Preparation of millimeter-sized spherical SiO₂–Al₂O₃ with various acid catalysts for the acetalization of glycerol with acetone

Through the sol-gel-oil ammonia column method, millimeter-sized spherical SiO₂–Al₂O₃ particles were successfully prepared using aluminum isopropoxide and varying amounts of tetraethyl orthosilicate. The impact of different Al/Si molar ratios on the structure and performance of SiO₂–Al₂O₃ materials was thoroughly investigated. The surface of the samples was analyzed for acidic sites (Brønsted and Lewis acids) both qualitatively and quantitatively. The millimeter-sized spherical SiO₂–Al₂O₃ materials were used as a catalyst in the Solketal production process, involving acetalization of acetone and glycerol. The glycerin conversion rate reached 88.67% and the Solketal selectivity reached 93.28% when the SiO₂–Al₂O₃ spherical particles reached with Al/Si molar ratio of 8. The spherical SiO₂–Al₂O₃ exhibits high catalytic activity in the acetalization reaction due to its large specific surface area, thermal stability, and moderate Brønsted and Lewis acidity.