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A green and efficient process was developed for the conversion of biomass-derived ethyl levulinate (EL) into c-valerolactone (GVL) using supercritical ethanol as the hydrogen donor and the reaction medium over low-cost and eco-friendly ZrO 2 catalysts, which were prepared by the precipitation method and characterized by BET, SEM, XRD, FT-IR, TGA-DTA, TPD-NH 3 and TPD-CO 2 . The results indicated that amorphous ZrO 2 with a high specific surface area and a large number of acid-base sites exhibited the highest catalytic activity, an excellent GVL yield of 81.5% with 95.5% EL conversion was achieved at 523 K over 3 h. In addition, combined with the results of poisoning experiments, a plausible mechanism of catalytic transfer hydrogenation (CTH) via a six-membered ring transition state was also presented.

The scientific community has been seeking cost-competitive and green solvents with good dissolving capacity for the valorization of lignocellulosic biomass. At this point, deep eutectic solvents (DESs) are currently emerging as a new class of promising solvents that are generally liquid eutectic mixtures formed by self-association (or hydrogen-bonding interaction) of two or three components. DESs are attractive solvents for the fractionation (or pretreatment) of lignocellulose and the valorization of lignin, owing to the high solubility of lignin in DESs. DESs are also employed as effective media for the modification of cellulose to afford functionalized cellulosic materials, such as cellulose nanocrystals. More interestingly, biomassderived carbohydrates, such as fructose, can be used as one of the constituents of DESs and then dehydrated to 5-hydroxymethylfurfural in high yield. In this review, a comprehensive summary of recent contribution of DESs to the processing of lignocellulosic biomass and its derivatives is provided. Moreover, further discussion about the challenges of the application of DESs in biomass processing is presented.