Sulfur-vacancy enriched MoS2@Carbon catalyst for multi-isomerization of xylose to lyxose, arabinose, ribose

Xylose, a primary sugar component of lignocellulosic biomass, is isomers or epimers of many high-value or rare added pentose. Traditional utilization of xylose predominantly involves dehydration to furfural or hydrogenation to xylitol. In this work, we prepared a carbon-supported molybdenum disulfide catalyst (MoS 2 @C) via a hydrothermal pretreatment, which facilities multi-step isomerization of xylose toward three high-value monosaccharides: lyxose, arabinose, and ribose. NH 3 -TPD and EPR characterizations proved that abundant MoS 2 and S vacancy sites are generated on carbon surface. S 2− species function as Lewis basic sites to stabilize key intermediates and facilitates hydrogen transfer. These dual-functional sites jointly promote a sequential isomerization and epimerization of xylose pathways. Multi-isomerization process of xylose was occurred by MoS 2 @C at 120°C. The isomers and epimers including lyxose (20.06%), arabinose (15.87%), and ribose (10.84%) were obtained in water. A multi-step reaction sequence includes sequential 1,2-hydrogen migration and carbon skeleton rearrangement, leading to synthesis of arabinose and ribose. Furthermore, a mechanistic hypothesis for multi-isomerization process of xylose by MoS 2 @Carbon catalyst was proposed, sulfur species promote hydrogen transfer and carbon rearrangement through nucleophilic attack and vacancy-assisted mechanisms. This study provides an effective catalyst design strategy and mechanistic basis for the conversion of xylose into high-value products using molybdenum disulfide.