Synergy of highly dispersed Pd and the oxygen-vacancy-promoted hydrodeoxygenation of lactic acid to propionic acid

Abstract

Enhancing the chemoselective C–O bond cleavage of lactic acid (LA) into propionic acid (PA) is a challenge. Herein, MoO_3−x and Pd/MoO_3−x were used as catalysts for the highly selective transformation of LA to PA. It was found that defects in MoO₃ as oxygen vacancies promoted the selectivity of PA, while the highly dispersed Pd species enhanced LA conversion. Impressively, the introduction of the highly dispersed Pd species accelerated the reaction rate of lactic acid conversion as the selectivity of PA remained the same or slightly increased. Defects and the introduction of Pd species could increase the electron density and narrow the band gap, which favored the reduction of LA to form PA. The Pd/MoO_3−x catalyst system could be reused almost five times without any deactivation, showing an excellent stability. This work provides an efficient strategy for the selective hydrodeoxygenation of LA to PA, with enhanced PA selectivity from 62.3% to 92.4% achieved by integrating surface defects with highly dispersed Pd species, which manifests great potential in the synthesis of biopropionic acid.