Catalytic acetalization of biomass glycerol with acetone over TiO2–SiO2 mixed oxides
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TiO2–SiO2 catalysts for glycerol acetalization with acetone are synthesized by the sol–gel method and characterized by N2 adsorption–desorption, X-ray diffraction, NH3-temperature programmed desorption, Fourier transform infrared spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy techniques in the present work. The effects of catalyst preparation and acetalization parameters such as reaction time, acetone/glycerol ratio, catalyst amount and reaction temperature on acetalization are investigated simultaneously. Pyridine adsorption results indicate that Ti–Si mixed oxides naturally only consist of Lewis acidic sites. The results of catalyst preparation and characterization show that Brønsted acidic sites can be produced after Ti–Si mixed oxides adsorb water molecules, and TiO2–SiO2 (Si/Ti = 1) calcined at 550 °C exhibits the most total acidic density leading to the highest catalytic property in glycerol acetalization. The glycerol catalytic acetalization mainly occurs on the Brønsted acidic sites. The effects of acetalization parameters indicate that the formation of the main product 5-membered ring ketal 2,2-dimethyl-1,3-dioxolane-4-yl methanol (about 90 %) is governed by kinetics. About 95 % glycerol conversion in acetalization is obtained under the optimum conditions.