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 MoS 2 nanosheets containing rich sulfur vacancies by lithium exfoliation. With the increase of the lithium exfoliation time, sulfur vacancy in MoS 2 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 H 2 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 MoS 2 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.