Recent achievements in CO2-assisted and CO2-catalyzed biomass conversion reactions
Carbon dioxide (CO2) has attracted great interest as a catalyst and reaction medium for the conversion of lignocellulosic biomass into value-added commodity chemicals. In this review, we focus on the use of CO2 in the pretreatment of raw biomass (for example, to isolate sugar monomers from the polymeric components of lignocellulosic biomass) and subsequent hydrolysis, as well as in different reactions to yield valuable platform chemicals from feedstocks derived from the raw biomass (e.g., dehydration, hydrogenation, and hydrodeoxygenation). In this respect, this review gives a summary of the enhancement in biomass conversion reactions achievable by utilizing CO2 and the roles of CO2 in this enhancement. Recent achievements (mostly in the past five years) in CO2-catalyzed and CO2-assisted biomass conversion reactions in various systems are highlighted. The prospect of transforming biomass feedstocks to platform chemicals using CO2 is also discussed, and important points and challenges facing further research into the CO2-driven conversion of biomass are highlighted.