Lingqin Shen

Hydrothermal conversion of high-concentrated glycerol to lactic acid catalyzed by bimetallic CuAux (x = 0.01–0.04) nanoparticles and their reaction kinetics

Catalytic hydrothermal conversion of highly concentrated glycerol to lactic acid was investigated over bimetallic CuAux (x = 0.01–0.04) nanoparticle catalysts. The bimetallic CuAux nanoparticles were prepared by the wetness chemical reduction method and characterized by XRD, TEM, HRTEM, XPS, and atomic absorption spectrophotometry techniques. Metallic Cu and Au nanoparticles coalesced to form secondary bimetallic nanoparticles with an alloy trend. The bimetallic CuAux nanoparticles exhibited higher catalytic activity for the conversion of highly concentrated glycerol (2−3 mol L−1) to lactic acid than both sole monometallic Cu and Au nanoparticles, probably due to the alloying tendency between the metallic Cu and Au nanoparticles. When the reaction was carried out with the initial glycerol and NaOH concentrations of 3.0 and 3.3 mol L−1 at 200 °C for 2 h, the yields of lactic acid over the bimetallic CuAu2, CuAu3, and CuAu4 catalysts were above 83% and the formation rate of lactic acid was more than 0.17 mol gcat−1 h−1. The carbon balance values ranged from 89.2% to 92.9%. The reaction activation energies for glycerol conversion over the bimetallic CuAu1, CuAu2, CuAu3, and CuAu4 catalysts were 64.0, 53.4, 46.8, and 36.9 kJ mol−1, respectively. The hydrothermal conversion of high-concentrated glycerol to lactic acid catalyzed by the bimetallic CuAux nanoparticles is an alternative to the conventional fermentation process starting from carbohydrate.

Hydrogenation of 3-nitro-4-methoxy-acetylaniline with H2 to 3-amino-4-methoxy-acetylaniline catalyzed by bimetallic copper/nickel nanoparticles

Monometallic Cu, monometallic Ni, and bimetallic CuxNiy nanoparticles were prepared by a wet chemical reduction method. A Cu–Ni alloy phase was formed in the bimetallic CuxNiy nanoparticles. The bimetallic CuxNiy nanoparticles exhibited higher catalytic activity for the hydrogenation of 3-nitro-4-methoxy-acetylaniline (NMA) to 3-amino-4-methoxy-acetylaniline (AMA) with H2 than the sole Ni nanoparticles, which was ascribed to the effect of the Cu–Ni alloy phase. When the reaction was catalyzed over the bimetallic Cu0.7Ni0.3 catalyst at 140 °C for 2 h, the AMA selectivity was 99.4% when the NMA conversion was 95.7%. The reaction activation energy for NMA hydrogenation was 19.74 kJ mol−1.

Comparative analysis of oxidative mechanisms of phloroglucinol and dieckol by electrochemical, spectroscopic, cellular and computational methods

Numerous studies have been carried out on the redox activities of phenolic compounds from terrestrial plants, however, the redox pathway of phlorotannins, a type of marine algae-derived polyphenol, is far from clear. In the present study, the redox mechanisms of two phlorotannins, phloroglucinol (PL) and dieckol (DL), were comparatively scrutinized. Differential pulse voltammetry was conducted in the pH range 2.0–12.0 to determine the acid–base dissociation constant (pKa) and the number of electrons and protons involved in the redox reactions of two phlorotannins. Cyclic voltammetry was applied to obtain the heterogeneous electron transfer rate constant (k0). By means of computational calculation, UV-vis spectroscopy, and electrochemical analysis, it is proposed that PL oxidation in the whole pH range undergoes two steps which are dominated by proton-coupled electron transfer (PCET) (pH ≤ 9) and sequential proton-loss electron transfer (SPLET) mechanisms (pH > 9), respectively. In contrast, the multiple steps taking place in the DL oxidation process rely on PCET (pH ≤ 5), mixed SPLET/PCET (5 10) mechanisms, respectively. Also, the lower proton affinity and ionization potential values of DL, which are attributed to its conjugated Cπ–O–Cπ moieties, lead to relatively higher redox activity as compared to PL in various chemical and cellular models. These findings may provide useful insights into the oxidative conversion of phlorotannins in their biological and chemical processes.

Selective Oxidation of 1,2-Propanediol to Carboxylic Acids Catalyzed by Copper Nanoparticles

Copper nanoparticles with different particle sizes were prepared by a wet chemical reduction method in the presence of organic modifiers, such as citric acid (CA), hexadecyl trimethyl ammonium bromide, Tween-80 (Tween), and polyethylene glycol 6000. Selective oxidation of sustainable 1,2-propanediol with O2 to high-valued lactic, formic, and acetic acids catalyzed by the copper nanoparticles in an alkaline medium was investigated. The small-sized CuCA nanoparticles with the average particle size of 15.2 nm favored the formation of acetic and formic acids while the CuTween nanoparticles with the average particle size of 26.9 nm were beneficial to the formation of lactic acid. The size effect of copper nanoparticles on the catalytic oxidation of 1,2-propanediol to the carboxylic acids was obvious.