Selective Hydrogenation of Lactic Acid to 1,2-Propanediol over Highly Active Ruthenium-Molybdenum Oxide Catalysts

Modification of Ru/C with a small amount of MoOx (RuMoOx/C) enhanced the catalytic activity in the hydrogenation of L‐lactic acid to form 1,2‐propanediol and maintained high selectivity. The turnover frequency based on the amount of Ru over the optimized RuMoOx/C catalyst (Mo/Ru molar ratio=1:16) was 114 h−1 at 393 K, which was about 4 times higher than that over Ru/C. The same effect of MoOx was obtained over RuMoOx/SiO2, although RuMoOx/SiO2 showed slightly lower activity than that of RuMoOx/C. RuMoOx/C achieved a high yield of 95 % in 18 h at 393 K and was applicable to various carboxylic acids to provide the corresponding alcohols in high yields. Modification with MoOx also brought about suppression of racemization and (S)‐1,2‐propanediol was obtained in high enantiomeric excess at 353 K. Based on kinetic analysis and characterization data, such as XRD, TEM, CO adsorption by a volumetric method, FTIR spectroscopy, and X‐ray absorption spectroscopy, for RuMoOx/C and RuMoOx/SiO2, the catalyst structure and reaction mechanism are proposed. Minor adjustment for major effects: Modification of supported ruthenium catalysts with a small amount of molybdenum oxide (RuMoOx/C, RuMoOx/SiO2) enhances the catalytic activity for the hydrogenation of L‐lactic acid to give (S)‐1,2‐propanediol with high selectivity. The turnover frequency is roughly four times higher than over Ru/C. The results reported are encouraging for the design of selective hydrogenation catalysts and the development of synthesis methods of alcohols.