catalyst can be conveniently recycled from the reaction system
by using a magnet and no deactivation has been observed after
at least five cycles of reaction. The overall synthetic process for
the nanocomposite is simple and rapid, and it is envisioned
that this synthetic approach may be readily extended to MRCs
that contain catalytically active metals other than Ag.
This work was financially supported by the National
Natural Science Foundation of China (20731003) and the
National Basic Research Program of China (2007CB613303).
The authors thank Xuejing Cao for assistance with the SEM
measurements.
Notes and references
Fig. 4 Yield of styrene epoxide versus reaction time catalyzed by
Ag–Fe nanocomposite. The photographs demonstrate the separa-
3
O
4
z The Brunauer–Emmett–Teller (BET) surface area of the Ag–Fe
nanocomposite material measured using N adsorption and deso-
. X-ray photoelectron spectroscopy
XPS) analysis of Ag3d spectra further confirms that the Ag species
3 4
O
tion of the catalyst by a magnet.
2
2
ꢁ1
g
rption at 77 K is 35.1 m
(
on the surface of the nanocomposite is metallic silver (ESIw).
3 4
Table 1 Catalytic performance of Ag–Fe O nanocomposite, Ag and
a
a simple mixture of Ag and Fe
Catalyst (%) SO (%)
100
3 4
O for the epoxidation of styrene
1. L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133.
2
. L. N. Lewis, Chem. Rev., 1993, 93, 2693; R. M. Crooks, M. Zhao,
L. Sun, V. Chechik and L. K. Yeung, Acc. Chem. Res., 2001, 34,
C
S
Y
Y
B
(%)
Y
O
(%)
TOF
1
81.
Ag–Fe
Ag
3
O
4
84.0
64.0
42.8
11.1
9.8
12.6
4.9
26.2
44.6
1473.3
539.8
761.6
3
. M. Shokouhimehr, Y. Piao, J. Kim, Y. Jang and T. Hyeon,
Angew. Chem., Int. Ed., 2007, 46, 7039; T.-J. Yoon, W. Lee,
Y.-S. Oh and J.-K. Lee, New J. Chem., 2003, 27, 227;
S. C. Tsang, V. Caps, I. Paraskevas, D. Chadwick and
D. Thompsett, Angew. Chem., Int. Ed., 2004, 43, 5645;
P. D. Stevens, J. Fan, H. M. R. Gardimalla, M. Yen and
Y. Gao, Org. Lett., 2005, 7, 2085; D. K. Yi, S. S. Lee and
J. Y. Ying, Chem. Mater., 2006, 18, 2459; R. Abu-Reziq,
H. Alper, D. Wang and M. L. Post, J. Am. Chem. Soc., 2006,
128, 5279; A. Hu, G. T. Yee and W. Lin, J. Am. Chem. Soc., 2005,
99.0
95.9
Mixture
a
C
S
= conversion of styrene, YSO = yield of styrene oxide,
= yield of benzaldehyde, Y = yield of other by-products;
Y
B
O
TOF = mmol of styrene oxide formed per mol of Ag per hour;
reaction time: 13 h.
mixture of Ag and Fe O particles (Fig. S7w) with a composi-
3
4
1
27, 12486.
. L. Espinal, S. L. Suib and J. F. Rusling, J. Am. Chem. Soc., 2004,
26, 7676; D. S. Pinnaduwage, L. Zhou, W. Gao and
tion identical to that of the Ag–Fe O nanocomposite. The
3
4
4
TOF value of the mixture was found to be only about one half
of that of the Ag–Fe nanocomposite material (Table 1).
These observations indicate that the composition of Ag and
Fe nanoparticles in the Ag–Fe nanocomposite en-
1
3
O
4
C. M. Friend, J. Am. Chem. Soc., 2007, 129, 1872;
V. R. Choudhary, R. Jha and P. Jana, Green Chem., 2006, 8, 689.
5
. R. J. Chimenta
Y. Cesteros and P. Salagre, J. Mol. Catal. A: Chem., 2006, 258,
46; F. J. Williams, D. P. C. Bird, A. Palermo, A. K. Santra and
R. M. Lambert, J. Am. Chem. Soc., 2004, 126, 8509;
R. J. Chimentao, I. Kirm, F. Medina, X. Rodrıguez,
˜
o, F. Medina, J. L. G. Fierro, J. E. Sueiras,
3
O
4
3 4
O
hances the catalytic activity of Ag. It has been reported that
oxygen vacancies on the surface of iron oxide assist in
3
1
2
´
˜
supplying reactive oxygen. Similarly, in our catalytic system,
the Fe nanoparticles may assist in providing additional
Y. Cesteros, P. Salagre, J. E. Sueiras and J. L. G. Fierro, Appl.
Surf. Sci., 2005, 252, 793.
3
O
4
reactive oxygen besides that generated by the Ag particles.
This additional reactive oxygen transfers to the surface of the
proximate Ag particle in the composite easily, and hence
facilitates the epoxidation of styrene molecules adsorbed on
the Ag surface. In addition, it is worthwhile to point out that
6
7
. B. Wiley, Y. Sun, B. Mayers and Y. Xia, Chem.–Eur. J., 2005, 11,
454; Y. Sun and Y. Xia, Science, 2002, 298, 2176.
. X.-H. Li, D.-H. Zhang and J.-S. Chen, J. Am. Chem. Soc., 2006,
128, 8382; H. Deng, X. Li, Q. Peng, X. Wang, J. Chen and Y. Li,
Angew. Chem., Int. Ed., 2005, 44, 2782.
8. X. Lu, L. Au, J. McLellan, Z.-Y. Li, M. Marquez and Y. Xia,
Nano Lett., 2007, 7, 1764.
the Ag–Fe
remain almost intact after five cycles of catalytic reaction
Fig. S7w). The robustness of the nanocomposite lays the
3 4
O nanocomposite particles are rather robust and
9
. Y. Zhu, W. Zhao, H. Chen and J. Shi, J. Phys. Chem. C, 2007,
11, 5281.
1
(
1
0. D. E. Zhang, X. J. Zhang, X. M. Ni, J. M. Song and H. G. Zheng,
Cryst. Growth Des., 2007, 7, 2117; B. H. Sohn, R. E. Cohen and
G. C. Papaefthyrniou, J. Magn. Magn. Mater., 1998, 182, 216;
S. Santra, R. Tapec, N. Theodoropoulou, J. Dobson, A. Hebard
and W. Tan, Langmuir, 2001, 17, 2900.
foundation for repeated use of the catalyst.
In summary, a one-pot synthetic route based on PVP-
complexing has been reported for the preparation of a unique
Ag–Fe
3
O
4
nanocomposite MRC. This MRC is highly efficient
11. R. Xu, D. Wang, J. Zhang and Y. Li, Chem.–Asian J., 2006, 1,
888.
for the epoxidation of styrene to form styrene epoxide, and the
Fe O nanoparticles in the composite not only function as a
1
2. M. M. Schubert, S. Hackenberg, A. C. v. Veen, M. Muhler,
V. Plzak and R. J. Behm, J. Catal., 2001, 197, 113; H. Liu,
A. I. Kozlov, A. P. Kozlova, T. Shido and Y. Iwasawa, Phys.
Chem. Chem. Phys., 1999, 1, 2851.
3
4
magnet for efficient magnetic separation but also enhance the
catalytic performance of the Ag nanocrystal component. The
3
416 | Chem. Commun., 2008, 3414–3416
This journal is ꢀc The Royal Society of Chemistry 2008