Low Loading of CoRe/TiO2 for Efficient Hydrodeoxygenation of Levulinic Acid to γ-Valerolactone

Abstract

CoRe bimetallic catalysts with low loading were designed for hydrodeoxygenation of levulinic acid to γ-valerolactone. Results show that the 1 wt % Co0.5Re0.5/TiO2 catalyst achieved the highest yield of γ-valerolactone (>99%) at 220 °C, 3 h, a 1,4-dioxane solvent and Co/levulinic acid molar ratio of 1:1760, with a turnover frequency (TOF) of 1328 h–1. The catalyst can be reused four times with only slight activity loss. The catalyst was characterized with various physicochemical measurements, and its adsorption styles with H2 and levulinic acid were calculated by density functional theory. The results reveal that four main factors are related to its excellent catalytic performance. First, the Re oxides synergize with Co by spillover of the dissociated H atoms, which increases the apparent dispersion of Co and promotes the reaction. Second, the low loading of 1 wt % allowed the metal nanoparticles to be well dispersed with a very fine size of ca. 1.24 nm, which may expose more active sites to the substrate and result in a higher catalytic efficiency. Third, CoRe formed an amorphous alloy with the formula Co-ReO1.6, which showed a synergistic effect during the reaction. Finally, the TiO2 support was nonporous and hydrophilic, which would be beneficial for the mass diffusion of the reaction components to be adsorbed/desorbed onto the vicinity of the metallic active sites and lead to a high TOF in the hydrodeoxygenation process.