Conclusions

From this study we can extract the following remarks:

• In the oxidized state, the studied Cu-ZrO2 system is formed of a hydroxylated solid solution of copper and zirconia and a variable amount of free CuO.

• In a partially reduced state, the solid solution is maintained until 250°C. Beyond this temperature, copper diffuses to the surface and a complete demixing of the solid solution is obtained between 550°C and 600°C with a clear crys-tallographic evolution of the ZrO2 phase to cubic or quadratic form. Besides, metallic copper appears less or more rapidly according to the composition and the dimension of the copper oxide grains.

• During the activation step of the catalysts in H2 (150°C or 250°C), Cu+ species inserted in the zirconia network and Cu0 are formed.

• The catalysts have been tested in isoprene and carbon dioxide hydrogenation reactions, in both cases solids showing the best activity are found to follow the decreasing order: (Cu/Zr1) > (Cu/Zr0.5)K > (Cu/Zr0.5) > (Cu/Zr2)> (Cu/Zr0). Moreover, (Cu/Zr0.5)K presents a good selectivity to methanol while (Cu/Zr1) is more selective toward methane.

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