Wasteless Synthesis and Properties of Highly Dispersed MgAl2O4 Based on Product of Thermal Activation of Gibbsite

The study showed that the interaction of the product of centrifugal thermal activation of gibbsite with an aqueous solution of magnesium nitrate at a cationic ratio Mg:Al = 1:2 leads to the formation of mixed double hydroxides both under hydrothermal treatment at 150 degrees C and at room temperature. The subsequent thermal treatment at 550 degrees C of the product of mild interaction leads to similar to 90% alumina-magnesia spinel and similar to 10% MgO, while the treatment of the hydrothermal interaction product leads to similar to 100% spinel with the stoichiometric composition MgAl2O4. The obtained spinel samples possess a high specific surface area (above 100 m(2)/g) and a hierarchical pore structure formed by the micron-level particles of different sizes (1-2 and 10-20 mu m) consisting of similar to 70 nm crystallites with similar to 3 nm pores; the samples differ mostly in the total volume and quantitative ratio of the pores. The samples have Lewis acid sites of moderate strength on the surface, the amount of which is much lower to how it is when compared with a sample prepared by precipitation in that they also differ by quantity from each other as well (503 mu mol/g for stoichiometric spinel and 304 mu mol/g for sample with admixture of MgO). As the calcination temperature is raised to 850 degrees C, the acidity decreases-only weak Lewis acid sites are observed, the amount of which is also higher for stoichiometric spinel (161 and 39 mu mol/g, respectively). The method proposed for the synthesis of alumina-magnesia systems provides a high dispersion and a much lower surface acidity for the oxides; in addition, it minimizes or completely excludes wash water, in distinction to the precipitation method.

Automated summary

The study showed that the interaction between gibbsite and magnesium nitrate solution can lead to the formation of mixed double hydroxides with different compositions. The resulting spinel samples have a high specific surface area and a hierarchical pore structure. The synthesis method proposed in this study provides better dispersion and lower surface acidity compared to the precipitation method.