esters was less than 3% in every reaction. In marked contrast to
h-NbW, in agreement with the data of alkylations given in Table
structural characterizations revealed that the nanofiber structure
with partially reduced tungsten oxide species was indispensable
to afford high catalytic activity in the Friedel–Crafts reactions.
2
, c-NbW was almost inactive in the reaction (entry 4). In addi-
tion, the yield of ketones was almost three-times higher than that
obtained with H-b zeolite (supplied by PQ Co., Si/Al
2
¼ 25, entry
5
). This fact indicated the superior nature of h-NbW calcined in
References
N
2
. The recycle use of the h-NbW catalyst was possible, as can be
1
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3
2 K. Tanabe, in Catalysis-Science and Technology, ed. J. R. Anderson
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4+
reduced tungsten atoms (probably W ) in the crystalline Nb O –
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2
3
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4
C. Tagusagawa, A. Takagaki, A. Iguchi, K. Takanabe, J. N. Kondo,
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14
oxides exhibit the Brønsted acid character. Probably, the
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5
6
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5
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3
inferred that the role of N is to keep the inert atmosphere while
2
6
0 K. Okumura, J. Jpn. Pet. Inst., 2009, 52, 219.
1, 3904.
reducing nanofibers with oxalate anions or ammonium cations.
1
1
1 M. L. Sanju ꢀa n, A. Kuhn, M. T. Azcondo and F. Garc ꢀı a-Alvarado,
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4
. Conclusions
1
1
Hydrothermal synthesis of Nb O –WO was carried out over
5
2
x
4
3.
3 S. Yamazoe, Y. Hitomi, T. Shishido and T. Tanaka, J. Phys. Chem. C,
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a mixed solution of Nb and W in an autoclave at 443 K.
Synthesized Nb O –WO had a long nano-crystalline structure
2
5
x
2
with ca. 10 nm diameter as observed by FE-SEM and TEM. It
14 H. Belatel, H. Al-Kandari, F. Al-Kharafi, F. Garin and A. Katrib,
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exhibited a high catalytic activity in the Friedel–Crafts alkyl-
ations and acylations when it was calcined in N
was effective in enhancing the catalytic activity of N
Nb –WO . Comparison of the catalytic performance and
2
. Ar bubbling
1
5 O. Kirilenko, F. Girgsdies, R. E. Jentoft and T. Ressler, Eur. J. Inorg.
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G. Polol, Eur. J. Inorg. Chem., 2006, 3413.
2
-calcined
2
O
5
x
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J. Mater. Chem., 2011, 21, 229–235 | 235