversion and product selectivity over various catalysts at different reaction temperatures (reaction conditions: WHSV¼2 hꢀ1, ntert -butanol/nphenol¼2:1, time:
h). (a) SO2
ꢀ 2ꢀ 2ꢀ
/Zr-MCM-48-25; (b) SO /Zr-MCM-48-50; (c) SO /Al-MCM-48-25; (d) SO / Al-MCM-48-50; (e) Zr-MCM-48-25; (f) Al-MCM-48-25
2-
2
4 4 4 4
2
ꢀ
of the phenol conversion over various catalysts, the SO
4
/Zr-
perature range of 100–180 1C, the selectivity to 4-TBP increased
with increase of reaction temperature, accompanied with the
selectivity to 2-TBP and 2, 4ꢀDTBP decreased. This may be owing
to the following reasons: with increase of reaction temperature,
steric hindrance of 2-TBP increased [36]. The other one is that
the dealkylation is dominant at higher temperature leading to
the effortless formation of 4-TBP with low steric hindrance.
MCM-48-25 solid acid catalyst exhibits the highest catalytic
activity among all catalysts. This may be due to the amount of
2
ꢀ
the strong acid sites for SO
that of the others samples (see Fig. 3). Therefore, the SO
4
/Zr-MCM-48-25 sample is more than
2
ꢀ
4
/Zr-
MCM-48-25 catalyst can be regarded as the ideal catalyst for the
alkylation reaction of phenol with tert-butyl alcohol and the
optimum reaction temperature should be 140 1C. Moreover,
it is noted that the phenol conversion is related to the metal
2
ꢀ
Moreover, the maximum selectivity to 4-TBP over SO
4
/Zr-MCM-
48-25 catalyst is 93.8% at 180 1C, accompanied with the maximum
selectivity to 2, 4-DTBP of 57.7% at 100 1C. This suggests that the
higher temperature is favorable for the formation of 4-TBP and the
2,4-DTBP is easily formed at the lower temperature.
2
ꢀ
content in sample. For SO
4
/Zr-MCM-48 samples, the phenol
conversion increased with the variation of the Si/Zr molar
ratio from 50 to 25, implying that the solid acid catalyst with
higher Zr content exhibits high catalytic activity. This is probably
attributed to increase in amount of acid sites with increase in Zr
2
ꢀ
content. Similar trend was also observed over SO
catalysts.
4
/Al-MCM-48
3.6.2. Effect of weight hour space velocity on phenol conversion and
product selectivity
On the other hand, it is notably found that the major products
over various catalysts are 4-TBP, 2-TBP and 2, 4-DTBP according to
Fig. 6. No 2, 6-DTBP and 2, 4, 6-TTBP were observed. In the tem-
Fig. 7 shows the effect of weight hour space velocity (WHSV)
2
ꢀ
on alkylation of phenol with tert-butyl alcohol over SO
MCM-48-25 catalyst. As shown in Fig. 7, the phenol conversion
4
/Zr-

T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
79
1
00
100
80
60
40
20
0
Table 2
Recyclability of solid acid catalyst.
8
6
4
2
0
0
0
0
0
Catalyst
Experimental Conversion
Selectivity of
run
of phenol (wt%) products (wt%)
Phenol
2-
4-
2,4-
DTBP
2
4
2
TBP
TBP
TBP
TBP
,4DTBP
2ꢀ
SO
SO
4
/Zr-MCM-48-
5
1
2
3
4
1
2
3
4
91.6
90.3
89.7
88.3
74.5
73.3
72.4
70.9
3.3
3.6
3.9
4.3
6.2
6.7
6.8
7.1
82.4 14.3
81.6 14.8
81.3 14.8
80.5 15.2
66.2 27.6
65.5 27.8
65.1 28.1
64.6 28.3
2
2
4
ꢀ
/Al-MCM-48-
5
2
1
2
3
4
5
6
-
1
WHSV(h )
Reaction conditions: 0.5 g catalyst, n(tert-butanol)/n(phenol)¼2.0, reaction
Fig. 7. Effect of different WHSVs on phenol conversion and product selectivity
ꢀ
1
over SO2
ꢀ
time¼2 h, WHSV¼2.0 h , reaction temperature¼140 1C.
4
/Zr-MCM-48-25 catalyst (reaction conditions: ntert-butanol/nphenol¼2:1,
time¼2 h, temperature¼140 1C).
As shown in Fig. 8, it is found that in the temperature range of
100–180 1C, the phenol conversion gradually decreased with the
increase of reaction time from 2 to 7 h. This may be attributed to
the coke formation aroused by longer contact time resulting in the
deactivation of the catalyst.
1
00
8
6
4
2
0
0
0
0
0
o
3.7. Recyclability of solid acid catalyst
100 C
o
1
20 C
To examine the recyclability of the solid acid catalyst, the four-
2
ꢀ
2ꢀ
4
o
cycle experiments over SO
4
/Zr-MCM-48-25 and SO
/Al-MCM-
140 C
4
8-25 catalysts were respectively carried out at 140 1C for 2 h
ꢀ
1
under 2:1 M ratio of ntert-butanol/nphenol and 2 h
of WHSV. The
results are presented in Table 2. Interestingly, the two solid acid
catalysts can be continuously used four times under the same
experimental condition without significant decreasing in phenol
conversion and selectivity to 4-TBP, suggesting that the two
mesoporous solid acid catalysts have good stability and good
reusability. The decreasing in phenol conversion may be owing
to the catalyst deactivation.
o
1
60 C
o
1
80 C
2
3
4
5
6
7
Time-on-Stream / (h)
Fig. 8. Effect of reaction time and reaction temperature on phenol conversion
over SO2
ꢀ
/Zr-MCM-48-25 catalyst (reaction conditions: ntert-butanol/nphenol¼2:1,
4
ꢀ
1
WHSV¼2 h ).
4. Conclusions
ꢀ
1
decreased from 91.6% to 78.1% with increase of WHSV from 2 h
ꢀ
1
2ꢀ
2ꢀ
to 5 h . This may be attributed to the following: one reason is
that the diffusion of the products in channel is difficult at lower
space velocity. The other one is due to the shorter contact time
between the reactant (phenol and tert-butyl alcohol) and catalyst
at higher space velocity. In two cases, the phenol conversion
decreased [32].
Several SO4 /Zr-MCM-48 and SO4 /Al-MCM-48 solid acid
catalysts were prepared by wet impregnation method using Zr
(or Al)-MCM-48 mesoporous molecular sieves derived from
hydrothermal method as starting materials. Compared with the
Zr (or Al)–MCM-48, SO /Zr-MCM-48 and SO4 /Al-MCM-48 solid
acid catalysts still maintained the cubic mesoporous framework of
2
ꢀ
2ꢀ
4
Furthermore, it is observed that with the increase of WHSV
MCM-48, however, the mesoporous ordering slightly decreased.
ꢀ
1
ꢀ1
from 2 h to 3 h , the selectivity to 4-TBP decreased from 82.7%
The four solid acid catalysts all have certain amount of strong acid
ꢀ
1
ꢀ1
2ꢀ
to 64.1%. With further increase of WHSV from 3 h to 5 h , the
selectivity to 4-TBP slightly changed. On the contrary, the selec-
tivity to 2, 4-DTBP increases from 14.8% to 31.7% with the increase
sites except for the weak acid sites. Among all catalysts, the SO4 /
Zr-MCM-48-25 catalyst exhibits the highest catalytic activity in
alkylation of phenol with tert-butyl alcohol. When the molar ratio
ꢀ
1
ꢀ1
of WHSV from 2 h
to 3 h . While the selectivity to 2, 4-DTBP
of tert-butyl alcohol:phenol is 2:1, reaction time is 2 h, the WHSV
ꢀ
1
ꢀ1
ꢀ1
almost unchanged with increase of WHSV from 3 h
to 5 h
.
is 2 h
and the reaction temperature is 140 1C, a maximum
Furthermore, it is noted from Fig. 7 that with the increase of
WHSV, the selectivity to 2-TBP slightly increases. This is probably
due to the shorter residence time of reactants in fixed-bed reactor
aroused by increase of WHSV, which is favorable for single-
alkylation reaction.
phenol conversion of 91.6% with 81.8% selectivity to 4-TBP was
achieved.
Acknowledgments
3
.6.3. Effect of reaction time on phenol conversion
The authors are grateful to National Natural Science Foundation
of China (21004031) and Senior Personality Fund of Jiangsu
University (12JDG106).
Fig. 8 depicts the effect of reaction time and reaction tempera-
2
ꢀ
ture on phenol conversion over the SO
4
/Zr-MCM-48-25 catalyst.

80
T. Jiang et al. / Journal of Solid State Chemistry 218 (2014) 71–80
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