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, Mössbauer 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 Brønsted 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.
Highlights
Due to dwindling reserves of accessible fossil resources and the increasing demand for fuels and chemicals, there is a growing need to develop efficient catalytic routes from renewable lignocellulosic biomass to fuels and chemicals
The bimetallic catalysts are denoted as Fe-Re(x:y)/TiO2 in which x:y stands for the atomic Fe/Re ratio
A series of Fe-Re supported on TiO2 (P25) catalysts were tested for hydrogenation of levulinic acid in water
Summary
Due to dwindling reserves of accessible fossil resources and the increasing demand for fuels and chemicals, there is a growing need to develop efficient catalytic routes from renewable lignocellulosic biomass to fuels and chemicals. The first example of catalytic hydrogenation of LvA was already reported more than 50 years ago by Broadbent et al [20] These researchers employed an unsupported Re black catalyst and were able to reach a 71 % yield of GVL after 18 h reaction at 106 °C at a H2 pressure of 150 bar. Non-noble copper-based catalysts such as Cu/ZrO2 [24], Cu/SiO2 [25], Cu-Cr [26], and Cu-Fe [27] have been reported to be effective for producing GVL from LvA, they typically require a higher reaction temperature and/or long reaction time for achieving high LvA conversion. Higher conversion and selectivity of carboxylic acid hydrogenation were achieved with a Ni-Re catalyst compared to its single-metal and Pt-based counterparts [33]. We report a novel TiO2-supported Fe-Re bimetallic catalyst system, which is highly active in the hydrogenation of LvA to GVL under mild conditions.
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