Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
AMN-094-P
SYNTHESIS OF TIN OXIDE-MODIFIED MESOPOROUS MCM-41 AND
CATALYTIC ACTIVITY IN NOPOL SYNTHESIS
Le Thi Hoa, Tran Thuy Thai Ha, Dinh Quang Khieu, Tran Thai Hoa
College of Sciences, Hue University, 77 Nguyen Hue, Hue city, Viet nam
Email: trthaihoa@yahoo.com
ABSTRACT
In the present paper, tin oxide modified MCM-41 materials (Sn-MCM-41) were synthesized through
the direct incorporation of tin oxide into MCM-41 framework. The obtained materials were characterized by
X-ray diffraction (XRD), scanning and transmission electron microscope (SEM, TEM), Diffuse reflectance
ultraviolet (DRUV-Vis) and isotherms of nitrogen adsorption/desorption. The Sn-MCM-41 samples exhibits
excellent surface properties with high tin content and highly ordered mesoporous structure. The possible
mechanism of the formation of mesoporous structure of Sn-MCM-41 was discussed. Results on
heterogeneous catalytic synthesis of nopol from -pinene and paraformaldehyde over obtained catalysts were
also presented.
Keyword: Sn containing MCM41, Sn- MCM41 catalytists, synthesis of Sn-MCM41, synthesis nopol.
used as a catalyst for nopol synthesis have been
reported [1]. Terpenes are widely employed to
produce a wide variety of products such as
aromas, food additives, agrochemicals and
pharmaceuticals. Among terpenses -and pinenes are the major components of wood
turpentine and of numerous other volatile oils. pinene is a precursor of nopol, an optically active
bicyclic primary alcohol, useful in the preparation
of soap perfumes, and household products [7].
Current paper presents systematic studies
on the optimization of several synthesis variables
to obtain Sn-MCM-41 with highly ordered
mesoporous structure and large tin content and the
catalytic properties in nopol synthesis was
discussed.
1. INTRODUCTION
The discovery of mesoporous molecular
sieves (MCM family) by Mobil researches in
1991 triggered worldwide research interest in
developing various mesoporous catalysts that
overcome the inherent diffusional limitations in
the microporous zeolites. Because of the unique
one-dimensional channel walls and simple
synthesis procedures, synthesis and modifications
of MCM-41 materials have been insensitively
interested than that of MCM-48 and MCM-50
materials. Many transition metals such as Ti, Fe,
Co
and Cr were incorporated into silica
framework of MCM-41 [2, 3,4]. Among them, tin
containing MCM-41 (Sn-MCM-41) was attracted
due to unique catalytic properties. Tin can a be
introduced after the synthesis and removal of the
template by calcination , by deposition of a
volatile organometallic species.
Sn-MCM-41
could be prepared by chemical deposition of
tetraethyl tin followed by a thermal treatment in
air [6].
Among catalytic application, Sn-MCM-41
were found to be a good catalyst for hydroxylation
of phenol and 1-napthol [5]. However, the
applications of these mesoporous Sn-MCM-41 in
areas other than the oxidation/epoxidation
catalysis have limited [9]. Recently, Sn-MCM-41
2. EXPERIMENTAL
Sn-MCM-41 materials were synthesized
using tetraethyl orthosilicate (TEOS) and tin (IV)
chloride (SnCl4.4H2O) as silicon and tin
precursors,
respectively.
Cetyltrimethyl
ammonium bromide (CTAB, Aldrich) was used as
the structured –directing agent. The preparation
procedure of Sn-MCM-41 materials is processed
by two experimental series. Series A was
described as follows: 0.5 g of CTAB and 8 mL
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Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
chromatography (GC-HP 6890 – MS-HP- 5973).
The quantification of nopol and -pinene was
carried out by multi point calibration curves using
dodecane as internal standard. Conversion and
selectivity were determined using Eqs (1)-(2),
respectively.
NaOH 2M was dissolved in 480 ml distilled water
under vigorously stirred condition at 80oC for 30
minutes, then follow adding a prescribed amount
of SnCl4.5H2O (molar ration of Sn/Si = 0.07, 0.1,
0.2, 1). Finally, 10 mL of TEOS was added slowly
for more 3 hours with constant stirring. Afterward,
the resultant solid was filtered, washed and dried
at 100oC. After it was calcined 250oC for 1 hours
and at 550oC for 5 hours to obtain the products.
Sn-MCM-41 samples with Sn/Si molar ratios of
0.07, 0.1, 0.2, and 1 were finally obtained and
denoted as Sn-MCM-41(0.07), Sn-MCM-41(0.1).
Sn-MCM-41(0.2)
and
Sn-MCM-41(1),
respectively. For series B, the molar ratio of Sn/Si
was fixed by 0.1. The NaOH concentration was
changeable by varying the volume of NaOH 2M
and remained the constant total volume. The
composition of chemicals and name of samples
was listed in Table 1.
Table 1. Gel compositions of samples synthesized
in the condition of changable concentration of NaOH
VNaOH
Samples
8.Sn-MCM-41 (0,1)
9.Sn-MCM-41 (0,1)
10.Sn-MCM-41(0,1)
11.Sn-MCM-41(0,1)
12.Sn-MCM-41(0,1)
13.Sn-MCM-41(0,1)
(mL,
2M)
8
9
10
11
12
13
V H 2O
(mL)
479
478
477
476
475
444
VTEOS
(mL)
10
10
10
10
10
10
% Conversion =
% Selectivity =
C
ti
 Ctf 
  pinene
 Cti   pinene
C 
tf
C
ti
 Ctf
nopol

x100% (1)
x100%
(2)
  pinene
Cti and Ctf correspond to the initial and final
concentration, respectively.
3. RESULTS AND DISCUSSION
NaOH
concentration
(M)
0.32
0.36
0.40
0.44
0.48
0.52
The mesoporous phases of Sn-MCM-41
were monitored by powder low-angle X-ray
diffraction (XRD), recorded on 8D Advance
(Bruker, Germany) with CuK radiation.
Morphology of samples was observed by SEM
(JSM-5300LV). Nitrogen adsorption/desorption
isotherms of calcined samples were obtained using
Micromeritics at 77K. UV-Vis diffuse reflectance
spectra were recorded on JASCO V-550 UV/Vis
spectrophotometer using BaSO4 as matrix.
A known amount of catalyst (0.2 g of
10.Sn-MCM-41(0.1)) and the known amount of
reactants (molar ratio 5 mmol -pinene: 10 mmol
paraformaldehyde = 1:2) with solvent of toluene
(6 mL) was taken in a two neck round botton
flask. The botton flask was immersed in an oil
bath controlled at the range of 253 -373K.The
reaction products were identified by gas
965
Aim of study is the synthesis of Sn-MCM41 with highly ordered mesoporous structure and
high tin content. The introduction of tin into
MCM-41 was hindranced
due to the high
precipetation of Sn(IV) in alkaline medium results
in degrading the surface properties of the obatined
materials. In the present work, two series of
experiemtals were carried out. For the series A,
the amount of Sn introduction into MCM-41
increases.
The effect of tin in mesoprous structure of
Sn-MCM-41 was investigated by XRD as shown
in Fig. 1a. It was found that the characteristic
peaks of MCM-41 such as (100), (110) and (200)
were not observed in the samples with molar ratio
of Sn/Si = 0.2 ÷ 1 indicating that mesoporous
structures were not formed. As the large amount
of tin(IV) is introduced into synthezied gels, the
hydrolysis of Sn(IV) produces too large amount of
H+ that the mesoporous structure of MCM-41 is
unfavored to form. The broaden peaks of (100)
were observed in the samples with molar ratio of
Sn/Si = 0.1÷ 0.07. The results replied that the
mesoprorous structure of Sn-MCM-41 could be
formed in these case but still poorly ordred
mesostructure. For second series of experimetals,
the molar ratio of Sn/Si was fixed by 0.1
Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
The NaOH concentration in synthesized
gel not only effect on mesoporous structure but
also on their mophologies as shown the SEM
observation of Fig. 2. The mophology tends to
transfer from to spherical particles to sheets as
NaOH concentration increases. The samples
prepared with NaOH concentration less than 0.44 M
remains spherical particles around 200-400 nm
while the samples with NaOH concentration more
than 0.44 M consist of sheets as shown in Fig. 2.
The dispersed degree of tin incorporation
into MCM-41 were investigated by EDX as shown
in Fig.3a. The 4 points were analysed randomly
that show the same molar ratio of
Sn/Si
indicating the tin oxides were highly dispersed in
silica framework. In addion, the molar ratio of
Sn/Si around 0.12 was very close to molar ratio of
Sn/Si of 0.1 in synthesized gel. Hence, tin in
synthesized gel was almost incorporated in silica
framework.
Fig.3b shows the UV-Vis diffuse
reflectance spectra of the different tin-containing
MCM-41. For MCM-41 sample, the spectrum is
mainly composed of very small absorption at 270
nm. The adsorption band at 220 nm of Sn-MCM41(0.1) was observed, in agreement with a
tetrahedral coordinated tin. For high tin loadings, a
small shoulder, characteristic of hexacoordinated
tin, can be observed near 260 nm in Sn-MCM-41
(0.2) [10]. Depending on the amount of tin
loading, tin can substitute Si in framework or
agglomerate forming tin oxide clutters.
Fig.4 shows nitrogen adsorption/desorption
isotherm of Sn-MCM-41. Nitrogen adsorption
isotherm of each sample exhibited a sharp and
well-developed step in the relative pressure range
of 0.2-0.4 characteristic of capillary condensation
of nitrogen within uniform mesopores. From N2
isotherms of MCM-41 and 10.Sn-MCM-41(0.1),
clear type IV nitrogen physisorption curves,
characteristic of unique capillary condensation in
mesopores can be seen. However, the capillary
condensation step of 9 or 11.Sn-MCM-41 are
much less pronounced. The presence of hysteresis
loop at high relative pressure region of 9.SnMCM-41 often indicates the marcropores which is
attributed to the void between the primary particle
constituting the main bulk phase.
(110)
Intensity (a.u)
(200)
(100)
and the NaOH concentration was changeable.
200
Sn-MCM-41 (0,07)
MCM-41
Sn-MCM-41 (0,1)
Sn-MCM-41 (0,2)
Sn-MCM-41 (1)
0
1
2
3
4
5
 (degree)
6
7
8
Fig. 1 a. XRD patterns of samples prepared with
different molar ratios of Sn/Si.
Fig. 1b shows XRD patterns of samples
synthesized in the condition of changeable
concentration of NaOH. As can be seen from Fig.
1b, the intensity of (100) increases with the
increase in the NaOH concentration. The intensity
of XRD reachs maxium at NaOH concentration
around 0.40M corresponding the sample of 10-SnMCM-41(0.1). The characteristic peaks of (110)
and (200) was obsered clearly in this samples
indicating the samples posseses high orderedly
mesoporous structure.
200
13.Sn-MCM41 (0,1)
Intensity (a.u)
12.Sn-MCM41 (0,1)
11.Sn-MCM41 (0,1)
10.Sn-MCM41 (0,1)
9.Sn-MCM41 (0,1)
8.Sn-MCM41 (0,1)
0
1
2
3
4
5
6
7
AMN-094-P
8
 (degree)
Fig. 1 b. XRD patterns of samples prepared
with different NaOH concentration.
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Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
a
b
c
d
Fig. 2. SEM observations of MCM-41 (a); 10.Sn-MCM-41(0.1) (b) ; 11.Sn MCM-41(0.1) (c); 12Sn-MCM-41(0.1) (d).
002
0,1
220
SnLa
1200
600
Sn-MCM-41(0,2)
Sn-MCM-41(0,1)
SnLr
SnLl
900
SnLr2,
SnLb
Counts
1500
Abs.
OKa
1800
260
SiKa
2100
SnLb2
2400
300
MCM-41
0
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
150
200
250
300
350
400
450
Wavelength (nm)
keV
Fig. 3. a. EDX spectrum of 10.Sn-MCM-41(0.1); b. DR-UV-Vis spectra of Sn-MCM-41.
V (cc.g STP)
25
-1
d
c
b
a
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Fig. 4. Adsorption/desorption isotherms of samples:
a. MCM-41; b. 9Sn-MCM-41(0.1);
c. 10.Sn-MCM-41(0.1); d. 11. Sn-MCM-41(0.1).
967
Scheme 1. The proposed scheme of
formation for Sn-MCM-41.
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Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
The MCM-41 support material had a
BET surface area of 1437 m2.g-1 before and a BET
surface area of 707 m2.g-1 (10.Sn-MCM-41(0.1))
after modification by tin. The significant decrease
in SBET of other sample are caused by both serious
blockage pore and partial collapses of mesopores
due to large tin oxide particles situated out silica
frameworks. The sample of 10.Sn-MCM-41(0.1)
with good surface properties will be used in
catalytic investigation.
Based the results of synthesis of SnMCM-41 by two different ways, the synthesized
scheme was illustrated in Scheme 1. As CTAB
molecules were diluted in alkaline solution. The
micelles were formed with the hydrophobic cores
of CTA+ directed inside and hydrophilic surface
of ammonium located outside. The reaction
pathway is S+I- where S+ is CTA+ and I- is
silicate. As the Sn(IV) cations were added in the
synthesized gel, the proposed reaction pathway is
S+(OH-,Sn-4+)I-. In alkaline medium, tin could
incorporate into silica matrix as tetragonal species
or self-condensation of tin hydroxide forming tin
oxide with large coordination than 4 as proposed
by Liu and et [10].The increase in the amount of
Sn results in the rapid hydrolysis of Sn(IV)
leading to the decrease in pH. Hence, the system
S+(OH-,Sn4+)I- will be able to more and more
random structure. At a certain amount of tin, the
tin hydroxide self-condensate to form –Sn-O-SnO- . As a results, the amorphous mixture of silica
and tin oxide were formed in stead of
mesoporpous materials (pathway A). But this
problem could be solved by adjusting the NaOH
concentration. The S+(OH-,Sn4+)I- pathway will be
improved by the adding OH- and the optimized
condition to get highly ordered mesoporous
structure will be obtained at a certain NaOH
conditions as shown pathway B of scheme 1.
The synthesis of nopol via Prins
condensation of -pinene with paraformaldehyde
using Sn-MCM-41 in the liquid phase reaction
conditions was illustrated in Scheme 2.
AMN-094-P
Table 2 presents the results of GC-MS analysis
of products for the synthesise of nopol. The
conversion of -pinene increases with the increase
in temperature from 353K to 373K. The reaction
proceeds faster at 373K, but resulted in a decrease
in the selectivity for nopol, due to formation of
camphene and limonene, -terpinene as side
products. The reaction carried out at 363oC gave
better conversation of -pinene as well as higher
selectivity to nopol, so all further studies were
carried out at 363K.
Table 2. Condensation reaction of β-pinene and
paraformaldehyde at different time and temperature
Temperature
Time
Conversion Selectivity
(K)
reaction
β-pinen
to nopol
(hours)
(%)
(%)
353
6
0
0
353
9
0.1
Trace
353
12
32.0
7,31
363
6
0.9
Trace
363
9
22.6
81.6
363
12
27.0
80.0
373
6
5.4
13.8
373
9
9.6
12.4
373
12
45.0
42.4
The polarity of the solvent was found to
play an important role in -pinene conversion. The
solvents with high dielectric constants such as nbutanol (18), isopropanol (20), methanol (33) and
ethanol (24.6) provide very low conversions to
nopol (1.6 %÷ 2.5%). The lowest dielectric
constant of toluene (2.4) is favored for the
formation of nopol (27.0%).
4. CONCLUSIONS
Sn- MCM-41 material was synthesized
successfully via a hydrothermal method with
direct incorporation of Sn (IV) under alkaline
conditions. Tin species incorporated into MCM-41
framework is dispersed in homogeneous form.
The resulting Sn-MCM-41 material via direct
process possesses high specific surface areas,
large mesopores and thick pore walls in
comparison with the blank MCM-41. The
obtained Sn-MCM-41 material exhibits catalytic
Sheme 2. Prins condensation of -pinene and
paraformaldehyde to nopol over Sn-MCM-41.
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Proceedings of IWNA 2011, November 10-12, 2011, Vung Tau, Vietnam.
activity for Prins condensation of -pinene and
paraformaldehyde to nopol. The sovent of toluene
with low dielectic constant using in reaction
provides the conversition as well as selectivity
higher than other solvent with higher dielectric
constants such as butanol, propanlo or methanol.
AMN-094-P
5. P. P. Sammuel, S. Shylesh, A. Singh, J. Mol.
Cat. A: Chemical 266 (2007) 11-20.
6. R. Burch, V. Caps, D. Gleeson, S. Nishiyama,
S.C. Tsang, Appl. Catal. A: Chem. 194/195 (2000)
297.
7. S. V. Jadhav, K. M. Jinka, H.C. Bajaj, Applied
Catal. A: Gen. 390 (2010), 158-165
8. Tinoco, Sauer, Wang & Puglisi, Physical
Chemistry Prentice Hall 2002 p. 134.
9. T. R. Gaydhankar, P. N. Joshi, P. Kalita, R.
Kumar, J. Mol. Cat. A: Chem. 265 (2007) 306315.
10. Z.C.Liu, H.R.Chen, W.M.Huang, J.L.Gu,
W.B.Bu, Z.L.Hua, J.L.Shi (2005), Mic. Mes. Mat.
89, pp.270-275.
References
1. A. L. Villa de P, E. Alarcon, C. Montes de C,
Cat.Today 107-108 (2005) 942-948.
2. E. A. Alarcon, A. L. Villa, C. M. D. Correa,
Mic. Mes. Mats 122 (2009) 208-215.
3. M. Selvaraj, A. Pandurangan, K. S. Seshadri, P.
K. Sinha, K. B. Lai, Applied. Catal. A. Gen. 242
(2003) 347-364.
4. M. Selvaraj, B. H. Kim, T. G. Lee, Chem. Lett.
34 (2005) 1290-1291.
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