Designation of highly efficient catalysts for one pot conversion of glycerol to lactic acid

Production of lactic acid from glycerol is a cascade catalytic procedure using multifunctional catalysts combined with oxidative and acidic catalytic sites. Therefore, a series of silver-exchanged phosphomolybdic acid catalysts (Ag(x)H(3−x)PMo(12)O(40), x = 1 ~ 3, abbreviated as Ag(x)PMo) was designed and applied in glycerol oxidation with O(2) as an oxidant to produce lactic acid (LA) without adding any base. Among all, total silver exchanged phosphomolybdic acid (Ag(3)PMo) was found to be the most active one with LA selectivity of 93% at 99% conversion under mild conditions of 5 h at 60 °C. The exceptionally high efficiency was contributed to the generation of strong Lewis acid sites, enhanced redox potentials and water-tolerance. More importantly, Ag(3)PMo was tolerant in crude glycerol from biodiesel production. And the reaction mechanism was also discussed. Meanwhile, Ag(3)PMo acted as a heterogeneous catalyst for 12 recycles without loss of activity.