Preparation of H-mordenite/MCM-48 composite and its catalytic performance in the alkylation of toluene with tert-butanol

Article abstract of DOI:10.1134/S0036024417090345

A series of HM/MCM-48 samples with different SiO₂/Al₂O₃ molar ratio were prepared by sol-gel method. The prepared catalysts were characterized by XRD, N₂ adsorption-desorption, NH₃-TPD, FT-IR, SEM, and TEM techniques, and their catalytic performance was investigated in alkylation of toluene with tert-butanol. The adsorption capacity and the acid sites amount of HM/MCM-48-4 sample prepared by growing MCM-48 on the surface of HM zeolite are much higher than that of their mechanical mixture (HM/MCM-48(4) sample) due to its biporous structure; it shows higher catalytic performance than other HM/MCM-48 samples. The influence of reaction conditions on the catalytic performance of HM/MCM-48-4 zeolite was discussed. Toluene conversion of 41.4% and p-tert-butyltoluene selectivity of 73.5% were obtained at the weight ratio of toluene to HM/MCM-48-4 of 5, reaction temperature of 453 K, reaction time of 5 h and the molar ratio of toluene to tert-butanol of 0.5.

Full text of DOI:10.1134/S0036024417090345

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2017, Vol. 91, No. 9, pp. 1669–1675. © Pleiades Publishing, Ltd., 2017.
CHEMICAL KINETICS
AND CATALYSIS
Preparation of H-Mordenite/MCM-48 Composite and Its Catalytic
Performance in the Alkylation of Toluene with tert-Butanol1
Zhiwei Zhoua,b, Fuling Chenga, Juan Qinc, Pengcheng Yua, Lin Xub, Zhiqiang Gub,
Xiaoqin Liua, and Wenliang Wu a,*
aCollege of Chemical Engineering, Nanjing Tech University, Nanjing 210009, China
bJiangsu Yangnong Chemical Group Co., LTD., Yangzhou 225009, China
cTechnology and Finance Service Center of Jiangsu Province, Productivity Center of Jiangsu Province, Nanjing 210042, China
*e-mail: wwl@njtech.edu.cn
Received February 25, 2016
Abstract—A series of HM/MCM-48 samples with different SiO2/Al2O3 molar ratio were prepared by sol-gel
method. The prepared catalysts were characterized by XRD, N2 adsorption-desorption, NH3-TPD, FT-IR,
SEM, and TEM techniques, and their catalytic performance was investigated in alkylation of toluene with
tert-butanol.The adsorption capacity and the acid sites amount of HM/MCM-48-4 sample prepared by
growing MCM-48 on the surface of HM zeolite are much higher than that of their mechanical mixture
(HM/MCM-48(4) sample) due to its biporous structure; it shows higher catalytic performance than other
HM/MCM-48 samples. The influence of reaction conditions on the catalytic performance of HM/MCM-
48-4 zeolite was discussed. Toluene conversion of 41.4% and p-tert-butyltoluene selectivity of 73.5% were
obtained at the weight ratio of toluene to HM/MCM-48-4 of 5, reaction temperature of 453 K, reaction time
of 5 h and the molar ratio of toluene to tert-butanol of 0.5.
Keywords: toluene, HM/Al-MCM-48, sol-gel method, tert-butylation, p-tert-butyltoluene
DOI: 10.1134/S0036024417090345
INTRODUCTION
because of its special cubic three-dimensional struc-
ture [12], which can increase the diffusion speed of
reactants and reduce the frequent blocking. However,
the lack of hydrothermal stability becomes a more and
more significant obstacle for their practical applica-
tions [13]. To overcome the above disadvantages, one
of the efforts is to introduce zeolites into the frame-
work of mesoporous materials and prepare the sam-
ples with optimal properties [14–17]. However, the
synthesis of HM/MCM-48 materials was not yet pub-
lished because of the narrow synthesis cross-region
and harsh synthesis conditions of MCM-48 [18–20].
In this work, a series of HM/MCM-48 samples
with different Si : Al molar ratio were successfully pre-
pared by growing MCM-48 on the surface of NaM
zeolite. Catalytic performance of the prepared com-
posites was investigated in tert-butylation of toluene.
As an important chemical raw material, p-tert-but-
yltoluene (PTBT) is widely used in the synthesis of
pharmaceuticals, pesticides and food additives. In the
industry, it is always prepared by alkylation of toluene
with different reagents in the presence of liquid cata-
lysts, such as AlCl3, H2SO4, and polyphosphoric acid,
etc. [1], which are corrosive and generally not reus-
able. Some solid acid catalysts including zeolites have
been developed to avoid these problems due to their
environmental viability, lack of corrosivity, and good
reusability [2–7].
The selectivity of alkylation process toward PTBT
over mordenite is higher than over other zeolites,
because its pore size is very close to the molecular
diameter of PTBT [8]. However, its catalytic activity is
rather limited due to its minor pore size, which causes
diffusion hindrance, critical carbon deposition and
fast deactivation [9, 10]. To solve these problems,
ordered mesoporous materials, such as M41S and
SBA, have been explored [11]. As an important mem-
ber of M41S family, the mesoporous molecular sieve
MCM-48 is more predominant than MCM-41 in
catalysis, adsorption and separation processes,
1. EXPERIMENTAL SECTION
1.1. Catalyst Preparation
NaM zeolite (Si : Al = 25) was purchased from the
Catalyst Plant of Nankai University. NaM/MCM-48
samples with different Si : Al molar ratio were synthe-
sized according to the literature using cetyltrimeth-
ylammonium bromide (CTAB) as a structure-directing
1
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1669

1670
ZHIWEI ZHOU et al.
agent [20, 21]. In a typical procedure, 0.083 g NaAlO2, tron microscope (FESEM), and by TEM using a
JEOL JEM-200CX transmission electron micro-
scope.
7 g CTAB, and 0.6 g NaOH were added to 40 g of dis-
tilled water at room temperature. After stirring for
0.5 h, tetraethoxysilane (9 mL) was added dropwise,
and the mixture was kept for another 0.5 h. NaM zeo-
lite (4 g) powder was added to the gel formed. The
mixture was transferred to a Teflon-lined autoclave
and heated at 373 K under autogenous pressure with-
out agitation for 72 h. The product was collected by fil-
tration, washed with distilled water and dried at 353 K
for 12 h. The prepared sample was calcined in static air
at 823 K for 6 h to remove the organic template and
marked as NaM/MCM-48-2. The prepared samples
are referred as NaM/MCM-48-n (where n is the mass
ratio of NaM to MCM-48). For comparison, the
MCM-48 sample was prepared in the absence of
NaM. All prepared samples were subjected to ion
exchange with NH4NO3 to obtain HM/MCM-48-n
catalysts, which were then evaluated in the alkylation
of toluene with tert-butanol. For comparison, the
sample marked as HM/MCM-48(4) was prepared by
mechanical mixing HM with MCM-48 taken in a
weight ratio of 4.
1.3. Catalytic Reaction
The catalytic alkylation of toluene with tert-buta-
nol was carried out in a 100 mL stainless steel auto-
clave equipped with a magnetically driven impeller.
The catalyst sample (0.2 g) was added to a mixture of
tert-butanol and toluene (with various molar ratios);
n-hexane was used as the solvent. The reactor was
flushed for multiple times with nitrogen to replace air.
The experiments were carried out at the initial pres-
sure of 0.6 MPa by filling with N2. The final reaction
pressure wolud depend on the reaction temperature, at
a stirring speed of 800 rpm, at different temperatures.
Then the reactor was cooled down to room tempera-
ture and the reaction mixture was analyzed on a
SP-6890 gas chromatograph equipped with a SE-30 col-
umn (0.25 μm × 50 m) and a flame ionization detector
(FID).
2. RESULTS AND DISCUSSION
1.2. Catalyst Characterization
2.1. Catalyst Characterization
2.1.1. XRD patterns. The XRD patterns of the pre-
pared samples are shown in Fig. 1. It can be seen from
Fig. 1a that the neat MCM-48 sample shows well-
defined XRD peaks at 2.7° and 3.1°, which can be
assigned to (211) and (220) reflections. The character-
istic diffraction peak for HM/MCM-48-n samples
corresponding to (220) reflection disappeared, and
the peak intensity of (211) reflection decreased with
increase in HM amount in the sample. This can be
attributed to the partial destruction of ordered pores.
From Fig. 1b, all the samples exhibit the same charac-
teristic peaks as the parent HM sample. Rather than
HM/MCM-48(4) sample, the intensities of peaks
decreased gradually with the increase in the weight
amount of MCM-48.
2.1.2. Nitrogen adsorption-desorption isotherms.
Nitrogen adsorption-desorption isotherms for differ-
ent samples are shown in Fig. 2. The HM zeolite sam-
ple is characterized by a typical type I isotherms,
which indicate its microporous structure. Similar to
MCM-48, all the HM/MCM-48-n samples have a
type IV adsorption-desorption isotherms, suggesting
their mesoporous character. The adsorption capacity
of the HM/MCM-48-n samples decreased with the
increase of amount of HM. In spite of the same weight
ratio of HM to MCM-48, the adsorption capacity of
HM/MCM-48-4 is much higher than observed for the
HM/MCM-48(4) sample, which may be attributed to
its biporous structure.
X-ray powder diffraction patterns of the samples
were obtained on a Bruker D8 instrument with Ni-fil-
tered CuKα radiation (λ = 0.154 nm) at 40 kV and
30 mA. The scanning rate was 0.05 deg/s; the patterns
were recorded in 2θ ranges of 1°–5° and 5°–70°.
Nitrogen adsorption-desorption isotherms of the
samples were measured at 77 K using Micromeritics
Tristar 3000 system. The surface area was calculated by
the BET method in the partial pressure (P/P0) range
from 0.01 to 0.99. The volume of mesopores was cal-
culated from the adsorption branch of the isotherms
using the BJH model [22]; the volume of micropores
was determined by t-plot method [23]. Temperature-
programmed desorption of ammonia was carried out
in a quartz U-tube reactor; 300 mg sample was used
for each measurement. The sample was pretreated in
the He stream at 823 K for 60 min and then cooled
down to 373 K. After that, 5% (vol/vol) NH3/He mix-
ture was passed for 30 min and then the reactor was
purged with the He stream for 40 min. The tempera-
ture was raised from 373 to 1073 K at a rate of
10 K min–1. The consumption of NH3 from the reac-
tant stream was recorded by TCD. Fourier transform-
infrared spectra were measured on the Thermo Nico-
let NEXUS spectrometer in KBr pellets. The sample
was pretreated in vacuum (10–2 Pa) at 573 K for 3 h and
then cooled down to room temperature. The Si/Al
ratio was measured by inductively coupled plasma
OES (Optima 2000 DV, PerkinElmer, USA) after the
sample had been dissolved in HF solution. The mor-
Table 1 summarizes the physical properties of dif-
phology of the prepared catalysts was studied by SEM ferent samples. It can be seen that Si : Al molar ratio,
using a Hitachi S-4800 field-emission scanning elec- total pore volume and the specific surface area of the
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(b)
(a)
g
a
f
e
b
c
d
d
c
b
e
f
2
3
4
5
6 10
2θ, deg
20
30
40
50
60
70
2θ, deg
Fig. 1. (a) Low-angle and (b) wide-angle XRD patterns of (a) MCM-48, (b) HM/MCM-48-2, (c) HM/MCM-48-3,
(d) HM/MCM-48-4, (e) HM/MCM-48-5, (f) HM/MCM-48(4), (g) HM.
VSTP/(cm3/g)
600
a
b
c
500
d
e
400
f
g
300
200
100
0
0.2
0.4
0.6
0.8
1.0
P/P0
Fig. 2. Liquid N adsorption-desorption isotherms for (a) MCM-48, (b) HM/MCM-48-2, (c) HM/MCM-48-3,
2
(d) HM/MCM-48-4, (e) HM/MCM-48-5, (f) HM/MCM-48(4), (g) HM.
HM/MCM-48-n samples decreased with increase in increases with the increase in weight amount of HM
the weight amount of HM in the sample. Compared to zeolite. Compared to the HM/MCM-48(4) sample,
the HM/MCM-48-4 sample, the specific surface the acid sites amount of HM/MCM-48-4 sample are
area, Si : Al molar ratio, and total pore volume of much higher, especially the weak acidity, which is
HM/MCM-48(4) sample prepared by mechanical owing to the decrease of Al-OH in the structure of
mixing was higher because of their independence MCM-48 [25].
between HM and MCM-48 zeolites.
2.1.4. FT-IR spectra. FT-IR spectra of 2,4-
dimethylquinoline adsorbed on different samples are
shown in Fig. 4. The band at 1645 cm–1 can be
assigned to the interaction between 2,4-dimethylquin-
oline and Brønsted acid sites [15]. From Fig. 4, the
maximum band for HM zeolite and minimum band
2.1.3. NH3-TPD curves. Figure 3 shows NH3-TPD
curves for different samples. Two ammonia desorption
peaks, one at low temperature (503 K) and another at
high temperature (773 K), were observed for all sam-
ples. The HM sample is mainly in weak acidity,
whereas the MCM-48 is mainly in strong acidity. for MCM-48 sample at 1645 cm–1 are observed, which
Compared to the MCM-48 sample, the weak acidity indicates that Brønsted acid sites on HM zeolite are
of HM/MCM-48-n samples has been promoted, and much higher than MCM-48 sample. The Brønsted
the acid strength of HM/MCM-48-n samples acid sites would be promoted for different
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ZHIWEI ZHOU et al.
Table 1. Physical properties of different samples
Average pore
size, nm
Vmicro (cm3 g–1)a Vmeso (cm3 g–1)b Vtotal (cm3 g–1)
SBET (m2/g)
n(Si : Al)c
Samples
MCM-48
0.06
0.15
0.16
0.22
0.25
0.24
0.28
0.71
0.38
0.33
0.26
0.19
0.23
0.03
0.92
0.58
0.52
0.49
0.46
0.51
0.29
3.59
3.35
2.93
2.67
2.65
2.83
1.87
43
31
28
26
25
28
23
973.07
693.20
618.67
522.72
488.09
550.17
425.75
HM/MCM-48-2
HM/MCM-48-3
HM/MCM-48-4
HM/MCM-48-5
HM/MCM-48(4)
HM
a
b
c
t-Plot method.
BJH method.
Measured by ICP-AES
HM/MCM-48-n samples with the weight amount of clearly present when the scale was magnified to 20 nm,
HM zeolite increasing. However, the band at which is shown in Fig. 6b. Therefore, according to
1645 cm–1 of HM/MCM-48-n samples is lower than
HM/MCM-48 (4) sample, which may be owing to the
cap of MCM-48 on the surface of HM zeolite [15].
SEM, TEM, and FTIR results, we can conclude that
MCM-48 was grown on the surface of HM zeolite.
2.1.5. SEM analysis. SEM micrographs of differ-
ent samples are shown in Fig. 5. It can be seen that
MCM-48 sample consists from amorphous floccules
and HM is composed of elliptic particles. The
HM/MCM-48-n samples basically have the same
morphology as the HM zeolite, but some flocculating
substances on the surface can be observed due to the
growth of MCM-48 on their surface. Meanwhile, the
flocculating substances become less with the weight
ratio of HM zeolite increasing.
2.1.6. TEM analysis. The TEM analysis for
HM/MCM-48-4 sample is shown in Fig. 6. The
translucent structure can be observed (Fig. 6a) at the
edge of shadow and the lattice stripe of MCM-48 was
2.2. Catalytic Tests
The catalytic performance of different samples in
the alkylation of toluene with tert-butanol is summa-
rized in Table 2. In all cases, the main products are
identified as PTBT and m-tert-butyltoluene (MTBT).
However, o-tert-butyltoluene (OTBT) cannot be
found in the products; this is attributed to the sterical
hindrance. 3,5-Di-tert-butyltoluene (DTBT) having
two tert-butyl groups in the meta positions, is the
minor byproduct of the reaction. It can be seen from
Table 2 that toluene conversion is only 9.5% on the
MCM-48 catalyst. Because it has higher concentra-
tion of acid sites, especially weak ones, toluene con-
version of 18.4% can be obtained on the HM catalyst.
Catalytic performance of HM/MCM-48-n catalyst is
much higher than that of MCM-48, and toluene con-
version can reach up to 21.2% on the HM/MCM-48-
4, which may be owing to its appropriate BET surface,
acidity and biporous structure. Compared to
HM/MCM-48(4) catalyst, catalytic activity of
HM/MCM-48-4 sample is higher because of its spe-
cific physicochemical properties, rather than simple
mixture of HM and MCM-48. The selectivity of TBT
on the HM zeolite is highest because of its smallest
pore size. The selectivity towards PTBT increases with
the weight ratio of HM zeolite increasing, whose pore
size is close to the molecular diameter of PTBT.
Because HM/MCM-48-4 catalyst shows the highest
catalytic activity, the following studies on the effect of
reaction conditions were performed using this catalyst.
g
e
d
c
f
b
a
100
200
300
400
500
600
700
Temperature, °C
2.3. Effect of Reaction Conditions
Figure 7a shows the effect of reaction temperature
on the catalytic performance over HM/MCM-48-4
catalyst. Both toluene conversion and PTBT selectiv-
Fig. 3. NH -TPD curves for (a) MCM-48, (b) HM/MCM-
3
48-2, (c) HM/MCM-48-3, (d) HM/MCM-48-4,
(e) HM/MCM-48-5, (f) HM/MCM-48(4), (g) HM.
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PREPARATION OF H-MORDENITE/MCM-48 COMPOSITE
1673
g
f
e
d
c
b
a
1700
1650
1600
1550
1500
1450
1400
Wavenumber, cm−1
Fig. 4. FT-IR spectra of 2,4-dimethylquinoline adsorbed on (a) MCM-48, (b) HM/MCM-48-2, (c) HM/MCM-48-3,
(d) HM/MCM-48-4, (e) HM/MCM-48-5, (f) HM/MCM-48(4), and (g) HM.
2 μm
2 μm
2 μm
2 μm
(а)
(d)
(b)
(e)
(c)
(f)
2 μm
2 μm
Fig. 5. SEM micrographs of (a) HM, (b) HM/MCM-48-2, (c) HM/MCM-48-3, (d) HM/MCM-48-4, (e) HM/MCM-48-5,
and (f) MCM-48.
200 nm
200 nm
(а)
(b)
Fig. 6. TEM photos for HM/MCM-48-4 with different scales.
ity are affected severely by reaction temperature. A sig- temperature, toluene conversion decreases, probably
nificant increase in toluene conversion from 15.6 to due to dealkylation of TBT at higher temperatures. It
21.2% can be obtained when reaction temperature was was probably on this account that a rise of TBT selec-
increased to 453 K. Upon further increase in reaction tivity was obtained with the increase of reaction tem-
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1674
ZHIWEI ZHOU et al.
Table 2. Catalytic performances of different samples for the alkylation of toluene with tert-butanol
Distribution of products/%
Toluene
conversion, %
STBT, %
SPTBT, %
Catalysts
MCM-48
HM/MCM-48-2
HM/MCM-48-3
HM/MCM-48-4
HM/MCM-48-5
HM/MCM-48(4)
HM
OTBT
MTBT
PTBT
DTBT
9.5
13.7
17.4
21.2
19.4
16.5
18.4
0
0
0
0
0
0
0
25.4
23.2
20.6
20.0
18.3
21.4
18.2
71.7
74.8
77.8
78.7
80.1
77.1
81.5
2.9
2.0
1.6
1.3
0.6
1.5
0.3
97.1
98.0
98.4
98.7
99.4
98.5
99.7
73.8
76.3
79.1
79.7
80.6
78.3
81.7
Reaction conditions: W(toluene)/W(catalyst) = 10; calcination temperature of catalyst 523 K; n(toluene) : n(tert-butanol) : n(n-hexane) =
1 : 2 : 10; reaction temperature 453 K; initial pressure 1.0 MPa; reaction time 3 h.
S
is the molar ratio of mono-tert-butyltoluene to TBT. S
is the molar ratio of PTBT to TBT.
TBT
PTBT
perature. However, PTBT selectivity was declined as a dehydration of tert-butanol, carbonization and then
result of the isomerization of PTBT into MTBT, covered the acid sites, a negative effect on toluene
which is more stable at higher temperatures [7]. PTBT conversion was found when the molar ratio is more
selectivity of only 62.1% can be obtained at 493 K.
than 2. On the contrary, the PTBT selectivity
increased slightly because of depressing of the isomer-
ization of PTBT to MTBT.
Figure 7b shows the influence of molar ratio of tert-
butanol to toluene on the catalytic performance of
HM/MCM-48-4 catalyst. It can be seen from Fig. 7b
that toluene conversion can reach up to 24.1% when butanol with different catalyst loadings was investi-
the molar ratio of tert-butanol to toluene was 2. gated, and the results are shown in Fig. 7c. It can be
Because of oligomerization of the isobutene formed by seen that the catalyst loading affects both toluene con-
The liquid phase alkylation of toluene with tert-
96
(a)
(b)
84
80
76
72
68
28
24
20
16
24
20
16
12
44
92
88
84
80
64
60
440
460
480
500
1
2
3
4
Reaction temperature, K
n(tert-butyl alcohol)/n(toluene)
88
84
80
76
72
80
36
32
28
24
(c)
(d)
78
76
74
72
70
40
36
32
4
6
8
10
3
4
5
6
W(Catalyst)/W(toluene)
Reaction time, h
Fig. 7. Effect of reaction conditions on toluene conversion and PTBT selectivity (a) reaction temperature; (b) n(tert-buta-
nol)/n(toluene); (c) W(catalyst)/W(toluene); (d) reaction time.
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kept constant with the catalyst loading further increas-
ing because the alkylation of toluene with tert-butanol
is a continuous and reversible reaction. PTBT selec-
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as a result of the dealkylation of DTBT and the isom-
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uene conversion kept constant when the reaction time
is more than 5 h because the alkylation of toluene with
tert-butanol was a continuous and reversible reaction,
which suggests that the reaction reaches its steady
state. PTBT selectivity was dropped when the reaction
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Kagaku Kaishi, 595 (1989).
The HM/MCM-48-n samples were successfully
prepared under the hydrothermal conditions, and the
catalytic performance was investigated in the tert-
butylation of toluene with tert-butanol. TEM and FT-
IR spectra of 2,4-dimethylquinoline-adsorbed results
showed that the HM/MCM-48-n samples are formed
by growth of MCM-48 on the surface of HM zeolites.
HM/MCM-48-4 sample shows a higher catalytic
activity than HM/MCM-48(4) prepared by the
mechanical mixing owing to its biporous structure and
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ACKNOWLEDGMENTS
This work was supported by Jiangsu Planned Proj-
ects for Postdoctoral Research Funds (1302121C);
Open Project of Beijing Key Laboratory for Enze Bio-
mass and Fine Chemicals; Project Funded by the Pri-
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Higher Education Institutions.
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