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Abstract

In the present work, a methodology is proposed for the synthesis of metal-based hydrogenation catalysts supported on hierarchically porous carbon pellets, which are suitable for industrial flow processes. For the preparation of the carbon support, durum semolina is used as the carbon source, in addition to ZnO nanopowder as the porogenic templating agent. Owing to their large surface area of 756 m²/g and mesopore volume of 0.49 cm³/g (QSDFT N₂ adsorption), the extruded cylindrical pellets (2.4 × 3.5 mm) offer excellent properties as a support material for highly active catalyst pellets, tailored to the use in large packed bed reactors.
The performance of the Ni/C and Pt/C catalysts, prepared with several metal loadings from the support pellets, is investigated in packed-bed flow reactors for two important applications of biomass valorization: the hydrogenation of the bioderived platform molecules 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) to the value-added chemicals 2,5-dimethylfuran (DMF) and γ-valerolactone (GVL), respectively. Aiming at the development of sustainable processes, only water and ethanol are used as green solvents in these processes.
In the selective hydrogenation of HMF in ethanol over the synthesized 21wt Ni/C catalyst, a DMF yield of 80.5 (99.0 conversion) is obtained at 150 °C. High catalytic stability is observed during the whole operation period of 33 h.
For the hydrogenation of LA to GVL in water at 160 °C, the prepared 2.7wt Pt/C catalyst provides excellent GVL yield of 96.4 (98.9 conversion) and a Pt time yield of 54.7 molGVL/h/molPt (66.2 conversion).
With formic acid (FA) as an alternative and renewable hydrogen source, the GVL selectivity was further enhanced to 98.7 (65.3 LA conversion) and a 92.6 GVL yield (97.7 LA conversion) was obtained, using the same type of 2.7wt Pt/C catalyst at 220 °C. The high activity and remarkable selectivity of the FA-assisted hydrogenation demonstrates its potential for a sustainable and self-sufficient integrated refining strategy of sugars to GVL, in which in situ formed FA can be employed as a bioderived reducing agent.