Electron-Rich Ruthenium on Nitrogen-Doped Carbons Promoting Levulinic Acid Hydrogenation to γ‑Valerolactone: Effect of Metal–Support Interaction

Ru has been found to be a highly efficient catalyst for producing γ-valerolactone from the hydrogenation of levulinic acid. However, the active species on Ru nanoparticles (NPs) are still unclear. Here, we synthesized a series of Ru NPs with tunable chemical states obtained by altering the interaction with carbon-nanotube-based supports, achieved by the strategies of doping carbon nanotubes with N and S atoms, changing the amount of dopants, and varying the loading of Ru. The surface species of the supported Ru NPs, identified by X-ray photoelectron spectroscopy, were linked to the catalytic activities instrinsically. We found that the Ru NPs possessing Ru⁰ with lower binding energy (Ru 3p) showed higher activity independent of the parameters of synthesis. Theoretical calculations indicated that the electron-rich Ru⁰ enhanced LA hydrogenation through facilitating R–COOH breaking into R–CO and −OH, suggesting a powerful tool modifying the catalytic activity of carbon-supported metals by manipulating the electronic metal–support interaction.