Continuous liquid phase acylation of toluene over HBEA zeolite: Solvent effects and origin of the deactivation

Article abstract of DOI:10.1016/j.molcata.2014.09.038

The continuous liquid phase Friedel-Crafts acylation of toluene (T) by acetic anhydride (AA) over HBEA zeolite was carried out in a fixed bed reactor, with acetic acid (AC) as a solvent. 4-Methylacetophenone (4-MAP) was selectively formed in the initial reaction stage. However, a rapid catalyst deactivation occurred with a sharp decrease of the conversion of acetic anhydride, and this was mainly caused by 4-MAP and heavy compounds ('coke') existing in the zeolite pore, which poisoned the active sites of the catalyst. The use of excess toluene and moderate acetic acid enhanced catalyst activity and stability to some extent as it limited both the retention of 4-MAP and the formation of 'coke'. Moreover, a considerable reduction of Broensted acid sites after deactivation revealed that the toluene acylation is primarily a Broensted acid catalyzed reaction.

Full text of DOI:10.1016/j.molcata.2014.09.038

Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Continuous liquid phase acylation of toluene over HBEA zeolite:
Solvent effects and origin of the deactivation
∗
Zhihua Chen, Wenqi Chen, Tianxia Tong, Aiwu Zeng
State Key Laboratory of Chemical Engineering, Tianjin Chemical Synergy Innovation Center, Tianjin University, Institute of Chemical Engineering and
Technology, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 July 2014
Received in revised form
The continuous liquid phase Friedel–Crafts acylation of toluene (T) by acetic anhydride (AA) over HBEA
zeolite was carried out in a fixed bed reactor, with acetic acid (AC) as a solvent. 4-Methylacetophenone (4-
MAP) was selectively formed in the initial reaction stage. However, a rapid catalyst deactivation occurred
with a sharp decrease of the conversion of acetic anhydride, and this was mainly caused by 4-MAP and
heavy compounds (‘coke’) existing in the zeolite pore, which poisoned the active sites of the catalyst. The
use of excess toluene and moderate acetic acid enhanced catalyst activity and stability to some extent as
it limited both the retention of 4-MAP and the formation of ‘coke’. Moreover, a considerable reduction of
Broensted acid sites after deactivation revealed that the toluene acylation is primarily a Broensted acid
catalyzed reaction.
2
5 September 2014
Accepted 28 September 2014
Available online 7 October 2014
Keywords:
Acylation
Zeolite
Toluene
© 2014 Elsevier B.V. All rights reserved.
Solvent effect
Deactivation
1
. Introduction
Friedel–Crafts acylation is an important step for synthesizing
Many studies have been devoted to improving the activity and
selectivity of acylation of toluene with acetic anhydride [17,21–26].
Derouane et al. [23] concluded that HBEA zeolite was definitely
the preferred catalyst on acetylation of toluene with acetic anhy-
dride due to its large and interconnected channels when compared
with H-FAU(Y), H-MOR and H-MFI. Moreover, excellent selectivity
(>98%) of 4-methylacetophenone has been obtained when HBEA
zeolite was used as a catalyst [17,21,23,24]. However, zeolites eas-
ily suffered from fast deactivation because of the poisoning of the
active sites by adsorption of the products and pore blockage due
to “coke”-type large molecules, which strongly limited the use of
zeolites in commercial processes [21]. Besides, we observed that
almost all present studies on acylation of toluene by acetic anhy-
dride over zeolites are carried out in batch reactors, which make
the investigation of deactivation difficult and these researchers’
emphases were generally placed on the activity and selectivity but
not the stability of the catalysts.
aromatic ketones, which are used as prominent intermediates
in the production of valuable industrial and fine chemicals such
as pharmaceuticals, insecticides, plasticizers, dyes and perfumes
[
1–6]. This process conventionally has been carried out by using
homogeneous catalysts Lewis acid (e.g., metal halides [7]) or Broen-
sted acid (e.g., H SO , HCl, HF [3]), which leads to many problems
2
4
concerning handling, safety, corrosion, waste disposal etc. [8].
To overcome these drawbacks, considerable efforts have been
made to search for eco-friendly solid and reusable heteroge-
neous catalysts, particularly the zeolites such as ZSM-5 [9–11],
H␤ [3,6,12,13], and HY [13–15]. Besides, it is a promising way to
use less hazardous acylating agents, i.e., carboxylic acids and their
anhydrides, instead of acyl halides. The acylation of active aromatic
rings such as anisole [16–18] and 2-methoxynaphthalene [4,17],
or higher active heteroaromatic compounds such as thiophene,
pyrroles and furans [5,19,20], is carried out with very good yields
and selectivities on zeolites. However, the results obtained from
lower active aromatic rings like toluene and benzene are poorer.
In this work, continuous liquid phase acylation of toluene with
acetic anhydride over HBEA zeolite (Si/Al = 27.6) was first carried
out in a fixed bed reactor. Excess toluene and appropriate acetic
acid were used. The aim of this paper is to understand the origin
of deactivation of zeolites and the effects of solvent. Catalysts were
recovered and extracted in a soxhlet with dichloromethane. The
parent and deactivated HBEA zeolites were compared through the
analysis of SEM, TGA, 13C NMR MAS, Al NMR MAS, and the FT-
IR spectroscopy of adsorbed pyridine. It shows that the organic
[
21]
27
∗ Corresponding author. Tel.: +86 13920404701.
E-mail address: awzeng@tju.edu.cn (A. Zeng).
http://dx.doi.org/10.1016/j.molcata.2014.09.038
381-1169/© 2014 Elsevier B.V. All rights reserved.
1

2
32
Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
Fig. 1. Acylation of toluene in fixed bed reactor apparatus diagram.
13C NMR and 27Al NMR spectra were recorded on a 300 MHZ
Varian Infinity plus NMR spectrometer in order to investigate the
kind of carbon deposit and the form of aluminum. The scanning
frequency was 75.4 MHz and pulse delay was 5.0-s. The MAS speed
compounds adsorbed/retained in the zeolites (4-MAP and ‘coke’)
are responsible for the deactivation of zeolites. Besides, a toluene-
rich reactant mixture and moderate acetic acid are preferable to
limiting the deactivation to some extent.
(spin rate) was 8 kHz. Chemical shifts (ı) were reported in ppm on
behalf of the kind of carbon deposit and the form of aluminum,
respectively.
2
. Experimental
The acidity of the zeolite samples before and after deactivation
was determined by the pyridine adsorption–desorption method
performed on a Nicolet 750 infrared spectrometer coupled to a con-
2
.1. Materials
Toluene (99.5%) and acetic anhydride (98.5%) were procured
◦
ventional high vacuum system. The samples were calcined at 450 C
from Tianjin Jiangtian Chemical Technology Co., Ltd. Acetic acid
99.5%) and dichloromethane (99.5%) were supplied by Tian-
for 120 min in an in situ IR gas cell under vacuum prior to pyridine
(
◦
adsorption. Then the temperature was cooled down to 90 C. Pyri-
jin Guangfu Institute of Fine Chemistry. Tetraethyl ammonium
hydroxide (TEAOH) was employed by Aladdin Reagent Co., Ltd. Alu-
minosilicate was purchased from Nankai University Catalyst Co.,
Ltd. All materials were used without further purification.
dine was adsorbed for 30 min and then the physisorption pyridine
◦
◦
was evacuated at 200 C and 350 C for 20 min, respectively.
2.2. Catalyst preparation and characterization
2.3. Reaction procedure
The HBEA sample was made according to the method reported
Continuous experiments were carried out in a fixed reactor
(Fig. 1) consisting of a stainless steel tube (8 mm in diameter, 28 cm
in length) kept in an electrical heater mounted in a vertical man-
ner. 5.6 (or 2.8) g of the HBEA zeolite (Si/Al = 27.6) was kept in
by Matsukata et al. [27]. Each 10 g powder of HBEA was mixed with
g Al O and 4 g nitric acid solution (10 wt%) into homogenate,
3
2
3
extruded and cut into a short cylinder of 4 mm in length and 3 mm
◦
in diameter. The granular zeolite was dried at 120 C for 2 h, and
the middle isothermal region of the reactor. The catalyst was acti-
◦
◦
then calcined at 450 C for 5 h in a muffle furnace.
vated in situ before the reaction by heating for 2 h at 200 C in a N
2
◦
The bulk Si/Al molar ratios of the samples were determined by
XRF. The BET surface area and total pore volume were determined
flow (100 ml/min). Then the temperature was decreased to 120 C
and the reaction pressure was controlled at 0.2 MPa in N2 flow
(30 ml/min). Typically, the mixtures of toluene, acetic anhydride,
and acetic acid with a molar ratio of 20:1:0.5 were introduced at the
top of the reactor by a metering pump (flow rate 0.1 ml/min). The
liquid products were taken at regular intervals and analyzed with
a gas chromatography (GC, Agilent 7890A) equipped with a flame
ionization detector (FID) and DB-FFAP capillary column (30 m in
length and 0.25 mm in diameter).
◦
using a Micromeritics ASAP2020 volumetric instrument at −196 C
using nitrogen adsorption isotherms.
The morphologies of the parent and deactivation zeolites were
examined with a HIT-S4800 scanning electron microscopy (SEM).
TG/DTG profiles were performed on a PerkinElmer Diamond
◦
−1
under a
TG/DTA instrument, with a heating rate of 15 C min
nitrogen flow rate of 20 ml/min.

Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
100
233
Since the toluene was overdosed compared with acetic anhy-
dride (in molar), the conversion of substrate was calculated based
on acetic anhydride (AA):
a
b
80
XAA = %
(AA at time = 0) − % (AA at time = t)
the rate of rise of 4-MAP yield
the rate of rise of conversion AA
× 100
(1)
%
(AA at time = 0)
The yield (mol%) and selectivity of 4-MAP were calculated as
follows:
60
40
20
0
Y4-MAP = %
mol (4-MAP at time = t)
× 100
(2)
%
mol (AA at time = 0)
GC peak area of 4-MAP
Conversion AA
S4-MAP
=
× 100
sum of the GC peak of 2-MAP, 3-MAP and 4-MAP
(3)
4-MAP Yield
0
1000
2000
3000
4000
5000
The organic compounds retained on the external zeolite surface
and in the micropores were recovered at the end of the experiment.
The used catalyst underwent a double-extraction methodology.
The first extraction was made according to the description by Rohan
et al. [28]. The deactivated catalyst was treated in a soxhlet for
Time on Stream (min)
Fig. 2. AA conversion (mol%) and 4-MAP yield (mol%) vs time during continuous
acylation of toluene (T) with acetic anhydride (AA) over HBEA zeolite (a) and their
◦
rate of change (b). Experimental conditions: T/AA/AC molar ratio = 20:1:0.5; 120 C;
8
h using dichloromethane as solvent. Then the dichloromethane
−1
LHSV = 0.426 h .
was evaporated and the remaining organic material was analyzed
by GC–MS. The zeolites therefore experienced a second extrac-
tion by dissolving in a solution of sodium hydroxide (10 mol/L),
after that the organic species was extracted with dichloromethane
and analyzed by GC–MS. Through such a methodology, most of the
adsorbed compounds could be recovered.
gradually to 15 mol% and the rate of change is on the brink of 0
by 1500 min. In this paper, the catalyst is regarded as deactivation
when the yield of 4-MAP is below 15 mol%.
3
. Results and discussion
3.3. Effects of solvent
3
.1. Characterization of zeolites
In the liquid phase synthesis of functional compounds, solvents
are often used for some practical reasons such as solubilization of
reactants and products, heat transfer with exothermic reactions
and improvement of the rate, stability and selectivity of reactions
[30]. Dimroth and Reichardt [30,31] regarded solvents as structured
isotropic continuum composed of individual solvent molecules
with their own solvent/solvent interactions, and took into account
specific solute/solvent interactions such as hydrogen-bonding and
The bulk Si/Al molar ratio of HBEA zeolite used in this work
was 27.6 (determined by XRF), and the XRD crystallinity was
1
was 542 m /g (micropore surface area = 449 m /g; external surface
area = 93 m /g) (determined by the BET method), the total pore
◦ ◦
00% (XRD signal 2ꢀ = 7.8 and 22.5 ); The total surface area
2
2
2
3
volume was 0.209 cm /g (determined by the t-plot method).
N
EPD/EPA interactions. Thus, ET (30) and normalized values E ,
T
3
.2. Influence of time on the production of 4-MAP
the empirical parameters of solvent polarity are proposed. For
Friedel–Crafts acylation, Fromentin et al. [4] studied the influence
of the polarity of solvents on the activity and selectivity of zeo-
lite HBEA in the acetylation of 2-methoxynaphthalene with acetic
anhydride. It is noted that high polar solvent, such as sulfolane
The acylation of toluene by acetic anhydride over 5.6 g zeolite
◦
HBEA was carried out in liquid phase at 120 C, 0.2 MPa in a fixed
bed reactor, with acetic acid as a solvent. The mixed molar ratio
of toluene, acetic anhydride and acetic acid was 20:1:0.5 (Table 1).
LHSV for mixture (volume of mixture introduced per volume of cat-
alyst per hour) was 0.426 h . Whatever the time-on-stream (TOS),
the selectivity to 4-MAP is very high (>96%). 3-MAP, 2-MAP, di-
acetylated toluene and traces of other heavy compounds appear
as secondary products. It should also be remarked that some acetic
anhydride undergoes hydrolysis to form acetic acid during the reac-
tion, especially at short TOS.
N
(E = 0.410), can compete with the reactant molecules for diffu-
T
sion inside the pores and for adsorption on the acid sites, reducing
therefore the rates of the main reaction. High deacetylation rate
is obtained with non-polar solvent such as 1-methylnaphthalene
−1
N
T
(E = 0.412) which cannot solvate the acylium ion intermediates.
And high acetylation and isomerization rates are obtained in the
presence of a solvent of intermediate polarity such as nitroben-
zene (E TN = 0.324). The effect of solvent polarity is similar to the
one found by Moreau et al. [32]: An increase in the solvent polarity
lead to the increased competitive adsorption between solvent and
reactants on the active sites.
As seen from Fig. 2a, there is initially a huge difference between
the yield of 4-MAP and the conversion of AA (maintains at 100%,
approximately), due to the strong adsorption retention of 4-MAP
[
29] and acetic anhydride in the zeolite pores, as well as the hydrol-
ysis of acetic anhydride. Meanwhile, the increase in the yield of
-MAP can also illustrate the retention of 4-MAP. Fluctuation trend
The research on solvents has always been a topic of inter-
est, because many of the solvents generally used throughout both
academia and industry are regarded as toxic, volatile, unsafe or high
consumption in terms of environmental protection. This includes
the development of environmentally benign neoteric solvents, con-
stituting a series of novel solvents with desirable, less hazardous,
new properties [30]. In fact, considering the development of a
4
of the yield of 4-MAP is similar to the conversion of AA (Fig. 2b).
And the yield of 4-MAP reaches a plateau (30 mol%) at 400–600 min
on stream. This plateau is likely to be ascribed to the equilibrium
between the rate of formation and adsorption of 4-MAP on the
zeolites. After that, both the yield of 4-MAP and the conversion
of AA rapidly decrease to a yield of about 26 mol%, after which
the decreasing rates tend to be stable. The yield of 4-MAP drops
sustainable chemistry, the best solvent will be no solvent at all.
Hence, in this work, toluene (E TN = 0.099) and acetic acid (ET
N
=
0.648), which were reactant or product as well, were considered as

2
34
Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
25
20
15
10
5
0
32
T/AA=20
a
b
28
24
20
16
12
8
AC/AA=0.5
AC/AA=0
T/AA=10
AC/AA=1.5
AC/AA=3
T/AA=5
T/AA=1
1
00
200
300
400
500
600
700
800
Time on Stream (min)
1
00
200
300
400
500
600
Fig. 4. 4-MAP yield (mol%) vs time as a function of the acetic anhydride to acetic
acid (AC/AA) during continuous acylation of toluene (T) with acetic anhydride (AA)
over HBEA zeolite (a) and the 4-MAP selectivity (b). Experimental conditions: T/AA
Time on Stream (min)
Fig. 3. 4-MAP yield (mol%) vs time as a function of the toluene to acetic anhydride
T/AA) during continuous acylation of toluene (T) with acetic anhydride (AA) over
◦
−1
molar ratio = 20:1; 120 C; LHSV = 1.706 h .
(
◦
−1
.
HBEA zeolite. Experimental conditions: 120 C; LHSV = 1.706 h
opposite result (Fig. 4a). Different trend can be seen when it comes
to the selectivity of 4-MAP, the selectivity increased with the
increasing amount of acetic acid in raw material (Fig. 4b). This
is because the process of acetic anhydride being dissociated into
acetyl ions will be hindered in the presence of acetic acid. Thus the
selectivity of 4-MAP will be improved. Though acetic acid might
stabilize the acylium ion as well as the ionic intermediate formed
by the attack of acylium ion with toluene and promote acylation
reaction like nitrobenzene [7], superfluous acetic acid will com-
pete with the reactant molecules for adsorption in the acid sites,
which results in the decrease of the yield of 4-MAP (Fig. 4).
solvents in the acylation of toluene with acetic anhydride, without
other outside solvents being introduced.
Fig. 3 indicates that there is a significant improvement in the
yield of 4-MAP when the T/AA molar ratio increased from 1 to 20.
This is probably because the large excess of toluene helped to des-
orb the formed 4-MAP, and therefore reduced the inhibiting effect
of ketone. So toluene can also be regarded as a solvent in this pro-
cess. And toluene is generally much larger than the stoichiometric
when acylated by acetic anhydride over zeolites [21–23,26] unless
under the conditions of nitrobenzene as a solvent [17,24], or Fe-SBA
as the catalyst [24]. Fe-SBA is a kind of mesoporous molecular sieves
possessing larger pore diameter than the microporous ones, and
this structure contributes to the diffusion of reactants and products.
However, it is with less diffusion limitation that a lower selec-
tivity of 4-MAP was got (85.6%) in comparison with the result of
using HBEA (>98%). Nitrobenzene with intermediate polarity helps
desorption of 4-MAP formed within the micropores and does not
have remarkable competitive adsorption with reactants, and thus
could favor the catalytic activity. However, it is in urgent need to
find out a new solvent for the substitution of hazardous solvents
such as nitrobenzene. In this work, acetic acid was considered as
another solvent.
3.4. The origin of deactivation
3.4.1. Carbon deposits: composition and kinetic minimum
cross-sectional diameter
Zeolite BEA is generally described as a three-dimensional
intersecting channel system, which consists of two mutually
perpendicular straight channels, each with a cross-section of
0.66 nm × 0.67 nm (or 6.6 A˚ × 6.7 A˚ ) run in the x- and y-directions,
and a sinusoidal channel of 0.56 nm × 0.56 nm runs parallel to the
z-direction [33]. The average pore diameter of HBEA zeolite used
in this work was 0.56 nm. Aluminum atoms in HBEA zeolite pro-
duce Broensted and Lewis acid sites. Broensted acid sites have
external OH groups, which present both on the internal and exter-
nal surface, while the Lewis acid sites are the exposed three-fold
The effect of acetic acid is illustrated in Fig. 4. Appropriate
amount of acetic acid added in raw material could increase the
yield of 4-MAP, while excess acetic acid would result in the
Table 1
Acylation of toluene with acetic anhydride over zeolites in batch reactor.
Year
Catalyst
T/AA molar
ratio
Catalyst/AA
weight ratio
Temperature
( C)
Time (h)
Solvent
XAAa
YMAPb
S4-MAPc
Ref.
◦
1
997
000
HY, HZSM-5
140:1
20:1
1:1
250
150
12
4
None
None
74 mol%
[23]
[22]
78 mol%
2
BEA, Nano-BEA
0.5:1
58%
46 wt% (35 mol%)
80 wt% (61 mol%)
40 mol%
>98%
>98%
≥99.5%
100%
100%
98.7%
85.6%
83%
2
2
000
004
HBEA
HBEA, La-BEA
20:1
1:2
0.36:1
0.13:1
115
135
24
6
None
Nitrobenzene
[24]
[25]
50%
6%
6
2
2
2
005
007
013
HBEA
FeSBA-1
Nano-BEA, Hierar-BEA
5:1
1:2
20:1
0.7:1
0.05:1
0.5:1
100
150
120
1
4
1.7
Ph-NO2
None
None
11%
77.2%
54.8%
[17]
[26]
[27]
76.8%
HBEA
20:1
0.8:1
150
6
None
77.8% 36.3 mol%
96%
This work
a
b
c
XAA: the conversion of acetic anhydride.
YMAP: the yield of methylacetophenone.
S4-MAP: the selectivity of 4-methylacetophenone.

Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
235
coordinated Al3+ ions, predominantly presenting on the internal
surface [34–36]. The windows in zeolite crystal structures indicate
molecular sieving capabilities and control access to the catalyti-
cally active internal sites [37]. The steric hindrance of remaining
organic material on the external zeolite surface and in the micro-
pores was evaluated from the calculated dꢁ (kinetic minimum
cross-sectional diameters) of the organic molecules using Chem-
Bio 3D Ultra 12.0. The concept of kinetic minimum cross-sectional
diameter is derived from de (minimum cross-sectional diameters),
which is amended by Lennard–Jones model [38]
de
21/6
dꢁ =
(4)
It has been proposed on the assumption that the spherical sym-
metric molecules enter into the zeolite pore in the minimized state
of barrier potential. It is expected to be very instructive for pre-
dicting shape selective adsorption of zeolites and their catalytic
behaviors [39].
As shown in Table 2, the dꢁ of main components (compo-
nents 1–4) are smaller than the pore opening of HBEA zeolite
(
0.66 × 0.67 nm, 0.56 × 0.56 nm), that is, the main components tend
to not be controlled by the diffusion limitation of the zeolite. Thus
it can account for their strong polarity adsorption on the acid sites
rather than their steric blockage resulting in the retention in the
zeolite pores. These are also the similar cases with components
6
–8, 10 and 12. However, 4-methylphenyl anhydride (dꢁ = 0.84 nm)
(
component 5), butyl isobutyl phthalate (dꢁ = 0.80 nm) (component
9
) and 3-phenyl-1-p-tolyl-propenone (dꢁ = 0.83 nm) (component
1
1) molecules are larger than the pore opening of the zeolite, which
are probably trapped at the channel intersections.
Fig. 5. The SEM images of the parent and deactivated samples.
3.4.2. Reasons for deactivation of zeolites
In order to explore the reasons for deactivation of zeolites, the
differential thermal analysis (DTA), and the results are shown
in Fig. 6a and b, respectively. Both the parent and deactivation
samples have a peak of weight loss in the range of 50–200 C,
13
27
analytical methods of the SEM, TGA, C MAS NMR, Al MAS NMR,
and the FT-IR spectroscopy of adsorbed pyridine were taken.
The morphologies of the parent and deactivation HBEA zeolites
were analyzed by SEM and the results are presented in Fig. 5. SEM
image (Fig. 5a) shows the particles of the parent HBEA zeolite are in
the range of 0.2–1 ␮m. They consist of loose aggregates of minute
elementary crystals 30–100 nm in size and are evenly distributed.
However, SEM image of the deactivation catalyst (Fig. 5b) shows
there is a severe carbon deposition on the surface of the catalysts,
which might block the acidic sites of the catalyst, leading to the
decrease of the reaction rate.
◦
4 wt% and 8 wt%, respectively, which is mainly caused by surface
moisture adsorbed from air and hydrated water. And for the deac-
tivated zeolite, it also includes the adsorbed organic compounds
of low molecular weight (fat hydrocarbon) (about 4 wt%) in the
reaction process. There is no weight loss for the parent zeolite
◦
until in the range of 430–520 C (1 wt%), which is attributed to
the template agent residue in the catalyst. However, the deac-
◦
tivated zeolite presents three exothermic bands at 200–250 C
◦
◦
(2 wt%), 250–330 C (2 wt%) and 330–520 C (5 wt%). At the range of
200–330 C, the peak of deactivated zeolite represented the main
◦
The amount of carbon deposit in the surface and channel of
the zeolites has been determined by thermogravimetric (TG) and
product methylacetophenone (MAP) and some other by-products
Parent zeolite
100
A
B
0.00
98
96
94
92
90
88
86
84
82
80
78
-
0.01
0.02
Deactivated zeolite
Parent zeolite
-
-0.03
-0.04
-0.05
-0.06
Deactivated zeolite
-0.07
0.08
-
0
100 200 300 400 500 600 700 800
Temperature/
0
100 200 300 400 500 600 700 800
Temperature/
Fig. 6. The TG/DTG curves of the parent and deactivated samples.

2
36
Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
Table 2
Heavy reaction products (main components) and their kinetic minimum cross-sectional diameters.
Components
Chemical structure
Molecular weight
Kinetic minimum
cross-sectional diameter dꢁ
(
nm)
O
1
. 4-Methylacetophenone
. 3-Methylacetophenone
226
226
0.53
0.63
O
2
O
3
4
. 2-Methylacetophenone
226
176
0.63
0.55
O
. (4-Methylbenzoyl)acetone
O
O
O
O
5
. 4-Methylphenyl anhydride
254
0.84
6
7
. 1-(4-Methylphenyl)-1-butanone
162
210
0.69
0.62
O
O
ꢀ
. 4,4 -Dimethylbenzophenone
O
ꢀ
8
9
1
. 3,3 -Dimethylbenzophenone
210
278
164
0.69
0.80
0.63
O
O
O
. Butyl isobutyl phthalate
0. Ethyl m-methylbenzoate
O
O
O
O
1
1
1. 3-Phenyl-1-p-tolyl-propenone
2. 4-Phenyl-but-3-en-2-one
222
146
0.83
0.66
O

Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
237
Octahedral Al
Tetrahedral Al
Deactivated zeolite
Deactivated zeolite
Parent zeolite
3
50 300 250 200 150 100 50
0
-50 -100 -150
Parent zeolite
ppm
Fig. 7. 13C MAS NMR of the parent and deactivated samples.
300 250 200 150 100 50
0
-50 -100 -150 -200 -250
ppm
such as (4-methylbenzoyl) acetone, 4-methylphenyl anhydride
Fig. 8. 27Al MAS NMR of the parent and deactivated samples.
ꢀ
and 4,4 -dimethylbenzophenone (Table 2), while at the range of
◦
3
30–520 C the peak is mainly belong to the aromatic oligomers
(
4 wt%) which are difficult to be extracted with methylene chlo-
carbon and aromatic oligomers equates to roughly 4:1:2, which can
be associated with the results (6:2:4) obtained by TG/DTA.
The influence of carbon deposit on zeolites framework could be
characterized by 27Al MAS NMR, as shown in Fig. 8. The state of alu-
minum framework changes when the zeolites channel is filled with
carbon deposit. There are two peaks corresponding to octahedral
and tetrahedral Al sites [41] in the range of −10–40 and 40–80 ppm,
respectively. The octahedral Al concentration tends to decrease on
the deactivated zeolite compared to the parent sample, while the
tetrahedral Al concentration keeps constant. This indicates that the
change of octahedral Al should be due to the adsorption of car-
bon deposit in the zeolites. Besides, the tetrahedral Al represents
Broensted acid sites, while the octahedral Al is on behalf of Lewis
acid sites. Therefore, Fig. 8 may indicate that the Broensted acid
is responsible for the Friedel–Crafts acylation reaction of toluene
with acetic anhydride.
ride, except the template agent (1 wt%). The mass ratio of low
molecular (4 wt%), MAP and its derivatives (4 wt%), and aromatic
oligomers (4 wt%) was approximately 1:1:1. The distribution of dif-
ferent forms of carbon containing fat hydrocarbon (4 wt% + 2 wt%),
aromatic carbon (4 wt% − 2 wt%) and aromatic oligomers (4 wt%)
was roughly equal to 6:2:4.
The 13C MAS NMR spectra of the deactivated and parent zeolites
are shown in Fig. 7. Derouane et al. [40] first studied the formation
and stability of coke deposits by the method of C MAS NMR dur-
ing the conversion reaction of methanol to hydrocarbons. Carbon
deposit mainly includes fat carbon, olefin carbon, aromatic car-
bon and poly aromatic carbon, etc. The peak signal of fat carbon
is between 10 ppm and 40 ppm, the signal between 125 ppm and
13
1
2
45 ppm belong to aromatic carbon, while between 130 ppm and
00 ppm is the characteristic signal of poly aromatic. For the deac-
tivated zeolites, the carbon deposit consisting of fat hydrocarbon,
aromatic carbon and aromatic oligomers in the channel and surface
is very serious, which presents two tall narrow bands at 10–40 and
The FT-IR spectra of the parent and deactivated HBEA zeolites
adsorbed pyridine probe molecule are compared in Fig. 9. Band at
−
1
+
1545 and 1455 cm can be attributed to pyridinium ions (PyH ,
Broensted acid site) and coordinative bound pyridine (PyL, Lewis
1
70–190 ppm, as well as a low broad band at 125–145 ppm. It is
13
−1
difficult to obtain accurate coke content by C MAS NMR spectra.
However, the distribution of peak area of fat hydrocarbon, aromatic
acid site), respectively [18,42–45]. The band at 1489 cm is asso-
ciated with adsorption on both Broensted and Lewis acid sites [43].
◦
◦
Fig. 9. FTIR spectra of pyridine-adsorbed parent and deactivated HBEA zeolites: (a) desorption at 200 C and (b) desorption at 350 C.

2
38
Z. Chen et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 231–238
Table 3
Result of IR spectra of Py adsorbed on the parent and deactivated HBEA zeolites after desorption at different desorption temperatures.
◦
◦
C
Sample
200
C
350
B acid site (mmol/g)
L acid site (mmol/g)
B/Ca
B acid site (mmol/g)
L acid site (mmol/g)
B/Ca
Parent zeolite
Deactivated zeolite
0.323
0.095
0.360
0.271
0.90
0.35
0.238
0.063
0.296
0.254
0.80
0.25
a
B/C: the ratio of B acid site to L acid site.
A reliable assessment of the concentration of surface acid sites can
be calculated by the integrated peak area [44], and the results of
Py-IR analysis of different samples are listed in Table 3. Calculated
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concentration of Broensted acid sites is decreased by 71% at 200 C,
◦
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[
[
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4
. Conclusions
[
[
The catalytic activity and stability of zeolite HBEA in a fixed
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