Synthesis of SAPO-34 Zeolite from Laponite and Its Application in the MTO Reaction

Article abstract of DOI:10.1002/ejic.202000183

In this work, SAPO-34 zeolite with high catalytic activity was successfully synthesized by hydrothermal method from laponite as the single Si source. Compared with the traditional method of synthesizing zeolites from clay, the laponite after swelling can be directly used in the synthesis process of zeolite. The crystallization behavior of SAPO-34 synthesized from laponite was investigated by XRD, FTIR, N₂ adsorption–desorption, SEM-EDX, ICP-MS, and DR-UV/Vis. The process can be summarized as follows: the Si and Mg elements were produced by the depolymerization of laponite, then the primary building units of SAPO-34 zeolite were formed under hydrothermal conditions; finally, the crystal nucleus began to form, and crystallization was triggered. Compared with the conventional SAPO-34 synthesized from TEOS, the SAPO-34 synthesized from laponite exhibited higher selectivity to light olefins and longer lifetime, which can be attributed to the suitable strength of acidity. This work points to a straightforward route to the synthesis of SAPO-34 from laponite.

Full text of DOI:10.1002/ejic.202000183

European Journal of Inorganic Chemistry
Accepted Article
Title: Synthesis of SAPO-34 zeolite from laponite and its application in
MTO reaction
Authors: Xueshuai Chen, Rongli Jiang, Zihan Zhou, and Xingwen
Wang
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000183
Link to VoR: https://doi.org/10.1002/ejic.202000183
01/2020

10.1002/ejic.202000183
European Journal of Inorganic Chemistry
FULL PAPER
Synthesis of SAPO-34 zeolite from laponite and its application in
MTO reaction
Xueshuai Chen[a], Rongli Jiang*[a], Zihan Zhou[a], Xingwen Wang[a]
[a]
X. Chen, Prof. Dr. R. Jiang, Z. Zhou, X. Wang
School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China
http://scet.cumt.edu.cn/8d/c5/c6674a363973/page.htm
E-mail: ronglij@cumt.edu.cn
Supporting information for this article is given via a link at the end of the document.
[15, 16]
space and high surface areas.
Owing to its high surface
Abstract: In this work, SAPO-34 zeolite with high catalytic activity
was successfully synthesized by hydrothermal method from laponite
as the single Si source. Compared with the traditional method of
synthesizing zeolites from clay, the laponite after swelling can be
directly used in the synthesis process of zeolite. The crystallization
behavior of SAPO-34 synthesized from laponite was investigated by
XRD, FTIR, N2 adsorption–desorption, SEM-EDX, ICP-MS and DR-
UV-Vis. The process can be summarized as follows: the Si and Mg
elements were produced by the depolymerization of laponite, then
the primary building units of SAPO-34 zeolite were formed under
hydrothermal conditions, and finally the crystal nucleus began to
form and crystallization was triggered. Compared with the
conventional SAPO-34 synthesized from TEOS, the SAPO-34
synthesized from laponite exhibited higher selectivity to light olefins
and longer lifetime, which can be attributed to the suitable strength
of acidity. This work points to a straightforward route to the synthesis
of SAPO-34 from laponite.
areas and layered structure, laponite can be used as promising
material with high reactivity to synthesize zeolite. Yet to the best
of our knowledge, the application of laponite as raw material to
synthesize zeolite as Si source has not been reported yet.
In this study, laponite after swelling was used in the synthesis
process of zeolite as silicon source without calcination or acid-
base treatment. Laponite itself contains Li and Mg atoms, which
were subsequently introduced into the framework of SAPO-34
zeolite. Modification of SAPO-34 catalyst with metal cations can
change its surface properties and improve the catalytic
performance of SAPO-34 catalyst. [17] This work points to a facile
and green route to the synthesis of SAPO-34 containing metal
cations via the depolymerization and reorganization of laponite.
The research broadens the range of raw materials for the
synthesis of zeolite and improves the added value of laponite.
Results and Discussion
Characterization of zeolite
Introduction
XRD patterns of laponite and the samples synthesized at
180 °C for different time are shown in Fig. 1. It shows that the
intensity of peaks of laponite were almost disappeared after
heating under hydrothermal conditions for 4.5 h (Fig. 1 S-4.5),
implying that the laponite was depolymerized in hydrothermal
condition, and the structure of SAPO-34 was not formed in this
period. When the crystallization time was prolonged to 9 h as
shown in Fig. 1 (S-9), the characteristic peaks of SAPO-34
appeared. S-9 sample exhibited a chabazite (CHA) framework
Zeolites have been widely applied in the chemical industry
benefiting from their uniform molecular sized pores, excellent
2]
catalytic activity and great stability.[1, Silicoaluminophosphate
zeolite SAPO-34 with CHA topological structure has been
proven to be the best catalyst for the production of ethylene and
propylene in the methanol to olefins (MTO) reaction because of
its shape selectivity and moderate strength of acidity.[3] The
conversion of methanol to olefins (MTO) provides an efficient
structure
with
characteristic
diffraction
peaks
at
route for converting carbon containing resource into light olefins
9.5°,12.8°,16.2°,20.5° and 30.8°, typically for SAPO-34 as
5]
through methanol as intermediate.[4,
At present, traditional
[18, 19]
reported in literatures,
suggesting the synthesis of SAPO-
SAPO-34 zeolites are synthesized mainly from chemicals by
adding organic templates and crystallizing under hydrothermal
conditions. The properties of zeolite vary greatly due to the
different of raw materials.
34 zeolite from laponite clay is reliable. When the crystallization
time was prolonged to 54 h, no additional peaks appeared or
disappeared during an extra 45 h after the characteristic peaks
of SAPO-34 had been appeared, which suggests that the
SAPO-34 zeolite obtained from the laponite is very stable.
In recent years, researchers have noticed the great potential
of minerals in zeolite synthesis, such as kaolinite [6-8], halloysite[9],
diatomite[10, 11], coal fly ash[12], and palygorskite[13]. In the above
methods, the raw materials activation processes are usually
calcinated or treated by acid or alkali, which lead to a large
number of energy consumption and waste liquor. Herein we
report a green strategy to synthesize SAPO-34 zeolite directly
from laponite as a new silicon source for the synthesis of zeolite.
Different from the above-mentioned mineral materials for
synthetic zeolite, the laponite does not need calcination or acid -
base treatment before the synthesis of zeolite.
Laponite is a layered hydrous magnesium silicate, consisting
of a layer of octahedrally coordinated magnesium oxide and two
parallel layers of tetrahedrally coordinated silica in 1:2
stoichiometric ratio. [14] Some of the Mg atoms in the framework
of laponite are replaced by Li atoms. Laponite has received
extensive attention benefiting from its flexibly adjusted interlayer
1
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10.1002/ejic.202000183
European Journal of Inorganic Chemistry
FULL PAPER
obviously at 1008 cm−1 and 480 cm−1, which indicates that the
Si-O vibrations of the tetrahedral sheet are broken. The results
show that in the early stage of the crystallization, the thermally
activated laponite has been already depolymerized in the
alkaline environment, which is also consistent with the results of
Fig. 2b. Meanwhile, when crystallization time exceeded 4.5 h,
the peak strength at 649 cm-1 also gradually increased,
indicating that the double 6 rings of SAPO-34 zeolite began to
form and gradually strengthened. The vibration band at
720ꢀcm−1 is assigned to the symmetric stretching vibration of P-O
(or Al-O), while that at 1100ꢀcm−1 is credited for the asymmetric
stretching vibration of O-P-O.[23] The peak at 480 cm−1 can be
credited for [SiO4] tetrahedron stretching vibration, revealing
that the Si species depolymerized from laponite have
incorporated into the tetrahedral framework of SAPO-34 during
the crystallization process.[21]
Figure 1. XRD patterns of laponite and the samples synthesized at 180 °C for
4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-36) and 54ꢀh (S-54).
To get a better understanding of the crystallization process,
the laponite and the samples synthesized at 180°C for different
time were carefully investigated by SEM, as shown in Fig. 2. The
laponite shows a lamps shape consisting of lamellas (Fig. 2a).
After heating the reactant for 4.5 h, the laponite particles were
depolymerized and formed a large number of spherical particles
spontaneously (Fig. 2b). After 9 h of heating, the ellipsoidal
particles gradually grew into cubes with rough surface (Fig. 2c).
With the prolongation of crystallization time, SAPO-34 crystals
with rough surface tended to be regular cubes and the particles
size of SAPO-34 remained unchanged (Fig. 2d, e, and f), which
are in accordance with the XRD results.
Figure 3. FTIR spectra of the laponite and the samples synthesized at 180 °C
for 4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-36) and 54ꢀh (S-54).
The nitrogen adsorption-desorption isotherms of the laponite
and the samples synthesized at 180 °C for different time are
shown in Fig. 4. Different from S-18, S-36, and S-54, the
hysteresis loops are observed at P/P0ꢀ=ꢀ0.6–0.9 for laponite, S-
4.5 and S-9 samples. The obvious hysteresis loop at P/P0ꢀ=ꢀ0.6–
0.9 denotes the mesopore in the material.[24] The hysteresis for
S-9 represents the inter-crystalline mesopore, while the
hysteresis for laponite and S-4.5 represents the intracrystalline
mesopore (fig. 2 b and c), which shows the SAPO-34 zeolite
with defects in the crystals has been formed when the
crystallization time reaches 9 h. The adsorption isotherms
exhibit steep uptakes in the region P/P0 < 0.1, which is due to
the existence of microporous structure. As can be seen, the
sample S-4.5 initially shows lower nitrogen uptake than laponite
in the region P/P0<0.1, implying that the laponite has been
degraded in the reaction system. It can be noticed that the
adsorption-desorption isotherm of samples tends to be type I
curves with the increase of heating time, which indicates that the
SAPO-34 crystals became more and more regular. These
results are consistent with the analysis above. Physicochemical
properties of laponite and the samples synthesized at 180 °C for
different time are further summarized in the Table 1. It is
noteworthy that when the crystallization time was prolonged to
18 h, the relative crystallinity reached 94.9%, indicating that the
SAPO-34 zeolite with high crystallinity can be obtained in a short
time by using laponite as silicon source. Additionally, during the
crystallization process, the Smcico and Vmcico of the samples
increase, and the increasing trend is basically consistent with its
Figure 2 SEM images of laponite and the samples synthesized at 180 °C for
4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-36) and 54ꢀh (S-54).
The FTIR was applied to analyze the change of chemical
states of laponite and the samples synthesized at 180 °C for
different time. As shown in Fig. 3, the peak at 635 cm−1 is
[20, 21]
assigned to the exisiting 6 rings,
which confirms the
formation of the CHA structure. The spectrum of laponite shows
the peak at 1008 cm-1, relating to Si-O vibrations and the peak at
649 cm-1, corresponding to the Mg-OH bending vibration. [22] It is
worth noting that after crystallization for 4.5 h, the peak at
649 cm−1 almost disappeared, resulting the Mg-O octahedrons in
laponite are destroyed. In addition, the peaks have been weaken
2
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10.1002/ejic.202000183
European Journal of Inorganic Chemistry
FULL PAPER
relative crystallinity.
species from the depolymerized laponite are gradually involved
in the reaction. The acid amount of the samples synthesized
from laponite are further summarized in the Table 2.
Figure 4. The nitrogen adsorption-desorption isotherms of the laponite and the
samples synthesized at 180 °C for 4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-
36) and 54ꢀh (S-54).
Figure 5 NH3-TPD analysis of the laponite and the samples synthesized at
180 °C for 4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-36) and 54ꢀh (S-54).
Table 1. Physicochemical properties of laponite and the samples synthesized
Table 2. The acid amount of the samples synthesized from laponite
at 180 °C for 4.5ꢀh (S-4.5), 9ꢀh (S-9), 18ꢀh (S-18), 36h (S-36) and 54ꢀh (S-54).
(mmol NH3 g-1).
a
b
Sample
s
SBET
Smcico
(m2 g-
Sexter
(m2
g-1)
128
335
66
Vtotal
Vmcico
Relative
Samples
Weak acid
Strong acid
Total acid
(m2 g-
(cm3 g-
(cm3 g-
Cystallization
S-9
0.746
0.774
0.784
0.864
0.236
0.366
0.388
0.408
0.982
1.14
1
1
1
1
)
)
)
)
c (%)
S-18
S-36
S-54
laponite
S-4.5
S-9
368
335
623
642
712
718
240
0
0.188
0.806
0.354
0.257
0.277
0.286
0.059
0
0
1.172
1.272
0
557
614
697
705
0.211
0.230
0.260
0.269
42.1
94.9
98.4
100
S-18
S-36
S-54
28
As a silicon source for the synthesis of SAPO-34 zeolite,
laponite also contains Mg and Li. To determine the elements
composition of SAPO-34 synthetized from laponite, the energy-
dispersive X-ray spectroscopy (EDX) analysis and elemental
mapping was carried out. The EDX elemental mapping results
and corresponding SEM image of S-54 are illustrated in Fig.6.
The SEM-EDX results show that the composition of S-54 contain
P-, Al-, Si- ,Mg- and O- atoms. It is well known that P -, Al -, Si -,
O- are the skeleton atoms of SAPO-34, whose distribution are
consistent with the SEM image (Fig. 6). So the Mg atoms of
sample S-54, which are from the raw material laponite, also
corresponding to the SEM image of S-54, indicating that Mg
elements are introduced into the framework. Besides, no phase
of MgO is found in XRD analysis, so the Mg elements are
incorporated into the framework of S-54. The exact chemical
composition of the sample was determined by ICP-MS. The test
result is Li0.019Mg1Al7.1Si1.83P6.3, which proves our analysis above
directly.
15
13
aVolume adsorbed at p/p0 = 0.99.
bDetermined by the t-Plot method.
cBased on the crystallinity of S-54.
In order to investigate the acidity properties of the SAPO-34
zeolite, NH3-TPD was carried out and the results are shown as
Fig. 5. The temperature of desorption indicates the strength of
acidity and the peak area of desorption refers to the amount of
acidity.[25] As shown in the Fig. 5, neither laponite nor S-4.5 has
strong acid sites. Meanwhile, when heating time exceeds 4.5 h,
the strong acidity peak of samples appeared. The samples are
observed similar acidity patterns with peaks at >300 °C and
<300 °C due to strong and weak acidic sites respectively.[26] The
weak acid sites are assigned the defect structural OH groups
(including Si-OH, P-OH and Al-OH), and the strong acidic sites
are assigned to Si-OH–Al hydroxyl groups.[27] The acid areas of
samples (S-9, S-18, S-36 and S-54) are different, which
depends on the amount of Si contents in the skeleton of zeolite.
On the other hand, the acid amounts of samples may also be
related to their microporous characteristics (especially the
microporous area). Table 1 shows that the micropore areas of
the above samples are different and in order S-54 (718m2/g) >
S-36 (712m2/g) > S-18 (642m2/g) > S-9 (623m2/g), which are
basically consistent with the acid amounts order of the samples.
The strong acid amounts are usually produced by the
isomorphic substitution of silicon atoms for aluminum or
phosphorus atoms in the framework of luminophosphate [AlPO4]
microporous molecular sieves.[28] With the increase of
crystallization time, the strong acid amounts of SAPO-34 zeolite
are gradually enhanced and stabilized, which implies that the Si
3
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10.1002/ejic.202000183
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Then the species migrated from the laponite participated into
synthesis system. The primary building units of SAPO-34 zeolite
could be formed by the Mg and Si species depolymerized from
laponite, phosphate anions, morpholinium cations and Al-OH at
the desirable temperature.[6, 32] At last, the crystal nucleus began
to form, and the primary building units continued to grow rapidly
on the crystal nucleus. A possible reorganization procedure from
the depolymerized laponite to the SAPSO-34 is schematically
illustrated in Fig. 8.
Figure 6. SEM images of S-54, and corresponding EDX elemental mapping
(Si, O, P, Al, and Mg).
To take insight into the chemical states of Mg atoms in the
SAPO-34 zeolite synthesized from laponite, diffuse reflectance
UV–vis spectra was performed. The diffuse reflectance UV–vis
spectra of S-T, S-9, and S-54 are given in Fig. 7. No absorption
band is seen for S-T, S-9, and S-54 samples in the visible region
of the spectra. In the UV region, all the samples show a broad
band at about 220 - 260 nm, which attributes to Al-O charge
Figure 8. Schematic illustration of a possible formation process of the SAPO-
34 zeolite synthesized from laponite.
Catalytic Performance on MTO Reaction
SAPO-34 catalysts are widely used as MTO catalyst to
convert carbon containing resource into light olefins through
methanol as intermediate.[33] To demonstrate the advantages of
the SAPO-34 catalyst synthesized from laponite, the MTO test
was performed. The methanol conversion as a function of time
on stream over SAPO-34 catalysts at 390 °C are presented in
Fig. 9 a. The catalyst lifetime obtained at 100% methanol
conversion over SAPO-34 catalysts are 193 min for S-T and 318
min for S-54. More significantly, the deactivation rate of the S-54
is much lower than S-T. In order to explore the reason for the
difference in catalytic lifetime of the two catalysts, NH3-TPD test
was carried out. The exact chemical composition of the S-T and
S-54 were determined by ICP-MS. The test result of S-54 is
Li0.019Mg1Al7.1Si1.83P6.3, and the chemical composition of S-T is
Si0.49Al1.21P1. So the aluminum content in S-54 is higher than that
of S-T. The SAPO-34 zeolite with high aluminum content was
indicative of a high acid site density, and vice versa.[34] This is
also in good agreement with the results of TPD. As shown in
Figure 9 b, the sample S-54 has lower acidic strength and acidic
concentration in the strong acid sites compared with the
conventional SAPO-34 (S-T) synthesized from TEOS, which can
slow down formation of the coke.[35] The Mg and Li elements can
be introduced into the zeolite by using laponite as the Si source,
which can deactivate the stronger acid sites of the catalyst. In
addition, MeAPSO-34 catalysts exhibit better catalytic stability
and light olefin selectivity during the MTO reaction as compared
to parent catalyst.[27] The catalytic performance and the product
distributions are shown in Table 3. As showed in Table 3, the S-
54 synthesized from laponite contributes to higher yield of light
olefin than S-T. It is worth noting that compared with S-T, the
light olefin selectivity of S-54 increased by nearly 10%. These
results reveal that the selectivity, yield of light olefin and catalyst
life of MTO reaction are significantly improved by the zeolite
synthesized from laponite compared with conventional SAPO-34
synthesized from TEOS.
transfer transitions of tetrahedral AlO4 species in or outside the
[29,30]
framework.
Moreover, the band at 260 nm is assigned
to the tetrahedral Mg species.[31] So it can be concluded that Mg
has been incorporated into the framework of SAPO-34 during
the crystallization process. The results are also consistent with
the results of SEM-EDX.
Figure 7. DR-UV-Vis spectra of samples: (a) S-T, (b)S-9 and (c) S-54.
Discussion on formation mechanism
From the above discussion, the crystallization mechanism of
SAPO-34 synthetized from laponite can be summarized as
follows: during the stirring and initial heating period of the
reactants, the laponite was attacked by morpholine, Al-OH,
hydroxyl ion and phosphate in the synthesis system. The ligands
coordinated with Si or Mg atoms in the surface of laponite, which
probably contributes to the progressive surface peeling of Mg
coordinated units connected with Si atoms, implying that all or
part of the Mg and Si species could turn into an amorphous state.
Unraveling the reaction mechanism is a big challenge in MTO
4
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10.1002/ejic.202000183
European Journal of Inorganic Chemistry
FULL PAPER
conversion. For the MTO process, the dual-cycle hydrocarbon
pool schematic comprised of olefinic and aromatic methylation
cycles has been well accepted.[36,37] In the induction period, the
methanol was generated polymethylbenzene compounds, which
are the most important active intermediate in the methanol
conversion process.[38] The Benzene with low methyl substitution
is the active intermediate of ethylene, and the ethylene is mainly
formed by (poly)methylbenzene and dealkylation cycles.[39]
Another important product propylene is produced through olefin
methylation and cracking cycles.[40] During the MTO reaction,
SAPO-34 zeolite synthesized from laponite possesses lower
acidic concentration in the strong acid sites than SAPO-34
zeolite synthesized from TEOS. The low acidic concentration
can provide a low aromatic/CH3 ratio, which is beneficial to
improve the selectivity of light olefins.[18] More comparative data
on S-T and S-54 are included in the supplementary materials.
Experimental Section
Materials
Methanol (AR 98%), aluminum isopropanol (AR 98%), tetraethyl
orthosilicatewas (TEOS, 28wt% SiO2) and morpholine were all
purchased from China National Pharmaceutical. Phosphoric acid (AR,
85wt%) was purchased from Aladdin Reagent Co., Ltd. Laponite RD, a
synthetic hectorite, was purchased from Rockwood Additives Ltd (UK).
As
a
white
powder
and
its
empirical
composition
is
Na0.7[(Si8Mg5.5Li0.3)O20(OH)4]. It is
thickness of 1 nm and a diameter of about 25 nm.[41] Deionized (DI) water
a
disk-shaped clay particle with
a
was produced by water system in the lab. All reagents were invoked as
purchased without any further purification.
Preparation
Laponite suspension of 8wt/% was prepared according to the steps
described by Tan et al.[42] Laponite was gradually dispersed in deionized
water to form an aqueous dispersion, and then the concentration of
aqueous dispersion was adjusted to 8wt%. At last, the aqueous
dispersion was sealed for one week to swell the laponite particles
completely. The SAPO-34 zeolite was prepared by
a hydrothermal
method using morpholine (Mor) as the template. The optimized molar
composition of the resulting mixtures was 1.0 Al2O3: 1.0 P2O5: 3.0 Mor:
0.6 SiO2: 80 H2O. The sources of the framework elements were
aluminum isopropanol, 85wt% phosphoric acid, laponite (8wt%), water
and morpholine (Mor). The synthesis gel was prepared by slowly adding
16.4g of aluminum isopropoxide powder to a solution containing 10.44g
of Mor and 31.4g of deionized water with continuous stirring. After stirring
for 2 h, 7.84g of phosphoric acid was added drop-wise to the above
solution under stirring for 1 h. At last, 28.5g of laponite suspension
(8wt%) was added into the solution under stirring for 4 hours at 30 °C to
disperse the laponite completely. The mixture was transferred into a
teflon-lined stainless steel autoclave, which was heated at 180 °C for
different time. The heating time was ranging from 4.5 to 54 h (4.5, 9, 18,
36, and 54), corresponding SAPO-34 samples were denoted as S-4.5, S-
9, S-18, S-36 and S-54, respectively. Under the same synthesis
conditions and molar composition, the sample synthesized from TEOS
was named S-T, and the sample was synthesized at 180 °C for 54 h. The
synthesis of S-T sample was to compare its catalytic performance with
that synthesized from laponite.
Figure 9. (a) Methanol conversion as a function of time on stream over SAPO-
34 catalysts. (Reaction conditions: t = 390 °C, WHSV = 1 h−1); (b) NH3-TPD
analysis of the S-T and S-54.
Table 3. Products Selectivity of SAPO-34 Catalysts during the reaction
period of MTO reaction at 390 °C with a methanol feeding rate of 0.3
mL/h and corresponding WHSV of 1.0 h−1
.
TOS
Selectivity(%)
Sample
s
+
=
=
(min)
Ethyl
ene
Propyle
prop
ane
20.3
10.6
11.8
8.5
C4
C5
C2
C3
+
ne
30
22.4
28.2
27.3
34.6
34.2
37.5
37.6
42.3
10.1
9.5
4.8
3.8
4.5
3.6
56.6
65.7
64.9
76.9
S-T
193
30
9.9
All the samples were recovered by centrifugation, washing, and then
oven-drying at 110 °C for 12 h. The final samples were calcined at
550 °C for 8 h in order to remove the organic templates that resided in
the pores of the samples.
S-54
318
8.3
Characterization
Conclusion
X-ray powder diffraction (XRD) patterns of the SAPO-34 zeolites were
recorded in the range of 5−60° on a Bruker D8 diffraction equipped with
Cu Kα radiation (λ = 0.154 nm, 35 kV, 40 mA). The morphology of all the
samples were obtained by using a FEI QUATA Q400 field emission
scanning electron microscope (SEM) with energy-dispersive X-ray (EDX)
spectrometer. Nitrogen adsorption–desorption isotherms of the
calcinated samples were measured at -196 °C, using a volumetric gas
sorption analyzer (QuantaChrome IQ) after being degassed at 300 °C for
6 h. The surface areas were calculated using BET method, and the
micropore volume were calculated by the t-Plot method. The acidity of
the SAPO-34 catalysts were characterized by temperature-programmed
desorption of ammonia (NH3-TPD).[43] The NH3-TPD measurements were
In summary, SAPO-34 zeolites were synthesized and
characterized by using laponite as the single Si source, and its
crystallization mechanism and MTO catalytic performance were
investigated as well. Laponite itself contains Li and Mg atoms
which could be introduced into the SAPO-34 zeolite via
depolymerization-reorganization
of
laponite
during
the
crystallization process. Metal incorporation can reduce the
amount of stronger acid sites and improve catalytic performance.
Therefore, the preparation of SAPO-34 zeolite by using laponite
as the Si source is an attractive option to enhance the catalytic
performance for MTO reaction. The methodology also can be
easily extended to the preparation of other zeolites.
performed on
a
Chem BET TPR/TPD Chemisorption Analyzer,
QuantaChrome instruments. The chemical composition of S-54 sample
was determined by inductively coupled plasma mass spectroscopy (ICP-
MS; Agilent). Diffuse reflectance UV–vis spectra of the samples of were
5
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10.1002/ejic.202000183
European Journal of Inorganic Chemistry
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Acknowledgements
The work was supported by the National Natural Science
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Keywords: SAPO-34 zeolite • laponite • crystallization • MTO
reaction
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10.1002/ejic.202000183
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Entry for the Table of Contents
Zeolites
SAPO-34 zeolite was successfully synthesized from laponite as the single Si source. laponite itself contains Li and Mg atoms, which
were subsequently introduced into the structure of SAPO-34 via depolymerization-reorganization of laponite. Metal incorporation can
reduce the amount of stronger acid sites and enhance the catalytic performance for MTO reaction.
7
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