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The design of an "H"‐shaped reactor has been studied to satisfy the possibility of using a triphasic medium to transform d‐glucose into 5‐hydroxymethylfurfural (HMF) by a hybrid catalytic process using an immobilized glucose isomerase, allowing the isomerization of D‐glucose to d‐fructose, and a heterogeneous chemical catalyst to catalyze the dehydration of d‐fructose to HMF. The various parameters influencing the transport of d‐fructose within the reactor were studied, namely the difference in pH between the two aqueous phases, the agitation and the quantity of 3,4‐DCPBA/Aliquat336® used to extract and transport continuously the d‐fructose. The pH discrepancy, which must be between 5.0 and 5.5, turns out to be the real driving force behind the extraction of D‐fructose. The D‐Fru/3,4‐DCPBA molar ratio of 1/0.25 allowed the transport of more than 80 % of the D‐fructose initially present and shows that the same molecule of 3,4‐DCPBA is involved at least twice in the transport of D‐fructose and that the 3,4‐DCPBA/Aliquat336® couple performs a turnover within the organic phase. Finally, a HMF production yield of 30.9 % and an isomerization yield of 79.1 % were obtained, illustrating the shift in the isomerization equilibrium made possible by a D‐fructose extraction yield of 96.8 %. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide NAD(P)H is a prolific cofactor in oxidoreductases biochemistry, but its high cost and the stoichiometric amounts motivates significant research for establishing efficient solutions for regenerating NAD(P)H from NAD(P)+. This study presents nanoparticles of gold/layered double hydroxides (AuNPs/LDH) as nanoplatforms with highly efficient photocatalytic response for solar‐light promoted NADH regeneration. The novel photocatalysts are obtained via self‐assembling of ZnAlLDH and AuNPs by using the manifestation of the "structural memory" of the anionic clay in gold salt solution. The chemical composition, structural, optical and nanotextural features of AuNPs/LDH have been assessed by transmission electron microscopy (TEM), energy dispersive X‐Ray Spectroscopy (EDX), powder X‐ray diffraction (XRD), and UV‐Vis Spectroscopy (UV‐Vis). It was found that, at pH 8 and in the presence of flavin mononucleotide (FMN) as a mediator and using water as an electron donor, the regeneration the NADH under solar light is defined by a rate of 20.5 μM/h. Furthermore, the regenerated NADH cofactor is tested in presence of Horseradish Peroxidase (HRP) enzyme to promote the hydrogen peroxide reduction. [ABSTRACT FROM AUTHOR]

BACKGROUND Unlike Pt and Au, Ag has recently been reported to be an active catalyst for the synthesis of glycolic acid from the liquid phase oxidation of glycerol ( GLY). In order to provide comparative information about the kinetics of this reaction using Pt, Au or Ag, a kinetic model was derived for each catalyst (Ag/, Pt/ and Au/ Al2O3), using the experimental results obtained at different temperatures. RESULTS A power-law kinetic model was proposed for each catalyst, which included the Khang-Levenspiel model to evaluate potential catalyst deactivation. All three kinetic models predicted well the experimental concentrations. Pt/ and Au/ Al2O3 showed higher kinetic rate constants, the highest being that of the production of glyceric acid. The lower the metal particle size, the higher the kinetic rate constant of the production of glyceric acid was. Deactivation parameters played an important role in the model of Pt/ Al2O3, so that Au/ and Ag/ Al2O3 seemed to be more resistant to deactivation. CONCLUSIONS This work reports the first kinetic model for the oxidation of GLY using an Ag-based catalyst. It showed a noticeable kinetic rate constant for the production of glycolic acid. The activation energies obtained were in the range 48-97 kJ mol−1. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Through biomass valorization, sugars can become a major carbon resource for the production of fuels and chemicals by using catalysis. Hybrid catalysis, a direct combination of biocatalysis and chemocatalysis, may yield innovative solutions. 5-Hydroxymethylfurfural (5-HMF) is a platform molecule derived from glucose, for which fructose is a key intermediate. To overcome the thermodynamic enzymatic equilibrium between glucose and fructose, two methodologies based on hybrid catalysis are described herein. In the first method, the glucose isomerase and fructose-to-5-HMF dehydration chemocatalysts are simultaneously implemented in a multiphasic way to imply the complexation and transport of fructose. The second method proposes a route through sorbitol, obtained by the hydrogenation of glucose. Sorbitol is then enzymatically converted into fructose, whereas regeneration of the cofactor is performed in situ with an organometallic complex as a chemocatalyst. [ABSTRACT FROM AUTHOR]

In the present study, kinetic analysis and modelling of the glycerol oxidation reaction over unsupported Au particles were performed. The reaction pathways, which were determined in agreement with the experimental results, comprise two types of reactions, namely oxidation and C-C cleavage. A homogeneous catalytic reaction model was proposed by considering the occurrence of the non-catalytic reaction, the effect of the temperature, as well as NaOH and catalyst concentrations. The proposed kinetic model could adequately describe the data. The reaction under basic conditions but in the absence of a catalyst favoured the formation of C-C cleavage products (glycolic and formic acids), while in the presence of unsupported Au particles the oxidation to glyceric acid and the direct oxidation of glycerol to formic acid were promoted. Finally, it was observed that the formation of tartronic acid was not promoted by the catalyst and followed the non-catalytic route. Practical applications: The building of a kinetic model for glycerol oxidation in liquid phase using gold-based catalyst allows to better understand the mechanism leading to oxidation and C-C cleavage responsible to some change of selectivities in the process. The model parameters obtained in this study would be used to scale an industrial unit in a reactor modeling. The present work describes a homogeneous catalytic kinetic model of the glycerol (GLY) oxidation, by using unsupported Au nanoparticles. The proposed model includes the occurrence of the non-catalysed reaction in basic media and the effect of the reaction temperature, NaOH/GLY ratio and GLY/Au ratio. The model predicted well the experimental results. Unsupported Au nanoparticles were selective to glyceric acid and C-C cleavage products like formic and glycolic acids. [ABSTRACT FROM AUTHOR]

A quasi-homogeneous solution of gold nanoparticles prepared by the Turkevich method was used as an unconventional catalyst in the oxidation of glycerol (GLY) in the liquid phase. The highest obtained conversion was 100 % after 3 h of reaction at 100 °C under an oxygen atmosphere (5 bar). The main products were glyceric, glycolic, formic, tartronic, and oxalic acid with selectivities of 28, 36, 25, 9, and 2 %, respectively. Traces of hydroxypyruvic and acetic acid were also detected (combined selectivities below 1 %). To elucidate the reaction mechanism and specify the role of gold nanoparticles in the oxidation process, a series of experiments under various reaction conditions were carried out. The effect of reaction temperature, oxygen pressure, gold concentration, and GLY/base molar ratio was investigated. All catalytic results were systematically compared to the corresponding noncatalytic base-induced transformations (blank tests). Such an approach allowed us to separate and clarify the respective driving parameters for the transformation of GLY (presence of a base and activity of the gold catalyst). The reaction mechanism comprised a series of oxidation and CC cleavage reactions, whereas additional oxidation-reduction reactions (of the Cannizzaro type) could also occur in the presence of the base. [ABSTRACT FROM AUTHOR]

The cover image, by José Antonio Díaz et al., is based on the Research Article Kinetic modelling of the glycerol oxidation in the liquid phase: comparison of Pt, Au and Ag AS active phases, DOI: . Photo Credit: CNRS Photothèque / Cyril FRESILLON. [ABSTRACT FROM AUTHOR]