Mickaël Capron

Selective catalytic oxidation of glycerol: perspectives for high value chemicals

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.

Towards the Sustainable Production of Acrolein by Glycerol Dehydration

The massive increase in biodiesel production by transesterification of vegatable oils goes hand-in-hand with the availability of a large volume of glycerol, which must be valorized. Glycerol dehydration to acrolein over acid catalysts is one of the most promising ways of valorization, because this compound is an important chemical intermediate used in, for example, the DL-methionine synthesis. In this Minireview, we give a detailed critical view of the state-of-the-art of this dehydration reaction. The processes developed in both the liquid and the gas phases are detailed and the best catalytic results obtained so far are reported as a benchmark for future developments. The advances on the understanding of the reaction mechanism are also discussed and we further focus particularly on the main obstacles for an immediate industrial application of this technology, namely catalyst coking and crude glycerol direct-use issues.

A long-life catalyst for glycerol dehydration to acrolein

While the initial catalytic performances of silica-supported silicotungstic acid are high in the glycerol dehydration reaction, they rapidly decrease with time on stream and the acrolein yield quickly decreases.

Dimerization of mono-ruthenium substituted α-Keggin-type tungstosilicate [α-SiW11O39RuIII(H2O)]5− to µ-oxo-bridged dimer in aqueous solution: synthesis, structure, and redox studies

We report the dimerization of a mono-ruthenium(III) substituted α-Keggin-type tungstosilicate [α-SiW11O39RuIII(H2O)]5− to a µ-oxo-bridged dimer [{α-SiW11O39Rum}2O]n− (m = III, n = 12; m = IV/III, n = 11; m = IV, n = 10). Single crystal X-ray structure analysis of Rb10[{α-SiW11O39RuIV}2O]·9.5H2O (triclinic, P, with a = 12.7650(6) A, b = 18.9399(10) A, c = 20.2290(10) A, α = 72.876(3)°, β = 88.447(3)°, γ = 80.926(3)°, V = 4614.5(4) A3, Z = 2) reveals that two mono-ruthenium substituted tungstosilicate α-Keggin units are connected through µ-oxo-bridging Ru–O–Ru bonds. Solution 183W-NMR of [{SiW11O39RuIV}2O]10− resulted in six peaks (−63, −92, −110, −128, −132, and −143 ppm, intensities 2 : 2 : 1 : 2 : 2 : 2) confirming that the µ-oxo bridged dimer structure is maintained in aqueous solution. The dimerization mechanism is presumably initiated by deprotonation of the aqua-ruthenium complex [α-SiW11O39RuIII(H2O)]5− leading to a hydroxy-ruthenium complex [α-SiW11O39RuIII(OH)]6−. Dimerization of two hydroxy-ruthenium complexes produces the µ-oxo bridged dimer [{α-SiW11O39RuIII}2O]12− and a water molecule. The Ru(III) containing dimer is oxidized by molecular oxygen to produce a mixed valence species [{α-SiW11O39RuIV-III}2O]11−, and further oxidation results in the Ru(IV) containing [{α-SiW11O39RuIV}2O]10−.

Highly Efficient and Stable CeNiHZOY Nano‐Oxyhydride Catalyst for H2 Production from Ethanol at Room Temperature

Dedicated to the Fritz Haber Institute, Berlin, on the occasion of its 100th anniversaryHydrogenandfuelcellsarecrucial toanycleanenergy policy.At the international level, hydrogen has been proposed as amajor energy vector that could contribute to the reduction ofthe global dependence toward fossil fuels and to the loweringof greenhouse-gas emissions and atmospheric pollution.

Structural, textural and acid–base properties of carbonate-containing hydroxyapatites

Carbonate-containing hydroxyapatites with different Ca/P ratios and optionally containing Na+ cations were successfully synthesized using a precipitation method. The solids were extensively characterized by XRD, LEIS, XPS, IR, TGA and NMR. Further, their acid–base properties were determined by NH3-TPD, PEA-XPS, CO2-TPD and by pulsed liquid chromatography using benzoic acid as a probe. The so-obtained structural, textural and acid–base properties could be finely correlated to give a clear picture of the system. The acidic properties of hydroxyapatites were attributed to Ca2+, surface HPO42− and OH− vacancies and the basic properties were attributed to PO43−, OH− and CaO species. The fine-tuning of the amount, of the nature and the strength of acid–base properties derived by varying the carbonate content in hydroxyapatites can find applications in catalysis, which was illustrated by isopropanol reactivity.

Regeneration of silica-supported silicotungstic acid as a catalyst for the dehydration of glycerol.

The dehydration reaction of glycerol to acrolein is catalyzed by acid catalysts. These catalysts tend to suffer from the formation of carbonaceous species on their surface (coking), which leads to substantial degradation of their performances (deactivation). To regenerate the as-deactivated catalysts, various techniques have been proposed so far, such as the co-feeding of oxygen, continuous regeneration by using a moving catalytic bed, or alternating between reaction and regeneration. Herein, we study the regeneration of supported heteropolyacid catalysts. We show that the support has a strong impact on the thermal stability of the active phase. In particular, zirconia has been found to stabilize silicotungstic acid, thus enabling the nondestructive regeneration of the catalyst. Furthermore, the addition of steam to the regeneration feed has a positive impact by hindering the degradation reaction by equilibrium displacement. The catalysts are further used in a periodic reaction/regeneration process, whereby the possibility of maintaining long-term catalytic performances is evidenced.

Direct conversion of methanol into 1,1-dimethoxymethane: remarkably high productivity over an FeMo catalyst placed under unusual conditions

We report here the highest productivity ever observed in the direct conversion of methanol into 1,1-dimethoxymethane (ca. 4.6 kgDMM h−1 kgcat−1 at 553 K), this result being obtained over an FeMo catalyst. This catalyst is industrially used to selectively convert methanol into formaldehyde but has never before been applied to the present reaction. Placing this FeMo catalyst under unusual reaction conditions, i.e., using a feed rich in methanol, completely changed its behaviour in terms of selectivity: the massive production of 1,1-dimethoxymethane, instead of formaldehyde, was observed.

Reactivity of ethanol over hydroxyapatite-based Ca-enriched catalysts with various carbonate contents

The Guerbet reaction of ethanol to produce heavier products was performed over a series of extensively characterized carbonate-containing hydroxyapatites (HAPs) with different Ca/P ratios and thus different densities, strengths and natures of acid and basic sites. These properties were correlated with the reactivity of the solids and an optimal ratio between the amount of acid and basic sites was evidenced (ca. 5). The best performance was accordingly obtained over the Hap-CO3 catalyst, which gave a yield of 30% of heavier alcohols at 40% ethanol conversion.

Quasi-Homogeneous Oxidation of Glycerol by Unsupported Gold Nanoparticles in the Liquid Phase

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.