Maintenance of large surface area of alumina heated at elevated temperatures above 1300 °C by preparing silica-containing pseudoboehmite aerogel

Silica-containing pseudoboehmite aerogel was prepared so that the surface area of alumina was maintained large after heating at elevated temperatures. Below 1300 °C, depending on the amount of silica added, the prepared samples transformed to γ-, δ-, and θ-alumina with columnar shaped particles, but not to α-alumina. As a result of the suppression of the phase transformation, heated samples had large pore volume (0.6–1.8 cm3/g) and large surface area (70–300 m2/g). After heating at 1400 °C, while complete transformation to α-alumina occurred for 2.5 and 10 wt% silica with the additional formation of mullite for the latter, θ-alumina still remained present up to 5 wt% silica. When there was no formation of mullite, the surface area was quite large (23–37 m2/g). The cause for the maintenance of large surface area of alumina was discussed from the structure of the starting alumina source and the effect of the added silica.