Jean-Sébastien Girardon

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.

Highly controlled synthesis of nanometric gold particles by citrate reduction using the short mixing, heating and quenching times achievable in a microfluidic device

Homodispersed 1.8 nm gold nanoparticles were obtained reproducibly in high yields using the classical Turkevich protocol at a high concentration in a continuous flow capillary reactor. The microfluidic reactor made from commercially available items permitted short mixing, heating and quenching times which are the key parameters of this synthesis.

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.

A new experimental cell for in situ and operando X‐ray absorption measurements in heterogeneous catalysis

A new X-ray absorption cell dedicated to in situ and operando experiments in heterogeneous catalysis has been built and tested. The cell consists of several boron nitride and stainless steel plates linked together using graphite seals. It allows the measurement of XANES and EXAFS spectra of heterogeneous catalysts within a wide range of photon energies in transmission mode under the flow of various oxidative and reductive gas mixtures at elevated temperatures. The cell is compact and easy to build. Catalysts are loaded into the cell as powders. The use of boron nitride and a small beam pathlength in the cell result in a low absorption of the X-ray beam at lower energies. The cell was tested by in situ characterizing cobalt species during oxidative and reductive pre-treatments of a silica-supported Fischer-Tropsch catalyst. An operando study of methanol conversion over alumina-supported molybdenum catalysts was also carried out.

Performance of Ag/Al2O3 catalysts in the liquid phase oxidation of glycerol – effect of preparation method and reaction conditions

This paper presents a systematic study of alumina supported silver catalysts, a novel catalytic system proposed for the liquid phase aerobic partial oxidation of glycerol to glycolic acid, the smallest α-hydroxyacid with numerous industrial applications (raw material in the chemical industry, ingredient in textiles, food, cosmetics, plastics, adhesives, pharmaceuticals, etc.). We evaluated the effect of the preparation method, the silver loading and the type of alumina support on the properties and the activity of the solids. We showed that numerous parameters can affect the catalytic performances, the most important of which were the following: the type of solvent used during preparation, the basicity and phase composition of the support, as well as the amount of base used during glycerol oxidation. The most active catalysts were at the same time the most selective ones to glycolic acid, which clearly differentiates the silver catalysts from other noble metals conventionally used in glycerol oxidation, such as Au, Pd and Pt, characterized by a high selectivity to glyceric acid. The best results in terms of conversion and selectivity to glycolic acid were obtained over the catalyst prepared by the chemical reduction method in a basic methanol solution, using formaldehyde as a reductant. After 3 h of reaction at 60 °C under 5 bar of oxygen pressure over such a catalyst loaded with 3.6 wt% Ag, an 85% glycerol conversion together with a 57.1% selectivity to glycolic acid were achieved. Moreover, the catalysts showed good stability in the continuous mode and very good resistance to the impurities present in a crude glycerol fraction.

Hybrid Catalysis: A Suitable Concept for the Valorization of Biosourced Saccharides to Value-Added Chemicals

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.

From sequential chemoenzymatic synthesis to integrated hybrid catalysis: Taking the best of both worlds to open up the scope of possibilities for a sustainable future

Enzymatically catalyzed reactions are highly efficient but higher scale extrapolation is limited to a certain class of stable and easily recyclable enzymes. Homogeneously and/or heterogeneously catalyzed reactions are often limited by the multiphasic nature of catalytic systems and/or variations in the distribution of active sites. For these reasons, the development of highly selective and efficient hybrid catalysts is especially needed, and it is now well admitted that disruptive innovation is highly desirable in process engineering, (bio)catalyst design and materials science. Optimal integration of all types of catalysis is the key for efficient global implementation of sustainable processes. This review gives an overview of all the pathways that integrate chemical and biological catalysis, beginning with combined chemoenzymatic processes in cascade to progressively open the field of hybrid catalysis in a one-pot concomitant execution. We have emphasized the factors that have to be considered to understand the catalytic synergy between these systems. A better understanding of hybrid catalytic systems is an essential tool not only in the choice of the best route of their implementation but also in the synthesis of a wide range of fine chemicals in many fields, with a particular emphasis on their production from renewables.