Probing the Synergistic Effects of Au, Pd and CeO₂ Facilitating the Au-Pd/CeO₂-Catalyzed Selective Oxidation of 1,2-Propanediol to Lactic Acid

CeO₂-supported Au and Pd nanocatalyst (Au-Pd/CeO₂) was developed and used in the oxidation of 1,2-propanediol (1,2-PDO). Notably, by tuning catalyst composition and reaction conditions, the product selectivity could be well controlled to produce lactic acid (LA) majorly, which was one of the top twelve bio-based platform molecules with very broad application scopes. The catalyst with Pd/(Au + Pd) molar ratio at 0.25 should be the preferable catalyst was screened out to be preferable, affording LA in 92.0% selectivity, while 88.0% of 1,2-PDO was converted under mild reaction conditions (0.3 MPa of O₂ at 80 °C for 3 h). The superior catalytic activities of Au-Pd/CeO₂ probably attributed to the strong interactions between Au and Pd nano particles (NPs), as being reflected by High resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectra (XPS) characterizations. Moreover, strong interactions between Au and Pd NPs making it easy to generate active oxygen species. Superoxide radicals can oxide the first hydroxyl group of 1,2-PDO to carboxyl group, while H₂O₂ can easy caused C-C bond breaks and generate unwanted by-products.