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 degrees C for 2 h. It is found that the as-prepared xerogels convert into gamma-Al2O3 at 400-800 degrees C and then to alpha-Al2O3 at 1000-1050 degrees C. Two successive changes in SBET are observed in the gel phase transformations. Microporous alumina with a pore size < 16 Angstrom can be prepared at calcination temperatures of 200-300 degrees C (S-BET = 674 m(2)/g) while mesoporous alumina materials with uniform pore sizes of 29-74 Angstrom can be obtained at 400-1000 degrees 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.