Catalytic transformations of cellulose and cellulose-derived carbohydrates into organic acids

• Catalytic conversions of cellulose to organic acid have been highlighted.
• Reaction involves multi-steps such as isomerization and retro-aldol fragmentation.
• Design of bifunctional or multifunctional catalytic systems is the key.

The efficient utilization of lignocellulosic biomass for the production of chemicals and fuels is of high significance from the viewpoint of establishing sustainable society. The selective transformation of cellulose, the main component of lignocellulosic biomass, into platform chemicals, which can be easily converted to various chemicals or fuels in the subsequent step, under mild conditions is a promising route. Organic acids such as levulinic acid, lactic acid, gluconic acid, and formic acid are important platform chemicals, and the conversion of carbohydrates into organic acids has attracted much attention in recent years. The present short review article highlights recent research progress in the development of new routes for the production of organic acids from cellulose or cellulose-derived carbohydrates. In particular, we will demonstrate that the bifunctional catalysts coupling the acid sites for the activation of the glycosidic bonds via hydrolysis and the metal nanoparticles for the oxidation of glucose intermediate show promising performances for the conversion of cellulose into gluconic acid in water in the presence of O2. The multifunctional catalysts or catalytic systems combining the abilities of isomerization and dehydration–rehydration or retro-aldol fragmentation can provide levulinic acid or lactic acid from cellulose under anaerobic conditions. The reaction mechanism in each case will also be discussed to gain insights into how the CC or CO bonds in cellulose or glucose are activated and cleaved and the roles of catalysts in these steps.

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