Oxidation of 1,2-Propanediol to Carboxylic Acid Over Hydroxyapatite Nanorod-Supported Metallic Cu⁰ Nanoparticles

Hydroxyapatite nanorod-supported metallic Cu⁰ nanoparticle catalysts (Cu_x/HAP) were prepared by the wetness chemical reduction method. The metallic Cu⁰ nanoparticles were well dispersed on the surfaces of the HAP nanorods. The alkaline HAP nanorods inhibited the crystal growth of the metallic Cu0 nanoparticles. The HAP nanorods also retarded the oxidation of the metallic Cu⁰ nanoparticles. The Cu_x/HAP catalyst exhibited a higher catalytic activity for the oxidation of 1,2-propanediol with gaseous oxygen to lactic, acetic, and formic acids with the total selectivity of 70.3% even at a lower reaction temperature of 140 °C. The total selectivity of lactic, acetic, and formic acids reached 93.1% at a mild reaction temperature of 180 °C. However, the sole monometallic Cu⁰ nanoparticles or HAP nanorods had no catalytic activity for the oxidation of 1,2-propanediol. The metallic Cu⁰ nanoparticles and alkaline HAP nanorods in the Cu_x/HAP catalyst synergistically catalyzed the oxidation of 1,2-propanediol to carboxylic acid.