Liquid-phase alkylation of benzene with ethylene over postsynthesized MCM-56 analogues

Article abstract of DOI:10.1016/j.apcata.2012.07.028

MCM-56 analogues were postsynthesized via a mild acid treatment technique from hydrothermally synthesized MCM-22 lamellar precursors with Si/Al ratios of 15-45. The physicochemical properties of MCM-56 were characterized by XRD, SEM, N₂ adsorption, XPS, ²⁹Si and ²⁷Al MAS NMR, NH₃-TPD and pyridine adsorption IR techniques. In comparison to MCM-22 with 3-dimensional MWW topology, the postsynthesized MCM-56 showed a broad X-ray diffraction of emerged 1 0 1 and 1 0 2 reflections and possessed a structural disorder along the layer stacking direction. Composed of partially delaminated MWW nanosheets, MCM-56 analogues had a larger external surface than MCM-22. The MCM-56 and MCM-22 catalysts were employed in the liquid-phase alkylation of benzene with ethylene. MCM-56 analogues exhibited a higher yield of ethylated benzenes and a higher catalytic stability than MCM-22, proving to serve as promising solid-acid catalysts for processing bulky molecules in petrochemical industry.

Full text of DOI:10.1016/j.apcata.2012.07.028

Applied Catalysis A: General 443–444 (2012) 103–110
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Liquid-phase alkylation of benzene with ethylene over postsynthesized
MCM-56 analogues
Bin Zhanga,b, Yongjun Jia, Zhendong Wanga, Yueming Liua, Hongmin Sunb, Weimin Yangb, Peng Wua,∗
a Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, PR
China
b Shanghai Research Institute of Petrochemical Technology, SINOPEC, North Pudong Rd. 1658, Shanghai 201208, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
MCM-56 analogues were postsynthesized via a mild acid treatment technique from hydrothermally
synthesized MCM-22 lamellar precursors with Si/Al ratios of 15–45. The physicochemical properties
of MCM-56 were characterized by XRD, SEM, N2 adsorption, XPS, 29Si and 27Al MAS NMR, NH3-TPD and
pyridine adsorption IR techniques. In comparison to MCM-22 with 3-dimensional MWW topology, the
postsynthesized MCM-56 showed a broad X-ray diffraction of emerged 1 0 1 and 1 0 2 reflections and pos-
sessed a structural disorder along the layer stacking direction. Composed of partially delaminated MWW
nanosheets, MCM-56 analogues had a larger external surface than MCM-22. The MCM-56 and MCM-22
catalysts were employed in the liquid-phase alkylation of benzene with ethylene. MCM-56 analogues
exhibited a higher yield of ethylated benzenes and a higher catalytic stability than MCM-22, proving to
serve as promising solid-acid catalysts for processing bulky molecules in petrochemical industry.
© 2012 Elsevier B.V. All rights reserved.
Received 1 March 2012
Received in revised form 21 July 2012
Accepted 23 July 2012
Available online 28 July 2012
Keywords:
MCM-56 analogue
MCM-22
Postsynthesis
Liquid-phase alkylation
Ethylbenzene
1. Introduction
conditions was first commercialized by Mobil/Badger. Thereafter,
a series of zeolites were investigated to exhibit promising catalytic
Alkylation of benzene is an important process in petrochemical
industry [1–3]. As one of the most useful alkylbenzenes, ethyl-
benzene (EB) is used as feedstock for the production of styrene,
the raw material for polystyrene, acrylonitrile–butadiene–styrene
(ABS), styrene–acrylonitrile (SAN) resins, styrene–butadiene elas-
tomers and latexes, as well as other unsaturated resins [4]. The
worldwide capacity of ethylbenzene currently reaches 35 million
metric tons per year. Its global demand is estimated to grow by
about 4.1% annually in the period of 2009–2014 and by 3.3% per
year over the ten years of the forecast.
Nowadays, ethylbenzene is mainly produced by the alkylation of
benzene with ethylene or ethanol using acid catalysts [5]. The con-
ventional catalysts for this reaction are mineral acids such as alu-
minum chloride and phosphoric acid. These homogeneous catalysts
cause a number of problems in terms of handling, safety, corrosion,
and waste disposal in spite of their relatively high activity and long
lifetime [6–8]. An immense endeavor has been put to develop alter-
native catalytic systems that are more environmentally friendly. As
a result, the ethylbenzene production technology has progressively
shifted to zeolite-based processes [9]. Using ZSM-5 based catalyst
[10,11], the process of ethylbenzene production under gas-phase
performances. USY [7,12], Beta [13,14] and MCM-22 [15,16] have
been successively commercialized for the liquid-phase alkylation
of benzene which is operated at low temperatures and high pres-
sures with the advantage of a better control and a longer catalyst
life. With respect to the ethylbenzene production with USY, Beta or
MCM-22 as the catalyst, MCM-22 possesses a higher selective for
ethylated benzenes at a lower benzene/ethylene molar ratio, which
is benefit for reducing the recycling amount of benzene [17].
MCM-22 zeolite with the MWW topology [18], one of the
most representative zeolite developed by Mobil [19], is struc-
turally analogous to SSZ-25 [20], PSH-3 [21], ITQ-1 [22] and
MCM-49 [23]. Originated from a lamellar precursor, the MCM-
22 structure is composed of three pore systems. One is the
2-dimensional (2D) sinusoidal 10-membered ring (MR) chan-
nel with elliptical ring cross section of 0.45 nm × 0.55 nm, which
runs through the intralayers of the MWW nanosheets. The
other interlayer 10-MR channel contains 12-MR supercages of
0.71 nm × 0.71 nm × 1.82 nm. It has also 12-MR side pockets or half
cups on the outer crystallite surfaces external, providing more
accessible acid sites for catalytic reactions.
As an important member of MWW family, MCM-56 has been
paid more attention because its side pockets on the external surface
are easily accessible by large molecules [24]. Consisting of disor-
dered collection of MWW sheets but more exposed side pockets,
MCM-56 is claimed to possess a partially delaminated structure in
∗
Corresponding author. Fax: +86 21 62232292.
E-mail address: pwu@chem.ecnu.edu.cn (P. Wu).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.07.028

104
B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
comparison to 3D crystalline MCM-22. MCM-56 was once prepared
only by hydrothermal synthesis from the synthetic gels similar to
MCM-22. The hydrothermal synthesis of MCM-56 usually needs
a more careful control for crystallization time and temperature in
comparison to the synthesis of MCM-22. Furthermore, the variation
of the Si/Al ratios is limited in the direct hydrothermal synthesis of
MCM-56 [25].
Recently, we developed a facial postsynthesis method for
preparing MCM-56 analogues MWW-type aluminosilicate or
titanosilicate precursors with changeable Al or Ti content [26,27],
which is based on the fact that 2D lamellar precursors are of
soft materials with a structural diversity. In comparison to corre-
sponding 3D MWW counterparts, the obtained MCM-56 analogues
exhibit enhanced catalytic activity in the reactions such as alkene
epoxidation and 1,3,5-triisopropyl benzene cracking.
With the purpose to develop more active and selective catalysts
than 3D MCM-22 for the alkylation of benzene, we postsynthesized
MCM-56 analogues having a wide range of Si/Al ratios through
a mild acid treatment in this study. The resulting materials were
characterized for the structural features and physicochemical prop-
erties in detail. Their catalytic performance was investigated in the
liquid-phase alkylation of benzene with ethylene.
windows, where it was evacuated at 773 K for 2 h before the pyri-
dine adsorption. The adsorption was carried out by exposing the
wafer to a pyridine vapor (1.3 kPa) at room temperature for 0.5 h.
The IR spectra of chemically adsorbed pyridine were recorded after
evacuation at 473 K, 573 K or 673 K for 1 h. The acid-site distribu-
tion was measured with NH3 temperature programmed desorption
(NH3-TPD) on an apparatus equipped with a thermal conductivity
detector (TCD). A sample of 150 mg was activated in helium flow
at 873 K for 1 h. It was then cooled to 373 K where adsorption of
NH3 and desorption physically adsorbed NH3 were preformed. The
NH3-TPD profile was recorded by heating the sample from 373 K
to 873 K at a rate of 10 K min−1 and under helium flow at the rate
of 30 cm3 min−1. Solid-state MAS NMR spectra were recorded on
a Bruker DMX Advance 500 spectrometer. 29Si NMR spectra were
recorded at 59.62 MHz with a pulse length of 5 ␮s and a spinning
rate of 4 kHz, while 27Al NMR spectra were recorded at 78.20 MHz
with a pulse length of 0.31 ␮s and a spinning rate of 12 kHz. Si/Al
molar ratios were determined by inductively coupled plasma (ICP)
elemental analyses on a Varian 725-ES optical emission spectrom-
eter. X-ray photoelectron spectroscopy (XPS) measurements were
performed on ESCALAB 250 (VG) using Al K␣ (hꢁ = 1486.6 eV) radi-
ation.
2. Experimental
2.4. Catalytic reactions
2.1. Synthesis MCM-22 precursors and H-MCM-22 samples
The prepared catalysts, MCM-22 and MCM-56 analogues, were
pressed into self-supported tablets under 20 MPa pressure using
an electric tablet machine. They were then scrapped to collect the
granules with a griddle of 10–20 mesh. The shaped tablets were
tested for liquid-phase alkylation of benzene with ethylene in a
fixed bed reactor. The catalyst (1 g) was loaded into the middle
of the stainless reactor (L = 750 mm, D = 10 mm), and it was acti-
vated at 673 K under nitrogen flow to eliminate any adsorbed water.
The reactor was then brought to the reaction temperature of 463 K
where the alkylation was operated continuously at 3.0 MPa, ben-
zene to ethylene molar ratio of 3.0 and weight hourly space velocity
(WHSV) of 1.0 or 2.0 h−1 for ethylene. The reaction products were
collected and analyzed with an Agilent 6820 gas chromatograph
equipped with a flame ionization (FID) detector and a HP-FFAP
(50 m × 0.32 mm × 0.25 ␮m) capillary column. In poisoning exper-
iments, 2,4-dimethylquinoline (DMQ), employed as a poisonous
substance, was co-fed into the reactor continuously at a rate of
50 ␮L h−1 by mixing in benzene.
MCM-22 lamellar precursors were hydrothermally synthesized
using hexamethyleneimine (HMI) as a structure-directing agent
(SDA) following the literature reported previously [9]. Silica gel
(40 wt.%) and Al2(SO4)3·18H2O were used as silicon and aluminum
sources, respectively. The precursors were crystallized from the
gels with molar compositions of 1.0 SiO2:1/n Al2O3:0.10 NaOH:0.45
HMI:20.0 H2O, where n was 30, 40, 60 and 90. The crystallization
was carried out in Teflon-lined stainless autoclaves under rota-
tion (200 rpm) at 423 K for 4 days. The precipitates were filtered,
washed with deionized water and dried at 373 K overnight. The
as-synthesized precursors, denoted as MCM-22(P), were calcined
in air at 723 K for 5 h to remove the organic SDA species. Calcined
MCM-22 in sodium-form was ion exchanged with 1 M NH4NO3 at
room temperature for 6 h twice and then calcined at 723 K for 5 h
to obtain the proton-type sample, H-MCM-22.
2.2. Postsynthesis of MCM-56 analogues
3. Results and discussion
MCM-56 analogues were prepared from MCM-22(P) by postsyn-
thesis method that we reported elsewhere [27]. Under mild acid
treatment conditions, MCM-22(P) was structurally transferred to
MCM-56 readily. In a typical preparation, MCM-22(P) was treated
with 0.1 M HNO3 at a solid-to-liquid weight ratio of 1:20 and room
temperature for 1 h. The acid treated samples were subsequently
calcined and changed into proton-type MCM-56 using the same
procedures mentioned above for H-MCM-22.
3.1. Postsynthesis of MCM-56 analogues with various Si/Al ratios
The MCM-22(P) precursors were synthesized at various Si/Al
ratios (15, 20, 30 and 45) using HMI as SDA. The XRD patterns
of these precursors before and after acid treatment with 0.1 M
HNO3 are given in Fig. 1. The precursors all showed the 0 0 1 and
0 0 2 diffraction peaks in the 2ꢂ region of 3–7◦, characteristic of
a layered structure with the MWW sheets stacking along the c-
direction (Fig. 1A). In addition, the MCM-22(P) samples also showed
three well resolved diffractions due to 1 0 0, 1 0 1 and 1 0 2 planes.
The diffractions related to the crystalline MWW sheets parallel to
the ab-planes such as 3 1 0 plane were also clearly observed in
higher angle region. The XRD patterns matched well with that of
the MWW lamellar precursor reported in the literature [18,28].
Thus, the materials with a pure MWW phase were obtained at
different Si/Al ratios. Fig. 1B shows the XRD patterns of directly
calcined MCM-22 precursors. They were obviously different from
those of corresponding precursors. Upon calcination, the 0 0 1 and
0 0 2 diffractions shifted to higher angles with reduced intensities,
2.3. Characterization methods
The crystallinity of the samples was characterized by X-ray
powder diffraction (XRD) patterns on a Bruker D8 Advance diffrac-
tometer equipped with a rotating anode and Cu-K␣ radiation
˚
(ꢀ = 1.5405 A). Scanning electron microscopy (SEM) was performed
on a Hitachi S-4800 electron microscope. N2 adsorption was car-
ried out at 77 K on a BELSORP-MAX instrument. The samples were
degassed under vacuum at 383 K for 4 h and then at 623 K for 6 h.
Fourier transform infrared spectra (FTIR) were obtained with a
Nicolet FTIR-380 spectrometer at room pressure. A self-supported
wafer (50 mg and Ø 2 cm) was set in a quartz IR cell sealed with CaF2

B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
105
A
B
d
d
c
c
b
a
b
a
5
10
15
20
25
30
5
10
15
20
25
30
2Theta (degree)
2Theta (degree)
C
D
broad line
broad line
d
c
d
c
b
a
b
a
5
10
15
20
25
30
5
10
15
20
25
30
2Theta (degree)
2Theta (degree)
Fig. 1. XRD patterns of MCM-22 precursors (A), directly calcined MCM-22 precursors at 823 K (B), MCM-56 analogues as-made from the MCM-22 precursors by treatment
in 0.1 M HNO3 for 0.5 h (C), and calcined MCM-56 analogues at 823 K (D). The samples were hydrothermally synthesized at Si/Al ratio of 15 (a), 20 (b), 30 (c) and 45 (d),
respectively.
and were almost invisible in the patterns. On the other hand, the
h k 0 diffractions such as 1 0 0 and 3 1 0 peaks remained practically
unchanged, indicating that the structural change took place essen-
tially along the c-axis. It means that 2-dimensional (2D) lamellar
precursors were transformed into 3D MWW structure as a result
of interlayer dehydration/condensation of the hydroxyl groups on
the layers upon calcination.
only in their arrangement and stacking format. The broad band in
the 2ꢂ region of 7–11◦ could be taken as a clear evidence for the
formation of a structure analogue to MCM-56 [29]. Fig. 1D showed
the XRD patterns of the MCM-56 analogues calcined at 723 K for
5 h. The patterns remained the same in terms of the overlapped
1 0 1 and 1 0 2 diffractions, which indicates that the structure of
MCM-56 analogues was thermally stable.
However, the MCM-22(P) samples were converted to the
products which showed MCM-56-like XRD patterns after a mild
acid treatment in 0.1 M HNO3 at room temperature (Fig. 1C).
The line positions and relative intensities of the peaks were in
good agreement with those reported for directly synthesized
MCM-56 aluminosilicates [24]. They were featured by a very
broad diffraction in the 2ꢂ region of 7–11◦, since the 1 0 1 and
1 0 2 diffractions overlapped seriously. Nevertheless, the ab-
plane-related diffractions parallel to such as 1 0 0 and 3 1 0 peaks
remained well-resolved. To distinguish the reported MCM-56
aluminosilicates that were hydrothermally synthesized under
controlled conditions, we denote the present postsynthesized
materials as MCM-56 analogues. It seems that the acid treatment
kept the MWW sheets almost intact but caused a structural change
We once reported that a mild acid treatment may extract par-
tially the organic SDA molecules intercalated between the MWW
layers, leading to an unbalanced array or stacking of the layers
[27,29]. After further calcination, the interlayer condensation then
takes place in a way which is different from an ordinary manner
in direct calcination of the precursor. Fig. 2 summarizes possible
formation mechanism of postsynthesized MCM-56 analogues. The
disordered collection of MWW layers may make more edges of
the structure expose to the outside, thus MCM-56 is claimed to
possess a partially delaminated structure [30]. As a result, the
MCM-56 analogues were prepared successfully by postsynthesis
from the corresponding MCM-22 precursors. In direct synthesis,
the formation of MCM-56 structure is needed to optimize the
crystallization degree and gel compositions [25]. However, by

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B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
Fig. 2. Strategy for post-synthesizing MCM-56 analogue.
using present postsynthesis technique with a mild acid treatment,
the structure of MCM-56 analogues was constructed readily from
fully crystallized precursors independent of Si/Al ratio.
(see Fig. S2 in Supplementary information), verifying that MCM-56
possessed a more exposed external surface [28]. According to anal-
ysis using t-plot method [31], the external surface area of MCM-56
analogue was 145 m2 g−1, which was larger than that of MCM-22
(118 m2 g−1). This was in agreement with the results reported on
hydrothermally synthesized MCM-56 which was assumed to be
composed of the MWW sheets arrayed in a disordered manner
and have so-called partially delaminated structure [25,28].
3.2. Physicochemical properties of MCM-56 analogues
The scanning electron micrograph (SEM) images of MCM-22 and
MCM-56 analogue are shown in Fig. S1 in Supplementary infor-
mation. MCM-22 was composed of thin pellet-like crystallites,
approximately 0.02–0.05 ␮m in thickness and 0.2–0.5 ␮m in
length. The SEM image of MCM-56 analogue indicated that its crys-
tallites also appeared to be thin platelets with the same crystal size
as MWW-22. The HNO3 treatment and subsequent calcination had
no significant influence on the crystallite morphology, although
the XRD patterns clearly evidenced a structural transformation
occurred along the c-axis. The acid treatment-induced structure
change probably occurred at a nanometer or subnanometer scale
but not at a micrometer level.
The physicochemical properties of MCM-22 and MCM-56
analogue were characterized by various techniques (Table 1). They
were both obtained from the same precursor synthesized at Si/Al
ratio of 15. The XPS and ICP analyses indicated that the Si/Al molar
ratio on the crystallite surface of MCM-22 was equal to the bulk
ratio determined, suggesting the Al distribution was relatively
uniform throughout the crystallites. On the other hand, the Si/Al
molar ratio of MCM-56 analogue increased from 15.8 in the bulk
phase to 17.9 on the surface, indicating a slight dealumination
took place during acid treatment especially on the crystallite
surface. This phenomenon was in accordance with that reported
in previous literature [27]. In comparison with MCM-22, MCM-56
analogue showed a slightly lower N2 adsorption amount in the
isotherm at P/P0 = 0–0.75, but a higher amount in higher P/P0 region
29Si spectroscopy was used to investigate the development of
external silanols (Fig. 3A). All the bands matched well with those
previously reported for MCM-22 [32–34]. H-MCM-56 showed a
more intensive resonance around −100 ppm which was assigned
to the Q3 sites such as Si(OH)(SiO)3 and Si(OAl)(SiO)3 [28]. Since
the acid treatment caused a partial dealumination during the post-
synthesis of H-MCM-56, the −100 ppm resonance was considered
to originate mainly from the Si(OH)(SiO)3 groups. 27Al MAS NMR
spectra of H-MCM-22 and H-MCM-56 both showed clearly two sets
of signals, that is, a broader band with a maximum at 55 ppm and
a low frequency signal around 0 ppm (Fig. 3B), which are assigned
to tetrahedral and octahedral Al species, respectively [35].
IR spectra were measured to investigate the characters of
hydroxyl groups and acid sites in H-MCM-22 and H-MCM-56 ana-
logue. The bands at 3745 cm−1 and 3620 cm−1 are attributed to
the external isolated silanols and the structure Si(OH)Al hydroxyls
associated with framework Al, respectively [36]. MCM-56 analogue
showed a more intensive band at 3745 cm−1 than that of MCM-
22 (see Fig. S3 in Supplementary information), which is probably
related to a large portion of MWW sheets exposed on the external
surface. The reduced intensity of the 3620 cm−1 band in MCM-
56 analogue is partially due to the framework dealumination by
acid treatment. A disordered collection of MWW sheets may also
cause a part of structural hydroxyl groups decrease. The pyridine
adsorption and desorption spectra were further taken to measure
the acidic properties of H-MCM-22 and H-MCM-56. The desorption
of pyridine was performed at different temperatures (473–673 K)
to give information about the strength of acid sites. The band at
1545 cm−1 due to pyridinium ion could be taken as the evidence of
Brønsted acid sites, whereas the band at 1450 cm−1 due to coor-
dinated pyridine corresponds to Lewis acid sites [36]. And the
pyridine molecules adsorbed on these two kinds of acid sites both
contribute to the band at 1490 cm−1. The spectra of H-MCM-22 and
H-MCM-56 analogue were both dominated by the 1545 cm−1 band
(Fig. 4), indicating they were characteristic of Brønsted acidity. In
comparison to H-MCM-22, H-MCM-56 showed slightly decreased
intensity at 1545 cm−1 band, which might be caused by the dis-
ordered stacking of MWW sheets. After desorption at 673 K, the
1450 cm−1 band was still observed and showed relatively a high
Table 1
A comparison of physicochemical properties between H-MCM-22 and H-MCM-56
analogue.
c
Sample
Bulk
Surface Vmicropore
Specific surface
Si/Ala
Si/Alb
(cm3 g−1
)
area (m2 g−1
)
d
c
e
Stotal
Smicropore
Sexternal
H-MCM-22 15.5
H-MCM-56 15.8
15.7
17.9
0.17
0.14
476
415
358
270
118
145
a
Given by ICP.
Given by XPS.
b
c
Micropore volume and surface area were calculated by t-plot method.
Calculated by BET method.
Sexternal = Stotal − Smicropore
d
e
.

B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
107
A
B
Tetrahedral
Octahedral
3
Q
b
b
a
a
-80
-100
-120
120
80
40
0
-40
Chemical shift (ppm)
Chemical shift (ppm)
Fig. 3. 29Si (A) and 27Al (B) MAS NMR spectra of H-MCM-22 (a) and H-MCM-56 (b).
intensity (see Table S1 in Supplementary information), implying
the zeolites contained strong acid sites.
to MCM-22, the advantage of MCM-56 in production of isopropyl-
benzene is closely related to its open external surface which makes
the active sites more accessible to the reactant molecules [41]. The
successful postsynthesis of MCM-56 encouraged us to investigate
its catalytic behaviors in the reactions involving bulky substrates.
As an important reaction for producing ethylbenzene, the alky-
lation of benzene with ethylene is currently catalyzed by solid-acid
catalysts of zeolites, that is, H-ZSM-5 catalyst in gas-phase reactions
and H-Beta or H-MCM-22 in liquid-phase reactions. This reaction
is comprised of complicated processes, which includes the alkyla-
tion of benzene with ethylene to ethylbenzene, further alkylation of
ethylbenzene to diethylbenzenes or poly ethylbenzenes [13], iso-
merization of ethylbenzene, oligomerization of ethylene [42] and
generation of other aromatic hydrocarbons [43]. Table 2 compares
the catalytic activity and product distribution between H-MCM-
22 and H-MCM-56 analogue in liquid-phase alkylation of benzene
with ethylene operated continuously at 3.0 MPa and 463 K. The
reaction products were made up of ethylbenzene (EB), xylenes
(Xys), para-diethylbenzene (p-DEB), ortho-diethylbenzene (o-DEB),
meta-diethylbenzene (m-DEB), triethylbenzenes (TEB), C9–C11 and
other by-products. As shown in Fig. 5, the yield of ethylated ben-
zenes (EBs, including EB, DEB and TEB) varied with the reaction
NH3-TPD profiles of H-MCM-22 and H-MCM-56 analogue are
shown in Fig. S4 in Supplementary information. They exhibited des-
orption peaks typically characteristic of MCM-22 zeolite [37,38].
The peak around 487 K corresponded to the desorption of ammo-
nia adsorbed on weak acid sites, whereas the peak at 668 K was
assigned to the desorption of ammonia adsorbed on strong acid
sites. In agreement with above IR spectra of pyridine adsorption, the
amount of acidic sites in H-MCM-56 decreased slightly in compari-
son to H-MCM-22. Nevertheless, showing the ammonia desorption
peaks at the same temperatures, these two zeolites were compa-
rable in the strength of acid sites.
3.3. Catalytic properties of H-MCM-56 analogues in alkylation of
benzene with ethylene
Hydrothermally synthesized MCM-56 is reported to show
unique catalytic performance as a solid-acid catalyst which was
similar or even superior to other zeolites such as ZSM-5, Beta and
MCM-22 in particular reactions such as benzene alkylation [24,30]
and as an adsorbent for separation processes [39,40]. In comparison
1.2
1.2
A
B
1490
1490
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
1545
1545
1450
1450
c
c
b
a
b
a
1700
1600
1500
1400
1700
1600
1500
1400
Wavenumber (cm-1
)
Wavenumber (cm-1)
Fig. 4. IR spectra of H-MCM-22 (A) and H-MCM-56 (B) after pyridine adsorption and then desorption at 473 K (a), 573 K (b) and 673 K (c) for 1 h, respectively.

108
B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
Table 2
Catalytic activity and product distribution in the liquid-phase alkylation of benzene with ethylene on H-MCM-22 and H-MCM-56 analogue.a
Catalystb
Benzene conv. (%)
Product distribution (%)
EB
m-DEB
p-DEB
o-DEB
TEB
Xys
C9–C11
Others
H-MCM-22
H-MCM-56
27.7
32.9
81.6
82.6
4.3
4.2
3.9
3.5
6.5
6.5
1.4
1.5
0
0
0.3
0.2
2.0
1.5
a
Reaction conditions: catalyst, 1.0 g; temperature, 463 K; pressure, 3.0 MPa; benzene/ethylene molar ratio, 3.0; ethylene WHSV, 1.0 h−1; TOS = 20 h.
The zeolite catalysts were prepared from the same precursor, MCM-22-P(15).
b
A
B
30
20
10
30
20
10
b
b
a
a
0
0
0
50
100
0
50
100
TOS (h)
TOS (h)
Fig. 5. A comparison of catalytic performance between H-MCM-22 (a) and H-MCM-56 (b) with different Si/Al ratios. The samples were prepared from MCM-22-P(15) (A)
and MCM-22-P(20) (B), respectively. Reaction conditions: catalyst, 1.0 g; temperature, 463 K; pressure, 3.0 MPa; benzene/ethylene molar ratio, 3.0; ethylene WHSV, 2.0 h−1
.
the reactions were carried out either at ethylene WHSV of 1.0 h−1
time on different WHSV of ethylene. A reasonable comparison
is thus made by using the results obtained at time on stream
(TOS) of 20 h, where both MCM-22 and MCM-56 gave the highest
activity. Obtained from the same MCM-22 precursor (Si/Al = 15),
the H-MCM-56 analogue showed an enhanced benzene conver-
sion and ethylbenzene selectivity in comparison to H-MCM-22
counterpart (Table 2). Moreover, the operating conditions play an
important role in catalytic performances and duration. For liquid-
phase alkylation of benzene with ethylene, a high WHSV of ethylene
is beneficial for increasing the production capacity of alkylben-
zenes, which is however accompanied by a quicker deactivation
of the catalyst (see Fig. S5 in Supplementary information). Herein,
or 2.0 h−1 depending on different purpose.
In commercial process for ethylbenzene production, diethyl-
benzenes and triethylbenzenes are also regarded as objective
products in addition to ethylbenzene because they are finally
converted into high valuable and desirable ethylbenzene product
through catalytic transalkylation with benzene. Thus, the sum of
mono- and poly-ethylbenzenes is employed to evaluate the catalyst
performance in benzene ethylation. The dependence of ethylated
benzenes (EBs, including EB, DEB and TEB) and EBs selectivity on
the Al content in H-MCM-22 and H-MCM-56 is presented in Fig. 6.
The catalysts were prepared from the MCM-22 precursors with
Fig. 6. Dependence of ethylated benzenes (EBs) (A) and EBs selectivity (B) on the Al content in H-MCM-22 (a) and H-MCM-56 (b). Reaction conditions: catalyst, 1.0 g;
temperature, 463 K; pressure, 3.0 MPa; benzene/ethylene molar ratio, 3.0; ethylene WHSV, 1.0 h−1; TOS = 20 h.

B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
109
A
B
100
98
96
94
92
90
100
a
a
98
b
b
96
94
92
90
0
20
40
60
80
100
0
20
40
60
80
100
TOS (h)
TOS (h)
Fig. 7. A comparison of EBs selectivity between H-MCM-22 (a) and H-MCM-56 (b). The samples were prepared from MCM-22-P(15) (A) and MCM-22-P(20) (B), respectively.
Reaction conditions: see Fig. 6.
Si/Al molar ratios of 15, 20, 30 and 40. An obvious improvement
in EBs yield was achieved by post-converting the precursors into
H-MCM-56 analogues especially in the region of high Al content.
The increase of EBs yield became less with deceasing Al content, i.e.
increasing Si/Al ratio. Meanwhile, the EBs selectivity in total prod-
ucts was also enhanced to a certain degree by post-synthesizing
MCM-56 analogues (Fig. 6B).
In order to investigate whether MCM-56 analogue was superior
to MCM-22 in duration and lifetime, the reaction was carried out
at an increased WHSV of ethylene (2.0 h−1) and the reaction time
was prolonged to 100 h of TOS. As shown in Fig. 5, two sets of cat-
alysts prepared form the precursors with Si/Al molar ratios of 15
and 20 were compared. Generally, the reactions took about 15 h
to reach the highest catalytic activity. MCM-56 showed almost a
stable reaction level at TOS of 20–75 h, while MCM-22 deactivated
more rapidly after 20 h. The EBs selectivity was always maintained
around 98% independent of reaction time (Fig. 7). H-MCM-56 not
only showed higher EBs yield and but also exhibited to be more
durable than H-MCM-22 especially in the sample at Si/Al molar
ratio of 15 (Fig. 5A). The EBs yield merely decreased from ∼30% to
∼27% during 100 h of TOS.
40
30
20
10
0
Catalyst
Fig. 8. Effect of 2,4-DMQ addition on the alkylation of benzene with ethylene on H-
MCM-22 and H-MCM-56. Reaction conditions: catalyst, 1.0 g; temperature, 463 K;
pressure, 3.0 MPa; benzene/ethylene molar ratio, 3.0; ethylene WHSV, 1.0 h−1; 2,4-
DMQ feed (if added), 50 ␮L h−1; benzene feed, 19.2 mL h−1; TOS = 20 h.
To clarify the role of external surface in the alkylation of ben-
zene with ethylene, 2,4-dimethylquinoline (2,4-DMQ) with too
large molecular dimension to enter into the 10-MR pores of MWW
zeolites was employed to poison selectively the acid sites on the
external surface [44]. When the reactions were carried out in the
absence of 2,4-DMQ, the EBs yield was 24% and 30% for H-MCM-22
and H-MCM-56 prepared from the same precursor (Si/Al = 15),
respectively (Fig. 8). When the 2,4-DMQ was co-fed with benzene
into the reactor, the alkylation was essentially retarded, giving
extremely low EBs yields. In the case of esterification of acetic acid
with ethanol, that is, a reaction involving only small molecules,
H-MCM-22 was even slightly more active than H-MCM-56 (see
Fig. S6 in Supplementary information). Furthermore, the addition
of 2,4-DMQ into the reactants had no obvious influence on the
conversion of acetic acid for both catalysts. Above results indicated
that 2,4-DMQ may poison selectively the acid sites on the external
surface but not those located in the 10-MR channels. The benzene
ethylation that involves bulky molecules in both reactants and
products is assumed to be catalyzed by the acid sites existing in
open reaction spaces, those located in the 12-MR side pockets
(or half cups) on the external surface of the MWW layers in case
of MCM-22 [15]. Possessing a partially delaminated structure
and characteristic of larger external surface, MCM-56 analogue
is benefit to the bulky reactions such as benzene ethylation. The
larger external surface would be also effective for suppressing the
catalyst deactivation by coke formation.
4. Conclusions
MCM-56 analogues with various Al contents have been post-
synthesized from fully crystallized MCM-22 precursors by a mild
acid treatment. A partial removal of interlayer organic species in the
precursors probably induces a disordered collection and stacking of
MWW layers, leading to a large portion of external surface exposed
to the outside and partially delaminated structure of MCM-56 ana-
logues. This endows MCM-56 catalysts with higher accessibility
to bulky reactant molecules and then higher yields of ethylated
benzenes as well as catalytic stability than conventional MCM-22
catalyst in the liquid-phase alkylation of benzene with ethylene.
Acknowledgements
We gratefully acknowledge the NSFC of China (220925310
and U1162102), the Shanghai Municipal Education Commission

110
B. Zhang et al. / Applied Catalysis A: General 443–444 (2012) 103–110
(11CXY20), Ministry of Science and Technology (2012BAE05B02),
and the Shanghai Leading Academic Discipline Project (B409) for
financial support.
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found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
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