Probing the pore structure of hierarchical EU-1 zeolites by adsorption of large molecules and through catalytic reaction

Article abstract of DOI:10.1177/1747519820936594

The adsorption of toluene and 1,3,5-trimethylbenzene and the catalytic transformation of 1,3,5-trimethylbenzene are applied as probing approaches to characterize the pore system of hierarchical EU-1 zeolites prepared using organofunctionalized fumed silica as the silicon source. The adsorption and diffusion of toluene and 1,3,5-trimethylbenzene are significantly improved in the hierarchical EU-1 zeolites compared with the conventional microporous EU-1 zeolite. The adsorption kinetics of toluene and 1,3,5-trimethylbenzene suggested that introducing mesopores significantly increases the rate of adsorption and improved the diffusion of large molecules. In the catalytic transformation of 1,3,5-trimethylbenzene, the conversion of 1,3,5-trimethylbenzene on the hierarchical EU-1 zeolites is doubled compared with the conventional microporous EU-1 zeolite, due to the improved diffusion of bulky molecules and enhanced accessibility of active sites in the hierarchical EU-1 structure. Although isomerization is the main reaction, differences are observed in the product ratios of isomerization to disproportionation between the hierarchical EU-1 zeolites and the microporous counterpart with different times on stream. The transformation of 1,3,5-trimethylbenzene over the hierarchical EU-1 zeolites has a higher isomerization to disproportionation ratio than that over the microporous EU-1 zeolite; this is due to the increased mesoporosity.

Full text of DOI:10.1177/1747519820936594

936594CHL0010.1177/1747519820936594Journal of Chemical ResearchGuo et al.
research-article2020
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Journal of Chemical Research
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Probing the pore structure of hierarchical EU-1
zeolites by adsorption of large molecules and
through catalytic reaction
https://doi.org/10.1177/1747519820936594
DOI: 10.1177/1747519820936594
journals.sagepub.com/home/chl
Zaibin Guo, Wenming Hao , Jinghong Ma and Ruifeng Li
Abstract
Theadsorptionoftolueneand1,3,5-trimethylbenzeneandthecatalytictransformationof1,3,5-trimethylbenzeneareapplied
as probing approaches to characterize the pore system of hierarchical EU-1 zeolites prepared using organofunctionalized
fumed silica as the silicon source. The adsorption and diffusion of toluene and 1,3,5-trimethylbenzene are significantly
improved in the hierarchical EU-1 zeolites compared with the conventional microporous EU-1 zeolite. The adsorption
kinetics of toluene and 1,3,5-trimethylbenzene suggested that introducing mesopores significantly increases the rate
of adsorption and improved the diffusion of large molecules. In the catalytic transformation of 1,3,5-trimethylbenzene,
the conversion of 1,3,5-trimethylbenzene on the hierarchical EU-1 zeolites is doubled compared with the conventional
microporous EU-1 zeolite, due to the improved diffusion of bulky molecules and enhanced accessibility of active sites
in the hierarchical EU-1 structure. Although isomerization is the main reaction, differences are observed in the product
ratios of isomerization to disproportionation between the hierarchical EU-1 zeolites and the microporous counterpart
with different times on stream. The transformation of 1,3,5-trimethylbenzene over the hierarchical EU-1 zeolites has
a higher isomerization to disproportionation ratio than that over the microporous EU-1 zeolite; this is due to the
increased mesoporosity.
Keywords
1,3,5-trimethylbenzene adsorption, disproportionation, hierarchical EU-1 zeolite, isomerization, toluene adsorption
Date received: 11 March 2020; accepted: 3 June 2020
Introduction
College of Chemistry and Chemical Engineering, Taiyuan University of
Technology, Taiyuan, P.R. China
EU-1 zeolite has a one-dimensional pore system of 10-mem-
bered ring (10-MR) channels (0.54×0.41nm) running along
the [100] direction and connected to side pockets by a 12-mem-
bered ring (12-MR) (cross section of 0.68×0.58nm; 0.8nm
Corresponding authors:
Wenming Hao, College of Chemistry and Chemical Engineering, Taiyuan
University of Technology, Taiyuan 030024, P.R. China.
depth) in the [001] direction. The unique pore system with nar- Email: haowenming@tyut.edu.cn
row channels and wide pockets in EUO-type zeolite allows it to
Jinghong Ma, College of Chemistry and Chemical Engineering, Taiyuan
University of Technology, Taiyuan 030024, P.R. China.
demonstrate very interesting and special catalytic performance
in different reactions involving hydrocarbon transformation.1–6 Email: majinghong@tyut.edu.cn

2
Journal of Chemical Research 00(0)
However, the medium-size one-dimensional channel EU-1
zeolite has the drawbacks of a slow diffusion rate and low
accessibility of the active sites within the channels and side
pockets for large organic molecules. It is found that the narrow
channel of EU-1 zeolite is easily blocked by the deposition of
coke molecules.1 In order to solve this problem, mesopores
were introduced into the EU-1 zeolite making a hierarchical
pore structure, which can improve the diffusion of large reac-
tants and product molecules and can make more active sites
accessible to bulky molecules.2–7
210
EU-1-0
EU-1-1
EU-1-2
180
150
120
90
EU-1-2
EU-1-1
EU-1-0
5
10 15 20 25 30 35
0.0
0.2
0.4
0.6
0.8
1.0
2θ (degrees)
Relative pressure (P/P0)
(a)
(b)
There are two main strategies for making hierarchical
zeolites, namely, top-down approaches (post-synthesis treat-
ment, for example, desilication or dealumination) and bot-
tom-up approaches (e.g. templating methods).8 The
post-synthesis treatment often changes the chemical compo-
sition of the zeolite, which reduces its thermal and hydrother-
mal stability, and to loss of a significant amount of Brønsted
acid sites.4 In the templating methods, soft templates such as
cationic polymers and multivalent cationic surfactants have
been applied to synthesize hierarchical EU-1 zeolite.3,7 We
have reported another route using organofunctionalized
fumed silica as the silicon source in the conventional hydro-
thermal system to synthesize hierarchical EU-1 zeolite.9
Characterization of the texture of the hierarchical zeolites
is an important but challenging task. Gas adsorption of N2 at
77K, Ar at 87K, and CO2 at 273K has become the standard
method to characterize the pore structure of a porous material,
Figure 1. (a) XRD patterns and (b) nitrogen adsorption/
desorption isotherms at 77K for the EU-1 zeolites.
Table 1. Pore structure parameters of the EU-1 zeolites.
Sample SBET (m2/g)a Vtot (cm3/g)b Vmic (cm3/g)c Vmeso (cm3/g)d
EU-1-0 354
EU-1-1 399
EU-1-2 424
0.20
0.24
0.31
0.11
0.12
0.10
0.09
0.12
0.21
aSBET is the surface area determined by the BET model.
bVtot is the total pore volume.
cVmic is the micropore volume.
dVmeso is the mesopore volume.
with particular reference to the assessment of surface area and 1,3,5-TMB as probe molecules and the catalytic transfor-
pore size distribution.10 However, these small gaseous mole- mation of 1,3,5-TMB to characterize the pore structure of
cules are not enough to monitor the real applications. Several hierarchical EU-1 zeolites synthesized from organofunc-
organic vapors with large molecular size are applied as probe tionalized fumed silica.
molecules to study the pore structure of porous materials,
especially for the pores with molecular sieve effects.11,12
Results and discussion
Xylenes and 1,3,5-trimethylbenzene (TMB) have been
applied as probes to study the adsorption and diffusion in
mesoporous zeolites in our previous studies.13,14 Moreover,
the use of catalytic reactions with probe molecules is also a
versatile tool to characterize the pore structure of a porous
catalysts.15 The activity and product selectivity are usually
analyzed to evaluate the pore structure based on the shape
selectivity effects on the sizes of reactant molecules, transi-
tion states, intermediates, and product molecules. TMB is
such a probe molecule and has three isomers with kinetic
molecular size in the order of 1,3,5-TMB > 1,2,3-TMB >
1,2,4-TMB. The transformation of TMBs can be catalyzed by
zeolites, among which isomerization between the TMB iso-
mers, disproportionation of TMBs to xylenes and tetrameth-
ylbenzenes (TeMBs), and dealkylation to xylenes, toluene,
benzene, and lower olefins have been recognized as the main
reaction pathways in this complex reaction system.16 Medium
pore zeolites including EU-1 impose significant steric con-
straints for large TMB molecules. Diffusion of TMBs into the
one-dimensional channel system of EU-1 is rather slow, and
the conversion of TMB over EU-1 zeolites is usually signifi-
cantly slow. It was shown that the transformation of 1,3,5-
TMB molecules occurs mainly on the “external” surface of
the zeolites with medium pore size.17
Characterization of the EU-1 zeolites
The EU-1 zeolites prepared using organofunctionalized
fumed silica as the silicon source (EU-1-1, 2) showed the
typical characteristic peaks of an EUO framework topology
structure, with similar crystallinity as compared to the con-
ventional microporous EU-1 zeolite synthesized with
unfunctionalized fumed silica (EU-1-0), as shown in the
X-ray diffraction (XRD) patterns in Figure 1(a). The
involvement of organic functional groups did not influence
the crystallization significantly. However, the N2-adsorption/
desorption results shown in Figure 1(b) confirmed the intro-
duction of mesopores into the EU-1 zeolites using organo-
functionalized fumed silica as the silicon source. As shown
in the N2 adsorption/desorption isotherms, the isotherm of
EU-1-0 has a small hysteresis loop in the high relative pres-
sure region, due to the nature of the small crystalline assem-
bled particle as shown in Supplemental Figure S1. The
adsorption increased gradually as the ratio of organic func-
tional groups increased, which is caused by the introduction
of mesopores. The pore structure parameters derived from
the isotherms are summarized in Table 1. The Brunauer-
Emmet-Teller (BET) surface area and pore volume of the
EU-1 zeolites increased with an increase in the functionali-
zation, which is related to the increase of mesoporosity. The
micropore volume remained similar among the EU-1
Hierarchical EU-1 zeolites with extra mesopores could
potentially improve the diffusion of large molecules within
the structure. Herein, we used the adsorption of toluene and

Guo et al.
3
EU-1-0
EU-1-1
EU-1-2
1.6
1.2
0.8
0.4
0.0
1.6
1.2
0.8
0.4
0.0
1.6
1.2
0.8
0.4
0.0
T = 293 K
T = 293 K
T = 293 K
T = 308 K
T = 323 K
T = 308 K
T = 323 K
T = 308 K
T = 323 K
0
5
10 15 20 25 30
0
5
10 15 20 25 30
0
5
10 15 20 25 30
Pressure (mbar)
Pressure (mbar)
Pressure (mbar)
(a)
(b)
(c)
Figure 2. Toluene adsorption isotherms of the EU-1 zeolites (EU-1-0 (a), EU-1-1 (b), EU-1-2 (c)) at different temperatures.
zeolites, while the pore volume due to the mesopores
100
increased from EU-1-0 to EU-1-2. The mesoporous EU-1
zeolites have similar composition compared with the con-
ventional EU-1. The framework Si/Al ratios of EU-1(0) and
EU-1(2) are 12.6 and 12.9, from the 29Si magic angle spin-
ning nuclear magnetic resonance (MAS-NMR) results.
EU-1-0
EU-1-1
EU-1-2
0.8
0.6
0.4
0.2
0.0
80
60
40
20
0
Toluene adsorption
Toluene was used as a probe molecule to characterize the
pore structure of the EU-1 zeolites. The toluene adsorption
isotherms of the EU-1 zeolites in the pressure range of
0–30mbar at three different temperatures are presented in
Figure 2. The conventional microporous EU-1 zeolite
showed the isotherm close to a type I isotherm (Figure
2(a)), which has a sharp increase of adsorption in the low-
pressure region corresponding to micropore filling, fol-
lowed by a plateau at higher pressures. The isotherms of the
hierarchical EU-1 zeolites shown in Figures 2(b) and (c)
are a combination of both type I and type IV isotherms,
which show adsorption at low pressure by micropores, but
also gradually increased adsorption at higher pressures by
mesopores. At the same temperature, the toluene adsorp-
tion by EU-1-2 is higher than those of EU-1-0 and EU-1-1,
which agrees well with the trend of the amount of
mesopores. It is therefore apparent and obvious that the
introduction of mesopores enhanced the adsorption of tolu-
ene by the EU-1 zeolites.
The temperature-programmed desorption (TPD)
curves in Figure 3 show the desorption of toluene from
the EU-1 zeolites with increasing the temperature. The
derivative curve (solid line) of the desorption curve
(dashed line) shows the desorption speed of toluene mol-
ecules from the EU-1 zeolites as a function of tempera-
ture. The desorption speed increased with the rising of
temperature and slowed down after reaching a peak at
around 80°C. The derivative curves have mainly one
peak at around 80°C with a small peak at around 280°C,
which indicates that the EU-1 zeolite has two adsorption
sites with one being the major adsorption site. It is worth
50 100 150 200 250 300 350 400
(ꢀ
T
C)
Figure 3. Toluene TPD curves for the EU-1 zeolites.
noting that the desorption of toluene occurs more easily
for the hierarchical zeolites (EU-1-1, 2) than for the con-
ventional microporous zeolite (EU-1-0). The peak at
around 80°C shifted to a lower temperature when the
mesoporosity increased, indicating the weaker interac-
tion between the adsorbate and adsorbent.
The adsorption kinetics of toluene on the EU-1 zeolites
were measured at 308K at a pressure range of 0.5–1mbar to
obtain the adsorption rate constant (k), and under a constant
pressure of 1mbar to determine the effective diffusion time
constant (Deff/R2). As shown in Figure 4(a) and (b), the hier-
archical EU-1 zeolites adsorb toluene much faster than the
conventional microporous EU-1 zeolite. The adsorption
speed increased with increasing mesoporosity. The kinetic
curves obtained in the pressure range of 0.5–1mbar were fit-
ted to the pseudo first-order kinetic model (equation (1)) to
give the adsorption rate constants (k), which are presented in
Table 2. The equation fitted well with the kinetic curve, as is
supported by the high values of R2. The adsorption rate con-
stant (k) reflects the adsorption rate of an adsorbate being
adsorbed onto an adsorbent. A high adsorption rate constant
(k) indicates a high adsorption rate. In the adsorption of tolu-
ene, the hierarchical EU-1 zeolites with mesopores have
higher values of adsorption rate constants (k) compared with
conventional microporous EU-1 zeolite, and the k values

4
Journal of Chemical Research 00(0)
Table 2. The adsorption rate constants (k values) and effective
diffusion time constants (Deff/R2) of toluene adsorption on the
EU-1 zeolites.
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
k (s−1)
R2
Deff/R2 (s−1)
R2
ꢀ
ꢀ
Sample
5.1×10−5
5.1×10−4
2.0×10−3
0.9951
0.9980
0.9997
P = 0.5-1 mbar
EU-1-0
EU-1-1
P = 1 mbar
EU-1-0
EU-1-1
EU-1-2
EU-1-0
EU-1-1
EU-1-2
0.006
0.019
0.073
0.9963
0.9947
0.9876
EU-1-2
0
40 80 120 160 200 240
0
300 600 900 1200 1500 1800
Time (s)
Time (s)
(a)
(b)
EU-1-1 to EU-1-2. As shown in Table 3, the adsorption rate
constant (k) of EU-1-2 is larger than that of EU-1-1, which
is attributed to the fact that the increased mesoporosity
allows much faster adsorption into the adsorption site
within the EU-1 zeolites. The effective diffusion time con-
stant (Deff/R2) of EU-1-2 increased compared with that of
EU-1-1, confirming the dramatically improved diffusion of
1,3,5-TMB into the adsorption site of the hierarchical EU-1
zeolites due to the increased mesoporosity.
Figure 4. The toluene adsorption kinetics on the EU-1 zeolites
at 308K, under pressure of 0.5-1 mbar (a) and 1mbar (b).
increased with the increasing of mesoporosity following the
order of EU-1-0<EU-1-1<EU-1-2.
The effective diffusion time constants (Deff/R2) were
extracted from the kinetic curves obtained under a constant
pressure of 1mbar following equation (3) and are presented
in Table 2. The high values of R2 showed good fitness. The
effective diffusion time constant (Deff/R2) is an indicator of
the diffusion rate of an adsorbate being adsorbed into an
adsorbent, which excludes the influence of the morphology
of the zeolite particle by involving the radius (R). A high
effective diffusion time constant (Deff/R2) refers to a high
diffusion rate. It can be seen that the introduction of mes-
oporosity dramatically improved the diffusion of toluene
into the adsorption site of EU-1 zeolites, which is indicated
by the higher Deff/R2 value of hierarchical EU-1 zeolites
than that of the conventional microporous EU-1 zeolite,
following the same order as the adsorption rate constants
(k): EU-1-0<EU-1-1<EU-1-2.
The catalytic transformation of 1,3,5-TMB was applied
as a probing reaction for the hierarchical EU-1 zeolites,
which is a complex reaction including mainly isomeriza-
tion and disproportionation.16,18–20 Moreover, the products
of these reactions can react with each other and with the
original reactants as well.16 The conversion of bulky mole-
cules tends to be more diffusion controlled, because the
majority of the active sites of the zeolite are within its
pores. Since the kinetic diameter of the 1,3,5-TMB mole-
cule is larger than the pore openings of EU-1 zeolite with a
one-dimensional pore system, the reaction of 1,3,5-TMB is
presumed to occur only on the external surface of the
10-MR EU-1 zeolite,21 which is supported by the low con-
version of 1,3,5-TMB over the conventional microporous
EU-1 zeolite as shown in Figure 7(a). The active sites
within the micropore system of EU-1 zeolite are not acces-
sible to the 1,3,5-TMB molecules. However, the hierarchi-
cal EU-1 zeolites with more mesopores show higher
conversions (roughly doubled) compared to the conven-
tional microporous EU-1 zeolite. It is well known that the
transport and diffusion of reactants and products influences
the outcome of the reaction.22,23 As has been confirmed by
the adsorption performance, the introduction of mesopores
dramatically improved the adsorption and diffusion of
1,3,5-TMB molecules within the hierarchical EU-1 zeo-
lites. The improved activity of hierarchical EU-1 zeolites in
the transformation of 1,3,5-TMB is largely contributed to
the enhanced diffusion of the reactant molecules and the
improved accessibility of active sites by mesopores. The
conversion of 1,3,5-TMB over all the studied EU-1 zeolites
dropped with longer time on stream in the continuous reac-
tion, which is caused by the deactivation of the active sites
located in the pore openings close to the surface.
1,3,5-TMB adsorption and catalytic
transformation
The 1,3,5-TMB adsorption isotherms of the EU-1 zeolites
were measured at three different temperatures (308, 323,
and 338K) and are presented in Figure 5. It can be seen in
Figure 5(a) that EU-1-0 has a very low adsorption of 1,3,5-
TMB, which is attributed to the fact that 1,3,5-TMB mole-
cules with a molecular size of 0.87nm cannot be adsorbed
into the one-dimensional channel of EU-1 zeolite (pore
opening is 0.58×0.41nm). The adsorption of 1,3,5-TMB
can only happen on the external surface of the microporous
EU-1-0. However, with the increase of mesoporosity in the
hierarchical EU-1 zeolites, the adsorption of 1,3,5-TMB
increased gradually (Figures 5(b) and (c)). It is obvious that
the introduction of mesopores offers more adsorption sites
for larger molecules in the hierarchical EU-1 zeolites.
The adsorption kinetic curves of 1,3,5-TMB on the hier-
archical EU-1 zeolites are shown in Figure 6(a) and (b).
The conventional microporous EU-1 has very limited
adsorption of 1,3,5-TMB, which is not presented. 1,3,5-
TMB has a larger molecular size than toluene and cannot
enter the 10-MR pores of EU-1 zeolite. However, the
adsorption speed of 1,3,5-TMB increased when the mes-
oporosity of the hierarchical EU-1 zeolites increased from
As shown in Table 4, the products of the transformation
of 1,3,5-TMB are mainly those derived from isomerization,
disproportionation, transalkylation, and dealkylation reac-
tions.16,18,23 In the isomerization reaction, 1,3,5-TMB was
isomerized into 1,2,4-TMB and 1,2,3-TMB, following the
potential monomolecular mechanism.16 In the dispropor-
tionation reaction, one 1,3,5-TMB molecule reacts with
another by transfer of one methyl group leading to one

Guo et al.
5
EU-1-0
EU-1-1
EU-1-2
1.5
1.2
0.9
0.6
0.3
0.0
1.5
1.2
0.9
0.6
0.3
0.0
1.5
1.2
0.9
0.6
0.3
0.0
T = 308 K
T = 308 K
T = 308 K
T = 323 K
T = 338 K
T = 323 K
T = 338 K
T = 323 K
T = 338 K
0
1
2
3
4
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Pressure (mbar)
Pressure (mbar)
Pressure (mbar)
(a)
(b)
(c)
Figure 5. 1,3,5-TMB adsorption isotherms of the EU-1 zeolites (EU-1-0 (a), EU-1-1 (b), EU-1-2 (c)) at different temperatures.
Table 3. The adsorption rate constants (k values) and effective
diffusion time constants (Deff/R2) of 1,3,5-TMB adsorption on
the EU-1 zeolites.
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
k (s−1)
R2
Deff/R2 (s−1)
R2
ꢀ
ꢀ
Sample
EU-1-1
EU-1-2
0.014
0.103
0.9966
0.9932
4.5×10−4
2.7×10−3
0.9993
0.9977
P = 0.5-1 mbar
EU-1-1
EU-1-2
P = 1 mbar
EU-1-1
EU-1-2
50 100 150 200 250
Time (s)
0
20
40
60
80
0
Time (s)
(a)
I/D ratio showed some differences among the various EU-1
zeolites under different conditions. The I/D ratios over hier-
archical EU-1 are higher than those obtained from the con-
ventional microporous EU-1 zeolite, which indicates that
more isomerization occurred over the hierarchical EU-1
zeolites due to the improved diffusion of reactants and
enhanced accessibility of the active sites in the mesopores.
The conversions of 1,3,5-TMB are similar over EU-1-1 and
EU-1-2, and the I/D ratio could be reasonably compared
between the two hierarchical EU-1 zeolites. It can be seen
in Figure 7(b) that the I/D ratio over EU-1-2 is higher than
that over EU-1-1, which is attributed to that the diffusion of
reactants was enhanced and isomerization can happen more
easily with a higher mesoporosity.
(b)
Figure 6. 1,3,5-TMB adsorption kinetics on the EU-1 zeolites
at 308K, under pressure of 0.5-1 mbar (a) and 1mbar (b).
xylene and one TeMB molecule, followed by a bimolecular
mechanism.23,24 The product distribution in Table 4 shows
that 1,2,4-TMB and 1,2,3-TMB are the major products,
among which 1,2,4-TMB was formed with a much higher
rate than 1,2,3-TMB, since the diameter of 1,2,4-TMB is
smaller than that of 1,2,3-TMB and the rate of formation is
kinetically controlled by the pore system. It is obvious that
isomerization is the main reaction in the catalytic transfor-
mation of 1,3,5-TMB over the EU-1 zeolites, which is quite
different from the reaction over USY zeolite.18 The isomer-
ization of 1,3,5-TMB into 1,2,4-TMB and 1,2,3-TMB
accounts for more than 90% of the product selectivity,
which agrees well with the findings of Röger et al.,21 who
reported that isomerization reached a selectivity of about
90% in the 1,2,4-TMB transformation over HZSM-5 zeo-
lite and that the 1,2-methyl-shift was shown to take place
on the external surface of the zeolite crystal. It has also
been demonstrated by Se-Ho et al.17 that the isomerization
of 1,2,4-TMB occurs mostly on the external surface of the
10-MR zeolite, while disproportionation happened in the
microporous channel system. From the product distribu-
tion, the ratios of isomerization to disproportionation (I/D
ratio) from different times on stream were calculated and
are presented in Figure 7(b). Although the isomerization is
the main reaction in the transformation of 1,3,5-TMB, the
Conclusion
The pore structure of hierarchical EU-1 zeolites, prepared
using organofunctionalized fumed silica as the silicon
source, is characterized using the adsorption of toluene
and 1,3,5-TMB as probe molecules, and the transforma-
tion of 1,3,5-TMB as the probe reaction. The hierarchical
EU-1 zeolites showed significantly improved adsorption
and diffusion of bulky molecules compared with the con-
ventional microporous EU-1 zeolite. The toluene and
1,3,5-TMB adsorption capacity of hierarchical EU-1 zeo-
lites increased with increasing mesoporosity. The toluene
TPD results showed that the desorption of toluene occurs
more easily for the hierarchical zeolites than for the con-
ventional microporous zeolite. In addition, the adsorption
kinetics of toluene and 1,3,5-TMB showed that the

6
Journal of Chemical Research 00(0)
Table 4. The distribution (mol%) of aromatic products
obtained from the EU-1 zeolites after a time of 6h on stream at
673K.
28
24
20
16
12
25
20
15
10
5
1 h
2 h
4 h
6 h
Aromatic aromatics
HEU-1-0
HEU-1-1
HEU-1-2
HEU-1-0
HEU-1-1
HEU-1-2
Benzene
Toluene
Xylenes
1,2,4-TMB
1,2,3-TMB
TeMBs
0.85
2.03
4.40
83.12
7.10
2.50
0.31
1.63
2.87
86.58
6.98
1.65
0.58
1.37
2.56
87.21
6.75
1.53
0
HEU-1-0 HEU-1-1 HEU-1-2
1
2
3
4
5
6
Reaction time (h)
Catalyst
(a)
(b)
TMB: trimethylbenzene.
Figure 7. (a) Conversion of 1,3,5-TMB over the EU-1 zeolites
and (b) the ratio of isomerization to disproportionation (I/D
ratio) at 673K.
of the organic moiety of the organofunctionalized fumed
silica as 17.5% and 30.5%, which corresponds to x = 0,
0.072, and 0.182, respectively.
increased mesoporosity in the hierarchical EU-1 zeolites
resulted in higher adsorption rates and faster diffusion for
large molecules.
The synthesis of hierarchical EU-1 zeolites was started
from a solution prepared by mixing distilled H2O, NaOH,
NaAlO2, HMBr2 (hexamethonium bromide), NaF, NH4NO3,
seed (0.5wt% of the total solution) and organofunctional-
ized fumed silica, according to the molar composition of 60
SiO2/Al2O3/5.5 Na2O/700 H2O/2 NH4NO3/2 NaF/6 HMBr2.
After being stirred at room temperature for 4h, the resulting
gel was transferred into an autoclave and heated at 373 for
18h, followed by crystallization at 413K for 12days. The
resulting product was washed with distilled H2O until the
pH was neutral, and then dried at 373K for 12h, followed
by calcination under an air atmosphere at 873K for 5h. The
hierarchical EU-1 zeolites were coded as EU-1-n (n = 1, 2,
following the increase of organic functionalization). A con-
ventional microporous EU-1 was synthesized following the
same process but with fumed silica without functionaliza-
tion and was named EU-1-0.
To make the catalysts for 1,3,5-TMB transformation,
the EU-1 zeolites were subjected to ion-exchange three
times using 1M NH4NO3 with a liquid-to-solid ratio of
100mL/g at 333K for 2h. After being washed with dis-
tilled H2O, dried at 373K for 12h and calcinated at 823K
for 5h, the catalysts were obtained and named as HEU-
1-n (n = 0, 1, 2).
Because of the enhanced diffusion of the bulky reactant
molecules and improved accessibility of active sites within
the EU-1 zeolite pore system, the conversion was doubled
in the transformation of 1,3,5-TMB over the hierarchical
EU-1 zeolites compared with the conventional micropo-
rous EU-1 zeolite. The product I/D ratios in the reaction
catalyzed by the hierarchical EU-1 zeolites were higher
than those over the microporous EU-1 zeolite, which is
ascribed to the better diffusion and improved accessibility
of active sites in the mesopores of the hierarchical EU-1
zeolites.
It can be concluded that the significantly improved
adsorption and diffusion of toluene and 1,3,5-TMB and the
catalytic performance in the transformation of 1,3,5-TMB
confirmed the improvement of mesoporosity in the hierar-
chical EU-1 zeolites using organofunctionalized fumed
silica as the silicon source, which leads to more active sites
in the one-dimensional pore system with 10-MR channels
accessible to large reactant molecules. Such hierarchical
EU-1 zeolites could further enhance the catalytic perfor-
mance in reactions involving other bulky molecules.
Experiment
Characterization
Preparation of hierarchical EU-1 zeolite
The powder XRD patterns of the as-synthesized EU-1 zeo-
lites in the range of 5°–35° were recorded on a Shimadzu
XRD-6000 diffractometer with CuKα radiation, using a
step size of 0.02° and a counting time of 10s. Quantachrome
QUADRASORB SI equipment was used to obtain the N2
adsorption–desorption isotherms (77K). Before each meas-
urement, the sample was degassed at 613K under vacuum
for 5h. The total surface area, SBET, was obtained from the
BET equation; the micropore volume (Vmic) was calculated
from the t-plot method; the total pore volume (Vtot) was
measured from the N2 adsorption at a relative pressure p/p0
of 0.99. The mesopore volume (Vmeso) was calculated from
Hierarchical EU-1 zeolites were prepared using organo-
functionalized fumed silica as the silicon source, following
the protocol we developed previously.9 The fumed silica
was functionalized with TPOAC (dimethyloctadecyl[3-
(trimethoxysilyl)propyl]ammonium chloride) according to
the molar ratio of SiO2/x organosilane/6 CH3OH/60 H2O (x
= 0.072, 0.182). In a typical process, 20g of fumed silica
(Degussa, Aerosil 200) was dissolved in 400mL of distilled
water. The mixture was stirred (100r/min) under reflux at
373K for 1h, before 20mL of TPOAC (here x is 0.182)
was added, and the mixture was continuously refluxed for
another 8h at 373K. After being washed thoroughly with
ethanol and dried at 393K for 12h, organofunctionalized
fumed silica with different ratios was obtained.
Thermogravimetric (TG) analyses indicated the percentage
the difference between Vtot and Vmic.
29Si solid-state MAS-
NMR spectroscopy analysis was performed on a Bruker
Avance III 500-MHz spectrometer operating at resonance
frequencies of 99.36MHz.

Guo et al.
7
reactor. Prior to the reaction, the catalyst was pelletized,
crushed, sieved into particles with a size of 200–400µm,
and loaded into the reactor, followed by in situ heat treat-
ment at 723K under a nitrogen atmosphere for 4h. The
weight hourly space velocity (WHSV) of 1,3,5-TMB was
kept at 0.26h−1. The product effluents were analyzed
online using an Agilent 7890B gas chromatograph
equipped with a flame ionization detector (FID) and a
HP-AL/S capillary column. The products were studied
according to different aspects: the I/D ratio is calculated by
I/D=(1,2,4-TMB+1,2,3-TMB,mole)/(xylenes+TeMBs,
mole).
Adsorption of toluene and 1,3,5-TMB
The adsorption isotherms and kinetic curves with toluene
and 1,3,5-TMB as the adsorbates using the EU-1 zeolites
were measured on an intelligent gravimetric analyzer (IGA-
002; Hiden, Warrington, UK). The apparatus has a very
sensitive microbalance with an accuracy of ±0.1μg to
record the weight changes of the adsorbents under the con-
trol of a computer.
Before the adsorption measurements, the EU-1 zeolites
(50mg) were treated at 673K under a vacuum of 10−7 mbar
for 5h to remove the impurities and moisture until the sam-
ple weight became constant. After being cooled to the set
temperature (308–338K in this study), the vapor of the
adsorbate was gradually introduced into the sample chamber
until the set pressure was reached. The adsorption isotherms
were obtained by recording the mass changes at the set pres-
sures (0–30mbar for toluene and 0–6mbar for 1,3,5-TMB)
when the adsorption reached equilibrium.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The TPD curves of toluene on the EU-1 zeolites was
obtained from the same equipment by recording the weight
changes of the saturated samples at 298K under a vacuum of
10−7 mbar, while the temperature increased from 298 to
673K.
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: The
study was supported by the Applied Basic Research Program of
Shanxi Province (no. 201801D221127).
The kinetic curves at 308K were obtained by recording
the mass change with time, in the pressure range of 0.5–
1mbar, and at a constant pressure of 1mbar, respectively.
The kinetic curves obtained at the pressure range of 0.5–
1mbar were fitted to the pseudo first-order kinetic model
(equation (1))25
ORCID iD
Wenming Hao
https://orcid.org/0000-0002-4176-1899
Supplemental material
Supplemental material for this article is available online.
qt = q∞ 1− e−kt
(
)
(1)
References
where k is the pseudo first-order rate constant, t is the
adsorption time, and q∞ and qt are the adsorption capacity
of the adsorbent at equilibrium and at time t, respectively.
Assuming the morphology of the sorbent particle is
spherical, the kinetic curves obtained at a constant pressure
of 1mbar were fitted by the following equation (2) to calcu-
late the diffusion coefficient (D)26
1. Martins J, Birot E, Guillon E, et al. Micropor Mesopor Mat
2013; 171: 238.
2. Ahmed MHM, Muraza O, Yoshioka M, et al. Micropor
Mesopor Mat 2017; 241: 79.
3. Mota FM, Eliášová P, Jung J, et al. Catal Sci Technol 2016;
6: 2735.
4. Ahmed MHM, Muraza O, Al-Amer AM, et al. Appl Catal A:
Gen 2015; 497: 127.
∞
5. Li XF, Ren PC, Zhang YT, et al. Chinese J Chem Eng 2016;
24: 1577.
6. Rahbari ZV, Khosravan M and Kharat AN. Russ J Appl
Chem 2017; 90: 1315.
7. Pan SX, Wu QM, Wang X, et al. Micropor Mesopor Mat
2016; 235: 246.
8. Li KH, Valla J and Garcia-Martinez J. Chemcatchem 2014;
6: 46.
9. Dai G, Ma JH, Xiao H, et al. Mater Res Bull 2018; 100: 76.
10. Thommes M, Kaneko K, Neimark AV, et al. Pure Appl
Chem 2015; 87: 1051.
11. Van Bavel E, Meynen V, Cool P, et al. Langmuir 2005; 21:
2447.
qt
6
π2
1
n2
= 1−
exp(−n2π2Dt/R2 )
(2)
∑
q∞
n=1
The simplified version of equation (2) is
qt
6
Dt
(3)
=
q∞
R
π
where q∞ is the adsorption capacity of the adsorbent at equi-
librium, qt is the adsorption at time t, R is the radius of the
assumed adsorbent sphere, t is the adsorption time, and D
refers to the diffusion coefficient. Considering the zeolite
crystal is not spherical, the effective diffusion time constant
Deff/R2 was applied to eliminate the effect of morphology
from the zeolite crystal in this study.
12. Vinh Thang -H, Huang QL, Eic M, et al. Langmuir 2005; 21:
5094.
13. Xu D, Ma JH, Song AX, et al. Adsorption 2016; 22: 1083.
14. Song AX, Ma JH, Xu D, et al. Catalysts 2015; 5: 2098.
15. Weitkamp J and Ernst S. Catal Today 1994; 19: 107.
16. Al-Khattaf S, Akhtar MN, Odedairo T, et al. Appl Catal A:
Gen 2011; 394: 176.
Transformation of 1,3,5-TMB
Transformations of 1,3,5-TMB were carried out at 673K
under atmospheric pressure in a continuous flow fixed bed
17. Se-Ho P and Hyun-Ku R. Catal Today 2000; 63: 267.
18. Tukur NM and Al-Khattaf S. Energ Fuel 2007; 21: 2499.

8
Journal of Chemical Research 00(0)
19. Waziri SM, Aitani AM and Al-Khattaf S. Ind Eng Chem Res 23. Čejka J, Kotrla J and Krejčí A. Appl Catal A: Gen 2004; 277:
2010; 49: 6376. 191.
20. Al-Khattaf S, Ali SA, Aitani AM, et al. Catal Rev 2014; 56: 24. Odedairo T, Balasamy RJ and Al-Khattaf S. Catal Sci
333. Technol 2012; 2: 1275.
21. Röger HP, Möller KP and O’Connor CT. J Catal 1998; 176: 68. 25. Lagergren S. Veternskapsakad Handl 1898; 24: 1.
22. Li YC, Wang H, Dong M, et al. Rsc Adv 2015; 5: 66301. 26. Karge HG and Weitkamp J. Springer, 2008.