First triple-functional polyoxometalate Cs10.6[H2.4GeNb13O41] for highly selective production of methyl levulinate directly from cellulose

Abstract

The first triple-functional polyoxometalate Cs10.6[H2.4GeNb13O41] (CsGeNb) was evaluated for its catalytic activity in production of methyl levulinate (ML) from biomass substrates in methanol. Higher conversion of cellulose (86.0%) and higher yield of ML (53.0%) were obtained under optimized reaction conditions of 0.1 g of cellulose, 0.04 mmol of catalyst, and 6 mL of methanol at 165 °C for 10 h, due to its mixed Bronsted acid sites, Lewis acid sites, and base sites, being measured for the first time. Reaction intermediates in methanolysis of fructose, glucose, and cellulose provided some insight into the reaction pathways, while methyl glucoside and methyl fructoside (MF) were key intermediates generated by Bronsted acid and Lewis acid or base sites. Assisted by microwave irradiation, the efficiency could be improved to 55.4% yield of ML within 3 h. Meanwhile, CsGeNb acted as a heterogeneous catalyst through six recycles without loss of activity.