Performances\nand Mechanisms of Dehydration of Levoglucosan\nto Levoglucosenone over Cesium Heterpolyacid Salts

Bio-based platform chemicals are\nof great significance to future\ngreen fine and commodity chemicals. This study reports the performances\nand mechanisms of solvothermal dehydration of levoglucosan (LGA),\nthe main precursor from noncatalytic pyrolysis of cellulose with a\nyield up to 80 wt %, to levoglucosenone (LGO) using cesium heteropolyacid\nsalts at the catalyst in DMSO solvent. Catalyst characterizations\nrevealed that cesium was well doped in the cubic of heteropolyacids,\nand the cesium doping ratio substantially influenced the catalytic\nperformances toward LGO. LGO yield first increased and then decreased\nwith the increase of cesium doping ratios, which is consistent with\nthe change trends of pore structures and Brønsted/Lewis acid\nsite ratios of the cesium heteropolyacid salts. LGO was obtained with\nthe maximum yield at 41.2% over Cs<sub>2</sub>H<sub>2</sub>SiW<sub>12</sub>O<sub>40</sub> compared to 39.2% over Cs<sub>2.5</sub>H<sub>0.5</sub>PW<sub>12</sub>O<sub>40</sub>. The catalyst can be regenerated\nby calcination without losing its catalytic performances. In addition,\ndensity functional theory calculation was used to reveal the mechanism\nfor LGO formation, and the rate-determining step was the first step\nof the dehydration reaction with the energy barrier of 166 kJ/mol.