Ru/ZrO2 Catalysts for Transfer Hydrogenation of Levulinic Acid with Formic Acid/Formate Mixtures: Importance of Support Stability

Abstract

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The transfer hydrogenation of levulinic acid to γ-valerolactone using an equimolar mixture of formate/formic acid in water was investigated using Ru/ZrO2 catalysts. Ru/ZrO2 with < 3 wt. % loading were more active than those with higher loadings. The stability of the catalysts is of concern as the reaction occurs under acidic and hydrothermal conditions. To minimize metal leaching, the Ru/ZrO2 catalysts were prepared by a sol-gel process to entrap the ruthenium nanoparticles within the support. Despite insignificant leaching of Ru, the used catalyst was deactivated after the first run. No agglomeration of Ru particles could be observed by TEM and XRD. However, the zirconia support had transformed from a predominantly tetragonal crystal phase to the monoclinic form. X-ray photoelectron spectroscopy revealed a decrease in the surface Ru/Zr ratio. Doping with 0.1 wt. % SiO2 successfully stabilized the tetragonal phase of zirconia and the recycled catalyst maintained its high activity in reuse.