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

Abstract

The effects of promoters on Ru nanoparticles (≥2 nm) catalysts for NH3 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 NH3 synthesis. The addition of 5wt.%K onto Ru/MgO NCs leads to a significantly high NH3 synthesis rate of 21.7 mmolNH3 gcat−1h−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 NH3 synthesis at mild conditions.