Mohammad G. Al-Shaal

Exploring the ruthenium catalysed synthesis of γ-valerolactone in alcohols and utilisation of mild solvent-free reaction conditions

Levulinic acid and alkyl-levulinates have been hydrogenated using a range of supported catalysts. The different reaction outcomes obtained in alternate solvents have been rationalized and the influence of varying catalyst supports examined. A range of solvent free conditions have been investigated with complete LA conversion obtained at temperatures as low as 25 °C.

Solvent-free γ-valerolactone hydrogenation to 2-methyltetrahydrofuran catalysed by Ru/C: a reaction network analysis

2-Methyltetrahydrofuran (2-MTHF) is considered to be an attractive biomass based platform chemical with high potential as a biofuel compound and as a green solvent. 2-MTHF can be synthesised from bio-based levulinic acid (LA) and γ-valerolactone (GVL). Herein the optimum reaction conditions for the hydrogenation of GVL over Ru/C have been studied. A full conversion of GVL has been obtained under solvent free conditions with a maximum yield of 2-MTHF of 43%. The optimized conditions have been employed in a mechanistic study of the synthesis of 2-MTHF. Several side reactions have been investigated to explore the full reaction network of this heterogeneously catalysed system and to elucidate the factors influencing product selectivity. Additionally an efficient solvent-free hydrogenation reaction of LA into 2-MTHF could be achieved delivering 90% conversion of LA with a yield of 2-MTHF of 61% by removing water from the system in a two-step approach.

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Butyl levulinate was prepared starting from α-angelica lactone and butanol over Amberlyst® 36. Different reaction conditions were optimized, which resulted in full conversion and 94% selectivity toward the ester at 75 °C. A reaction network analysis reveals pseudo-butyl levulinate and levulinic acid as intermediates in the preparation of butyl levulinate. The mild protocol was successfully applied for different alcohols and compared with the esterification of levulinic acid. Overall, this study identifies α-angelica lactone as a better candidate than levulinic acid for the heterogeneously catalysed preparation of levulinic acid esters. A catalyst screening shows that also zeolites and zirconia-based catalysts are able to catalyse the reaction. However, the transformation of the intermediate pseudo-butyl levulinate into butyl levulinate requires acid sites of sufficient strength to proceed.

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.

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.