Organic and Inorganic Sol-Gel Routes for Preparing Mesoporous γ-Alumina Powder

This paper presents a comparative study of mesoporous γ-alumina preparation using organic and inorganic sol-gel processes. Aluminum chloride and aluminum isopropoxide (AIP) served as aluminum sources for the inorganic and organic routes, respectively. In the inorganic method, aluminum chloride was hydrolyzed with ammonium hydroxide at various hydrolysis ratios (10, 21, 31, 41, 52, 62). For the organic route, AIP was hydrolyzed at 85 ℃ with hydrolysis ratios ranging from 9 to 200 (mol H2O/mol AIP) for comparison. A parametric study was conducted to analyze the effects of initial precursor concentration, hydrolysis ratio, and nitric acid to AIP ratio in the organic route. Physical characterization and phase evaluation of the γ-alumina samples were conducted using XRD, N2-Physisorption, and TEM. The BET surface areas of the mesoporous γ-alumina materials ranged from 209 to 299 m2/g for the inorganic method, and 362 to 378 m2/g for the organic method. The mean pore diameter of the γ-alumina powders was approximately twice as large in the inorganic method compared to the organic method, with values of 8.9 nm and 4.8 nm, respectively. Optimal sol-gel process parameters for the organic method were identified as an initial AIP concentration of 0.1 M, a hydrolysis ratio of 150, and a nitric acid to AIP ratio of 0.3. The inorganic sol-gel method, which is cost-effective and easy to handle, produced results comparable to those reported in the literature.