Effects of Different Solvents on Hydrogenation of Acetic Acid over Pt/TiO<sub>2</sub> for Bioethanol Production

Abstract

Bioethanol production from lignocellulosics via acetic acid fermentation is a potential way to substitute gasoline with more improved carbon utilization efficiency than the conventional alcoholic fermentation processes. Accordingly, hydrogenation of acetic acid to ethanol is a very important step to realize this acetic acid-based process. In this communication, hydrogenation mechanism of acetic acid into ethanol on a Pt catalyst supported on TiO2 (titania) was characterized from the solvent effects. The Pt/TiO2 catalyst was quite effective in hexane, a nonpolar solvent, to give ethanol and ethyl acetate from acetic acid in relatively high yields, while the catalytic activities were reduced in tetrahydrofuran (THF) and water, polar solvents. These results evidently support the catalytic mechanism: Ti atoms of the TiO2 surface act as a Lewis acid to activate the carbonyl carbon of acetic acid, which leads to the efficient hydrogenation of acetic acid at the interface between Pt and TiO2. Suppression of the ethyl acetate formation in THF and water, which could be formed via the common activated state of acetic acid on TiO2, also supports this catalytic mechanism.