Highly Selective Oxidation of 1,2-Propanediol to Lactic Acid Using Pd Nanoparticles Supported on Functionalized Multi-Walled Carbon Nanotubes

1,2-Propanediol, with its highly functionalized molecular structure and abundant availability, serves as a viable feedstock for high-value chemicals. The oxidation of 1,2-propanediol can potentially yield lactic acid, an important commodity chemical. Herein, we report the catalytic oxidation of 1,2-propanediol in the presence of NaOH, using Pd nanoparticles (NPs) supported on various functionalized multi-walled carbon nanotubes (MWCNTs). Both single-factor experiments and the response surface methodology were employed to investigate the optimal operating parameters. It was found that nitrogen doping promotes strong metal–support interactions between the active components and the support. Under optimal reaction conditions (123 °C, 1.25 MPa O2 pressure, 4 h, and a NaOH/1,2-PDO molar ratio of 4.0), a high lactic acid yield of 68.3% was achieved using nitrogen-doped MWCNT-supported Pd nanoparticles as the catalyst. The selectivity for lactic acid decreased with increasing reaction time, temperature, NaOH/1,2-PDO molar ratio, and O2 pressure, while the conversion rate increased correspondingly. After five cycles, the conversion of 1,2-PDO slightly decreased to 76.2%, while the LA selectivity remained high at 84.9%. Additionally, the reaction pathway was further investigated, confirming the formation mechanism of lactic acid.