Amandine Cabiac

Non-catalyzed and Pt/γ-Al2O3-catalyzed hydrothermal cellulose dissolution–conversion: influence of the reaction parameters and analysis of the unreacted cellulose

Hydrothermal dissolution and/or conversion of cellulose Avicel® occurred at 190 °C under 5 MPa of H2 in the absence of catalyst. This reaction is temperature and time dependent. A dissolution–conversion ratio of 35% was obtained after 24 h of reaction and glucose and HMF were detected as monomeric products in a global yield of less than 5%, indicating that the majority of the products are composed of soluble oligo- and polysaccharides. The unreacted cellulose was analyzed using XRD, 13C solid state NMR, TGA-DTA and SEM and compared to the initial cellulose. We showed that although morphology changes occurred during the reaction, no modification of the crystallinity was observed and that hydrothermal treatment did not affect a specific part of the cellulose polymer. The presence of Pt/γ-Al2O3 increased the initial rate of dissolution–conversion significantly as well as the distribution of the monomeric products. Pt and H2 atmosphere were seen to increase the dissolution–conversion ratio however their role has not been yet well established.

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.

Cellulose conversion with tungstated-alumina-based catalysts: influence of the presence of platinum and mechanistic studies.

The performances of platinum supported on tungstated alumina (Pt/AlW) in the hydrothermal conversion of cellulose at 190 °C under H2 pressure were evaluated and compared to that of Pt-free tungstated alumina (AlW). We show that the presence of Pt significantly increased the extent of conversion and led to a different product distribution with the formation of acetol and propylene glycol as the main products and a global yield of up to 40 %. Based on previous reports, we propose the formation of pyruvaldehyde on the Lewis acid sites of the tungstated alumina as a key intermediate. Pyruvaldehyde can then be transformed to acetol and propylene glycol or lactic acid depending on the presence or absence of supported Pt.

Catalytic conversion of cellulose to C2–C3 glycols by dual association of a homogeneous metallic salt and a perovskite-supported platinum catalyst

A novel catalytic system based on the combination of a homogeneous metallic salt and a platinum catalyst supported on a zirconium-based oxide was explored for the selective conversion of cellulose to C2–C3 glycols. Parameters such as the nature of the homogeneous catalyst, support effects and operating conditions were systematically varied to evaluate the potential of this dual catalytic system. Sharp analysis of reaction pathways led us to identify an optimal combination of cerium chloride and a barium zirconate-based platinum catalyst for the production of ethylene glycol and propylene glycol exhibiting substantial selectivities (>40%). The recyclability and the possible deactivation mechanisms of the catalytic system were ultimately investigated.

Xylitol Hydrogenolysis over Ruthenium-Based Catalysts: Effect of Alkaline Promoters and Basic Oxide-Modified Catalysts

The aqueous‐phase hydrogenolysis of xylitol into glycols over Ru/C was performed in the presence and absence of a wide range of concentrations of Ca(OH)2 to investigate the reaction pathway. Without base, epimerization and cascade decarbonylation were the predominant reactions with high selectivities to C5 and C4 alditols and light alkanes at full conversion. Glycol production was obtained by the addition of Ca(OH)2 to promote the retro‐aldol reaction. It competed with reactions without base and became the main reaction for a OH−/ xylitol molar ratio Rmol(OH/xylitol) of 0.13, and high selectivities to glycols (56 %) and glycerol (16 %) were observed. However, lactate was a byproduct at up to 27 % with a high base amount (Rmol(OH/xylitol)=0.68). Bifunctional Ru/metal oxide/C catalysts (metal: Zn, Sn, Mn, Sr, W) were synthesized and were able to cleave the C−C bond into glycols without a base promoter. The 3.1 wt %Ru/MnO(4.5 %)/C catalyst was the most active (220 h−1) with reasonable selectivity to glycols (22 %) and glycerol (10 %) and a low production of lactate (<1 %). Nevertheless, metal oxide leaching of the catalyst was observed likely because of the production of traces of lactate.

Ru-(Mn-M)OX Solid Base Catalysts for the Upgrading of Xylitol to Glycols in Water

A series of Ru-(Mn-M)OX catalysts (M: Al, Ti, Zr, Zn) prepared by co-precipitation were investigated in the hydrogenolysis of xylitol in water to ethylene glycol, propylene glycol and glycerol at 200 ◦C and 60 bar of H2. The catalyst promoted with Al, Ru-(Mn-Al)OX, showed superior activity (57 h−1) and a high global selectivity to glycols and glycerol of 58% at 80% xylitol conversion. In comparison, the catalyst prepared by loading Ru on (Mn-Al)OX, Ru/(Mn-Al)OX was more active (111 h−1) but less selective (37%) than Ru-(Mn-Al)OX. Characterization of these catalysts by XRD, BET, CO2-TPD, NH3-TPD and TEM showed that Ru/(Mn-Al)OX contained highly dispersed and uniformly distributed Ru particles and fewer basic sites, which favored decarbonylation, epimerization and cascade decarbonylation reactions instead of retro-aldol reactions producing glycols. The hydrothermal stability of Ru-(Mn-Al)OX was improved by decreasing the xylitol/catalyst ratio, which decreased the formation of carboxylic acids and enabled recycling of the catalyst, with a very low deactivation.