A Sol-Gel Ruthenium-Niobium-Silicon Mixed-Oxide Bifunctional Catalyst for the Hydrogenation of Levulinic Acid in the Aqueous Phase

A mixed-oxide nanomaterial with composition (RuO2)0.038(Nb2O5)0.024(SiO2)0.938 was prepared by a one-pot sol–gel route. The synthesis was entirely performed at room temperature, by using easy-to-handle precursors and avoiding the employment of any toxic and/or polluting reactant. One of the samples was synthesised in the presence of a non-ionic surfactant acting as both pore directing agent and metal complexing agent, obtaining a high-specific-surface-area material characterized by a very good dispersion of the metallic species. In both cases, nanomaterials characterized by a complete reducibility of Ru species were obtained. The reduced nanomaterials acted as effective bifunctional catalysts in the hydrogenation of levulinic acid (LA) to γ-valerolactone, performed under mild conditions in the aqueous phase. The catalyst prepared without surfactant showed good stability and no activity loss during all the performed cycles. By contrast, some deactivation phenomena took place with the surfactant-templated catalyst. These phenomena were ascribed to both the partial surface oxidation and the surface adsorption of LA molecules giving deactivation during the second run.