Aluminium-containing mesoporous benzene-silicas with crystal-like pore wall structure

Article abstract of DOI:10.1039/b507437a

Mesoporous benzene-silicas with a high content of tetrahedral aluminium in the framework (Si/Al = 37 and 59) were successfully synthesized, as evidenced by X-ray diffraction, N₂ sorption analyses, transmission electron microscopy and solid state ¹³C CP-MAS, ²⁷Al and ²⁹Si MAS NMR spectroscopy. These materials have well-ordered 2D hexagonal mesostructure with a molecular scale periodicity in the pore walls. The existence of the phenylene groups in the framework greatly enhances the hydrothermal stability of the aluminium-containing mesoporous benzene-silicas. The acidity of the mesoporous benzene-silicas arising from the incorporated aluminium was measured by the FT-IR spectra of pyridine adsorption measurements. The organic groups bridged in the mesoporous framework affect significantly the acidity of the resultant materials although most aluminium atoms are in tetrahedral coordination. These materials are catalytically active for alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b507437a

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www.rsc.org/materials | Journal of Materials Chemistry
Aluminium-containing mesoporous benzene-silicas with crystal-like pore
wall structure
Qihua Yang,* Jie Yang, Zhaochi Feng and Ying Li
Received 25th May 2005, Accepted 2nd August 2005
First published as an Advance Article on the web 23rd August 2005
DOI: 10.1039/b507437a
Mesoporous benzene-silicas with a high content of tetrahedral aluminium in the framework
(Si/Al 5 37 and 59) were successfully synthesized, as evidenced by X-ray diffraction, N2 sorption
analyses, transmission electron microscopy and solid state 13C CP-MAS, 27Al and 29Si MAS
NMR spectroscopy. These materials have well-ordered 2D hexagonal mesostructure with a
molecular scale periodicity in the pore walls. The existence of the phenylene groups in the
framework greatly enhances the hydrothermal stability of the aluminium-containing mesoporous
benzene-silicas. The acidity of the mesoporous benzene-silicas arising from the incorporated
aluminium was measured by the FT-IR spectra of pyridine adsorption measurements. The
organic groups bridged in the mesoporous framework affect significantly the acidity of the
resultant materials although most aluminium atoms are in tetrahedral coordination. These
materials are catalytically active for alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol.
Most mesoporous silicas and PMOs reported to date have
1. Introduction
amorphous pore walls, which would hinder their use for
The periodic mesoporous organosilicas (PMOs) represent
various potential applications. Mesoporous benzene-silica with
one of the recent breakthroughs in the fields of materials
a hexagonal array of mesopores and crystal-like pore walls
chemistry.1–3 Synthesized from the bridged organosilane pre-
cursor, (R9O)3SiR(OR9)3, PMOs have some unique properties
that cannot be obtained by other approaches, such as uniformly
distributed organic groups in the mesoporous framework with
maximum loading of up to 100%. Also, the organic groups
bridged in the mesoporous framework will not block the pores
and the chemical/physical properties of the materials can be
tuned by varying the bridged organic groups.4–6 These novel
materials promise to have a wider range of application
possibilities compared with the traditional mesoporous silicas.
Synthesis of mesoporous organosilicas with new structures
and compositions is very important for studying their potential
applications in the fields of separation, chromatography, large
molecular release systems, and catalysis. Incorporation of
heteroatoms in PMOs can provide a new approach for the
synthesis of mesoporous materials with new compositions and
multifunctionalities. Transition metals (Ti and Ru) have been
incorporated in the framework of mesoporous organosilicas
and improved catalytic activity was observed for titanium-
containing mesoporous organosilicas in epoxidation and
ammoxidation.7–9 The unique surface properties of PMOs
are believed to contribute to the enhanced catalytic activity of
the material. Recently, our group reported the synthesis and
catalytic properties of hydrothermally stable aluminium-
containing mesoporous ethane-silicas.10 Compared with the
large number of studies of heteroatom-substituted mesoporous
silicas,11–13 heteroatom-substituted mesoporous organosilicas
still remain a new field to be explored.
was first reported by Inagaki and co-workers.14 Later they
demonstrated that the molecular scale periodicity could also be
observed for mesoporous material with biphenylene bridged in
the mesoporous framework.15 Aluminium-containing ethylene-
bridged mesoporous organosilicas with molecular scale
periodicity were described by Mokaya and co-workers
recently.16 However, the aluminium content in these ethylene-
bridged mesoporous organosilicas is very low (Si/Al 5 350
and 240). The increase of the aluminium content in the
mesoporous organosilicas should be one of the key factors
for their applications as catalysts and adsorbents because the
tetrahedrally coordinated trivalent aluminium atoms are
believed to be the major interaction sites for guest molecules
and the origin of acidity.17
Here, we report on the synthesis and properties of meso-
porous benzene-silicas with crystal-like pore wall structure
and a high content of tetrahedral aluminium. These materials
have bifunctional character derived from both tetrahedral
aluminium and phenylene groups in the mesoporous frame-
work. The effects of aluminium on mesostructure, molecular
periodicity and hydrothermal stability of the mesoporous
benzene-silicas were investigated. The acidity and catalytic
properties of aluminium-containing mesoporous organosilicas
with different types of organic groups bridged in the frame-
work were compared.
2. Experimental
2.1 Materials
State Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian,
116023, China. E-mail: yangqh@dicp.ac.cn; Fax: +86-411-84694447;
Tel: +86-411-84379552
All materials were analytical grade and used as purchased
without further purification. Octadecyltrimethylammonium
chloride (C18TMACl) and aluminium isopropoxide
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[Al(i-OPr)3] were purchased from Sigma-Aldrich Company
Ltd. (USA). 1,4-Bis(triethoxysilyl)benzene (BTEB) was pre-
pared according to the literature.18 Mesoporous benzene-silica
was synthesized according to the literature.14
multipoint Brunauer–Emmett–Teller (BET) surface area was
calculated over the relative pressure range P/Po 5 0.1–0.2. The
pore diameter was calculated from the adsorption branch using
the Barrett–Joyner–Halenda (BJH) method. Transmission
electron microscopy (TEM) was performed using a JEM-
2010 instrument at an acceleration voltage of 100 kV. 27Al
(104.1 MHz), 13C (100.5 MHz) and 29Si (79.4 MHz) MAS
NMR spectra were recorded in a 4 mm ZrO2 rotor on a Bruker
DRX-400 spectrometer equipped with a magic angle spin
probe. 27Al signals were referenced to a 0.5 M aqueous
solution of aluminium nitrate. 13C and 29Si signals were
referenced to tetramethylsilane (TMS).
2.2 Synthesis of aluminium-containing mesoporous benzene-
silicas (MBS-Al-n)
The typical synthesis procedure for aluminium-containing
mesoporous benzene-silica was as follows: octadecyltrimethyl-
ammonium chloride (C18TMACl) (1.66 g) was dissolved in
deionized water (46.00 g), followed by addition of 3 M NaOH
(8.00 g). 1,4-Bis(triethoxysilyl)benzene (BTEB) (2.00 g) was
poured into the above mixture, and the solution was stirred at
room temperature for 20 min, then the desired amount of
aluminium isopropoxide [Al(i-OPr)3] was added as a solid.
Finally, the mixture was stirred vigorously at room tempera-
ture for an additional 12 h, and aged under reflux at 98 uC for
another 24 h. The white precipitate was filtered, repeatedly
washed with deionized water and dried at 100 uC. The sample
was denoted as MBS-Al-n. The Si/Al ratio in the initial gel
mixture was 40/1 and 15/1 for MBS-Al-1 and MBS-Al-2,
respectively. The surfactant was extracted by stirring 1 g of
as-synthesized material in 200 mL of ethanol containing 1.0 g
of HCl (37 wt%) at 60 uC for 6 h. To investigate the hydro-
thermal stability, the surfactant free material was subjected to
refluxing in deionized water (with 1 L of water per gram of
solid) for 100 h. After cooling to room temperature, the
powder product was filtered and dried at 100 uC.
IR spectra of adsorbed pyridine were taken on a Thermo
Nicolet NEXUS 470 FT-IR spectrometer. The weight of
the pellet was y5–6 mg. The samples were made into self-
supporting wafers and were evacuated in an IR cell at 350 uC for
100 min. IR background spectra were recorded after the samples
were cooled to room temperature. Pyridine was then admitted
into the IR cell and the IR spectra of adsorbed pyridine were
recorded after degassing at 150 and 350 uC for 30 min.
3. Results and discussion
3.1 Framework composition
The Si/Al ratio of the surfactant-free MBS-Al-1 and MBS-Al-2
is 59 and 37, respectively, as determined by elemental analyses
(Table 1). The actual content of the incorporated aluminium is
lower than that in the initial gel mixture, which may be due
to the different hydrolysis and condensation rates between
(EtO)3Si–C6H4–Si(OEt)3 and Al(i-OPr)3.
2.3 Catalytic experiment
The 27Al MAS NMR spectrum of MBS-Al-2 (Si/Al 5 37) is
depicted in Fig. 1. It exhibits a strong resonance at 55 ppm,
which is characteristic of tetrahedral aluminium centers
(T center). The weak resonance at 0 ppm is due to the
aluminium species in octahedral coordination (O center), which
is usually assigned to the extra-framework aluminium centers.
From the T/O ratio, we can see that more than 90 mol% of
aluminium is tetrahedrally coordinated in the framework of the
mesoporous benzene-silica. The 13C CP MAS NMR spectrum
of MBS-Al-2 gives the signal of the phenylene groups at
134.0 ppm (Fig. 2), indicating that the phenylene groups in the
material are intact.14 The weak resonances at 29.7 and 58.4 ppm
are from the mixture of surfactant residues and ethanol groups
formed during surfactant extraction process.14 The 29Si MAS
NMR spectrum shows two signals at 271.4 and 281.1 ppm,
which can be assigned to the T2 [SiC(OH)(OSi)2] and T3
[SiC(OSi)3] sites of silicon species bonded with phenylene
The alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol
was performed in a 25 mL flask. A mixture of 0.125 mmol 2,4-
di-tert-butylphenol (Aldrich), 0.125 mmol cinnamyl alcohol
(Aldrich), 62.5 mg catalyst in 6.25 mL isooctane was stirred at
95 uC for 24 h. After reaction, the mixture was filtered and the
filtrate was analyzed on an Agilent 6890 gas chromatograph
equipped with a flame ionization detector and an OV-1
capillary column (30 m 6 0.25 mm 6 0.3 mm) using 1,3-di-
tert-butylbenzene as an internal standard.
2.4 Characterization
X-Ray powder diffraction (XRD) patterns were recorded on a
Rigaku D/Max 3400 powder diffraction system using Cu Ka
radiation. The nitrogen sorption experiments were performed
at 2196 uC on an ASAP 2000 system, the samples were
outgassed at 100 uC for 10 h before the measurement. The
Table 1 Physicochemical properties of aluminium-containing mesoporous benzene-silicas before and after hydrothermal treatment
BET surface
area/m2 g21
Pore
diameter/nm
Pore
volume/cm3 g21
Wall
thickness/nmc
Sample
Si/Ala
Si/Alb
d100/nm
Mesoporous benzene-silica
Refluxed 100 h
MBS-Al-1
Refluxed 100 h
MBS-Al-2
4.6
4.6
4.5
4.7
4.6
5.1
822.7
686.4
681.7
785.8
869.4
824.9
c
3.0
2.8
3.0
2.8
2.8
2.3
0.83
0.62
0.58
0.80
0.82
0.93
2.3
2.5
2.1
2.6
2.5
3.5
40
15
b
59
37
Refluxed 100 h
a
Si/Al in the initial gel mixture. Si/Al in the mesoporous materials. Estimated from a0-pore diameter, where a0 5 2d100/!3.
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Fig. 1 27Al MAS NMR spectrum of the representative MBS-Al-2.
groups, respectively (Fig. 2). The absence of a Q site (in the
range of 290 to 2110 ppm) suggests a stable Si–C bond under
the present synthesis conditions. The results of the elemental
analyses and solid state NMR reveal that benzene-silicas with a
high content of tetrahedral aluminium in the framework have
been successfully synthesized.
Fig. 3 XRD patterns of the materials (a) mesoporous benzene-silica;
(b) MBS-Al-1; (c) MBS-Al-2.
lattice (p6mm). MBS-Al-1 with incorporation of aluminium in
the mesoporous framework only shows one sharp diffraction
peak (100) with strongly decreased intensity. Compared with
MBS-Al-1, the diffraction peak of MBS-Al-2 with higher
aluminium content is broad. The disappearance of the (110)
and (200) diffraction peaks in the XRD patterns of MBS-Al-1
and MBS-Al-2 suggests that the mesostructure was disturbed
by the incorporation of aluminium in the framework. Despite
the absence of the (110) and (200) diffractions in the XRD
patterns of MBS-Al-1 and MBS-Al-2, the TEM images of
MBS-Al-1 still clearly show the formation of an ordered
mesostructure with a hexagonal arrangement of mesoporous
channels (Fig. 4), revealing that MBS-Al-1 and MBS-Al-2
have ordered 2D hexagonal mesostructures.
3.2 Mesostructure and porosity
The XRD patterns of the aluminium-containing mesoporous
benzene-silicas are displayed in Fig. 3. In the low angle
diffraction region (2h , 10 degrees), the mesoporous benzene-
silicas exhibit three diffraction peaks, corresponding to the
(100), (110) and (200) reflections of a hexagonal symmetry
Fig. 2 13C CP MAS and 29Si MAS NMR spectra of the representa-
tive MBS-Al-2 (* refers to the side bands and $ refers to the carbon
species of the surfactant residues and ethanol).
Fig. 4 TEM images of the representative MBS-Al-1 in the direction
of the pore axis (a) and perpendicular to the pore axis (b).
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Fig. 5 N2 sorption isotherms of the materials before (a) and after (b) hydrothermal treatment.
Besides the diffraction peak in the lower-angle diffraction
region (2h , 10 degrees), three additional peaks with
d-spacings of 0.76, 0.38 and 0.25 nm were observed in the
XRD patterns of all materials. They are assigned to a periodic
arrangement of the hydrophobic benzene layers and hydro-
philic silica layers within the pore walls.14,19 The intensity of
these diffraction peaks decreases as the aluminium contents in
the initial gel mixture increases. The decrease of the long range
order was also observed for aluminium-containing ethylene-
bridged mesoporous organosilica, probably due to the fact
that the p–p interactions were disturbed by aluminium
incorporated in the mesoporous framework.16 The additional
broad reflection at d 5 0.42 nm, that was also observed in
the original mesoporous benzene-silica, is not due to any
contamination of the amorphous materials but due to the
amorphous nature of the atomic arrangements of Si and O in
the silica layers of the benzene-silica materials.
consistent with the XRD results. An additional H1 hysteresis
loop (P/Po 5 0.5–1.0) also appears in the isotherms of MBS-
Al-1 and MBS-Al-2, which was attributed to the voids between
the particles.20 The results of XRD, TEM and N2 sorption
analysis reveal that the mesoporous benzene-silicas with
tetrahedral aluminium coordinated in the framework have an
ordered 2D hexagonal mesostructure along with a molecular
scale periodicity. One of the most important factors related
with mesoporous aluminosilicates is the hydrothermal stabi-
lity. The low hydrothermal stability of mesoporous silicas
restricts their wide applications.11 Therefore, the hydrothermal
stability of aluminium-containing mesoporous benzene-silicas
was investigated.
3.3 Hydrothermal stability of the materials
Our and other groups found that the hydrothermal stability of
mesoporous organosilicas with ethane, phenylene and ethylene
bridged in the framework is greatly improved compared with
mesoporous silicas.5,10,16 XRD (Fig. 6) and N2 sorption
isotherms (Fig. 5) were performed on materials before and
after hydrothermal treatment. The XRD pattern of meso-
porous benzene-silica after treatment clearly shows three well-
resolved diffraction peaks at low angle (2h , 10 degrees) and
N2 sorption isotherms of the materials are given in Fig. 5.
All materials show typical type IV isotherms with a capillary
condensation step at P/Po in the range of 0.2 to 0.4, suggesting
uniform pore size distributions. Compared with mesoporous
benzene-silicas, the capillary condensation steps for MBS-Al-1
and MBS-Al-2, especially for MBS-Al-2, are less pronounced,
indicating a less ordered mesoporous structure, which is
Fig. 6 XRD patterns of the materials before (a) and after (b) hydrothermal treatment.
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three additional peaks at medium angle (10 , 2h , 40),
suggesting that both mesostructure and molecular scale
periodicity are stable in boiling water even for 100 h.
Resembling mesoporous benzene-silica, the hexagonal meso-
structure and molecular scale periodicity of MBS-Al-1 and
MBS-Al-2 after treatment were also well maintained as noted
by the (100) peak and three additional diffractions at medium
angle. The intensity of the (100) diffraction peak of MBS-Al-1
and MBS-Al-2 is significantly increased after hydrothermal
treatment, while the intensity of the (100) diffraction peak of
mesoporous benzene-silica decreased slightly after the treat-
ment. These results show that incorporation of aluminium in
mesoporous benzene-silicas can enhance the hydrothermal
stability of the materials. A similar phenomenon was also
reported previously for the aluminium-containing mesoporous
silicas.11 The increased d(100) spacing was observed for
both MBS-Al-1 and MBS-Al-2 after treatment, implying an
expansion of the unit cell.
Fig. 7 IR spectra of pyridine desorbed on MBS-Al-n: (a) MBS-Al-1;
(b) MBS-Al-2.
The nitrogen adsorption/desorption isotherms of meso-
porous benzene-silica and MBS-Al-2 after the treatment
resemble those of the untreated ones, clarifying the stable
mesostructure of the materials. The physicochemical pro-
perties of the mesoporous materials before and after hydro-
thermal treatment are listed in Table 1. After the treatment,
mesoporous benzene-silica exhibits a decrease (y16%) in
surface area accompanied with a decrease in pore volume.
Interestingly, unlike mesoporous benzene-silica, the BET
surface area and pore volume of MBS-Al-1 and MBS-Al-2
were slightly increased after the treatment (Table 1). The walls
of all materials become thicker after the treatment. This is
probably due to the further condensation of incompletely
condensed silicon species during the process of the hydro-
thermal treatment.
mesoporous benzene-silica, which cannot be accessed by
pyridine molecules. MBS-Al-2 with higher aluminium content
(Si/Al 5 37) exhibits strong vibrations of pyridine adsorbed on
Lewis acid sites (1455 and 1623 cm21) and on Brønsted acid
sites (1547 and 1640 cm21) and the vibrations of pyridine
associated with both Lewis and Brønsted acid sites in addition
to hydrogen-bonded pyridine. The FT-IR spectra of MBS-Al-
n clearly show that the number of both Lewis and Brønsted
acid sites increases as the amount of aluminium in the
framework increases, thus indicating a clear relationship
between framework aluminium and the number of acid sites.
Generally, increasing the evacuation temperature of pyridine
will reduce the number of acid sites capable of retaining the
pyridine.21 Upon degassing of MBS-Al-2 at 350 uC for 30 min,
the hydrogen-bonded pyridine was removed almost comple-
tely. The decreased intensity of the peak at 1545 cm21 indicates
the number of Brønsted acid sites is decreased. Noticeably, no
obvious decreasing of the peak intensity at 1455 cm21 was
observed, implying that the strength of Lewis acid sites
on MBS-Al-2 is strong. However, this is not the case for
aluminium-substituted mesoporous silicas. During our studies
of the acidic properties of Al-SBA-15 with similar Si/Al ratio
as that of MBS-Al-2, we found that the number of both
Brønsted acid sites and Lewis acid sites is decreased with
increasing desorption temperature.22 The above results indi-
cate that the network component of aluminium-containing
mesoporous materials has a great influence on the acidic
properties of the materials. For further understanding of
the influence of the phenylene groups on the acidity of the
mesoporous material, the total amounts of Brønsted and
Lewis acidic sites of the materials were calculated based on the
following formula:23
From the above structural characterizations, we can see that
aluminium-containing mesoporous benzene-silicas are hydro-
thermally stable. The high hydrothermal stability of the
materials is mainly attributed to the combined advantages of
the hydrophobic surface of mesoporous benzene-silica and the
incorporation of aluminium in the mesoporous framework.
3.4 Acidic properties of aluminium-containing mesoporous
benzene-silicas
FT-IR spectra of pyridine adsorption were used to evaluate
and analyze the strength and type of acid sites (Lewis and
Brønsted) on MBS-Al-n. Fig. 7 shows the IR spectra of
pyridine in the region between 1650 cm21 and 1400 cm21
following its adsorption on MBS-Al-n and subsequent thermal
treatment at different temperature. Unexpectedly, MBS-Al-1
(Si/Al 5 59) only shows the strong vibrations at 1595 and
1447 cm21 due to hydrogen-bonded pyridine, and a relatively
weak vibration at 1491 cm21 assigned to pyridine associated
with both Lewis and Brønsted acid sites (pyridine desorbed at
150 uC). The vibrations of pyridine adsorbed on Lewis acid
sites (1455 and 1623 cm21) and Brønsted acid sites (1547 and
1640 cm21) cannot be observed, indicating that MBS-Al-1 has
a very low concentration of surface acid sites. The extremely
low acid concentration on MBS-Al-1 may be due to the fact
that most of the aluminium is buried in the framework of
Total amount of acidic sites (mmol g21) 5 [1.88 6 IA(B) 6
R2/W] + [1.42 6 IA(L) 6 R2/W], where IA (B or L) 5 integrated
absorbance of Brønsted or Lewis band (cm21); R 5 radius of
catalyst disk (cm); W 5 weight of disk (mg).
The amount of Brønsted acid sites and Lewis acid sites for
MBS-Al-1 calculated using the above formula is near zero.
Because we cannot get the base-line separation of peaks of
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pyridine adsorbed on Lewis acidic sites (1455 cm21) and
H-bonded pyridine (1445 cm21) (pyridine desorption at
150 uC), the amount of Lewis acid sites of MBS-Al-2 was
calculated based on splitting of the two peaks. The total
with the aluminium content, which is consistent with the
results of pyridine adsorption experiment.
Previously, we reported the synthesis and catalytic pro-
perties of aluminium-containing mesoporous ethane-silicas.10
Aluminium-containing mesoporous ethane-silica (MES-Al-1)
has a similar Si/Al ratio and structural order as MBS-Al-1. In
the same reaction, the main product for aluminium-containing
mesoporous ethane-silica (Si/Al 5 54) is product 2 without
formation of product 3. Comparing the catalytic data of MBS-
Al-1 (Si/Al 5 59) with aluminium-containing mesoporous
ethane-silica (Si/Al 5 54), we can propose that aluminium
incorporated in the ethane-bridged mesoporous framework
generates a larger amount of acid sites with moderate
strength than that incorporated in the phenylene-bridged
mesoporous framework at similar aluminium content and
aluminium coordination environment. The catalytic activity of
MBS-Al-1 is lower than aluminium-containing mesoporous
ethane-silica. The lower catalytic activity is probably due to
the small amounts of acid sites on MBS-Al-n and the slow
diffusion rates of the reactants and products in the mesopores
of MBS-Al-n, which is caused by strong interaction between
the phenylene groups of MBS-Al-n and reactants/products
through p–p bonding of the aromatic ring.
amount of acidic sites of MBS-Al-2 (Si/Al
5 37) is
0.14 mmol g21. For comparison, aluminium-containing meso-
porous ethane-silica (MES-Al-1) with an Si/Al ratio of 54 was
synthesized.10 The total amount of acidic sites of this material
is 0.35 mmol g21. The amount of acidic sites on MBS-Al-2
(Si/Al 5 37) is much lower than that on MES-Al-1 (Si/Al 5 54).
The pyridine adsorption experiments show that aluminium
tetrahedrally coordinated in the framework of mesoporous
benzene-silica tends to generate smaller amounts of acid sites
than that in the framework of mesoporous ethane-silica.
3.5 Catalytic properties of aluminium-containing mesoporous
benzene-silicas
The aluminium-containing mesoporous benzene-silicas with
molecular scale periodicity were used as catalysts for the
alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol.
This reaction is a sterically demanding condensation phase
reaction and is susceptible to the acidic strength of the active
sites.24 Consequently, the selectivity and the conversion of this
reaction are suitable indicators to evaluate the effectiveness of
the diffusion of the reactants through the mesopores and the
acid sites with moderate strength.
4. Conclusions
Mesoporous benzene-silicas with a high content of tetrahedral
aluminium and crystal-like pore wall structure were success-
fully synthesized. The resultant materials with both meso- and
molecular scale periodicity are hydrothermally stable in boiling
water. The hydrophobic character of the materials and
aluminium incorporation in the mesoporous framework
mainly contribute to the high hydrothermal stability. The
All materials are catalytically active for this reaction
(Table 2). Three main products were formed. The formation
of desired compound 1 is catalyzed by acid sites with moderate
strength. Product 2 is probably the intermediate of product 1.
Compound
3 is formed by dealkylation of 2,4-di-tert-
butylphenol and was previously observed on zeolites.25
A
ethane-bridged mesoporous network generates
a greater
drastic difference in product selectivity was observed between
MBS-Al-1 (Si/Al 5 59) and MBS-Al-2 (Si/Al 5 37). The main
product for MBS-Al-1 (Si/Al 5 59) is compound 3 with
selectivity up to 51.3%, while MBS-Al-2 (Si/Al 5 37) gives
compound 2 as the main product without formation of
compound 3. The selectivity of 1 + 2 was much higher on
MBS-Al-2 than that on MBS-Al-1. The catalytic data indicate
that the amount of acid sites with moderate strength increases
amount of acid sites than the phenylene-bridged mesoporous
network with similar Si/Al ratio and aluminium coordina-
tion environment. The aluminium-containing mesoporous
ethane-silica exhibits higher catalytic activity than aluminium-
containing mesoporous benzene-silica in alkylation of 2,4-di-
tert-butylphenol with cinnamyl alcohol under identical
reaction conditions. This one-pot synthesis method provides
the possibility for incorporating various kinds of functional
groups in the mesoporous organosilicas.
Table 2 Alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol
in the presence of MBS-Al-na
Acknowledgements
The authors thank Professor Can Li for the pyridine
adsorption experiment. This work was financially supported
by the National Natural Science Foundation of China
(20303020), National Basic Research Program of China
(2003CB615803) and Talent Science Program of the Chinese
Academy of Sciences.
Conversion
(%)
Catalyst
1
2
1 + 2
3
Othersc
MBS-Al-1
MBS-Al-2
25.3
31.7
27.5
—
27.5
51.3 21.2
26.6 46.4 73.0
11.7 61.9 73.6
—
—
27.0
26.4
References
MES-Al-1b 59.3
a
1 T. Asefa, M. J. MacLachlan, N. Coombs and G. A. Ozin, Nature,
1999, 402, 867.
Conversion is based on 2,4-di-tert-butylphenol. Reaction
conditions: 2,4-di-tert-butylphenol (0.125 mmol), cinnamyl alcohol
(0.125 mmol), catalyst (62.5 mg), isooctane (6.25 mL), 95 uC, 24 h.
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Aluminium containing mesoporous ethane-silica with Si/Al
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5
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