Preparation and characterization of equimolar SiO₂–Al₂O₃–TiO₂ ternary aerogel beads

Crack-free mesoporous equimolar SiO₂–Al₂O₃–TiO₂ ternary aerogel beads have been synthesized and characterized. Silica sol, alumina sol, and titania sol were synthesized individually to prevent the formation of inhomogeneous structure due to the different hydrolization and polymerization rate of individual precursor. After mixing these three types of acidic sols, SiO₂–Al₂O₃–TiO₂ ternary beads were prepared by the ball dropping method. The ternary aerogel beads were typically mesoporous, showing high surface area (305 m² g⁻¹), large pore volume (1.32 cm³ g⁻¹), and high surface acid amount (0.884 mmol NH₃ g⁻¹). Moreover, the acid sites of the ternary aerogel beads showed higher thermal stability than those of binary aerogel beads. Gradient drying (GD), supercritical drying (SD), ambient drying (AD), extended aging (EA) and hydrophobic modifying drying (HM) have been employed to investigate the effects of drying method on the characteristics of the aerogel beads. The surface areas of the ternary aerogel beads obtained by different drying methods decrease in the sequence EA > HM > GD > SD > AD. The ternary aerogel beads have been characterized by scanning electron microscopy, nitrogen adsorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FTIR), solid-state NMR, temperature-programmed desorption measurements, pyridine adsorption FTIR, and differential scanning calorimetry.