Catherine Especel

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.

Insights into the Oxidation State and Location of Rhenium in Re‐Pd/TiO2 Catalysts for Aqueous‐Phase Selective Hydrogenation of Succinic Acid to 1,4‐Butanediol as a Function of Palladium and Rhenium Deposition Methods

ReOx‐Pd/TiO2 catalysts prepared from different 2 wt %Pd/TiO2 catalysts using two protocols for the deposition of the Re promoter (successive impregnation and catalytic reduction) were characterized by different techniques to better understand the nature of the active and selective sites implied in the aqueous‐phase hydrogenation of succinic acid to 1,4‐butanediol. Regardless of the support and Re introduction method, it was established that varying amounts of Pd and Re were in very close proximity without electronic interaction in the reduced catalysts. A high fraction of Re always remained partially oxidized to generate a bimetallic catalyst that can provide the necessary bifunctional sites to enable the selective hydrogenolysis of the intermediate γ‐butyrolactone to 1,4‐butanediol. Depending on the method of promotion, the ReOx species that interact with Pd were deposited as clusters with different spatial Re–Re interactions.

Influence of Re–M interactions in Re–M/C bimetallic catalysts prepared by a microwave-assisted thermolytic method on aqueous-phase hydrogenation of succinic acid

Carbon-supported Re–M (M = Pt and Rh) bimetallic catalysts with controlled size and composition were synthesized by using a microwave-assisted thermolytic method and evaluated in the aqueous phase hydrogenation of succinic acid. The Re–M interaction contributes to the inhibition of aggregation of particles and to the improvement in the catalytic activity for succinic acid hydrogenation through decreasing the activation energy. The Re–M interaction favors the ring opening of γ-butyrolactone, an intermediate product, to 1,4-butanediol instead of the hydrogenation and dehydration to tetrahydrofuran observed over a Re/C catalyst. The kinetic study proves that the Re–M interaction can increase the relative formation rate of 1,4-butanediol more than that of tetrahydrofuran, while the strength of the Re–M interaction has a limited influence on the product selectivity. It was shown that the Re–Rh interaction can reduce the direct hydrogenolysis of succinic acid, but it cannot avoid the hydrogenolysis of 1,4-butanediol, thus limiting the selectivity to this product. According to the kinetic mechanism, ring opening of γ-butyrolactone is favored at low temperature while direct hydrogenation to tetrahydrofuran is favored at high temperature.

Influence of rhodium content on the behavior of Rh/SiO2–Al2O3 catalysts for selective ring opening of decalin

The influence of the Rh content of catalysts supported on SiO2–Al2O3 (SIRAL 70 and 80, with 70 and 80 wt% of SiO2) on the activity and selectivity for selective ring opening of decalin was studied at 325 and 350 °C. An optimum metal content was found at 1.5 wt% of rhodium. Both supports present moderate and strong acid sites. For the selective opening of decalin, the best metal/support combination was found with Rh(1.5)/SIRAL 70 balancing the support acidity together with the hydrogenolytic activity of the metal. A linear correlation was established between the amount of coke deposited and the formation of dehydrogenated compounds.