Polyethylene Glycol-Assisted Synthesis of High Specific Surface Area and Pore Volume γ-Al2O3 Using Sol-Gel Method

In this study, the effects of polyethylene glycol on the structural properties of gamma-alumina (γ-Al2O3) synthesized via a modified sol-gel process was investigated. To this end, polyethylene glycol (PEG) and aluminum isopropoxide (Al(OPri)) were used as the structure-directing agent and aluminum precursor, respectively. Nitrogen adsorption-desorption analysis was performed to obtain the specific surface area, pore-volume, and pore size distributions of the γ-Al2O3 samples synthesized with different mole ratios of PEG/Al(OPri). The maximum specific surface area (344 m2/g) and the pore volume (2.2 cm3/g) was obtained for the γ-Al2O3 prepared with a PEG/Al(OPri) mole ratio of 0.05. These surface area and pore volumes were about 40 and 340% higher than the sample synthesized in the absence of PEG. It was also observed that increasing the mole ratio of PEG/Al(OPri) to more than 0.05 had no significant effect on the structure of γ-Al2O3. The best sample was further studied by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses and the results were compared with the commercial γ-Al2O3 prepared from Merck Company with a specific surface area and pore volume of 174 m2/g and 0.5 cm3/g, respectively. XRD analysis showed that the crystallite sizes of the best-synthesized sample and Merck product were 7 and 13 nm, respectively. Unlike previous γ-Al2O3 synthesis methods, in which synthetic samples with a high specific surface area typically had a small pore volume, the use of PEG in the sol-gel process could significantly increase both the specific surface area and the pore volume. Furthermore, PEG-assisted synthesis of γ -Al2O3 was less complex than the other methods.