Electron-Rich Ruthenium Single-Atom Alloy for Aqueous Levulinic Acid Hydrogenation

Modulation of the electronic structure of metal-based catalysts proves to be useful for optimizing the catalytic activity. However, precise modulation of the electronic structure at the atomic scale remains challenging, because of the invariant electronic structure of single atoms and the difficulty in achieving the size limit for tailored alloy particles. Herein, we report a RuCo single-atom alloy (SAA) catalyst with precisely tailored electron-rich Ru atoms confined into the Co lattice, skillfully fabricated by pyrolysis of Ru-containing ZIF-67 with a tuned Ru feed content. The structure of RuCo SAAs is well investigated by various characterization techniques, including aberration-corrected scanning transmission electron microscopy, high-energy X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. It is found that the RuCo SAAs with more electron-rich Ru atoms are more active toward aqueous levulinic acid (LA) hydrogenation to γ-valerolactone, delivering an extremely large turnover frequency value of 3500 h–1, 27 fold higher than that over the state-of-art 5 wt % Ru/C catalyst and much higher than those over electron-deficient Ru single atoms and Ru-containing alloyed particles. Combined experimental investigation and computational modeling reveal that the remarkable activity originates from the intrinsic RuCo SAA active site in which the electron-rich Ru single-atom boosts C═O/H2 adsorption and H2 dissociation to H atoms and especially facilitates the γ-C of LA hydrogenation, which is the rate-determining step for LA hydrogenation. This study will shed light on the precise tailoring of the electronic structure at the atomic scale and also provides insight into the development of SAA catalysts for biomass conversion.