Selective oxidation of 1,2-propanediol to lactic acid catalyzed by nanosized Mg(OH)2-supported bimetallic Au–Pd catalysts

•Oversupplied 1,2-propanediol was efficiently converted to high valuable lactic acid.•Bimetallic Au–Pd/Mg(OH)2 catalysts were prepared by the sol-immobilization method.•Au and Pd nanoparticles were coalesced together to form secondary nanoparticles.•Au and Pd nanoparticles synergistically catalyzed the oxidation of 1,2-propaneidol.•A power function type kinetic model well fitted the experimental data.

1,2-Propanediol co-produced in the dimethyl carbonate production is oversupplied in market. 1,2-Propanediol can also be facilely produced starting from glycerol, which is oversupplied in the biodiesel production. Catalytic conversion of low-valued 1,2-propanediol to high-valued and environmental benign lactic acid was investigated under mild reaction conditions over Au–Pd/Mg(OH)2 catalysts in our present work. The Au–Pd/Mg(OH)2 catalysts were prepared by the sol-immobilization method and characterized by XRD, SEM, HRTEM, UV–vis DRS, and O2-TPD techniques. Small-sized Au and Pd nanoparticles were coalesced together to form secondary nanoparticles, which were well dispersed on the surfaces of Mg(OH)2 nanoslices. The Au and Pd nanoparticles synergistically catalyzed the oxidation of 1,2-propanediol with O2 to lactic acid in an alkaline solution. When the catalytic oxidation of 1,2-propanediol was carried out over Au0.75Pd0.25/Mg(OH)2 catalyst at 60 °C for 240 min, the lactic acid selectivity of 88% was obtained at the 1,2-propanediol conversion of 97.5%. A power-function type reaction kinetic model well fitted the experimental data, r=−dCP/dt=kCP0.8PO21.4Wcat1.0. The reaction activation energy was 64 kJ mol−1.

Graphical abstract1,2-Propanediol can be efficiently oxidized to lactic acid over Au–Pd/Mg(OH)2 catalysts.Figure optionsDownload full-size imageDownload high-quality image (126 K)Download as PowerPoint slide