Abstract: Solid acid catalysts SO2-4/SiO2-TiO2 with different SiO2/TiO2 ratios and calcined at different temperatures were prepared by mechanical mixing and impregnation methods. The catalysts were used for esterification of ethanol and acetic acid. SO2-4/40%SiO2-TiO2 prepared by mechanical mixing and calcination at 400 ℃ exhibited the highest activity, and the acetic acid conversion was nearly 100% in partial reflux rectifying esterification and up to 84% in total reflux esterification, which was close to the chemical equilibrium composition. X-ray diffraction patterns indicated that SiO2 inhibited the excessive formation of titanium oxide sulfate. The combination of tetragonal crystal anatase TiO2, orthorhombic crystal titanium oxide sulfate, and cubic crystal titanium with high surface area SiO2 ensured the high activity of the catalysts. Infrared spectra showed that the addition of SiO2 helped the formation of Ti-O-Si linkage which enhanced the strong bonding of SO2-4 with the catalyst surface. The sulfate species bonded were in bidentately chelating and covalent sulfate structures. Thermogravimetric-differential scanning calorimetry proved that SO2-4 was hardly removed with the addition of SiO2 and the temperature for transformation of anatase to rutile was lowered.

Key words: sulfuric acid, silica, titania, solid acid catalyst, bio-oil, acetic acid, ethanol, esterification