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

Document Type : Research Article

Authors

School of Chemical, Petroleum, and Gas Engineering, Iran University of Science and Technology, Tehran, I.R. IRAN

Abstract

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.

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References

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