Synergistic catalysis of Ru0-Ru3+ in MOF supported ultrafine Ru nanoparticles catalyst promotes ethyl levulinate to γ-valerolactone

Synthesis of bifunctional catalysts is very important for the hydrogenation of biomass to advanced biofuels, but its efficient regulation is difficult. In this work, a tunable bifunctional Ru/LaQS catalyst with Lewis acid and metal hydrogenation sites was prepared by stable MOFs (LaQS) supported ultrafine Ru nanoparticles (NPs). When the optimal Ru2/LaQS catalyst catalyzed bio-based ethyl levulinate (EL) to γ-valerolactone (GVL), the EL conversion and GVL selectivity reached 99.9% under mild conditions of 100 °C. The excellent catalytic performance is mainly attributed to the synergistic effect of Ru0-Ru3+ on ultrafine Ru NPs with only 1.60 nm generated by metal-support interaction, which is proved by experimental characterization and theoretical calculation. Moreover, the electron density of hydrogenation active site Ru0 and the content of acidic site Ru3+ can be modulated by Ru loading. Among them, the activation of H2 was promoted by the high electron density of Ru0 generated through metal-support electronic interactions. The enhanced medium-strong acidic site Ru3+ not only improved the activation of EL, but also promoted the intramolecular dealcoholization of the intermediate to GVL. The synergistic catalytic mechanism of Ru0-Ru3+ on ultrafine Ru NPs was speculated. The excellent stability was mainly attributed to the metal-support interaction stabilizing the ultrafine Ru NPs, which prevents the agglomeration and loss of Ru NPs during cycling. This work provides an in-depth understanding of the bifunctional catalytic mechanism, which is of guiding significance for the design and preparation of MOFs-based catalysts for biomass hydrogenation.