Ionic Liquid/Polyoxometalate Hybrid Catalyst with Tunable Functionalities for Boosting the Selectively Oxidative Transformation of Biobased Carbohydrates

Abstract

Biomass oxidation by synergic catalysis appears to be an efficient and sustainable approach for biomass valorization. Here we demonstrate the oxidation of glucose and its upstream biomass derivatives to glycolic acid (GA) under O2 in the presence of polyoxometalates (POM) hybridized with ionic liquids (ILs). Particularly, 61.0% selectivity of GA with 88.2% conversion and excellent carbon balance was obtained by [C2COOHMIM]4PMoV. The catalytic system was also applicable to the oxidation of raw lignocellulose. The IL-POM hybrids exhibited excellent recyclability. Time-dependent reaction, temperature-dependent NMR, and computational studies revealed that IL with carboxyl groups was supposed to suppress over-oxidation via stabilization of sugar intermediates, while the superiority of V1/IL-POM originated from the single-substituted V on the 4H site of POM. Thus, the adsorption of protonated glucose was more exothermic and kinetically favorable with the barrier of 0.41 eV. This strategy is expected to provide clues for efficient biomass conversion over multifunctional catalysts.

Ionic liquid-stabilized metal oxoclusters: from design to catalytic application

“…Similarly, IL [C 2 OHC 1 Im]Br (1-(hydroxyethyl)-3-methylimidazole bromide) was assembled with H 5 PV n Mo 12− n O 40 ( n = 1–3) to form POM–ILs with different V molar ratios. 108 Among them, [C 2 COOHC 1 Im] 4 PVMo 11 O 40 could oxidize glucose and its upstream biomass derivatives to glycolic acid under O 2 with 88% conversion and 61% selectivity, which is even applicable to the oxidation of raw lignocellulose.…”