Sustainable synthesis of zeolites without addition of both organotemplates and solvents

Article abstract of DOI:10.1021/ja500098j

The development of sustainable and environmentally friendly techniques for synthesizing zeolites has attracted much attention, as the use of organic templates and solvents in the hydrothermal synthesis of zeolites is a major obstacle for realizing green and sustainable synthesis ways. Recently, the introduction of the organotemplate-free synthesis method allowed avoiding the use of organic templates, but water as solvent was still required; solvent-free routes on the other hand beared the potential to significantly reduce the amount of polluted wastewater, but organic templates were still present. In this work, we have demonstrated a combined strategy of both organotemplate- and solvent-free conditions to synthesize aluminosilicate zeolites Beta and ZSM-5 (S-Beta and S-ZSM-5), two of the most important zeolites relevant for industry. The samples are thoroughly characterized by XRD patterns, SEM images, N ₂ sorption isotherms, UV-Raman spectra, and ²⁹Si and ²⁷Al MAS NMR spectra. The results demonstrate that S-Beta and S-ZSM-5 zeolites exhibit almost the same textural parameters (e.g., BET surface area and pore volume) and catalytic performance in cumene cracking and m-xylene isomerization as those of conventional Beta and ZSM-5 zeolites synthesized under hydrothermal conditions (C-Beta and C-ZSM-5). The organotemplate- and solvent-free syntheses of S-Beta and S-ZSM-5 take place at a low-pressure regime and are free of harmful gases as well as give high product yields together with highly efficient consumption of the starting raw materials. These advantages plus the very simple procedures opened the pathway to a highly sustainable zeolite synthesis protocol compared to conventional methods currently employed for C-Beta and C-ZSM-5. Very interestingly, this simple synthesis is a good model for understanding zeolite crystallization. The detail characterizations indicate that the S-Beta crystals are formed from the assembly of zeolite building units, mainly 4MRs, while the 5MRs in the framework are just formed in the crystallization of S-ZSM-5, rather than existence in the starting solid mixture. During the crystallization processes, small traces of water play an important role for the hydrolysis and condensation of silica and/or aluminosilicate species.

Full text of DOI:10.1021/ja500098j

Article
pubs.acs.org/JACS
Sustainable Synthesis of Zeolites without Addition of Both
Organotemplates and Solvents
†
†
§
‡
†
,†
§
Qinming Wu, Xiong Wang, Guodong Qi, Qiang Guo, Shuxiang Pan, Xiangju Meng,* Jun Xu,
§
‡
‡
,‡
#
#
Feng Deng, Fengtao Fan, Zhaochi Feng, Can Li,* Stefan Maurer, Ulrich Muller,
̈
,
†
and Feng-Shou Xiao*
†
Department of Chemistry, Key Lab of Applied Chemistry of Zhejiang Province, Zhejiang University, Hangzhou, 310007, P. R. China
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Center for Magnetic Resonance, Wuhan
§
Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, 430071, P. R. China
‡
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, P. R. China
#Process Research and Chemical Engineering, BASF SE, 67056, Ludwigshafen, Germany
*
S Supporting Information
ABSTRACT: The development of sustainable and environ-
mentally friendly techniques for synthesizing zeolites has
attracted much attention, as the use of organic templates and
solvents in the hydrothermal synthesis of zeolites is a major
obstacle for realizing green and sustainable synthesis ways.
Recently, the introduction of the organotemplate-free syn-
thesis method allowed avoiding the use of organic templates,
but water as solvent was still required; solvent-free routes on
the other hand beared the potential to significantly reduce the
amount of polluted wastewater, but organic templates were still present. In this work, we have demonstrated a combined strategy
of both organotemplate- and solvent-free conditions to synthesize aluminosilicate zeolites Beta and ZSM-5 (S-Beta and S-ZSM-
5
), two of the most important zeolites relevant for industry. The samples are thoroughly characterized by XRD patterns, SEM
29
27
images, N sorption isotherms, UV-Raman spectra, and Si and Al MAS NMR spectra. The results demonstrate that S-Beta
2
and S-ZSM-5 zeolites exhibit almost the same textural parameters (e.g., BET surface area and pore volume) and catalytic
performance in cumene cracking and m-xylene isomerization as those of conventional Beta and ZSM-5 zeolites synthesized under
hydrothermal conditions (C-Beta and C-ZSM-5). The organotemplate- and solvent-free syntheses of S-Beta and S-ZSM-5 take
place at a low-pressure regime and are free of harmful gases as well as give high product yields together with highly efficient
consumption of the starting raw materials. These advantages plus the very simple procedures opened the pathway to a highly
sustainable zeolite synthesis protocol compared to conventional methods currently employed for C-Beta and C-ZSM-5. Very
interestingly, this simple synthesis is a good model for understanding zeolite crystallization. The detail characterizations indicate
that the S-Beta crystals are formed from the assembly of zeolite building units, mainly 4MRs, while the 5MRs in the framework
are just formed in the crystallization of S-ZSM-5, rather than existence in the starting solid mixture. During the crystallization
processes, small traces of water play an important role for the hydrolysis and condensation of silica and/or aluminosilicate
species.
1
. INTRODUCTION
reactants, but the solvents occupy a large space in autoclaves,
1
−37
which strongly influence the product yield.
autogenous pressure and polluted wastes from the solvents also
In addition, high
Zeolites, especially aluminosilicate zeolites, have been widely
used as catalysts in the industrial processes of oil refining and
production of fine chemicals due to their high surface area, large
pore volume, uniform microporous channels, and excellently
1
−37
results in safety and environmental concerns.
Recently, to overcome the drawbacks brought from using toxic
and costly organic templates, an organotemplate-free synthesis
route was successfully developed based on a seed-directed route
for synthesizing aluminosilicate zeolites, where the zeolite
crystals are grown from the induction of zeolite seeds in the
1
−29
thermal and hydrothermal stabilities.
In general, zeolites are
made in a so-called solvothermal synthesis in the presence of
toxic and costly organic templates and large amounts of solvents
such as water and/or alcohols, often in sealed autoclaves under
autogenous pressure.
not only increases the zeolite cost but also results in the
production of harmful gases for removing the organic templates
3
8−64
30,31
absence of any organic templates.
Later, this synthesis has
The use of expensive organic templates
39
been quickly scaled up by BASF (Ludwigshafen, Germany).
1
−37
by combustion at high temperature.
in the solvothermal synthesis is to ensure efficient transport of
The presence of solvents
Received: January 6, 2014
Published: February 19, 2014
©
2014 American Chemical Society
4019
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Article
However, this methodology normally gives relatiely low zeolite
yield, which is due to the use of a large amount of water
solvent.
sample was prepared from ion exchange with 1 M NH
4
NO
3
solution and
calcination at 500 °C for 4 h. The ion exchange was repeated once.
Characterization. X-ray powder diffraction (XRD) patterns were
measured with a Rigaku Ultimate VI X-ray diffractometer (40 kV, 40
mA) using CuK (λ=1.5406 Å) radiation. The N sorption isotherms at
3
8−64
In the previous works, great efforts were made for increasing
α
2
zeolite product yields and reducing autogenous pressure as well
the temperature of liquid nitrogen were measured using Micromeritics
ASAP 2020 M and Tristar system. The sample composition was
determined by inductively coupled plasma (ICP) with a Perkin-Elmer
3300DV emission spectrometer. Scanning electron microscopy (SEM)
experiments were performed on Hitachi SU-1510 electron microscopes.
UV Raman spectra were measured with a Jobin-Yvon T64000 triple-
32,65−67
as reduction of polluted residues in the synthesis.
In 1990,
Xu et al. reported synthesis of zeolites from dry gel conversion or
65
vapor phase transport technique. Later, Matsukata and co-
workers designed a similar steam-assisted conversion to prepare
6
6
̈
zeolites. Schuth and co-workers have reported hydrothermal
−
1
67
stage spectrometer with spectral resolution of 2 cm . The laser line at
zeolite syntheses from “dry” starting materials. These syntheses
significantly increase zeolite product yield but still require the
presence of organic templates. In addition, Morris et al. have
developed an ionothermal synthesis route for synthesizing
zeolites, where the safety concerns are completely eliminated due
3
5
25 nm of a He/Cd laser was used as an exciting source with an output of
0 mW. The power of the laser at the sample was ∼3.0 mW. Al and Si
27
29
III
MAS NMR spectra were recorded on a Bruker AVANCE 500WB
spectrometer. Single-pulse 27Al MAS spectra were acquired using a 4
mm probe with a short radio frequency (rf) pulse of 0.25 μs
(corresponding to a π/15 flip angle), a pulse delay of 1.0 s, and a
32
to very low vapor pressure of the ionic liquids. Notably, the
ionic liquids in the synthesis served as both solvents and organic
templates.
29
spinning rate of 12 kHz. Single-pulse Si MAS NMR experiments with
1
H decoupling were performed using a 7 mm probe with a π/4 pulse
width of 4.0 μs, a 60 s pulse delay, and a spinning rate of 4 kHz.
Catalytic tests. Cumene cracking was performed at 300 °C by pulse
injections. In each run, 50 mg of catalyst was used, the pulse injection of
the reactant was 0.4 μL, and the reaction flow rate was 55 mL/min.
Catalytic m-xylene isomerization to p-xylene was carried out in a
fixed-bed reactor. The zeolite sample (200 mg, 20−40 mesh) was first
activated in dry air at 450 °C for 2 h and then cooled to reaction
temperature (350 °C) in a flow of dry nitrogen. m-Xylene was fed
More recently, Ren et al. and Jin et al. reported solvent-free
synthesis of aluminosilicate and aluminophosphate-based
zeolites with advantages of increasing zeolite yield and
6
8,69
eliminating high-pressure conditions.
Morris et al. high-
lighted the importance of the solventless synthesis and pointed
out that the combination of solventless synthesis and organo-
template-free routes should be the ultimate goal for synthesizing
zeolites on an environmental sustainable basis. A particularly
interesting candidate might be the BEA* structure as it was
demonstrated that Beta can be prepared without the use of
organic SDA, and furthermore Beta is known as an excellent
−1
(
WHSV = 3 h ) by a metering pump, vaporized in a preheated
assembly, and then passed through the catalyst. The product was
analyzed by online gas chromatography (GC1690) with FID detector
using HP-FFAP column.
70
catalyst for many industrial relevant processes.
3
. RESULTS AND DISCUSSION
In this work, we report a novel strategy for synthesizing BEA*
and MFI zeolite structures by combination of organotemplate-
and solvent-free routes. The synthetic processes and the zeolite
properties were carefully investigated. The zeolites synthesized
show comparable textural parameters and catalytic performance
to conventional zeolites synthesized under hydrothermal
conditions.
Synthesis of Beta Zeolite. Figure 1 shows XRD pattern,
29
SEM image, N sorption isotherms, and Si MAS NMR
2
2. EXPERIMENTAL SECTION
Materials. Aluminum sulfate [Al (SO ) ·18H O, AR, 99%,
2
4
3
2
Sinopharm Chemical Reagent Co., Ltd.], sodium hydroxide (NaOH,
AR, 96%, Sinopharm Chemical Reagent Co., Ltd.), Na SiO ·9H O
2
3
2
(
SiO of 20 wt.%, Tianjin Guangfu Chemical Reagent Co, Ltd.), solid
2
silica gel (Qingdao Haiyang Chemical Reagent Co, Ltd.), NaAlO2
Sinopharm Chemical Reagent Co, Ltd.), SiO ·3H O (homemade), and
(
2
2
ammonium nitrate (NH NO , AR, 99%, Beijing Chemical Reagent Co.,
4
3
Ltd.) were used without further purification.
Synthesis. As a typical run for the synthesis of Beta zeolite without
addition of water as solvent, 6.34 g of SiO ·3H O (hydrated form of
2
2
solid silica gel), 0.73 g of NaAlO , 0.48 g of NaOH, and 0.34 g of calcined
2
Beta seeds (Si/Al = 12.5) were added together. After grinding for 10−20
min, the powder mixture was transferred to an autoclave and sealed.
After heating at 120 °C for 9 days, the sample was completely
crystallized (designated as S-Beta), giving 3.0 g product. The H-form of
the sample was prepared by ion exchange with 1 M NH NO solution
Figure 1. (a) XRD pattern, (b) SEM image, (c) N
and (d) 29Si NMR spectrum of S-Beta sample. The measurement of the
sorption isotherms,
2
N sorption isotherms is from the H-form and the other measurements
2
from as-synthesized S-Beta sample.
4
3
and calcination at 500 °C for 4 h. The ion-exchange procedure was
repeated once.
spectrum of Beta zeolite synthesized without addition of both
organotemplate and water (S-Beta). The XRD pattern shows a
series of characteristic peaks associated with BEA structure
As a typical run for the synthesis of ZSM-5 zeolite without addition of
water as solvent, 1.5 g of NaSiO ·9H O (SiO , 20wt.%), 0.65 g of
3
2
2
Al (SO ) ·18H O, 1.35 g of solid silica gel, and 0.17 g of calcined ZSM-5
2
4
3
2
(
(
Figure 1a). The SEM image exhibits almost perfect crystals
Figure 1b), confirming relatively high crystallinity. The N2
(
Si/Al = 150) seeds were added together. After grinding for 10−20 min,
the powder mixture was transferred to an autoclave and sealed. After
heating at 180 °C for 13 h, the sample was completely crystallized
sorption isotherms displays typical Langmuir-type curve (Figure
1c). Typical for microporous materials a steep increase at low
(
designated as S-ZSM-5), giving 1.9 g product. The H-form of the
4
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29
Figure 2. (A) XRD patterns, (B) SEM images, (C) UV-Raman spectra, (D) Si NMR spectra of S-Beta samples crystallized at (a) 0, (b) 2, (c) 4, (d) 5,
e) 7, and (f) 9 days, respectively.
(
relative pressure 10−6 < P/P < 0.01, due to the filling of
4.72−5.12 and the SiO /Al O ratios close to 17 are suitable for
0
2
2
3
micropores by N is observed. Correspondingly, the sample BET
synthesis of S-Beta.
2
2
3
surface area and micropore volume are 464 m /g and 0.21 cm /g,
respectively, in good agreement with those (445 m /g and 0.21
To get a better understanding of the synthesis, the
crystallization process of S-Beta has been intensively investigated
by XRD, SEM, UV-Raman, and NMR techniques, as shown in
Figure 2 and Figure S2. The photographs of the samples
crystallized at various time in a closed glass tube (Figure S3)
show that the samples are always in a solid phase during the
crystallization process, indicating full solid conversion. Before
crystallization, the sample shows very weak peaks associated with
Beta seeds (Figure 2A-a), which are related to the Beta seeds
existing in the starting mixtures. After crystallization for 2 days,
the sample displays stronger peaks associated with BEA zeolite
(Figure 2A-b). At the same time, small amounts of crystalline
products were visible via SEM (Figure 2B-b). Increasing the
crystallization time from 4 to 7 days, the XRD peaks gradually
grow in intensity (Figure 2A-c-e). Correspondingly, more S-Beta
zeolite crystals were observed in the isolated solid (Figure 2B-d).
When the crystallization time reaches 9 days, S-Beta with high
crystallinity can be obtained (Figure 2A-f and B-f). The
dependence of S-Beta crystallinity on crystallization time is
shown in Figure S4.
2
3
cm /g) of Beta zeolite synthesized in the presence of water under
hydrothermal conditions (C-Beta, Figure S1). The 29Si NMR
spectrum (Figure 1d) exhibits peaks at about −115.0, −110.3,
−104.7, and −98.2 ppm. The peaks at −115 and −110.3 ppm are
assigned to Si(4Si) species; the peak at −104.7 ppm is assigned to
Si(3Si,1Al) and/or Si(3Si,1OH); the peak at −98.2 ppm is
assigned to Si(2Si,2Al), Si(2Si,1Al,1OH), and/or Si(2Si,2OH).
ICP analysis shows that Si/Al ratio in the product is ∼5.9.
Notably, Beta seeds play an important role in the synthesis. If
Beta seeds are absent in the solid starting mixtures, the obtained
products are always amorphous or MOR zeolite (Run 1 in Table
S1). After addition of Beta seeds to the starting mixtures, S-Beta
zeolites with good crystallinity are obtained (Run 2 and 3 in
Table S1). In addition, it is found that the ratios of SiO /Na O
2
2
and SiO /Al O also strongly influence the synthesis of S-Beta
2
2
3
zeolite. When the SiO /Na O ratio is lower than 4.52, the
2
2
product contains GIS and MOR impurity (Run 4, Table S1).
When the SiO /Na O ratio is higher than 5.67, the product
2
2
comprises MOR impurity (Run 5, Table S1). When the SiO2/
Al O ratio is 12, the product contains GIS and MOR impurity
Figure 2C shows UV-Raman spectra recorded for S-Beta
samples crystallized at various time. The initial aluminosilicate
solid mixture shows a major broad band at 493 cm− associated
with four-membered rings of T−O−T (4MRs). In addition, the
2
3
1
(
Run 6, Table S1). When the SiO /Al O is 17, S-Beta zeolite is
2 2 3
obtained (Run 2, Table S1). Therefore, the SiO /Na O ratios at
2
2
4
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aluminosilicate solid mixture in the absence of Beta seeds also
−1
shows a broad band at 493 cm (Figure S5), suggesting that this
band should result from the solid mixture, rather than the Beta
seeds. Notably, the band at 493 cm− in Figure 2C-a gradually
1
−1
shifted to lower wavenumber (485 cm ), which is attributed to
the rearrangement and self-assembly of zeolite building units,
mainly 4MRs. After crystallization for 4 days, UV-Raman
−1
spectrum gives weak band at 342 cm associated with six-
−
1
membered rings (6MRs), 396 cm associated with five-
−1
membered rings (5MRs), and 431, 460, and 485 cm associated
7
1,72
with 4MRs.
By increasing the crystallization time to 9 days,
−1
the sample shows strong bands at 342, 396, 431, and 460 cm
associated with characteristic bands of Beta zeolites,
with complete disappearance of the band at 485 cm . This
observation suggests that the formation of S-Beta zeolite mainly
results from assembling zeolite building units at 485 cm .
71,72
together
−
1
−1
Usually, it is well-known that 4MRs, 5MRs, and 6MRs are
building units for construction of Beta zeolite structure.
7
1,72
Figure 3. (a) XRD pattern, (b) SEM image, (c) N sorption isotherms,
2
29
and (d) Si NMR spectrum of S-ZSM-5 sample. N sorption isotherm is
However, as observed in UV-Raman spectra, the starting solid
mixture predominantly consists of 4MRs, suggesting that 4MRs
might be the active building units for crystallization of S-Beta
zeolite, while 5MRs and 6MRs are just formed after the
formation of the S-Beta zeolite framework.
2
obtained from the H-form, other measurements are as-synthesized S-
ZSM-5 sample.
a steep increase at low relative pressure 10− < P/P < 0.01, due to
6
0
Figures 2D and S2 show Si and 27Al NMR spectra of solid
samples obtained from crystallization at various time (0−9 days).
The structural information on S-Beta samples is presented in
Tables S2 and S3. Before crystallization, the Si(2Si) species are
dominant (intensity 36.1%, Figure 2D-a). After crystallization for
29
the filling of micropores by N is observed. The sample BET
2
2
3
surface area and micropore volume are 345 m /g and 0.16 cm /g,
which is comparable with those (350 m /g and 0.16 cm /g) of
conventional MFI zeolite (Figure S6). The Si NMR spectrum
Figure 3d) shows signals at −114.8, −112.2, and −106.7 ppm.
2
3
29
(
2
days, the Si(2Si) signal intensity is decreased to 21.5%, while
The peaks at −114.8 and −112.2 ppm are assigned to Si(4Si)
species; the peak at −106.7 ppm is assigned to Si(3Si,1Al) and/
or Si(3Si,1OH). ICP analysis shows that Si/Al ratio of S-ZSM-5
is about 13. In the synthesis of S-ZSM-5, the use of ZSM-5 seeds
and adjusting SiO /Al O ratios is very important. When the
the Si(3Si) signal intensity increases (33%) (Figure 2D-b). This
phenomenon might be related to the rearrangement of zeolite
building units. At the same time, a broad signal in the range of
2
7
5
0−70 ppm is observed in the Al NMR spectrum, mainly
2
2
3
73
attributed to Al(3Si) and Al(4Si) species (Figure S2-b). It is
worth mentioning that the concentration of Si(2Si) species is
increasing with the crystallization time from 2 to 4 days, while
decreasing with the crystallization time from 4 to 9 days. The
enrichment of Si(2Si) species should be assigned to the
hydrolysis of silica species due to the presence of a little amount
of water in the solid mixture, while the remarkable reduction of
Si(2Si) species at elongated crystallization period could be
attributed to the crystallization of zeolites by condensation of
Si(2Si) species containing hydroxyl groups. After crystallization
for 9 days, the 2 Si NMR spectrum exhibits major peaks at
ZSM-5 seeds are absent in the synthesis, the obtained solids are
always amorphous materials (Run 1, Table S4); when ZSM-5
seeds are present, perfect ZSM-5 crystals could be obtained (Run
2, Table S4). These results confirm the importance of ZSM-5
seeds for synthesizing S-ZSM-5 zeolite. In addition, when the
ratio of SiO /Al O in the synthesis is 20, the product exhibits
2
2
3
MOR impurity (Run 3, Table S4); when the SiO /Al O ratio
2
2
3
reaches to 40, the product contains an impurity of dense phase
(Run 4, Table S4). Therefore, the suitable SiO /Al O ratio is
2
2
3
found at about 28.5. Notably, when totally anhydrous reagents
(such as fumed silica) are used or ambient pressure is performed,
we cannot synthesize S-ZSM-5 zeolite owing to the shortage of a
few water in the synthesis system. These results confirm the
importance of a few water in the synthesis. The minimum
amount of water required for the synthesis of S-ZSM-5 zeolite
with good crystallinity is a H O/SiO ratio of at least 1.0.
9
−
104.7 and −110.5 ppm associated with Si(3Si) and Si(4Si)
27
species (Figure 2D-f). Simultaneously, the Al spectrum shows a
major peak at 57 ppm (Figure S2-f), corresponding to tetrahedral
coordination of framework Al. These results are consistent with
those of Beta zeolite synthesized under hydrothermal con-
2
2
4
2
ditions.
Interestingly, S-ZSM-5 product could be used as seeds to
synthesize S-ZSM-5-2nd sample in the following run under the
template-free and solvent-free conditions (Run 5, Table S4).
The crystallization of S-ZSM-5 has also been monitored with
XRD, SEM, UV-Raman, and 29Si and Al NMR techniques
(Figures 4 and S7). Similarly to BEA, the photographs of the
samples crystallized at various time in a closed glass tube (Figure
S8) show that the synthesis of S-ZSM-5 is a solid process. Before
crystallization, the XRD pattern gives weak signals associated
with ZSM-5 seeds (Figure 4A-a). After crystallization for 3 h, the
intensity of the MFI related signals is lower (Figure 4A-b),
indicating that the ZSM-5 seeds are partially dissolved in the
alkaline solid mixture at 180 °C. After further elongation of the
crystallization time to 5.5 h, the peaks associated with MFI
From our observation we suggest that S-Beta crystals are
formed from the assembly of zeolite building units, which mainly
consist of 4MRs. During this process, the hydrolysis and
condensation of silica species occur, suggesting an important role
of a little amount of water in the synthesis.
27
Synthesis of ZSM-5 Zeolite. Figure 3 shows XRD pattern,
2
9
SEM image, N sorption isotherms, and Si MAS NMR
2
spectrum of ZSM-5 zeolite synthesized without addition of
both organotemplate and water (S-ZSM-5). The XRD pattern
gives a series of characteristic peaks associated with MFI
structure (Figure 3a). The SEM image shows typical MFI crystal
morphology (Figure 3b). Figure 3c shows N sorption isotherms,
2
giving a Langmuir-type curve. Typical for microporous materials
4
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29
Figure 4. (A) XRD patterns, (B) SEM images, (C) UV-Raman spectra, (D) Si NMR spectra of S-ZSM-5 samples crystallized at (a) 0, (b) 3, (c) 5.5, (d)
, (e) 13, and (f) 17 h, respectively.
9
2
9
27
structure grow again (Figure 4A-c). At the same time, typical
ZSM-5 crystals are visible in the SEM of the isolated products
Figures 4D and S6 show the Si and Al NMR spectra of S-
ZSM-5 samples crystallized at various time (0−17 h). The
structural information on S-ZSM-5 is presented in Tables S5 and
S6. Before crystallization, Si(4Si) and Si(3Si) signals are
dominant (52.4% and 32.1%). After crystallization for 3 h, the
signal intensity of Si(3Si) species is significantly reduced
(18.2%), probably due to hydrolysis of silica species in the
presence of a little amount of water in the solid mixture. At the
same time, the signal intensity of Si(4Si) species is slightly
increased (59.2%) owing to condensation of silica species.
Increasing the crystallization time from 3 to 9 h, the Si(4Si)
signals gradually increase, which is assigned to crystallization of
S-ZSM-5 zeolite. When the crystallization time extends 13 h, no
obvious change in the intensity of the Si(4Si) signal can be
observed, indicating that the crystallization of S-ZSM-5 zeolite is
completed. The 27Al NMR spectra for all the samples show a
sharp signal centered near 55 ppm, indicating tetrahedral
coordination of the Al species.
(Figure 4B-c). Increasing the crystallization time to 9 h, the
intensity of XRD peaks gradually increases (Figure 4A-d).
Correspondingly, more MFI zeolite crystals are formed (Figure
4
B-d). When the crystallization time extends 13 h, no obvious
change in crystallinity can be observed anymore (Figure 4A-f).
The dependence of S-ZSM-5 crystallinity on crystallization time
is displayed in Figure S9.
Figure 4C shows UV-Raman spectra recorded for S-ZSM-5
samples crystallized at various time. Before crystallization, the
−1
sample exhibits a very weak band at 380 cm and strong bands at
−1
2−
4
55 and 995 cm . The two strong bands are assigned to SO
4
species, while the very weak band should be assigned to 5MRs,
which might result from the ZSM-5 seeds added to the solid
mixture. In comparison, it does not observe any bands at near
1
3
80 cm− for the solid mixture in the absence of ZSM-5 seeds
(
Figure S10). After crystallization for 9 h, the sample exhibits
−1
strong band at 380 cm , which is assigned to 5MRs in the
framework. These results suggest that the 5MRs in the
framework are mainly formed in the crystallization of S-ZSM-
From the observations during the crystallization, it is difficult
to find the building units of 5MRs in the starting solid materials
except for the presence of a small amount of zeolite seeds,
although MFI structure is rich in 5MRs. The 5MRs are just
formed during crystallization of S-ZSM-5 zeolite, rather than
being starting building units for the formation of S-ZSM-5. The
important role of small amounts of water in the synthesis of S-
5. By increasing the crystallization time from 9 to 17 h, the sample
UV-Raman spectra give higher band intensity, in agreement with
increasing the sample crystallinity. These results confirm that the
5MRs are formed in the crystallization of S-ZSM-5.
4
023
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ZSM-5 can be observed in the change in Si(3Si) concentration,
related to the hydrolysis and condensation of silica species during
the course of the crystallization.
hydrothermal synthesis, water occupies a large space of the
autoclave volume. For example, when 3.68 g of SiO sources was
2
crystallized in 15 mL of an autoclave, it was obtained 3.0 g of S-
Catalytic Tests. Figure 5 shows the catalytic properties of S-
Beta product. In contrast, when 0.83 g of SiO source was
2
Beta in cumene cracking, respectively, S-ZSM-5 in m-xylene
crystallized in the same autoclave under conventionally hydro-
thermal conditions, it was obtained only 0.22 g of Beta-SDS
39
product. (4) A significant reduction of reaction pressure,
achieved by both organotemplate- and solvent-free synthesis
conditions, giving good safety concerns. (5) High efficiency for
consumption of the starting raw materials, due to the removal of
solvents for dissolution of partial nutrients in the synthesis. In
addition, not consumed nutrients dissolved in the solvents and
the conventional hydrothermal synthesis are added to the
wastewater. (6) A simple and convenient procedure, which
means to save energy and cost in the synthesis of zeolite.
Considering these advantages, it is suggested that S-Beta and S-
ZSM-5 can be named as sustainable obtained zeolites. Very
importantly, the zeolites synthesized from the combined route of
both organotemplate- and solvent-free route show almost the
same textural parameters (BET surface area and pore volume)
and catalytic properties in cumene cracking, respectively, m-
xylene isomerization compared to conventional zeolites. The
combination of sustainable zeolite synthesis with comparable
properties allows to widely apply these S-Beta and S-ZSM-5
zeolites in industrial processes in the near future.
ASSOCIATED CONTENT
Supporting Information
Characterization details. This material is available free of charge
via the Internet at http://pubs.acs.org.
■
*
S
AUTHOR INFORMATION
■
Corresponding Authors
mengxj@zju.edu.cn
canli@dicp.ac.cn
fsxiao@zju.edu.cn
Notes
The authors declare no competing financial interest.
Figure 5. (a) Catalytic cumene cracking over S-Beta (□ conv.) and C-
Beta (■ conv.) zeolites and (b) catalytic performance in m-xylene
isomerization over S-ZSM-5 (□ conv.; ■ sel.) and C-ZSM-5 (○ conv.;
ACKNOWLEDGMENTS
■
●
sel.) zeolites as a function of number and time.
This work is supported by the Natural National Science
Foundation of China (21273197, 21333009, and 21203165),
National High-Tech Research and Development program of
China (2013AA065301), BASF SE, and Fundamental Research
Funds for the Central Universities (2013XZZX001).
isomerization, which is found to be very comparable with those
of conventional Beta and ZSM-5 zeolites. Notably, in both
cumene cracking and m-xylene isomerization, S-Beta and S-
ZSM-5 zeolites exhibit almost the same activity and selectivity as
well as very similar catalyst life. These results indicate that S-Beta
and S-ZSM-5 have comparable catalytic properties with
conventional corresponding zeolites.
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