Abstract
γ-valerolactone (GVL) is an important value-added chemical with potential applications as a fuel additive, a precursor for valuable chemicals, and polymer synthesis. Herein, different monometallic and bimetallic catalysts supported on γ-Al2O3 nanofibers (Ni, Cu, Co, Ni-Cu, Ni-Co, Cu-Co) were prepared by the incipient wetness impregnation method and employed in the solvent-free hydrogenation of levulinic acid (LA) to GVL. The influence of metal loading, metal combination, and ratio on the activity and selectivity of the catalysts was investigated. XRD, SEM-EDS, TEM, H2-TPR, XPS, NH3-TPD, and N2 adsorption were used to examine the structure and properties of the catalysts. In this study, GVL synthesis involves the single-step dehydration of LA to an intermediate, followed by hydrogenation of the intermediate to GVL. Ni-based catalysts were found to be highly active for the reaction. [2:1] Ni-Cu/Al2O3 catalyst showed 100.0% conversion of LA with >99.0% selectivity to GVL, whereas [2:1] Ni-Co/Al2O3 yielded 100.0% conversion of LA with 83.0% selectivity to GVL. Moreover, reaction parameters such as temperature, H2 pressure, time, and catalyst loading were optimized to obtain the maximum GVL yield. The solvent-free hydrogenation process described in this study propels the future industrial production of GVL from LA.
Highlights
Due to the concomitant increase of the global consumption of fossil fuels and the rapid depletion of its reserves, research attention has shifted to the investigation and development of sustainable alternatives for fossil fuels as our primary energy source [1]
All the isotherms obtained for the catalysts display a type IV isotherm with H3 hysteresis loops
The specific surface area of catalysts was calculated by the Brunauer–Emmett–Teller (BET) method based on the adsorption data in the relative pressure range of 0.05–0.25
Summary
Due to the concomitant increase of the global consumption of fossil fuels and the rapid depletion of its reserves, research attention has shifted to the investigation and development of sustainable alternatives for fossil fuels as our primary energy source [1]. Lignocellulosic biomass is considered to be one of the most promising replacements of fossil fuels since it is a highly renewable, naturally abundant, carbon-neutral energy source [2]. Levulinic acid (LA), a five-carbon molecule that can be produced from both the C5 and C6 sugars of the lignocellulose, was recognized by the US Department of Energy as one of the top 10 biomass-derived compounds that can potentially replace fossil fuels [3]. GVL can be synthesized from the hydrogenation of LA, and it offers a tremendous number of applications as a food ingredient, green solvent, fuel additive, and a platform chemical for the production of consumer goods [5,6]. Considering the accessibility of LA as a feedstock and the potential industrial applications of GVL, the hydrogenation of LA to GVL was found to be a promising pathway in biomass conversion reactions. As represented by Scheme 1, GVL can be synthesized from two reaction
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