Towards High Surface Area α-Al 2 O 3 -Mn-Assisted Low Temperature Transformation.

When impregnated with manganiferous precursors, γ-Al 2 O 3 may be converted into α-Al 2 O 3 under relatively mild and energy-saving conditions. In this work, a manganese assisted conversion to corundum at temperatures as low as 800 °C is investigated. To observe the alumina phase transition, XRD and solid-state 27 Al-MAS-NMR are applied. By post-synthetical treatment in concentrated HCl, residual manganese is removed up to 3 wt.-%. Thereby, α-Al 2 O 3 with a high specific surface area of 56 m 2 g -1 is obtained after complete conversion. Just as for transition alumina, thermal stability is an important issue for corundum. Long-term stability tests were performed at 750 °C for 7 days. Although highly porous corundum was synthesized, the porosity decreased with time at common process temperatures.