Tuning clusters-metal oxide promoters electronic interaction of Ru-based catalyst for ammonia synthesis under mild conditions

Abstract

Ammonia (NH3) is an excellent candidate for hydrogen storage and transport. However, producing NH3 under mild conditions is a long-term, arduous task. Atomic cluster catalysts (ACCs) have been shown to be effective for catalytic N2-to-NH3 conversion, opening the door to the development of efficient catalysts under mild conditions. Still, ACC formation with thermally stable catalytic sites remains a challenge because of their high surface free energy. Herein, we report anchoring Ba and/or Ce onto Ru ACCs (2 wt% Ru atomic clusters supported on N-doped carbon) to form so-called clusters–metal oxide promoters electronic interaction (CMEI) to stabilize the Ru atomic clusters. The resulting Ba/Ce/Ru ACCs significantly boost the NH3 synthesis rate to 56.2 mmolNH3 gcat−1 h−1 at 400 °C and 1 MPa, which is 7.5-fold higher than that of Ru ACC. The strengthened CMEI between the Ba/Ce and Ru atomic clusters across the Ba/Ce/Ru ACC enables electron transfer from Ba and/or Ce to Ru atomic clusters. As such, the electron-enriched Ru atom could facilitate electron transfer to N≡N bond π* orbitals, which would weaken the N≡N bond and drive the eventual conversion of N2 to NH3. This study offers insight into the role of CMEI in Ru ACCs and provides an effective approach for designing stable atomic cluster catalysts for NH3 synthesis.