Dialkylation of Naphthalene with Isopropanol
143
final catalysts are designated as xH PO /AlMCM-41(20), x
3
mixture was isolated from the catalyst by centrifugation.
Product analysis was done on a Shimadzu model 14A gas
chromatograph, equipped with a wide bone OV-17 (60 m)
capillary column and a FID detector. The product analysis by
GC and GC–MS revealed the formation of monoalkylated
products 1-isopropylnapthalene (1-IPN) and 2-isopropyl-
naphthalene (2-IPN), dialkylated products 2,6-diisopro-
plynapthalene (2,6-DIPN) and 2,7-diisopropylnaphthalene
(2,7-DIPN); other DIPN isomers and other products were
tri- and tetraisopropylnaphthalenes, alkylnaphthalenes with
at least one substituent other than the isopropyl group, pro-
pylene oligomers, etc.
4
being the weight percentage of H PO used for impregna-
3
4
tion, and AlMCM-41(20) indicating that the sample with
SiO /Al O = 20 was used as support.
2 3
2
2
.4 Instrumental
FT-IR spectra of the catalyst were recorded on a Brucker
IFS-66 single channel Fourier transform spectrometer with
the KBr pellet method. Textural analyses were determined
from nitrogen adsorption–desorption isotherms, obtained at
7
7 K using a Micromeritics Gemini apparatus. The samples
were degassed for 2 h at 283 K. Specific surface area was
obtained by the BET method, microporous surface area by
means of the t method, and total pore volume from the
adsorption at P/P° 0.95. X-ray diffraction (XRD) patterns
were recorded over non-oriented powder samples between 1
and 70° (2h) at a scanning speed of 2°/min by using a
Siemens D-500 diffractometer, at 40 kV and 30 mA, and
employing filtered Cu Ka radiation. The equipment was
connected to a DACO-MP microprocessor and used Dif-
fract-AT software. The acidity of the samples was evaluated
from the Fourier transform IR spectra of adsorbed pyridine,
measured using a JASCO FT/IR (680 plus) spectrometer.
Approximately 40–50 mg of material that had been previ-
ously calcined in air for 4 h at 773 K were pressed (for
3 Results and Discussion
3.1 Characterization of the Catalysts
Detailed physicochemical characterization of the catalysts is
found in our earlier reports [21, 22]. However, salient
inferences obtained from the characterization results are
precisely outlined here. The XRD data indicate that
AlMCM-41 samples exhibit the ordered hexagonal structure
characterized by an intense reflection peak at a d spacing of
3.8 nm [22]. The intensity of this low angle reflection peak
did not change as the H PO loading increased. The specific
3
4
2
-2
3
min at 15 tonnes/cm pressure under approximately 10
surface area of AlMCM41 samples as calculated by the BET
2
method ranges between 1038 and 668 m /g. H PO loading
Torr vacuum) into a self supporting wafer of 15 mm
diameter. The pretreated wafer was equilibrated with
3
4
induces a drastic decrease in the specific surface area, to
2
values ranging between 40 and 90 m /g, mostly due to
2
6 mmHg of pyridine at 473 K for 1 h and evacuated at 473
and 573 K for 1 h in dynamic vacuum. After each treat-
ment, an IR spectrum was recorded at room temperature.
High resolution MAS-NMR experiments were per-
formed at room temperature in a Bruker AVANCE-400
external surface area, as micropore surface areas were in the
2
range 4–6 m /g. However, this change did not produce any
structural distortions of the AlMCM-41. Consequently, it
seemed reasonable to propose that loading of H PO on
3
4
2
9
spectrometer, operating at 79.49 MHz ( Si signal),
AlMCM-41 did not change the regular arrangement of
uniform channels of the support [23]. It might be interesting
to mention that by loading of approximately 30 wt% of
phosphotungstic acid on AlMCM-41, the specific surface
area of the support decreased by less than 20% [24], but
loading the same support by approximately the same weight
percent of H PO , the surface area decreased to a large
2
04.26 MHz ( Al signal), 161.98 MHz ( P signal),
7
31
1
1
2
05.84 MHz ( Na signal) and 400.13 MHz ( H signal).
3
1
2
9
31
1
Si, P, H (I = 1/2) MAS-NMR spectra were recorded
after p/2 pulse irradiation (4 ls), using a 500 kHz filter.
2
.5 Reaction Procedure
3
4
extent. Probably the crystalline structure of the phospho-
tungstic acid (Keggin units) and the amorphous structure of
Isopropylation reactions were carried out under batch
reaction conditions using an autoclave in the temperature
region of 473–623 K, at autogenous pressure conditions.
The feed was naphthalene:2-propanol:n-hexane molar ratio
3
1
the phosphoric acid could explain this difference. The
MAS NMR spectra of 30 wt% H PO /AlMCM-41(200)
P
3
4
exhibited two peaks at -10 and 0 ppm which may corre-
1
:2:10, and to this mixture 0.5 g of a freshly activated
spond to P atom in pyrophosphoric acid or terminal groups
3
-
catalyst was added. Activation of the catalyst was usually
and monomeric PO4 groups, respectively. From analysis
of Si, Al and P NMR signals, the formation of Si–O–Al–O–P
bridges seemed to be favoured at the surface of AlMCM-41
catalysts [22]. The FT-IR spectrum for the 30 wt% H PO /
done by calcining it at 573 K in N for 2 h. The autoclave
2
temperature was then slowly raised to the required tem-
perature and maintained at the desired temperature during
the reaction period of 2.5 h. After the reaction, the auto-
clave was cooled to room temperature. The reaction
3
4
AlMCM-41(70) sample after adsorption of pyridine shows
-
1
bands of pyridine adducts in the region 1650–1450 cm
.
123