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tallization of CuO and Co O at the extremes, as evidenced
3
4
by PXRD. Liquid phase hydroxylation of phenol was carried
out over these catalysts using H O as an oxidant. Among the
2
2
catalysts studied, CuCo31 showed the maximum activity with
a catechol : hydroquinone ratio close to 3.4. An increase in
substrate : catalyst ratio enhanced the conversion of phenol.
Oxidants other than H O and solvents other than water did
2
2
not show measurable conversion of phenol. Normalized activ-
ities (based on TON) of these catalysts indicated maximum
values for cobalt-rich catalysts (CuCo13 and CuCo15), sug-
gesting the role of cobalt in enhancing the intrinsic activity of
copper, possibly through electronic modiÐcation. A reaction
pathway involving hydroxyl radical is proposed, Scheme 1.
Acknowledgements
29 J. H. Ashley and P. C. H. Mitchel, J. Chem. Soc. A, 1969, 2730.
30 S. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam, 2nd edn., 1984.
V.R. thanks Mr. A. Montero and Ms. O. Prieto for their
assistance in obtaining some of the experimental results. He
also thanks CICyT (grant IN96-0252) and MCyT (grant
MAT2000-1148-C02-01) for Ðnancial support. SK thanks the
Council of ScientiÐc and Industrial Research, New Delhi and
Indian National Science Academy, New Delhi (BS/YSP-22)
for Ðnancial assistance granted under Young Scientist
Schemes.
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36 F. M. Labajos, V. Rives and M. A. Ulibarri, J. Mater. Sci., 1992,
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