5-hydroxymethylfurfural (HMF) is one of the most important renewable platform-chemicals, a very valuable precursor for the synthesis of bio-fuels and bio-products. In this work, the hydrogenation of HMF to two furan diols, 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), both promising renewable monomers, was investigated. Three commercial catalysts, Ru/C, Pd/C and Pt/C, were tested in the hydrogenation of aqueous HMF solutions (2-3 wt%), using a metal loading of 1 wt% respect to HMF content. By appropriate tuning of the process conditions, either BHMF or BHMTHF were obtained in good yields, and Ru/ C resulted the best catalyst for this purpose, allowing us to obtain BHMF or BHMTHF yields up to 93.0 and 95.3 mol%, respectively. This catalyst was also tested for in the hydrogenation of a crude HMF-rich hydrolyzate, obtained by one-pot the dehydration of fructose. The influence of each component of this hydrolyzate on the hydrogenation efficiency was investigated, including unconverted fructose, rehydration acids and humins, in order to improve the yields towards each furan diol. Moreover, ICP-OES and TEM analysis showed that the catalyst was not subjected to important leaching and sintering phenomena, as further confirmed by catalyst recycling study.

γ-Valerolactone (GVL) has been identified as a sustainable platform chemical for the production of carbon-based chemicals. We here report an experimental study on the catalytic hydrogenation of levulinic acid (LA) in water to GVL in a packed bed reactor using supported Ru catalysts (carbon, alumina, and titania) with particle sizes in the millimeter range (C LA,0 = 1.2 mol/L, LA feed = 1 mL/min, H 2 feed = 30 mL/min, 90 °C, 45 bar, and WHSV = 30 g feed /g cat •h). Intraparticle diffusion limitations for hydrogen and LA were confirmed by performing LA hydrogenation experiments with different catalyst particle sizes (0.5 wt % Ru/C) and supported by calculations. The best performance was obtained with Ru/C, showing high LA conversion during 6 h on stream with negligible deactivation. Ru/Al 2 O 3 was found to be less active, and stability was also considerably reduced due to the reactivity of the support. Ru/TiO 2 was considerably less reactive, though stability was better than that for the alumina based counterpart. A long duration test (52 h) for Ru/C (0.5 wt % of Ru) showed a small though significant reduction in LA conversion (from 95 to 82 mol %). Catalyst characterization studies showed a significant decrease in the specific surface area of the catalyst (from 1110 m 2 /g to 390 m 2 /g) and sintering of the Ru particles (TEM-HAADF).

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Current lignin fractionation methods use harsh conditions that alter the native lignin structure, resulting in a recalcitrant material which is undesired for downstream processing. Milder fractionation processes allow for the isolation of lignins that are high in β-aryl ether (β-O-4) content, however, at reduced extraction efficiency. The development of improved lignin extraction methods using mild conditions is therefore desired. For this reason, a flow-through setup for mild ethanosolv extraction (120 °C) was developed. The influence of acid concentration, ethanol/water ratio, and the use of other linear alcohol co-solvents on the delignification efficiency and the β-O-4 content were evaluated. With walnut shells as model feedstock, extraction efficiencies of over 55% were achieved, yielding lignin with a good structural quality in terms of β-O-4 linking motifs (typically over 60 per 100 aromatic units). For example, lignin containing 66 β-O-4 linking motifs was obtained with an 80:20 n-propanol/water ratio, 0.18 M H2SO4 with overall a good extraction efficiency of 57% after 5 h. The majority of the lignin was extracted in the first 2 hours and this lignin showed the best structural quality. Compared to batch extractions, both higher lignin extraction efficiency and higher β-O-4 content were obtained using the flow setup.

γ-Valerolactone (GVL) is readily obtained by the hydrogenation of levulinic acid (LA) and is considered a sustainable platform chemical for the production of biobased chemicals. Herein, the performance and stability of Ru-based catalysts (1 wt % Ru) supported on TiO 2 (P25) and ZrO 2 (monoclinic) for LA hydrogenation to GVL is investigated in the liquid phase in batch and continuous-flow reactors using water and dioxane as solvents. Particular attention is paid to the influence of possible impurities in the LA feed on catalyst performance for LA hydrogenation. Benchmark continuous-flow experiments at extended times on-stream showed that the deactivation profiles are distinctly different for both solvents. In dioxane, the Ru/ZrO 2 catalyst is clearly more stable than Ru/TiO 2 , whereas the latter is slightly more stable in water. Detailed characterization studies on spent catalysts after long run times showed that the deactivation of Ru/TiO 2 is strongly linked to the reduction of a significant amount of Ti 4+ species of the support to Ti 3+ and a decrease in the specific surface area of the support in comparison to the fresh catalyst. Ru/ZrO 2 showed no signs of support reduction and displayed morphological and structural stability; however, some deposition of carbonaceous material is observed. Impurities in the LA feed such as HCOOH, H 2 SO 4 , furfural (FFR), 5hydroxymethylfurfural (HMF), humins, and sulfur-containing amino acids impacted the catalyst performance differently. The results reveal a rapid yet reversible loss of activity for both catalysts upon HCOOH addition to LA, attributed to its preferential adsorption on Ru sites and possible CO poisoning. A more gradual drop in activity is found when cofeeding HMF, FFR, and humins for both solvents. The presence of H 2 SO 4 , cysteine, and methionine all resulted in the irreversible deactivation of the Ru catalysts. The results obtained provide new insights into the (ir)reversible (in)sensitivity of Ru-based hydrogenation catalysts to potential impurities in LA feeds, which is essential knowledge for next-generation catalyst development.