Preparation of Ru–Sn/C Catalysts and Their Performance in Hydrogenation of Lactic Acid

Ru–Sn/C catalysts were prepared by the conventional impregnation method and characterized by XRD, H2-TPR, visible light absorption, EDX and XPS. The combination of metal sources, RuCl3, Ru(NO)(NO3)3, Ru(NO3)3, SnCl2, SnCl4 and Sn(OCOCH3)2, significantly influenced the metal structure of the catalysts. Using RuCl3 and SnCl4 as the metal sources, no XRD peaks for metals were observed and high dispersion of metals was estimated. On the other hand, use of RuCl3 and SnCl2 or Ru(NO3)3 and Sn(OCOCH3)2 resulted in a distinct XRD pattern determined to be a RuSn intermetallic compound of body-centered cubic structure. Presumably a type of complex formed between RuCl3 and SnCl2 or Ru(NO3)3 and Sn(OCOCH3)2 during the impregnation procedure. Hydrogenation of lactic acid to 1,2-propanediol was investigated with a 200 mL autoclave between 150 °C and 200 °C under 2-6 MPa of hydrogen (initial pressure at room temperature). The catalyst prepared from RuCl3 and SnCl4 had superior activity compared to reported catalysts under the following reaction conditions; 0.55 M lactic acid, 150 °C, 5.7 MPa of hydrogen and 4 h with 0.80 g of 5 % Ru–5.9 % Sn/C catalyst. The yield and productivity of this catalyst were 99.0 % and 0.51 g g-cat−1 h−1 (6.7 mmol g-cat−1 h−1), respectively. The high yield was achieved because no substantial consecutive hydrogenation of 1,2-propanediol occurred on the binary catalyst.