1,6-Hexanediol (1,6-HDO) can be synthesized via aqueous-phase hydrogenation of dimethyl adipate (DMA). However, this process requires high temperatures (>200 °C) over Ru catalysts and suffers from low selectivity when reaching high low-temperature activity. In this study, highly selective RuSn/SiO 2 catalysts were developed for the DMA-to-1,6-HDO transformation. The Sn addition demonstrated a promotion effect on the selectivity of 1,6-HDO due to the inhibition of the undesired hydrogenolysis of C-C and C-O bonds. The optimized 4Ru2Sn/SiO 2 catalyst afforded a high 1,6-HDO selectivity of ~98.4% at ~100% DMA conversion, almost double the value obtained over 4Ru/SiO 2 in H 2 O under 1 2 0 °C and 8 MPa H 2 . Additionally, the 4Ru2Sn/SiO 2 catalyst can be reusable up to five recycling cycles with almost unchanged activity and selectivity. Sn was found to be in close contact with the Ru centers in the form of SnO x , which reduces the proportion of Ru 0 species in RuSn/SiO 2 , thereby significantly suppressing hydrogenolysis side reactions and enabling high selectivity toward 1,6-HDO in the aqueous phase. The present results clearly indicate the beneficial effect of Sn on enhancing 1,6-HDO selectivity in Ru-based catalysts during the low-temperature hydrogenation of DMA in aqueous medium, suggesting potential applicability to a wide range of ester compounds. RuSn/SiO 2 catalysts were discovered to afford a high yield of 1,6-hexanediol in the hydrogenation of dimethyl adipate at low temperatures, which is due to the inhibitory effect of Sn addition on the hydrogenolysis of 1,6-hexanediol. • RuSn/SiO 2 was selective for the low-temperature hydrogenation of DMA to 1,6-HDO. • Sn improved the 1,6-HDO selectivity by inhibiting the hydrogenolysis reaction. • The optimized 4Ru2Sn/SiO 2 catalysts afforded 98.4% yield of 1,6-HDO at 120°C • Sn could reduce the Ru 0 proportion and account for the high 1,6-HDO selectivity.
Fu et al. (Sun,) studied this question.