Synthesis of High-Surface-Area Alumina Using Aluminum Tri-sec-butoxide−2,4-Pentanedione− 2-Propanol−Nitric Acid Precursors

Transparent alumina gels have been prepared with a simple precursor system, aluminum tri- sec -butoxide−2,4-pentanedione−2-propanol−nitric acid, at optimal acacH/ASB mole ratios of 0.3−0.4. The specific surface areas ( S BET ) of the prepared gels are in the range 552−560 m 2 /g after calcination at 400 °C for 2 h. It is found that the as-prepared xerogels convert into γ-Al 2 O 3 at 400−800 °C and then to α-Al 2 O 3 at 1000−1050 °C. Two successive changes in S BET are observed in the gel phase transformations. Microporous alumina with a pore size < 16 Å can be prepared at calcination temperatures of 200−300 °C ( S BET = 674 m 2 /g) while mesoporous alumina materials with uniform pore sizes of 29−74 Å can be obtained at 400−1000 °C using the same starting xerogel. On the basis of a large set of gelation data, it is believed that the hydrolysis of the alkoxides takes place before the condensation. The causes for the observed gel transparency and for the generation of high surface areas are also discussed on the basis of the results of synthesis experiments and the findings of XRD/FTIR/DTA/TGA/BET/BJH investigations.