Conversion of biomass to γ-valerolactone by catalytic transfer hydrogenation of ethyl levulinate over metal hydroxides
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A series of low-cost readily-assembled eco-friendly metal hydroxides were examined as catalysts in the synthesis of a novel platform molecule, γ-valerolactone (GVL), from biomass-derived ethyl levulinate (EL) via hydrogen transfer reaction. Among these catalysts, ZrO(OH)2·xH2O was found to be most active. EL conversion of 93.6% and GVL selectivity of 94.5% were achieved when 2-propanol was used as a hydrogen donor at 473K with a reaction time of only 1h. The complete reaction pathway and the probable main by-products for the conversion of EL to GVL were clearly deduced for the first time. The ZrO(OH)2·xH2O catalyst could be reused at least ten times without any significant loss of catalytic activity. Furthermore, characterizations were carried out on the fresh and spent ZrO(OH)2·xH2O catalysts with XRD, FT-IR, BET, TGA-DTA. Combined with the results of poisoning experiments, a plausible mechanism for catalytic transfer hydrogenation (CTH) of EL to GVL was proposed to be consisted of a catalytic cycle involving a six member ring transition state. ? 2013 Elsevier B.V.