A novel, shape-selective H-MCM-22/MCM-41 composite catalyst: Synthesis, characterization and catalytic performance

Article abstract of DOI:10.1016/j.catcom.2010.08.014

A novel, shape-selective H-MCM-22/MCM-41 composite catalyst is synthesized for the first time by overgrowing MCM-41 over the external surface of H-MCM-22. Results of FT-IR characterization with 2,4-dimethylquinoline adsorption indicate that the Br?nsted acidic sites of H-MCM-22 located on the external surface can virtually be completely covered by the generated layer of MCM-41. When applied to the synthesis of p-xylene by the alkylation of toluene with dimethyl carbonate, the H-MCM-22/MCM-41 composite exhibits significant enhancement in p-xylene selectivity, which can be ascribed to the decrease in the number of external Br?nsted acid sites of the composite.

Full text of DOI:10.1016/j.catcom.2010.08.014

Catalysis Communications 12 (2010) 95–99
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
A novel, shape-selective H-MCM-22/MCM-41 composite catalyst: Synthesis,
characterization and catalytic performance
a
a
a
a
a,
b,
Bing Xue , Jie Xu , Chongfu Xu , Runze Wu , Yongxin Li ⁎, Kai Zhang ⁎
a
College of Chemistry and Chemical Engineering, Jiangsu Polytechnic University, Changzhou, Jiangsu, 213164, China
National Engineering Laboratory for Biomass Power Generation Equipment, North China Electric Power University, Changping, Beijing, 102206, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 May 2010
Received in revised form 29 July 2010
Accepted 13 August 2010
Available online 21 August 2010
A novel, shape-selective H-MCM-22/MCM-41 composite catalyst is synthesized for the first time by
overgrowing MCM-41 over the external surface of H-MCM-22. Results of FT-IR characterization with 2,4-
dimethylquinoline adsorption indicate that the Brønsted acidic sites of H-MCM-22 located on the external
surface can virtually be completely covered by the generated layer of MCM-41. When applied to the
synthesis of p-xylene by the alkylation of toluene with dimethyl carbonate, the H-MCM-22/MCM-41
composite exhibits significant enhancement in p-xylene selectivity, which can be ascribed to the decrease in
the number of external Brønsted acid sites of the composite.
Keywords:
Composite
H-MCM-22/MCM-41
Para-Selectivity
Alkylation
© 2010 Elsevier B.V. All rights reserved.
Dimethyl carbonate
1
. Introduction
Zeolites such as ZSM-5 and MCM-22 have been used widely as
preparation of micro/mesoporous composites including recrystalliza-
tion of originally amorphous matter, utilization of nanocrystalline
zeolite seeds and formation of mesoporous zeolite single crystals have
been reported [20]. Catalytic applications of composite materials are
more or less limited to acid-catalyzed reactions related to petro-
chemical technologies [15,21]. Van Bekkum and coworkers [22] have
reported the synthesis of MCM-41/faujasite composite by overgrow-
ing MCM-41 on faujasite zeolites. The results indicate that the
faujasite surface is covered with an MCM-41 layer of 5–20 nm
thickness. We have synthesized a shape-selective H-MCM-22/MCM-
41 composite by overgrowing MCM-41 over the external surface of H-
MCM-22 and obtained an interesting result in the synthesis of p-
xylene over this composite. For alkylation of toluene with dimethyl
carbonate (DMC) the H-MCM-22/MCM-41 composite exhibits high
para-selectivity along with high toluene conversion, which is both
novel and convenient compared with the traditional modification
techniques used to cover the external acidic sites of zeolites. To the
best of our knowledge, there have been no reports on the selective
synthesis of p-xylene using a shape-selective H-MCM-22/MCM-41
composite catalyst.
We have previously reported the synthesis of p-xylene by
alkylation of toluene with DMC as the alkylating agent [23] and
established that DMC is a much more efficient methylating agent than
methanol. In this study, the synthesis of p-xylene by alkylation of
toluene with DMC was carried out over H-MCM-22/MCM-41
composite. The relationship between acidity and catalytic perfor-
mance is discussed in detail, particularly in correlation to the
enhancement of the para-selectivity by covering the external
Brønsted acid sites with the generated layer of MCM-41.
shape-selective catalysts for catalytic reactions such as the synthesis
of p-xylene [1–3]. However the acidic sites on the external surface of
zeolite usually cause some side reactions and deminish the para-
selectivity [4]. To obtain high para-selectivity, it is necessary to cover
the acidic sites on the external surface of zeolites. A number of
modification techniques have been reported, such as impregnation of
metallic or non-metallic compounds [5–8], pre-coking [9,10], chem-
ical vapor deposition of silica (SiO
deposition of silica (SiO -CLD) [13,14]. Although a significant
2
-CVD) [11,12] and chemical liquid
2
improvement in para-selectivity has been achieved by loading
metallic or non-metallic oxide compounds over zeolite, an obvious
decrease in catalytic activity is inevitable. The in situ pre-coking
modification of zeolite is often difficult to perform and this
modification has to be repeated after regeneration of the zeolite
2 2
catalyst. SiO -CVD or SiO -CLD modification with simple silica
alkoxides, such as tetra-ethyl-orthosilicate (TEOS), is the usual
method for improving para-selectivity of zeolite. However, to obtain
the desired para-selectivity, a long and complicated process is
2 2
necessary during the SiO -CVD and SiO -CLD modification.
Composite zeolites, especially micro/mesoporous composite, have
been paid much attention due to their synergistic performance in
catalytic reactions [15–19]. Recently, new synthetic approaches for
⁎
Corresponding authors. Li is to be contacted at Tel./fax: +86 519 86330135. Zhang,
Tel.: +86 10 61772413; fax: +86 10 61772234.
E-mail addresses: liyx@em.jpu.edu.cn (Y. Li), kzhang@ncepu.edu.cn (K. Zhang).
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.08.014

96
B. Xue et al. / Catalysis Communications 12 (2010) 95–99
2
. Experimental
The products collected were analyzed using a GC fitted with an FFAP
capillary column and a flame ionization detector (FID).
2
.1. Catalyst preparation
3
. Result and discussion
MCM-22 zeolites with a Si/Al ratio of 50 were synthesized by
hydrothermal crystallization according to a published procedure
24,25]. The protonic form of MCM-22, denoted as H-MCM-22, was
obtained by ion-exchange of the as synthesized MCM-22 with
aqueous NH NO solution, and then calcined at 823 K for 3 h.
3.1. Physicochemical characterization
[
Fig. 1 shows XRD patterns of the H-M-22/M-41 composite with
weight ratios of H-MCM-22 to MCM-41 from 1:1 to 7:1. It is seen
that the meso-structure is well formed when the weight ratio of H-
MCM-22 to MCM-41 is lower than 3:1. With an increase in the
amount of H-MCM-22 in the composite, the peak intensity of the
MCM-41 decreases significantly. When the weight ratio of H-M-22/
M-41composite is increased to 7:1, the characteristic peaks
corresponding to MCM-41 (110 and 200) can no longer be detected
by XRD. As shown in Fig. 1B, the characteristic peak position of the
H-MCM-22 shows no obvious change with increasing weight ratio of
H-MCM-22 to MCM-41 and the H-MCM-22 peak intensity increases
slightly with an increasing amount of H-MCM-22 in the composite.
4
3
To synthesize the H-MCM-22/MCM-41 composite, a sol–gel of
MCM-41 was first prepared according to a published procedure [26].
While stirring, a certain amount of H-MCM-22 zeolite was added to
the colloidal precursor of MCM-41. The mixture was then stirred for a
few minutes, followed by hydrothermal crystallization at 383 K for a
set period of time. After cooling to the room temperature, the
resulting solid product was filtered, washed thoroughly with
deionized water and dried at 393 K. The composite samples were
then obtained by calcining the product at 823 K for 6 h in air. By
varying the weight of H-MCM-22 added to the MCM-41 gel, several H-
MCM-22/MCM-41composite with different weight ratios of H-MCM-
The SiO
ratios of H-MCM-22 to MCM-41 from 1:1 to 7:1 is shown in Table 1.
The SiO /Al ratio obviously increases with a decrease in the
weight ratio of H-MCM-22 to MCM-41. For all the composites
investigated, the SiO /Al ratio shown in Table 1 is slightly lower
2 2 3
/Al O ratio of the H-M-22/M-41 composite with weight
2
2 to MCM-41 were prepared, denoted as H-M-22/M-41(x:1), where
x represents the theoretical weight ratio of H-MCM-22 to MCM-41in
the composite zeolite.
2
2 3
O
2
2 3
O
2
.2. Characterization of catalysts
than that of the due value. It is indicated that a small quantity of H-
MCM-22 is desiliconized during the crystallization in sol–gel of
MCM-41 [27], which is in agreement with the results of XRD.
The pore properties of the H-M-22/M-41 composite zeolites are
characterized by nitrogen sorption measurement. Fig. 2 shows the
nitrogen sorption isotherm of H-M-22/M-41 composite with
different weight ratios of H-MCM-22 to MCM-41. As shown in
X-ray diffraction (XRD) measurements were conducted using a
Rigaku D/max2500PC diffractometer with Cu Kα (λ=1.54 Å) radiation.
°
°
The diffractograms were recorded in 2θ range 5–40 in steps of 0.02
with a count time of 15 s. The Si and Al contents of the zeolites were
obtained using a Panalytical Magix PW2403 spectrometer (XRF).
2
N adsorption/desorption analyses were obtained at 77 K using a
physical adsorption instrument (Micromeritics ASAP 2010, USA). Before
measurement, the samples were degassed at 523 K under vacuum until
a final pressure of 1×10−3 kPa was reached. The specific surface area
was calculated according to the BET isothermal equation.
Sample acidity was measured by NH
desorption (NH -TPD) using a Quantachrome CHEMBET-3000 instru-
ment. A 200 mg sample was pre-treated at 823 K for 1 h in dry helium
3
temperature-programmed
3
−
1
(
flowing at 50 ml min ), cooled to 393 K, then exposed to 10v% NH
3
/He
mixture for 0.5 h. After purging the catalyst with He for 0.5 h, the TPD plot
−
1
was obtained at a heating rate of 10 K min
thermal conductivity detector (TCD) signal and temperature
corresponding to NH desorption were recorded simultaneously. The
amount and temperature of the desorbed NH corresponded qualitatively
to the amount and strength of the acid sites.
from 393 to 823 K. The
3
3
FT-IR spectroscopy with pyridine and 2,4-dimethylquinoline (2,4-
DMQ) adsorption was carried out using a Bruker FT-IR spectrometer
(
TENSOR 27) together with a high temperature vacuum chamber. The
−
1
scanning range was from 1700 to 1400 cm
4
and the resolution was
−
1
cm . The sample powder was pressed into a self-supporting wafer.
Prior to each experiment, the catalysts were evacuated (1 Pa) at 653 K
for 3 h, and then cooled at 303 K for 2 h, and then exposed to 4 KPa of
pyridine or 2,4-DMQ solubilized in CH
2 2
Cl (30 μmol for 1 mL solvent)
for 5 min, and finally evacuated for 1 h at 303 K. After adsorption of
−
1
pyridine the samples were heated to 473 K at 10 K min
spectra were recorded.
and the
2
.3. Catalyst testing
Alkylation of toluene with DMC was carried out in vapor phase in a
fixed bed, continuous, down-flow reactor at 653 K. About 3 g of the
catalyst (as pellets of 20–40 mesh) was packed in the middle of the
reactor and calcined in a dry nitrogen flow for about 1 h at 653 K
before reaction. The reaction mixture consisting of toluene and DMC
was introduced at the top of the reactor by means of a micropump.
Fig. 1. X-ray diffraction of H-M-22/M-41 (x:1) composite composite zeolites. a) x=1;
b) x=2; c) x=3; d) x=4; e) x=5; f) x=6; g) x=7.

B. Xue et al. / Catalysis Communications 12 (2010) 95–99
97
Table 1
a
Alkylation of toluene with DMC over H-M-22/M-41 composite .
Catalysts (H-M-22/M-41)
7:1
6:1
5:1
4:1
3:1
2:1
1:1
b
SiO
2
/Al
2
O
3
49
50
52
54
57
63
80
Conversion (%)
Product selectivity (%)
Benzene
Xylenes
Trimethylbenzenes
Others
36.4
34.2
30.4
24.7
18.7
13.2
10.1
3.2
72.7
21.3
2.8
2.9
74.6
20.1
2.4
2.3
76.2
19.6
1.9
1.8
82.4
14.2
1.6
1.7
86.7
10.3
1.3
1.5
90.1
7.2
1.2
91.2
6.8
1.2
0.8
Xylene isomers (%)
Para-xylene
Meta-xylene
Ortho-xylene
26.3
51.7
22.0
33.6
42.7
23.7
42.5
33.7
23.8
57.0
19.8
23.2
63.2
16.3
20.5
64.1
15.3
20.6
65.3
14.7
20.0
a
Conditions: temperature=653 K; WHSV=1.0 h−1; feed ratio n(toluene):n(DMC)=4:1.
Obtained by XRF.
b
Fig. 3. NH
3
–TPD patterns of H-M-22/M-41 (x:1) composite zeolites. a) x=1; b) x=2;
Fig. 2, the nitrogen sorption isotherm for H-M-22/M-41 (1:1)
exhibits the typical IV sorption isotherm, which indicates a typical
mesoporous solid [28]. A sharp increase in the isotherm of H-M-22/
c) x=3; d) x=4; e) x=5; f) x=6; g) x=7.
1
M-41 (1:1) at p/p
0
=0.2–0.4 was observed, which also indicates the
seen at 1540 cm− . The combination of both Lewis and Brønsted acid
sites is manifested in a mingled band at 1490 cm . Obviously, the
amounts of the Brønsted acid sites and Lewis acid sites on the H-M-22/
M-41 compositeincrease simultaneously with increasing weightratio of
−
1
presence of mesopores in the H-M-22/M-41 composite. The steep
rise seen at higher relative pressure indicates the presence of
macropores, which are attributed to the inter-particle spaces [29].
With an increasing weight ratio of H-MCM-22 to MCM-41, the sharp
3
H-MCM-22 to MCM-41 in agreement with the results of NH -TPD
increase in the isotherm of H-M-22/M-41 at p/p
For H-M-22/M-41 (7:1), a sharp increase in the H-M-22/M-41 isotherm
at p/p =0.2–0.4 is not observed, which can be attributed to a decrease
in mesopores.
0
=0.2–0.4 attenuates.
characterization. There are no acidic sites over the surface of the pure
silica molecular sieve MCM-41 and therefore the acidic sites detected by
FT-IR, as shown in Fig. 4 are mainly provided by H-MCM-22. The
increase in the weight ratio of H-MCM-22 to MCM-41 results in an
increase in the amount of both the Brønsted and Lewis acid sites. For the
H-M-22/M-41 composite with higher amount of H-MCM-22, the total
number of Brønsted acid sites is obviously higher than that of the Lewis
acid sites, which is similar to the result of pure H-MCM-22 zeolite
reported by Corma and coworkers [30].
0
3
.2. Acidity characterization
Fig. 3 shows the NH
with different weight ratios of H-MCM-22 to MCM-41. For the H-M-
2/M-41 (1:1) composite, only one desorption peak is detected at
3
-TPD patterns of H-M-22/M-41 composite
2
Guisnet and coworkers have reported that the bulkier base, 2,4-
dimethylquinoline (2,4-DMQ) molecule, can only be chemisorbed on
the external Brønsted acidic sites and part of the inner acidic sites
(located near the surface of the crystallite edges) [31,32]. With the
method employed for H-MCM-22 poisoned with 2,4-DMQ, it is possible
to estimate the number of theexternal Brønstedacidic sites. The number
of the external Brønsted acidic sites of H-MCM-22 zeolites is found
approximately equal to 9–14% [32]. In order to investigate the coverage
of the external Brønsted acidic site on H-MCM-22 by the MCM-41 in the
composite, FT-IR with 2,4-DMQ adsorption was carried out over H-M-
22/M-41 composite with different weight ratios of H-MCM-22 to MCM-
41. With all the H-M-22/M-41 composite samples, 2,4-DMQ adsorption
followed by desorption at 473 K resulted in a large change in the
about 510 K, which can be attributed to the desorption of ammonia
from the weakly acidic sites. With an increasing amount of H-MCM-22
zeolite, the peak intensity of the weakly acidic sites clearly increases.
Furthermore, a broadened hump at about 720 K can also be observed
on the TPD curve of the H-M-22/M-41 (5:1) composite, which may be
attributed to the desorption of ammonia from the strongly acidic sites.
A slight increase in the strongly acidic sites is detected with increasing
amounts of H-MCM-22 zeolite in the composite.
The acid properties of H-M-22/M-41 composite with different
weight ratios of H-MCM-22 to MCM-41 were examined by FT-IR
spectroscopy using the pyridine-adsorption technique, as shown in
−
1
Fig. 4. The band seen at 1450 cm is due to pyridine adsorbed on Lewis
acid sites, while pyridine adsorbed on Brønsted acid sites gives the band
−
1
intensity of the bands at about 1645 cm , which corresponds to the
Fig. 2. Nitrogen sorption isotherm of H-M-22/M-41 (x:1) composite zeolites. □, x=1;
Fig. 4. FT-IR with pyridine adsorption of H-M-22/M-41 (x:1) composite zeolites
○
, x=3; Δ, x=5; ∇, x=7.
evacuated at 673 K. a) x=1; b) x=2; c) x=3; d) x=4; e) x=5; f) x=6; g) x=7.

98
B. Xue et al. / Catalysis Communications 12 (2010) 95–99
adsorbed 2,4-DMQ molecules. As shown in Fig. 5, the H-M-22/M-41
7:1) composite exhibits the highest intensity at 1645 cm−1 among all
These results are readily explained by the change in external acidic
sites of the catalysts. As previously reported [34], alkylation of toluene
with DMC is referred to as an electrophilic substitution reaction and p-
xylene is obtained as the primary product over the Brønsted acid sites
of the catalyst. Isomerization of p-xylene occurs easily over the
external Brønsted acid sites of H-MCM-22 zeolite because the meta
isomer has been reported to be thermodynamically more stable than
the other isomers. Therefore, the selectivity for p-xylene is only close
to the equilibrium composition of xylene isomers over pure H-MCM-
22 zeolite [23]. The improvement in p-xylene selectivity can be made
over modified MCM-22 in the alkylation of toluene [1,34]. Inagaki et
al. [35] has reported that the selectivity for para-xylene can be
obviously increased over collidine poisoned MCM-22 and ITQ-2
zeolite because the nonselective alkylation on the external acid sites
of the zeolites was effectively inhibited. As characterized by FT-IR
with 2,4-DMQ adsorption, the external Brønsted acid sites decreases
gradually, which effectively suppressed the isomerization of p-xylene.
For the H-M-22/M-41 (3:1), H-M-22/M-41 (2:1) and H-M-22/M-41
(1:1) composite, the external Brønsted acidic sites of H-MCM-22 have
been completely covered by the generated MCM-41 layer. Therefore,
no obvious difference in p-xylene selectivity is observed for these
three composites. It is plausible that the increase in selectivity for p-
xylene over the H-M-22/M-41 composite that occurred with the
decrease in the weight ratio of H-MCM-22 to MCM-41 is consistent
with a gradual reduction of the amount of external Brønsted acid sites
on the composite.
Benzene is also observed as a product, which probably results from
toluene disproportionation. As previous reported, trimethylbenzenes
are mainly formed by subsequent alkylation of xylenes over the
external surface Brønsted acid sites [23]. With a decrease in the
weight ratio of H-MCM-22 to MCM-41, selectivity for benzene and
trimethylbenzenes are dramatically reduced, which indicates that the
disproportionation of toluene and the subsequent alkylation of
xylenes are suppressed because of the significant decrease in Brønsted
acid sites.
We have previously reported the selective synthesis of p-xylene by
alkylation of toluene with DMC over MgO modified MCM-22 zeolite
[23]. Comparatively, the H-M-22/M-41 composite catalyst clearly
exhibits highest activity for the alkylation of toluene with DMC at a
similar p-xylene selectivity. During the MgO modification process, the
MgO dispersed over the surface of MCM-22 zeolites neutralizes not
only the acidic sites located on the external surface but also the acidic
sites located in the pores. Consequently, the activity of MgO modified
MCM-22 gradually decreases with increasing amounts of MgO. As
mentioned above, during the synthesis of the H-M-22/M-41 compos-
ite, the acidic sites of H-MCM-22 located on the external surface were
almost completely covered by the generated layer of MCM-41, while
the acidic sites in the channels of H-MCM-22 zeolite were only slightly
affected. Therefore, a higher activity for the alkylation of toluene with
DMC is obtained over the H-M-22/M-41 composite.
(
the catalysts investigated, which indicate that the H-M-22/M-41 (7:1)
composite has the largest number of uncovered external Brønsted acidic
site. With a decrease in the weight ratio of H-MCM-22 to MCM-41, the
peak intensity at 1645 cm− gradually decreases, which means more
and more external surface of H-MCM-22 zeolite is covered by the layer
of MCM-41 and obvious decrease in the numbers of external Brønsted
acidic site is resulted. There is no significant difference detected in peak
1
−
1
intensity at 1645 cm
for H-M-22/M-41 (3:1), H-M-22/M-41 (2:1)
and H-M-22/M-41 (1:1), which suggests that the external Brønsted
acidic sites of H-MCM-22 are almost completely covered by the
generated MCM-41 layer when the weight ratio of H-MCM-22 to
MCM-41 is bellow 3:1. As mentioned above, 2,4-DMQ can also be
chemisorbed on part of the inner acidic sites. Therefore, the low
−
1
intensity peak seen at 1645 cm over H-M-22/M-41 (3:1), H-M-22/M-
4
2
1 (2:1) and H-M-22/M-41 (1:1) can be ascribed to chemisorption of
,4-DMQ molecule on the inner acidic sites located near the surface of
the crystallite edges.
3
.3. Catalyst performances
Alkylation of toluene with DMC was carried out over H-M-22/M-41
composite with different weight ratios of H-MCM-22 to MCM-41, as
shown in Table 1. Of the catalysts investigated, the H-M-22/M-41 (7:1)
composite exhibits the highest conversion of toluene. The conversion
of toluene decreases considerably with a decreasing amount of H-
MCM-22 zeolite in the composite, especially for H-M-22/M-41 (1:1).
As previously reported [2], catalytic synthesis of p-xylene by toluene
alkylation has been mostly considered as a typical acid-catalyzed
process and the protonic sites have been recognized as the active sites.
Accordingly, it is reasonable that the highest conversion of toluene
corresponds to H-M-22/M-41 (7:1) composite with the highest acid
3
concentration as characterized by NH -TPD and FT-IR with pyridine
adsorption [33]. The total number of Brønsted acid sites in per gram
composite decreases gradually with a decrease in the weight ratio of
H-MCM-22 to MCM-41, resulting in a decrease in the toluene
conversion [27].
The product distributions for the alkylation of toluene with DMC
over H-M-22/M-41 composite with different weight ratios of H-MCM-
2
2 to MCM-41 are presented in Table 1. Over the H-M-22/M-41 (7:1)
composite, the selectivity for p-xylene is only 26.3%, which is only
slightly higher than the equilibrium composition of xylene isomers.
The selectivity for p-xylene increases significantly with decreasing H-
MCM-22 zeolite content in the composite, up to 63.2% for H-M-22/M-
4
1 (3:1). With further decrease in the weight ratio of H-MCM-22 to
MCM-41, only a slight increase in p-xylene selectivity is observed.
The product distributions obtained over H-M-22/M-41 composite
at similar toluene conversion by changing the weight hourly space
velocity expressed in terms of gram of feed per gram catalyst per hour
(
WHSV) are shown in Table 2. The selectivity for p-xylene obviously
increases with a decrease in the weight ratio of H-MCM-22 to MCM-
1 in the composite. Compared with the results shown in Table 1,
4
conversion of toluene clearly decreases with decreasing contact time,
while the selectivity for p-xylene was only slightly affected. It can be
concluded that the influence of contact time on p-xylene selectivity is
negligible compared to the change in acidity.
4
. Conclusions
A novel, shape-selective H-M-22/M-41 composite is synthesized
by overgrowing MCM-41 over the external surface of H-MCM-22,
Fig. 5. FT-IR with 2,4-dimethylquinoline adsorption of H-M-22/M-41 (x:1) composite
zeolites evacuated at 473 K. a) x=1; b) x=2; c) x=3; d) x=4; e) x=5; f) x=6; g) x=7.
which exhibit a significant increase in p-xylene selectivity and high

B. Xue et al. / Catalysis Communications 12 (2010) 95–99
99
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(
Alkylation of toluene with DMC over H-M-22/M-41 composite at similar toluene
conversion levels .
a
(
[
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Catalysts (H-M-22/M-41)
7:1
9.5
6:1
8.5
5:1
7.0
4:1
3.0
3:1
1.0
2:1
0.7
1:1
0.4
WHSV (h−1)
Conversion (%)
Product selectivity (%)
Benzene
Xylenes
Trimethylbenzenes
Others
Xylene isomers (%)
Para-xylene
Meta-xylene
Ortho-xylene
18.1
17.7
18.3
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18.7
18.2
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74.3
20.6
2.2
2.3
76.7
18.9
2.1
2.0
79.2
17.2
1.6
1.5
84.9
12.1
1.5
1.7
86.7
10.3
1.3
2.1
88.2
8.2
2.4
87.8
8.7
[
[
[
1.5
1.1
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26.4
50.2
23.4
37.6
42.1
20.3
44.5
32.6
22.9
58.2
19.1
22.7
63.2
16.3
20.5
63.5
15.7
20.8
64.8
15.2
20.0
[
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Conditions: temperature=653 K; feed ratio n(toluene):n(DMC)=4:1.
[
1
[
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We deeply appreciate the financial support from National Natural
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