Solid acidities of SiO_2-TiO_2/montmorillonite composites synthesized under different pH conditions

摘要

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 ℃.