Facile preparation of nanocrystal-assembled hierarchical mordenite zeolites with remarkable catalytic performance

Article abstract of DOI:10.1016/S1872-2067(15)60960-3

The present study reports a novel strategy to fabricate nanocrystal-assembled hierarchical MOR zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the c-axis, which facilitates mass transfer in the 12-membered ring channels of MOR zeolite for the conversions involving bulky molecules. The facile method involves the combined use of tetraethylammonium hydroxide (TEAOH) and commercial surfactants, in which TEAOH is essential for the construction of nanocrystal assemblies. The surfactant serves as a crystal growth-inhibiting agent to further inhibit nanocrystalline particle growth, resulting in enhanced mesoporosity. The hierarchical MOR assembled particles, constructed of 20-50-nm crystallites, exhibit superior catalytic properties in the alkylation of benzene with benzyl alcohol compared with the control sample, as the hierarchical MOR possesses a larger external surface area and longer c-axis dimension. More importantly, the material shows improved activity and stability in the dimethyl ether carbonylation to methyl acetate reaction, which is a novel route to produce ethanol from syngas.

Full text of DOI:10.1016/S1872-2067(15)60960-3

Chinese Journal of Catalysis 36 (2015) 1910–1919
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Facile preparation of nanocrystal‐assembled hierarchical mordenite
zeolites with remarkable catalytic performance
Yangyang Yuan a,b,c, LinyingWanga,b, Hongchao Liua,b, PengTiana,b,#, Miao Yanga,b, Shutao Xua,b,
ZhongminLiua,b,
*
a National Engineering Laboratory for Methanol to Olefins, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning,
China
b Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
c University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The present study reports a novel strategy to fabricate nanocrystal‐assembled hierarchical MOR
zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the
c‐axis, which facilitates mass transfer in the 12‐membered ring channels of MOR zeolite for the
conversions involving bulky molecules. The facile method involves the combined use of tetrae‐
thylammonium hydroxide (TEAOH) and commercial surfactants, in which TEAOH is essential for
the construction of nanocrystal assemblies. The surfactant serves as a crystal growth‐inhibiting
agent to further inhibit nanocrystalline particle growth, resulting in enhanced mesoporosity. The
hierarchical MOR assembled particles, constructed of 20–50‐nm crystallites, exhibit superior cata‐
lytic properties in the alkylation of benzene with benzyl alcohol compared with the control sample,
as the hierarchical MOR possesses a larger external surface area and longer c‐axis dimension. More
importantly, the material shows improved activity and stability in the dimethyl ether carbonylation
to methyl acetate reaction, which is a novel route to produce ethanol from syngas.
Received 16 July 2015
Accepted 18 July 2015
Published 20 November 2015
Keywords:
Nanocrystal‐assembled
Mordenite
Tetraethylammonium hydroxide
Surfactant
Catalytic activity
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
channel (0.65 nm × 0.70 nm), a compressed 8‐MR channel
(0.26 nm × 0.57 nm) parallel to the c‐axis, and an additional
Zeolites are important heterogeneous catalysts in oil refin‐
ing and petrochemical industries because of their unique pore
structures, large surface area, strong acidity, and excellent hy‐
drothermal stability [1,2]. Mordenite (MOR), one of the most
important members in the zeolite family, has exhibited excel‐
lent performance in catalysis, such as toluene disproportiona‐
tion, hydroisomerization, alkylation, dimethylamine synthesis,
and dimethyl ether carbonylation [3–5]. The channel system of
MOR zeolite consists of a straight 12‐membered ring (MR)
8‐MR channel (0.34 nm × 0.48 nm) along the b‐axis [6]. How‐
ever, MOR is generally referred to as a one‐dimensional zeolite
as the 8‐MR channels are too small for most molecules to in‐
gress. This unique pore structure may impose severe diffusion
limitations in catalytic processes, leading to underutilization of
the active sites and resulting in rapid deactivation, especially
for the reactions involving bulky molecules [7–9]. In recent
years, the quest for enhancing the catalytic efficiency and pro‐
longing catalyst life has stimulated much research on improv‐
* Corresponding author. Tel: +86‐411‐84379998; Fax: +86‐411‐84379289; E‐mail: liuzm@dicp.ac.cn
# Corresponding author. Tel: +86‐411‐84379218; Fax: +86‐411‐84379289; E‐mail: tianpeng@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21101150, 21476228, 21473182).
DOI: 10.1016/S1872‐2067(15)60960‐3 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 11, November 2015

Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
1911
ing the mass transport properties.
sembled morphology with a longer c‐direction dimension. In
addition, the hierarchical zeolite is applied as a catalyst for the
dimethyl ether (DME) carbonylation to methyl acetate (MA)
reaction, which is a novel route to produce ethanol from syn‐
gas.
Integrating mesopores into the zeolite structures or de‐
creasing the crystal size has proven to be an effective way to
overcome the inherent diffusion limitations and improve the
catalysis efficiency of zeolites [10–23]. Mesoporous MOR zeo‐
lites are hitherto mainly synthesized via a top‐down approach
through dealumination or sequential dealumination‐desilica‐
tion treatment [9,24,25]. A one‐step, bottom‐up synthesis of
mesoporous MOR is highly desirable; however, this remains a
challenging task, despite the significant developments in the
synthesis of hierarchical zeolites, such as ZSM‐5 and beta. Re‐
cently, Xiao and co‐workers [26] successfully synthesized mi‐
2. Experimental
2.1. Materials and synthesis
The chemical reagents used in the experiments included
NaAlO2 (54.5% Al2O3, 40.9% Na2O, Tianjin Guangfu Chemical
Co.), colloidal silica (30.1% SiO2, Qingdao Chengyu Chemical
Co.), TEAOH (25.0% in water, Xiamen Pioneer Technology Co.,
Ltd.), NaOH (Tianjin Kemiou Chemical Reagent Co.), C12H25‐
cro‐sized MOR nanofiber bundles when assisted by
a
self‐designed cationic copolymer containing quaternary am‐
monium groups. Jo and Ryoo et al. [27] reported a zeo‐
lite‐seeding route to synthesize mesoporous MOR zeolite with
nanorod‐like morphology by employing organosilane surfac‐
tants as a mesopore‐generating agent. Very recently, Li and
co‐workers [28] synthesized H‐MOR nanosheet assemblies
through a conventional hydrothermal reaction in the absence
of templating agents. However, the above‐mentioned MOR
nanofibers and nanorods show a narrowed a‐b cross section,
whereas the growth along the c‐axis direction is less inhibited,
suggesting that the 12‐MR channels in these hierarchical MOR
zeolites have the longest dimension and implying that the mass
transport in this direction remains restricted.
Synthesis of zeolite nanocrystals with reduced size in three
dimensions decreases the diffusion pathway irrespective of the
direction of travel. There are, however, only a few examples
reported where nanocrystalline MOR have been effectively
synthesized in such a manner. Kubota’s group [29] has report‐
ed the preparation of MOR nanocrystals of ~80 nm in diameter
using a hydrophobic structure‐directing agent, N,N,N’,N’‐tetra‐
ethylbicyclo[2.2.2]oct‐7‐ene‐2,3:5,6‐dipyrrolidinium. In addi‐
tion, the divalent cation N,N,N,N’,N’,N’‐hexaethylpentanediam‐
monium was also reported to direct the synthesis of nanoscale
MOR [30,31]. Recently, Ryoo et al. [32] developed a multivalent
surfactant‐capping route to synthesize nanocrystalline zeolites
including MOR, FAU, CHA, and MFI. By using a self‐designed
prolinol derivative surfactant C18H37N+(Me)2C6H12N+(CH3)2
CH2C6H4CH2N+(CH3)(C4H7CH2OH) as a capping agent, MOR
nanocrystals could be readily prepared. They attributed the
nanocrystal formation to the multiple valencies on the surfac‐
tant and thereby the introduction of a strong binding effect of
the surfactant molecules on the substrate surfaces compared
with monovalent surfactants.
N+(CH3)2‐C2H4‐N+(CH3)2‐C12H25Br2 (C12‐2‐12
, Henan Titaning
Chemical Technology Co.), hexadecyltrimethylammonium
bromide (CTAB, Energy Chemical), sodium dodecylbenzene‐
sulphonate (SDBS, Energy Chemical), and Pluronic F‐127 (Mr =
12600 g/mol, Sigma). All the above reagents were used without
further purification.
A typical synthesis procedure was as follows. NaOH and
surfactant (C12‐2‐12) were dissolved in H2O to prepare a clear
solution. Thereafter, TEAOH was added to the solution drop‐
wise followed by the addition of NaAlO2. Then, colloidal silica
was added to the mixture under vigorous stirring. The final
mixture with a composition of SiO2:0.033Al2O3:0.25Na2O:
0.10TEAOH:0.05C12‐2‐12:40H2O was stirred for additional 3 h to
obtain a homogenous gel prior to being transferred into a
stainless steel autoclave. The sol‐gel was subjected to hydro‐
thermal crystallization at 130 °C for 5–7 d and rotated at 60
rpm. The products were recovered by centrifugation, washed
with deionized water, dried overnight at 120 °C and finally
calcined at 550 °C for 5 h to remove the organic species. The
protonated samples were obtained by ion exchange with
NH4NO3 aqueous solution (1 mol/L, 1 g calcined sample in 10
mL solution) at 80 °C under stirring. The ion exchange was
repeated three times and every ion exchange solution was for 2
h. The samples were recovered by centrifugation, washed with
deionized water, and dried at 120 °C before calcination at 550
°C for 4 h.
2.2. Characterization
Powder XRD patterns were recorded on a PANalytical X’Pert
PRO X‐ray diffractometer with Cu Kα radiation (λ = 0.154059
nm) and a scan step width of 0.026°. The chemical composition
of the samples was measured using a Philips fluorescence (XRF,
Magix‐601 X‐ray) spectrometer. Morphology was observed
using scanning electron microscopy (SEM, SU8020). N2 adsorp‐
tion‐desorption isotherms were obtained on a Micromeritics
ASAP 2020 system at –196 °C. The total surface area was cal‐
culated based on the BET model. Micropore volume and mi‐
cropore surface area were calculated using the t‐plot method.
Pore size distribution of the mesopores was determined by the
BJH method based on the desorption branch of the isotherms.
Solid state NMR experiments were performed on a Varian
Herein, we report a facile and direct approach to synthesize
nanocrystal‐assembled hierarchical MOR zeolites by subjecting
the crystallization to relatively low temperatures (130 °C) in
the presence of tetraethylammonium hydroxide (TEAOH) and
commercial surfactant. The role of TEAOH and surfactants in
the generation of the hierarchical assembled structure is inves‐
tigated in detail and the physicochemical properties of the
products are well characterized. The catalytic performance of
the hierarchical MOR zeolites is evaluated via the benzylation
of benzene with benzyl alcohol (BA) and compared with the
control sample and hierarchical MOR having nanosheet‐as‐

1912
Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
Infinity Plus 400 WB spectrometer with a BBO MAS probe op‐
erating at a magnetic field strength of 9.4 T. The resonance
frequencies were 104.2 and 79.4 MHz for 27Al and 29Si, respec‐
tively. Chemical shifts were referenced to Al(NO3)3 (1.0 mol/L)
for 27Al and 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate sodium salt
(DSS) for 29Si. The spinning rates of the samples at the magic
angle were 4 and 6 kHz for 27Al and 29Si, respectively.
Temperature‐programmed desorption of ammonia (NH3‐
TPD) was measured on a Micromeritics 2920 chemical adsorp‐
tion instrument. After pre‐treating the samples at 650 °C for 1 h
under flowing He, the samples (40–60 mesh, 0.20 g) were
cooled down to 150 °C and saturated with NH3 gas. Thereafter,
NH3‐TPD was performed in a constant flow of He (20 mL/min)
from 150 to 650 °C at a heating rate of 10 °C/min.
mospheric pressure. In a typical run, 34 mL of benzene was
added with 0.20 g catalyst, which had been pre‐calcined at 500
°C for 4 h. The reaction mixture was stirred at 80°C for 30 min,
followed by the addition of 2.0 mL of BA. Liquid samples were
withdrawn at intervals. The liquid products were analyzed by
gas chromatography using an Agilent 7890 connected to an FID
detector using a 50‐m HP‐5 column. The products were identi‐
fied by GC‐MS analysis.
3. Results and discussion
3.1. Synthesis and characterization of nanocrystal‐assembled
hierarchical MOR zeolites
1,3,5‐triisopropylbenzene (TIPB) cracking was performed
in a fixed‐bed reactor at atmospheric pressure. The sample
(40–60 mesh, 200 mg) was loaded into the reactor and dehy‐
drated in N2 (50 mL/min) at 500 °C for 1 h prior to the reaction.
The temperature of the catalyst bed was adjusted to 210 °C
under N2 and fed with vaporized TIPB (85 °C) in N2 (50
mL/min). The products were analyzed online by gas chroma‐
tography (Agilent 6890) attached to an FID detector using an
HP‐5 column.
Nanocrystal‐assembled hierarchical MOR zeolite (designat‐
ed as MOR‐M) was hydrothermally synthesized in the presence
of TEAOH and surfactant C12‐2‐12 at 130 °C. The reproducible
synthetic conditions are summarized in Table 1. For compari‐
son, the material synthesized under similar conditions in the
absence of TEAOH and surfactant is used as a control sample
(designated as MOR‐C, sample 12 in Table 1). Fig. 1 shows the
XRD patterns of MOR‐M (sample 1) and MOR‐C, which exhibit
characteristic diffraction peaks of mordenite structure and
confirm the phase purity of the samples. SEM micrographs pro‐
vide detailed information on the morphology of the samples. As
shown in Fig. 2(a), MOR‐M consists of near‐spherical particles
with rough surfaces ranging from 10 to 20 μm. Increased mag‐
nification (Fig. 2(b)) reveals that these aggregates are com‐
posed of interconnected nanocrystallites, forming an abun‐
dance of interstitial voids, generating a hierarchical structure.
Fig. 2(c) displays the TEM micrograph of MOR‐M, from which
nanocrystals possessing 20 to 50‐nm dimensions could be
clearly observed. This nanocrystal‐assembled morphology is
believed to be favorable for catalytic reactions because of the
shortened diffusion path. Furthermore, the formation of the
nanocrystal assemblies benefits solid‐liquid separation after
the synthesis. Indeed, the spherical architectures of MOR‐M are
very stable, preserving their morphology almost intact after
2.3. Catalytic performance
DME carbonylation experiments were performed in a con‐
tinuous flow fixed‐bed stainless steel reactor. The catalyst
(40–60 mesh, 1.0 g) was packed in the reactor and pre‐treated
under N2 at 500 °C for 2 h. The catalyst sample was cooled to
200 °C prior to a reactant gas mixture (5% DME, 35% CO, and
60% H2) being introduced into the reactor at a gas hourly space
velocity (GHSV) of 1500 mL/(g·h). Reaction pressure was 2.0
MPa. The outlet gas was analyzed online using a gas chromato‐
graph (Agilent 7890A) equipped with TCD and FID detectors.
The liquid phase benzylation of benzene with BA was per‐
formed in a three‐necked round‐bottom flask equipped with a
reflux condenser and heated in an oil bath at 80 °C under at‐
Table 1
Summary of synthetic conditions and textual properties of the MOR products.
Starting gel composition a
Surface areac (m2/g)
Pore volumec (cm3/g)
Sample
Si/Alb
x
y
SBET
Smicro
369
352
302
371
330
316
343
340
367
364
370
344
Sext
102
76
Vmicro
0.17
0.16
0.14
0.17
0.16
0.15
0.16
0.16
0.17
0.17
0.17
0.16
Vtotal
0.62
0.43
0.76
0.69
0.71
0.48
0.44
0.40
0.20
0.21
0.23
0.26
1 (MOR‐M)
2
3
4
0.1
0.1
0
0.1
0.23
0.1
0.1
0.1
0
0.05 (C12‐2‐12
0
0.05 (C12‐2‐12
0.10 (C12‐2‐12
0.05 (C12‐2‐12
0.02 (CTAB)
0.05 (SDBS)
0.40 d (F‐127)
0
0
)
9.1
8.1
8.8
—
471
428
524
477
425
493
478
460
390
399
408
384
)
)
)
222
106
95
177
135
120
23
5
6
7
8
—
—
—
—
—
—
9e
10 e
11 e
12 (MOR‐C)
0.1
0.1
0
35
0.05 (C12‐2‐12
0
)
—
7.0
38
40
a The starting gel composition is SiO2 : 0.033 Al2O3 : 0.25 Na2O: x TEAOH : y surfactant : 40 H2O (130°C, 7 d). b Determined by XRF. c SBET corresponds
to the BET surface area. Smicro and Vmicro are micropore surface area and micropore volume determined by the t‐plot method, respectively. Sext = SBET
Smicro. Vtotal is calculated at p/p0 = 0.99. d Mass ratio of F‐127/SiO2. e Control experiments conducted at 180 °C for 20 h.
–

Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
1913
450
1.0
0.8
0.6
0.4
0.2
0.0
(b)
(a)
400
350
300
MOR-M
250
200
150
100
50
MOR-M
MOR-C
MOR-C
50
0
0.0 0.2 0.4 0.6 0.8 1.0
0
40
80
120
Relative pressure (p/p0)
Pore diameter (nm)
10
20
30
40
2 /( o
)
Fig. 3. (a) N2 adsorption‐desorption isotherms of MOR‐M and MOR‐C;
(b) The BJH pore size distribution curve of MOR‐M calculated from
the desorption branch.
Fig. 1. XRD patterns of the as‐synthesized samples MOR‐M and MOR‐C.
into the pores, enhancing diffusion and mass transfer, thus
improving the catalytic efficiency.
(a)
(b)
(d)
Solid state27Al and 29Si MAS NMR spectra were employed to
investigate the local atomic coordination environments of
MOR‐M and MOR‐C. As shown in Fig. 4(a), there only exists one
sharp peak centered at δ = 54 in the 27Al MAS NMR, corre‐
sponding to tetrahedral coordinated aluminum species. No
peak around δ = 0 is observed, which indicates that all the Al
atoms were incorporated in the framework. Two major peaks
centered at –112 and –105 and a less intense peak at –99 are
evident in the 29Si MAS NMR spectra, which are ascribed to the
Si(0Al), Si(1Al), and Si(2Al) species, respectively. Notably, the
Si(0Al) signal in the spectrum of the MOR‐M sample is more
intense than that of MOR‐C, implying a higher Si/Al ratio of the
former material [34]. The results are consistent with the XRF
data—the Si/Al ratio being 9.1 and 7.0 for MOR‐M and MOR‐C,
respectively.
(c)
Fig. 2. (a) Low‐magnification SEM micrograph of MOR‐M; (b)
High‐magnification SEM micrograph of MOR‐M; (c) TEM micrograph of
MOR‐M; (d) SEM micrograph of MOR‐C.
To elucidate the role of TEAOH and C12‐2 ‐12 surfactant in the
formation of nanocrystal‐assembled hierarchical structures,
control experiments were conducted with a single TEAOH tem‐
plate, a single C12‐2‐12 surfactant and different ratios of the two
organics while keeping other conditions unchanged. The ex‐
perimental conditions and textual properties of the products
ultrasonic treatment for 30 min. Conversely, the MOR‐C sample
possesses plate‐like morphology consisting of closely packed
crystallites (Fig. 2(d)). The distinct morphology between the
two samples suggests that the nucleation and growth of MOR
crystals are significantly modified by the introduction of
TEAOH and C12‐2‐12
.
54
Fig. 3 presents the N2 sorption isotherms and BJH pore size
distribution curve of the samples. MOR‐M exhibits the type IV
isotherm with a hysteresis loop at a relative pressure of
0.80–0.95, which demonstrates the existence of intercrystal
meso/macroporosity [33]. The corresponding BJH pore size
distribution curve derived from the desorption branch indi‐
cates that it is rather broad with a mean pore size of ~30 nm.
Comparatively, MOR‐C presents a type I adsorption curve typi‐
cal of microporous materials with a small uptake of N2 at high
relative pressure. Table 1 shows the textual properties of the
samples. In comparison with the control sample MOR‐C,
MOR‐M exhibits a higher BET surface area (471 m2/g) and
larger pore volume (0.62 cm3/g) owing to the decreased crystal
size and the formation of meso‐ and macropores. It is envisaged
that the abundant porosity associated with the nano‐sized
crystals in MOR‐M offers improved ingress of guest molecules
27Al
29Si
-112
-105
-99
MOR-M
MOR-M
MOR-C
MOR-C
0
150 100
50

-50 -60 -80 -100 -120 -140 -160

Fig. 4. 27Al and 29Si MAS NMR spectra of MOR‐M and MOR‐C.

1914
Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
are listed in Table 1. Fig. 5 illustrates the SEM micrographs of
the samples. Sample 2 synthesized with a TEAOH/SiO2 ratio of
0.1 shows an aggregated morphology similar to MOR‐M, im‐
plying that nanocrystal‐assembled mordenite could be ob‐
tained with low concentrations of TEAOH at 130 °C. Thermal
analysis confirms the existence of TEA+ in the product with a
mass loss of 8.2% in the temperature range of 300–700 °C. The
surface area (428 m2/g) and pore volume (0.43 cm3/g) of sam‐
ple 2 are smaller than that of MOR‐M, possibly owing to larger
nanocrystal sizes (50–70 nm). Sample 3 presents variation in
its morphology as nanosheet assemblies are formed upon the
addition of C12‐2‐12 surfactant only in the initial gel. From Fig.
5(b), it can be seen that each individual nanosheet has a thick‐
ness of ~30 nm and a length of ~500 nm. The corresponding
FFT diffractograms reveal that the longest dimension of the
nanosheet runs along the c‐axis direction. This is expected con‐
sidering that multivalent surfactants could serve as a capping
agent to direct the formation of MOR nanorods and nanosheets
(having a preferential growth along the c‐direction) as reported
by Ryoo and co‐workers [32]. The nanosheet assembly exhibits
much larger external surface area and higher mesopore volume
than MOR‐M and MOR‐C. Further increasing the concentration
of C12‐2‐12 or TEAOH in the gel has little effect on enhancing the
mesoporosity of the products (samples 4 and 5). It is thus con‐
cluded that the smaller molecule TEAOH alone can decrease the
MOR crystal size and induce hierarchical structure formation.
The addition of the surfactant to the sol‐gel is not essential for
the formation of nanocrystal assemblies; however, the com‐
bined presence of TEAOH further inhibits crystal growth im‐
proving the external surface area. TEAOH is generally used in
the synthesis of high‐silica MOR zeolites [35,36], while the use
of TEAOH to form hierarchical MOR remains less explored.
Herein, it is suggested that TEAOH functions as a mi‐
cropore‐directing agent, which induces significantly more nu‐
clei, leading to smaller crystal sizes. Additionally, TEA+ has been
reported to adsorb on the crystal surface [37,38], preventing
excessive interconnection among nanocrystallites, prompting
the formation of the final morphology.
Interestingly, the growth inhibition effect of the surfactant is
not limited to C12‐2‐12. By applying the present synthetic strate‐
gy, nanocrystal‐assembled MOR could be hydrothermally syn‐
thesized with various conventional surfactants, such as CTAB,
SDBS, and F‐127 (samples 6–8 in Table 1). All three samples
present irregular micrometer‐sized morphology composed of
very small nanoparticles (Fig. 5). The type IV isotherms associ‐
ated with the BJH pore size distribution of the samples are giv‐
en in Fig. 6, which clearly indicate the presence of mesopores in
the structures. Comparatively, the single use of each surfactant
in the absence of TEAOH could not produce the nanocrys‐
tal‐assembled hierarchical structure. This confirms again that
the presence of TEAOH is vital to the generation of the nano‐
crystal assembly, whereas the surfactant serves more as a
growth‐inhibiting agent possibly through interaction with the
negatively charged crystal surface [39] or the TEA+ adsorbed
on the surface [37,38].
(a)
(c)
(e)
(g)
(b)
(d)
Further samples were synthesized at higher temperatures
(180 °C) to investigate the effect of crystal growth behavior as a
function of crystallization temperature (samples 9–11 in Table
1). All products exhibit distinct morphology from the corre‐
sponding samples synthesized at 130 °C possessing the same
sol‐gel compositions. Sample 9 synthesized in the absence of
TEAOH and C12‐2‐12 displays elliptic micrometer‐sized mor‐
(f)
350
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
300
250
200
150
100
50
Sample 6
Sample 7
Sample 8
(h)
Sample 6
Sample 7
Sample 8
0
0.0 0.2 0.4 0.6 0.8 1.0
1
10
Pore diameter (nm)
100
Relative pressure (p/p0)
Fig. 5. SEM micrographs of sample 2 (a), 3 (b), 6 (c), 7 (d), 8 (e), 9 (f), 10
(g), and 11 (h) in Table 1. The inset in (b) shows the HRTEM micro‐
graph and the corresponding selected FFT diffractogram viewed along
the (100) axis.
Fig. 6. (a) N2 adsorption‐desorption isotherms and (b) the pore size
distribution curves of the samples. The pore size distributions are de‐
rived from the desorption branches of the isotherms.

Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
1915
phology with smooth surfaces. After the introduction of
80
70
60
50
40
30
20
10
0
TEAOH, the product (sample 10) possesses rough surfaces
composed of closely packed nanoscale particles. A low external
surface area of 35 m2/g and a dramatically reduced pore vol‐
ume of 0.21 cm3/g are observed, indicating that the adsorption
of TEA+ on the crystal surface and its inhibition on crystal in‐
tergrowth may be significantly weakened at higher tempera‐
tures. In addition, sample 11 synthesized with the addition of
both TEAOH and C12‐2‐12 displays well‐defined morphology with
overlapped slabs on the particle surface. Here the external sur‐
face area decreases to 38 m2/g. These results demonstrate that
the morphology and porosity of the products are sensitive to
the crystallization temperature with lower temperatures fa‐
voring the formation of the present hierarchical structure
[40,41].
MOR-M
MOR-C
0
20 40 60 80 100 120 140 160 180 200
Time on stream (min)
Fig. 8. Catalyticcracking conversionof 1,3,5‐triisopropylbenzene (TIPB)
over protonated MOR‐M and MOR‐C catalysts. Reaction conditions:
vaporized TIPB in nitrogen (50 mL/min, 85 °C) as feed, 210 °C, 0.20 g
catalyst.
3.2. Acidity and catalytic performance of MOR‐M
3.2.1. Acidity of the zeolites
catalytic activity of MOR‐M and the ability to resist deactivation
in TIPB cracking when compared with the conventional stand‐
ard confirms the higher concentration of acid sites located on
the external surface of the sample.
NH3‐TPD experiments were performed to investigate the
acid properties of the samples. Fig. 7 presents the NH3‐TPD
profiles of MOR‐M and MOR‐C. Both data sets exhibit two peaks
assigned to weak and strong acid sites, respectively. The
stronger acid strength associated with the MOR‐M sample may
relate to variation in framework Al distribution resulting from
the use of the TEAOH template [42]. In addition, MOR‐M has a
lower acid concentration compared with the control sample,
owing to its slightly higher Si/Al ratio.
The acid sites located on the external surface of the samples
were further evaluated by the TIPB cracking reaction. As the
TIPB molecule possesses a kinetic diameter of 0.95 nm, ingress
to the 12‐MR channel of the mordenite zeolite is prevented and
thus the first‐order cracking of TIPB selectively occurs on the
external acid sites [43]. Fig. 8 illustrates the conversion of TIPB
as a function of time on stream. MOR‐M shows a high initial
conversion of 77.5%, whereas only 29.1% conversion is ob‐
tained on MOR‐C. After the reaction had progressed for 3 h, a
clear decrease of the TIPB conversion occurs over both cata‐
lysts. The conversion on MOR‐M drops to 34.4%, maintaining
44% of the initial conversion. However, the MOR‐C standard
after 3 h on stream gives only 6.8% TIPB conversion, corre‐
sponding to 23.3% of the fresh conversion value. The superior
3.2.2. Catalytic performance of MOR‐M in the benzylation of
benzene with benzyl alcohol (BA)
The liquid phase benzylation of benzene with BA was per‐
formed to investigate the catalytic properties of the samples in
the acid‐catalyzed reactions involving bulky molecules. As pre‐
sented in Fig. 9, MOR‐M exhibits significantly improved cata‐
lytic activity than the control sample, MOR‐C, during the entire
reaction time. The BA conversion is 2.8% at t = 0.5 h and grad‐
ually rises to 12.0% with reaction time, prolonged to 4 h, when
using MOR‐C as the catalyst. Comparatively, the conversion of
BA over the hierarchical MOR‐M increases rapidly as a function
100
80
60
40
20
0
80
60
MOR-C
MOR-M
MOR-M
Sample 2
Sample 3
MOR-C
40
20
0
0
1
2
3
4
5
6
Time (h)
200
300
400
500
600
Fig. 9. A comparison of the catalytic performance of the protonated
samples in the benzylation of benzene with BA. Reaction conditions: 1.0
mL BA, 34 mL benzene, 0.20 g catalyst, 80 °C.
Temperature (oC)
Fig. 7. NH3‐TPD curves of the protonated MOR‐M and MOR‐C samples.

1916
Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
of time and a complete conversion of 100% is readily achieved
at a reaction time of 3 h, showing the enhanced catalytic effi‐
ciency over the conventional standard. Moreover, the selectivi‐
ty of the target product diphenylmethane (DPM) over MOR‐M
reaches close to 90%, 15%–30% higher than the correspond‐
ing MOR‐C sample throughout the reaction. In principle, the
acid sites responsible to polarize BA to produce an electrophilic
intermediate play a crucial role in the present reaction [9,44].
However, the observed catalytic performance does not corre‐
late well to the acid properties of the catalysts. Considering that
both MOR‐M and MOR‐C possess similar acid strength, and the
former possesses a lower acid concentration than the latter, the
improved activity and selectivity than MOR‐C is thought to be
attributed to the shortened diffusion path together with a
higher concentration of acid sites on the external surface.
To further demonstrate the excellent catalytic performance
of the present nanocrystal‐assembled hierarchical MOR‐M,
samples 2 and 3 were also tested as catalysts and the results
are given in Fig. 9. Sample 2, synthesized from a TEAOH/SiO2
ratio of 0.1, displays good catalytic activity, being only slightly
lower than MOR‐M. This is somewhat expected as sample 2 has
similar morphology, but with a smaller external surface area
and pore volume compared with MOR‐M. A further reduction in
activity is observed over sample 3, which converts less BA than
both MOR‐M and sample 2 until a conversion of 100% is
reached at t = 5 h. Here, the diffusion limitation is believed to be
the main reason for the inferior catalytic activity of sample 3
with the highest external surface area and largest pore volume
among the samples. The nanosheet‐assembled morphology of
sample 3, in which the 12‐MR channels run parallel to the
longest dimension, would result in a relatively slow diffusion
and thus slow down the reaction inside the channels. These
results clearly demonstrate that decreasing the crystal size of
MOR zeolites, especially in the c‐direction, effectively enhances
mass transfer in the 12‐MR channels, producing superior cata‐
lytic activity as observed with MOR‐M.
45
40
35
30
25
20
15
10
5
MOR-M
MOR-C
0
100
90
80
70
60
50
40
30
MOR-M
MOR-C
20
0
5
10
15
25
Time on stream (h)
Fig. 10. DME conversion and MA selectivity of DME carbonylation over
protonated MOR‐M and MOR‐C catalysts. Reaction conditions: 200 °C,
2.0 MPa, DME/CO/H2 = 5/35/60 (vol%), GHSV = 1500 mL/(g·h).
MOR‐M exhibits significantly improved activity compared with
MOR‐C during the entire run time. An induction period of about
4 h is observed on MOR‐M, during which the conversion of
DME increases from 35.2% at 1.5 h to 40.4% at 4 h. Thereafter,
the conversion of DME gradually drops to 13.6% at 23.5 h,
maintaining 33.6% conversion. For MOR‐C standard material,
the conversion of DME is relatively stable during the first 3 h
(~30%), which then finally decreases to 4.2% after a reaction
time of 23.5 h. This value amounts to only 13.9% of the initial
conversion, implying a faster deactivation over MOR‐C than on
the hierarchical sample. The improved activity and an‐
ti‐deactivation ability of MOR‐M should arise from the reduced
diffusion limitations and the abundant porosity, which leads to
a more efficient utilization of the acid sites in the side‐pocket
8‐MR channels [31].
3.2.3. Catalytic performance of MOR‐C in the carbonylation of
dimethyl ether (DME) to methyl acetate (MA)
The selectivity of MA over MOR‐M and MOR‐C also shows
differences, though both samples display a similar trend fol‐
lowing the decrease of DME conversion. MOR‐M is able to sus‐
tain a high level of MA selectivity over a longer period of time
than on MOR‐C. The selectivity drops to 59.8% on the hierar‐
chical zeolite at 23.5 h, whereas only a selectivity of 40.3% on
the conventional zeolite is observed. The results indicate that
the side reactions, which occur in the 12‐MR channels, are like‐
ly to be suppressed by the improved mass transport of the
product. The coke content on the catalysts after 23.5 h of reac‐
tion was further detected by TG analysis. Three peaks are ob‐
served in the DTG curves (Fig. 11), corresponding to phy‐
sisorbed water, soft cokes, and hard cokes, respectively [48].
The total coke amount was 6.5 wt% for the deactivated MOR‐M,
while a much higher coke deposition was found on MOR‐C
(11.3 wt%). This implies that the coke formation is much slow‐
er on MOR‐M, further confirming the advantage of the short‐
ened diffusion length.
The carbonylation of DME to MA is a key step to produce
ethanol from syngas. Mordenite zeolite has proven to be the
most promising catalyst with high activity and MA selectivity
[45]. According to the literature, the target reaction exclusively
proceeds in the 8‐MR side‐pockets of MOR zeolite, whereas the
acid sites in the 12‐MR main channels prompt the occurrence
of side reactions resulting in coke formation and fast deactiva‐
tion [46,47]. It is expected that the shortened diffusion path in
MOR‐M facilitates mass transfer and enhances catalyst activity
and stability.
Pre‐adsorption of pyridine on the acid sites located in the
straight channels has been verified to be an effective way to
retard the catalyst deactivation and significantly prolong the
lifetime [46]. However, here, the catalytic reactions are con‐
ducted without pyridine pre‐adsorption, to clearly compare the
catalytic performance of the hierarchical MOR‐M and MOR‐C.
Fig. 10 presents the DME conversion and MA selectivity as a
function of time on stream over the samples. It is evident that

Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
1917
and improves the porosity of the products. However, the sur‐
factant used in the present system is not limited to C12‐2‐12. Sev‐
eral commercial surfactants including CTAB, anionic SDBS and
neutral F‐127 also exhibit the ability to decrease the nanocrys‐
tal size when used in conjunction with TEAOH. More im‐
portantly, the nanocrystal assemblies show much higher cata‐
lytic activity in benzylation of benzene with BA in comparison
with the control sample, and the hierarchical MOR possesses a
longer c‐axis dimension and larger external surface area. The
results demonstrate that the decreased crystal size of the MOR
zeolite, especially in the c‐direction, could effectively prompt
mass transport in the 12‐MR channels, leading to superior cat‐
alytic efficiency. In addition, the material also displays en‐
hanced activity and anti‐deactivation behavior in the DME car‐
bonylation reaction. This attractive approach, employing com‐
mercially available templates and surfactants, provides an ef‐
fective and viable way to synthesize MOR nanocrystal assem‐
blies with excellent catalytic performance.
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
100
95
MOR-C
90
85
80
100
0.06
0.05
0.04
0.03
0.02
0.01
0.00
MOR-M
95
90
85
80
0
200
400
600
800
References
Temperature (oC)
Fig. 11. TG‐DTG curves of the coked catalysts after 23.5 h of DME car‐
bonylation reaction.
[1] Corma A. Chem Rev, 1997, 97: 2373
[2] Weitkamp J. Solid State Ionics, 2000, 131: 175
[3] Cheung P, Bhan A, Sunley G J, Law D J, Iglesia E. J Catal, 2007, 245:
110
[4] Tromp M, van Bokhoven J A, Oostenbrink M T G, Bitter J H, de Jong
K P, Koningsberger D C. J Catal, 2000, 190: 209
[5] Becker K A, Karge H G, Streubel W D. J Catal, 1973, 28: 403
[6] Meier W M. Z Kristall, 1961, 115: 439
[7] Boronat M, Martínez C, Corma A. Phys Chem Chem Phys, 2011, 13:
2603
[8] Ordomsky V V, Ivanova I I, Knyazeva E E, Yuschenko V V, Zaikov‐
skii V I. J Catal, 2012, 295: 207
4. Conclusions
We developed a facile synthetic strategy to fabricate hier‐
archical MOR zeolites that results in nanocrystal‐assembled
morphology composed of 20–50‐nm crystallites dramatically
reducing mass transport limitation. Detailed investigation
shows that the use of TEAOH itself at lower crystallization
temperatures could decrease the crystal size and generate hi‐
erarchical structures constructed by the interconnection of
nanocrystals. The introduction of the cationic C12‐2‐12 surfactant
in the TEAOH‐containing sol‐gel further reduces the crystal size
[9] Leng K Y, Wang Y, Hou C M, Lancelot C, Lamonier C, Rives A, Sun Y
Y. J Catal, 2013, 306: 100
[10] Yang M, Tian P, Wang C, Yuan Y Y, Yang Y, Xu S T, He Y L, Liu Z M.
Graphical Abstract
Chin. J. Catal., 2015, 36: 1910–1919 doi: 10.1016/S1872‐2067(15)60519‐6
Facile preparation of nanocrystal‐assembled hierarchical mordenite zeolites with remarkable catalytic performance
Yangyang Yuan, LinyingWang, Hongchao Liu, PengTian*, Miao Yang, Shutao Xu, ZhongminLiu*
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;University of Chinese Academy of Sciences
Commercial
TEAOH
surfactant
100
80
60
40
20
0
100
80
60
40
20
0
130 oC
Nanocrystal-assembled MOR
Conventional MOR
NaAlO2
SiO2
NaOH
H2O
0
1
2
3
4
5
6
7
Time (h)
Nanocrystal-assembled MOR
A facile synthetic strategy is developed to fabricate hierarchical mordenite (MOR) zeolites assembled by 20–50‐nm crystallites, which
exhibit greatly enhanced activity, selectivity, and stability in catalytic reactions.

1918
Yangyang Yuan et al. / Chinese Journal of Catalysis 36 (2015) 1910–1919
Chem Commun, 2014, 50: 1845
[32] Jo C, Jung J, Shin H S, Kim J, Ryoo R. Angew Chem Int Ed, 2013, 52:
10014
[33] Liu Y, Zhou X Z, Pang X M, Jin Y Y, Meng X J, Zheng X H, Gao X H,
Xiao F S. ChemCatChem, 2013, 5: 1517
[11] Tosheva L, Valtchev V P. Chem Mater, 2005, 17: 2494
[12] Holm M S, Taarning E, Egeblad K, Christensen C H. Catal Today,
2011, 168: 3
[13] Chen L H, Li X Y, Rooke J C, Zhang Y H, Yang X Y, Tang Y, Xiao F S,
Su B L. J Mater Chem, 2012, 22: 17381
[34] Oumi Y, Kakinaga Y, Kodaira T, Teranishi T, Sano T. J Mater Chem,
2003, 13: 181
[14] Ivanova I I, Knyazeva E E. Chem Soc Rev, 2013, 42: 3671
[15] Möller K, Bein T. Chem Soc Rev, 2013, 42: 3689
[16] Serrano D P, Escola J M, Pizarro P. Chem Soc Rev, 2013, 42: 4004
[17] Verboekend D, Milina M, Mitchell S, Pérez‐Ramírez J. Cryst Growth
Des, 2013, 13: 5025
[18] Li K H, Valla J, Garcia‐Martinez J. ChemCatChem, 2014, 6: 46
[19] Yuan Y Y, Tian P, Yang M, Fan D, Wang L Y, Xu S T, Wang C, Wang D
H, Yang Y, Liu Z M. RSC Adv, 2015, 5: 9852
[35] Lu B W, Tsuda T, Oumi Y, Itabashi K, Sano T. Microporous Mesopo‐
rous Mater, 2004, 76: 1
[36] Lv A L, Xu H, Wu H H, Liu Y M, Wu P. Microporous Mesoporous
Mater, 2011, 145: 80
[37] Li F, Yang L L, Xu G, Huang X Q, Yang X, Wei X, Ren Z H, Shen G, Han
G R. J Alloys Compd, 2013, 577: 663
[38] Jelfs K E, Slater B, Lewis D W, Willock D J. Stud Surf Sci Catal, 2007,
170: 1685
[20] Wang Q Y, Wei Y X, Xu S T, Zhang M Z, Meng S H, Fan D, Qi Y, Li J Z,
Yu Z X, Yuan C Y, He Y L, Xu S L, Chen J R, Wang J B, Su B L, Liu Z M.
Chin J Catal, 2014, 35: 1727
[21] Tao H X, Yang H, Zhang Y H, Ren J W, Liu X H, Wang Y Q, Lu G Z. J
Mater Chem A, 2013, 1: 13821
[39] Che S N, Liu Z, Ohsuna T, Sakamoto K, Terasaki O, Tatsumi T. Na‐
ture, 2004, 429: 281
[40] Valtchev V P, Tosheva L, Bozhilov K N. Langmuir, 2005, 21:
10724
[41] Larsen S C. J Phy Chem C, 2007, 111: 18464
[42] Dědeček J, Sobalík Z, Wichterlová B. Catal Rev‐Sci Eng, 2012, 54:
135
[22] Li X Y, Sun M H, Rooke J C, Chen L H, Su B L. Chin J Catal, 2013, 34:
22
[23] Yang J H, Chu J, Wang J Q, Yin D H, Lu J M, Zhang Y. Chin J Catal,
2014, 35: 49
[24] Huang S J, Liu X H, Yu L L, Miao S, Liu Z N, Zhang S, Xie S J, Xu L Y.
Microporous Mesoporous Mater, 2014, 191: 18
[25] Góra‐Marek K, Tarach K, Tekla J, Olejniczak Z, Kuśtrowski P, Liu L
C, Martinez‐Triguero J, Rey F. J Phy Chem C, 2014, 118: 28043
[26] Tang T D, Zhang L, Fu W Q, Ma Y L, Xu J, Jiang J, Fang G, Y Xiao F S. J
Am Chem Soc, 2013, 135: 11437
[43] Tarach K, Góra‐Marek K, Tekla J, Brylewska K, Datka J, Mlekodaj K,
Makowski W, López M C I, Triguero J M, Rey F. J Catal, 2014, 312:
46
[44] Coq B, Gourves V, Figuéras F. Appl Catal A, 1993, 100: 69
[45] Cheung P, Bhan A, Sunley G J, Iglesia E. Angew Chem Int Ed, 2006,
45: 1617
[46] Liu J L, Xue H F, Huang X M, Wu P H, Huang S J, Liu S B, Shen W J.
Chin J Catal, 2010, 31: 729
[27] Kim J, Jo C, Lee S, Ryoo R. J Mater Chem A, 2014, 2: 11905
[28] Liu Y H, Zhao N, Xian H, Cheng Q P, Tan Y S, Tsubaki N, Li X G. ACS
Appl Mater Interfaces, 2015, 7: 8398
[29] Inagaki S, Watanabe Y, Nishita Y, Kubota Y. Chem Lett, 2013, 42:
186
[47] Boronat M, Martínez‐Sánchez C, Law D, Corma A. J Am Chem Soc,
2008, 130: 16316
[48] Zhou H, Zhu W L, Shi L, Liu H C, Liu S P, Xu S T, Ni Y M, Liu Y, Li L L,
Liu Z M. Catal Sci Technol, 2015, 5: 1961
[30] Lee S H, Lee D K, Shin C H, Paik W C, Lee W M, Hong S B. J Catal,
2000, 196: 158
[31] Xue H F, Huang X M, Ditzel E, Zhan E S, Ma M, Shen W J. Ind Eng
Chem Res, 2013, 52: 11510
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