Double-active sites cooperatively catalyzed transfer hydrogenation of ethyl levulinate over a ruthenium-based catalyst

Presently, designing high-performance catalyst systems for the sustainable production of chemicals through biomass conversions is of significant importance for large-scale practical application. As for heterogeneous catalysts, the high dispersion of active species can play a vital role in guaranteeing their superior performance. In this regard, the combination of active species with a favorable support matrix is crucial for achieving highly dispersive character of active species and the formation of cooperation between them. Herein, we first synthesized a novel ruthenium-based catalyst, Ru/Zn-Al-Zr layered double hydroxide (Ru/ZnAlZr-LDH), which was employed in the transfer hydrogenation of biomass-derived ethyl levulinate (EL) into γ-valerolactone (GVL) using 2-propanol as hydrogen donor. Extensive characterizations revealed that the interaction between Ru species and the ZnAlZr-LDH matrix helped enhance the dispersion of Ru species on the LDH and also determined the nature of electron-rich Ru species. Furthermore, a cooperative effect between double-active sites on the catalyst, e.g. a large amount of surface hydroxyl groups and highly dispersive electron-rich Ru species, was beneficial to the formation of both activated six-membered ring transition state and active ruthenium-hydride species in the course of EL transfer hydrogenation, thereby resulting in an unparalleled activity with a fastest GVL formation rate of 1250 μmol gcat−1 min−1 to date, with respect to other Zr- or Ru-based catalysts previously reported.