Influence of the metal nature (Ni,Cu, Mg) on the surface acid-base properties of mixed oxides elaborated from LDH
Résumé
Lamellar double hydroxides with different proportions of Ni, Cu, Mg and Al were prepared and calcined at 723 K to obtain mixed oxides with acid–base and redox properties. The acidic and basic sites of the surface of these catalysts were characterized by adsorption microcalorimetry, XPS coupled with adsorption experiments and catalytic conversion of cyclohexanol. The adsorption experiments were performed with NH3 for the characterization of the acidic sites and with SO2 for that of the basic sites. The acidic sites are relatively weak and heterogeneous and of Lewis type. On the contrary, the basic sites are strong and homogeneous and of Brönsted (mainly) and Lewis type. The acidity and the basicity increase with the ratio Ni/Cu, whereas the basicity decreases with increasing Mg/Al