106
N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
Al-MCM-41 with different Si/Al ratios was prepared by
the addition of aluminum sulfate to the Si-MCM-41 gel
to get the molar composition 1 SiO2:0.33 TMAOH:0.55
CTMABr:60 H2O:x Al2O3. Al-MCM-41 with Si/Al ra-
tios of 20, 30, 50, and 100 was prepared by the variation
of x in the gel composition from 0.005 to 0.025 moles.
In all cases, the gel was aged at room temperature for 5 h
with stirring and heated in an autoclave at 383 K for 5 days
under autogenous pressure. The solid product was filtered,
washed, dried, and calcined at 823 K for 8 h to get the final
product. The product was characterized by X-ray diffraction
(XRD) (Rigaku D/MINI-Flex X-ray diffractometer, 40 kV,
20 mA, Ni filtered Cu-Kα), scanning electron microscopy
(JEOL JSM 5200), nuclear magnetic resonance (Brucker
MSL-300), and N2 adsorption. The samples were charac-
terized for their acidity by the temperature-programmed
desorption (TPD) of NH3 (Micromeritics, Autochem Z910).
The standard procedure for TPD measurements involved the
activation of the sample in flowing He at 873 K (3 h), cool-
ing to 298 K, and adsorbing NH3 from a stream of He–NH3
(10%), removing the physically adsorbed NH3 by desorb-
ing in He at 373 K for 1 h, and finally carrying out the TPD
experiment by raising the temperature of the catalyst in a
programmed manner (10 K min−1). The TPD curves were
deconvoluted into two peaks, and the areas under the peaks
were converted into meq NH3 per gram of catalyst based
on injection of known volumes of the He–NH3 mixture un-
der similar conditions. All of the samples were calcined at
823 K for 8 h prior to use in catalytic experiments.
3. Results and discussion
3.1. Physicochemical characterization
3.1.1. X-ray diffraction
The XRD patterns of calcined Si- and Al-MCM-41
are shown in Fig. 1. The physicochemical properties of
MCM-41 with different Si/Al ratios are presented in Ta-
ble 1. The XRD patterns are similar to those reported for
MCM-41 materials [9] and show low angle (110) and (200)
peaks for all of the samples, which is characteristic of long-
range order of crystallinity of the materials. Kresge et al.
[9] indexed these peaks for a hexagonal unit cell, the pa-
rameter for which was calculated with the equation a0 =
√
2d100/ 3 (Table 1). The table shows that the d100 reflection
of Al-MCM-41 is shifted to higher values compared with
its siliceous analogue. This is probably due to the frame-
work substitution of Al in the MCM-41 structure [11]. The
change in the T–O–T bond angle with Al substitution prob-
ably causes long-range disorder in the system and explains
the slightly broader XRD peaks in Al-containing samples
(Fig. 1).
3.1.2. Nuclear magnetic resonance
The 27Al magic-angle spinning nuclear magnetic reso-
nance (MAS NMR) spectrum of calcined Al-MCM-41 with
APE (purity 99%) required for the reaction was synthe-
sized by the reaction of allyl bromide and phenol in ethanol
and purified by standard methods. The reactions were car-
ried out in batch mode in a two-necked round-bottomed
flask (capacity 25 ml) in a nitrogen atmosphere, with the use
of 0.67 g of APE in 10 g of solvent (tetrachloroethylene,
Loba Chemie) with 0.075 g of freshly calcined catalyst.
Aliquots of the reaction mixture were collected at different
time intervals and analyzed by gas chromatography (Var-
ian gas chromatograph; column: CP Sil 5CB, 30 m; i.d.
0.05 mm; FID detector). The products were identified by
gas chromatography-mass spectroscopy (GC-MS) and gas
chromatography-infrared spectroscopy (GC-IR).
Fig. 1. XRD patterns of calcined Si-MCM-41 and Al-MCM-41 with differ-
ent Si/Al ratios.
Table 1
Physicochemical properties of Al-MCM-41 samples
a
b
b
Sample
Si/Al ratio
(XRF)
d
spacing
Unit cell a
parameter (Å)
Surface area
(m /g)
Pore diameter
(Å)
100
0
a
2
(Å)
Si-MCM-41
–
36.78
38.05
39.76
40.49
43.69
40.45
36.92
44.31
44.38
47.19
1094
1219
997
28.58
27.23
30.02
31.44
33.67
Al-MCM-41 (100)
Al-MCM-41 (50)
Al-MCM-41 (30)
Al-MCM-41 (20)
110.1
53.2
31.0
20.8
873
785
a
As-synthesized sample.
Calcined sample.
b