Cu, N codoped carbon nanosheets encapsulating ultrasmall Cu nanoparticles for enhancing selective 1,2-propanediol oxidation

In the selective oxidation of biomass-based 1,2-propanediol (PDO) with oxygen as the terminal oxidant, it is challenging to improve the lactic acid (LA) selectivity for nonnoble metal nanoparticles (NPs) due to their limited oxygen reduction rate and easy C–C cleavage. Given the high economic feasibility of nonnoble metals, i.e., Cu, in this work, copper and nitrogen codoped porous carbon nanosheets encapsulating ultrafine Cu nanoparticles (Cu@Cu-N-C) were developed to realize highly selective of PDO oxidation to LA. The carbon-encapsulated ultrasmall Cu0 NPs in Cu@Cu-N-C have high PDO dehydrogenation activity while N-coordinated Cu (Cu-N) sites are responsible for the high oxygen reduction efficacy. Therefore, the performance of catalytic PDO conversion to LA is optimized by a proposed pathway of PDO → hydroxylacetone → lactaldehyde → LA. Specifically, the enhanced LA selectivity is 88.5%, and the PDO conversion is up to 75.1% in an O2-pressurized reaction system (1.0 MPa O2), superior to other Cu-based catalysts, while in a milder nonpressurized system (O2 flow rate of 100 mL min−1), a remarkable LA selectivity (94.2%) is obtained with 39.8% PDO conversion, 2.2 times higher than that of supported Au nanoparticles (1% Au/C). Moreover, carbon encapsulation offers Cu@Cu-N-C with strong leaching resistance for better recycling.