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

Abstract

This work reported the coupling reaction of lactic acid (LA) to produce pyruvic acid (PyA) and propionic acid (PA) simultaneously over defect-rich MoS 2 nanosheets. The process intensification linked to dehydrogenation of LA and hydrodeoxygenation of LA brings about the advantage that is not supplied additionally with oxygen and hydrogen, achieving a green and safe route. The defected structure is characterized by highresolution transmission electron microscopy (HRTEM) and positron annihilation lifetime spectroscopy (PALS), which promotes the catalytic performance for the coupling reaction of LA. To fully understand the importance of the defected structure, the catalytic performance of defect-free MoS 2 is also evaluated. It is found that the PyA/PA ratio is less than 1 and acetaldehyde selectivity is relatively high, suggesting that the produced hydrogen from the dehydrogenation of LA is insufficient for hydrodeoxygenation of LA over defect-free MoS 2 , and the difference of hydrogen comes from the side reactions of decarbonylation and decarboxylation of LA. Unlike the defect-free MoS 2 , the dehydrogenation of LA over the defect-rich MoS 2 can provide sufficient hydrogen for hydrodeoxygenation of LA, so that the side reactions are drastically weakened. The widened interplanar spacing can fully expose the defect and the LA reactant molecule is more accessible to defective sites, which can endow a better catalytic activity. Surface hydrophilicity can improve adsorption and transfer, and better activity is observed over the defect-rich MoS 2 and widened defect-rich MoS 2 . At 300 °C and a LA LHSV of 2.6 h −1 under an inert atmosphere, the catalyst offers a satisfactory total selectivity to pyruvic acid and propionic acid of about 85%, and the molar ratio of pyruvic acid/propionic acid is 1.1.

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

“…Lactic acid (LA) is usually selected as a model compound for conversion into other chemicals via deoxygenation. 6,7 For example, propionic acid (PA), 8,9 acrylic acid, [10][11][12] 2,3-pentanedione, 13,14 acetaldehyde, 15 and 1,2propanediol 16,17 can be obtained via the catalytic conversion of lactic acid. With the current huge demand for bio-based preservatives, the production of propionic acid from biolactic acid has displayed tremendous potential.…”

Boosted oxidative dehydrogenation of lactic acid into pyruvic acid on polyvinylpyrrolidone modified Fe2O3

“…1–3 However, this route has always faced low selectivity to PA since the LA molecule contains both hydroxyl and carboxyl groups, which can be converted into a variety of chemical products such as acrylic acid, 4–6 acetaldehyde, 7,8 2,3-pentanedione, 9,10 1,2-propanediol, 11,12 and propionic acid. 13–17…”

“…24,25 For example, oxygen vacancies in TiO 2 and ZrO 2 can drastically enhance the catalytic performance of the WGS reaction (water–gas shift reaction). 22,23 Similarly, a sulfur vacancy in MoS 2 is observed to enhance the catalytic performance of the HDO reaction (hydrodeoxygenation reaction) of p -methylphenol 26 and LA 15,16 into methylbenzene and propionic acid, respectively. According to XPS spectra of O 1s, the PVP-modified RC has richer oxygen vacancies than RC, suggesting that unsaturated Fe atoms in the PVP-modified RC are richer than in RC accordingly.…”

“…[1][2][3] However, this route has always faced low selectivity to PA since the LA molecule contains both hydroxyl and carboxyl groups, which can be converted into a variety of chemical products such as acrylic acid, 4-6 acetaldehyde, 7,8 2,3-pentanedione, 9,10 1,2propanediol, 11,12 and propionic acid. [13][14][15][16][17] To enhance the selectivity of PA, several measures including content and crystal face regulation were used to construct catalysts for improving the adsorption of LA, and surfacecatalytic reaction. FePO 4 catalysts were first evaluated, and the M phase composed of Fe 2+ and Fe 3+ achieved 60% LA conversion and 62% PA selectivity.…”