1
80
H. Tao et al. / Journal of Solid State Chemistry 200 (2013) 179–188
crystals with large intra-crystalline voids from a preferential
dissolution of the conventional TS-1 crystal core by a post-
synthesis treatment of the calcined zeolite crystals with highly
alkaline TPAOH solutions, due to a lower crystallinity as compared
to the external shell. ZSM-5 with very regular hollow architectures
were also synthesized from a preferential dissolution of the core of
the crystals, followed by a re-crystallization in the presence of
templating molecules [29].
Herein, we report a facile method for the synthesis of hollow
zeolite microspheres (HZS) in the presence of organosilanes via a
dissolution–recrystallization procedure. Based on the desilication
mechanism, excessive sodium hydroxide was added into a conven-
tional zeolite synthesis system. At the first stage of crystallization,
zeolite microspheres with a core/shell structure were formed in the
presence of organosilanes, hollow zeolite microspheres with zeolite
nanocrystals aggregated structures were fabricated at the second
stage of hydrothermal treatment via a dissolution–recrystallization
procedure. In addition, the acidic properties of the hollow zeolite
isotherms were measured at ꢀ196 1C with a Micromeritics ASAP
2020 M sorption analyzer. Before measurements, the samples
were outgassed at 300 1C for 6 h. The scanning electron micro-
scopy (SEM) was collected on a Hitachi S-4800 microscope
operating at 15 kV. TEM images were obtained from JEM-2010
instrument operating at 200 kV. 27Al MAS NMR spectra were
recorded on a Bruker DRX-400 Spectrometer equipped with a
magic angle spin probe at room temperature. The compositions of
various samples were determined by inductively coupled plasma
atomic emission spectrometry (ICP-AES) on a Thermo Scientific
IRIS Intrepid spectrometer. Pyridine-adsorbed FT-IR spectra were
carried out on a Nicolet Model 710, the samples were grounded
into fine powders and pressed into very thin self supporting
wafers. The discs were mounted in a quartz IR cell equipped with
a CaF2 window and a vacuum system. Prior to adsorption, the
samples were pretreated in situ at 500 1C for 2 h under evacua-
tion, then cooled to 50 1C where pyridine vapor was introduced
into the cell for 0.5 h. The physically adsorbed pyridine was
removed by evacuating at 50 1C for 1 h, after that, the sample
was heated in vacuum for 1 h at 100 1C, and a spectrum was
recorded. Temperature-programmed desorption of ammonia
3
microspheres were characterized by NH -TPD and pyridine-adsorbed
FT-IR, the probe reactions involving large and small molecules were
used to compare the catalytic performance of hollow zeolite micro-
spheres with conventional zeolite ZSM-5. As compared to the layer-
by-layer technique and conventional dissolution–recrystallization
process, this synthesis method is very simple and convenient, for
the whole dissolution–recrystallization procedure was processed only
in the mother liquid, which can avoid the complicate multistep and
time-consuming processes in the layer by layer technique and the
calcination of the parent zeolites before dissolution–recrystallization
treatment (conventional dissolution–recrystallization process).
3
(NH -TPD) was performed by using a homemade apparatus
PX200 (Tianjin Golden Eagle Technology Limited Corporation).
The sample (50 mg) was pretreated at 550 1C for 2 h and then
cooled down to 50 1C under a N
adsorption saturation was reached, followed by a flow of N
1 h at 90 1C. Then the temperature was raised from 90 1C to
2
flow. Pure NH
3
was injected until
2
for
ꢀ
1
550 1C with a heating rate of 10 1C min
and the amount of
desorbed ammonia was detected by using thermal conductivity
detector (TCD) at 110 1C.
2
. Experimental section
2.3. Catalytic characterization
þ
2.1. Synthesis of hollow zeolite microspheres
All the samples (ZSM-5) were transferred to H type ZSM-5 by
ꢀ
1
4 3
ion exchange with NH NO (1 mol L ) at 80 1C for 3 h, which
Hollow zeolite microspheres were synthesized using the com-
repeated three times, finally all the samples were calcined at
mercial organosilanes (FY-4903) from the Guangzhou fluorine
reason silicon science and technology limited company without
550 1C for 3 h.
further purification. In a typical synthesis, 0.082 g of NaAlO
2
, 4.06 g
2.4. Acetalization of cyclohexanone
of tetrapropylammonium hydroxide (TPAOH, 25 wt%) and 0.16 g of
NaOH were dissolved in 14.4 g of deionized water, the temperature
of the solution was raised and kept at 80 1C. Then, 4.17 g of
tetraethyl orthosilicate (TEOS) and 0.8 g of organosilanes were
added to this solution, the resulting mixture was continuously
stirred for an additional 2 h to obtain a homogeneous mixture. The
mixture was then transferred to a stainless-steel, Teflon-lined
autoclave and crystallized at 140 1C for 2 days, then the autoclave
was quenched to room temperature and kept for several hours,
followed by the second hydrothermal treatment at 120 1C for
The acetalization of cyclohexanone was carried out batch-wise
in a round-bottomed flask equipped with a flux condenser and a
magnetic stirrer. In a typical reaction, 0.05 g of catalyst (H form)
was dispersed in a solution containing 10 mL of methanol and
0.098 g of cyclohexanone. The solution was stirred at 50 1C for
4 h. The reaction mixtures were analyzed by a Perkin-Elmer
Clarus 500 gas chromatography with a SE-54 column. The product
mixture was further confirmed by GC–MS.
þ
3
days. Finally, the resulting product was recovered by filtration,
2.5. Alkylation of toluene with benzyl chloride
washed with deionized water and dried in an oven at 100 1C over
night. To remove the templates completely, the product was first
calcined at 350 1C for 5 h, then calcined at 650 1C for 5 h with a rate
of 1 1C min-1, this hollow zeolite microspheres sample is desig-
nated as HZS. The samples obtained at various crystallization time
in the presence of organosilane are designated as S-0 to S-6 (see
Table 1 in detail). Sample obtained without organosilane under the
same condition of HZS was denoted as S. In addition, conventional
ZSM-5 was also synthesized according to Ref. [30].
2
The catalytic reactions were carried out under N in a three-
necked flask equipped with a reflux condenser. In a typal run,
.38 g of toluene, 1.9 g of benzyl chloride and 0.05 g of catalyst
1
were mixed with stirring, then the reaction temperature was
raised to and kept at 80 1C for 3 h. The reaction mixtures were
separated by centrifugation and analyzed by a Perkin-Elmer
Clarus 500 gas chromatography with a SE-54 column. The product
was further confirmed by GC–MS.
2.2. Characterizations
3. Results and discussion
Powder XRD patterns were recorded on a Bruker D8 FOCUS
Hollow zeolite microspheres (HZS) were synthesized by add-
ing organosilane to a conventional hydrothermal system via a
dissolution–recrystallization procedure. X-ray powder diffraction
diffractometer using CuK
a radiation (40 kV and 40 mA) with the
ꢀ
1
scanning rate of 61 min . Nitrogen adsorption and desorption