Tuning the Selectivity of the Hydrogenation/Hydrogenolysis of 5-Hydroxymethylfurfural under Batch Multiphase and Continuous-Flow Conditions.

The hydrogenation/hydrogenolysis of 5-hydroxymethylfurfural (HMF) has been carried out either under single (aqueous) phase or batch multiphase (MP) conditions using mutually immiscible aqueous/hydrocarbon phases, 5 % Ru/C as a catalyst, and both with and without the use of trioctylmethyl phosphonium bis-(trifluoro methane) sulfonimide ([P8881 ][NTf2 ]) as an ionic liquid (IL). Alternatively, the hydrogenation of HMF was explored in the continuous-flow (CF) mode with the same catalyst. By changing reaction parameters, experiments were optimized towards the formation of three products: 2,5-bis(hydroxy methyl)furan (BHMF), 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), and 1-hydroxyhexane-2,5-dione (HHD), which were obtained in up to 92, 90, and 99 % selectivity, respectively, at quantitative conversion. In particular, the single (aqueous) phase reaction of HMF (0.2 m) carried out for 18 h at 60 °C under 30 bar of H2 , allowed the exclusive synthesis of BHMF from the partial (carbonyl) hydrogenation of HMF, while the MP reaction run at a higher T and p (100 °C and 50 bar) proved excellent to achieve only HHD derived from a sequence of hydrogenation/hydrogenolysis. It is worth noting that under MP conditions, the catalyst was perfectly segregated in the IL, where it could be recycled without any leaching in the aqueous/hydrocarbon phases. Finally, the hydrogenation of HMF was explored in a H-Cube® flow reactor in the presence of different solvents, such as ethyl acetate, tetrahydrofuran, and ethanol. At 100 °C, 50 bar H2 , and a flow rate of 0.1 mL min-1 , the process was optimized towards the formation of the full hydrogenation product BHMTHF. Ethyl acetate proved the best solvent.

Selective Hydrogenation of 5-Hydroxymethylfurfural to 1-Hydroxy-2,5-hexanedione by Biochar-Supported Ru Catalysts.

The development of sustainable and efficient catalysts -namely Ru supported on activated biochars- is carried out for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 1-hydroxy-2,5-hexanedione (HHD). Activated biochars obtained from pyrolysis and steam-based physical activation of two different biomasses from animal (leather tannery waste; ALw ) and vegetal (hazelnut shells; AHSw ) origins show completely different chemical, textural, and morphological properties. Compared to ALw , after impregnation with 0.5 wt % Ru, AHSw , with inner micro-mesochannels and cavities and higher layer stacking disorder, leads to better trapping and anchoring of Ru nanoparticles on the catalyst and a suitable Ru single crystal dispersion. This leads to a highly active Ru/AHSw catalyst in the proposed reaction, giving more than 80 % selectivity to HHD and full HMF conversion at 100 °C with 30 bar H2 for 3 h. Ru/AHSw also shows promising performance compared to a commercial Ru/C catalyst.