Solvent Effect in Hydrogenolysis of Xylitol over Bifunctional Ru/MnO/C Catalysts under Alkaline-Free Conditions

The hydrogenolysis reaction of biomass-derived xylitol to glycols and glycerol has been carried out in different water/organic solvent mixtures over a bifunctional Ru/MnO/C catalyst under alkaline-free conditions at 60 bar H2 and 200 °C. In pure water, the retro-aldol reaction takes place. However, decarbonylation and epimerization are the dominant reactions and produce C4 and C5 alditols, which limits the overall selectivity to glycols and glycerol (30%). When 90:10 vol % water/1,4-dioxane and water/2-PrOH solutions are used as solvents, the product distribution is very similar to the one in water. Meanwhile, in 90:10 vol % water/primary alcohol (ROH with R = Me, Et, nPr, nBu), the overall selectivity to glycols and glycerol is greatly enhanced (up to 70%), whereas the selectivity to C4 and C5 alditols is reduced. In a solution with a higher MeOH proportion of 20 vol %, the glycols are detected with even higher selectivity; however, some deactivation of the catalyst is observed. TGA analysis of the used ...