Potassium promoter regulates electronic structure and hydrogen spillover of ultrasmall Ru nanoclusters catalyst for ammonia synthesis

The effects of promoters on Ru nanoparticles (≥2 nm) catalysts for NH 3 synthesis have been extensively elaborated, but their roles on ultrasmall Ru nanoclusters (NCs, 1–2 nm) remain largely unknown and need to be further uncovered. Herein, a series of K-promoted MgO supported Ru NCs were synthesized and investigated for NH 3 synthesis. The addition of 5wt.%K onto Ru/MgO NCs leads to a significantly high NH 3 synthesis rate of 21.7 mmol NH3 g cat −1 h −1 at 400 °C and 0.2 MPa, close to the thermodynamic equilibrium. Out studies reveal that anchoring K onto Ru NCs can increase the electron density and cause an upshift of the d -band center of Ru entities. Moreover, the addition of K regulates the hydrogen affinity and accelerates the migration of hydrogen from the Ru NCs surface to MgO support, which is crucial in avoiding the hydrogen poisoning effect on Ru NCs. With the synergistic effect of the Ru NCs sites bridged by H-spillover, makes the K-mediated Ru/MgO NCs catalysts efficient for NH 3 synthesis at mild conditions.