Abstract
Mild-condition ammonia synthesis from N2 and H2 is a long-thought-after scientific goal and a practical need, especially for the intensively pursued "green ammonia" production using renewable H2. Barium-containing materials have recently attracted significant attention as promising catalysts, catalyst supports, or mediators for effective ammonia synthesis under mild conditions. Here, we report that the ternary barium-ruthenium complex hydride, Ba2RuH6, displays outstanding catalytic activity, which is nearly an order of magnitude higher than that of the active BaO-promoted Ru metal (BaO-Ru/MgO) catalyst at temperatures below 573 K. Different from the Ru metal catalyst, the kinetic parameters of Ba2RuH6 catalyst exhibit interesting temperature dependence. The catalytic center, function mechanism, and kinetic behaviors of Ba2RuH6 catalyst are investigated with a combined experimental and computational approach. We find that the N2 reduction reaction (NRR) is preferentially carried out on a defected Ba2RuH6 (110) surface with Ba and H vacancies, in which a complex active center consisting of three Ba atoms and one Ru atom plus the coordinating hydridic hydrogens catalyze nondissociative hydrogenolysis of N2 through the dynamic and synergistic engagement of all of the components of Ba2RuH6 in mediating electron and proton transfers. Specifically, barium plays a unique and vital role in the whole process by directly donating electrons and bonding with reacting NxHy species. Based on the proposed reaction pathway, the catalytic and kinetic performances of the Ba2RuH6 catalyst are analyzed with the energetic span model, and the calculated turnover frequencies are comparable to the experimental results under the ammonia synthesis conditions applied in this study.
Original language | English |
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Journal | ACS Catalysis |
Volume | 12 |
Issue number | 7 |
Pages (from-to) | 4194-4202 |
Number of pages | 9 |
ISSN | 2155-5435 |
DOIs | |
Publication status | Published - 2022 |
Keywords
- Ammonia synthesis
- Complex hydride
- Ba2RuH6
- Nondissociative N2 activation
- Density function theory