Hydrogenation of levulinic acid to γ-valerolactone over Fe-Re/TiO2 catalysts

Abstract Hydrogenation of levulinic acid to γ-valerolactone is a key reaction in the valorization of carbohydrates to renewable fuels and chemicals. State-of-the-art catalysts are based on supported noble metal nanoparticle catalysts. We report the utility of a bimetallic Fe-Re supported on TiO2 for this reaction. A strong synergy was observed between Fe and Re for the hydrogenation of levulinic acid in water under mild conditions. Fe-Re/TiO2 shows superior catalytic performance compared to monometallic Fe and Re catalysts at similar metal content. The hydrogenation activity of the bimetallic catalysts increased with Re content. H2-TPR, XPS, XANES, EXAFS, Mossbauer spectroscopy, TEM, and low-temperature CO IR spectroscopy show that the bimetallic catalysts contain metallic Re nanoparticles covered by FeOx species and small amounts of a Fe-Re alloy. Under reaction conditions, the partially reduced surface FeOx species adsorb water and form Bronsted acidic OH groups, which are involved in dehydration of reaction intermediates. Under optimized conditions, nearly full conversion of levulinic acid with a 95% yield of γ-valerolactone could be achieved at a temperature as low as 180 °C in water at a H2 pressure of 40 bar.