Ru/SiO2 Catalyst for Highly Selective Hydrogenation of Dimethyl Malate to 1,2,4-Butanetriol at Low Temperatures in Aqueous Solvent

Catalytic selective hydrogenation of esterified malic acid to produce 1,2,4-butanetriol (1,2,4-BT) using H 2 as the reducing reagent suffers from the low 1,2,4-BT selectivity. Here, Ru/SiO 2 catalyst was employed for selective hydrogenation of dimethyl malate (DM) to produce 1,2,4-BT, which gave abnormal high DM conversion (100%) and 1,2,4-BT selectivity (92.4%) in aqueous solvent at 363 K, especially, the 1,2,4-BT yield even is higher than the optimal catalyst reported (Ru-Re, 79.8%). The reaction pathways for the DM hydrogenation on Ru/SiO 2 were also proposed, suggesting that extremely high 1,2,4-BT selectivity require for the much high hydrogenation rates at low temperatures, where side-reaction transesterification rates are relatively low. The extremely high hydrogenation activity and 1,2,4-BT selectivity on Ru/SiO 2 in aqueous solvent at low temperatures arise from that H 2 O may coordinate to Ru 2+ and prevent the reduction of Ru 2+ to Ru under high H 2 pressure. Ru/SiO 2 surface presents abundant Ru 2+ in aqueous solvent, can activate H 2 through heterolytic cleavage mode to form hydride, which can significantly increase hydrogenation rates of C = O groups at low temperatures. In addition, the activity and 1,2,4-BT selectivity on Ru/SiO 2 catalyst only reduced by 2.3% and 2.6%, respectively over a period of 550 h. Graphical Abstract