Lactic Acid Esterification on Titania–Silica Binary Oxides

Abstract

Lactic esters were synthesized with good yields by the reaction between lactic acid and n-butanol/ethanol over titania–silica binary oxides. These catalysts had various atomic ratios and were prepared by a coprecipitation method. XRD, n-butylamine adsorption, nitrogen adsorption, and SEM/EDS were used to characterize the oxides. In general, the turnover frequency for ester formation increased with increasing Ti content. However, the catalyst with Ti/Si atomic ratio = 1/3 (TS13) exhibited the highest ester yield (92.3%) because it had the largest surface area and the greatest amount of acid sites. The optimum Ti/Si atomic ratio for esterification is different from that (Ti/Si ∼ 9/1) reported previously for alkene isomerization. For lactic acid esterification, different optimum catalyst compositions were observed for Ti–Si, Ti–Al, and Ti–Zr mixed oxides (the best Ti/M atomic ratios = 1/3, 1/1, and 3/1 when M = Si, Al, and Zr, respectively), which might be caused by the electronegativity and acid strength di...