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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]

The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H2 but with a change in structure and chemical ordering. [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]

Notably available from the cellulose contained in lignocellulosic biomass, glucose is a highly attractive substrate for eco-efficient processes towards high-value chemicals. A recent strategy for biomass valorization consists on combining biocatalysis and chemocatalysis to realise the so-called chemo-enzymatic or hybrid catalysis. Optimisation of the glucose conversion to 5-hydroxymethylfurfural (HMF) is the object of many research efforts. HMF can be produced by chemo-catalyzed fructose dehydration, while fructose can be selectively obtained from enzymatic glucose isomerization. Despite recent advances in HMF production, a fully integrated efficient process remains to be demonstrated. Our innovative approach consists on a continuous process involving enzymatic glucose isomerization, selective arylboronic-acid mediated fructose complexation/transportation, and chemical fructose dehydration to HMF. We designed a novel reactor based on two aqueous phases dynamically connected via an organic liquid membrane, which enabled substantial enhancement of glucose conversion (70%) while avoiding intermediate separation steps. Furthermore, in the as-combined steps, the use of an immobilized glucose isomerase and an acidic resin facilitates catalyst recycling. [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]

Time-dependent SERS intensity recorded over a drop-coated coffee-ring pattern of p-MBA with gold colloids was investigated as a function of the specific laser power applied. Pure electromagnetic enhancement produced stochastic intensity variations of the whole SER spectra, which were mainly correlated with evolutions of the background intensity. Besides long-term, non-reversible spectral changes caused by plasmon-induced decarboxylation of p-MBA, transient original spectral profiles showing additional lines were also observed as the specific power reached 5.5 × 104 W cm−2. An unprecedented qualitative and quantitative study of SERS intensity variations based on the complementary use of both extreme deviation and cross-correlation statistics is provided, which resulted in an improved understanding of SERS mechanisms. More precisely, cross-correlation analysis made it possible to follow the evolution of groups of modes assigned to one species or sharing the same symmetry while so-called individual events denote particular resonance structures, whose occurrence was tentatively related to a photo-thermally activated motion of the gold nanostructures. [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]

Due to its three hydroxyl groups, glycerol is a potential starting material for various high value fine chemicals such as dihydroxyacetone, tartronic acid and mesoxalic acid. The corresponding oxidation reactions are catalysed by various metals such as palladium, platinum, bismuth or gold. Nevertheless, the selectivity not only depends on the type of the active phase, but is also influenced by numerous parameters such as the metal particles size, the pore size of the support and the pH of the reaction medium. This review not only describes the recent developments in the field of research for new catalysts but also spotlights the role of the reaction conditions as well as the possible transport limitations in this tri-phasic system. Furthermore, an economical analysis of some processes is given, which shows that this is realistic to envision sustainable production of, e.g., dihydroxyacetone. [ABSTRACT FROM AUTHOR]

Chemisorption of propene and propane was studied in a pulse reactor over a series of cobalt silica-supported Fischer-Tropsch catalysts. It was shown that interaction of propene with cobalt metal particles resulted in its rapid autohydrogenation. The reaction consists in a part of the propene being dehydrogenated to surface carbon and CH x chemisorbed species; hydrogen atoms released in the course of propene dehydrogenation are then involved in hydrogenation of remaining propene molecules to propane at 323-423 K or in propene hydrogenolysis to methane and ethane at temperatures higher than 423 K. The catalyst characterization suggests that propene chemisorption over cobalt catalysts is primarily a function of the density of cobalt surface metal sites. A correlation between propene chemisorption and Fischer-Tropsch reaction rate was observed over a series of cobalt silica-supported catalysts. No propane chemisorption was observed at 323-373 K over cobalt silica-supported catalysts. Propane autohydrogenolysis was found to proceed at higher temperatures, with methane being the major product of this reaction over cobalt catalysts. Hydrogen for propane autohydrogenolysis is probably provided by adsorbed CH x species formed via propane dehydrogenation. Propene and propane chemisorption is dramatically reduced upon the catalyst exposure to synthesis gas (H2/CO = 2) at 323-473 K. Our results suggest that cobalt metal particles are probably completely covered by carbon monoxide molecules under the conditions similar to Fischer-Tropsch synthesis and thus, most of cobalt surface sites are not available for propene and propane chemisorption. [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]