Under microwave heating, 84.0% fructose conversion with ca.
63.0% HMF yield was observed after 30 min of reaction time
over a sulfated zirconia (SO42-/ZrO2, 20 mg) using a mixture
acid (SiO2–SO3H) modified silica gel for fructose dehydration.
No significant effect of support particle size was observed.
The catalyst was efficiently and easily recycled over seven
times without significant loss in its activity and selectivity in
dehydration of fructose to HMF.
◦
of acetone-DMSO (70 : 30 w/w) as a solvent at 160.0 C.32
In this context, the present results are promising for fructose
conversion (99.9%) at a lower reaction temperature (130.0 ◦C).
Furthermore, it is reported that sulfonylchloride (SiO2-SO2Cl)
and sulfuric acid (SiO2-SO3H) modified silica gel catalysts gave
high conversions of fructose (92.0 and 95.0%, respectively) and
moderate yields of HMF (60.0 and 63.0%, respectively) under
microwave irradiation (200 W),4 which are almost identical with
the results obtained over SILnPs. However, the activities of both
catalysts decreased to almost zero after the three recyclability
tests, while the present results show a catalyst with high efficiency
and that can be recycled over seven times without significant
loss in its activity and selectivity. Therefore, our experiments
in conjunction with results from the literature indicate that the
silica supported ionic liquid nanoparticles catalysts synthesized
in this study are more promising catalysts than H-form of ZSM-
5 and mordenite zeolites as well as Amberlyst-15, commercially
available Dowex 50wx8–100 ion exchange resin, sulfonylchloride
(SiO2-SO2Cl) and sulfuric acid (SiO2-SO3H) modified silica gel.
Higher % HMF yields (80.0 to 90.0%) were reported using
some homogeneous ionic liquid catalytic systems,2,19 but they
use very large amounts of ionic liquid for the dehydration of
fructose to HMF and required vigorous post reaction work-
up to recover the costly IL from the reaction mixture, while
the SILnPs catalyst developed in the present study is easy to
separate from reaction mixture, easily and efficiently recycled
and contains a small amount of ionic liquid on the surface
of silica nanoparticles, which will also be beneficial from the
economic and environmental point of view.
Acknowledgements
Authors are grateful to Prof. Dr F. Domingues for access to
HPLC instrument and helpful discussion in product analysis.
K.B.S. is thankful to FCT-Portugal for financial support in
terms of Post-Doctoral fellowship (SFRH/BPD/44803/2008).
We would like to thank Dr A. V. Gira˜o for her support in TEM
analysis and Maria Jorge Pratas for help with experimental
design.
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Silica supported ionic liquid nanoparticle catalysts having varied
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348 | Green Chem., 2011, 13, 340–349
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