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Graphical abstract Highlights • First demonstration of efficient glycerol oxidation by laser activation of Gold Nanoparticles. • Glycerol oxidation is induced by thermoplasmonic effect of photoexcited GNPs. • More than 90% of Glycerol are converted after 2 h without any external source of heat. • The laser activation is 2.5 times more efficient than thermal activation at 60 °C. • Hot electron transfer between GNPs and TiO 2 contributes to the enhancement. Abstract In this work, we highlight the feasibility of new efficient catalytic processes by laser excitation, exemplified in the reaction of oxidation of glycerol over catalysts based on supported gold nanoparticles. We show that this catalytic oxidation reaction can efficiently proceed via laser excitation of surface plasmon resonance of gold nanoparticles, inducing local thermal heating effect. While the reaction did not occur in the absence of any external heat source, with this original approach, 88% of glycerol was converted after 2 h, leading to the formation of glyceric acid and tartronic acid as main products. The photonic activation led to 2.5 times more efficient conversion than an equivalent thermal activation by conventional heating source. Investigations of the laser power and the nature of support catalyst revealed a significant contribution of electron transfer from plasmonic nanoparticles to TiO 2 in the oxidation reaction. [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]

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]

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]

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]

The activity of four different noble metals (Ag, Au, Pd and Pt) in the liquid phase oxidation of pure glycerol was confronted with the results obtained with a crude glycerol fraction, received from a large-scale biodiesel production plant. The catalysts were characterized by numerous techniques, giving insight into actual metal loading (elemental analysis by ICP and XRF), surface morphology (nitrogen absorption methods—BET and porosity), chemical state of both the support and the metal (XRD and XPS), and, finally, the metal particle size distribution (TEM microscopy). A good dispersion of totally reduced noble metal particles of a nanometric size (an average metal diameters were equal 3.5 nm, 4.2 nm, 4.7 nm and 21.2 nm for respectively Pd, Pt, Au and Ag) was accompanied with a comparable values of total metal loadings on the alumina support (from 0.95 and 0.96 wt.% for Pt and Pd, up to 0.98 and 1.13 wt.% for Au and Ag supported catalysts, respectively). In terms of initial reaction rate, the most active sample was the Au/Al 2 O 3 catalyst, both using pure (12976 mol h −1 mol Au −1 ) or crude glycerol (1230 mol h −1 mol Au −1 ). However, comparison of the selectivities and conversions after 1–2 h shows that the most robust and resistant catalyst – toward the impurities present in crude glycerol – is Pd/Al 2 O 3 , with a loss of conversion less than 50% (in respect to analogous reaction using pure glycerol) and almost unchanged high selectivity to glyceric acid (close to 80–90%). Ag/Al 2 O 3 also showed a relatively high resistance to impurities in terms of glycerol conversion, but with a drastic modification of its selectivity. The activity of the two other catalysts was dramatically affected with a conversion divided by ca. 4 and even 10 for the Pt and the Au catalysts, respectively, when using crude glycerol instead of pure glycerol. Finally, the effect of each main impurity (MONG-NM, i.e. , matter organic non-glycerol and non-methanol; ash; methanol; sulphur compounds) was independently studied. In any case, the sulphur compounds and MONG-NM were the impurities the most detrimental for the performances of catalysts. Thus, they should be removed in priority from crude glycerol fractions before reaction, while ashes and methanol should not be considered as completely undesirable. [ABSTRACT FROM AUTHOR]

Highlights: [•] Three methods for fine control of the deposition of gold nanoparticles on oxide supports are compared. [•] Thiol moieties inhibit the oxidation reaction more strongly than conventional antioxidants do. [•] Glycerol oxidation is blocked by the presence of SH groups on the catalysts surface. [Copyright &y& Elsevier]