Enhancing activity without loss of selectivity - Liquid-phase alkylation of benzene with ethylene over MCM-49 zeolites by TEAOH post-synthesis

Article abstract of DOI:10.1016/j.apcata.2015.03.005

As-synthesized and calcined MCM-49 zeolites were post-synthesized by tetraethylammonium hydroxide to tailor their morphology, texture properties, acid sites and catalytic performances. With post-synthesis by tetraethylammonium hydroxide, both as-synthesiz

Full text of DOI:10.1016/j.apcata.2015.03.005

Applied Catalysis A: General 497 (2015) 135–144
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Enhancing activity without loss of selectivity – Liquid-phase
alkylation of benzene with ethylene over MCM-49 zeolites by TEAOH
post-synthesis
Yanchun Shi, Enhui Xing, Wenhua Xie, Fengmei Zhang∗, Xuhong Mu, Xingtian Shu
State Key Laboratory of Catalytic Materials and Reaction Engineering, Research Institute of Petroleum Processing, Sinopec, Beijing 100083, China
a r t i c l e i n f o
a b s t r a c t
Article history:
As-synthesized and calcined MCM-49 zeolites were post-synthesized by tetraethylammonium hydroxide
to tailor their morphology, texture properties, acid sites and catalytic performances. With post-synthesis
by tetraethylammonium hydroxide, both as-synthesized and calcined MCM-49 zeolites have showed
remarkable morphology change from rose-like shape into disorderly packed irregular MWW sheets, and
improved surface areas, pore volumes and acid sites without obvious loss of crystallinity. The samples
before and after tetraethylammonium hydroxide treatment were used as catalysts in liquid-phase alkyl-
ation of benzene with ethylene. Importantly, a prominent increase in ethylene conversion was observed
without loss of ethylbenzene selectivity over post-synthesized MCM-49 catalysts in liquid-phase alkyl-
ation of benzene with ethylene.
Received 29 November 2014
Received in revised form 3 March 2015
Accepted 5 March 2015
Available online 19 March 2015
Keywords:
MCM-49
Tetraethylammonium hydroxide
Post-synthesis
© 2015 Elsevier B.V. All rights reserved.
Liquid-phase alkylation
Ethylebenzene
1. Introduction
MWW zeolite crystals are in the form of sheet-like discs or aggre-
gates of cross-linked discs of 2–5 ␮m in diameter and 10–40 nm in
Ethylbenzene (EB) is an important chemical intermediate for
plastic and rubber production with a current capacity of 3.5 ×107
tons per year, growing at by 3.3% annually over the next decade of
the forecast [1,2]. Compared with conventional AlCl3 process, two
zeolite-based EB processes, vapor-phase (ZSM-5) and liquid-phase
processes (USY, Beta, MCM-22), show combined virtues of easy sep-
aration, low corrosion, high activity and shape selectivity [3–8]. Due
to low reaction temperature, there are obvious advantages such as
high EB selectivity and long catalyst life in the liquid-phase process.
Regardless of somewhat low in catalytic activity, MWW zeolites
inspire much more focus due to superior EB selectivity at lower
benzene/ethylene molar ratio for the sake of energy consumption
[9–11].
MWW zeolites [12–21] contain PSH-3, ERB-1, SSZ-25, MCM-22,
MCM-49, MCM-56, MCM-36, ITQ-1, ITQ-2 and UZM-8 zeolites. As
well known, hexamethyleneimine (HMI), as an effective structure-
directing agent, is potent to synthesize MWW zeolites. Because
of its effective structure-directing capability in the formation of
MWW zeolites, it is difficult to avoid the accumulation of MWW lay-
ers and realize the morphology control of MWW zeolites. Typically,
thickness [22,23], and there are the typical pores of MWW topol-
ogy structure: 12 MR “cups” (0.71 nm × 0.71 nm × 0.91 nm) on the
external surface, the supercages defined by 12 MR (0.71 nm out-
side diameter × 1.82 nm height) through 10 MR opening windows
(0.41 nm × 0.54 nm), and the two-dimensional sinusoidal 10 MR
pores (0.41 nm × 0.54 nm). It has been verified that active cen-
ters of MWW zeolites are mainly located in 12 MR “cups” on the
outer surface to be more easily accessed in liquid-phase alkyl-
ation of benzene with ethylene, using 2,4,6-trimethyl-pyridine
(0.62 nm × 0.56 nm) as probe molecules [10,24,25]. It is deduced
that 12 MR “cups” on the outer surface show little restriction on
the diffusion of reactant toward the active centers. Therefore, these
active centers are believed to be responsible for the unique cat-
alytic performanceof MWW catalysts, referred to as “surface pocket
catalysis” [26,27]. Generally, the morphology, textural properties
and acidities of MWW zeolites significantly affect the accessibil-
ity of active centers and their catalytic properties in liquid-phase
alkylation of benzene with ethylene.
To increase the accessibility and amount of active centers, equal
to improving the alkylation performances, many efforts have been
devoted to synthesizing MWW zeolites as follows: preparing small
grain size [28], pillaring [18,29], swelling [30], interlayer-expansion
[31,32], delaminating [33,34], and introducing mesopores by acidic
[35] or alkaline treatments [36–38]. Particularly, post-synthesis
of MWW zeolites in acidic or alkaline solution is an efficient
∗
Corresponding author. Research Institute of Petroleum Processing Sinopec,
Xueyuan Road 18, Beijing, China. Tel.: +86 010 82368698.
E-mail address: zhangfm.ripp@sinopec.com (F. Zhang).
http://dx.doi.org/10.1016/j.apcata.2015.03.005
0926-860X/© 2015 Elsevier B.V. All rights reserved.

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Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
way to introduce mesopores to tailor their catalytic properties.
Most of researchers have studied that the calcined MWW zeo-
lites were treated in NaOH solution, and mesopores were assuredly
introduced into the frameworks of zeolites by desilication. Xu et al.
[38] reported that when template-containing MCM-22 zeolite was
alkali-treated, desilication mainly occurred in the Al-poor regions,
which broke the crystal sheets into smaller particles. However,
there were still two problems in post-synthesis of MWW zeolites in
NaOH solution: firstly, in such harsh alkaline conditions, mesopores
were generated by obvious desilication (parent zeolites SiO2/Al2O3
50–60, product zeolites SiO2/Al2O3 20–30) inevitably led to loss
of crystallinity, which usually resulted in the disappointing per-
formances of post-synthesized MWW zeolites. On the whole, due
to tight connection between MWW layers and harsh NaOH treat-
ment, it was difficult to control the degree of desilication (loss of
SiO2/Al2O3), and this post-synthesis usually led to the loss of crys-
tallinity, especially uncontrollable crystallinity loss of outer surface.
It is well known that liquid-phase alkylation of benzene with eth-
ylene mainly proceed in the 12 MR “cups” on the outer surface of
MWW zeolites. The loss of crystallinity in NaOH solution would
inevitably cause the loss of crystallinity on the outer surface firstly,
which is really a disaster for liquid-phase alkylation of benzene
with ethylene. Secondly, with intermediate EB as the target prod-
uct in a consecutive reaction, the other contradictory issue is the
trade-off between ethylene conversion and EB selectivity, which is
usually featured by “improved ethylene conversion and decreased
EB selectivity”. As well known, the relationship between conversion
and selectivity of intermediate product in a consecutive reaction
has been well described in research papers and classic textbooks on
reaction engineering [39,40], and there is a common phenomenon
that the intermediate as the target product selectivity is almost
100% at low conversion, and the increase of conversion is accom-
panied by the decrease of intermediate product selectivity.
in Hunan Jianchang Petrochemical Company, Sinopec via
temperature-controlled phase transfer hydrothermal syn-
thesis [41]. The batch composition in terms of molar ratio
was: SiO2/Al2O3 = 25, NaOH/SiO2 = 0.18, HMI/SiO2 = 0.3, aniline/
SiO2 = 0.2, H2O/SiO2 = 15. The synthesis was carried out at 145 ◦C
for 72 h with stirring speed at 15 Hz. The product was filtered,
washed with deionized water until pH value 7, and dried at 100 ◦C
overnight. Samples were calcined at 550 ◦C in ambient air for 6 h
in a muffle furnace to remove organics.
Post-synthesis of MCM-49 in TEAOH solution: As-synthesized
and calcined MCM-49 zeolites were treated in TEAOH solution.
The typical batch composition in terms of molar ratio was:
TEAOH/SiO2 = 0.1, H2O/SiO2 = 15. Post-synthesis of MCM-49 zeo-
lites was carried out in a Teflon-lined autoclave at 150 ◦C under
rotating conditions (30 r min−1) for various time (8 h, 16 h, 24 h).
The products were recovered by filtration, washed with deionized
water until pH value 7 and dried in oven at 100 ◦C overnight in order
to remove the physically adsorbed water molecules. Subsequently,
post-synthesized samples of as-synthesized MCM-49 and calcined
MCM-49 in TEAOH solution were named as TMP-x with HMI, and
TMC-x without HMI, respectively; x represented treatment time
(h).
H-type zeolites: H-MCM-49 zeolite was prepared by twice liquid-
phase ion-exchange with NH4NO3 solution at 90 ◦C for 2 h, filtrated
and dried at 100 ◦C overnight, finally calcined at 550 ◦C for 6 h. Post-
synthesized MCM-49 zeolites needed just one time ion-exchange
because of the ion-exchange between TEAOH and Na+ during the
post-synthesis. The composition among MCM-49 zeolites, NH4NO3,
and deionized water on the basis of mass ratio was: 1:1:20. As-
synthesized MCM-49 zeolite was named as H-MCM-49 zeolite,
according to treatment time at 16 h, post-synthesized MCM-49 zeo-
lites were named as H-TMP-16 (as-synthesized MCM-49 as the
parent zeolite), and H-TMC-16 (calcined MCM-49 as the parent
zeolite) zeolites, respectively.
Considering the fact of the layered MCM-49 zeolites not
enduring a harsh treatment in NaOH solution, in this paper, organic-
alkaline was selected to post-synthesize MCM-49 zeolites with
preservation of crystallinity and to tailor their morphology, text-
ural properties, acidities, and catalytic performances. Till now,
there have been few reports on the post-synthesis of MCM-49 zeo-
lites by organic-alkali treatment only. It is well summarized that
*BEA and MWW zeolites are excellent catalysts for liquid-phase
alkylation of benzene with ethylene, due to their special topology
structure directed by tetraethylammonium hydroxide (TEAOH) and
HMI, respectively. Obviously TEAOH with larger molecular dimen-
sions than HMI directs the larger channels of *BEA than MWW. As
for *BEA zeolite, liquid-phase alkylation of benzene with ethylene
proceed with high ethylene conversion within the 12 MR channels
due to little restriction. However there is low ethylene conversion
over MWW zeolite because of its structure restriction on liquid-
phase alkylation of benzene with ethylene. HMI is weeded out
because of its strong capability in formation and connection of
MWW layers. Therefore, TEAOH with lower alkalinity than NaOH
is intentionally selected to post-synthesize MCM-49 zeolites with
the preservation of crystallinity to tailor their morphology, texture
properties, acidities, and catalytic performances in liquid-phase
alkylation of benzene with ethylene. As-synthesized and calcined
MCM-49 zeolites (SiO2/Al2O3 molar ratios at about 21) were cho-
sen as parent zeolites to control the degree of desilication during
post-synthesis.
Catalyst preparation: The NH4-type samples (70 wt.%) with Na2O
content less than 0.05 wt.% and Al2O3 (30 wt.%) were mixed and
extruded. The Al2O3, which showed almost no activity in liquid-
phase alkylation of benzene with ethylene, was used as binder
to increase the mechanical strength of catalysts. The extruded
catalysts were then crushed and the −16/+20 mesh fraction was
collected and subjected to calcinations at 550 ◦C for 6 h to obtain
corresponding H-type catalysts. The H-type catalysts derived from
TMP-16 (as-synthesized MCM-49 as the parent zeolite) and TMC-
16 (calcined MCM-49 as the parent zeolite) zeolites were named as
H-TMP-16 and H-TMC-16 catalysts.
2.2. Characterization
X-ray diffraction (XRD) patterns of samples were collected on
X’pert X-ray diffractometer (PANalytical Corporation, Netherlands)
with filtered Cu K␣ radiation at a tube current of 40 mA and a
voltage of 40 kV. The scanning range of 2ꢀ was 5–35◦. The rela-
tive crystallinity of the samples was calculated according to the
sum of the peak intensities at 2ꢀ of 14.3◦, 22.7◦, 23.7◦ and 26.0◦ of
calcined zeolites through calcination at 550 ◦C for 6 h, and the crys-
tallinity of calcined MCM-49 zeolite via temperature-controlled
phase transfer hydrothermal synthesis was defined as the refer-
ence with relative crystallinity at 100%. The crystal morphology
was measured on a FEI Quanta scanning electron microscopy
(SEM). The elemental analyses of the solids were performed on an
X-ray fluorescence (XRF) spectrometer MagiX (Philips). Nitrogen
adsorption–desorption isotherms were recorded on a Micromeri-
tics ASAP 2010 instrument. The samples were first out gassed under
vacuum at 90 ◦C for 1 h and at 350 ◦C for 15 h. The total surface area
was obtained by application of the BET equation using the relative
pressure range of 0.05–0.16 in the nitrogen adsorption isotherm
2. Experimental
2.1. Preparation of MCM-49 zeolites and H-type catalysts
Hydrothermal synthesis of MCM-49 zeolite: Parent MCM-
49 zeolite was synthesized in the 1 m3 demonstration unit

Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
137
as range of linearity (using a molecular cross-sectional area for N2
of 0.162 nm2). The micropore volume was calculated by the t-plot
method.
by-products (diphenylethane) in our work. The ethylene con-
version, EB selectivity, DEB selectivity and DEB distribution of
selectivity were calculated based upon these formulas as follows:
The acidic properties of H-type zeolites were measured by
Fourier transform infrared spectrometer (FTIR), using pyridine (Py)
as probe molecules. Py-FTIR spectra were obtained on a FTS3O00
FTIR spectrometer by scans of 64 with a resolution of 4 cm−1. Self-
supporting thin wafers were pressed and placed in a quartz IR cell
with CaF2 windows, which used in pyridine adsorption studies.
Prior to the measurements, each sample was dehydrated under
vacuum 10−3 Pa at 350 ◦C for 1 h, and then cool down to 50 ◦C for
pyridine adsorption. The IR spectra of the samples before pyridine
adsorption were recorded at different temperatures (50 ◦C, 200 ◦C
and 350 ◦C), and after adsorbing pyridine for 10 s, the samples were
purged under vacuum 10−3 Pa to higher temperatures at a heating
rate of 10 ◦C min−1. Then the IR spectra of pyridine on samples were
recorded at different temperatures (50 ◦C, 200 ◦C and 350 ◦C). All
the spectra given in this work were difference spectra. The amounts
of Brønsted and Lewis acid sites were calculated according to the
acid sites of adsorbed pyridine area.
xdiphenylethane
xEB
2xDEB
MDEB
3xTEB
MTEB
H =
+
+
+
;
MEB
Mdiphenylethane
xDEB = xp-DEB + xo-DEB + xm-DEB
;
M: molar mass (g/mol); x: mass percentage concentration (wt.%)
from GC analysis; H: molar number percentage concentration
(mol%) of ethyl.
(1) Ethylene conversion (%): Cethylene = H/(H + xethylene/Methylene
)
)
)
× 100%
(2) EB selectivity (%): SEB = xEB/(xEB + xDEB + xTEB + xdiphenylethane
× 100%
(3) DEB selectivity (%): SDEB = xDEB/(xEB + xDEB + xTEB + xdiphenylethane
× 100%
(4) DEB distribution of selectivity:
m(p-DEB)/m(DEB) = xp-DEB/(xp-DEB + xm-DEB + xo-DEB) × 100%;
m(m-DEB)/m(DEB) = xm-DEB/(xp-DEB + xm-DEB+xo-DEB)×100%;
m(o-DEB)/m(DEB) = xo-DEB/(xp-DEB + xm-DEB + xo-DEB) × 100%.
29Si MAS NMR experiments were performed on a Bruker
AVANCE III 500WB spectrometer at a resonance frequency of
99.3 MHz using a 7 mm double-resonance MAS probe. The magic-
angle spinning speed was 5 kHz in all experiments, and a typical ꢁ/6
pulse length of 1.8 ␮s was adopted for 29Si resonance. The chemical
shift of 29Si was referenced to tetramethylsilane (TMS).
3. Results and discussion
3.1. Post-synthesis of MCM-49 zeolites
27Al MAS NMR experiments were performed on a Bruker
AVANCE III 600WB spectrometer at a resonance frequency of 156.4
using a 4 mm double-resonance MAS probe at a sample spinning
rate of 13 kHz. The chemical shift of 27Al was referenced to 1 M
aqueous Al(NO3)3. 27Al MAS NMR spectra were recorded by small-
flip angle technique using a pulse length of 0.4 ␮s (<ꢁ/15) and a
recycle delay of 1 s.
In the following experiments, as-synthesized and calcined
MCM-49 zeolites were treated in TEAOH (TEAOH/SiO2 = 0.1,
H2O/SiO2 = 15) solution at 150 ◦C for various time (8 h, 16 h, and
24 h). The XRD patterns of the parent and organic–alkaline treating
samples are shown in Fig. 1, and it can be observed that the diffrac-
tion patterns of all treated samples are in good agreement with
parent MCM-49 zeolites. The crystallinity of all samples was cal-
culated according to the sum of the peak intensities at 2ꢀ of 14.3◦,
22.7◦, 23.7◦ and 26.0◦ of calcined samples, and the relative crys-
tallinity of calcined MCM-49 zeolite via the temperature-controlled
phase transfer hydrothermal synthesis was defined as the reference
with relative crystallinity at 100% for all post-synthesized samples
from both as-synthesized and calcined MCM-49 zeolites. It could
be clearly seen that the relative crystallinity of post-synthesized
samples first decreased and then increased. The relative crys-
tallinity of TMP-8 (Fig. 1A) and TMC-8 (Fig. 1B) samples decreased
to 94% firstly, which might be attributed to the slight destruction of
MCM-49 framework in TEAOH solution. Interestingly, the relative
crystallinity of TMP-16 and TMP-24 samples in Fig. 1A increased
with longer treatment time, reaching up to 100% and 102%, and so
did TMC-16 and TMC-24 samples approaching to 96% in Fig. 1B. The
results indicated that the first thing was to destroy the framework
of MCM-49 slightly in TEAOH solution at the initial treatment time,
and then it was possible for TEAOH to incorporate into MWW lay-
ers. Therefore, one thing was that TEAOH could act as a filling-space
agent, and the other thing was that the amorphous aluminosil-
icate could be removed by TEAOH to purify zeolitic pores and
crystals, which might contribute to their relative crystallinity for
post-synthesized samples at longer treatment time. It can be clearly
proved that the relative crystallinity of TMP-x samples was higher
than those of TMC-x, indicating that the presence of HMI within
as-synthesized MCM-49 zeolite would serve a protective agent for
MWW framework in TEAOH treatment, but as for calcined MCM-
49 zeolite, TEAOH might only clean the pores and crystals to purify
the zeolite and acted as a space-filling agent.
13C CP/MAS NMR experiments were performed on a Bruker
AVANCE III 600WB spectrometer at a resonance frequency of
150.9 MHz using a 4 mm double-resonance MAS probe at a sample
spinning rate of 7.5 kHz. The chemical shift of 13C was determined
using a solid external reference, hexamethylbenzene (HMB). 13C
CP/MAS NMR spectra were recorded by using a recycle delay of 5 s
and a contact time of 2 ms.
The liquid 13C NMR experiments were performed on a Varian
INOVA 500 spectrometer at a resonance frequency of 125.6 MHz
using a 5 mm double-resonance probe. The chemical shift of
13C was referenced to tetramethylsilane. 13C NMR spectra were
recorded by small-flip angle technique using a pulse length of
3.2 ms (ꢁ/6) and a recycle delay of 4 s.
2.3. Liquid-phase alkylation of benzene with ethylene
The liquid-phase alkylation of benzene with ethylene was car-
ried out in a stainless-steel fixed bed reactor. 8 mL catalyst was
located in the center of the reactor and loaded with nitrogen-
purged. Benzene was pumped into reactor to fully fill the bed under
reaction pressure, and then the temperature was raised up to 200 ◦C
before ethylene was introduced. The alkylation conditions were as
follows: 3.5 MPa of pressure, 3 h−1 of weight hourly space veloc-
ity (WHSV) of benzene, and 12/1 of benzene/ethylene molar ratio,
200–260 ◦C of temperature. At each temperature the reaction was
given at least 15 h to reach a steady state condition before samples
were collected for analysis. The reaction products were analyzed
by an Agilent 6890 gas chromatograph (GC) equipped with a flame
ionization detector and a capillary column. It is well known that
the alkylation of benzene with ethylene was a consecutive reac-
tion, and the reaction products were made up of ethylbenzene
(EB), para-diethylbenzene (p-DEB), ortho-diethylbenzene (o-DEB),
meta-diethylbenzene (m-DEB), triethylbenzenes (TEB), other
To further clarify the interaction between TEAOH and MWW
layer structure, liquid 13C NMR and solid 13C CP/MAS NMR
measurements were performed to offer an insight into the post-
synthesis of as-synthesized and calcined MCM-49 zeolites in

138
Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
A
B
Fig. 1. XRD patterns of parent and post-synthesized MCM-49 zeolites (A: post-
synthesis of as-synthesized MCM-49 zeolite, a: calcined MCM-49, b: TMP-8, c:
TMP-16, d: TMP-24; B: post-synthesis of calcined MCM-49 zeolite, a: calcined MCM-
49, b: TMC-8, c: TMC-16, d: TMC-24).
Fig. 2. Liquid 13C NMR of TEAOH and mother liquor (A: a: TEAOH solution, b: mother
liquid of TMP-16, c: mother liquid of TMC-16); 13C/P MAS NMR spectra of parent
and post-synthesized MCM-49 zeolites (B: a: as-synthesized MCM-49, b: TMP-16,
c: TMC-16)
TEAOH solution. The 13C NMR spectra of TMP-16 and TMC-16
mother liquor were shown in Fig. 2A. Compared with TEAOH solu-
tion, TEAOH did not decompose during the post-synthesis with the
same resonances at 8 and 54 ppm without any other resonances
detected, and there were some other resonances at 26, 27 and
47 ppm in mother liquor of TMP-16 in agreement with those of
HMI [22]. The results indicated that some HMI was replaced or
exchanged by TEAOH into mother liquor during the post-synthesis.
There were also two new resonances at 11 and 49 ppm in the
mother liquor obtained from TMP-16 (as-synthesized MCM-49
zeolite by TEAOH treatment) in Fig. 2A-b, and these two resonances
were in accordance with those of triethylamine in water, which
indicated that TEAOH might decompose to form triethylamine on
the basis of Hofmann degradation during the post-synthesis. How-
ever interestingly, there were not any typical resonances at 11
or 49 ppm in the mother liquor obtained from TMC-16 (calcined
MCM-49 zeolite by TEAOH treatment) in Fig. 2A-c.
retained, while the C1 resonance at 57 ppm seemed very weak
due to the involvement of aniline into the hydrothermal synthe-
sis [41]. For TMP-16 (Fig. 2B-b) and TMC-16 (Fig. 2B-c) samples, it
was obvious to see that post-synthesized MCM-49 samples showed
new strong intensity resonances at 8 and 54 ppm, which meant
that TEAOH molecules could incorporate into both as-synthesized
and calcined MCM-49 zeolites. Besides, there was an obvious new
resonance at 48 ppm for TMC-16 sample, which may be ascribed
to triethylamine formed via the Hofmann degradation of TEAOH
during the post-synthesis process in Fig. 2B-c. According to the
result of liquid 13C NMR (Fig. 2A-c), there were not any typical
resonances at 11 or 49 ppm in the mother liquor obtained from
TMC-16 (calcined MCM-49 zeolite by TEAOH treatment) in, which
was proposed that TEAOH incorporated into MCM-49 zeolite and
then some decomposed within MCM-49 zeolite, not decomposed
in the mother liquor. It was difficult for triethylamine molecules to
get out of framework and to enter into mother liquor because of
blocking effects of calcined MCM-49 zeolite with rigid 3D structure
and tight connection between MWW layers. As for TMP-16 sam-
ple, the resonance at 48 ppm (triethylamine) overlapped with that
of at 49 ppm (HMI), which was in agreement with the result of liq-
uid 13C NMR spectra of TMP-16 mother liquor in Fig. 2A-b. Based
on above results, post-synthesis of as-synthesized and calcined
Additionally, Fig. 2B displays the 13C CP/MAS NMR spectra of
as-synthesized and calcined MCM-49 samples treated in TEAOH
(TEAOH/SiO2 = 0.1, H2O/SiO2 = 15) solution at 16 h. As well known,
there were three resonances of HMI in the parent MCM-49 zeo-
lite: the C1 resonances of HMI occurred at 48 and 57 ppm, and
the C2, C3 resonances overlapped at 27 ppm; the C1 resonances
at 48 and 57 ppm were ascribed respectively to HMI located in
the intra-layered and inter-layered regions [22]. For as-synthesized
MCM-49 zeolite in this paper, the C1 resonance at 48 ppm was

Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
139
Fig. 3. SEM images of as-synthesized and corresponding post-synthesized MCM-49 zeolites (a: as-synthesized MCM-49, b: TMP-8, c: TMP-16, d: TMP-24).
MCM-49 zeolites in TEAOH solution was achieved by the incor-
poration of TEAOH into parent zeolites.
just at 18, which was close to the lower SiO2/Al2O3 limit of MCM-
49 by conventional hydrothermal synthesis. As well known, the
lower SiO2/Al2O3 of MCM-49 zeolites could offer the more acid
sites and the better acid density, which would be beneficial for
the liquid-phase alkylation of benzene with ethylene. With the
preservation of the crystallinity, the surface areas and pore vol-
umes of post-synthesized samples increased obviously, but for
TMC-8 sample. On one hand, as for calcined MCM-49 by TEAOH
treated at 8 h, the surface area, micro surface area, pore volume and
As shown in Fig. 3 (as-synthesized MCM-49 as the parent
zeolite) and Fig. 4 (calcined MCM-49 as the parent zeolite), the mor-
phology of post-synthesized samples has been tailored remarkably.
Although the morphology showed their irregular sheets packed dis-
orderly, post-synthesized MCM-49 samples showed high relative
crystallinity in Fig. 1, indicating that they were well crystallized
but packed in disorder. The morphology was obviously different
from rose-like shape of the parent MCM-49 zeolite in Fig. 3a (as-
synthesized MCM-49 as the parent zeolite) and Fig. 4a (calcined
MCM-49 as the parent zeolite). Particularly, it was more disorder
for as-synthesized MCM-49 zeolite treated in TEAOH solution in
Fig. 3b and c demonstrating that it is easier to be tailored into
smaller MWW sheets by TEAOH in with HMI incorporated in MCM-
49 zeolite. With prolonging the treatment time, these irregular
MWW sheets packed in disorder had a tendency to accumulate
together again in Fig. 3d. The results of SEM images directly show
the interaction of TEAOH, HMI and MWW layers, and because of the
incorporation of TEAOH into MWW layers, post-synthesized MCM-
49 zeolites has been tailored significantly from rose-like shape into
small MWW sheets packed in disorder. What is more, due to little
structure-directing performance of TEAOH for synthesizing MWW
zeolites, the connection between the MWW layers became loose
and not such tight. The special morphology of post-synthesized
MCM-49 zeolites would affect their textural properties and acidity,
furthermore, the irregular MWW sheets packed disorderly of post-
synthesized MCM-49 zeolites would offer more opportunities for
reactants to access the active centers than those of parent MCM-49
zeolite, which could be benefit for their catalytic performances.
Table 1 presents the textural properties of parent and post-
synthesized samples. The SiO2/Al2O3 of post-synthesized samples
at 18, were lower than that of the parent MCM-49 zeolite because
of somewhat desilication in TEAOH solution. With long treatment
time, the SiO2/Al2O3 of post-synthesized samples did not change,
micro pore volume of TMC-8 sample were 471 m2 g−1, 401 m2 g−1
,
and 0.51 cm3 g−1, respectively, which was lower than those of
TMP-8 sample (494 m2 g−1, 410 m2 g−1, and 0.58 cm3 g−1, respec-
tively). These results suggest that the presence of HMI within
as-synthesized MCM-49 zeolite could serve a protective agent for
the MWW framework in TEAOH treatment; but as for calcined
MCM-49 zeolite, TEAOH might only clean the pores and crystals
to purify the zeolite pore system. On the other hand, the micro
pore volume of TMC-8 sample was 0.19 cm3 g−1, higher than that
of TMP-8 sample, which indicated that TEAOH could clean easily the
amorphous phase in the MWW layers for calcined MCM-49 zeolite
in absence of HMI.
TMP-16 and TMC-16 samples with high relative crystallinity, the
surface areas increased obviously from 460 m2 g−1 to 503 m2 g−1
and 494 m2 g−1, the micro surface areas increased from 371 m2 g−1
to 416 m2 g−1 and 420 m2 g−1, but the exterior surface areas
decreased from 89 m2 g−1 to 87 m2 g−1 and 74 m2 g−1, respectively;
the total volumes increased from 0.56 cm3 g−1 to 0.68 cm3 g−1
and 0.63 cm3 g−1, and the micro volumes had slight increase
from 0.17 cm3 g−1 to 0.19 cm3 g−1, and 0.19 cm3 g−1. There was
no obvious enhancement of surface areas and pore volumes for
post-synthesized samples by increasing treatment time from 16
to 24 h. Obviously, TMP-x and TMC-x samples have better surface
area, micro-surface area and pore volumes than the parent MCM-
49 zeolite, indicating that MCM-49 zeolites may be tailored their
textural properties in TEAOH solution with preservation of high

140
Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
Fig. 4. SEM images of the calcined MCM-49 and corresponding post-synthesized MCM-49 zeolites (a: calcined MCM-49, b: TMC-8, c: TMC-16, d: TMC-24).
Table 1
Texture properties of parent calcined MCM-49 zeolite and post-synthesized MCM-49 zeolites by TEAOH treatment.
Sample no.
a (MCM-49)
SiO2/Al2O3
21
SBET (m2 g−1
)
Smicro (m2 g−1
)
Vmicro (cm3 g−1
)
Vtotal (cm3 g−1
)
RC (%)
100
Na2O (wt.%)
0.55
460
371
0.17
0.56
(A) TEAOH + as-synthesized MCM-49 zeolite
b-TMP-8 (8 h)
c-TMP-16 (16 h)
d-TMP-24 (24 h)
18
18
18
494
503
505
410
416
421
0.17
0.19
0.19
0.58
0.68
0.67
94
100
102
0.24
0.22
0.16
(B) TEAOH + calcined MCM-49 zeolite
b-TMC-8 (8 h)
c-TMC-16 (16 h)
d-TMC-24 (24 h)
18
18
18
471
494
495
401
420
421
0.19
0.19
0.19
0.51
0.63
0.64
94
96
96
0.21
0.15
0.16
relative crystallinity. Also there was ion-exchange phenomenon
during post-synthesis, showing that TEAOH assuredly incorporated
into the parent MCM-49 zeolites. This was the reason why post-
synthesized MCM-49 samples needed only one time ion-exchange
to meet the requirement of Na2O contents (<0.05 wt.%). Addition-
ally, TMC-x samples showed lower Na2O contents than those of
TMP-x samples, mainly because the protective role of HMI for TMP-
x samples decreased the efficiency of ion-exchanging capabilities
between Na+ and TEAOH. This post-synthesis in TEAOH solution
offers an excellent way to increase surface areas and pore volumes
with the preservation of high crystallinity.
liquid-phase alkylation of benzene with ethylene, more disorderly
packed the MWW sheets and higher pore volumes would offer
less restriction of reactants and products, and better accessibility
of active centers. Finally, TMP-16 and TMC-16 samples with high
crystallinity, high surface areas and pore volumes, and especially
irregular sheets packed in disorder, were selected to prepare H-type
zeolites for characterizations, and alkylation catalysts to evaluate
their catalytic performances, with the parent H-MCM-49 zeolite as
a comparison.
3.2. Properties of H-type zeolites
Comparing TMP-x to TMC-x samples, it is easy to find that there
was a clear advantage for as-synthesized MCM-49 zeolite by TEAOH
treatment, with high crystallinity, surface area and pore volume.
Calcined MCM-49 zeolite possessed the rigid 3D structure and tight
connection of MWW layered structure, however, for as-synthesized
MCM-49 zeolite, the layered structure did not connect so closely.
Therefore, it is more effective to select as-synthesized MCM-49
zeolite as the parent zeolite for TEAOH post-synthesis. With the
preservation of high relative crystallinity, post-synthesized MCM-
49 zeolites showed the small MWW sheets and packs in disorder,
and improved the surface areas and pore volumes. Generally, for
As well known, there was desilication phenomenon during post-
synthesis in TEAOH solution, and the SiO2/Al2O3 ratio decreased
from 21 (the parent MCM-49 zeolite) to 18 (post-synthesized sam-
ples), indicating that there were more acid sites and higher acid
density of post-synthesized samples. The acidity distribution and
the amount of acid sites of MCM-49 before and after TEAOH treat-
ment were characterized by the Py-FTIR in Table 2. Remarkably,
the amounts of both Lewis and Brønsted acid sites were increased
by TEAOH treatment. Take an example of the results at 200 ◦C, for
H-TMP-16 sample, Lewis acid sites increased from 189 ␮mol g−1 to

Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
141
Table 2
Acid properties of H-type zeolites.
Samples
200 ◦
C
350 ◦
C
Lewis acid (␮mol g−1
)
Brønsted acid (␮mol g−1
)
B/L
Lewis acid (␮mol g−1
)
Brønsted acid (␮mol g−1
)
B/L
a (H-MCM-49)
b (H-TMP-16)
c (H-TMC-16)
189
327
390
402
518
423
2.13
1.58
1.08
168
261
244
375
450
385
2.23
1.72
1.58
327 ␮mol g−1 and Brønsted acid sites increased from 402 ␮mol g−1
to 518 ␮mol g−1, suggesting that there would be similar amount of
newly generated Lewis and Brønsted acid sites on as-synthesized
MCM-49 zeolite during TEAOH post-synthesis. Interestingly, for
H-TMC-16 samples, Lewis acid sites increased from 189 ␮mol g−1
to 390 ␮mol g−1 and Brønsted acid sites increased slightly from
402 ␮mol g−1 to 423 ␮mol g−1, indicating that there would be more
Lewis acid sites newly emerged on calcined MCM-49 zeolite dur-
ing TEAOH post-synthesis. This result shows us a way to adjust the
distribution of acid types. For H-TMP-16 sample, the increase in
both Lewis and Brønsted acid sites enlighten us to consider that the
framework of MCM-49 zeolite could not only be protected appro-
priately, but also generated new Lewis and Brønsted acid sites with
presence of HMI incorporated within MCM-49. On the contrary,
for calcined MCM-49 zeolite in TEAOH solution, the increase of
acid sites was almost Lewis acid sites. The increase of acid sites
determined by Py-FTIR would offer better accessibility of acid sites,
that is to say, post-synthesized MCM-49 zeolites (H-TMP-16 and H-
TMC-16) would offer more active centers and better accessibility of
active centers for reactants. During post-synthesis of MCM-49 zeo-
lites, not only did it tailor the morphology and textural properties,
but also increased the amount of acid sites. The special morphol-
ogy of small MWW sheets and packs in disorder, the higher surface
area and pore volumes, and the increase of the acid sites would
offer less restriction, more opportunities for benzene to access the
active centers, more active centers and better accessibility to active
centers, which are benefit for their catalytic performance.
27Al MAS NMR spectra of post-synthesized samples were
expected to give an insight into the effects of TEAOH treatment
on the distribution of Al in Fig. 5A. Upon calcination, all the sam-
ples showed the occurrence of extra-framework aluminum with
a sharp peak at about 0 ppm, which indicated that high tempera-
ture calcinations caused dealumination to some extent. The 27Al
MAS NMR spectra of MWW zeolites were both comprised of three
tetrahedral Al resonances centered at 49, 56 and 61 ppm [42]. Par-
ticularly, there were two phenomena: an increasing tendency for
the intensity of tetrahedral Al at 49 ppm and a decreasing tendency
for the intensity of tetrahedral Al at 61 ppm after TEAOH treatment,
which illustrated that the environment of Al sites in the tetrahedral
frameworks had been changed during TEAOH treatment. As shown
in Fig. 5B, the 29Si MAS NMR spectra of the calcined samples are sim-
ilar to those presented in parent MCM-49, with five peaks at about
−99, −105, −111, −114, and −119 ppm. These peaks are mainly
associated with Si sites of MWW zeolites as follows: −99 ppm ∼ Si
(1Al) and −105 ppm to −119 ppm ∼ Si (0Al) [42].
Fig. 5. 27Al (A)/29Si (B) MAS NMR spectra of H-type zeolites.
MWW sheets different from original rose-like shape, higher sur-
face areas and pore volumes, and more amounts of acid sites,
post-synthesized MCM-49 zeolites may offer more active sites and
better accessibility for the reactants. We are really interested in
how the morphology, texture property, acidity and accessibility of
active centers influence the catalytic properties of H-type catalysts
in the liquid alkylation of benzene with ethylene.
3.3. Alkylation performances of H-type catalysts
The initial goal in our paper is to post-synthesize MWW zeo-
lites by TEAOH with the preservation of high crystallinity and
improve their surface areas, pore volumes and acid sites. Accord-
ing to the above results, post-synthesized MWW zeolites not only
truly have high relative crystallinity retained, but also have tail-
ored the morphology, textural property, acidity and accessibility
of active centers. With high crystallinity preserved irregular small
The alkylation performances of H-type catalysts are shown in
Fig. 6A and B. As well known, the alkylation of benzene with
ethylene is a consecutive reaction, and with EB as the target
product, the trade-off between ethylene conversion and EB selec-
tivity must be carefully weighed and considered, and it is usually
featured by “improved ethylene conversion and decreased EB selec-
tivity” [39,40]. All H-type catalysts showed somewhat increased

142
Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
were 95.4%, 95.5% and 95.6% for the parent H-MCM-49 catalyst,
H-TMP-16 and H-TMC-16 catalysts, respectively. With the tem-
perature increasing, the EB selectivity of post-synthesized samples
maintained a little higher or at least no lower than that of the
parent H-MCM-49 catalyst regardless of slight fluctuation, espe-
cially for H-TMP-16 catalyst. These results confirmed that an
excellent method for catalyst preparation, with the preservation
of high crystallinity, small MWW sheets packed in disorder and
more active centers to offer more opportunities for benzene to
access the active centers, can make a significant breakthrough
for enhancing activity without loss of EB selectivity. In the eval-
uation, there was the identical benzene WHSV−1 at 3 h−1 and
benzene/ethylene molar ratio at 12 for all catalysts. Because of the
same feeding ethylene, the activity increase of post-synthesized
catalysts means the more EB to be produced and the less ethyl-
ene for EB to produce DEB, TEB and other by-products. Therefore,
it can be observed an increase in ethylene conversion without
loss of EB selectivity over post-synthesized H-MCM-49 catalysts in
liquid-phase alkylation of benzene with ethylene. That is, the post-
synthesized H-MCM-49 catalysts by TEAOH treatment could make
a significant breakthrough of the trade-off between ethylene con-
version and EB selectivity, mainly because with the preservation of
high relative crystallinity, post-synthesized H-MCM-49 catalysts
possessed more irregular MWW sheets packed, higher surface area
and pore volumes, more active centers, and better accessibility of
active centers than those of the parent H-MCM-49 catalyst.
A
B
In all, with the preservation of high crystallinity, it could
be post-synthesized MCM-49 zeolites in TEAOH solution, which
improved surface areas, pore volumes, and acid sites to offer more
active centers. Certainly, the morphology of MCM-49 has tailo-
red dramatically from rose-like shape to small irregular sheets
packed in disorder, which could also afford more opportunities
for reactants to access active centers. Because of these advantages,
post-synthesized H-MCM-49 catalysts performed superior alkyl-
ation performance, enhancing ethylene conversion without loss
of EB selectivity in Fig. 6. For post-synthesized MCM-49 zeolites
in TEAOH solution, the physical–chemical properties and catalytic
performances were improved obviously. This result of alkylation
performance may highlight a new strategy for enhancing both cat-
alytic activity and intermediate selectivity. This synthesis concept
should be applicable to many reactions that are diffusion limited,
and require reaction occurring on the external surface due to the
change of the morphology and improvements in accessibility to
active centers.
Fig. 6. Ethylene conversion (%, A) and ethylbenzene selectivity (%, B) of H-type
catalysts (a: H-MCM-49; b: H-TMP-16; c: H-TMC-16; Liquid-phase alkylation
conditions: 8 mL catalysts, T = 200–260 ◦C, p = 3.5 MPa, benzene WHSV−1 = 3.0 h−1
,
benzene/ethylene molar ratio = 12.0).
ethylene conversion with the rise of temperature, but presented
slightly decreased EB selectivity. This result still falls into a rule
like “see-saw”, which is usually encountered in a consecutive reac-
tion with intermediate product as the target product, that is, it is a
common phenomenon that the ethylene conversion increased with
the rise of temperature, and the EB selectivity decreased.
DEB selectivity and DEB distribution: Fig. 7A and B shows that
DEB selectivity and DEB distributions over H-type catalysts in the
liquid-phase alkylation of benzene with ethylene. The DEB selec-
tivity for all H-type catalysts increased by the rise of temperatures
regardless of slight fluctuation for the parent H-MCM-49 catalyst.
In alkylation, high EB selectivity would directly be related to low
DEB selectivity. At low temperature, it can be seen that the high
degree of selectivity over all H-type zeolites for o-DEB, as shown in
Fig. 7B, and that o-DEB decreased by the temperature range from
200 ◦C to 260 ◦C. On the contrary, the low degree of selectivity for
m-DEB gradually was generated. As well known, p-DEB has the
smallest molecular diameter among of the three DEB isomers, while
space-filling models have shown that the o-DEB has the most favor-
able configuration for active centers of H-type zeolites. With the
temperature rising, more and more m-DEB was produced by the
isomerization of o-DEB, and in the meantime, the selectivity of p-
DEB almost had no change. Additionally, at high temperature, it
is obvious to see the gradual trend of DEB isomers moving toward
the thermodynamic equilibrium values with the mass ratios of DEB
isomers were maintained as 64 (for m-DEB):30 (for p-DEB):6 (for
o-DEB) [10], respectively. It could be worthy that less o-DEB (kinet-
ically favorable) was generated over H-TMP-16 at initial reaction
For H-TMP-16 and H-TMC-16 catalysts, the corresponding eth-
ylene conversion has been improved remarkably, compared to the
parent H-MCM-49 catalyst in Fig. 6A from 96.6% for H-MCM-49
to 99.9% for H-TMP-16 and 99.3% for H-TMC-16 just at 200 ◦C.
Firstly, as for H-TMP-16 catalyst, obtained from as-synthesized
MCM-49 zeolite by TEAOH treatment, the ethylene conversion had
approached up to 100% from 200 to 260 ◦C, which indicated that
there was excellent accessibility of active centers. Secondly, for
H-TMC-16 catalyst from calcined MCM-49 zeolite by TEAOH treat-
ment, the ethylene conversion increased gradually up to 100% by
the rise of temperature. Compared to the parent H-MCM-49 cat-
alyst, the superior activity of post-synthesized samples indicated
that there might be more active centers and superior accessibility
of active centers for liquid-phase alkylation of benzene with eth-
ylene, especially for H-TMP-16 catalyst, which was in accordance
with the results of characterizations, such as more irregular MWW
sheets, higher surface areas, pore volumes, and more acid sites to
offer more active centers and better accessibility.
Importantly, it is simultaneous for post-synthesized catalyst to
achieve (or at least maintain) high EB selectivity in Fig. 6B. Take
an example of EB selectivity at 200 ◦C, it can be seen that there

Y. Shi et al. / Applied Catalysis A: General 497 (2015) 135–144
143
5.0
4.5
4.0
3.5
ethylene conversion were observed without loss of EB selectivity
over post-synthesized MCM-49 catalysts, which were attributed
to more active centers and better accessibility of active centers.
This post-synthesis concept of MWW zeolites based on large size of
organic–alkali and mild organic–alkali treatment, one is to tailor the
morphology, textural property and acidity with the preservation of
crystallinity, and the other is to enhance both catalytic activity and
selectivity, which could be applicable to many diffusion limited or
extra-surface reactions.
A
a (H-MCM-49)
b (H-TMP-16)
c (H-TMC-16)
Acknowledgments
This work was supported by the National Basic Research Pro-
gram of China (973 Program, No. 2012CB224805). Special thanks
to the Department of Analysis in Research Institute of Petroleum
Processing Sinopec.
200
210
220
230
240
250
260
Temperature (oC)
References
B
60
50
40
30
20
10
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