Ruthenium Supported on High-Surface-Area Zirconia as an Efficient Catalyst for the Base-Free Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid.

Several ZrO2 -supported ruthenium catalysts were prepared and utilized in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Full conversion of HMF and almost perfect selectivity towards FDCA (97 %) were achieved after 16 h by using pure O2 as an oxidant and water as a solvent. The catalytic tests show that the size of the Ru particles is crucial for the catalytic performance and that the utilization of high-surface-area ZrO2 leads to formation of very small Ru particles. Superior activity was obtained for catalysts based on ZrO2 that had been synthesized by a surface-casting method and has high surface areas up to 256 m2 g-1 . In addition to good activity and selectivity, these catalysts show also high stability and constant activity upon recycling, confirming the suitability of Ru/ZrO2 in the base-free oxidation of HMF.

Synthesis of Butyl Levulinate Based on α-Angelica Lactone in the Presence of Easily Separable Heteropoly Acid Catalysts.

A series of choline (Ch)-exchanged heteropoly acids (HOCH2 CH2 N(CH3 )3 )x H(6-x) P2 W18 O62 [abbreviated as Chx H(6-x) P2 W18 O62 , x=1-6] was synthesized and used as catalysts for the reaction of α-angelica lactone (alpha-AL) with n-butanol to form butyl levulinate (BL). The solubility of Chx H(6-x) P2 W18 O62 in the reaction mixture was temperature dependent: The catalysts were soluble under the reaction conditions and precipitated upon cooling of the reaction mixture. This facilitated recovery of the catalysts from the liquid phase. Importantly, an increase of the Ch content caused a decrease of the catalyst solubility. Catalytic activity of Chx H(6-x) P2 W18 O62 for the reaction with n-butanol appeared to be in good agreement with the concentration of Brønsted-acidic sites. The results suggest that the reaction proceeded through formation of pseudo-butyl levulinate as intermediate. Ch2 H4 P2 W18 O62 exhibited the best balance between catalytic activity and temperature-dependent solubility. The yield of BL reached 79.4 % at full conversion of alpha-AL at a moderate temperature of 75 °C in an open system. Chx H(6-x) P2 W18 O62 could be successfully reused five times without significant loss of activity.

The Role of the Hydrogen Source on the Selective Production of γ-Valerolactone and 2-Methyltetrahydrofuran from Levulinic Acid.

A mechanistic study of the hydrogenation reaction of levulinic acid (LA) to 2-methyltetrahydrofuyran (MTHF) was performed using three different solvents under reactive H2 and inert N2 atmospheres. Under the applied reaction conditions, catalytic transfer hydrogenation and hydrogenation with molecular H2 were effective at producing high yields of γ-valerolactone. However, the conversion of this stable intermediate to MTHF required the combination of both hydrogen sources (the solvent and the H2 atmosphere) to achieve good yields. The reaction system with 2-propanol as solvent and Ni-Cu/Al2 O3 as catalyst allowed full conversion of LA and a MTHF yield of 80 % after 20 h reaction time at 250 °C and 40 bar of H2 (at room temperature). The system showed the same catalytic activity at LA feed concentrations of 5 and up to 30 wt%, and also when high acetone concentration at the beginning of the reaction were added, which confirmed the potential industrial applications of this solvent/catalyst system.

Efficient, solvent-free hydrogenation of α-angelica lactone catalysed by Ru/C at atmospheric pressure and room temperature.

The hydrogenation of α-angelica lactone was investigated over Ru/C. A mild protocol was developed, which resulted in full conversion and 96% selectivity toward γ-valerolactone. The reaction network was investigated and α-angelica lactone was employed in the one-pot conversion into 2-methyltetrahydrofuran, demonstrating its superiority as a platform molecule in potential biorefinery schemes.