Catalysis Science & Technology
Paper
formation of the benzaldehyde by-product generated through
the oxidative cleavage pathway, which offers much improved
results in terms of selectivity and yield (Table 2, entry 3). For
the epoxidation of stilbene, trans-stilbene transformed to its
corresponding epoxide much faster than cis-stilbene due to
the steric effect (Table 2, entries 4 and 5). The high conversion
and selectivity of the corresponding epoxides indicate that
the catalytic activity enhancement was from the composition
of Fe3O4 nanoparticles and the uniform silica shell in the
Fe3O4–CuO@meso-SiO2 composite, and the synergistic effects
among the three components (Fe3O4, CuO and meso-SiO2)
made the as-prepared Fe3O4–CuO@meso-SiO2 composite an
efficient and stable catalyst for the olefin epoxidation reactions.
As a result, our catalytic system performed much more
efficiently than any other system reported in the literature
employing t-BuOOH as the oxidant.34,37,46
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A novel magnetically recyclable and highly efficient core–shell
Fe3O4–CuO@meso-SiO2 catalyst was designed and synthe-
sized for styrene epoxidation. The components and the struc-
ture of the composite microspheres provided the hybrid
catalyst with improved catalytic properties and attractive fea-
tures. Fe3O4 microspheres could be used not only as a func-
tional support with good dispersion and magnetic separation
but also as a co-catalyst via offering electrons to CuO, and
subsequently promoting its catalytic activity. The mesoporous
SiO2 shell with perpendicularly aligned pore channels offered
a physical shield to prevent the aggregation and outflow of
the CuO and Fe3O4 nanoparticles, and it provided mass
transfer channels for the catalytic reaction as well. Therefore
the multifunctional catalyst with well-designed structures
provides a highly efficient, well-dispersed, easily separated,
and excellently circulated catalytic system for styrene epoxida-
tion. This strategy may be extended to the design of
multifunctional nanohybrids that contain catalytically active
metals/metal oxides other than CuO.
Acknowledgements
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We would like to thank the PetroChina Innovation Foundation
(no. 2012D-5006-0504) and the National High Technology
Research and the Development Program of China (863 Program)
(no. 2013AA031702) for their support.
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