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aer 2 h, demonstrating that oxidation of aromatic aldehyde to of V
2
O
5
/WO
3
composition exhibit high catalytic activity and
the corresponding carboxylic acid is a catalytic process. These stability in oxidation of various substituted aryl alcohols. These
results suggest the strong oxidizing character of the 4% V O / results point to the great potential of these mesoporous heter-
2
5
WO material.
ostructures in catalytic oxidation reactions.
3
It is noteworthy that the presence of electron-donating or
electron-withdrawing group has a moderate effect on the cata-
lytic activation of aromatic alcohols. For example, the electron
Acknowledgements
rich alcohols 2 (X ¼ –OCH
3
) reacted to form the corresponding
Financial support by the Greek Ministry of Education under
Excellence grant (ARISTEIA-2691) and THALES project (MIS
ketone in excellent (>99%) yield in 1 h reaction time. Similarly,
alcohols bearing electron-withdrawing substituent such as p-
bromobenzyl alcohol (4), p-chlorobenzyl alcohol (5) and p-
nitrobenzyl alcohol (6) were oxidized to the corresponding
carbonyl compounds with 96–98% conversion. However, the
oxidation reaction proceeds slightly faster as the electron-
donating ability of the substituent functionality increases, see
Fig. S9b of the ESI.† Specically the pseudo rst-order reaction
rates, shown in Table 3, indicate an about three times faster
kinetic rate for 2 (MeO-substituted) oxidation relative to the
oxidation of 3 (Me-substituted), 5 (Cl-substituted) and 6 (NO2-
substituted); kMeO/kMe ¼ 2.6, kMeO/kCl ¼ 2.9 and kMeO/kNO2 ¼ 3.5.
Similar, p-methylbenzyl alcohol (8) was also oxidized to the
corresponding aldehyde (8a) in a faster reaction rate (approxi-
mately two times) compared to the electron poor alcohols 7 and
377064) are kindly acknowledged.
Notes and references
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2
9, i.e. possessing the electron-decient H- and NO -groups in
para position, respectively. It should be stressed that steric
properties of the substituent seem to not affect signicantly the
reaction process. For example, in the case of substrate 10 where
the a-substituent is a phenyl group, the rate of the catalytic
reaction is about 1.3-times higher to that of 2 alcohol, which
contained a methyl group next to the benzylic carbon. These
2 5 3
results clearly show that our 4% V O /WO catalyst is able to
catalyze the oxidation of hindered primary and secondary
aromatic alcohols with high efficiencies in presence of t-
BuOOH.
8 K. Jiao, B. Zhang, B. Yue, Y. Ren, S. Liu, S. Yan, C. Dickinson,
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9
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Conclusions
In summary, ordered mesoporous tungsten(IV) oxide and
vanadium oxide (V O ) nanocomposite frameworks have been 10 E. Rossinyol, A. Prim, E. Pellicer, J. Arbiol, F. Hern ´a ndez-
2
5
successfully prepared via a two-step wet chemical deposition
and nanocasting method, using amino-functionalized SBA-15
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that mesoporous V /WO heterostructures retain a signi- 12 F. Jiao, A. H. Hill, A. Harrison, A. Berko, A. V. Chadwick and
cant degree of crystalline structure of the silica template, dis- P. G. Bruce, J. Am. Chem. Soc., 2008, 130, 5262.
2
O
5
3
playing an organized matrix of parallel-arranged nanorods. The 13 F. Jiao and P. G. Bruce, Adv. Mater., 2007, 19, 657.
elemental composition of the inorganic structure was 14 H. Yen, Y. Seo, R. Guillet-Nicolas, S. Kaliaguine and F. Kleitz,
conrmed by EDS analysis, while the presence of V
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diffuse reectance UV-vis and Raman spectroscopy. According 2010, 64, 1379.
to these results, the V species dispersed evenly throughout 16 I. Tamiolakis, I. N. Lykakis, A. P. Katsoulidis, M. Stratakis
the pore wall, forming a solid-solution structure with WO
oxide. The catalytic activity of V /WO mesoporous is strongly
2
O
5
Chem. Commun., 2011, 47, 10473.
2 5
O
3
and G. S. Armatas, Chem. Mater., 2011, 23, 4204;
G. S. Armatas, A. P. Katsoulidis, D. E. Petrakis,
P. J. Pomonis and M. G. Kanatzidis, Chem. Mater., 2010,
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2
O
5
3
related to the chemical composition of inorganic framework,
with particular relevance of the V O content on the surface.
2
5
Although, pure mesoporous WO
WO
3
2 5
and bulk composite V O /
microparticles show little activity, mesoporous structures
3
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