A comparative study on the thermal stability, textural, and structural properties of mesostructured γ-Al2O3 granules in the presence of La, Sn, and B additives

Mesoporous γ-alumina is widely used as catalyst support in various catalytic reactions of industrial interest. However, due to the instability of γ-alumina at elevated temperatures, many efforts have been reported to inhibit the α-alumina phase transition through doping with suitable metalloids, as well as transition, post-transition, or rare-earth elements. In the present study, undoped and La-, Sn-, and B-doped alumina granules were synthesized via sol-gel/oil drop method with the aim to clarify the role of the additives and their content on the porous structure as well as on the chemical, structural, and microstructural behavior of γ-alumina. XRD and DTA/TG results demonstrated that thermal stability of transition aluminas increases more than 100 °C by 3 wt% lanthanum and tin doping; however, boron doping seems to have only negligible effect on the thermal stability. On the other hand, based on nitrogen adsorption-desorption analysis, tin and boron-doped aluminas showed a higher surface area at 750 °C (between 214.74 m2/g to 245.97 m2/g) but higher loss in the surface area after calcination at 1200 °C (between 25.45 m2/g to 8.57 m2/g). On the contrary, the 3 wt% La-doped alumina sample, with a relatively high surface area at 750 °C (227.17 m2/g), exhibited the highest surface area after calcination at 1200 °C (53.07 m2/g). 27Al MAS NMR and HRTEM studies indicated that the presence of 3 wt% La in alumina structure leads to thermal and mesoporous structure stability up to 1200 °C by inhibiting oxygen lattice restructuring. These results provide a comparative perspective of La, B, and Sn additives' behavior in γ-alumina.