Highly Selective Oxidation of Styrene Over FeCl3-Imidazolium Ionic Liquid Grafted SBA-15
90
2.3 Catalytic Test
80
Three mL of styrene and 0.2 g of FeSIL was added into a
70
three-necked fask ftted with magnetic stirrer and a con-
denser. The fask was heated in water bath to 80 °C under
Conversion
Selectivity to BzH
Selectivity to BzA
60
stirring, and then 8.1 mL of 30% H2O2 was slowly dripped
50
into the reaction mixture and the resulting mixture had been
reacted at 80 °C for 5 h. After the reaction completed, the
40
mixture solution was fltered to remove the catalyst FeSIL.
30
The reaction mixture was extracted by 5 mL of toluene.
The extracted organic phase was analyzed by GC (Agilent
20
GC7820) and GC–MS (Agilent GC7890-MS5975C) using
10
HP-5 column (30 m×0.32 mm×0.25 μm) and FID detector
60
70
80
90
100
(GC).
Reaction temperature (oC)
2.4 Adsorption of Styrene and H2O2
Fig. 1 Efect of reaction temperature on the oxidation. Reaction con-
dition: reaction time 5 h, catalyst 0.2 g, molar ratio of H2O2 to styrene
4:1
In situ DRIFTS spectra were recorded by an FT-IR spec-
trometer (Brucker TENSOR II) equipped with a difuse
refectance optics accessory (Harrick Scientifc products
Inc.). The FeSIL sample was heated to 400 °C for 2 h in
vacuo before measurement. The styrene and/or H2O2 spe-
cies were introduced onto the catalyst surface by high-pure
N2 gas (purity 99.99%) for 2 h, followed by evacuating from
the system to about 9.8×10−4 Pa. After that, the DRIFTS
spectra were measured at 80 °C half an hour under vacuo
condition.
be homolytic decomposition into ·OH radicals or heterolytic
dissociation into ·OOH radicals by the interaction of vari-
ous metal compound catalysts [18]. In any case, the radicals
played a key role for oxidizing the organic substrates. Mean-
while, some transition metal compound catalysts, especially
iron compounds could efectively catalyze rapid decomposi-
tion of H2O2 into O2 and H2O, especially at higher reaction
temperature [13]. It was the rapid decomposition of H2O2
perature. Besides, higher selectivity to benzaldehyde (BzH)
was observed in this progress and only one byproduct was
benzoic acid (BzA), which was in agreement with our pre-
vious reported work using Fe3O4 as catalyst [13]. The high
selectivity for Fe containing catalysts was ascribed to Fe
active species limiting BzH further oxidation to phenol [12].
Certainly, the temperature raising was advantageous to the
selectivity to BzA.
3 Results and Discussion
3.1 Catalytic Activity of FeSIL
T h e c a t a ly s t F e S I L wa s p r e p a r e d by
FeCl3-1-methyl-3-(chloropro pyl-triethoxysilane) imida-
zolium ionic liquid grafted on SBA-15. The characteriza-
tion results in previous report [17] indicated that Fe load-
(0.71 mmol/g) by ICP-MS with the nonuniform distribution
of FeCl3 on FeSIL surface. This prepared FeSIL was used
for free-solvent oxidation of styrene with H2O2 as oxidant.
Its catalytic performance was reported as the following.
The infuence of reaction temperature on the oxidation
of styrene with H2O2 oxidant was conducted and the results
were depicted in Fig. 1. It was clear that the conversion was
gradually increased as the reaction temperature going up.
The increment extent of the conversion with the temperature
was so smooth that it approached to 37.5% at 60 °C and
45.0% at 100 °C, indicating that the efect of the reaction
temperature on the catalytic process was slight. This phe-
nomenon was likely related to rapid decomposition of H2O2
over Fe-containing catalyst. According to the previous report
[15], oxidizing action of H2O2 for organic substrates could
able. As shown in Fig. 2, the sharp increase in the conver-
sion from 7.0 to 43.1% was observed as the catalyst dose
increasing from 0.1 to 0.2 g, followed by smooth increment
of the conversion from 43.1 to 47.5% when continuously
increasing the catalyst amount from 0.2 to 0.3 g. Moreover,
the selectivity to BzH was decreased from 95.7 to 68.9%
as the catalyst dose raising from 0.1 g to 0.3 g, which was
attributed to BzH further oxidized into BzA. The increase
in dose of the catalyst used in this system would lead to
increase in amount of active sites on the catalyst surface.
These excess active sites promoted the oxidation of styrene
into BzH. Certainly, they could enhance BzH further oxi-
dized into benzoic acid (BzA), for example, the selectivity
to BzA was raised from 4.3 to 31.1% when the dose of the
catalyst raising from 0.1 to 0.3 g, which necessarily led to
1 3