Highly Selective Oxidation of Ethyl Lactate to EthylPyruvate Catalyzed by Mesoporous Vanadia–Titania

摘要

The direct oxidative dehydrogenation of lactates with molecular oxygen is a “greener” alternative for producing pyruvates. Here we report a one-pot synthesis of mesoporous vanadia–titania (VTN), acting as highly efficient and recyclable catalysts for the conversion of ethyl lactate to ethyl pyruvate. These VTN materials feature high surface areas, large pore volumes, and high densities of isolated vanadium species, which can expose the active sites and facilitate the mass transport. In comparison to homogeneous vanadium complexes and VOx/TiO2 prepared by impregnation, the meso-VTN catalysts showed superior activity, selectivity, and stability in the aerobic oxidation of ethyl lactate to ethyl pyruvate. We also studied the effect of various vanadium precursors, which revealed that the vanadium-induced phase transition of meso-VTN from anatase to rutile depends strongly on the vanadium precursor. NH4VO3 was found to be the optimal vanadium precursor, forming more monomeric vanadium species. V⁴⁺ as the major valence state was incorporated into the latticeof the NH4VO3-derived VTN material, yieldingmore V⁴⁺–O–Ti bonds in the anatase-dominantstructure. In situ DRIFT spectroscopy and density functional theorycalculations show that V⁴⁺–O–Ti bonds areresponsible for the dissociation of ethyl lactate over VTN catalystsand for further activation of the deprotonation of β-hydrogen.Molecular oxygen can replenish the surface oxygen to regenerate theV⁴⁺–O–Ti bonds.