Catalysis Science & Technology
Paper
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Fig. 8 Proposed mechanism of the epoxidation of alkene with
DIM–CIM–PW in liquid–liquid–solid triphase catalytic system.
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the W sites of the [PO4(WO3)4]3−, leading to the generation of
the peroxo–tungstate complex [PO4{WO(O2)2}4]3− that is sup-
posed to be the active site for epoxidation. Then, the peroxo–
tungstate complex is resumed to the original state of WO
by inserting its oxygen into the alkene reactant in oil phase
to produce an epoxide product. In this liquid–liquid–solid
triphase system, the hydrophilic –COOH groups and hydro-
phobic –C12H25 chains on the surface of the catalyst act as
“trapping agent” for H2O2 and alkene molecules through
hydrophilic–hydrophilic or hydrophobic–hydrophobic interac-
tions, respectively, and thus promote the catalytic activity of
DIM–CIM–PW. Though the above proposal is able to reason-
ably explain our reaction results, it is presently tentative and
more direct evidence is needed to make it clearer.
4. Conclusion
In summary, we have synthesized a novel amphiphilic POM-
paired copolymer catalyst DIM–CIM–PW for the liquid–
liquid–solid triphase epoxidation of alkenes with H2O2. The
new catalyst exhibits high catalytic activity and selectivity,
plus the advantages of convenient recovery and steady reus-
ability. The peroxo–tungstate species in PW anions act as the
active centres for epoxidation reactions, while the amphi-
philic catalyst structure as a “trapping agent” for both the
hydrophobic alkene substrates and the hydrophilic H2O2
molecules, and thus the catalytic activity is largely promoted.
The design strategy for the present catalyst might be a significant
step towards the design of heterogeneous catalysts with inte-
grated and enhanced properties for more catalytic processes.
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Acknowledgements
The authors thank the National Natural Science Foundation
of China (no. 21206052 and 21136005), the Opening Founda-
tion of the State Key Laboratory of Materials-Oriented Chemi-
cal Engineering (no. KL13-09), and MOE & SAFEA for the 111
Project (no. B13025).
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