Efficient and selective hydrogenation of aqueous acetic acid on Ru–Sn/TiO2 for bioethanol production from lignocellulosics

Process via acetic acid fermentation has been proposed as a potential way to produce bioethanol from lignocellulosics with improved carbon utilization efficiency as compared to the conventional alcoholic fermentation. This article reports Ru–Sn/TiO2 as an effective hydrogenation catalyst for aqueous acetic acid as the last step of this process. Although a larger loading of Ru to TiO2 rather increased the gas by-production, the additional use of Sn significantly improved the ethanol selectivity by the stronger suppression effect on the gas by-production. Finally, the loading levels of 2–4 wt% of Sn to 4 wt%Ru/TiO2 were found to be optimal for efficient and selective hydrogenation of acetic acid to ethanol in water. With 4 wt%Ru–4 wt%Sn/TiO2 catalyst, aqueous acetic acid solutions (10, 45 and 100 g/L) were converted to ethanol in 98.2, 92.7 and 92.8 mol%, respectively, at 170 °C/H2 15 MPa. This catalytic system would make the acetic acid-based bioethanol production practical.