Engineering support-dependent structures of Co catalysts on MgO, MgAl, and Al₂O₃ for selective transformation of levulinic acid to γ-valerolactone

Abstract

Selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is a benchmark reaction in lignocellulosic biomass valorization. In this study, we investigated the structure–activity relationships of Co catalysts supported on γ-Al₂O₃, MgO, and MgAl. Catalysts were synthesized via incipient wetness impregnation and characterized using ex-situ and in-situ techniques to elucidate structural properties. The oxide supports exerted a strong influence on Co dispersion, oxidation state, and acid–base characteristics. Co/Al₂O₃ provided high surface area and well-dispersed Co⁰ species, whereas Co/MgO stabilized larger, partially oxidized particles of low reducibility. In contrast, Co/MgAl exhibited an intermediate state of predominantly Co⁰ with minor Co²⁺ species, accompanied by high H₂ adsorption and suitable acidity and basicity. Under 30 bar H₂ in 2-propanol, Co/MgAl achieved 100 % LA conversion and 86 % GVL yield at 120 °C within 2 h, outperforming Co/MgO and Co/Al₂O₃. Isotopic labeling with D₂O and 2-PrOD₈ confirmed dual hydrogenation pathways via direct H₂ activation and solvent-mediated transfer hydrogenation. Regeneration–recycling tests further demonstrated the superior stability of Co/MgAl, retaining 80 % GVL yield after four cycles with minimal Co leaching. These findings emphasize the role of support-induced structural modulation in LA hydrogenation, establishing Co/MgAl as a robust platform for scalable LA-to-GVL upgrading.