Xylitol Hydrogenolysis over Ruthenium‐Based Catalysts: Effect of Alkaline Promoters and Basic Oxide‐Modified Catalysts

The aqueous‐phase hydrogenolysis of xylitol into glycols over Ru/C was performed in the presence and absence of a wide range of concentrations of Ca(OH) 2 to investigate the reaction pathway. Without base, epimerization and cascade decarbonylation were the predominant reactions with high selectivities to C 5 and C 4 alditols and light alkanes at full conversion. Glycol production was obtained by the addition of Ca(OH) 2 to promote the retro‐aldol reaction. It competed with reactions without base and became the main reaction for a OH − / xylitol molar ratio R mol (OH/xylitol) of 0.13, and high selectivities to glycols (56 %) and glycerol (16 %) were observed. However, lactate was a byproduct at up to 27 % with a high base amount ( R mol (OH/xylitol)=0.68). Bifunctional Ru/metal oxide/C catalysts (metal: Zn, Sn, Mn, Sr, W) were synthesized and were able to cleave the C−C bond into glycols without a base promoter. The 3.1 wt %Ru/MnO(4.5 %)/C catalyst was the most active (220 h −1 ) with reasonable selectivity to glycols (22 %) and glycerol (10 %) and a low production of lactate (<1 %). Nevertheless, metal oxide leaching of the catalyst was observed likely because of the production of traces of lactate.