DSpace at VNU: Ti-MCM-41 with various Ti contents: Synthesis, characterization and catalytic properties in oxidation of α-pinene

e-Journal of Surface Science and Nanotechnology

27 December 2011

Conference - IWAMN2009 -

e-J. Surf. Sci. Nanotech. Vol. 9 (2011) 539-543

Ti-MCM-41 with Various Ti Contents: Synthesis, Characterization and
Catalytic Properties in Oxidation of α-Pinene∗
Tran Thi Nhu Mai, Nguyen Van Quyen, Nguyen Thanh Binh, and Le Thanh Son
Faculty of Chemistry, Hanoi University of Science,
Vietnam National University, No.334-Nguyen Trai Str., Hanoi, Vietnam

Giang Thi Phuong Ly and Nguyen Thi Ha†
Faculty of Technology Chemistry, Hanoi University of Technology, No.1-Dai Co Viet Str., Hanoi, Vietnam
(Received 24 November 2009; Accepted 24 May 2010; Published 27 December 2011)
Ti-MCM-41 with various ratios Ti/Si was synthesized successfully and characterized by some measurements as
XRD, DR-UV-Vis, TEM, EDAX and N2 -Adsorption. The peak in bands 230 nm in DR-UV-Vis spectroscopy
showed that Ti was in tetrahedral coordination. The TEM, EDAX images indicated that the obtained materials
were of ordered mesoporous structures in the samples with low ratio of Ti/Si. Moreover, increasing the thickness
of material wall calculated by BJH method was due to the incorporation of titanium in the framework. The oxidation of α-pinene over Ti-MCM-41 with various ratios Ti/Si indicated that the possibility of Ti in the tetrahedral
coordination gave a priority to the selectivity of α-pinene oxide. The Ti content of materials system increased, consequently the conversion of the reaction and the pinandiol product yield increased. [DOI: 10.1380/ejssnt.2011.539]
Keywords: Ti-MCM-41; EDAX; N2 -Absorption; Epoxidation; α-pinene; H2 O2

I.

INTRODUCTION

Nowadays, due to the increasingly important sustainability for the chemical industry, there are a lot of research interests to produce the new chemicals from renewable resources. Monoterpenes are cheap, abundant
and often fundamental raw chemicals for pharmaceutical,

fragrance and flavor industry. Oxidation of monoterpenes
could provide interesting intermediates for the synthesis of
new chemicals for the chemical industry such as epoxides,
terpenic aldehydes, alcohols and polihydroxyl. Among a
number of terpenes, α-pinene is an important substance
in the manufacture of a variety of synthetic aroma chemicals and its epoxide is isomerized to produce campholenic
aldehyde, which is an intermediate for the pharmaceuticals, agrochemicals and products for perfumery [1–5].
α-Pinene is a valuable starting material to obtain its important oxidation products pinene oxide, verbenone and
campholenic aldehyde. We have studied air oxidation of
α-pinene in order to improve the preparation of campholenic aldehyde in one-pot starting from α-pinene.
Titanosilicates containing tetrahedral Ti species in the
framework, being capable of activating hydrogen peroxide under liquid-phase conditions, prove to be promising
catalysts for the selective oxidation of a variety of organic
compounds [1–3]. The representative titanosilicate has
been TS-1 of the MFI structure, which was reported two
decades ago. The discovery of TS-1 has led to industrialized processes such as the hydroxylation of phenol to
hydroquinone and catecol, and the ammoxination of cyclohexanone to oxime [1, 3]. To solve the problems that
medium pores TS-1 encounters in bulky reactions, many
others titanosilicates with larger pore have also been de-

∗ This paper was presented at the International Workshop on Advanced Materials and Nanotechnology 2009 (IWAMN2009), Hanoi
University of Science, VNU, Hanoi, Vietnam, 24-25 November, 2009.
† Corresponding author: ,hant-fct@mail.
hut.edu.vn

veloped thereafter by hydrothermal synthesis or postsynthesis methods, for example Ti-β, Ti-ZSM-12, Ti-MOR,
Ti-MCM-48 [3]. Particularly, Ti-Beta with 12-membered
ring channels is a very attractive catalysts for the oxidation of cyclic and branched alkenes and alkanes [3].
Ti-containing mesoporous materials Ti-MCM-41 and Tisubstituted hexagonal mesoporous silica Ti-HMS have
also been synthesized [3–5]. Both materials pioneered the

potential to oxidize bulky molecular which cannot enter
the micropores of zeolites such as TS-1, TS-2 with the
MEL structure, and Ti-β.
In this paper, we report on the synthesis of Ti-MCM41 materials, together with a thorough characterization
of the catalysts by means of XRD, DR-UV-Vis, TEM,
EDAX in order to give some insight into the coordination state of Ti in Ti-MCM-41 samples, which is crucial
for proper understanding of their structure and catalytic
behavior. Finally, the effect of Ti content on catalyst for
activity and product distribution in α-pinene oxidation
was studied.

II.
A.

EXPERIMENTAL

Synthesis and characterization

The titanium-containing mesoporous materials (TiMCM-41) were prepared by hydrothermal synthesis using cetyltrimethylammonium bromide (CTMABr) as template, 25 wt% aqueous solution of tetramethylammonium
hydroxide (TMAOH, K + Na < 5 ppm). Tetraethoxysilane (TEOS) and tetrabutyl orthotitanate (TBOT) were
used as the Si and Ti sources, respectively. An alcoholic solution of CTMABr was added to a mixture of
TEOS and TBOT, following the methodology proposed
by Koyano and Tatsumi. Molar ratio of gel Si : Ti :
CTMABr : TMAOH : H2 O= 1 : x : 0.15 : 1.3 : 150
(where x = 0.01 ÷ 0.03). This gel was transferred into
teflon-lined stainless-steel autoclave and kept at 100◦ C
for 24 h. The solid product was recovered by filtration,
washed with doubly distilled water and dried at 60◦ C

c 2011 The Surface Science Society of Japan ( />ISSN 1348-0391 ⃝

539


Mai, et al.

Volume 9 (2011)

University of Science, Vietnam National University.

III.
A.

RESULTS AND DISCUSSION

Į
Į
Physicochemical
characterization of catalysts
Į
Į

and Ti- Ti/Si =
FIG. 1: XRD patterns of Ti-free and free
Ti-MCM-41
0.01; 0.02; 0.03.

vis
FIG. 2: Diffuse reflectance UV-vis spectra of vis
synthesized samspectra

spectra of
of synthesized
synthesized samples
samples
ples.

overnight. To remove the template, the samples were calcined at 550◦ C for 6 h. The catalysts were characterized
by XRD,DR-UV-Vis (V-650-spectro photometer Japan),
STEM Japan), N2 adsorption (Bell-Belsorp mini-Japan).
B.

Catalytic experiment

The oxidation of α-pinene with H2 O2 were performed
at 70◦ C in a glass flask reflux under vigorous stirring.
Typically, the reaction mixture consisted of 50 mg catalyst, 10 mmol of α-pinene, 2.5 mmol of H2 O2 and 17.5 ml
of acetonitrile solvent (MeCN), time reaction 60 minutes.
In all cases, the oxidant to substrate molar ratio was 1:4 in
order to minimize the possible Ti leaching. The products
were separated and identified by the gas chromatography
mass spectrometry GC-MS (Detector MS-HP 5689, column HP-5: 5% methylethylsiloxan 30 × 0.5 nm × 0.25
µm film thickness) at Petroleum Chemistry Center, Hanoi
540

The synthesis of Ti-MCM-41 has been carried out in
the absence of alkali cations since they usually promote
the formation of poor crystalline titanosilicates during the
synthesis of TS-1. Titanium loading of the catalysts was
varied by changing the amount of the Ti source in the
P

synthesis
gel. In this way, four catalysts as MCM-41, TiP
MCM-41(0.01), Ti-MCM-41(0.02) and Ti-MCM-41(0.03)
were prepared.
The hexagonal arrangement of these catalysts is confirmed by the XRD pattern shown in Fig. 1. The sharp
peak at 2.2 degrees is due to the diffraction plane 100
which indicates hexagonal symmetry. Two additional
high order-peaks were obtained in the case of MCM-41
and Ti-MCM-41(001) relating to the diffraction planes
110 and 200. In addition, there is a decrease in the intensity of this first peak, and an evident broadening for
all peaks when increasing amounts of Ti, maybe due to
a reduction in the long-range order of the structure. No
diffraction peaks in the region of higher angles (10-50)
could indicate the presence of bulk anatase in the samples and suggest that Ti-MCM-41 sample is a pure phase.
DR-UV-Vis spectroscopy is a very sensitive method for
characterization of the coordination site of Ti in zeolite
framework. The DR-UV-Vis spectra of the Ti-MCM-41
samples prepared with different Ti contents are shown
in Fig. 2. The intense of ligand-to-metal charge transfer
band at 230nm, which is present in all samples, clearly indicates that most of Ti ions are isolated and in tetrahedral
(Td) coordination. A shoulder at 250-270nm becomes significant in indicating the presence of higher coordinated
Ti species (in penta- or octahedral coordination) in the
samples with relatively high Ti content. This higher coordination environment of Ti could appear upon hydration
by insertion of water molecules as extraligands to the Ti
(Td) species during preparation.
Both the highly hydrophilic surface and the large surface area of these materials yield a high water adsorption
capacity which would lead to a high hydration of Ti ions
surface. The possibility of some Ti–O–Ti clustering in
the framework due to an incipient oligomerization of Ti
species containing Ti–O–Ti bonds cannot be unequivocally excluded. On the other hand, compared to the bulk

anatase TiO2 , the lack of an absorption band characteristic of octahedral extra-framework titanium at about 300330 nm in the Ti-MCM-41 samples with Ti content of
2 mol.% and 3 mol.% suggests that no separated titanium phase is formed during the synthesis process. In
contrast with other results, the intensity of the 230 nm
band is slightly increased, moreover this band does not
shift towards higher wavelengths when increasing amount
of titanium [6, 10]. From these results, it is possible to
conclude that the tetrahedral component of Ti (V) almost
remains even in the samples having high Ti content.
Nitrogen adsorption-desorption isotherms along with
the corresponding BJH pore size distribution are shown

(J-Stage: />

e-Journal of Surface Science and Nanotechnology

Volume 9 (2011)

FIG. 3: Nitrogen adsorption-desorption isotherm and pore size distribution.

FIG. 4: TEM images of Ti-MCM-41 samples with various Ti
contents.Ratio of Ti/Si from EDAX spectroscopy.

estimated to be 2.5 nm. The thickness of the mesoporous
shell and the average particle diameter of Ti-MCM-41 are
in good agreement with the respective parameters of the
Ti- mesoporous materials.
Besides, EDAX spectra taken from different regions are
shown in Fig. 4. The root spectrum corresponds to the
particle center and gives the value of mol. % of Ti in
the sample. The EDAX results on surface of the samples

showed that mounts of Ti varied according to the difference positions. This proves the possibility of Ti formation
is out of the framework mesoporous. In the Ti-MCM-41
with a high Ti content, the local elemental analysis performed by EDX confirmed that titanium oxide is located
within the mesoporous pore.

B.

FIG. 5: The products of the oxidation of α-pinene.

in Fig. 3.
The samples exhibit type IV isotherms with a sharp
infection at a relative pressure around P/P o = 0.34-0.45
and a corresponding narrow and strong band in the pore
size distribution curve, which is characteristic of well ordered mesoporous materials with a narrow and uniform
pore size distribution [11].
All the samples showed great surface areas which
ranged from approximately 1000 to 1150 m2 /g as seen in
Table I. The decreasing specific surface area with the Ti
content may be correlated to the decrease in the structural
order, as observed in the XRD patterns. Consequently, an
increasing amount of transition metal could obstruct the
structure-directing action of template and result in the
formation of partially broken pores as well as a lower surface area. On the other hand, the pore diameters increase
slightly when increasing Ti loadings.
The TEM images of the Ti-MCM-41 materials with various Ti contents are shown in Fig. 4. The TEM images
showed that the obtained materials with a low Ti content
were high ordered mesoporous structure and monodispersity of Ti of Ti-MCM-41. The diameter of the pore was

Oxidation of α-Pinene

The properties and product components of the α-pinene
oxidation were based on the nature of the catalyst. The
reaction products of the α-pinene oxidation over TiMCM-41 analyzed on GC-MS system were shown in Table II and Fig. 5. According to GC-MS, the mixture
contains the species which were formed by oxidation of
both double bond and allylic C–H. The formation of the
product I is attributed to the oxidation of π bond, the
compound V is produced by the rearrangement of III and
the VI are formed by hydrolysis and opening of oxirane
ring of α-pinene oxide. Products I and II are generated
by oxidation of allylic C–H bond.
As above results, the oxidation of α-pinene was established through many ways such as isomerization of αpinene, the direct epoxidation of C=C double bond forming α-pinene epoxide, oxidation follow radical mechanisms
in C-C allyl bond, and isomerization of the epoxide regarded as a reactive intermediate.
Over Ti-MCM-41 catalyst, the oxidation was carried
out in the mild condition and selectivity to α-pinene epoxide as a reactive intermediate.The selectivity to epoxide
over Ti-MCM-41 was due to Ti4+ atom substituted isomorphic Si atom in the framework [4, 6].
The isomerization of α-pinene oxide regarded as a reactive intermediate over two catalysts gave the same campholenic aldehyde product (Fig. 6). Those are intermediate
chemicals, which have many applications in the synthesis

(J-Stage: />
541


Mai, et al.

Volume 9 (2011)

TABLE I: Surface properties and chemical composition of Ti-MCM-41 with different Ti contents and pure silica MCM-41.
Samples
MCM-41
Ti-MCM-41(0.01)

Ti-MCM-41(0.02)
Ti-MCM-41(0.03)

Ti content
% mol
0%
1%
2%
3%

SBET
[m2 /g]
1103
1145
1049
1063

Pore diamete
[nm]
2.89
2.65
2.65
2.60

Pore Volume
[cm3 /g]
0.923
0.9798
1.063
1.254

d(100)
[nm]
4.2
3.5
3.6
4.4

a0
[nm]
4.90
4.01
4.17
5.10

Wall thickness
[nm]
2.01
1.36
1.52
2.24

TABLE II: Oxidation of α-pinene with H2 O2 and Ti-MCM-41 (x).
Samples

Conv.(% )

Ti-MCM-41(0.01)
Ti-MCM-41(0.2)
Ti-MCM-41(0.03)

I
67.7
63.0
46.6

5.8
6.5
7.4

II
—
7.8
20.6

Selectivity (% )
III
IV
18.5
—
10.4
8.4
8.8
12.0

V
8.6
7.0
9.3

other
5.2
3.4
2.7

Reaction conditions: acetonitrile as solvent; time, 1.0 h; temperature, 60◦ C and H2 O2 as oxidant.

OH
O
Isomerization

Isomerization

Bronsted Acid

Lewis Acid
alpha -pinene oxide

O

Campholenic aldehyde

carveol

FIG. 6:FIG.
The6:isomerization
of the intermediate α-pinene
pineneepox7KHLVRPHUL]DWLRQRIWKHLQWHUPHGLDWHĮide (POX). 7KHLVRPHUL]DWLRQRIWKHLQWHUPHGLDWHĮ

of II and VI species during reaction shows that epoxide

is not stable at reaction conditions; furthermore it is easily hydrolyzed and rearranged by acid sites of catalyst.
The nature of acid sites was studied for these catalysts
by adsorption/desorption of pyridine followed by FTIR.
Results of acidity characterization showed that Lewis and
Bronsted acidity increased proportionally to Ti content.
The acidity also can explain the formation of species II,
as it is well known, Lewis acid sites induce the rearrangement of α-pinene oxide to campholenic aldehyde.

IV.

Theion
ionfragments
fragments of
of campholenic
campholenic aldehyde
from
GC7: The
aldehyde
from
GCFIG.FIG.7:
MS result.
$V DERYH UHVXOWV WKH R[LGDWLRQ RI Į

$Vchemical
DERYH UHVXOWV
WKH R[LGDWLRQ RI In
Į the GC-MS
of a fine
and pharmaceuticals.
VXFK DV LVRPHUL]DWLRQ

RI Į
VXFK
DV
LVRPHUL]DWLRQ
RI Į
result Fig. 7, it indicated that the typical m/z
fragment
IRUPLQJĮ
IRUPLQJĮ
ion of 108, 93, 67, 41, which are the typical fragment ions
of the fragment processing of campholenic aldehyde with
an efficient index of 90% to standard GC-MS mass spectroscopy.
Results of α-pinene oxidations over Ti modified MCMĮ As it can be seen,
41 catalysts are shown in TableWRII.
conventional reaction tests (with WR
H2ĮO2 addition only at
the beginning of reaction) practically show changes on activity when rising amounts of Ti. Based on the studied
reaction conditions, the change of Ti content on catalysts
has an7KHLVRPHUL]DWLRQRIĮ
effect on product distribution. The smooth growth
7KHLVRPHUL]DWLRQRIĮ

542

CONCLUSION

Ti-MCM-41 molecular sieves with various compositions
have been successfully prepared by direct synthesis. In all
cases, solids with high specific surface area, high pore volume and a narrow pore size distribution were obtained.
Ti was incorporated into the silica framework mainly in

the tetrahedral isolated sites. At high Ti content, the
broadening of the main DR-UV-Vis band with a shoulder
at about 260-270 nm can be assigned to a higher coordination of Ti probably due to water molecules adsorbed
on the catalyst as well as to the formation of some Ti-OTi clustering in the framework. However, a segregated
TiO2 anatase phase was not observed for any sample.
The materials synthesized here showed a good activity
for the epoxidation of α-pinene using H2 O2 as oxidant.
The α-pinene conversion level and the nature of oxidation products were strongly influenced by the structure of
the catalyst, the degree of metal loading and the chemical
environment around the active sites. The main oxidation
product was the α-pinene oxide, being the by-products
the corresponding
prodĮ
Į hydrolysis and allylic oxidation
ucts. The epoxide Įyield reached a maximum valueĮ at an
Ti content in the catalyst of approximately 1 wt.% .
Į

Į

Acknowledgments

This study is supported by Grants-in-Aid from Vietnamese Government Fund.

(J-Stage: />

e-Journal of Surface Science and Nanotechnology

[1] V. R. Elias, M. E. Crivello, E. R. Herrero, S. G. Casuscelli,
and G. A. Eimer., Ind. Eng. Chem. Res. 48, 9076 (2009).

[2] D. Q. Khieu, D. T. Quang, T. D. Lam, N. H. Phu, J. H.
Lee and J. S. Kim, J. Incl. Phenom. Macrocycl. Chem.
65, 73 (2009).
[3] K. Lin, P. P. Pescarmona, H. Vandepitte, D. Liang, G. V.
Tendeloo and P. A. Jacobs, J. Catalysis 254, 64 (2008).
[4] A. Corma, S. Iborra and A. Velty, Chem. Rev. 107, 2411
(2007).
[5] N. T. Ha, T. T. N. Mai, N. V. Quyen and G. T. P. Ly,
Vietnam J. Chem. 46, 301 (2008).
[6] P. Patnamy and Srinivas, Adv. Catal. 48 (2004).

Volume 9 (2011)

[7] P. Wu and T. Tatsumi. Chem. Mater. 1, 1657 (2002).
[8] A. Szegedi, Z. Konya, D. Mehn, E. Solymar, G. PalBorbely, Z. E. Horvath, L. P. Biro and I. Kirici, App.
Catalysis A: General 272, 257 (2004).
[9] C.-F. Cheng, D. H. Park and J. Klinowski, J. Chem. Soc.,
Faraday Trans. 93 193 (1997).
[10] F. Hoffmann, M. Cornelius, J. Morell, and M. Froba,
Angew. Chem. Int. Ed. 45, 3216 (2006).
[11] H. P. Lin, Y. R. Cheng, C. R. Lin, F. Y. Li, C. L. Chen,
S. T. Wong, S. Cheng, S. B. Lui, B. Z. Wan, C. Y. Mou,
C. Y. Tang and C. Y. Lin, J. Chem. Soc., 46, (1999).

(J-Stage: />
543