Preparation of SiO
2
–Al
O
2 3
and Its Supported Co
3
O
4
Catalysts
151
the chlorinated compounds are environmentally unfriendly
and photonitrosation of cyclohexane is a process of high
energy consumption. Moreover, all of the above methods
still underwent the multi-step conversion from elementary
material.
of helium. After cooling to 120 ꢁC, a mixture of 10% NH3-
90% He was introduced until the acid sites of the catalyst
were saturated with NH . Finally, desorption was carried
3
out from 10 ꢁC to 1000 ꢁC at a heating rate of
-
1
10 ꢁC min
.
Although from both synthetic and industrial points of
view, considerable attentions have been focused on the
development of a new system for the production of
e-caprolactam to overcome above-mentioned drawbacks.
Searching for a catalyst which has high conversion to
cyclohexane and high selectivity to e-caprolactam is the
key to the liquid phase nitrosation reaction. In this paper,
we found that these SiO –Al O and Co O /SiO –Al O
2 3
Fourier transform infrared (FT-IR) spectra of pyridine
temperature-programmed desorption was carried out on a
FT-IR adsorption system.
2.3 Typical Experimental Procedure
The catalytic reaction was carried out in a glass reactor
under atmospheric pressure. A mixture of cyclohexane,
nitrosyl sulfuric acid and catalyst was stirred at 81 ꢁC for
24 h in the presence of fuming sulfuric acid. After cooling
to 20 ꢁC, the inorganic phase was dissolved by deionized
water in ice-water bath and successively treated with
Ba(OH) to neutralize H SO . The pH value of solution
2
2
3
3
4
2
catalysts could efficiently catalyze the reaction of cyclo-
hexane with nitrosyl sulfuric acid to afford e-caprolactam
directly in the presence of fuming sulphuric acid.
2
2
4
2
Experimental
was adjusted to 7–8 [15–17]. The final product was ana-
lyzed using a LC-20AT and SPD-20A liquid chromato-
graph with 40:60 of CH OH:H O as eluant and detected at
2
.1 Catalyst Preparation
3
2
wavelength of 210 nm.
Amorphous SiO –Al O was prepared by sol–gel method.
2 2 3
Cogelling aluminum sec-butoxide dissolved in ethanol was
added to a solution of tetraethyl orthosilicate at 85 ꢁC with
vigorous stirring. The molar ratio of Si/Al was kept at 2.5.
Hydrolysis was performed by addition of a small amount of
water to the mixture. The solution became a rigid and
transparent gel immediately after addition of water. The gel
was recovered by filtration and dried in an oven at 120 ꢁC
overnight.
3 Results and Discussion
3.1 Physicochemical Properties of the Catalysts
Figure 1a shows the nitrogen adsorption–desorption curves
for SiO
Al exhibits a much higher nitrogen adsorption capacity
than SiO –Al . By contrast, SiO –Al shows an
–Al O and Co O /SiO –Al O . Co O /SiO –
2
2 3 3 4 2 2 3 3 4 2
Co O /SiO –Al O was prepared by impregnating the
3
O
2 3
4
2
2 3
prepared SiO –Al O in cobalt acetate solution for 1 h at
2 2 3
2
2
O
3
2
O
2 3
2
3
5 ꢁC (the loading amount of cobalt acetate were about
0 wt%), and then the resulted mixture was dried at 100 ꢁC
adsorption isotherm of type IV according to the IUPAC
classification and has a H4 hysteresis loop that is repre-
sentative of mesopores. The volume adsorbed for bare
for 10 h. Finally, it was heated from 20 ꢁC to corre-
sponding calcination temperature at a rate of 2 ꢁC min in
dry air and kept at this temperature for 5 h.
-
1
SiO –Al O steeply increases at a relative pressure (p/p )
2 2 3 0
of approximately 0.45, representing capillary condensation
of nitrogen within the uniform mesoporous structure.
2
.2 Catalyst Characterization
Co O /SiO –Al O shows an adsorption isotherm of type
3 4 2 2 3
IV and has a H3 hysteresis loop that is representative
capillary condensation of nitrogen within the non-uniform
mesoporous structure.
X-ray diffraction (XRD) data were collected using a Japan
?
Rigaku D/Max 2550 VB 18 kW X-ray diffractometer
under the following conditions: 40 kV, 30 mA, Cu Ka
radiation, with a scanning rate of 1ꢁ min in the range of
Figure 1b shows the pore size distribution calculated
-
1
from desorption isotherms of SiO
SiO –Al . A very broad pore size distribution is
observed in Co /SiO –Al , and its mean pore size
–Al O and Co O /
2 2 3 3 4
2
h = 5–85ꢁ.
Specific surface area, pore volume and pore size distri-
2
O
2 3
O
O
2 3
3
4
2
bution of the catalysts were measured using a NOVA-
calculated from the desorption branch by the BJH model is
3.85 nm. A large volume of irregular and non-uniform
2
200e automated gas sorption system.
Temperature-programmed desorption (TPD) of NH3
macropores are formed when Co
3
O
4
/SiO
2
–Al
2
O
3
is calci-
–Al O
2 3
was carried out on a CHEMBET-3000 instrument. The
sample (100 mg) was pretreated at a heating rate of
nated at 400 ꢁC. However, the mesoporous SiO
has a pore size distribution centered at 3.82 nm, and pos-
sesses relatively more uniform mesopores.
2
-
1
1
0 ꢁC min to 400 ꢁC and was held for 1 h under a flow
123