Investigation on textural and structural evolution of the novel crack-free equimolar Al2O3-SiO2-TiO2 ternary aerogel during thermal treatment

Abstract

Crack-free mesoporous equimolar Al2O3-SiO2-TiO2 ternary nanocomposite aerogel has been synthesized using an ethanol supercritical drying technique. The effects of heat treatment temperatures on its textural and structural evolution during thermal treatment are investigated in this study. XRD results reveal that only anatase phase is detected in the as-dried ternary aerogel, whereas peaks corresponding to silica and alumina phase are not shown due to its much faster polymerization rate of titania precursor. Structural transition from boehmite to γ-Al2O3 begins to occur at 450°C within the ternary aerogel, and this process is completed at nearly 615°C. The needle-like reticulated γ-Al2O3 grows along the anatase backbone, however, it is not evident in the XRD patterns. The morphologies of the ternary aerogel become more homogeneous after the structural transition, as indicated by the SEM analysis, which is also consistent with the BET results. With the increase of heat temperature up to 1050°C, the γ-Al2O3 phase disappears and no separate SiO2 is detected. At the same time, the silica-alumina network originates in a structure of Al-O-Si, and the silicon atoms incorporate into the alumina phase in the γ-Al2O3 structure, disordering the alumina primary particles. When the heat treatment temperature increases to 1200°C, mullitization begins to occur along the titania backbone, whereas silica crystallization happens at 1300°C. The 600°C calcinated ternary aerogel is typically mesoporous, showing high specific surface area (255.37m2/g), suitable average pore diameter (22.83nm) and large pore volume (1.34cm3/g). Moreover, the ternary aerogels show high surface acid activity at temperatures below 1000°C, which have future applications for ideal catalysts and catalyst supports at elevated temperatures.