Synthesis of Mg-Al mixed oxides with different distribution of basic sites

Abstract

The aim of this work is to compare the structure and basicity of Mg-Al mixed oxides with the same Mg/Al molar ratio (Mg/Al 2) synthesised by means of different procedures. We have focused on the preparation of Mg-Al mixed oxides by the thermal pre-treatment of hydrotalcites synthesized by co-precipitation method. The individual methods differed from the application of alkaline solution used to control the reaction pH. We used two solutions, 0.5 M Na2CO3 + 3 M NaOH and 2 M NaOH, respectively. Moreover, MgO and two Mg-Al mixed oxides available to large-scale were used to compare the structure and basicity with those of materials synthesized in laboratory. The structure and basicity of Mg-Al mixed oxides were analysed by using XRD, N2-adsorption, TGA, and TPD-CO2. As found, the Mg-Al mixed oxide prepared by the thermal pre-treatment of hydrotalcite material and synthesised in the concentrated NaOH solution has exhibited a lower total concentration of basic sites as well as lower relative amount of medium/strong basic sites, in comparison with the Mg-Al mixed oxides originating from the hydrotalcites in the carbonate form.