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

Abstract

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.

Synergistic Production of Pyruvic Acid and Propionic Acid over Defect-Rich MoS2

“…Here, it is noted that the sulfur vacancy-rich MoS 2 can efficiently use the external hydrogen for LA hydrodeoxygenation, and the sulfur vacancy has been confirmed as an active center. 22 As for W-DR-MoS 2 , the external hydrogen cannot be efficiently used, indicating that the defect is not mainly caused by the sulfur vacancy. In this regard, the unique structure of W-DR-MoS 2 is crucial for achieving the coupling reaction of LA to generate PyA and PA.…”

“…Biomass and its derivatives are focused for converting to value-added chemicals due to the richness, cheapness, and sustainability. − For example, lactic acid (LA) , derived from corn and other biomass is selected as a bioplatform molecule, which can be converted to various chemicals such as acrylic acid, − acetaldehyde, − 2,3-pentanedione, − propionic acid (PA), − 1,2-propanediol, − pyruvic acid (PyA), − and polylactic acid. , Among LA conversions, production of PyA is achieved via oxidative dehydrogenation of LA, in which oxygen is inputted into the reaction system to consume the hydrogen of the LA molecule. As for oxidative dehydrogenation of LA, the related catalysts, reaction conditions, and catalytic performances in previous reports are depicted in Table S1.…”

“…In fact, the hydrodeoxygenation of LA to PA over the defected MoS 2 has been achieved at 215 °C, 22 which is accessible to the reaction temperature for LA oxidative dehydrogenation to PyA (200−230 °C). 30,32 Notably, the reported defective MoS 2 possesses the defected structure caused by sulfur vacancies, and the S/Mo ratio is evidenced at less than 2.…”

Sustainable production of bio-propionic acid: synergy between vacancy and thermoelectron in MoS2/MoO3 composite-enhanced hydrodeoxygenation of lactic acid

“…In recent years, environmental pollution, energy crisis, and resource scarcity have necessitated us to develop clean technology and use renewable resources. [1][2][3][4][5][6][7] Lactic acid (LA), as a biomass derivative, can be converted into numerous chemicals such as poly-lactic acid, 8-10 2,3-pentanedione, 11,12 1,2-propanediol, 13,14 pyruvic acid, 15,16 acrylic acid, 17,18 and propionic acid, [19][20][21] which have all attracted widespread interest due to their highly functional properties. For example, poly-lactic acid is produced largely instead of traditional plastics due to its excellent degradability.…”

Nickel Foam@Reduced Graphene Oxide–Carbon Nanotube Composite as an Efficient Solar Evaporator for Water Purification and Electricity Generation

“…Freshwater is a very scarce and precious resource for drinking, agriculture, and industry due to its low reserve and uneven distribution. − Considerable amount of freshwater is still polluted by organic dyes in the form of industrial effluents, agricultural runoff, and chemical spills, intensifying the freshwater resource crisis. , Although the earth is covered with water by 70%, around 96.5% is seawater. , It is therefore key to solving the shortage of freshwater that the separation-purification technology for freshwater from seawater and wastewater should be continuously and studiously developed in the world. Currently, two methods including thermal desalination and reverse osmosis technology have been widely utilized for the desalination of seawater. − As for thermal desalination, solar evaporation is viewed as a hopeful and potential technology due to using unlimited solar energy. − Based on the solar steam system, there are three aspects for photothermal materials to achieve highly efficient evaporation . First, novel materials must be preferentially developed, which have strong and broad-band absorption of sunlight to maximize the input of energy.…”