The relevant role of TiO for enhancing the Ru/TiO-catalyzed conversion of levulinic acid to γ-valerolactone

Levulinic acid (LA), that can be obtained from the acidic hydrothermal carbonization of biomass, is a platform molecule with several possibilities to be transformed into useful chemicals. The hydrogenation of LA to γ-valerolactone (GVL) requires a bifunctional catalyst, with both metallic and acidic active sites. In this study, TiO2 was the selected support for its acidic properties, and Ru was the metal phase for its high activity in this reaction. 1% wt. Ru/TiO2 catalysts were prepared using either commercial P25 or TiO2 prepared by hydrothermal (HT) synthesis (with or without the addition of a low concentration HCl solution). The catalysts were used without previous reduction in catalytic tests carried out under mild reaction conditions, and the influence of the surface chemistry, porosity, crystalline structure, and oxygen vacancies on the TiO2 support, as well as the interaction between Ru and the TiO2 support were studied. All the catalysts demonstrated promising results under mild reaction conditions (24 – 65 % GVL yield), being the catalytic activity enhanced when using the Ru/HT-TiO2 catalysts compared to the analogous Ru/P25 one, indicating that a higher surface area improves catalytic performance. High GVL yield (65 %) and excellent reusability over three cycles were achieved with the best catalyst, synthesized without using HCl solution. Although isolating the effect of individual variables remains challenging, our results have shown that the surface chemistry content and composition in the synthesized TiO2 supports have some influence on the formation of Ru0 on them.