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Microporous and Mesoporous Materials 135 (2010) 116–123
Contents lists available at ScienceDirect
Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso
Effect of synthesis parameters on mesoporous SAPO-5 with AFI-type formation
via microwave radiation using alumatrane and silatrane precursors
Kanchana Utchariyajit, Sujitra Wongkasemjit *
The Petroleum and Petrochemical College, National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand
a r t i c l e i n f o a b s t r a c t
Article history: Mesoporous zeotype, SAPO-5, has been prepared using alumatrane and silatrane precursors, containing
Received 12 January 2010 alkanolamine ligands, via microwave radiation. Triethylamine (TEA) was used as a structure-directing
Received in revised form 27 May 2010 agent. The effects of the amount of silicon, the reaction conditions, viz. aging time, reaction time and tem-
Accepted 29 June 2010
perature, were investigated. All samples were characterized using X-ray diffraction (XRD), scanning elec-
Available online 3 July 2010
tron microscopy (SEM), transmission electron microscopy (TEM), X-ray fluorescence (XRF), and nitrogen
physisorption. The results showed a SAPO-5 zeotype with an AFI-type structure, having a hexagonal outer
Keywords:
surface morphology and an average pore diameter of 2–5 nm. The samples contained a classic single crys-
Alumatrane
Silatrane
tal SAPO-5 and a 10–100 nm mesoporous matrix nanostructure, also having AFI structure.
Microwave heating technique Ó 2010 Elsevier Inc. All rights reserved.
Mesoporous zeotype
SAPO-5
1. Introduction silica content on the synthesis of microporous SAPO-5 with an AFI
type has been studied by several groups [17–19], who showed that
Owing to the benefits from the combination of mesoporous Si atoms affected the AFI framework by hindering the crystalliza-
molecular sieves and zeolites [1–3], mesoporous zeotype, AlPO4- tion to form plate-like hexagonal crystals [19]. The use of alumina
5, has recently been studied and synthesized [2,4]. The AlPO4-5 zeo- and silica sources has also been reported to affect the phase purity
type with an AFI-type molecular sieve, having unidimensional 12- [17,20,21], crystallinity, acidity, and morphology of the products
membered rings of straight channels, exhibits excellent thermal [21,22]. Mesoporous materials related to AlPO4 and SAPO have
stability and is widely used in catalysis, separation [5], membranes, extensively been synthesized [23–26]. As reported [1–3], mesopor-
sensors, and nonlinear optics [6]. Egeblad et al. [2] prepared meso- ous zeolite and zeotype (such as BEA, MEL, CHA, MFI, and AFI) have
porous AlPO4-5 with an AFI type by introducing a carbon particle been successfully prepared. From our previous works of mesopor-
template via fluoride route under conventional heating for 3 days. ous AlPO4-5 [4] synthesized using alumatrane [27], and silatrane
However, we have successfully synthesized mesoporous AlPO4-5 [28] precursors, SAPO-5 has thus been further studied and synthe-
(AFI) zeotype within only 2 h using an alumatrane precursor con- sized in this work using these precursors and TEA as a structure-
taining a bulky group of trialkanoamine ligand, via a simpler route directing agent under microwave radiation. The effects of chemical
of microwaving [4]. As discussed by many researchers, the synthe- composition and reaction conditions were investigated.
sis of AlPOs, zeolites, and other porous materials under microwave
heating has overcome many of the drawbacks found in using con- 2. Experimental
ventional heating; for example, the ability to obtain fast crystalliza-
tion [7–10], high phase purity [11,12], high phase selectivity [13– 2.1. Materials characterization
15], and narrow particle size distribution [16].
The introduction of Si atoms to the neutral AlPO4-5 structure The functional groups of the materials were followed using a
generates silicoaluminophosphate, SAPO-5, capable of producing Fourier transform infrared (FTIR) spectrophotometer (Nicolet,
cation exchange properties and inducing Brønsted acid sites into NEXUS 670) with a resolution of 4 cm1. Thermogravimetric anal-
the framework, to be further used as acid catalysts, since it provides ysis (TGA) was carried out using TG-DTA (Pyris Diamond Perkin–
a much stronger interaction with the hydrocarbons [1]. The effect of Elmer) with a heating rate of 10 °C/min under nitrogen atmosphere
to determine the thermal stability. Pore volume and pore size dis-
tribution were measured using nitrogen at 77 K in an Autusorb-1
* Corresponding author. Tel.: +66 2 218 4133; fax: +66 2 215 4459. gas sorption system (Quantasorb JR). The samples were degassed
E-mail address: dsujitra@chula.ac.th (S. Wongkasemjit). at 250 °C under a reduced pressure prior to each measurement.
1387-1811/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.micromeso.2010.06.018K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123 117
Micropore and mesopore volumes were determined by the t- and 3.3. Preparation of SAPO-5 (AFI)-type zeotype
BJH methods (desorption), and the product morphology was stud-
ied using SEM (JEOL 5200-2AE SEM). The chemical composition of The alumatrane was mixed with a 1 M phosphoric acid solution
the samples was determined by XRF (Philips PW 2400) and an SEM while homogeneously stirring at room temperature. The silatrane
(JEOL JSM-5410LV) equipped with energy-dispersive analysis of X- was added to the mixture with various mole ratios of SiO2/Al2O3,
rays (EDAX, Oxford Link Isis Instrument). A TEM (JEOL JEM-2100) followed by adding TEA (Fisher Scientific) as a structure-directing
was used for characterizing the pore system of the samples. Calci- agent. The mixture was aged, with stirring, at various aging times
nation was performed in a Carbolite Furnace (CFS 1200) with a before being loaded into a Teflon line vessel sealed with a Teflon
heating rate of 1 °C/min. Hydrothermal crystallization by micro- cap and placed in a microwave oven. The reaction mixture was
wave heating was carried out in a Milestone’s Ethos microwave heated at various temperatures (180–200 °C) for various amount
solvent extraction lab station with a microwave radiation fre- of time (0.5–2 h). After reaction, the pH value was 6.5, being nearly
quency of 2.45 GHz. Crystallinity characterization of the samples the same as the pH value before the hydrothermal treatment. The
was done by XRD (Rigaku) with a Cu Ka source in the range of products were filtered, washed, and dried. The as-synthesized
5–60° and a step of 5°/min and was calculated by the following products were calcined at 550 °C for 7 h. The amount of SiO2, aging
equation: time, and reaction conditions were varied.
X X
%Crystallinity ¼ ð I= Is Þ 100
4. Results and discussion
where I is the line intensity of the sample and Is is the line intensity
In the present work, SAPO-5 with AFI-type material was pre-
of the standard sample, using the product having the highest crys-
pared using various reaction conditions and chemical composi-
tallinity, as identified by XRD and supported by SEM. The line inten-
tions of the atrane precursors under microwave radiation. The
sities of the XRD pattern at 2h equal to 7.5°, 14.9°, 19.8°, 21.1°, 22.5°,
XRD patterns of the products corresponded well with the structure
and 26.0° [29] were employed for these calculations.
pattern of the AFI-type topology reported in Refs. [2,19,30]. The
SEM images showed that all synthesized SAPO-5 samples had a
well-formed hexagonal outer surface. Using microwave heating,
3. Methodology
only 1–2 h synthesis time was needed for obtaining SAPO-5 that
was homogeneous in size, as also verified by Kodaira et al., who
3.1. Synthesis of alumatrane
synthesized AlPO-5 using microwaving and conventional tech-
niques [16]; the crystals obtained via the microwave heating gave
The preparation of the alumatrane followed the work of
a narrower particle size distribution than those obtained under
Opornsawad et al. [27] Aluminium hydroxide (0.1 mol, Sigma
conventional heating at 190 °C for 4 days. The microwave radiation
Chemical Co.), triisopropanolamine (TIS, 0.125 mol, Aldrich Chem-
appears to generate uniform and quick heating throughout the
ical Co., Inc., USA), and ethylene glycol (EG, 100 mL, J.T. Baker, Inc.,
synthesis mixture, resulting in the simultaneous formation of
Phillipsburg, USA) were mixed in a 250 mL two-necked round bot-
many nuclei of crystals. Moreover, Demuth et al. [17] used conven-
tom flask. The mixture was homogeneously stirred at room tem-
tional heating to synthesize non-homogeneous SAPO-5 at 210 °C
perature before being heated to 200 °C under nitrogen for 10 h.
for 70 h, followed by calcination at 850 °C for at least 24 h. In our
Excess EG was removed under vacuum (102 Torr) at 110 °C to ob-
case, the microwave synthesized SAPO-5 using atrane precursors
tain a crude product. The crude solid was washed with acetonitrile
needed to be calcined at only 550 °C for 7 h. Fig. 1 provides TGA
(Lab-Scan Company Co., Ltd.) and dried under vacuum at room
data of both SAPO-5 gel and as synthesized SAPO-5 in the temper-
temperature. The dried products were characterized using TGA
ature range of 30–900 °C. They both showed three decomposition
and FTIR.
transitions. According to our previous studies [27,28], the lowest
FTIR: 3700–3300 cm1 (m OH), 2750–3000 cm1 (m CH),
temperature weight loss was due to the elimination of water and
1650 cm1 (m OH overtone), 1460 cm1 (d CH), 1078 cm1 (m Al–
O–C), 500–800 cm1 (m Al–O). TGA: 33% char yield, which is larger
than the theoretical ceramic value of 23.7%. This may be due to
incomplete combustion, as confirmed by the black color of the
char.
3.2. Synthesis of silatrane
The silatrane was synthesized using a process identical to the
alumatrane synthesis [28]; that is, by mixing fumed silica
(0.1 mol, 99.8% SiO2, Sigma Chemical Co.), triethanolamine
(0.125 mol, Aldrich Chemical Co., Inc., USA), and EG (100 mL) in a
250 mL two-necked round bottom flask. The mixture was heated
to the boiling point of EG under nitrogen for 10 h. The remaining
EG was removed under vacuum at 110 °C to obtain a brownish
white solid, followed by washing with acetonitrile to obtain a
white powder and by drying under vacuum at room temperature
before characterization using TGA and FTIR.
FTIR: 3700–3300 cm1 (m OH), 2800–3000 cm1 (m CH), 1244–
1275 cm1 (m CN), 1170–1117 cm1 (m Si–O), 1093 cm1 (m Si–O–
C), 1073 cm1 (m CO), 785 and 729 cm1 (Si–O–C), 579 cm1 (m Fig. 1. TGA profiles of both SAPO-5 gel and as synthesized SAPO-5 prepared from
N ? Si). TGA: 19% ceramic yield, which is close to the theoretical the mixture composition Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at a reaction tem-
value of 18.5%. perature of 190 °C for 1 h.118 K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123
TEA while the others around 150– 350 °C and above 350 °C were increase in the aging time to 24 h produced crystals that were still
attributed to the loss of triethanolamine [28] and TIS molecules smaller in size, but which had less homogeneity than those aged
[27]. for 16 h. Moreover, the XRD patterns (Fig. 3) of the same samples
indeed show the pattern of a pure SAPO-5 structure without any
impurity, except the sample aged for 24 h (Fig. 3d), which showed
4.1. Effect of aging time
a small amount of impurity identified as the tridymite phase [32]
coexisting with the AFI-type structure. The impurity phase was
The SEM images shown in Fig. 2 illustrate SAPO-5 prepared
also observed by Chen and coworkers when loading a higher
from the reaction gels of Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O
amount of metal onto the AFI framework of AlPO4-5 [32]. A proper
aged, with stirring, for various amounts of time (4–24 h), and
aging time of 16 h was thus selected for further study.
heated at 190 °C for 1 h. To keep the pH value of the synthesis mix-
ture at near neutral, the mole ratio of the Al2O3/P2O5 was fixed at
1:2 throughout all conditions. It was found that smaller and more 4.2. Effect of reaction time
uniform SAPO-5 crystals were formed at prolonged aging time, ow-
ing to the higher number of nucleation centers created by the agi- The mixture composition, Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O,
tation of the gel, as discussed by Du and coworkers [31]. A further aging time, 16 h, and reaction temperature, 190 °C, were fixed in
Fig. 2. SEM images of SAPO-5 prepared from the mixture Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O heated at 190 °C for 1 h and aged for (a) 4 h, (b) 8 h, (c) 16 h, and (d) 24 h.
Intensity [cps]
** *
(d)
(c)
(b)
(a)
10 20 30 40 50
2Theta [º]
Fig. 3. XRD patterns of SAPO-5 synthesized from the mixture Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at 190 °C 1 h and aged for (a) 4 h, (b) 8 h, (c) 16 h, and (d) 24 h. (Note:
refers to the tridymite phase).K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123 119 order to investigate the effects of reaction time on the crystalliza- 4.3. Effect of reaction temperature tion of the SAPO-5. The reaction duration was varied from 0.5 to 2 h. The results in Fig. 4 show that the sample synthesized for The chemical composition, Al2O3:2P2O5:0.2SiO2:1.5TEA:750- microwave heating time of 0.5 h resulted in SAPO-5 crystals mixed H2O, aging time, 16 h, and reaction time, 1 h, were fixed to study in with some amorphous phase (Fig. 4a), implying that there was the effects of the reaction temperature, by varying it between not enough time for the SAPO-5 to be completely formed. On 180 and 200 °C (Fig. 5a–c). At the lowest microwave temperature, increasing the reaction time to 1 h, SAPO-5 crystals were obtained. 180 °C, it appears that the temperature was not high enough for As the reaction duration was increased to more than 1 h, a second- perfect crystals to be formed; amorphous growth covered the en- ary growth of SAPO-5 crystals started to occur and they became tire SAPO-5 product. This result was confirmed by the XRD pattern non-uniform. Thus, the reaction time of 1 h was chosen to study (Fig. 6a), showing not only a lower intensity but also a curved base the other effects. line, indicating the presence of an amorphous phase. When the Fig. 4. SEM images of SAPO-5 prepared from the mixture Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at 190 °C microwave heating for (a) 0.5 h, (b) 1 h, (c) 1.5 h, and (d) 2 h. Fig. 5. SEM images of SAPO-5 obtained from the mixture Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O for 1 h reaction time at reaction temperatures of (a) 180 °C, (b) 190 °C, and (c) 200 °C.
120 K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123
***
(c)
Intensity [cps]
(b)
(a)
10 20 30 40 50
2Theta [º]
Fig. 6. XRD patterns of SAPO-5 synthesized from the mixture Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O for 1 h reaction time at reaction temperatures of (a) 180 °C, (b) 190 °C, and
(c) 200 °C. (Note: refers to the tridymite phase).
temperature was increased to 190 °C, pure and uniform SAPO-5 to the SAPO-5 crystals, small amounts of tridymite [32] were also
crystals with a hexagonal plate-like structure (Figs. 5b and 6b) obtained (Fig. 6c). These results are in good agreement with the
were obtained. However, a reaction temperature of 200 °C did work done by Demuth et al. [17], who also obtained the pure phase
not seem to provide higher quality crystals because, in addition of SAPO-5 at a reaction temperature of 210 °C, did not obtain
Fig. 7. SEM images of SAPO-5 obtained from the mixture Al2O3:2P2O5:xSiO2:1.5TEA:750H2O at 190 °C for 1 h, where x is the SiO2/Al2O3 mole ratio of (a) 0, (b) 0.2, (c) 0.4, (d)
0.6, (e) 0.8, and (f) 1.0.K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123 121
SAPO-5 at lower temperatures (170–190 °C), and observed both who also indicated that the incorporation of Si atoms into an
the crystals of SAPO-5 and tridymite at temperatures higher than AFI-type framework influenced the crystal growth in the c-axis.
210 °C. In our case, trialkoxylamines generated from both silatrane Moreover, at higher silicon content loaded into the reactant gels
and alumatrane precursors during the reaction could act as co- (>0.2), amorphous impurity occurred along with the obtained hex-
directing agents to form pure phase SAPO-5 at 190 °C, as discussed agonal plate-like crystals, as confirmed by calculating the% crystal-
elsewhere [33]. These results indicate that there is a temperature– linity summarized in Table 1 and the XRD spectra shown in Fig. 8.
time optimum controlling the reaction conditions for the synthesis It can clearly be seen from Table 1 that the higher the amount of
of pure phase SAPO-5 materials. silicon loaded, beyond 0.2, the lower the crystallinity of obtained
SAPO-5 materials, as also reported by Akolekar [34] He studied
the effect of silicon amount (0–0.224 mol ratio of SiO2–Al2O3) in
4.4. Effect of silicon content SAPO-5 crystal, using pseudo-boehmite and Kieselgel 500 as
Al2O3 and SiO2 sources, respectively, and found that the crystallin-
A mixture composition of Al2O3:2P2O5:xSiO2:1.5TEA:750H2O ity of the SAPO-5 decreased with the increased silicon amount.
was used to study the effect of silicon loading into the AFI frame- From Fig. 8, showing only the SAPO-5 phase, we can conclude that
work. The amount of SiO2 was varied from a 0 to 1.0 mol ratio of
SiO2 to Al2O3. The SEM images of the crystals obtained from vari-
ous silicon contents are shown in Fig. 7. It was found that the sam- 0.8
ple prepared without silicon in the reactant gel showed a long
SiO2/Al2O3 mole ratio in product
hexagonal rod-like structure (Fig. 7a), which is characteristic of
AlPO4-5 with an AFI topology [4,29]. When loading silicon dioxide
into the same chemical composition of the gel, the crystal mor- 0.6
phology became short, plate-like, and hexagonal (Fig. 7b–f) shape.
This result is in agreement with the study of Demuth et al. [17],
Table 1 0.4
%Crystallinity of the SAPO-5 with AFI-type products
synthesized from the mixture Al2O3:P2O5:1.5-
TEA:750H2O at 190 °C for 1 h using different SiO2/
Al2O3 mole ratios. 0.2 EDX
SiO2/Al2O3 mole ratio Crystallinity (%)a XRF
No SiO2 99.72
0.2 100.00
0.4 78.45 0.0
0.6 62.90 0.0 0.2 0.4 0.6 0.8
0.8 54.36
SiO2 /Al2 O3 mole ratio in gel
1.0 17.64
a
The 100% crystallinity of SAPO-5, AFI crystal was Fig. 9. XRF and EDX/SEM results of the SiO2 content in the reactant gels and the
obtained from the sample synthesized using the same products synthesized from the mixture composition Al2O3:2P2O5:xSiO2:1.5-
condition. TEA:750H2O at 190 °C for 1 h.
110
210
220
410
213
100
200
002
102
311
400
(f)
(e)
Intensity [cps]
(d)
(c)
(b)
(a)
10 20 30 40 50 60 70 80
2Theta [º]
Fig. 8. XRD patterns of SAPO-5 synthesized from the mixture Al2O3:2P2O5:1.5TEA:xSiO2:750H2O at a microwave temperature of 190 °C for 1 h, where x is the SiO2 to Al2O3
mole ratio of (a) 0, (b) 0.2, (c) 0.4, (d) 0.6, (e) 0.8, and (f) 1.0.122 K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123
highly crystalline SAPO-5 could be synthesized with a SiO2-to- ing agent, and found that the obtained SAPO-5 also contained
Al2O3 mole ratio up to 0.8 in the reactant gels. The addition of sil- non-uniform mesopore structures generated by water vapor and
icon atoms into the AFI framework not only generates Brønsted oxides of carbon during calcination [37].
acid sites, as described earlier, but also controls the morphology
of the crystals. It is worth noting that for the long hexagonal rod-
4.5. Nitrogen physisorption
like crystals in which AFI grew preferentially in the c-direction
(Fig. 7a), the relative diffraction intensity of the h k l planes of
The nitrogen adsorption–desorption isotherms and pore size
{0 0 2} is much lower (Fig. 8a) while in the case of the short hexag-
distribution of the SAPO-5 materials obtained using the chemical
onal plate-like crystal of AFI-type (Fig. 7b–e), the intensity of the
composition Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O are shown in
same plane is very high (Fig. 8b–e), as compared to the other
Fig. 11. The obtained isotherms of type IV imply that these materi-
planes – {1 0 0}, {2 1 0} and {1 0 2}. This result is in agreement with
als exhibit a mesopore characteristic, similar to those found in
previous results obtained by Jhung et al. [19,35], who synthesized
other mesoporous zeolites [2,38]. It can be seen that all materials
microporous AFI crystals, both AlPO4-5 and SAPO-5, and found that
contain mesopores with an average pore diameter of about 2–
with plate-like hexagonal crystals in the case of Si loading into the
5 nm. The micropore and mesopore volumes for the samples pre-
AFI framework, the relative intensity of the {0 0 2} diffraction to
pared using different silicon contents are summarized in Table 2.
{1 0 0}, {2 1 0}, and {1 0 2} was also high.
The XRF and EDX/SEM results (Fig. 9) show the amounts of sil-
icon in the SAPO-5 products in comparison to those loaded in the 160
gels. The figure showed that the amount of the silicon in the prod-
Dv(d) [cc/A /g]
ucts was lower than the actual loading, indicating that not all of the
140
0
Si loaded in the synthesis gel was incorporated into the synthesis
product.
Volume [cc/g]
The existence of a mesopore SAPO-5 prepared using a chemical 120
composition of Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at a reaction
temperature of 190 °C for 1 h was confirmed using TEM. It was
100
found that the obtained hexagonal crystals (Fig. 10a) showed char- 0 50 100 150 200 250 300 350
acteristics of the AFI structure containing a one-dimensional chan- Pore Diameter [A0 ]
nel while the mesoporous nanostructure (not the hexagonal crystal 80
region) in Fig. 10b was also AFI type with hexagonal characteris-
tics, as confirmed by the SAED in Fig. 10c. The bright part in 60 Desorption
Fig. 10b denotes the presence of disordered mesoporous struc-
Adsorption
tures. As a result, the synthesized AFI products contained both clas-
sic single crystals 5–10 lm in size, consistent with the 1–10 lm 40
mesoporous matrix nanostructure of SAPO-5. Moreover, from ana- 0.0 0.2 0.4 0.6 0.8 1.0
lyzing the low angle XRD, there is no reflection at 2h lower than 5°, Relative Pressure [P/P0 ]
meaning there is no structural order in the mesopore matrix, as
claimed by Fang et al. [36]. Murthy et al. prepared SAPO-5 using Fig. 11. Nitrogen physisorption isotherm of SAPO-5 synthesized from the mixture
aluminum isopropoxide and Ludox 40 as aluminum and silica composition Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at a reaction temperature of
190 °C for 1 h. (Inset is the corresponding pore size distribution).
sources, respectively, and tripropylamine as the structure-direct-
Fig. 10. TEM results of SAPO-5 synthesized from the mixture composition Al2O3:2P2O5:0.2SiO2:1.5TEA:750H2O at a reaction temperature of 190 °C for 1 h; (a) hexagonal
crystal, (b) nonstructural mesoporous, and (c) SAED of the mesoporous nanostructure.K. Utchariyajit, S. Wongkasemjit / Microporous and Mesoporous Materials 135 (2010) 116–123 123
Table 2 of Science and Technology Thailand Project (DPST). Special thanks
Nitrogen physisorption data of the samples synthesized using different go to Mr. Robert Wright for the English proofreading.
SiO2/Al2O3 mole ratios at a reaction temperature of 190 °C for 1 h.
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