Selective oxidation of 1,2-propanediol to lactic acid catalyzed by hydroxylapatite nanorod-supported Au/Pd bimetallic nanoparticles under atmospheric pressure

• Oversupplied 1,2-propanediol was efficiently converted to high-valued lactic acid.
• Bimetallic Au–Pd/HAP catalysts were prepared by the sol-immobilization method.
• Electrons transfer from Pd to Au atoms occurred due to their coalescence.
• Au and Pd nanoparticles synergistically catalyzed the oxidation of 1,2-propanediol.
• Kinetics on bimetallic catalyst was different from that on monometallic catalyst.

Catalytic oxidation of oversupplied and low-valued 1,2-propanediol with O2 to high-valued and environmental benign lactic acid was investigated over hydroxylapatite nanorod-supported Au/Pd bimetallic nanoparticles (Au–Pd/HAP) under atmospheric pressure. The Au–Pd/HAP catalysts were prepared by the sol-immobilization method and characterized by XRD, HRTEM, XPS, and CO2-TPD techniques. Small-sized Au and Pd nanoparticles coalesced to form secondary bimetallic nanoparticles and well dispersed on the surfaces of HAP nanorods. When the catalytic oxidation of 1,2-propanediol was carried out over Au0.75Pd0.25/HAP catalyst at 353 K for 5 h in an alkaline solution, the lactic acid selectivity was 97.1% at the 1,2-propanediol conversion of 96.6%. The Au and Pd nanoparticles synergistically catalyzed the oxidation of 1,2-propanediol to lactic acid in an alkaline solution probably due to the electron transfer between Au and Pd atoms. The kinetics for the oxidation of 1,2-propanediol over Au–Pd/HAP bimetallic catalysts were different from those over Au/HAP and Pd/HAP monometallic catalysts.

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