Surface Area Study of High Area Cobalt Aluminate Particles Prepared by the Sol-Gel Method

Cobalt aluminate particles were prepared by the sol-gel method, starting from aluminum sec-butoxide and cobalt salts with a Co:Al ratio of 1:3. Samples with the same composition were also prepared by the citrate-gel method from cobalt and aluminum nitrates and citric acid. The particles were calcined to temperatures between 400 and 1000°C, for the formation of the mixed oxide having spinel structure. The surface properties of the different samples (BET surface area and pore size distribution) were measured. The highest BET surface area obtained (about 339 m²/g) corresponds to a sample prepared by cobalt acetate and aluminum sec-butoxide, calcined at 400°C. The surface area of the sample is reduced progressively as the sample is calcined to higher temperatures (to about 65 m²/g at 1000°C). Narrow pore size distributions were observed with average pore radius ranging from 17–20 Å, for samples heated to 400°C, to about 55–65 Å, for samples heated to 1000°C. The different surface areas and porosities obtained for particles prepared by different methods, different precursors or calcination temperatures, are discussed.