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

摘要

Silica-containing pseudoboehmite acrogel was prepared so that the surface area of alumina was maintained large after heating at elevated temperatures. Below 1300 degreesC, depending on the amount of silica added, the prepared samples transformed to gamma-, delta-, and theta -alumina with columnar shaped particles, but not to alpha -alumina. As a result of the suppression of the phase transformation, heated samples had large pore volume (0.6-1.8 cm(3)/g) and large surface area (70-300 m(2)/g). After heating at 1400 degreesC, while complete transformation to alpha -alumina occurred for 2.5 and 10 wt% silica with the additional formation of mullite for the latter, theta -alumina still remained present up to 5 wt% silica. When there was no formation of mullite, the surface area was quite large (23-37 m(2)/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. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 30]