Performances and Mechanisms of Dehydration of Levoglucosan to Levoglucosenone over Cesium Heterpolyacid Salts

Abstract

Bio-based platform chemicals are of great significance to future green fine and commodity chemicals. This study reports the performances and mechanisms of solvothermal dehydration of levoglucosan (LGA), the main precursor from noncatalytic pyrolysis of cellulose with a yield up to 80 wt %, to levoglucosenone (LGO) using cesium heteropolyacid salts at the catalyst in DMSO solvent. Catalyst characterizations revealed that cesium was well doped in the cubic of heteropolyacids, and the cesium doping ratio substantially influenced the catalytic performances toward LGO. LGO yield first increased and then decreased with the increase of cesium doping ratios, which is consistent with the change trends of pore structures and Brønsted/Lewis acid site ratios of the cesium heteropolyacid salts. LGO was obtained with the maximum yield at 41.2% over Cs₂H₂SiW₁₂O₄₀ compared to 39.2% over Cs_2.5H_0.5PW₁₂O₄₀. The catalyst can be regenerated by calcination without losing its catalytic performances. In addition, density functional theory calculation was used to reveal the mechanism for LGO formation, and the rate-determining step was the first step of the dehydration reaction with the energy barrier of 166 kJ/mol.