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Chemistry Letters Vol.36, No.7 (2007)
Novel Route to Synthesize Nanosized ꢀ-Zeolite with High Surface Area
Ayyamperumal Sakthivel, Kenichi Komura, and Yoshihiro Sugiꢀ
Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193
(Received April 2, 2007; CL-070355; E-mail: sugi@apchem.gifu-u.ac.jp)
Nanosized ꢀ-zeolite was synthesized in presence of two
templates viz., tetraethylammonium hydroxide and cetyltri-
methylammonium bromide by steaming dry-gel precursors.
helps to produce nanoprecursors and to convert them into nano-
crystals via steaming final dry-gel.10 The surfactant (in particu-
lar, CTMABr) was helpful to assemble nanosized crystals by
its interaction with silanol group of zeolite precursor in the
synthesis of nanosized ZSM-5 by flocculation method.10 Similar
kind of interaction occurred in the present case and, thus, results
in the formation of uniform nanosized ꢀ-zeolite. However, there
may be no interaction between CTMABr and TEAOH.
Figure 1 shows XRD patterns of calcined nanosized ꢀ-zeo-
lites with different SiO2/Al2O3 ratios (50, 75, and 100) in the
initial gel composition. They have pure ꢀ-zeolite phase with
high crystallinity. The crystallinities decreased slightly with
increasing SiO2/Al2O3 ratio. The intensity of the peaks was
also decreased in all samples after the calcination; however,
the peak pattern remains after the protonation by using NH4NO3
solution (see Figure S1 in Supporting Information).14 All the
samples in H-form were free from impurity phases. The broad-
ening of main peaks indicates that particle sizes are in nano-
level. Further, the low angle XRD of H-form samples (Figure
S1 in Supporting Information)14 showed the absence of any
mesostructural periodicity.
Because zeolites and their related molecular sieves have
uniform channel size, unique molecular shape selectivity, as
well as strong acidity and good thermal/hydrothermal stability,
they have been used for various catalytic applications.1–3 In
particular, ꢀ-zeolite with a three-dimensional large-pore system
is one of potential catalysts used in petro-refining and other
chemical industries.4 However, the poor diffusion efficiency
through their pores leads easily to insufficient activity and fast
deactivation.5 Such a diffusion limitation in the zeolites can be
avoided by the short diffusion paths by reducing the crystal
size.5–8 Several methods have been developed during the last
decades for the preparation of nanosized zeolites from colloidal
precursors under mild hydrothermal conditions.5–9 Recently,
Naik et al.10 synthesized nanosized ZSM-5 zeolites via two tem-
plates by three step (hydrothermal–flocculation–steaming) pro-
cedures. On the other hand, dry gel conversion (DGC) method,
in which an aluminosilicate gel dried in advance is crystallized
into a zeolitic phase in a water steam environment, has been
much interested as the new synthetic method for zeolites
and zeotype materials in recent years.11,12 It is interesting to
introduce dual template on DGC method for the synthesis of
nanosized microporous materials.
SEM image of nanosized ꢀ-zeolite (SiO2/Al2O3 = 100)
in Figure 2 shows that the ꢀ-zeolite has uniform particle size
of ca. 30–50 nm; however, the ꢀ-zeolite synthesized in the ab-
sence of CTMABr has the particle size of ca. 100–150 nm.
Table 1 summarizes the textural properties and ICP analysis
of ꢀ-zeolites. Their BET surface areas were in the range of 412–
602 m2ꢃgꢄ1 and the external surface areas of 124–136 m2ꢃgꢄ1
:
;
In the present investigation, we have examined the introduc-
tion of two templates, tetraethylammonium hydroxide (TEAOH)
and cetyltrimethylammonium bromide (CTMABr) for the syn-
thesis of nanosized ꢀ-zeolite by DGC method.
The gel composition was used for the synthesis of
nanosized ꢀ-zeolite: 1.0SiO2:0.37TEAOH:0.041CTMABr:
cumulative surface areas were in the range of 602–875 m2ꢃgꢄ1
however, conventional ꢀ-zeolite had surface are of 100–
200 m2ꢃgꢄ1. The observed high surface areas of nanosized ꢀ-
zeolite are mainly due to particle size. The surface area of the
ꢀ-zeolites increased with the decrease in aluminum content.
ICP analysis shows that all ꢀ-zeolites have the SiO2/Al2O3
ratios similar to initial gel composition.
0.072NaOH:(0.01–0.02)Al2O3:17H2O.
A typical synthesis
procedure is as follows: 15.57 g (37 mmol) of TEAOH solution
(35 wt %) was mixed with 1.12 g (7.2 mmol) of a 25.2 wt %
aqueous NaOH solution, followed by the addition of 15.02-g
colloidal silica (Ludox HS-40 (40 wt %)) containing 6.01 g
(100 mmol) of SiO2. Then, the mixture was stirred for 30 min.
SiO2/Al2O3
100
.
An appropriate amount of Al2(SO4)3 6H2O dissolved in
10.2 mL of warm water was added to the mixture, and the
resultant mixture was stirred for further 1 h. 1.49 g (4.1 mmol)
of CTMABr dissolved in 80 mL of ethanol was added to the
mixture and stirred for further 2 h. The gel was then dried for
about 6–7 h over an oil bath at 90 ꢁC with continuous stirring.
The dried gel was transferred to a Teflon cup (55 mm ꢂ
37 mm i.d.) placed in a Teflon-lined autoclave (100 mL) with
the support of a Teflon holder with a small amount of external
bulk water (ca. 0.2 g per 1 g (dry gel)) at the bottom of the
autoclave.12
75
50
50*
5
10
20
30
40
50
2θ
/deg
The crystallization of the dried gel was carried out at 175 ꢁC
for 1 day. The addition of CTMABr on the synthesis of ꢀ-zeolite
ꢀ
Figure 1. XRD patterns of nanosized ꢀ-zeolite. : synthesized
in the absence of CTMABr.
Copyright Ó 2007 The Chemical Society of Japan
Sakthivel, Ayyamperumal
