Fabrication of trifunctional polyoxometalate hybrids for cascade conversion of glycerol targeting to lactic acid
Lactic acid (LA) has been produced from cascade conversion being achieved under noble-metal and base free. Amino-acid functionalized polyoxometalates (POMs) LyxH3-xPMo12O40, (abbreviated as LyxH3-xPMo, x = 1-3, Ly = C6H15O2N2, lysine) with triple active sites were fabricated, which presented 87 % LA yield at 96 % glycerol conversion under mild reaction conditions, being attributed to the combination of basic sites, Brønsted acidic sites, suitable redox ability, and special microenvironment. Mechanism study showed that upon LyxH3-xPMo, glycerol was oxidized firstly to glyceraldehydes (GCA) and dihydroxyacetone (DHA) by redox sites, then the existence of basic sites led to the dehydration of DHA and GCA to pyruvaldehyde (PRA), and finally the Brønsted acid sites resulted to the hydration of PRA to LA. Meanwhile, the activation energies for different POMs were calculated using Arrhenius plots to confirm the effect of Ly2H1PMo for its highest efficiency. Such hybrids acted as heterogeneous catalysts with long duriation and stability.