Embryonic zeolite-assisted synthesis of SSZ-13 with superior efficiency and their excellent catalytic performance

Article abstract of DOI:10.1039/d1ta01452h

An X-ray amorphous material with a CHA-like structure, named embryonic CHA zeolite, has been designed and employed for the synthesis of SSZ-13, which leads to ultra-fast crystallization (1.5-12 h), wide product SiO₂/Al₂O₃ratio (SAR = 22-100) and high yield (82.8-92.9%). The usage ofN,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) for the synthesis can be controlled at unprecedentedly low amounts (TMAdaOH/SiO₂= 0.035-0.050). Characterization results reveal that the embryonic zeolite has a small particle size of 10-20 nm, large micro/mesopore volume and abundant double 6-ring units (subunits of the CHA structure). It provides ample active surface and subunits for the formation of the CHA structure and promotes the fast synthesis of SSZ-13 with a wide phase region. The resultant material (SAR = 23.2), after Cu²⁺exchange, exhibits superior NH₃-SCR activity and extraordinary hydrothermal stability (steaming at 800 °C for 16 h), implying its promising application for NO_xremoval. In addition, high-silica SSZ-13 shows good catalytic performance for the MTO reaction. It is anticipated that the embryonic zeolite-assisted strategy will benefit the synthesis of more industrially important zeolites.

Full text of DOI:10.1039/d1ta01452h

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Materials Chemistry A
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PAPER
Embryonic zeolite-assisted synthesis of SSZ-13
with superior efficiency and their excellent catalytic
performance†
Cite this: J. Mater. Chem. A, 2021, 9,
15238
Linying Wang,a Dali Zhu,ab Juan Wang,ac Wenhao Cui,ab Jingfeng Han,a Bing Li,a
a
a
abc
*
*
Dong Fan,
Peng Tian and Zhongmin Liu
An X-ray amorphous material with a CHA-like structure, named embryonic CHA zeolite, has been designed
and employed for the synthesis of SSZ-13, which leads to ultra-fast crystallization (1.5–12 h), wide product
SiO2/Al2O3 ratio (SAR ¼ 22–100) and high yield (82.8–92.9%). The usage of N,N,N-trimethyl-1-
adamantammonium hydroxide (TMAdaOH) for the synthesis can be controlled at unprecedentedly low
amounts (TMAdaOH/SiO2 ¼ 0.035–0.050). Characterization results reveal that the embryonic zeolite has
a small particle size of 10–20 nm, large micro/mesopore volume and abundant double 6-ring units
(subunits of the CHA structure). It provides ample active surface and subunits for the formation of the
CHA structure and promotes the fast synthesis of SSZ-13 with a wide phase region. The resultant
material (SAR ¼ 23.2), after Cu2+ exchange, exhibits superior NH3-SCR activity and extraordinary
hydrothermal stability (steaming at 800 ꢀC for 16 h), implying its promising application for NOx removal.
In addition, high-silica SSZ-13 shows good catalytic performance for the MTO reaction. It is anticipated
that the embryonic zeolite-assisted strategy will benefit the synthesis of more industrially important
zeolites.
Received 18th February 2021
Accepted 12th June 2021
DOI: 10.1039/d1ta01452h
rsc.li/materials-a
SiO2/Al2O3 ratio (SAR ꢂ 20) is desirable for the NH3-SCR reac-
tion aer Cu2+ exchange, as it can provide a large amount of
acid sites to adsorb NH3 molecules.11 However, for the MTO
reaction, high silica SSZ-13 becomes an appropriate choice,
because lower acid density can abate the hydrogen-transfer
reaction and coke deposition (deactivation).15
Introduction
Zeolites with inorganic crystalline frameworks have been widely
used in industry because of their well-dened micropores and
cavities, adjustable surface acidity and good thermal stability.1–3
The development of zeolite synthesis strategies facilitates the
creation of novel zeolitic materials, the improvement of
synthetic efficiency and the ne tuning of zeolite physico-
chemical properties, which would prompt the practical appli-
cation of zeolites.4–6
SSZ-13, a high-silica counterpart of natural chabasie, belongs
to the ABC-6 family of zeolites with three-dimensional channels
(0.38 ꢁ 0.38 nm) and large ellipsoidal cages (0.67 ꢁ 1 nm). It
has caught considerable attention because of its promising
catalytic performance in the conversion of methane to meth-
anol,7–9 selective catalytic reduction of NOx by NH3 (NH3-
SCR)10–13 and methanol-to-olen (MTO) reactions.14,15 Previous
studies have demonstrated that SSZ-13 with a relatively low
Hitherto, the most powerful organic structure-directing
agent (OSDA) for the formation of high-silica SSZ-13 has been
TMAdaOH, which, however, is highly expensive and leads to
high product cost. A great deal of effort has been made for the
synthesis of SSZ-13 over the past decades.16–22 Aer extensive
exploration, the usage of TMAdaOH for the crystallization of
SSZ-13 with a lower SAR is currently reduced to OSDA/SiO2 z
0.1.16 However, for high silica SSZ-13, a large amount of TMA-
daOH (OSDA/SiO2 $ 0.2) is still necessary, even involving the
use of toxic uoride ions.15,23,24 This is likely due to the increased
growth barrier of the high-silica framework. Besides the direct
synthesis, an inter-conversion methodology (using zeolites such
as FAU, GIS or beta as the precursor) was also developed.25–27 But
the use of the zeolite precursor increases the complexity of the
synthetic procedure and hinders its scale-up. In addition,
several alternative OSDAs have also been discovered for the
synthesis of SSZ-13. Unfortunately, most of them only exert the
structure directing effect under inter-conversion conditions,28–34
and all of them lead to SSZ-13 products with narrow and low
SARs. Hitherto, the efficient and cost-effective synthesis of SSZ-
13 with a controllable SAR has still remained a challenging task.
aNational Engineering Laboratory for Methanol to Olens, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China. E-mail:
tianpeng@dicp.ac.cn; liuzm@dicp.ac.cn
bUniversity of Chinese Academy of Sciences, Beijing 100049, China
cZhang Dayu School of Chemistry, Dalian University of Technology, Dalian, 116024,
China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d1ta01452h
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X-ray amorphous zeolitic materials (regarded as zeolite CHA-zeolite solution was added into the gel (10 wt% addition
precursors or embryonic zeolites) have attracted increasing based on silica) under stirring to form a gel with the composi-
attention in recent years.35–37 They possess zeolitic acidity/ tion of 1 SiO2 : 1/x Al2O3 : 0.048 Na2O : y TMAdaOH : 20.6 H2O,
oxidation, large external surface area and enhanced accessi- where x ranges from 20 to 100 and y ranges from 0.035 to 0.050.
bility of active sites, leading to improved catalytic activity. Such The gel was then charged into a 30 mL autoclave with a Teon
advantages become more evident when they are utilized for liner. The reaction was carried out under rotation (45 rpm) at
reactions involving large molecules. Spectroscopic character- 175–205 ꢀC for a few hours. Then the solid was separated by
ꢀ
izations have demonstrated that the Si and Al (Ti) atoms in the ltration, washed, and dried at 110 C overnight. The sample
amorphous materials have a short-range order and the micro- was named SSZ-13m, where m presents the product SiO2/Al2O3
structures of the materials are in close similarity to the crys- ratio detected by XRF.
tallized products. But the lack of long-range order makes these
materials X-ray amorphous.
Characterization
Given the high external surface area and abundant building
units of the X-ray amorphous zeolite precursors, it is envisioned
that besides catalytic applications, such materials may have
a powerful effect on promoting the crystallization of zeolites as
effective nuclei, as they could provide a vast amount of building
units with open accessibility and promote the nucleation and
crystallization. Herein, for the rst time we designed and
prepared an X-ray amorphous material with a CHA-like struc-
ture (named embryonic CHA zeolite) and explored its effect on
the synthesis of SSZ-13. It was found that the embryonic zeolite
has superior activity in inducing the crystallization of SSZ-13,
which allows the successful synthesis under an extremely low
usage of TMAdaOH together with a rapid crystallization rate
and wide product SAR. NH3-SCR and MTO reactions were
chosen to test the catalytic performance of the obtained SSZ-13.
A PANalytical X'Pert PRO X-ray diffractometer (Cu Ka radiation)
was employed to collect the powder X-ray diffraction (PXRD)
data. The inorganic elemental compositions were determined
with an X-ray uorescence (XRF, Philips Magix-601) spectrom-
eter. The crystal morphology was observed using a scanning
electron microscope (SEM, Hitachi SU8020). HRTEM images
were obtained on a transmission electron microscope (TEM,
JEM-2100). The textural properties were measured by N2 sorp-
tion at ꢃ196 ꢀC on a Micromeritics ASAP2020 volumetric
adsorption analyzer. Before the measurement, the sample was
pretreated at 350 ꢀC for 360 minutes. Thermal gravimetric
analyses (TG-DTG) were performed on a NETZSCH ATS 449 ꢃF13
ꢀ
ꢀ
analyzer from 33 to 900 C with a heating rate of 10 C min
.
The UV-Vis spectrum was collected on a UV-Vis-NIR spectro-
photometer (Varian Cary 5000) and BaSO4 was employed as the
background. UV-Raman spectra were collected using a home-
made single stage UV-Raman spectrograph with the resolution
of 2 cmꢃ1, the single-frequency UV laser line was 244 nm and
the output of the exciting source was 10 mW. The power of the
laser at the sample was about 2 mW. The solid-state NMR
experiments were carried out on a BrukerAvance III 600 spec-
trometer, which is equipped with a 14.1 T wide-bore magnet
using a 4 mm WVT double resonance MAS probe. The chemical
shis of 29Si, 27Al and 13C were referenced to Kaolinite at
ꢃ91.5 ppm, NH4Al(SO4)2$12H2O at ꢃ0.4 ppm and adamantine
at 38.5 ppm. The liquid 13C NMR analysis was performed on
a Bruker Avance III 400 using D2O as the deuterated reagent.
Experimental
Materials
The chemical reagents used for the experiments included:
sodium aluminate (48 wt% Al2O3, 36 wt% Na2O, Aladdin),
mesoporous silica gel (99 wt%, Qingdao Meigao Reagent Co.),
tetraethyl-orthosilicate (TEOS, 99 wt%, Kermel), aluminium
isopropoxide ($98 wt%, Aladdin), sodium hydroxide (NaOH,
99.9 wt%, Aladdin), N,N,N-trimethyl-1-adamantammonium
hydroxide (TMAdaOH, 25 wt% in H2O, Annaiji), ammonium
nitrate (NH4NO3, 99 wt%, Beijing Chemical Reagent Co., Ltd),
and copper acetate monohydrate (Cu(CH3COO)2$H2O, 99 wt%,
Tianjin Damao Chemical Reagent Co.).
Catalyst preparation
The NH4-form sample was obtained by ion exchange of the
calcined sample with NH4NO3 solution (1.0 M, liquid/solid ¼
15) at 80 ꢀC, each time is 2 h for a total of three times. The Cu-
form sample was prepared by ion exchange of the NH4-form
sample two times with Cu(CH3COO)2 solution (0.20 wt%,
Preparation of embryonic-CHA-zeolite solution
0.39 g aluminum isopropoxide was added into TMAdaOH
solution (6.08 g TMAdaOH solution in 7.10 g H2O) under stir-
ring to form a clear solution. Then, TEOS (5.00 g) was dropwise
added to obtain a nal gel. Aer stirring for 4 h, the gel was
placed into a stainless autoclave and heated under rotation (45
rpm) at 140 ꢀC for 14 h. The prepared solution is referred to as
embryonic-CHA-zeolite solution, which is used for the following
preparation of SSZ-13 zeolite without solid–liquid separation.
ꢀ
liquid/solid ¼ 50) at 80 C, and each time is 2 h, followed by
ltration and washing. All the ion-exchanged samples are dried
ꢀ
at 100 C for 12 h. The nal solid was calcined in an air atmo-
sphere at 550 ꢀC for 300 minutes to remove the organics. The Cu
content of Cu-SSZ-1323.2 was determined by XRF.
Embryonic zeolite-assisted synthesis of SSZ-13 zeolite
Catalytic test
Sodium aluminate, NaOH, TMAdaOH and deionized water were The NH3-SCR reaction was performed in a xed-bed quartz
mixed to form a clear solution before the addition of the silica reactor.38 For a detailed test, 0.30 g Cu-SSZ-13 and 1.90 g quartz
gel. Aer stirring for 5 minutes, a given amount of embryonic- beads (60–80 mesh) were mixed uniformly and loaded into the
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reactor. The catalyst was rstly heated in N2 to 550 ꢀC, and then 20 nm. No lattice fringes can be discerned, which implies the
the temperature was kept constant for 0.5 h in the presence of absence of crystallites and is in agreement with the XRD result.
the feed gas before the reaction. A Fourier transform infrared The N2 isotherms of the solid are displayed in Fig. 1c, which
spectrometer (Bruker) was chosen to detect the concentration of present a type of I + IV isotherms with an obvious hysteresis
NO, NO2, and N2O. The following formula was used to deter- loop in the range of P/P0 ¼ 0.7–1.0, suggesting the coexistence of
mine the NOx conversion:
NO conversion ð%Þ
ð ½NOꢄ ꢃ ½NOꢄ ꢃ ½NO2ꢄ ꢃ 2½N2Oꢄ
micropores and meso/macropores in the sample. In view of the
TEM result, the meso/macropores should originate from the
void space of adjacent nanoparticles. The large external surface
Þ
area (220 m2 gꢃ1) and meso–macropore volume (0.77 cm3 gꢃ1
)
in
out
out
out
¼
ꢁ 100%
½NOꢄ
in
observed for the solid also agree well with its small particle size.
Moreover, the micropore size distribution curve gives a much
broad peak with maximum at 0.55 nm, which is larger than that
of the well-crystallized SSZ-1334.1 (inset in Fig. 1c). The micro-
pore volume and micropore surface area of the solid sample are
0.10 cm3 gꢃ1 and 203 m2 gꢃ1, respectively, indicating its highly
microporous structure.39
MTO reaction was tested in a xed-bed reactor. 0.30 g H-SSZ-
13 (40–60 mesh) was transferred into the reactor before the
ꢀ
catalyst was activated at 550 C for 1 h (N2 as the carrier gas).
The feed methanol was imported by passing N2 (40.0 mL minꢃ1
)
through a saturator containing methanol at 35 ꢀC. The nal
products were analysed with a gas chromatograph (Agilent,
GC7890, FID detector and Poraplot Q-HT capillary column).
Fig. 1d shows the 13C MAS NMR spectrum of the solid. Four
well-resolved resonances attributed to the TMAda+ cation are
clearly observed, evidencing the intact inclusion of TMAda+ in
the solid.33 TG-DTG curves (Fig. 1e) further reveal that the
amorphous solid contains 25 wt% TMAda+, which is larger than
that (16 wt%) in the as-made SSZ-1334.1. Moreover, the OSDA
High-temperature (HT) hydrothermal treatment
The catalyst was hydrothermally treated at 750 or 800 ꢀC for 16 h
in the presence of 12.5% H2O in air with a GHSV of 90 000 hꢃ1
.
ꢀ
decomposition temperature (200–650 C)ꢀin the solid is much
broader than that in SSZ-1334.1 (400–650 C). This implies that
the local environments of OSDA cations in the amorphous solid
are more complex and part of OSDA cations have relatively weak
interactions with the aluminosilicate species.35
Results and discussion
Physicochemical properties of embryonic CHA zeolite
Fig. 1a presents the powder XRD pattern of the solid separated
from the prepared embryonic-CHA-zeolite solution. No diffrac-
tion peaks are observed, indicating the X-ray amorphous feature
of the solid. The TEM image shown in Fig. 1b reveals that the
solid is composed of uniform nanoparticles in the size of 10–
UV Raman is usually chosen to probe the zeolite structure
because it is quite sensitive to the framework/ring vibrations in
zeolites.39,40 It is especially powerful in supplying structural
information even for amorphous materials in the induction
Fig. 1 (a) XRD patterns, (b) TEM image, (c) N2 sorption isotherms (insets show the distribution of micropores), (d) 13C MAS NMR, (e) TG-DTG
curves and (f) UV-Raman spectra of the samples. As-made samples for (a), (b) and (d–f); calcined sample for (c).
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period of zeolite crystallization. Fig. 1f presents the UV-Raman
Moreover, all the embryonic zeolite-assisted syntheses are
spectrum of the solid. For comparison, the UV-Raman spec- complete in a short time (12 h) at 175 ꢀC with a high solid yield
trum of SSZ-13 is also shown in the gure. The strong band at of 82.8–92.9%. The crystallization time could be even shortened
330 cmꢃ1 is assigned to D6R in the CHA structure. The band at dramatically to 1.5 h (sample SSZ-1331.5) when the temperature
470 cmꢃ1 accompanied by a shoulder at 485 cmꢃ1 can be increased from 175 to 205 C. Such a wide range of crystalliza-
ꢀ
ascribed to the 4R in the CHA framework.41,42 Other bands in the tion temperature might be owing to its ultra-low gel alkalinity
spectra are mainly related to the TMAda+ cation. Overall, the (OHꢃ/SiO2 ¼ 0.137), which allows the OSDA to play its role in
UV-Raman spectra of the solid and SSZ-13 have high similarity. a dominant manner and avoids the formation of the impurity
Based on the above characterizations, it is clear that the phase. In addition, the ultra-low gel alkalinity should also
amorphous solid recovered from the prepared solution has the contribute to the high solid yield of the synthetic system by
characteristics of nanometer size, abundant micropores and decreasing the dissolution of silica.43 On the other hand, as
D6R units, although a large-scale three-dimensional crystalline a recent study revealed that the indispensable premise of the
structure has not yet been developed. Considering that D6R is fast crystal growth is to form high ordering nuclei,44 it is spec-
the most important composite building unit for the formation ulated that embryonic zeolites might rst promote the fast
of the CHA structure and the solution can yield the SSZ-13 formation of ordering CHA nuclei, which leads to the ultrafast
product aer a prolonged heating time (Fig. S1†), the amor- crystallization rate of SSZ-13 in this work. Apparently, the
phous solid is therefore named embryonic CHA zeolite to show strategy developed herein is highly efficient for the synthesis of
its close relationship with the CHA structure.
SSZ-13, characteristic of ultra-low OSDA dosage, wide phase
region, high yield and fast crystallization rate.
To verify the powerful effect of the embryonic-CHA-zeolite
solution for the crystallization of SSZ-13, two groups of
contrast experiments with different gel SARs were conducted,
including without the addition of embryonic-zeolite solution
(contrast A) and the use of H-SSZ-13 seeds in place of the
embryonic-zeolite solution (contrast B). The chosen seed has
a similar composition to that of the embryonic-CHA-zeolite
solution and the detailed parameters are shown in Fig. S3†
(XRD and SEM). Detailed synthesis parameters for the contrast
experiments are summarized in Table S1.† The corresponding
XRD patterns and SEM images of the contrast samples are
displayed in Fig. 2 and S4,† respectively. For the low SAR system,
the two contrast samples show obviously low crystallinity as
compared with SSZ-1334.1, although their crystallization took
a much longer time. Meanwhile, the SEM images also evidence
the existence of many amorphous particles in both contrast
Embryonic zeolite-assisted synthesis of SSZ-13
The embryonic-CHA-zeolite solution was directly employed for
the synthesis of SSZ-13. There are two advantages in doing so:
(1) there is no need for solid separation; (2) the residual OSDA in
the solution can be further utilized for the synthesis. The
representative synthesis results are summarized in Table 1.
Clearly, SSZ-13 can be obtained in a wide range of gel SARs and
the corresponding product SAR increases from 23.2 to 96.1. The
OSDA usage for the synthesis of the sample SSZ-1323.2 is as low
as OSDA/SiO2 ¼ 0.035, which is an unprecedentedly low TMA-
daOH dosage for the SSZ-13 synthesis. Following the increase of
gel SAR, more OSDA (OSDA/SiO2 ¼ 0.04–0.05) is needed to reach
complete crystallization, suggesting the incremental difficulty
in the formation of the high-silica CHA framework. To learn the
utilization efficiency of TMAda+ in the synthesis, the mother
liquid of SSZ-1334.1 recovered aer crystallization was analyzed
by 13C NMR. As shown in Fig. S2,† no signals assigned to
TMAda+ can be discerned, implying its complete consumption.
A
34.1 and B34.1. For the high SAR system, the difference between
contrast samples and SSZ-1396.1 becomes more evident, con-
rming the increased difficulty for the synthesis of the high-
Table 1 Synthesis conditions, product properties and yields of SSZ-13
Crystallization
Gel composition
conditions
Product
Phase
Sample
ma
na
xb
24.0
36.1
50.7
yb
T (ꢀC)
Time (h)
SARc
Yieldd (%)
SSZ-1323.2
SSZ-1334.1
SSZ-1347.1
SSZ-1369.1
SSZ-1396.1
SSZ-13am
SSZ-1333.2
SSZ-1331.5
23.8
38.0
57.0
95.0
190.0
N
0.009
0.014
0.014
0.020
0.025
0.025
0.014
0.014
0.035
0.040
0.040
0.045
0.050
0.050
0.040
0.040
175
175
175
175
175
175
195
205
12
6
6
10
10
24
3
CHA
CHA
CHA
CHA
CHA
CHA + amor.
CHA
23.2
34.1
47.1
69.1
96.1
—
92.8
91.9
92.9
92.3
82.8
—
74.9
116.6
264.0
36.1
38.0
38.0
33.2
31.5
92.0
87.3
36.1
1.5
CHA
a
b
Initial gel before the addition of embryonic-CHA-zeolite solution: 1 SiO2 : 1/m Al2O3 : 0.053 Na2O : n TMAdaOH : 27 H2O. Final gel for the
crystallization of SSZ-13: 1 SiO2 : 1/x Al2cO3 : 0.048 Na2O : y TMAdaOH : 20.6 H2O, which contains the sources from the embryonic-CHA-zeolite
solution (10% addition, based on SiO2). Product SiO2/Al2O3 determined by XRF. d Yield was determined by the mass of silica and alumina.
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well resolved characteristic diffraction peaks of the CHA-type
structure without impurities. N2 sorption isotherm was used
to test the pore structure of the calcined SSZ-1334.1. A typical
Langmuir-type curve was observed at 10ꢃ6 < P/P0 < 0.01 (Fig. 1c),
corresponding to the micropores in this material. The BET
surface area and pore volume are 0.30 cm3 gꢃ1 and 596 cm2 gꢃ1
,
respectively, which are comparable to those of high silica SSZ-13
reported before.34 The 27Al and 29Si MAS NMR spectra of SSZ-
1334.1 are illustrated in Fig. 3a and b, respectively. The 27Al NMR
spectrum contains only one sharp peak at 56.6 ppm, showing
the regular state of tetrahedral-coordinated Al species in the
framework.15 Two strong resonances centered at ꢃ111.4 and
ꢃ105.5 ppm dominate in the 29Si spectrum, which could be
assigned to Si(4Si0Al) and Si(3Si1Al) species, respectively. The
signal at ꢃ100 ppm could be assigned to Si(3Si)OH (Q3), arising
from the defects mentioned in the previous studies.45 Thus the
SAR deduced from the 29Si MAS NMR is in good agreement with
the composition determined by XRF. Moreover, there are four
resonance signals in the solid 13C MAS NMR spectrum (Fig. 1d),
which arises from the C species of TMAda+, evidencing that the
TMAda+ remained intact in the CHA cages of SSZ-13.33
Crystallization processes of SSZ-13 with different SARs
The crystallization processes of SSZ-13 with different gel SARs
under the assistance of embryonic-CHA-zeolite solution were
traced and the results are displayed in Fig. 4 and 5. It is clear
that all the three systems present characteristics of fast crys-
tallization, which is complete in 12 h. However, there also exist
Fig. 2 XRD patterns of (a) SSZ-1334.1, (b) SSZ-1396.1 and their contrast
samples. Contrast A: without the addition of embryonic-CHA-zeolite
solution; contrast B: using H-SSZ-13 seeds in place of embryonic- obvious differences among the systems. More specically, the
CHA-zeolite solution. The final gel compositions in (a) and (b) were
system of SSZ-1323.2 with a relatively low gel SAR has a longer
controlled to be the same as those of SSZ-1334.1 and SSZ-1396.1
,
induction period of 8 h; no obvious induction period can be
observed for the crystallization of SSZ-1334.1, and its solid
product is fully crystallized aer 4 h with a high yield of 90.8%.
When the gel SAR further increases, the induction period is still
inconspicuous, but its crystal growth rate becomes slow as
compared to the other two systems.
Previous studies have demonstrated that the content of Al
species in the gel determines the nucleation rate and the
number of nuclei, and ultimately affects the product
morphology and yield.15,46 The crystallization of SSZ-13 with
respectively.
silica sample. The crystallization of contrast A96.1 was quite
slow. When its crystallization time was prolonged to 96 h, some
amorphous material still existed accompanied by the formation
of some impurity. For contrast B96.1, STT impurity appeared
together with SSZ-13 aer 10 h, which showed little change until
96 h. These results clearly evidenced that the embryonic crystals
play a crucial role in the fast and efficient synthesis of SSZ-13.
Characterization of SSZ-13
Sample SSZ-1334.1 was chosen for various characterizations
(Fig. 1 and 3). The XRD pattern of SSZ-1334.1 (Fig. 1a) exhibits
Fig. 3 (a) 27Al and (b) 29Si MAS NMR spectra of the as-made sample
SSZ-1334.1
.
Fig. 4 Crystallization curves of SSZ-13s with different gel SARs.
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Fig. 5 SEM images of SSZ-13s with different gel SARs.
a low SAR needs more crystal nuclei, which may follow a non-
classical mechanism47 and gives products with spherical
morphology and a rough surface. This is consistent with the
longer induction period and crystal morphology observed for
SSZ-1323.2 (Fig. 5). For the sample with a relatively high SAR, the
crystallites tend to grow in a classical layer-by-layer mode,
resulting in crystals with cube-like morphology and larger size,
as presented for SSZ-1334.1 and SSZ-1396.1 (Fig. 5). Moreover, the
relatively slow crystal growth rate of SSZ-1396.1 also indicates the
difficulty in the formation of the high-silica CHA framework.
Catalytic performance in NH3-SCR and MTO reactions
Sample SSZ-1323.2 with a relatively low SAR was used as
a precursor for the preparation of the Cu-SSZ-13 catalyst. The Cu
content was measured to be 2.41 wt% (Cu : Al ¼ 0.275, ion
exchange level of 55%). Fig. 6 displays the dependence of the
NH3-SCR catalytic activity on reaction temperature over Cu-SSZ-
1323.2. The fresh catalyst displays NOx conversion of ꢂ100% in
a wide temperature range of 200–450 ꢀC at a large GHSV of
300 000 hꢃ1. When the reaction temperature increases to
550 ꢀC, a respectable conversion of 93.7% could still be
observed, evidencing the superior catalytic activity of Cu-SSZ-
1323.2. Given that the high-temperature hydrothermal stability
of Cu-SSZ-13 is vital for its practical application, the NH3-SCR
catalytic properties of hydrothermally aged Cu-SSZ-1323.2 are
further investigated and shown in Fig. 6. The NOx conversion
Fig. 7 Conversion and product selectivity as a function of methanol
throughput on H-SSZ-1396.1. Reaction conditions: 400 ꢀC, atmo-
spheric pressure, CH3OH WHSV ¼ 2 hꢃ1
.
remains higher than 90% in the range of 200–550 ꢀC aer
ꢀ
treatment at 750 C for 16 h. Even aer a harsher treatment at
800 ꢀC, more than 95% conversion could be achieved in the
range of 250–450 ꢀC, suggesting the excellent hydrothermal
stability of the Cu-SSZ-1323.2 catalyst.
Furthermore, high-silica SSZ-1396.1 was also tested as an
MTO catalyst to investigate its catalytic performance. The
reaction results are displayed in Fig. 7. Under the studied
conditions, H-ꢃfo1rm SSZ-1396.1 shows a methanol throughput of
5.2 gMeOH gcat in its lifetime (>99.5% methanol conversion).
The initial selectivity of ethene plus propene is 70.1 wt%, which
increases gradually to 83.5 wt% until the catalyst deactivation.
This result is also comparable to or even better than the catalytic
performance of high-silica SSZ-13 reported previously (synthe-
sized with a large amount of TMAdaOH, TMAdaOH/SiO2
¼
0.2),15,19 which implies the good quality of the high-silica SSZ-13
synthesized by the embryonic zeolite-assisted method.
Besides the success in the synthesis of SSZ-13, another
industrially important zeolite TS-1 (MFI topology) has also been
efficiently synthesized by utilizing the embryonic zeolite-
assisted strategy. The specic information will be reported in
detail in the future.
Fig. 6 NOx conversion as a function of temperature on fresh and
hydrothermally aged Cu-SSZ-1323.2. Feed gas: NO (0.05%), NH3
(0.05%), H2O (6.4%), O2 (6.4%) and N2. GHSV ¼ 300 000 hꢃ1
.
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Paper
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The manuscript was completed through the contributions of all
authors. All authors have given approval to the nal version of
the manuscript. Linying Wang carried out the experiments and
wrote the dra. Dali Zhu and Juan Wang took part in some of
the synthesis experiments. Wenhao Cui participated in parts of
the characterizations. Jingfeng Han carried out the UV-Raman
test. Bing Li tested the MTO performances. Peng Tian and
Zhongmin Liu guided the research project. Peng Tian and Dong
Fan modied the manuscript.
Conflicts of interest
There are no conicts to declare.
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The authors acknowledge the National Natural Science Foun-
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