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Avenue Albert Einstein, 69626 Vi/leurbanne, France A copper-cerium oxide sample prepared with an atomic ratio, Cu : Ce, of 0.01 has been studied by electron paramagnetic resonance (EPR) spectroscopy. A well resolved spectrum of copper(11) ion pairs has been evi denced and the hyperfine structure of the perpendicular components clearly appears. The high resolution can be explained by the presence of two nearly equivalent Cu2+ ions separated by an oxygen ion. A correlation in EPR parameters has been found between the signal corresponding to a single Cu2+ ion, a precursor of the dimer, and the copper(11) ion pair spectrum.

The catalytic behaviour of H5PV, Mo, , 0, , heteropoly acid in the oxidation of n-butane to maleic anhydride is analysed in relation to that of its partially salified Cs salt and their FTlR spectra, UV-VIS diffuse reflectance spectra, thermogravimetry and reducibility tests as well as solid state 51V NMR and EPR characterizations are also compared. At temperatures around 573 K the acid sample dehydrates with partial reduction and the formation of lacunar 0x0-anions but with preservation of the Keggin unit structure. The creation of inter-Keggin V-0-V bonds during dehydration is suggested. The presence of the alkali metal in the secondary structure inhibits these effects. The superior catalytic performance of the acid sample in butane transformation is discussed in terms of the role of the presence of V5+ sites associated with a n inter-Keggin interaction.

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