Alkali treatment upon MCM-49 zeolite with various contents of HMI in the presence of CTAB and application in anisole acylation with acetic anhydride

Article abstract of DOI:10.1016/j.apcata.2015.02.020

A series of MCM-49 zeolites with various contents of hexamethyleneimine (HMI), obtained by calcination at different temperatures, were alkali-treated in NaOH solution containing cetyltrimethylammonium bromide (CTAB). Changes in structural and acidic prope

Full text of DOI:10.1016/j.apcata.2015.02.020

Accepted Manuscript
Title: Alkali treatment upon MCM-49 zeolite with various
content of HMI in the presence of CTAB and application in
anisole acylation with acetic anhydride
Author: Huijuan Wei Sujuan Xie Ningning Gao Kefeng Liu
Xiaohang Liu Wenjie Xin Xiujie Li Shenglin Liu Longya Xu
PII:
S0926-860X(15)00112-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.02.020
APCATA 15257
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
26-10-2014
11-2-2015
12-2-2015
Please cite this article as: H. Wei, S. Xie, N. Gao, K. Liu, X. Liu, W. Xin, X. Li, S.
Liu, L. Xu, Alkali treatment upon MCM-49 zeolite with various content of HMI in the
presence of CTAB and application in anisole acylation with acetic anhydride, Applied
Catalysis A, General (2015), http://dx.doi.org/10.1016/j.apcata.2015.02.020
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Alkali treatment upon MCM-49 zeolite with various content
of HMI in the presence of CTAB and application in anisole
acylation with acetic anhydride
a,b
a
a,c
a,d
a,e
Huijuan Wei , Sujuan Xie , Ningning Gao , Kefeng Liu , Xiaohang Liu ,
a
a
a
a,
Wenjie Xin , Xiujie Li , Shenglin Liu , Longya Xu *
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, Dalian 116023, China
b
c
d
University of Chinese Academy of Sciences, Beijing 100049, China
Research Institute of Petroleum Processing, SINOPEC, Beijing 100083, China
Petrochemical Research Institute of Petrochina Company Limited, Beijing 100029,
China
e
PetroChina Liaohe Petrochemical Company, Panjin 124022, China
*
To whom correspondence should be addressed.
Prof. Longya Xu
State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
Dalian 116023, China
Tel/Fax: +86-411-84379279
E-mail: lyxu@dicp.ac.cn
Page 1 of 36

Abstract
A series of MCM-49 zeolites with various content of hexamethyleneimine (HMI),
obtained by calcination at different temperatures, were alkali-treated in NaOH
solution containing cetyltrimethylammonium bromide (CTAB). Changes in structural
and acidic properties of the resultant samples were systematically investigated by
transmission electron microscopy and scanning electron microscopy (TEM & SEM),
X-ray diffraction (XRD), N and Ar adsorption/desorption isotherms measurements,
2
ammonia temperature-programmed desorption (NH -TPD) and pyridine
3
2
9
adsorption/desorption followed by infrared measurements (Py-IR), as well as Si
MAS NMR techniques. It was revealed that only crevices were developed on the
crystals of MCM-49 zeolite samples with more HMI, resulting in the increase of acid
concentrations; whereas intracrystalline mesopores (ca. 3 nm) could be formed for the
samples with less HMI at the expense of framework destruction. A bit of ordered
mesoporous materials (OMMs) could also be detected from the latter samples,
because the presence of CTAB could induce the re-assembly of dissolved species
through the formation of micelle, originating from the desilication by NaOH. When
the modified MCM-49 samples were used as catalysts for anisole acylation with
acetic anhydride, due to the positive changes in acidities and pore structure properties,
they exhibited better catalytic performances for the reaction than the unmodified
HMCM-49 catalyst.
Keywords: MCM-49 zeolite; template; alkali-treatment; CTAB; acylation
Page 2 of 36

1
. Introduction
Friedel-Crafts acylation of aromatics is an important synthetic reaction in
manufacturing aromatic ketones, which are key intermediates in many chemical
industrial processes for the production of fine chemicals, agrochemicals,
pharmaceuticals and fragrances [1-5]. Replacing the traditional catalysts, such as
AlCl or HF, used in Friedel-Crafts acylation with zeolite benefits the economy,
3
environment protection and social safety greatly [2-8]. Guidotti et al. [6] compared
the catalytic performances of three kinds of zeolites (Beta, Y and MCM-22) for the
acetylation of aromatics, and found that MCM-22 showed an interesting activity
mainly due to the acid sites located on its external surface and exhibited good
resistance to deactivation.
MCM-49 zeolite with special plate-like morphology [9, 10] has the same
framework topology with MCM-22 [11-15]. It consists of two independent micropore
systems [16-19]: the two-dimensional sinusoidal channels with 10-ring pore openings
(0.41 nm × 0.51 nm) and the large cylindrical supercage system defined by 12-ring
(0.71 nm diameter × 1.82 nm height) with the 10-ring pore openings (0.41 nm × 0.54
nm). Moreover, there are hemi-supercages scattering over the surface (0.71 nm × 0.90
nm height) [16-19], which are called as “surface pockets”. However, the sole presence
of micropore in MCM-49 zeolite usually leads to diffusion limitations for transport of
guest molecules to the active sites, especially in the reaction involving relatively big
molecules, which severely restricts its catalytic application.
In order to overcome the diffusion limitations, many methods have been
developed, such as decreasing the size or thickness of zeolite crystals, synthesizing
hierarchical-pore zeolitic materials or post-treating the zeolites with steam, acidic or
basic solution [18, 20-25]. Desilication by alkali treatment has recently received
significant attention, because it is relatively easy to manipulate and can be applied to
various types of zeolites [26, 27]. Generally, tailored mesoporosity by desilication can
be achieved by altering the Si/Al ratio of the parent zeolites or the treatment
Page 3 of 36

conditions. However, there is a conflict between the preserving of acidity and the
creating of extra porosity. Especially for MWW type zeolites, their framework
structure is sensitive to the alkali treatment and usually no effective introduction of
intracrystalline mesopores can be realized [28].
Recently, it was extensively reported that desilication and re-assembly of
dissolved species would happen simultaneously when treating several zeolites such as
MOR, MFI, BEA, and FER or FAU with alkali in the presence of long-chain
alkylammonium surfactants, such as cetyltrimethylammonium bromide (CTAB) [26,
2
9-32]. The main role of CTAB is to protect zeolites from non-uniform leaching and
induce the re-assembly of dissolved species into the mesoporous phase by forming
micelles as suggested by Refs [26, 29, 32]. In addition to the concrete treatment
conditions, such as the concentrations of alkali and CTAB, temperature and time, the
degree of dissolution also seriously depends on the sequence of alkali and surfactant
addition. In our previous study, to result in a higher degree of dissolution, a stepwise
addition of alkali and CTAB to template-free MCM-49 zeolite was developed [10].
Due to the importance of the alkali and CTAB treatment on developing zeolite
acidity and mesopores, it has received much attention recently. Generally, common
o
treatment for the re-assembly are under hydrothermal conditions at 100-150 C for 24
h, which are close to those proposed for the synthesis of MCM-41 as reported in Refs
[30, 33]. In our preliminary study on this topic, it was found that milder and more
o
easily, as well as time-saving treatment under atmospheric conditions at 70 C for 1 h
were also available. In this work, such a kind of modification with simultaneous
addition of NaOH and CTAB to MCM-49 is investigated in detail. In order to finely
control the degree of dissolution, MCM-49 zeolites with various content of template
(hexamethylenimine, HMI) were first prepared via calcination of the pristine zeolite at
different temperatures and then were used for further modification. The changes of
structural properties and acidities for the as modified materials were characterized by
many techniques, such as transmission electron microscopy and scanning electron
microscopy (TEM
&
SEM), X-ray diffraction (XRD), N2 and Ar
2
9
adsorption/desorption isotherms measurements,
Si MAS NMR, ammonia
Page 4 of 36

temperature-programmed desorption (NH -TPD) and pyridine adsorption/desorption
3
followed by infrared (Py-IR) measurements, and their catalytic performances for the
acylation of anisole (AN) with acetic anhydride (AA) were evaluated. Based on the
results of characterizations and catalytic evaluation, the improvement of catalytic
activity of the modified materials could be attributed to the positive changes in
acidities and pore structure properties.
2
. Experimental
2.1. Catalyst preparation
MCM-49 zeolite with a Si/Al molar ratio of 11.0 was supplied by Tieling
Deshijie Chemical Limited Company, Liaoning, China, and labelled as
o
MCM-49S. It was calcined at 550 C for 4 h, and transformed into H-form
zeolite (denoted as HMCM-49) by conventional ion exchange method [34].
The as received MCM-49S was calcined at different temperatures for 4 h,
and the resultant sample was labelled as C
T
(
T
is the calcination temperature,
o
such as 150, 200, 250, 350, 450 or 550 C). C
T was treated in a mixed solution
of CTAB (0.27 M) and NaOH (0.6 M) with a desired amount of 10 mL/gzeolite at
o
7
0 C for 1 h, and afterwards was cooled down to room temperature in an cold
bath. Then the solution was adjusted to pH of 6 with 6 M HCl, followed by
stirring for 1 h at room temperature. Solid product was recovered through
o
o
centrifugal separation, dried at 110 C overnight and calcined at 550 C for 4 h.
H-form products (denoted as C -0.27C 0.6AT) were also obtained by
T
16
conventional ion-exchange. At last, all the samples were crushed and sieved
into 0.38-0.85 mm and stored for further use.
2.2. Catalyst characterization
Thermogravimetric analysis (TGA) was carried out with a Pyris Diamond
TG/DTA analyzer. All the TGA experiments were carried out under air with a flow
o
rate of 40 mL/min in a temperature range from 30 to 800 C at a ramp rate of 10
Page 5 of 36

o
C/min. For convenience, all TGA results were presented in differential
thermogravimetric (DTG) profiles.
Transmission electron microscopy (TEM) was performed on a FEI Tecnai G2
spirit microscope with an accelerating voltage of 120 kV, point resolution of 0.35 nm
and line resolution of 0.20 nm. Prior to observation, the samples were dispersed in
anhydrous alcohol using ultrasonic technique, and then the resultant suspension were
dropwise added to a copper grid and dried in air. Scanning electron microscopy (SEM)
was performed on a FEI Quanta-200 F field emission scanning electron microscope.
X-ray diffraction (XRD) patterns were collected on an X’ Pert PRO X-ray
diffractometer operated at 40 kV and 40 mA using Cu Kα radiation. The relative
crystallinity (RC) was estimated by comparing the sum of all the characteristic peak
o
o
o
o
o
intensities of 2θ at 10.0 , 14.3 , 16.0 , 22.7 and 26.0 of the prepared samples with
that of HMCM-49 (whose RC was assumed as 100%). Chemical compositions of the
sample were analyzed on a Philip Magix 601X X-ray fluorescene (XRF)
spectrometer.
o
N2 adsorption/desorption isotherms were measured at −196 C with a
Micromeritics ASAP-2020 apparatus. Prior to the measurement, samples were
o
−3
degassed at 350 C under a vacuum of 10 Pa for 10 h. However, all of CT samples
o
were pretreated at 120 C for 6 h to prevent residual HMI from being removed. The
Brunauer-Emmett-Teller (BET) equation was used to calculate the apparent surface
area with the adsorption date, and the micropore volume was estimated by the t-plot
method. Ar adsorption/desorption isotherms measurements were carried out at −186
o
o
C with the same instrument, and the samples were pretreated at 350 C under a
−
3
vacuum of 10 Pa for 10 h prior to analysis.
29
Si MAS NMR experiments were carried out on a Bruker DRX-400
spectrometer using 4 mm ZrO rotors. The spectra were recorded at 99.4 MHz with
2
the magic angle-spinning rate of 5 kHz.
Ammonia temperature-programmed desorption (NH -TPD) was carried out in a
3
U-shaped quartz micro-reactor (i.d. = 4 mm) which was connected to an on-line gas
chromatograph (Shimadzu GC-8A) equipped with a thermal conductivity detector
Page 6 of 36

(TCD). The TCD response was calibrated by doses containing known amounts of NH3.
o
In a typical experiment, the sample (140 mg) was firstly pretreated at 600 C for 0.5 h
under a He flow rate of 25 mL/min to remove any adsorbed organic species and
o
moisture, then cooled down to 150 C and saturated with NH . After the baseline
3
o
levelled off, the samples were heated at a heating rate of 19.6 C/min from 150 to 600
o
C.
Brønsted and Lewis acid sites concentrations of the prepared samples were
determined by pyridine adsorption/desorption followed by infrared (Py-IR)
measurements on a Vertex 70 IR spectrometer. The sample was pressed into a
o
self-supported wafer (ca. 10 mg), followed by evacuation at 250 C for 1 h in IR cell.
A spectrum was recorded as background after the wafer was cooled down to room
temperature. Subsequently, the wafer was exposed to pyridine vapor for 20 min at 0
o
o
C and then degassed at 150 C for 30 min. Finally, the Py-IR spectra of samples were
collected at room temperature.
2.3. Catalyst evaluation
The acylation of AN with AA was carried out in a continuous flow stainless steel
fixed-bed reactor. In a typical run, 1 g of catalyst was loaded at the central part of the
o
reactor and pretreated at 500 C for 1 h with a flow of N . Then, the catalyst was
2
o
cooled down to 110 C and the reactants were pumped into the reactor. The reaction
o
conditions were set as follows: 1.0 MPa, 110 C, the weight hourly space velocity
-1
(
WHSV) of 10.2 h with an AN/AA molar ratio of 5/1.
3
. Results and discussion
3.1. Preparation of MCM-49 zeolites with various HMI content
Referring to Ref. [35], MCM-49S samples were calcined at different
o
temperatures (150, 250, 350, 450 and 550 C) for 4 h to get samples with different
content of HMI template. Fig. 1 showed the DTG profiles of MCM-49S and CT
samples. It is clear that the DTG profiles recorded from MCM-49S and CT samples
Page 7 of 36

are quite different. There are four peaks in the DTG profile of MCM-49S sample. The
o
peak below 180 C could be attributed to desorption of the occluded water [11, 36].
Obviously, the other peaks of DTG profile were closely related to the removal of HMI
located in different pore systems. And the total weight loss because of the HMI
o
removal for MCM-49S sample was ~30.7%. The peaks appeared at 180-260 C with
o
corresponding weight loss of 5.1% and that at 350-480 C with corresponding weight
loss of 12.4% were mainly due to the removal of HMI physisorbed on the surface
pockets and that adsorbed inside the supercages [11, 12, 36], respectively. The peak at
o
~
610 C with corresponding weight loss of 13.2% could be assigned to the pyrolysis
of HMI inside the intralayer 10-ring sinusoidal channels of MCM-49 zeolite [11, 12,
6].
3
The DTG curve corresponding to “C150” sample was very similar to that of
o
“
MCM-49S”, meaning that calcination of MCM-49S at 150 C was unable to remove
HMI. However, the DTG curve of “C250” exhibited three peaks. Compared with that
o
of “MCM-49S”, the peak at 180-260 C was disappeared, indicating that after the
o
calcination of MCM-49S at 250 C, the HMI physisorbed on the surface pockets of
o
MCM-49 zeolite could be removed completely. Meanwhile, the peak at 350-480 C
was smaller than that of “MCM-49S”, implying the partial removal of HMI located in
the supercages.
o
Increasing the calcination temperature of MCM-49S to 350 C, the peak at
o
o
3
50-480 C nearly vanished, indicating that calcination of MCM-49S at 350 C for 4 h
could remove all the HMI physisorbed on the surface pockets and most of the HMI
located inside the supercages, as well as a small part of HMI located in the sinusoidal
o
channels. For the DTG curve of “C450” sample, the peak at 350-480 C disappeared
o
completely, and the peak at ~ 610 C decreased obviously, indicating that only a few
HMI retained in the sinusoidal channels. As expected, the DTG curve of “C550”
o
sample had no peak, in addition to the peak at below 180 C which is corresponding
to the desorption of occluded water, implying that HMI within different pore systems
has been removed completely.
Page 8 of 36

The accurate amount of HMI removed from MCM-49S samples after being
calcined at different temperatures were calculated based on the results of TGA
experiments, and the corresponding degrees of detemplation were listed in Table 1
(
column 2). For “C250”, 24% HMI was removed, while for “C350”, “C450” and
C550”, the corresponding degrees of detemplation were 44%, 75% and 100%,
respectively.
The textural properties of MCM-49S and CT series samples determined by N2
“
adsorption/desorption isotherms were also listed in Table 1. As expected, with the
increase of the calcination temperature, the BET surface areas and external surface
areas as well as pore volumes of the samples gradually increased. For MCM-49S
3
sample, no micropore could be detected (Vmicro = 0 cm /g), and its mesopore volume
3
was 0.24 cm /g, which should be mainly related to the existence of the interparticle
space. For CT series samples, with the increase of the calcination temperature, the
micropore volumes gradually increased, implying the removal of HMI from the
micropore systems, and their external surface areas and mesopore volumes followed
similar trend, which was possibly due to the increase of interparticle space during
the calcination. Interestingly, C350 sample exhibited a very low micropore volume
3
(
Vmicro = 0.02 cm /g), although most of HMI inside its supercages has been eliminated.
This is possibly attributed to that the supercages are partly blocked by some products
o
from the calcination at 350 C [35].
Based on the results mentioned above, we may deduce that, with the increase of
the calcination temperature, the HMI on the surface pockets was firstly removed, then
the HMI inside the supercages was secondly removed, and the HMI inside the
sinusoidal channels was finally removed. Thus, a series of MCM-49 samples with
various occluded HMI content (such as CT series samples) could be obtained by
changing the calcination temperature. This lays the foundation for investigating the
effect of alkali-treatment in CTAB contained NaOH solution on the physical-chemical
properties of MCM-49 zeolites with different HMI content.
Page 9 of 36

3
.2. Alkali-treatment of CT series samples in NaOH solution
containing CTAB
3.2.1. Effect on structural properties
CT series samples were further treated with the mixed solutions of 0.27 M CTAB
o
and 0.6 M NaOH at 70 C for 1 h, and then transformed into H-form samples
(
CT-0.27C 0.6AT) with conventional ion-exchange procedure. Fig. 2 displayed the
16
TEM images of HMCM-49 and CT-0.27C 0.6AT samples. HMCM-49 showed
1
6
regular crystal boundary and smooth surface (Fig. 2A), indicating that the as received
MCM-49S zeolite was in high crystallinity. In the case of C150-0.27C 0.6AT (Fig.
1
6
2
B) and C200-0.27C 0.6AT (Fig. 2C), several disordered gaps appeared on the edges
16
and surfaces of the crystal plates, while the crystal boundary remained practically
intact. For the TEM image of C250-0.27C 0.6AT (Fig. 2D), bits of ordered
1
6
mesoporous materials (OMMs) could be observed and the pore size was ca. 3.3 nm,
despite of the existence of the gaps similar to those of C150-0.27C 0.6AT and
1
6
C200-0.27C 0.6AT. Furthermore, some amorphous species appeared on the crystal
16
surfaces. As to C350-0.27C 0.6AT (Fig. 2E), intracrystalline mesopores were found
16
on some crystal sheets, as well as several crevices. Moreover, compared with
C250-0.27C 0.6AT, C350-0.27C 0.6AT exhibited more OMMs. For
C450-0.27C 0.6AT (Fig. 2F) and C550-0.27C 0.6AT (Fig. 2G) samples, similar
16
16
16
16
amounts of intracrystalline mesopores were uniformly distributed throughout the
crystal plates, and OMMs were easily observed in their TEM images, either attached
upon the external surfaces of MCM-49 crystals or isolated in the intercrystalline
space.
The SEM images of HMCM-49 and part of CT-0.27C 0.6AT samples were
1
6
shown in Fig. S1. HMCM-49 zeolite consisted of aggregates of thin crystal sheets,
and C150-0.27C 0.6AT sample showed a trend of deagglomeration on the edge. The
16
deagglomeration was further strengthened in C250-0.27C 0.6AT sample, which
1
6
showed few aggregates in its SEM image. It is interesting that the SEM image of
C550-0.27C 0.6AT was similar to that of HMCM-49, indicating that the
16
Page 10 of 36

deagglomeration was not keeping enhanced with the decrease of HMI and that there
were differences in the modification process of samples with different content of
HMI.
Javier Pérez-Ramírez et al. [35] have pointed out that the template-contained
Beta zeolite was virtually inert to Si leaching upon treatment with NaOH solution.
This opinion is also appropriate for MCM-49 zeolite, i.e., the HMI-containing regions
of MCM-49 zeolite are unavailable for alkali treatment. Specifically, for CT (T = 150,
2
00 and 250) materials, whose HMI located inside the supercages and sinusoidal
channels was still retained, the corresponding samples after being co-modified with
CTAB and NaOH just showed some crevices on the edges and surfaces of the crystal
plates instead of intracrystalline mesopores, as well as different degrees of
deagglomeration. This phenomenon is similar with that reported in Ref. [18], in which
it was suggested that the alkali treatment of template-containing MCM-22 zeolite only
broke the crystal sheets into smaller ones. As to C350, C450 and C550 materials, the
HMI located inside the supercages and sinusoidal channels was removed gradually,
and the corresponding samples after being co-modified with CTAB and NaOH
produced increasing amounts of intracrystalline mesopores. For C550-0.27C 0.6AT
1
6
sample, it actually was the alkali treatment of template-free zeolite in the presence of
surfactant, which is very similar to many other zeolites as reported in the recent years
[26, 29, 30, 37]. Based on the above mentioned results, it can be deduced that the
formation of intracrystalline mesopores can be mainly attributed to the desilication in
supercages and sinusoidal channels of MCM-49 zeolite.
It is interesting to notice that OMMs could be observed in some samples.
The formation mechanism of these OMMs can be supposed to be the
re-assembly of dissolved species formed during the desilication process around
the CTAB micells [10]. With the decrease of HMI content in CT samples, the
dissolved species (involving silicates, aluminosilicates and fragments of the
MCM-49 crystal) formed during the desilication process increased gradually.
When the dissolved species reached a certain amount, they could be
transformed to OMMs in the directing of CTAB micells. As a result, we could
Page 11 of 36

observe OMMs in CT-0.27C 0.6AT (T = 250, 350, 450 and 550) samples, and
16
the amounts of OMMs increased with the same sequences. Furthermore, the
Si/Al molar ratios measured by XRF were listed in Table 2, and it is interesting
that the Si/Al molar ratios of the modified samples just showed a slight
decrease compared with that of HMCM-49. This phenomenon is really
different from the obvious decrease of Si/Al molar ratios during the
conventional alkali treatment [9]. It is understandable that due to the presence
of CTAB, the re-assembly of the dissolved species plays key role in this issue.
To further confirm the effect of CTAB during the modification process,
C550-0.6AT was prepared by treating C550 with 0.6 M NaOH in order to make a
comparison with C550-0.27C 0.6AT, and its TEM image was displayed in Fig. 2(H).
16
As we can see, wide crevices (ca. 10 nm) and amounts of intracrystalline mesopores
appeared throughout the crystal plates, but no OMMs could be detected, indicating
that CTAB is necessary as a pore-directing agent in the formation of OMMs. Also,
some researchers [30] put forward that CTAB micelles could be adsorbed on the
external surface of zeolites and protect them from uncontrollable intensive destruction
by alkali. However, the protection of CTAB is unconspicuous in this work, perhaps
our alkali treatment conditions of MCM-49 zeolite is relatively severe.
XRD patterns of HMCM-49 and CT-0.27C 0.6AT and the corresponding
1
6
relative crystallinities (RCs) were presented in Fig. S2. The diffraction pattern of
HMCM-49 sample is in good agreement with that reported in Ref. [38]. All the other
samples exhibited the similar patterns with that of HMCM-49, evidencing that the
crystal structure of MCM-49 zeolite were maintained after the modification.
Compared with HMCM-49 (to take its RC of 100%), the RCs of CT-0.27C 0.6AT (T
1
6
=
150, 200 and 250) samples almost had no change, indicating that there was no
obvious framework destruction for these three samples. The XRD results of these
three samples were also in accordance with their corresponding TEM images, and
only a few disordered gaps could be found. However, for CT-0.27C 0.6AT (T = 350,
1
6
4
50 and 550) samples, since intracrystalline mesopores were formed on their crystal
sheets and the corresponding RCs decreased rapidly, implying that their frameworks,
Page 12 of 36

due to HMI being partially and/or almost completely removed, were destroyed
severely after the modification, as in the case of Beta zeolites reported in Ref. [35].
With the aim of identifying the OMMs, small angle XRD measurement was
carried out (the figure was not given here). The results indicated that no diffraction
o
peak was detected at 2θ < 5 for all samples, which might be attributed to the fact that
the amount of OMMs so formed is too small compared with that of MCM-49 crystals.
Furthermore, the order degree of the OMMs is too poor under our chosen treatment
conditions to be monitored.
To quantify the porosity of the samples, N adsorption/desorption isotherms
2
measurements on HMCM-49 and CT-0.27C 0.6AT were carried out. N
2
1
6
adsorption/desorption isotherms and BJH pore size distributions of different samples
were shown in Fig. 3. Clearly, HMCM-49 sample exhibited type I adsorption
isotherm, which is typical for zeolites. C150-0.27C 0.6AT still had type I adsorption
1
6
isotherm, and the micropore system did not change obviously despite some gaps
appeared on the crystal plates. For C350-0.27C 0.6AT, an unobvious hysteresis loop
1
6
existed in its N adsorption/desorption isotherms. The combination of type I and type
2
IV isotherms were observed for C550-0.27C 0.6AT, indicative of the formation of
1
6
mesopores.
In the BJH pore size distribution curves of HMCM-49 and CT-0.27C 0.6AT (T
1
6
=
150, 200, 250), no peak corresponding to mesopores was observed. As to that of
C350-0.27C 0.6AT, a very small peak appeared at ca. 3.0 nm, implying the existence
16
of some mesopores in the samples. While for the BJH curve of C450-0.27C 0.6AT, a
1
6
peak appeared at the same pore diameter of 3.0 nm, and the intensity of this peak was
much stronger than that of C350-0.27C 0.6AT. Meanwhile, the BJH pore size
1
6
distribution curve of C550-0.27C 0.6AT almost overlapped with that of
1
6
C450-0.27C 0.6AT. This was coincident with the results of TEM characterization, i.e.,
16
the similar amounts of intracrystalline mesopores presented throughout the crystal
plates of these two samples. Also only one peak at ca. 2.7 nm appeared at the BJH
pore size distribution curve of C550-0.6AT (Fig. 3C), and the peak intensity was
weaker than that of C550-0.27C 0.6AT obviously. This difference might be ascribed
16
Page 13 of 36

to the contribution of OMMs (pore size: ca. 3.3 nm) in C550-0.27C 0.6AT, however,
1
6
to exactly estimate the contribution is difficult. Dual-mesopores system can be
developed in the desilication and re-assembly processes of ZSM-5 zeolite as
suggested in Ref. [26], in which the smaller mesopores (ca. 3 nm) were attributed to
surfactant-induced re-assembly of dissolved species, and the larger mesopores (ca.
1
0-30 nm) resulted from desilication processes. However, only one peak at ca. 3.0 nm
was observed in the range of 2-50 nm in our present case, since the pore size of
mesopores from desilication (ca. 2.7 nm) is quite close to that of OMMs from
re-assembly (ca. 3.3 nm).
The textural properties of HMCM-49 and CT-0.27C 0.6AT samples
16
measured by N adsorption/desorption isotherms were presented in Table 2.
2
The textural property of HMCM-49 was quite similar to that of C550,
indicating that the protonation procedure used in this work only has few effect
on their textural properties. However, compared with HMCM-49, the samples
of C
T
-0.27C 0.6AT (
T
= 150, 200 and 250) showed a little increase in
1
6
3
mesopore volumes (from 0.35 to ca. 0.40 cm /g), and this can be attributed to
the generation of gaps on the edges or surfaces of the crystals. Meanwhile, the
micropore volumes of these samples were almost unchanged (from 0.17 to 0.16
3
cm /g), which coincided with the XRD results. Namely, these samples
maintained MCM-49 framework well. On the contrary, as for the samples of
CT-0.27C 0.6AT (T = 350, 450 and 550), their micropore volumes decreased
16
obviously, indicating that the MCM-49 framework was damaged significantly
after being co-modified by NaOH and CTAB. Moreover, mesopore volumes of
these samples increased obviously, especially for C450-0.27C 0.6AT and
16
C550-0.27C 0.6AT. Combined with the results of TEM and BJH pore size
1
6
distribution curves, it could be deduced that the obvious increase of mesopore
volumes should be attributed to the formation of intracrystalline mesopores.
Argon adsorption was usually thought to be more appropriate for
characterization of micropore materials than nitrogen adsorption [37, 39-41],
and the micropore volumes based on Argon adsorption (Vmicro,Ar) were given in
Page 14 of 36

Table 2. Although, for a certain sample, Vmicro,Ar and Vmicro,N2 had a little
difference, they both showed the similar trend with the increase of calcination
temperature upon MCM-49S.
To further investigate the chemical environment of framework Si atoms
29
and desilication after being treated with NaOH and CTAB, Si MAS NMR
was employed. The corresponding spectra of HMCM-49 and C -0.27C 0.6AT
= 150, 350 and 550) samples were shown in Fig. 4, as well as the ascriptions
T
16
(
T
of resonance peaks according to Ref. [18]. The proportion of different peaks
was calculated by corresponding peak area normalization method, and the
distribution of Si atoms on different T sites was listed in Table 3. For
C150-0.27C 0.6AT sample, the degree of desilication was slight, which has
1
6
been proved in the above-mentioned characterization, and there were less Si
atoms located on T3 site (24.9%) than that in HMCM-49 (27.6%), which could
be attributed to the selective extraction of Si atoms on T3 site. Moreover, Si
atoms located on T7 or T8 sites also showed a slight decrease, meaning the
minor extraction of the corresponding Si atoms. As to C350-0.27C 0.6AT and
16
C550-0.27C 0.6AT samples, the desilication was aggravated, and the area
1
6
+
proportions of the peaks for Si atoms on T3, T1 and T7 or T8 sites decreased
+
gradually, indicating the selective extraction of Si atoms on T3, T1 and T7 or
T8 sites for these two samples.
The H-K differential pore volume plots of N adsorption (the figure was not
2
given here) could not give information on the pore widths of the two independent
micropore systems. Therefore, Ar adsorption/desorption isotherms measurements
were carried out and the corresponding micropore size distributions of the four typical
samples were shown in Fig. S3. For the plot of HMCM-49, the peak at ca. 0.54 nm
could be attributed to the intralayer 10-ring sinusoidal channels [42], while the peak at
ca. 0.65 nm was related to the interlayer supercages with 10-ring windows. The plot
of C150-0.27C 0.6AT just had a slight decrease at 0.54 nm compared with that of
16
HMCM-49, in accordance with the above-mentioned conclusions that its micropore
volume remained nearly intact, and that Si atoms on T7 or T8 sites were slightly
Page 15 of 36

extracted, though the extraction of Si atoms on T3 site was not reflected here. As to
C350-0.27C 0.6AT and C550-0.27C 0.6AT, both the peaks at 0.54 nm and 0.65 nm
16
16
decreased, especially for the latter sample, further indicating that the micropore
structure and/or framework were damaged during the modification. The results also
2
9
supported the speculation derived from
Si MAS NMR. Specifically, for
C350-0.27C 0.6AT and C550-0.27C 0.6AT samples, the decrease of peak at 0.54
16
16
nm was related to the selective extraction of Si atoms on T7 or T8 sites, and the
decrease of peak at 0.65 nm was related to the selective extraction of Si atoms on T3
+
+
and T1 sites. Furthermore, the extraction of Si atoms on T3 and T1 sites resulted in
the expanded 10-ring opening of the supercage [18], which is corresponding to the
results shown in Fig. S3, i.e., their average pore diameter related to the supercages
was a little larger than that of HMCM-49.
In Section 3.1, it has been figured out that for C550-0.27C 0.6AT, HMI located
1
6
2
9
in pore systems was removed completely before the alkali treatment. Both Si MAS
+
NMR and micropore size distributions proved that Si atoms on T3 and T1 sites
(surface pockets or 10-ring openings of the supercages) and T7 or T8 sites (sinusoidal
channels) were selectively extracted in the desilication processes, resulting in the
formation of intracrystalline mesopores. However, for C350-0.27C 0.6AT, a small
1
6
part of HMI located inside the supercages and most of HMI located in the sinusoidal
channels were still retained before the alkali treatment. This should result in a harder
+
extraction of Si atoms on T7 or T8 sites (sinusoidal channels) than that on T3 and T1
sites (surface pockets or 10-ring openings of the supercages) in theory. Unfortunately,
29
the Si MAS NMR and micropore size distributions did not demonstrate this trend,
though the desilication of C350-0.27C 0.6AT was obviously milder than that of
1
9
6
2
C550-0.27C 0.6AT. According to the Si MAS NMR result and the retainment of
16
HMI for C150-0.27C 0.6AT (part of the HMI on the surface pockets would be eluted
16
during the treatment), it might be deduced that Si atoms on T3 site of the surface
pockets were selectively extracted for this sample, as well as a few Si atoms on T7 or
T8 sites.
Page 16 of 36

3.2.2. Effect on acidity
The acidity of HMCM-49 and CT-0.27C 0.6AT samples was firstly measured
1
6
by NH -TPD technique and the results were presented in Fig. 5. The concentration of
3
acid sites was determined by the amount of desorbed ammonia, while the NH3
desorption peak temperature could be closely related to the strength of acid sites [43].
The NH -TPD profiles were fitted by Gaussian method with three peaks [9], relating
3
to the weak, medium and strong acid sites, respectively. Meanwhile, the
corresponding acid site concentrations of different samples were determined by the
conventional method [18], and the results were listed in Table 4. Compared with
HMCM-49 (total acid concentration of 0.87 mmol/g), the total acid concentrations of
C150-0.27C 0.6AT and C250-0.27C 0.6AT increased gradually, and the highest total
16
16
acid concentrations could be found on C250-0.27C 0.6AT (1.04 mmol/g) and
1
6
C350-0.27C 0.6AT
(1.00 mmol/g) samples and then it decreased on
1
6
C450-0.27C 0.6AT (0.56 mmol/g) and C550-0.27C 0.6AT (0.54 mmol/g) samples.
16
16
The changing trends of weak, medium and strong acid site concentrations for the
series of samples were similar with that of total acid concentration.
The acidity of these samples was further characterized by Py-IR, and the
corresponding Py-IR spectra were presented in Fig. S4. The bands at ca. 1454 and
-1
1
545 cm were attributed to the pyridine adsorbed on Lewis and Brønsted acid sites
-1
respectively, and the bands at ca. 1490 cm were related to pyridine interacting with
both Brønsted and Lewis acid sites [44]. As shown in Fig. S4, with the decrease of
HMI content in the samples before the alkali-treatment, the band areas corresponding
to Brønsted acid sites increased firstly, and then decreased, which was similar with the
changing trend of various acid concentrations determined by NH -TPD, while the
3
band areas corresponding to Lewis acid sites decreased monotonously.
To calculate the acid concentrations, 1.67 and 2.22 cm/μmol were taken as the
integrated molar extinction coefficients of Brønsted and Lewis acid sites, respectively
[45]. The obtained concentrations of Brønsted and Lewis acid sites were listed in
Table 4. For CT-0.27C 0.6AT (T = 150, 250 and 350), the Brønsted acid
16
Page 17 of 36

concentrations increased gradually, and were higher than that of HMCM-49 (0.30
mmol/g). Especially for C350-0.27C 0.6AT, the Brønsted acid concentration was
1
6
0
.41 mmol/g, which was highest among the tested samples. Both C450-0.27C 0.6AT
16
and C550-0.27C 0.6AT samples exhibited lower Brønsted acid concentrations (0.23
16
mmol/g) than HMCM-49. Moreover, the Lewis acid concentrations gradually and
monotonously decreased, from HMCM-49 (0.21 mmol/g) to C550-0.27C 0.6AT
1
6
(0.10 mmol/g).
The distribution of Al atoms is non-uniform in the framework of zeolites [46],
and Al atoms can preserve the zeolite frameworks. In other words, Si atoms in the
Al-rich regions are more difficult to be extracted than those in the Al-poor regions [18,
4
7]. Based on these references, it could be deduced that for C150-0.27C 0.6AT and
16
C250-0.27C 0.6AT samples, desilication mainly occurred in the Al-poor regions,
16
bringing in crevices on the crystal sheets of MCM-49 with almost no framework
destruction, and resulted in the increase of Si-O-Al density in the framework. Thus
their Brønsted acid concentrations showed an enhancement compared with that of
HMCM-49. This effect was also available for the sample of C350-0.27C 0.6AT, and
1
6
the increase of Si-O-Al density in the framework was dominant, though its framework
was slightly damaged during the desilication. However, for the samples of
C450-0.27C 0.6AT and C550-0.27C 0.6AT, both the frameworks were severely
16
16
damaged, resulting in that the Brønsted acid concentrations decreased obviously.
Perhaps, the gradual and monotonous decrease in Lewis acid concentrations was due
to the removal of extraframework Al [18] during the modification.
3
.3. Catalytic performances of HMCM-49 and CT-0.27C 0.6AT
1
6
The acylation reaction of AN with AA was taken as a probe reaction to
investigate the catalytic performances of HMCM-49 and CT-0.27C 0.6AT catalysts.
1
6
The AA conversions vs. time on stream (TOS) over different catalysts were shown in
Fig. 6. When the HMCM-49 was used as catalyst, the initial conversion (the
conversion at the TOS of 2 h) of AA was 51.4%, and the detected products were
Page 18 of 36

acetic acid (AC) and methoxyacetophenone (MAP), with the selectively of 52.7% and
7.3%, respectively. Most of MAP in the product was in the para form (the selectivity
4
to p-MAP > 98%), which was consistent with our previous report [48]. After 9 h of
TOS, the AA conversion decreased to 28.9%, while the selectivity to p-MAP was
remained at almost the same level.
The AA initial conversions over all CT-0.27C 0.6AT catalysts were obviously
1
6
higher than that over HMCM-49, while their selectivities to the products were
comparable to each other. Specifically, for C150-0.27C 0.6AT catalyst, the AA initial
1
6
conversion was 82.3%, and decreased to 62.8% at TOS of 9 h. The declining rate of
AA conversion (23.7%) was obviously lower than that over HMCM-49 (43.8%). The
AA initial conversion over C250-0.27C 0.6AT was as high as 88.5%, about 37
1
6
percentage points higher than that over HMCM-49, and its declining rate of AA
conversion (24.2%) was comparable with that over C150-0.27C 0.6AT. The AA
1
6
initial conversions decreased to 79.6%, 74.6% and 72.4% for C350-0.27C 0.6AT,
1
6
C450-0.27C 0.6AT and C550-0.27C 0.6AT, respectively. Also, their declining rates
16
16
of AA conversion after reaction of 9 h (20.2%, 24.0%, 22.5%) were obviously lower
than that over HMCM-49.
For the acylation of AN with AA over Beta zeolite, it was reported that the total
acid sites concentration detected by NH -TPD is related to the catalytic activities, and
3
Brønsted acid sites play a predominant role [48]. The relations between total acid
concentration, mesopore volume and AA initial conversion for the series samples
were shown in Fig. 7. For CT-0.27C 0.6AT (T = 150, 200 and 250) catalysts, their
1
6
total (or Brønsted) acid concentrations were measured to be higher than that of
HMCM-49, and it is the main reason for the high activities of these three catalysts. In
addition, the crevices produced during the desilication processes, which presented as a
slight increase of mesopore volumes, could enhance the accessibility of acid sites to
some degree, by shortening the micropore diffusion path lengths [18]. As to
C350-0.27C 0.6AT, its total (or Brønsted) acid concentrations were comparable with
16
that of C250-0.27C 0.6AT, and its mesopore volume had an obvious increase due to
16
the coming into being of intracrystalline mesopores. However, the catalytic activity of
Page 19 of 36

C350-0.27C 0.6AT was slightly lower than that of C250-0.27C 0.6AT, implying that
16
16
crevices maybe more beneficial for the acylation than the intracrystalline mesopores.
For C450-0.27C 0.6AT and C550-0.27C 0.6AT catalysts, the total (or Brønsted)
16
16
acid concentrations were similar and both lower than that of HMCM-49 due to the
severely destruction of framework. But the large amounts of intracrystalline
mesopores produced during the desilication could improve the diffusion of reactants
[
30] and provide higher external surface areas [49], which is in favor of the acylation
6, 50]. As a result, the activities of C450-0.27C 0.6AT and C550-0.27C 0.6AT were
[
1
6
16
comparable and both higher than that of HMCM-49. Whether the OMMs played a
role in the acylation is still under study. Moreover, the existence of crevices or
intracrystalline mesopores could enhance the transport of coke precursors out of the
catalysts and therefore improve the resistance to the deactivation of the catalysts [30].
4
. Conclusion
The partial detemplated MCM-49 zeolite contained residual HMI in different
pore systems has been simultaneously modified with CTAB and NaOH. NaOH could
attack the HMI-free regions. For MCM-49 samples with more HMI retained, NaOH
treatment could produce some crevices on the edges and surfaces of the crystal plates
with no serious framework destruction, resulting in an obvious increase of total and
Brønsted acid site concentrations, as well as a monotonous decrease of Lewis acid site
concentrations. For MCM-49 samples with less or without HMI retained, the
framework was severely damaged and intracrystalline mesopores (ca. 3 nm) would be
developed and formed during the desilication. When the amount of dissolved species
reached a certain value, they could be transformed to OMMs in the directing of CTAB
micells. The catalytic evaluation of the acylation of AN with AA over HMCM-49 and
CT-0.27C 0.6AT series samples revealed that the catalytic activities of the samples
16
after NaOH and CTAB modification were significantly higher than that of untreated
HMCM-49. Combining the catalyst evaluation results with the characterization results,
the improvement of the catalytic activity over the modified materials can be mainly
Page 20 of 36

attributed to the positive changes in acidities (total and Brønsted acid site
concentrations) and pore structure properties.
Acknowledgements
The guidance and help of Professor Yide Xu is greatly appreciated.
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Page 22 of 36

Figure captions
Fig. 1 DTG profiles of MCM-49S and CT (T = 150, 250, 350, 450 and 550)
samples.
Fig. 2 TEM images of A: HMCM-49; B: C150-0.27C 0.6AT; C: C200-0.27C 0.6AT;
1
6
16
D: C250-0.27C 0.6AT; E: C350-0.27C 0.6AT; F: C450-0.27C 0.6AT; G:
16
16
16
C550-0.27C 0.6AT; H: C550-0.6AT.
16
Fig. 3 A: N2 adsorption/desorption isotherms of HMCM-49 and
-0.27C 0.6AT ( = 150, 350 and 550) samples; B: BJH curves of
-0.27C 0.6AT ( = 150, 200, 250, 350, 450 and 550)
samples; C: BJH curves of C550-0.27C 0.6AT and C550-0.6AT.
C
T
T
1
6
HMCM-49 and C
T
T
1
6
16
2
9
Fig. 4 Si MAS NMR spectra of HMCM-49 and C
T-0.27C 0.6AT (T = 150,
16
3
50 and 550) samples.
Fig. 5 NH -TPD profiles of HMCM-49 and CT-0.27C 0.6AT samples.
3
16
Fig. 6 Variations of AA conversion with time on stream over HMCM-49 and
CT-0.27C 0.6AT catalysts.
16
o
-1
Reaction conditions: 1.0 MPa, 110 C, WHSV(AN+AA) = 10.2 h , n(AN): n(AA) =
5
:1, time on stream = 9 h.
Fig. 7 Relations between mesopore volume, total acid concentration and acetic
anhydride initial conversion for HMCM-49 and CT-0.27C 0.6AT samples.
1
6
o
-1
Reaction conditions: 1.0 MPa, 110 C, WHSV(AN+AA) = 10.2 h , n(AN): n(AA) =
5
:1, time on stream = 2 h.
Page 23 of 36

Table 1
Textural properties of MCM-49S and CT (T = 250, 350, 450 and 550) samples.
HMI removed
SBET
Sexter
Vtotal
Vmicro
Vmeso
Samples
a
2
2
3
3
3
(%)
(m /g)
(m /g)
(cm /g)
(cm /g)
(cm /g)
MCM-49S
C250
0
62
64
62
64
0.24
0.27
0.30
0.47
0.49
0
0.24
0.27
0.28
0.32
0.31
24
44
75
0
C350
112
446
500
78
0.02
0.15
0.18
C450
105
108
C550
100
a: Data were calculated according to the results of TGA.
Page 24 of 36

Table 2
Textural properties of HMCM-49 and CT-0.27C 0.6AT samples.
1
6
a
2
2
3
b
3
c
3
Samples
HMCM-49
Si/Al
11.0
10.6
10.7
10.6
10.6
10.3
10.1
SBET (m /g)
492
Sexter (m /g)
Vmicro,N2 (cm /g)
Vmicro,Ar (cm /g)
Vmeso (cm /g)
118
172
165
174
240
366
361
0.17
0.16
0.16
0.16
0.14
0.10
0.11
0.15
0.15
0.15
0.14
0.13
0.08
0.08
0.35
0.40
0.42
0.43
0.49
0.57
0.57
C150-0.27C 0.6AT
531
1
6
C200-0.27C 0.6AT
526
1
6
C250-0.27C 0.6AT
527
1
6
C350-0.27C 0.6AT
562
1
6
C450-0.27C 0.6AT
606
1
6
C550-0.27C 0.6AT
603
1
6
a: Si/Al molar ratios measured by XRF.
b: Micropore volume determined by N adsorption.
2
c: Cumulative volume of Ar adsorbed in ≤ 1.0 nm pores.
Page 25 of 36

Table 3
Si distribution in the frameworks of HMCM-49 and CT-0.27C 0.6AT (T = 150, 350
1
6
2
9
and 550) samples characterized by Si MAS NMR.
The proportion of Si atoms on different T sites (%)
Samples
+
+
+
Q3
Q3
5.1
6.5
8.8
9.9
T2
24.7
26.8
28.3
32.6
T7,T8
24.3
23.8
21.1
18.5
T3
27.6
24.9
22.7
20.6
T6
8.5
T1
8.8
9.1
7.7
6.5
HMCM-49
1.0
0.3
0.9
2.6
C150-0.27C 0.6AT
8.6
1
6
C350-0.27C 0.6AT
10.5
9.3
1
6
C550-0.27C 0.6AT
1
6
Page 26 of 36

Table 4
Acid sites distributions measured by NH -TPD and Py-IR of HMCM-49 and
3
CT-0.27C 0.6AT samples.
16
Weak
Medium
Strong
Total
Brønsted
(mmol/g)
Lewis
Samples
b
(
mmol/g)
(mmol/g)
(mmol/g)
(mmol/g)
(mmol/g)
a
HMCM-49
0.34 (253)
0.14 (338)
0.19 (347)
0.18 (359)
0.18 (360)
0.11 (343)
0.10 (340)
0.39 (443)
0.41 (454)
0.42 (458)
0.40 (457)
0.20 (436)
0.20 (435)
0.87
0.98
1.04
1.00
0.56
0.54
0.30
0.32
0.40
0.41
0.23
0.21
0.19
0.13
0.12
0.12
0.10
C150-0.27C 0.6AT
0.38 (258)
0.44 (258)
0.42 (259)
0.25 (254)
0.24 (252)
1
6
C250-0.27C 0.6AT
1
6
C350-0.27C 0.6AT
1
6
C450-0.27C 0.6AT
1
6
C550-0.27C 0.6AT
0.23
1
6
o
a: Data presented in parentheses were the desorption peak temperatures ( C) of
NH -TPD profiles.
3
b: The total acid concentrations were determined from NH -TPD profiles.
3
Page 27 of 36

Fig. 1
Page 28 of 36

Fig. 2
A
C
E
B
D
F
G
H
Page 29 of 36