Low-temperature copper intercalation in sodium vanadium oxybronze: preparation and characterization
Résumé
The vanadium oxibronze alpha-NaV205 reacts with CuCl2 in water at 373 K affording a new compound, Cu0.5V2O5(H2O)0.5, which a high surface area for such an unsupported phase. The overall process is described as the replacement of two sodium ions by one copper ion and one water molecule. Structural and chemical investigations by visible and IR spectroscopy, X-ray powder diffraction, thermal analyses, and oxidation studies are described. It is suggested that the metastable structure of Cu0.5V205(H20)0.5 is reminiscent of the lamellar character of the precursor phase a'-NaV205. Heat treatment under inert atmosphere first leads to amorphization via dehydration with an activation energy of 110 kJ mol-l, then to the ß' Cu0.5V2O5 phase formation at 973 K. The oxidizing properties us hydrogen and carbon monoxide are compared with those of related compounds. For carbon monoxide oxidation, the temperature of carbon dioxide formation follows the order V2O5 > alpha'-NaV2O5 > ß'Cu0.5V2O5>CuO/V2O5>Cu0.5V2O5. Therefore the presence of copper involves a greater lability of the oxygen atoms of the V206 lattice. This effect is enhanced with the new compound Cu0.5V205. Preliminary results in the catalytic decomposition of 2-propanol show that Cu0.5V2O5 is selective for the oxidative dehydrogenation route whereas the other compounds are also active for dehydration.