Tailoring microstructural, textural and thermal properties of γ-alumina by modifying aluminum sec-butoxide with ethyl acetoacetate within a sol–gel synthesis

Abstract

The aim of this work was to derive γ-alumina from gels prepared by hydrolysis of aluminum (Al) sec-butoxide (Asb) chelated with ethyl acetoacetate (Eaa) in various ratios and to determine the effect of Eaa on the properties of obtained alumina. Gels and γ-alumina were investigated by nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy and N2 adsorption–desorption isotherms. The results show that the Eaa/Asb ratio greatly affects the gelation process. At higher Eaa/Asb ratios, hydrolysis resistant tris(ethyl acetoacetate)aluminum (III) is formed, causing a less complete gelation process. Aluminum coordination in samples varies from six-fold coordination in tris(ethyl acetoacetate)aluminum (III) to less defined five-fold coordinated sites of Al in the gel. Thermal treatment at 800 °C for 2 h induces γ-Al2O3 crystallization. A partial transformation to α-Al2O3 is observed after thermal treatment at 900 °C for 2 h for some samples. Transformation to α-Al2O3 after thermal treatment at 1000 °C for 2 h is complete for all samples. In addition to thermal stability of samples, the Eaa/Asb ratio also influences morphology of γ-Al2O3 crystallized at 800 °C. In samples with lower Eaa/Asb ratio, particles appear compact, but are cavernous for samples with higher Eaa/Asb ratios.