Synthesis of Secondary Monoalcohols from Terminal Vicinal Alcohols over Silica-Supported Rhenium-Modified Ruthenium Catalyst

The selective synthesis of secondary alcohols from 1,2-alkanediol by C-O hydrogenolysis, which has been less investigated than the synthesis of primary alcohols, was investigated with Ru-based catalysts and 1,2-propanediol (1,2-PrD) as a model substrate. The modification of Ru/SiO2 with ReOx achieved significant improvement of activity. The hydrogenolysis of 1,2-PrD over Ru-ReOx/SiO2 (Re/Ru = 0.5) initially formed both 2-propanol (2-PrOH) and 1-propanol (1-PrOH) with similar selectivity along with the formation of ≤ C2 compounds, and then 1-PrOH was preferably converted to propane; as a result, only 2-PrOH remained in the liquid phase with 23% yield at longer reaction time. This catalyst was reusable at least twice. The characterization with H2-TPR, XRD, TEM-EDX, XANES, and EXAFS showed that the Ru species in the Ru-ReOx/SiO2 catalysts were completely reduced in the reaction conditions, while a part of Re species were also reduced to partially reduced monomeric species (Reδ+Ox) without Re-Re direct bond located on the surface of Ru metal particles. This ReOx-modified Ru metal surface probably works as the active sites. The excess Re species was reduced to large Re metal particles; however, these Re metal particles are not involved in the catalysis.