Kinetic Studies on the Impact of Pd Addition to Ru/TiO2 Catalyst: Levulinic Acid to γ-Valerolactone under Ambient Hydrogen Pressure

The conversion of levulinic acid (LA) to γ-valerolactone (GVL) is one of the most important reactions from biomass-derived platform chemicals to value-added chemicals. In this work, bimetallic PdRu/TiO2 catalyst compared to monometallic Ru/TiO2 was designed for the conversion of LA to GVL at ambient H2 pressure. The highly dispersed Pd affected the reaction by two antagonistic effects: (I) increasing the reaction rate by promoting the activation of H2; (II) decreasing the reaction rate by lowering the activation ability of carbonyl group over Ru. The kinetic analysis refined by H2 concentration showed much lower apparent activation energy over 0.2Pd1Ru/TiO2 than that over Ru/TiO2. Finally, the catalysts were evaluated by both GVL productivity and catalyst cost to show increasing benefit of Pd addition at lower H2 pressure. This study offers both theoretical foundation and application instructions for high efficiency conversion of LA to GVL under mild conditions, especially ambient H2 pressure.