Influence of the preparation route on the basicity of La-containing mixed oxides obtained from LDH precursors

Abstract

A series of La-containing Mg(Al)O mixed oxide catalysts were obtained from layered double hydroxide (LDH) precursors following different La3+ incorporation methods, i.e., coprecipitation, impregnation and intercalation. Structural and textural properties investigated by XRD and N2 physisorption revealed a large range of specific surface areas of the materials and different ordering of the structures. The surface areas were between 18 and 230m2g−1 for the coprecipitated and intercalated samples, respectively, and rose to 330m2g−1 for the intercalated sample treated by sonication. The base properties of these samples, and for the sake of comparison of Mg(Al)O and Mg(La)O mixed oxides, were investigated by TPD of CO2 and by performing the highly demanding isomerization reaction of 2,3-dimethyl-1-butene (1). Strong base sites are introduced in the mixed oxide, when La3+ is incorporated by coprecipitation or intercalation in the Mg/Al LDH precursor. Finally, the relative values of the catalytic activities of the different mixed oxide found in the isomerization reaction of (1) showed that not only the densities of strong base sites, but also their accessibility was controlling the catalytic activities.