Alkali-Free Oxidation of 1,2-Propanediol to Lactic Acid over Intermetallic Cu1Pt Compounds

Abstract

Polylactic acid (PLA) plastics are the most popular biodegradable and biocompatible materials; however, their monomer, lactic acid (LA), is currently produced via an inefficient fermentation process. Herein, activated carbon-supported Pt–Cu intermetallic compounds were synthesized and utilized in the selective oxidation of 1,2-propanediol (1,2-PDO) toward LA without the participation of homogeneous alkali or a basic support. It was found that rhombohedral intermetallic Cu₁Pt compounds exhibited excellent performance and the calculated turnover frequency of each surface Pt atom reached 10 049 h^–1. The yield of free LA reached 64.6% with a complete conversion of 1,2-PDO at 100 °C within 2 h. Diverse characterization and DFT calculations revealed that Pt–Cu intermetallic compounds were active for the adsorption and/or activation of molecular oxygen and 1,2-PDO. Raman analysis of adsorbed 1,2-PDO further disclosed that 1,2-PDO contacted with rhombohedral intermetallic Cu₁Pt compounds strongly, and then the oxidation of the terminal hydroxyl group was performed preferentially, which promoted the formation of LA.