Sulfur Vacancy-Rich MoS2-Catalyzed Hydrodeoxygenation of Lactic Acid to Biopropionic Acid

The hydrodeoxygenation of lactic acid (LA) to propionic acid (PA) is of great significance for the conversion of biomass to valuable products; however, it remains a great challenge because of the trade-off between LA conversion and PA selectivity. Here, we prepared ultrathin MoS2 nanosheets containing rich sulfur vacancies by lithium exfoliation. With the increase of the lithium exfoliation time, sulfur vacancy in MoS2 is accordingly increased and LA adsorption and activation on sulfur vacancy is enhanced. Increasing sulfur vacancy lowered the valence band simultaneously and enhanced the dissociation of the H2 molecule. Density functional theory (DFT) calculations showed that the sulfur vacancy efficiently adsorbed α-C–OH of the LA molecule, weakened the C–O bond, and achieved selective conversion of LA to PA. At 215 °C, 92.4% of LA conversion and 95.8% PA selectivity were achieved over the sulfur vacancy-rich MoS2 nanosheets, which broke the activity–selectivity trade-off on hydrodeoxygenation of LA, and notably surpassed those of previously reported catalysts. More importantly, the activity of the catalyst remained almost unchanged after 8 cycles of reaction.