High production of levulinic acid from cellulosic feedstocks being catalyzed by temperature-responsive transition metal substituted heteropolyacids

Heteropolyacids (HPAs), super strong Brønsted acid solids, were recently reported to achieve cellulose conversion with high efficiency. To achieve higher levulinic acid (LA) yield, a series of Lewis metal-substituent phosphotungstic acids H n PW 11 LO 39 (HPWL, L = Cu II , Sn IV , Cr III , Zn II , Fe III ; L = Ti IV , Zr IV , oxygen is 40) were used as catalysts in polysaccharides conversion. Identification of the reaction intermediates and products provided some information for cellulose conversion pathway. H 5 PW 11 TiO 40 (Brønsted/Lewis acid = 2.84:1) was found to be most active with highest cellulose conversion giving highest glucose yield in water and highest LA yield in methyl isobutyl ketone (MIBK)/water. In addition, for overcome the drawbacks in mass transferring and separation, the temperature-responsive catalyst of HOCH 2 CH 2 N(CH 3 ) 3 H 4 PW 11 TiO 40 (ChH 4 PWTi) was prepared giving as high as 76.1% LA yield at 93.8% cellulose conversion more than those by HPWTi (65.6%, 90.5%). Also, ChH 4 PWTi was obtained 93.7% conversion and 70.9% yield at microwave. ChH 4 PWTi also presented higher feedstocks - tolerance to mono-, di- or polysaccharides and even lignocellulose (corn straw, pinewood, husk of xanthoceras, coconut shell) to LA. As highest as 33.0% LA yield at 68.0% conversion was obtained by ChH 4 PWTi from husk of xanthoceras under mild conditions. ChH 4 PWTi could be recycled 12 times without significant loss of activity, which showed longer duration.