Solid acidities of SiO2–TiO2/montmorillonite composites synthesized under different pH conditions

Abstract SiO 2 –TiO 2 /montmorillonite composites were prepared under acidic, neutral and basic conditions and the solid acidity of the resulting composites were determined. All the SiO 2 /TiO 2 ratio of the colloidal particles was set at 10 but the resulting SiO 2 /TiO 2 ratios were significantly richer in TiO 2 . The XRD patterns of the acidic composite showed expanding and broadening of the (001) reflection by intercalation of colloidal SiO 2 –TiO 2 particles, but the neutral and basic composites showed only broadening of the reflections and no intercalation. The specific surface areas of the acidic, neutral and basic composites (375, 237 and 247 m 2 /g, respectively) were much larger than of montmorillonite (6 m 2 /g). The average pore sizes were about 4, 15 and 50 nm, and the amounts of solid acidic sites measured by the NH 3 -TPD were 178, 95 and 86 µmol/g for the acidic, neutral and basic composites, respectively. The solid acid amount of the acidic composite was twice that of a commercial catalyst, K-10, (85 µmol/g) and much higher than the guest phase SiO 2 –TiO 2 gel (16 µmol/g) or the host phase montmorillonite (6 µmol/g). The TPD peak temperatures reflect the acid strength, and were similar in all the samples, ranging from 175° to 200 °C.