Direct conversion of carbohydrates to γ-valerolactone facilitated by a solvent effect

The carbohydrates (cellulose, starch, inulin, maltose, sucrose, glucose and fructose) were converted efficiently into gamma-valerolactone (GVL) over combined H3PW12O40 and Ru/TiO2 catalysts under mild conditions. The basicity of oxygen-containing solvents had a remarkable effect on the acid strength of H3PW12O40, which resulted in great variation in the yield of GVL. H3PW12O40 was more effective in 20 vol% water/gamma-butyrolactone than in pure water and other water/organic solvents (methanol, ethanol and 1,4-dioxane). GVL yields for inulin and fructose reached 70.5 mol% and 67.6 mol% respectively. Meanwhile, a GVL yield of 40.5 mol% was achieved for cellulose. In addition, a practical method for catalyst recycling and GVL separation was developed by adding sugar into the reaction mixture. H3PW12O40 and Ru/TiO2 maintained their activity after three recycling runs.