Highly efficient selective hydrogenation of levulinic acid to γ-valerolactone over Cu–Re/TiO₂ bimetallic catalysts

Abstract

Highly active and thermally stable Cu-Re bimetallic catalysts supported on TiO₂ with 2.0 wt% loading of Cu were prepared <i>via</i> an incipient wetness impregnation method and were applied for liquid phase selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in H₂. The effect of the molar ratios of Cu : Re on the physico-chemical properties and the catalytic performance of the Cu-Re/TiO₂ catalysts was investigated. Moreover, the influence of various reaction parameters on the hydrogenation of LA to GVL was studied. The results showed that the Cu-Re/TiO₂ catalyst with a 1 : 1 molar ratio of Cu to Re (Cu-Re(1 : 1)/TiO₂) exhibited the highest performance for the reaction. Complete conversion of LA with a 100% yield of GVL was achieved in 1,4-dioxane solvent under the reaction conditions of 180 °C, 4.0 MPa H₂ for 4 h, and the catalyst could be reused at least 6 times with only a slight loss of activity. Combined with the characterization results, the high performance of the catalyst was mainly attributed to the well-dispersed Cu-Re nanoparticles with a very fine average size (<i>ca.</i> 0.69 nm) and the co-presence of Cu-Re bimetal and ReO _<i>x</i> on the catalyst surface.