Cubic Pm3n mesoporous aluminosilicates assembled from zeolite seeds as strong acidic catalysts

Article abstract of DOI:10.1039/c5cy00184f

Cubic Pm3n mesoporous aluminosilicates isomorphous to SBA-1, with 3D interconnected pore structures, were assembled from Al-incorporating zeolite seeds at around pH 9 using cetyltriethylammonium bromide as a pore-directing agent. The resultant series of materials (termed Al-ZSBA-1) has the advantages of strong acidity from the zeolitic structure and good diffusivity of bulky reactants from the 3D interconnected mesopores. Al-ZSBA-1, with Al loading up to an Al/Si molar ratio of 0.057, still retains a cubic Pm3n structure and high surface area (ca. 600 m² g^-1). The acidities were stronger than the counter materials prepared using sodium silicate as the silica source (referred to as Al-SBA-1-alk). Moreover, all the Al(iii) ions in Al-ZSBA-1 retained their tetrahedral coordination after calcination at 823 K, while a portion of Al(iii) in Al-SBA-1-alk became octahedrally coordinated. When tested for the catalytic alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol, Al-ZSBA-1 gave higher flavan selectivities and yields in comparison to Al-SBA-1-alk, ZSM-5, and beta zeolites.

Full text of DOI:10.1039/c5cy00184f

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DOI: 10.1039/C5CY00184F
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ARTICLE TYPE
Cubic Pm3n Mesoporous Aluminosilicate Assembled from Zeolite Seeds
as Strong Acidic Catalysts
Tsung-Han Lin, Chia-Han Chen, Chi-Shuang Chang, Ming-Chang Liu, Shing-Jong Huang, and Soofin
Cheng*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Cubic Pm3n mesoporous aluminosilicate isomorphous to SBAꢀ1 with 3Dꢀinterconnected pore structures
was assembled by Alꢀincorporated zeolite seeds at pH around 9 using cetyltriethylammonium bromide as
poreꢀdirecting agent. The resultant materials (termed AlꢀZSBAꢀ1) owned the advantages of strong acidity
from zeolitic structures and good diffusivity of bulky reactants from 3Dꢀinterconnected mesopores. Alꢀ
ZSBAꢀ1 with Al loading up to a Al/Si molar ratio of 0.057 still retained the cubic Pm3n structure and
1
0
2
high surface areas (ca. 600 m /g). Their acidities were stronger than the counter materials prepared using
sodium silicate as the silica source (referred as AlꢀSBAꢀ1ꢀalk). Moreover, all the Al(III) ions in Alꢀ
ZSBAꢀ1 retained in tetrahedral coordination after calcination at 823 K, while a portion of Al(III) in Alꢀ
SBAꢀ1ꢀalk became octahedrally coordinated. In application to catalytic alkylation of 2,4ꢀdiꢀtertꢀ
butylphenol with cinnamyl alcohol, AlꢀZSBAꢀ1 gave higher flavan selectivities and yields, in comparison
to AlꢀSBAꢀ1ꢀalk, ZSMꢀ5, and beta zeolites.
1
5
2
3ꢀ26
desilication of zeolitic materials,
(iv) using carbon templating
1
. Introduction.
40 materials to incorporate mesopores during the synthesis of
27ꢀ29
zeolites,
and (v) assembly of mesoporous structures with
Zeolites are well crystalline aluminosilicates with open
30
zeolitic sheets. In method (i), the synthesis procedures are
tedious and the ordered mesoporous structure is often destroyed
in hydrothermal treatment. On the other hand, only disordered
mesopores are formed by methods (iii), (iv) and (v). MCMꢀ22
2
2
3
3
0
5
0
5
structures. The materials have been widely studied and applied in
oil refining and petrochemical industry as catalysts because they
possess high acidity and thermal stability. More recently,
1
,2
4
5
5
6
6
5
0
5
0
5
1
,3
zeolites have also been utilized in fine chemicals industry.
(
IZA code MWW) is the first identified zeolite formed by
However, the small pore sizes of less than 1.2 nm in zeolites
cause slow diffusion of the bulky reactants or even block large
molecules from approaching the active sites. In contrast, ordered
mesoporous materials facilitate the diffusion of large molecules
inside the pores and prevent the pore blockage. Nevertheless,
the mesoporous aluminosilicate materials have amorphous walls
and show weaker acid strength in comparison to those of
microporous zeolites. Therefore, much efforts have been put to
synthesize new types of materials, which combine the advantages
of both zeolites and mesoporous molecular sieves.
31
vertically aligning lamellar zeolite intermediate. The asꢀmade
MCMꢀ22 precursor (MCMꢀ22(P)) is the stacking of zeolitic
sheets through hydrogen bond and organic template with
repeating unit d(001) of 2.5 nm. Several methods such as
calcination, delamination, swelling and pillaring have been
applied to MCMꢀ22(P) in order to generate micro/mesoꢀporous
4
,5
structures namely MCMꢀ56, MCMꢀ36 and ITQꢀ2 in the past two
decades.
6
ꢀ9
32,33
However, the mesopores generated by pillaring or
exfoliation of MCMꢀ22(P) have wide distributed pore diameters.
Recently, Ryoo’s group designed a series of geminiꢀtype,
polyquaternary ammonium surfactants which could generate
micropores and mesopores simultaneously, and ordered
mesoporous structures (lamellar or hexagonal) with thin zeolitic
walls were synthesized based on the dualꢀtemplating concept.
The drawbacks are the tedious procedure and cost in synthesizing
the specially designed surfactants.
Among the mentioned methods, method (ii) using zeolite seeds
as the building units of mesoporous framework has shown the
advantage of facile control of the mesostructure through changing
different kinds of surfactants and hydrothermal conditions. The
The methods for the preparation of micro/mesoporous
1
0ꢀ13
materials can be classified into five categories,
partial crystallization of amorphous pore walls of mesoporous
silica,
namely, (i)
14ꢀ16
(ii) using zeolite seeds as the building units of
30,34
1
7ꢀ22
mesoporous framework,
(iii) controlled dealumination and
*
Department of Chemistry, National Taiwan University, Taipei 10617,
Taiwan.; TEL: +886-2-33661662; FAX: +886-2-2363-6359; E-mail:
chem1031@ntu.edu.tw
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DOI: 10.1039/C5CY00184F
mesoporous zeolite catalysts prepared by this method have been
demonstrated to exhibit high catalytic activities in acidꢀcatalyzed
reactions involving large molecules.
solution was kept around 9. The molar composition of the
reaction mixture was Na SiO /NaAlO /CTEABr/NaCl/H O=
2
3
2
2
3
5ꢀ37
60 1.0/0.01ꢀ0.07/0.26/6/400. After stirring for 10 min, the mixture
was aged at 273 K for 24 h. The solid product was recovered by
filtration, washing thoroughly with distilled water, and drying at
373 K overnight. To remove the template, the asꢀsynthesized
samples were calcined in air under static condition at 823 K for
Among the ordered mesoporous materials, threeꢀdimensional
interꢀconnected pore structures are usually favorable to the oneꢀ
5
0
5
0
5
0
5
0
5
38ꢀ40
dimensional array of pores due to better pore accessibility.
Cubic Pm3n phase SBAꢀ1 silica with interconnected network of
cageꢀtype pores was synthesized in strong acidic media (pH << 1) 65 10 h with the heating rate of 10 K/min.
with
surfactants
of
relatively
large
head
group
2
.2 Preparation of Al(III)-incorporated ZSM-5 Seeds
+
1
1
2
2
3
3
4
4
(C H (C H ) N , n = 12, 14, 16, 18), which tend to form
n
2n+1
2
5 3
5
,41,42
globular micelles.
The drawback of the material from
The ZSMꢀ5 seeds were prepared referred to the procedures in
practical applications has been the low stability of the asꢀmade
reference 58, except all the reagents were diluted to 3.5 times to
avoid the precipitation of zeolite. The solutions containing 1.5 g
4
3,44
samples toward washing with water.
Efforts have been made
to overcome this disadvantage by increasing the amount and 70 sodium silicate (SigamaꢀAldrich, 27wt% SiO
), 0.58
tetrapropylammonium bromide (TPABr, Acros, 98%), 9.6 g
deionized water and required amounts of NaAlO (Hayashi Pure
Chemical Ind., Ltd., 99+%) were neutralized with 1.2 M H
until a final pH of 11.2. After stirring at ambient temperature for
the framework of mesoporous silica is important in order to 75 1 h, the mixture was transferred to an autoclave and heated at 423
g
2
4
5,46
concentration of acid used
or concomitantly adding auxiliary
4
7
agents. On the other hand, under the strongly acidic synthesis
conditions, metal incorporation into SBAꢀ1 framework has been
2
SO4(aq)
2
48ꢀ51
very inefficient,
though the incorporation of metal ions into
introduce functionalities and broaden its applications.
K under static condition for different periods with various
amounts of Al contents. The ZSMꢀ5 zeolite was synthesized by
the same procedure illustrated as above except that the
hydrothermal time was 72 h.
Our laboratory has disclosed an alkaline route to prepare well
ordered cubic Pm3n silica by using sodium silicate as the silica
source and cetyltriethylammonium bromide (CTEABr) as the
poreꢀdirecting agent with the optimal pH value of the synthesis
80
2.3 Preparation of Cubic Pm3n Mesoporous Silica Assembled
from Al(III)-incorporated ZSM-5 Seeds
5
2,53
solution around 9.
In contrast to the conventional synthesis
conditions of SBAꢀ1, where large amount of mineral acid is
needed and tetraethylorthosilicate (TEOS) was the silica source,
the alkaline route is more economical and environmentally
friendly. Most of all, heteroꢀelements could be efficiently
incorporated into the silica framework through isomorphous
substitution and the cubic mesostructure of the resultant material
was stable toward washing with water and hydrothermal
treatment.
The procedures were similar to those for preparation of Alꢀ
SBAꢀ1ꢀalk, except Al(III)ꢀincorporated ZSMꢀ5 seeds were used
as the silica and aluminium sources. In a typical procedure, 0.712
g CTEABr was dissolved in the aqueous solution containing 2.32
g sodium chloride (Acros, 99.5%), a appropriate amount of
8
9
9
5
0
5
hydrochloric acid and 40 g H O. After stirring for 120 min at
2
room temperature, this mixture was cooled down to 273 K in ice
bath and stirred for 60 min. Then, ZSMꢀ5 seed solution was
added to this mixture under stirring. The molar composition of
the final mixture was Na SiO / NaAlO /TPABr/CTEABr/ NaCl/
In the present study, the effort was extended to synthesize
cubic Pm3n silica assembled from aluminium substituted ZSMꢀ5
seeds. The resultant materials were found to have higher
hydrothermal stability and stronger acidic strength in comparison
with the counter materials prepared from sodium silicate. The
catalytic properties were examined by carrying out the alkylation
of 2,4ꢀdiꢀtertꢀbutylphenol (DTBP) with cinnamyl alcohol to form
2
3
2
H O = 1.0/0.01~0.07/0.32/ 0.26/ 6/ 400. After stirring for 10 min,
2
the mixture was aged under static condition at 273 K for 24 h.
The solid product was recovered by filtration, washing
thoroughly with deionized water, and drying at 373 K overnight.
To remove the template, the asꢀsynthesized samples were
calcined in air under static conditions at 823 K for 10 h with the
heating rate of 10 K/min. The resultant materials are designated
5
3,54
flavan as a model reaction.
Flavans are a type of flavanoids,
which are a ubiquitous group of polyphenolic substances present
in most plants preserving the health of plants against infections
and parasites. Flavans have found numerous pharmacological
“xAlꢀZSBAꢀ1”, where x is the Al/Si molar percentage in the
5
5
56
100 synthesis solution.
applications as antioxidants, antimicrobial, antiꢀinflammatory
and antiꢀcancer drugs.
5
7
2.4 Characterization
Powder Xꢀray diffraction (XRD) patterns were recorded using
a PANalytical X’pert Pro diffractometer with Cu Kα radiation
operated at 40 mA and 45 kV. N2 adsorptionꢀdesorption
2
. Experimental section
2
.1 Preparation of Al(III)-incorporated Cubic Pm3n
Mesoporous Silica under Alkaline Condition
1
05 isotherms were measured using a Micromeritics Tristar 3000
system at liquid nitrogen temperature (77 K). Before the
measurements, the samples were degassed at 473 K for 10 h
50
Alꢀincorporated Pm3n mesoporous silica materials designated
“xAlꢀSBAꢀ1ꢀalk”, where x is the Al/Si molar percentage in the
ꢀ
3
under vacuum condition (10 torr). The surface area was
calculated by using BrunauerꢀEmmettꢀTeller (BET) method. Pore
10 size was determined by BarrettꢀJoynerꢀHalenda (BJH) method
using the desorption branch of the isotherms. Transmission
electron microscopy (TEM) was performed on a JEOL JEMꢀ
synthesis solution, were prepared referred to the procedures in
reference 52. CTEABr was first dissolved in an aqueous solution
containing sodium chloride and a small amount of hydrochloric
acid. To this mixture at 273 K, the aqueous solution containing
sodium aluminate and sodium silicate with Al/Si atomic ratios
varied in 1ꢀ7% was added so that the pH value of the final
1
55
1
200EX II Transmission Electron Microscope, operating at 80
2
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DOI: 10.1039/C5CY00184F
kV, and the scanning electron microscopy (SEM) images were
m*0.53 mm) using octane (Acros, 99+%) as an internal standard.
taken using a coldꢀfield emission Scanning Electron Microscope 60 The selectivities of alkylation products, 2,4ꢀdiꢀtertꢀbutylꢀ6ꢀ
2
9
27
(
Hitachi Sꢀ4800). The Si and Al NMR experiments were
cinnamylphenol (DTBCP) and flavan were determined by
assuming both compounds have the same FID response factors,
because pure DTBCP was not commercially available.
carried out at frequencies of 59.63 and 78.21 MHz, respectively,
on a Brucker MSLꢀ300 NMR spectrometer equipped with a
commercial 7 mm MASꢀNMR probe. The magicꢀangle spinning
frequencies were set to 5 kHz for all experiments. Chemical shifts
were externally referenced to Si(CH ) and 1M Al(NO3)3
solution. The Q /(Q +Q ) area ratios were obtained by
deconvolution of the peaks in the spectra using WinFit software.
The inductively coupled plasmaꢀmass spectrometry (ICPꢀMS) of
the samples dissolved in diluted HF aqueous solutions were taken
by using an Agilent 7700e ICP/MS instrument. Temperatureꢀ
5
0
5
0
5
0
5
0
3. Results and discussion
3
4
4
2
3
65
Fig. 1 shows the XRD patterns of the calcined materials
prepared at pH 9. The XRD patterns of the calcined AlꢀZSBAꢀ1
samples show three distinct diffraction peaks at 2θ~1.5−2.5°
indexed to the (200), (210), and (211) planes of cubic Pm3n
symmetry, and also some weaker diffraction peaks at 2θ~3−4°
1
1
2
2
3
3
4
5
9
7
7
8
0
5
0
assigning to the (222), (320), (321), and (400) planes. The
calcined AlꢀZSBAꢀ1 samples with Al/Si molar percentages lower
than 5% still retain three resolvable diffraction peaks at 2θ~1.5ꢀ
programmed desorption of ammonia (NH ꢀTPD) was performed
3
by a Micrometrics Autochem 2910 system equipped with a
thermal conductivity detector (TCD). Prior to the measurements,
the samples (ca. 300 mg) were preꢀtreated at 823 K for 1 h under
a He flow to eliminate physically adsorbed water. The samples
cooled to 373 K and then adsorbed NH for 30 min, followed by
purging with He gas again for another 30 min to eliminate
2
.5°, while the one synthesized with Al/Si = 7% has only a broad
peak in this region. These results imply that the wellꢀordered
mesopores in cubic Pm3n arrangement can be retained with the
Al/Si molar ratio up to 5% in the synthesis solution. It is also
noticed that no separated zeolite phase was formed since no
diffraction peaks corresponding to ZSMꢀ5 structure were detected
in the high angle regions (as shown in the inserted figures). On
the other hand, the counter samples synthesized using sodium
silicate instead of zeolite seeds as the silica source lose the
resolvable diffraction peaks at 2θ~1.5–2.5° when the Al/Si molar
percentages are only higher than 3%.
3
physically adsorbed ammonia. The NH ꢀTPD profiles were
3
measured over the temperature range of 373ꢀ823 K by using He
as a carrier gas of 30 mL/min. Prior to each FTꢀIR experiment,
compressed sample placed in the IR cell (with ZnSe windows)
was first subjected to evacuation treatment at 673 K for 3 h,
followed by cooled down to room temperature and then saturated
adsorption of pyridine for 0.5 h and subsequent removal of
physisorbed pyridine under vacuum overnight. Each FTꢀIR
(
A)
(B)
−1
spectra was acquired by scanning from 4000 to 400 cm ; 32
repeated scans were accumulated. The accessibility of Brønsted
acid sites in the materials was determined by ionꢀexchange with
cations of various sizes followed by acidꢀbase titration. Aqueous
solutions of sodium chloride (NaCl, 2 M), tetramethylammonium
chloride (TMACl, 0.05 M), and tetrabutylammonium bromide
(TBABr, 0.05 M) were used as the exchange agents. In a typical
experiment, 0.20 g of the solid was first dried at 200 °C for 1 day
and then added to 40 mL of aqueous solution containing the
corresponding salt. The suspension was mixed to reach
equilibrium for 6 h, then the solid was filtered and washed with a
small amount of water. Finally, the filtrate was titrated by 0.01 M
aqueous solution NaOH.
(d)
(
d)
(c)
(
c)
(b)
(b)
10 20 30 40
(a)
(a)
1
2
3
4
5
6
7
1
2
3
4
5
6
7
2
θ
2θ
85
Fig. 1 XRD patterns of calcined (A) AlꢀSBAꢀ1ꢀalk, (B) AlꢀZSBAꢀ1 with
2
.5 Catalytic Reaction Procedure
various Al/Si molar ratios: (a) 1%, (b) 3%, (c) 5%, and (d) 7%.
To generate Brønsted acid sites on AlꢀSBAꢀ1ꢀalk and Alꢀ
ZSBAꢀ1, the calcined samples were ionꢀexchanged with 1 M
The textural properties of the calcined AlꢀSBAꢀ1ꢀalk and Alꢀ
ZSBAꢀ1 samples were examined by N2 physisorption
experiments, and the results are shown in Fig. 2 and Table 1. All
the calcined samples have type IV isotherms according to the
IUPAC classification, and that was the characteristics of ordered
mesoporous materials. They are basically in the shape similar to
that of conventional SBAꢀ1 prepared in acidic condition. The
surface areas and pore volumes of AlꢀSBAꢀ1ꢀalk are 900−1100
4
5
5
5
0
5
NH Cl aqueous solution twice, followed by filtration, washing
4
with deꢀionized water, drying at 373 K and calcination again at
23 K. Before catalytic test, the catalyst was baked at 473 K at
9
0
8
least for 5 h to remove adsorbed moisture. The alkylation of
DTBP with cinnamyl alcohol was performed in a 50 mL flask
immersed in a thermostat bath with a magnetic stirrer. 100 mg of
the catalyst suspended in 12.5 mL solvent was mixed with 0.25
mmol of DTBP (Aldrich, 98%) and 0.25 mmol of cinnamyl
alcohol (Aldrich, 97%), and the reaction was proceeded at 368 K
for different reaction periods. After quenching the reaction by
cooling at room temperature, the liquid products were separated
from the solid catalyst by filtration and analyzed by a Shimadzu
GCꢀ2014 gas chromatograph (GC) equipped with a flame
ionization detector (FID) and a RTXꢀ5 capillary column (30
2
3
95
m /g and 0.75−0.82 cm /g, respectively. In comparison, the
2
surface areas of AlꢀZSBAꢀ1 samples are lower (600−800 m /g). It
is also noticeable that AlꢀZSBAꢀ1 samples contain small amounts
of microporous volumes while AlꢀSBAꢀ1ꢀalk samples do not.
SEM images show that both AlꢀZSBAꢀ1 and AlꢀSBAꢀ1ꢀalk
00 materials are generally spherical without any facets (Fig. 3). The
particle sizes of the materials synthesized in alkaline condition
1
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1
200
000
1600
(B)
(
A)
1400
1200
1000
1
(
d)
(d)
8
6
4
2
00
00
00
00
0
(
c)
800 (c)
(
b)
600
(
b)
a)
(
a)
400
(
200
0
0
0
.0 0.2 0.4 0.6 0.8 1.0
.0 0.2 0.4 0.6 0.8 1.0
P/P
adsorptionꢀdesorption isotherms of (A) AlꢀSBAꢀ1ꢀalk and (B) AlꢀZSBAꢀ1 samples with various Al/Si molar ratios: (a) 1%, (b) 3%, (c) 5%, and
P/Po
o
Fig. 2 N
2
3
3
(
d) 7%. Profiles are shifted in vertical axis by 200 cm /g STP between profiles in (A) and by 250 cm /g STP in (B).
5
Table 1 Physicochemical properties of calcined cubic Pm3n mesoporous silica samples prepared with various amounts of Al at alkaline condition.
2
a
3
3
b
c
Sample
d
210 (nm)
S
BET (m /g)
D
p
(nm)
V
total (cm /g)
V
micro (cm /g)
FWHM (ppm)
1
3
5
7
1
3
5
7
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
AlꢀZSBAꢀ1
3.6
3.8
4.0
4.1
4.1
3.8
3.8
1148
945
982
961
759
677
652
645
2.2
2.2
2.2
2.2
2.4
2.4
2.4
2.4
0.82
0.77
0.79
0.75
0.86
0.70
0.66
0.60
0
0
17.5
18.1
17.6
16.6
15.7
15.4
15.8
15.2
0
0
0.03
0.02
0.05
0.07
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
3.9
a
b
c
27
Calculated from desorption branch; Calculated from tꢀplot method; Solidꢀstate Al MAS NMR peak at 50 ppm.
vary in a large range from 0.1 to 1 ꢀm in diameter. They are
different from the particles of SBAꢀ1 synthesized by acidic route,
which have wellꢀdefined external morphology with crystal facets
TEM photographs shown in Fig. 4 confirm that the AlꢀSBAꢀ1ꢀalk
and AlꢀZSBAꢀ1 materials possessed longꢀrange ordering of the
3D cubic arrays. The average pore diameter determined from
6
0,61
10
15
20
and the particle sizes in 3ꢀ15 ꢀm.
The smaller particle sizes of 25 TEM photographs is around 2 nm, which is in consistence with
the materials synthesized in alkaline conditions are due to the
that from N sorption experiments.
Fig. 5 shows the FTꢀIR spectra of calcined AlꢀSBAꢀ1ꢀalk and
AlꢀZSBAꢀ1 samples in comparison to that of ZSMꢀ5. The peaks
2
5
2
faster precipitation rate of the silica. It is also noticeable that the
particle sizes decrease with the increase in Al content. Al atoms
in the synthetic solution probably act as nuclei for material
ꢀ
1
near 450, 800, 1100, and 1220 cm are assigned to the SiꢀOꢀSi
growth, and larger amount of nuclei leads to faster precipitation 30 bending and stretching vibrations of condensed silica framework.
6
2,63
and smaller particle size. On the other hand, the particle sizes of
AlꢀZSBAꢀ1 samples are less homogeneous than those of Alꢀ
SBAꢀ1ꢀalk. Large amounts of agglomerates of nanoꢀparticles can
be seen on AlꢀZSBAꢀ1 materials as the Al content increases, and
According to the FlanigenꢀKhatamiꢀSzymanski correlation,
these peaks are corresponding to internal vibration of Si(A1)O4
tetrahedra and are common to silica and quartz. For the cubic
Pm3n silica materials, these peaks are relatively broader in
that accounts for the abrupt increases in N sorption at high P/P0 35 comparison to those of ZSMꢀ5 due to the amorphous nature of
2
region in the N sorption isotherms observed in Fig. 2(B). The
the silica framework. In addition, a bending vibration of nonꢀ
2
4
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5
Fig. 3 SEM photographs of AlꢀSBAꢀ1ꢀalk (aꢀd) and AlꢀZSBAꢀ1 (eꢀh)
samples with various Al/Si molar ratios: (a, e) 1%, (b, f) 3%, (c, g) 5%, (d,
h) 7%.
25
Fig. 4 TEM photographs of AlꢀSBAꢀ1ꢀalk (aꢀd) and AlꢀZSBAꢀ1 (eꢀh)
samples with various Al/Si molar ratios: (a, e) 1%, (b, f) 3%, (c, g) 5%, (d,
h) 7%.
AlꢀSBAꢀ1ꢀalkQ
3
AlꢀZSBAꢀ1
4
Q
(
a)
b)
4
2
3
2
Q
Q /(Q +Q )
4
2
3
Q /(Q +Q )
1
asꢀmade 2%Al
(
0.87
asꢀmade 2%Al
.01
(
c)
d)
1.10
calc 2%Al
calc 2%Al
1.38
(
0
.31
1.22
asꢀmade 5%Al
asꢀmade 5%Al
calc 5%Al
4
000 3500 3000 2500 2000 11500 1000 500
ꢀ
Wavenumber (cm )
calc 5%Al
0
.96
1.28
ꢀ80
Fig. 5 FTꢀIR spectra of (a) ZSMꢀ5, (b) 2AlꢀSBAꢀ1ꢀalk, (c) 2AlꢀZSBAꢀ1
ꢀ
80
ꢀ100
ꢀ120
ꢀ140
ꢀ100
ꢀ120
ꢀ140
1
0
and (d) 5AlꢀZSBAꢀ1.
Chemical shift (ppm)
Chemical shift (ppm)
ꢀ
1
29
condensed silanol group appears at ca. 960 cm and the bending
and stretching vibrations of hydroxyl groups and physically
Fig. 6 Solid state Si MAS NMR of AlꢀSBAꢀ1ꢀalk and AlꢀZSBAꢀ1
3
0
before and after calcination.
ꢀ
1
adsorbed water appear at 1650 and 3450 cm , respectively. It is
noticeable that the walls of both AlꢀSBAꢀ1ꢀalk and AlꢀZSBAꢀ1
materials contain large amounts of silanol groups, akin to
amorphous silica. The absorption at 550ꢀ650 cm , on the other
hand, was assigned to the presence of a doubleꢀring of tetrahedra
For a ZSMꢀ5 structure, the latter
absorption appears near 550 cm . The intensity ratio of the peaks
at 550 to 450 cm is often used as a quantitative measurement of
zeolite crystallinity. The ratio for the ZSMꢀ5 sample is 0.77, and
the AlꢀZSBAꢀ1 materials have the ratios of 0.61–0.63, which are
only slightly higher than 0.58 for 2AlꢀSBAꢀ1ꢀalk. These results
imply that the zeolite seeds incorporated in the walls of Alꢀ
ZSBAꢀ1 materials have low crystallinity.
1
5
ꢀ
1
35
6
4,65
in the zeolitic framework.
29
The solid state Si MAS NMR spectra of the asꢀmade and
ꢀ
1
calcined AlꢀSBAꢀ1ꢀalk and AlꢀZSBAꢀ1 samples were shown in
Fig. 6 Two distinct resonance peaks at ꢀ100 and ꢀ110 ppm
ꢀ
1
2
0
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(A)
(B)
(A)
(B)
0
0
0
.10
.05
.00
0.10
0.05
0.00
(
d)
(
e)
d)
(e)
d)
(
d)
(
(
c)
(c)
(b)
(
(
c)
b)
a)
(c)
(b)
(
b)
(
(
a)
(
a)
(
a)
(
1
50 100 50
0
ꢀ50 ꢀ100 ꢀ150 150 100 50
0
ꢀ50 ꢀ100 ꢀ150
δ
(ppm)
2
δ
(ppm)
400 500 600 700
Temperature (K)
400 500 600 700
Temperature (K)
7
Fig. 7 Solid state Al MAS NMR spectra of calcined (A) AlꢀSBAꢀ1ꢀalk,
B) AlꢀZSBAꢀ1 with various Al/Si molar ratios: (a) 1%, (b) 3%, (c) 5%,
3
Fig. 8 NH ꢀTPD profiles of calcined (A) AlꢀSBAꢀ1ꢀalk, (B) AlꢀZSBAꢀ1
with various Al/Si molar ratios: (a) 1%, (b) 3%, (c) 5%, (d) 7%, and (e)
ZSMꢀ5.
(
and (d) 7%.
5
0
3
4
5
0
5
0
5
0
5
0
5
corresponding to Q and Q , respectively, as well as a weak
shoulder at ꢀ91 ppm for Q are clearly seen, where Q represents
Si in different coordination environments of Si(OSi) (OH)4ꢀn or
Si(OSi) (OAl) and n= 2–4. The relative integrated intensities of
2
n
the AlꢀZSBAꢀ1 materials have one shoulder peak at ca.573 K,
indicating that the AlꢀZSBAꢀ1 materials contain extra portions of
stronger acidic sites in comparison to AlꢀSBAꢀ1ꢀalk.
The nature of acidic sites on these porous materials was
examined by taking FTꢀIR spectra of the samples after pyridine
adsorption, and the results are shown in Fig. 9. The Lewis and
Brønsted acid sites are characterized by the pyridine ring
stretching vibrations appeared at 1454 and 1545 cm ,
respectively.
60 was found to vary with different samples. The 1545 cm peak for
AlꢀZSMꢀ5 is much stronger than 1456 cm peak, indicating that
AlꢀZSMꢀ5 has larger amount of Brønsted acid sites than Lewis
acid sites. Although the intensity of both peaks decrease with
desorption temperature, they are still detectable after desorption
treatment at 673 K. In comparison, 5AlꢀSBAꢀ1ꢀalk and 5Alꢀ
n
n
4ꢀn
3
4
2
the Q /(Q +Q ) signals for the asꢀmade AlꢀZSBAꢀ1 samples are
higher than those of asꢀmade AlꢀSBAꢀ1ꢀalk samples, implying
that the silicate condensation is more complete when zeolite
seeds instead of sodium silicate were used as the silica source.
The degree of silicate condensation was further increased when
these samples were calcined at 823 K for 6 h.
Fig. 7 shows the solid state Al MAS NMR spectra of the
calcined samples containing various amounts of Al(III). All the
AlꢀZSBAꢀ1 samples show only a single peak at 50 ppm,
assigning to the tetrahedrally coordinated aluminium. Moreover,
the peak intensity increases with the aluminium content. The
absence of signals around 0 ppm, which corresponds to Al(III)
ions in octahedral coordination, indicates that no extraꢀframework
alumina species were formed. In contrast, the AlꢀSBAꢀ1ꢀalk
samples with Al/Si molar ratios in the synthesis solutions higher
than 3% have an additional small peak appeared at 0 ppm in the
55
1
1
2
2
3
3
4
4
ꢀ
1
67ꢀ69
The relative intensity ratio of these two peaks
ꢀ
1
2
7
ꢀ
1
5
5
65
ꢀ
1
ZSBAꢀ1 both have 1454 and 1545 cm peaks in similar intensity
ꢀ
1
at 373 K, and the 1454 cm peak becomes dominant as the
desorption temperature increases, implying that the mesoporous
materials contain relatively large amounts of Lewis acid sites.
70 Moreover, small peaks are still retained at 1454 and 1545 cm for
AlꢀZSBAꢀ1 after desorption treatment at 673 K, while they
almost disappear for 5AlꢀSBAꢀ1ꢀalk. These results demonstrate
that the acidic strength of 5AlꢀZSBAꢀ1 is higher than 5AlꢀSBAꢀ
ꢀalk. The ratios of Brønsted/Lewis acidic sites, based on the FTꢀ
IR peak areas, are listed in Table 2. 5AlꢀZSMꢀ5 has a ratio of 2.1,
which is twice higher those of 5AlꢀZSBAꢀ1 (0.9) and 5AlꢀSBAꢀ
1ꢀalk (0.6). Nevertheless, the acidic property of 5AlꢀZSBAꢀ1
materials is between those of 5AlꢀZSMꢀ5 and 5AlꢀSBAꢀ1ꢀalk.
The accessibility of acidic sites in the Alꢀcontaining porous
samples was studied by ionꢀexchange of the protons on the
Brønsted acidic sites with cations of different sizes and the
exchange capacities were determined by titrating the filtrate with
NaOH aqueous solution.
. The exchange capacities of all samples decreased when the size
of ionꢀexchange agent became bigger. For 5AlꢀZSMꢀ5 sample,
the exchange capacity with Na is 0.67 mmol/g, which is ca. 80%
of Al content. This ratio is almost the same as the ratio of
Brønsted acid site determined by IR spectra of adsorbed pyridine
versus tetrahedral Al content determined by NMR reported by
Datka et al. The exchange capacity with TMA is slightly lower
0.62 mmol/g) and that with TBA decreases abruptly to 0.11
ꢀ
1
2
7
Al MAS NMR spectra. Extraꢀframework alumina species are
5
probably formed in these AlꢀSBAꢀ1ꢀalk samples. These results
imply that the Al(III) ions are better retained in the tetrahedral
sites of the mesoporous silica framework if they are incorporated
into the zeolite seeds first. In addition, the value of full width at
half maximum (FWHM) for the Al tetrahedral peaks provides a
measurement of the uniformity of Al microenvironment in both
1
7
8
8
9
5
0
5
0
3
7,66
zeolites and amorphous silicas.
For the AlꢀZSBAꢀ1 samples,
the FWHM values are all around 15 ppm and smaller than those
of AlꢀSBAꢀ1ꢀalk samples (Table 1). This result clearly evidences
that using zeolite seeds as silica source can increase the
uniformity of Al environment in the mesoporous materials.
The acidities of the calcined AlꢀZSBAꢀ1 samples were
compared with those of AlꢀSBAꢀ1ꢀalk and ZSMꢀ5 by carrying
70,71
The results are also shown in Table
2
out the NH ꢀTPD experiment, and the profiles were shown in Fig.
3
8. ZSMꢀ5 owns the largest acid amount and strongest strength
among the studied materials. Two strong and broad signals with
the maxima appeared at 484 and 706 K, indicating that there are
two kinds of acid sites in ZSMꢀ5. In contrast, the AlꢀZSBAꢀ1
materials have only one signal covering 373–700 K with the
maximum at ca. 450 K. Moreover, the AlꢀSBAꢀ1ꢀalk materials
+
72
+
+
(
have similar NH ꢀTPD profiles as that of AlꢀZSBAꢀ1. However,
3
6
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(A)
(B)
(C)
(d)
(d)
(d)
(
c)
b)
(
c)
b)
a)
(c)
(
(b)
(
(a)
(
a)
(
1
650 1600 1550 1500 1450 1400 1350 1650 1600 1550 1500 1450 1400 1350 1650 1600 1550 1500 1450 1400 1350
ꢀ1
ꢀ1
ꢀ1
Wavenumber (cm )
Wavenumber (cm )
Wavenumber (cm )
Fig. 9 The FTꢀIR spectra of calcined (A) 5AlꢀSBAꢀ1ꢀalk, (B) 5AlꢀZSBAꢀ1 (C) 5AlꢀZSMꢀ5 after pyridine adsorption and then desorption at different
temperatures: (a) 373 K, (b) 473 K, (c) 573 K, (d) 673 K.
Table 2 Al contents and cationꢀexchange capacities of various samples
Sample Al content Exchange capacity (mmol/gcat
b
)
Ratio of accessibility
Ratio of B/L
Ratio of B/L
a
c
d
(mmol/gcat
)
acid
acid
+
+
+
Na
TMA
TBA
5
5
5
AlꢀZSMꢀ5
0.84
0.92
0.80
0.67
0.51
0.50
0.62
0.11
0.47
16%
92%
82%
3.9
1.2
1.7
2.1
0.6
0.9
AlꢀSBAꢀ1ꢀalk
AlꢀZSBAꢀ1
0.50
0.48
0.41
a
b
+
+
c
d
5
Measured by ICPꢀMS; Calculated from the ratio of exchange capacities (TBA /Na ); Calculated from ionꢀexchanged method; Calculated from
pyridine adsorptionꢀdesorption FTꢀIR spectra.
+
+
mmol/g. The ratio of TBA /Na exchange capacities is 16%. 35 respectively. These results confirmed that most of the Brønsted
These results indicate that the micropore diameter of ZSMꢀ5 is
acidic sites on mesoporous SBAꢀ1 materials are accessible by
bulky TBA ions. However, the 5AlꢀZSBAꢀ1 sample has ca. 10%
+
+
too small to accommodate TBA ions. On the other hand, both
+
1
1
2
2
3
0
5
0
5
0
mesoporous SBAꢀ1 samples have Na exchange capacities
of the acidic sites probably buried inside the micropores of zeolite
+
around 0.5 mmol/g, which is ca. 55% and 62% of Al contents in
seeds and not accessible by bulky TBA ions.
+
5
AlꢀSBAꢀ1ꢀalk and 5AlꢀZSBAꢀ1, respectively. Since Na ions
should exchange with Brønsted acidic sites only, the difference 40 4. Catalytic alkylation of DTBP by cinnamyl
+
between Al content and Na exchange capacity should be the
content of Lewis acidic sites. The ratios of Brønsted/Lewis acidic
alcohol
+
The FriedelꢀCrafts alkylation of DTBP with cinnamyl alcohol
and the subsequent isomerization of DTBCP to yield flavan
Scheme 1) in the liquid phase were chosen as a model reaction to
evaluate the catalytic activities of Alꢀcontaining cubic Pm3n
mesoporous silica. This is a challenging catalytic reaction. The
first step of alkylation is a FriedelꢀCrafts reaction and needs
sites, calculated from Na ionꢀexchange, are shown in Table 2.
5
5
AlꢀZSMꢀ5 has a ratio of 3.9, which is much higher than those of
AlꢀZSBAꢀ1 (1.7) and 5AlꢀSBAꢀ1ꢀalk (1.2). It is reported that
the ratios of Brønsted/Lewis acidic sites on AlꢀSBAꢀ15 which has
2D hexagonal structure are ca. 0.5 and much lower than those of
zeolites. Our results show that AlꢀSBAꢀ1 has higher ratios of
Brønsted/Lewis acidic sites than AlꢀSBAꢀ15, but lower than
ZSMꢀ5. The proportion of the Brønsted/Lewis acidic ratios of
(
45
73
OH
OH
CH2OH
5
AlꢀZSMꢀ5, 5AlꢀSBAꢀ1ꢀalk and 5AlꢀZSBAꢀ1 is 3.3: 1: 1.4,
+
acid catalyst
which is very similar to the proportion of 3.5: 1: 1.5, calculated
from pyridine adsorption FTꢀIR spectra. These results
demonstrate that the ionꢀexchange method is as reliable as
pyridine adsorption FTꢀIR spectra in determining the ratio of
Brønsted/Lewis acidic sites on the sample.
cinnamyl alcohol
2
,4ꢀdiꢀtertꢀbutylꢀ6ꢀ
2
,4ꢀdiꢀtertꢀbutylphenol
cinnamylphenol (DTBCP)
(
DTBP)
O
For 5AlꢀSBAꢀ1ꢀalk samples, the exchange capacities only
decreases slightly when the size of exchange agent increases from
+
+
Na to bulky TBA . In comparison, more significant decrease is
flavan
+
+
seen on 5AlꢀZSBAꢀ1 sample. The ratios of TBA /Na exchange
capacities are 92% and 82% for 5AlꢀSBAꢀ1ꢀalk and 5AlꢀZSBAꢀ1,
50
Scheme 1 Reaction paths of alkylation of DTBP with cinnamyl
alcohol to form flavan.
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3
5
0
Table 3 Alkylation of DTBP with cinnamyl alcohol over homogeneous
acid catalysts
6
5
4
3
2
0
0
0
0
0
3
Catalyst
DTBP Cinnamyl Flavan
Flavan
yield
(%)
DTBCP
yield
(%)
25
20
flavan yield
DTBCP yield
TBP yield
conv.
alcohol
conv. (%)
Select.
(%)
(%)
DTBP conv.
1
5
0
5
0
H
2
SO
4
0
100
0
0
0
0
0
0
0
1
CH
3
COOH
0
10
0
a
Reaction conditions: 0.25 mmol DTBP, 0.25 mmol cinnamyl alcohol, 10
mg 35% H SO or 6 mg acetic acid, 12.5 mL isooctane, 368 K, 5 h
2
4
0
1
2
3
4
5
6
7
Reaction time (h)
Fig. 10 The DTBP conversion and the product yield as a function of
reaction time. ( : flavan yield, : transcinnamlphenol yield, : TBP
yield, and : DTBP conversion)
5
0
5
0
5
0
5
0
relatively strong acids to catalyze the reaction, while the second
isomerization reaction can be catalyzed by a relatively weak acid.
Moreover, there are several competitive reactions (as shown in
Scheme 2). To demonstrate this point, we have used sulfuric acid
ꢀ
○
△
★
and acetic acid containing similar acid amounts as the solid 45 form DTBCP, and the other is polymerization of cinnamyl
74
1
1
2
2
3
3
4
catalysts to representing the strong and weak acids in catalyzing
the reaction in homogeneous system under the same reaction
condition as that over solid catalysts. The results are summarized
in Table 3. When using H SO as the catalyst, the only reaction
alcohol to form oligomers or polymers. The cinnamyl alcohol
was found to be completely consumed in 10 min., while the
DTBP conversion is only 35% at this stage. This result indicates
that the polymerization of cinnamyl alcohol is still faster than
FriedelꢀCrafts alkylation over 5AlꢀSBAꢀ1ꢀalk catalyst. After the
consumption of cinnamyl alcohol, the DTBP conversion still
increases steadily with reaction time. It is due to the proceeding
of transalkylation between DTBP molecules. As a result, tertꢀ
butylphenol (TBP) and 2,4,6ꢀtriꢀtertꢀbutylphenol (TTBP) are
2
4
5
0
products obtained are the oligomers and polymers formed by
cinnamyl alcohol. It implies that polymerization of cinnamyl
alcohol is favorable to FriedelꢀCrafts reaction over strong acids.
On the other hand, no reaction was observed over acetic acid.
Therefore, the medium acid strength of zeolite and mesoporous
silica is most suitable for catalyzing this reaction.
Table 4 compares several solvents commonly used in the
literature for the catalytic reaction. Among them, isooctane and
dimethylacetamide (DMAc) could reach a reaction temperature of
55 formed as the side products.
The main product in the liquid phase at 10 min is DTBCP
formed through FriedelꢀCrafts alkylation of DTBP with cinnamyl
alcohol. The yield of DTBCP then decreases with reaction time
due to the isomerization of DTBCP to form flavan through
3
68 K, while acetonitrile (ACN) could only reach 355 K due to
its relatively lower boiling point. The highest DTBP conversion 60 Michael reaction. All DTBCP are converted to flavan, and
and flavan yield were observed in isooctane. In contrast, no
catalytic activity was seen using DMAc of a high dielectric
constant of 37.8 as the solvent. It is attributed to that DMAc of
high polarity and also as a weak base (pKa of its conjugate acid
theflavan yield reaches maximum after 5 h of reaction. All the
reaction pathways are illustrated in Scheme 2.
The effect of reaction temperature on the catalytic results over
5AlꢀSBAꢀ1ꢀalk is shown in Table 5. The DTBP conversion
around ꢀ0.5) will hinder the reaction by adsorbing strongly on the 65 increases with reaction temperature. Moreover, the flavan
catalytic active sites. On the other hand, the catalyst gave a lower
DTBP conversion and DTBCP yield using acetonitrile as solvents
than isooctane, but no flavan was formed. It is attributed to that
the isomerization of DTBCP to flavan is an endothermic reaction
selectivity reaches 60% at 368 K, but no flavan product is formed
at low reaction temperature of 333 K. This result is attributed to
that the isomerization of DTBCP to flavan is an endothermic
reaction. It is also noticeable that the total yields of flavan and
and unfavorable at low reaction temperature. Consequently, 70 DTBCP maintain around 37% and do not change significantly
isooctane is the most suitable solvent among the studied solvents,
and it is used hereafter.
Fig. 10 shows the DTBP conversion and product yields over
with the reaction temperature. The increased conversion of DTBP
at higher temperatures is thus contributed by transalkylation
reaction between DTBP molecules. It is to say that
transalkylation reaction is also an endothermic reaction.
In order to minimize the consumption of cinnamyl alcohol in
polymerization reaction, the amount of cinnamyl alcohol in
5
AlꢀSBAꢀ1ꢀalk catalyst as a function of reaction period. In the
first 10 min, two different reactions proceed simultaneously. One
is FriedelꢀCrafts alkylation of DTBP with cinnamyl alcohol to
75
Table 4 Alkylation of DTBP with cinnamyl alcohol with different solvents
Solvent
Rxn temp.(K)
Dielectric
constant
DTBP conv.
(%)
Flavan select.
(%)
Flavan yield
(%)
DTBCP yield
(%)
TBP yield
(%)
Isooctane
DMAc
ACN
368
368
355
1.94
37.8
37.5
53
<1
20
60
0
32
0
5
0
6
0
0
0
0
18
a
Reaction conditions: 0.25 mmol DTBP, 0.25 mmol cinnamyl alcohol, 125 mg catalyst (5AlꢀSBAꢀ1ꢀalk), 12.5 mL solvent, 5 h.
8
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Scheme 2 Reactions proceeded in different periods
Table 5 Alkylation of DTBP with cinnamyl alcohol with different
reaction temperature
Table 6 Alkylation of DTBP with cinnamyl alcohol with different molar
ratios of DTBP/cinnamyl alcohol
Reaction
temp. (K)
DTBP
conv.
%)
Flavan
select.
(%)
Flavan
yield
(%)
DTBCP
yield
(%)
TBP
yield
(%)
DTBP/
cinnamyl
alcohol
DTBP
conv.
(%)
Flavan
select.
(%)
Flavan
yield
(%)
DTBCP
yield
(%)
TBP
yield
(%)
(
3
33
53
68
34
43
53
0
0
35
29
5
0
0
6
0.5
1
39
53
61
13
60
51
5
35
5
0
6
3
3
24
60
10
32
32
31
2
0
13
a
a
5
Reaction conditions: 0.25 mmol DTBP, 0.25 mmol cinnamyl alcohol,
25 mg catalyst (5AlꢀSBAꢀ1ꢀalk), 12.5 mL isooctane, 5 h.
30
Reaction conditions: 0.25 mmol DTBP, 0.125ꢀ0.5 mmol cinnamyl
1
alcohol, 125 mg catalyst (5AlꢀSBAꢀ1ꢀalk), 12.5 mL isooctane, 368 K, 5 h.
reactants was reduced. Table 6 shows that DTBP conversion
indeed increases with increasing the molar ratio of
DTBP/cinnamyl alcohol. However, the flavan yield reaches the
relatively higher surface areas of AlꢀSBAꢀ1ꢀalk materials.
However, the flavan selectivities over AlꢀZSBAꢀ1 materials are
higher than those over AlꢀSBAꢀ1ꢀalk. These results demonstrate
1
1
2
2
0
5
0
5
maximum when the molar ratio of DTBP/cinnamyl alcohol is 1. 35 that the AlꢀZSBAꢀ1 materials can catalyze the Michael reaction
If the DTBP/cinnamyl alcohol ratio increases to 2, products of
transalkylation reaction between DTBP molecules also increase.
Therefore, an equimolar mixture of DTBP and cinnamyl alcohol
is the optimal ratio of the reactants for this reaction.
more efficiently than mesoporous materials of amorphous walls.
Moreover, the flavan selectivities over AlꢀZSBAꢀ1 materials are
similar to that over ZSMꢀ5, except 1AlꢀZSBAꢀ1 which has lowest
acidity. This is an indication that AlꢀZSBAꢀ1 materials own
Table 7 compares the Al contents and catalytic activities of Alꢀ 40 strong acidities from the zeolite seeds incorporated on the pore
ZSBAꢀ1 and AlꢀSBAꢀ1ꢀalk materials with those of ZSMꢀ5 and
Beta zeolites. Elemental analyses by ICPꢀMS show that the
amounts of Al(III) ions incorporated in either AlꢀZSBAꢀ1 or Alꢀ
SBAꢀ1ꢀalk were close to those in the synthesis solutions up to
walls. On the other hand, the TOF, which was calculated as
conversion of DTBP molecule per Al atom per hour, decreases
with the increase in Al loading for both AlꢀSBAꢀ1ꢀalk and Alꢀ
ZSBAꢀ1 materials, indicating that a portion of aluminium may be
Al/Si atomic ratio of 5%. Nevertheless, the Al contents in Alꢀ 45 buried inside the silica framework and not accessible by the
SBAꢀ1ꢀalk materials are slightly higher than those of AlꢀZSBAꢀ1,
except those of lowest Al contents, saying samples 1AlꢀZSBAꢀ1
and 1AlꢀSBAꢀ1ꢀalk.
reactants. Nevertheless, higher TOFs are obtained over the
mesoporous AlꢀSBAꢀ1ꢀalk and AlꢀZSBAꢀ1 catalysts in
comparison to those of microporous zeolites of similar Al
contents, inferring that the large mesopores of cubic Pm3n silica
The DTBP conversions over all the AlꢀSBAꢀ1ꢀalk materials
are higher than those over AlꢀZSBAꢀ1. Since even 1AlꢀSBAꢀ1ꢀ 50 should facilitate the bulky reactant and intermediate molecules to
alk, which has lower Al content than 1AlꢀZSBAꢀ1, has higher
DTBP conversion than 1AlꢀZSBAꢀ1, it is probably because of the
diffuse and access the acidic sites inside the pores. In contrast, the
zeolites give relatively low conversions due to its pore sizes of
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Table 7 Alkylation of DTBP with cinnamyl alcohol over AlꢀSBAꢀ1ꢀalk and AlꢀZSBAꢀ1 with different Alꢀloadings.
a
b
ꢀ1
Sample
Al/Si (%)
DTBP conv.
%)
Flavan
select. (%)
Flavan yield
(%)
DTBCP
yield (%)
TBP yield
(%)
TOF (h )
(
1
3
5
5
7
1
3
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
AlꢀZSBAꢀ1
1.1
2.6
4.8
4.8
5.7
1.0
3.4
5.5
5.4
5.9
5.0
2
30
45
50
48
52
37
47
53
52
58
28
25
0
0
29
5
0
3
3
3
4
0
4
6
6
6
3
0
71
76
75
75
0
32
38
36
39
0
0.30
0.19
0.18
0.16
0
4
c
5
4
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
36
14
5
49
60
60
60
72
48
23
32
31
35
20
12
0.16
0.14
0.14
0.14
0.10
5
5
7
5
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
AlꢀSBAꢀ1ꢀalk
c
6
5
AlꢀZSMꢀ5
2
d
Beta
14
0
0.14
a
a
b
Reaction conditions: 0.25 mmol DTBP, 0.25 mmol cinnamyl alcohol, 125 mg catalyst, 12.5 mL isooctane, 368 K, 5 h; Measured by ICPꢀMS; Based
c
d
on flavan yield.; Regenerated catalyst for second run; CP814E, Zeolyst International
smaller than 1 nm, which obstacle the reactants from diffusing
were efficient catalysts for the alkylation of DTBP by cinnamyl
5
0
5
into the pores and accessing the acidic sites. Among the catalysts 35 alcohol to yield flavan, and they showed higher catalytic
studied, 5AlꢀZSBAꢀ1 and 7AlꢀZSBAꢀ1 catalysts give the highest
flavan yield around 38ꢀ39%, relatively high DTBP conversion of
over 50%, and selectivity around 75% in the alkylation of DTBP
with cinnamyl alcohol.
activities than microporous Beta and ZSMꢀ5 zeolites due to the
facilitation of the diffusion of bulky reactant molecules in the
mesopores. The highest activity was obtained over 5AlꢀZSBAꢀ1
and 7AlꢀZSBAꢀ1, assembled from zeolite seeds, which gave over
1
After the catalytic reactions, the 5AlꢀZSBAꢀ1 and 5AlꢀSBAꢀ1ꢀ 40 50% conversion and 38ꢀ39% flavan yield. The results
alk catalysts were regenerated by calcination at 823 K for 4 h.
The regenerated catalysts were used under the same reaction
conditions as that of the fresh catalysts, and the results are also
listed in Table 7. The catalytic activities are well retained over
both regenerated catalysts in the second run. Besides, no
aluminium leaching occurred during the catalytic reaction based
on Al/Si analysis by ICPꢀMS technique on the regenerated
catalysts.
demonstrate that AlꢀZSBAꢀ1 materials combine the advantages
of strong acidity from zeolites and good diffusivity from
mesoporous molecular sieves.
1
Acknowledgment
45
Financial supports from the Ministry of Science and
Technology (NSC 101ꢀ2113ꢀMꢀ002ꢀ012ꢀMY3) and Ministry of
Education,
Taiwan
are
gratefully
acknowledged.
Acknowledgments are also extended to Y.ꢀY. Yang, C.ꢀY. Lin,
C.ꢀY. Chien, and Y.ꢀC. Chao of Ministry of Science and
5
. Conclusions
20
25
30
Aluminium incorporated cubic mesoporous silica of Pm3n 50 Technology for SEM, TEM, and ICPꢀMS experiments.
phase was successfully synthesized using ZSMꢀ5 seeds as the
silica source and CTEABr as the template at pH around 9. The
XRD patterns showed that wellꢀordered mesopores were retained
with the Al/Si molar ratio up to 5% in the synthesis solution.
Elemental analysis by ICPꢀMS showed that the amounts of
Al(III) ions incorporated in the solids were close to those in the
synthesis solutions up to Al/Si atomic ratio of 5%. From NH3ꢀ
TPD experiments, the acidic strength of AlꢀZSBAꢀ1 solids was
higher than that of AlꢀSBAꢀ1ꢀalk samples, but lower than that of
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Cubic Pm3n mesoporous aluminosilicate assembled from zeolite seeds as strong
acidic catalysts
Tsung-Han Lin, Chia-Han Chen, Chi-Shuang Chang, Ming-Chang Liu, Shing-Jong
Huang, and Soofin Cheng*
Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
Graphical Abstract
Cubic Pm3n mesoporous aluminosilicate with 3D interconnected pore structure,
assembled with Al-incorporated ZSM-5 seeds at pH 9 using CTEABr as
pore-directing agent, was an efficient catalyst in alkylation of 2,4-di-tert-butylphenol
with cinnamyl alcohol to form flavan.