EPOXIDATION OVER SILICA
357
they easily show the phosphorescence spectra with the fine
structure.
3. Romano, U., Esposito, A., Maspero, F., Neri, C., and Clerici, M. G.,
Stud. Surf. Sci. Catal. 55, 33 (1990).
4
5
6
. Notari, B., Stud. Surf. Sci. Catal. 37, 413 (1987).
. Armor, J. N., J. Catal. 70, 72 (1981).
. Kastanas, G. N., Tsigdinos, G. A., and Schwank, J., Appl. Catal. 44, 33
We treat here the heteroatoms as a clue to determine the
active sites for the photooxidation on pure silica surface.
The spectra of Mg-loaded silica and silica–alumina were
only clearly observed on samples evacuated at high temper-
ature, such as 1073 K. The activation by evacuation at high
temperature for photocatalysis (19) or photoluminescence
(
1988).
7. Matsumura, Y., Hashimoto, K., and Yoshida, S., J. Catal. 117, 135
1989).
(
8. Parmaliana, A., Frusteri, F., Miceli, D., Mezzapica, A., Scurrell, M. S.,
and Giordano, N., Appl. Catal. 78, L7 (1991).
(
12–14) is explained by desorption of water molecules or
9. Morikawa, A., Hattori, M., Yagi, K., and Otsuka, K., Z. Phys. Chem.
N.F. 104, 309 (1977).
hydroxyl groups on the surface. The desorption of hydroxyl
groups would produce coordinatively unsaturated sites on 10. Anpo, M., Yun, C., and Kubokawa, Y., J. Catal. 61, 267 (1980).
1
1
1
1
1
1
1
1. Ogata, A., Kazusaka, A., and Enyo, M., J. Phys. Chem. 90, 5201
1986).
2. Tanaka, T., Yoshida, H., Nakatsuka, K., Funabiki, T., and Yoshida, S.,
J. Chem. Soc. Faraday Trans. 88, 2297 (1992).
3. Yoshida, H., Tanaka, T., Funabiki, T., and Yoshida, S., J. Chem. Soc.
Faraday Trans. 90, 2107 (1994).
4. Yoshida, H., Tanaka, T., Satauma, A., Hattori, T., Funabiki, T., and
Yoshida, S., Chem. Commun. 1153 (1996).
the surface, and the sites would be concerned with photoex-
citation. The photoexcitation sites on Mg-loaded silica and
silica–alumina were proposed to be coordinatively unsatu-
rated Mg and Al sites on the surface of the tetrahedral silica
network (13, 14). By analogy, in the case of silica surface,
coordinatively unsaturated surface sites such as Si–(O–Si)3
are suggested to be the photoactive sites. The spectrum of
silica evacuated at 1073 K might seem to be slightly over-
lapped with the fine structure in the higher wavelength re-
gion (Fig. 1a). If the M–(O–Si)3 site model is acceptable,
(
5. Gritscov, A. M., Shvets, V. A., and Kazansky, V. B., Chem. Phys. Lett.
35, 511 (1975).
6. Tanaka, T., Ooe, M., Funabiki, T., and Yoshida, S., J. Chem. Soc.,
Faraday Trans. 1 82, 35 (1986).
7. Tanaka, T., Nojima, H., Yoshida, H., Nakagawa, H., Funabiki, T., and
Yoshida, S., Catal. Today 16, 297 (1993).
8. Blatter, F., Sun, H., and Frei, H., Catal. Lett. 35, 1 (1995).
9. Yoshida, H., Tanaka, T., Matsuo, S., Funabiki, T., and Yoshida, S.,
J. Chem. Soc., Chem. Commun. 761 (1995).
the differences on the photoactivity might be explained by
the difference of the central atom of the M–(O–Si)3 unit.
1
1
CONCLUSION
2
0. Yoshida, H., Tanaka, T., Yamamoto, M., Funabiki, T., and Yoshida, S.,
Chem. Commun. 2125 (1996).
It was found that silica catalyzed the partial oxidation of
propene to acetaldehyde and propylene oxide under photo- 21. Yoshida, S., Matsuzaki, T., Kashiwazaki, T., Mori, K., and Tarama, K.,
Bull. Chem. Soc. Jpn. 47, 1564 (1974).
2. Yoshida, H., Tanaka, T., Nakatsuka, K., Funabiki, T., and Yoshida, S.,
Stud. Surf. Sci. Catal. 90, 473 (1994).
3. Yoshida, T., Tanaka, T., Yoshida, H., Funabiki, T., Yoshida, S., and
Murata, T., J. Phys. Chem. 10890 (1995).
irradiation in the presence of O2. Mg-loaded silica exhib-
2
2
ited a higher activity for photooxidation than silica. Highly
dispersed and isolated magnesium oxide species on silica,
the local structure of which is proposed to be tetrahedral,
promoted the epoxidation of propene by O2 under irra- 24. Tench, A. J., and Pott, G. T., Chem. Phys. Lett. 26, 590 (1974).
2
5. Coluccia, S., Deane, A. M., and Tench, A. J., J. Chem. Soc. Faraday
Trans. 1 74, 2913 (1978).
diation selectively, while crystallites or island structure of
magnesium oxide on silica promoted the photooxidation to
acetaldehyde predominantly. The local structures of mag-
nesium oxide species were controlled by the preparation
2
2
6. Duley, W. W., J. Chem. Soc., Faraday Trans. I 80, 1173 (1984).
7. Anpo, M., Yamada, Y., Kubokawa, Y., Coluccia, S., Zecchina, A., and
Che, M., J. Chem. Soc., Faraday Trans. 1 84, 751 (1988).
method and loading amount of magnesium. The active sites 28. Yoshida, H., Yoshida, T., Tanaka, T., Funabiki, T., Yoshida, S., Abe,
T., Kimura, K., and Hattori, T., J. Phys. IV 7(C2), 911 (1997).
on the bare silica would be coordinatively unsaturated sites
2
9. Yoshida, T., Tanaka, T., Yoshida, H., Takenaka, S., Funabiki, T.,
Yoshida, S., and Murata, T., Phys. B 208 & 209, 581 (1995).
0. Kubokawa, Y., Anpo, M., and Yun, C., in “Proceedings, 7th Interna-
tional Congress on Catalysis, Tokyo, 1980” (T. Seiyama and K. Tanabe,
Eds.), Vol. B, p. 1170. Elsevier, Amsterdam, 1981.
which were produced by evacuation at high temperatures.
The active sites are the same in photometathesis as well as
photooxidation.
3
ACKNOWLEDGMENTS
31. Tsuji, H., Yagi, F., Hattori, H., and Kita, H., in “Proceedings, 10th
International Congress on Catalysis, Budapest, 1992” (L. Guczi,
F. Solymosi, and P. Tetenyi, Eds.), Vol. B, p. 1171. Akad e´ miai Kiad o´ ,
Budapest, 1993.
32. Yoshida, S., Magatani, Y., Noda, S., and Funabiki, T., J. Chem. Soc.,
Chem. Commun. 601 (1981).
X-ray absorption experiments were approved by the Joint Studies Pro-
gram (1991–1995) of UVSOR of the Institute for Molecular Science,
Okazaki, Japan. The authors thank Mr. Y. Honda for his help in XRF
measurement. H.Y. was supported by a grant in aid from the JSPS for
Japanese Junior Scientists.
33. Yoshida, S., Tanaka, T., Okada, M., and Funabiki, T., J. Chem. Soc.,
Faraday Trans. 1 80, 119 (1984).
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