The role of metallic and acid sites of Ru-Nb-Si catalysts in the transformation of levulinic acid to γ-valerolactone

The transformation of γ-valerolactone (GVL) into levulinic acid (LA) requires the use of bifunctional catalysts allowing the hydrogenation and lactonization steps to occur. The aim of this study is to clarify the role played by both redox (Ru) and acid (Nb) sites of the ruthenium-niobium-silicon mixed oxides catalysts, synthesized by sol-gel route, when this reaction is performed in mild conditions. The catalytic performances of the materials are related to an in-depth morphologic and structural characterization, demonstrating that the interaction between the two metals and their relative amount and dispersion are crucial in determining their activity. The results confirm the hydrogenation-dehydration consecutive reaction network and evidence the possibility to selectively produce either GVL or the intermediate γ-hydroxypentanoic acid by an accurate choice of the catalyst composition.