Michèle Besson

Chemoselective catalytic oxidation of glycerol with air on platinum metals

Abstract The transesterification of triglycerides extracted from oilseeds to obtain biodiesel fuel yields up to 14% by weight of glycerol as by-product. The liquid-phase oxidation of glycerol with air on platinum catalysts was investigated to prepare valuable oxidation products such as glyceric acid or dihydroxyacetone. The effect of the pH (pH range 2–11) and of different metal catalysts was studied. The selectivity to glyceric acid can be as high as 70% at 100% conversion on Pd/C at pH 11. On Pt/C catalyst, glyceric acid was still the main product (55% selectivity); but the deposition of bismuth on platinum particles orientates the selectivity towards the oxidation of the secondary hydroxyl group to yield dihydroxyacetone with a selectivity of 50% at 70% conversion.

Deactivation of metal catalysts in liquid phase organic reactions

The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO2 catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO2) are discussed.

Selective aqueous phase oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Pt/C catalysts: influence of the base and effect of bismuth promotion

5-Hydroxymethylfurfural (HMF) was quantitatively oxidized to 2,5-furandicarboxylic acid (FDCA) at 100 °C under 40 bar air in moderately basic aqueous solution in the presence of active carbon supported platinum and bismuth–platinum catalysts. The transformation of HMF into FDCA proceeded via the 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 2,5-diformylfuran (DFF) intermediates; both of these were very reactive and rapidly oxidized to 5-formylfurancarboxylic acid (FFCA), the subsequent oxidation of which was found to be the rate-limiting step. The preparation method of the platinum catalysts influenced the particle size of metallic platinum and modified the surface of the support, therefore determining the activity. The addition of a carbonate base (Na2CO3/HMF molar ratio = 2) led to faster overall conversion than bicarbonate (NaHCO3/HMF = 4) by maintaining an appropriate pH for the oxidation reaction. The ex situ or in situ addition of a bismuth promoter still accelerated the reaction; the highest activity was observed for a Bi/Pt molar ratio of ca. 0.2. Furthermore, the promoter helped to prevent some deactivation of the Pt catalyst upon recycling experiments. Quantitative conversion of HMF (0.1 M) and >99% yield of FDCA were achieved using a molar ratio of HMF to Pt of 100 and Na2CO3 as the homogeneous base in less than 2 h.

Selective Aerobic Oxidation of 5-HMF into 2,5-Furandicarboxylic Acid with Pt Catalysts Supported on TiO2- and ZrO2-Based Supports

Pt catalysts prepared over different metallic oxide supports were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in alkaline aqueous solutions with air, to examine the combined effect of the support and base addition. The base (nature and amount) played a significant role in the degradation or oxidation of HMF. Increasing amounts of the weak NaHCO3 base improved significantly the overall catalytic activity of Pt/TiO2 and Pt/ZrO2 by accelerating the oxidation steps, especially for the aldehyde group. This was highlighted by a proposed kinetic model that gave very good concentration-time fittings. Moreover, the promotion of the catalyst with bismuth yielded a PtBi/TiO2 catalytic system with improved activity and stability. Y2 O3  and La2 O3 ZrO2 -supported catalysts exhibited lower activity than Pt/ZrO2 , which suggests no cooperative effect of the weakly basic properties introduced and the homogeneous base. Quantitative oxidation of HMF (0.1 M) and high yields of FDCA (>99 %) were obtained in less than 5 h by using an HMF/Pt molar ratio of 100 and Na2 CO3 as a weak base over PtBi/TiO2 (Bi/Pt=0.22).

Heterogeneous catalytic hydrogenation of biobased levulinic and succinic acids in aqueous solutions.

Supported noble-metal catalysts (Ru, Pd or Pt) and the corresponding Re-promoted catalysts exhibit a high activity for the hydrogenation of biobased carboxylic acids. Levulinic acid and succinic acid are converted into the lactones or the diols depending on the nature of the catalyst and the reaction conditions. The highest selectivity to 1,4-pentanediol of 82 % is achieved at 140 °C in the presence of the 1.9 % Ru-3.6 % Re/C catalyst.

Stereoselective reduction of disubstituted aromatics on colloidal rhodium

Abstract Hydrogenation of disubstituted aromatic rings can be achieved under mild reaction conditions in a two-phase system in presence of RhCl3 and phase transfer agents such as trioctylamine. The catalytic system was optimized for the 2-methylanisole reduction by a proper choice of the amine/Rh ratio which should be high enough to stabilize very small colloidal rhodium particles and low enough to avoid deactivation. A high chemoselectivity and a high stereoselectivity to the Z isomer are obtained. Moreover enantioselective reductions of o-cresol derivatives were performed with colloidal rhodium stabilized and modified by chiral amines. Diastereoselective reductions were also obtained using chiral auxiliaries bound to the substrate.

Effect of oxygen functional groups on synthetic carbons on liquid phase oxidation of cyclohexanone

Abstract Synthetic carbons from phenolic resins were used as catalysts for the aqueous phase oxidation of cyclohexanone to C4–C6 dicarboxylic acids (adipic, glutaric and succinic acids) at 413 K under 50 bar total air pressure. The changes in microporous structure and surface chemistry, produced as a consequence of activation or heat treatment processes, were analyzed. Using CO2 or air as activating agent increased significantly the surface area and the total pore volume responsible for the activity. The surface chemistry of the samples was also modified and was characterized by titration with bases of different strength and with HCl, by temperature programmed desorption, and by X-ray photoelectron spectroscopy. To determine the role of surface oxygen functionalities on the catalytic behavior of the carbons, heat treatments in nitrogen at different temperatures were used to selectively eliminate oxygenated groups. Thus, treatment at temperatures of 1173 K eliminating the carbonyl/quinone groups decreased the selectivity to adipic acid and dicarboxylic acids. Introducing quinone groups during the synthesis of the carbons also improved the selectivity to adipic acid, proving that the mechanism of oxidation involves the quinone type groups on the carbon surface.

Selective catalytic oxidation of glyceric acid to tartronic and hydroxypyruvic acids

Abstract The catalytic oxidation, with air, of aqueous solutions of glycerol-derived oxygenates on carbon-supported platinum metals may be controlled to improve yields of valuable fine chemicals. The primary and secondary alcohol functions of glyceric acid, calcium salt, were selectively oxidised by varying the pH and employing a promoter. Under basic conditions, platinum catalyst yielded the tartronate salt (61% yield at 94% conversion, pH 10–11) and slightly higher yields were obtained on bismuth-promoted platinum (83% yield at 90% conversion, pH= 10–11). Hydroxypyruvic acid was obtained on bismuth-promoted platinum under acidic conditions (64% yield at 75% conversion, pH 3–4).

Catalytic oxidation with air of tartronic acid to mesoxalic acid on bismuth-promoted platinum

Mesoxalic acid (ketomalonic acid) was prepared by oxidative dehydrogenation with air of tartronic acid in aqueous solution on carbon-supported platinum-bismuth catalysts. By increasing the pH, using a higher catalyst/substrate ratio or increasing the temperature, higher yields could be obtained (maximum yield obtained of 65% at 80% conversion). The results obtained for this reaction and for the analogous catalytic oxidations of glyceric acid to hydroxypyruvic acid, and lactic acid to pyruvic acid, enabled a general reaction mechanism to be proposed for the selective oxidation of α-hydroxy acids to α-keto acids on platinum-bismuth catalysts.

Heterogeneous Transformation of Glycerol to Lactic Acid

Significant yields of lactic acid (LA) are obtained during the treatment of glycerol solution under inert gas with supported metallic catalysts under basic conditions. The nature of the atmosphere and the metal affected the activity and the selectivity of the reaction. Iridium-based catalysts are efficient for LA synthesis.