Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 142, Issue 33, Pages 14374-14383Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c06624
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Funding
- Element Strategy Initiative to Form Core Research Center of the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) [JPMXP0112101001]
- PRESTO Grant from the Japan Science and Technology Agency (JST) [JPMJPR18T6]
- Japan Society for the Promotion of Science (JSPS) [17H06153, JP19H05051, JP19H02512]
- JSPS [P18361, 18J00745]
- Grants-in-Aid for Scientific Research [18J00745] Funding Source: KAKEN
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Ammonia is one of the most important feedstocks for the production of fertilizer and as a potential energy carrier. Nitride compounds such as LaN have recently attracted considerable attention due to their nitrogen vacancy sites that can activate N-2 for ammonia synthesis. Here, we propose a general rule for the design of nitride-based catalysts for ammonia synthesis, in which the nitrogen vacancy formation energy (E-NV) dominates the catalytic performance. The relatively low E-NV (ca. 1.3 eV) of CeN means it can serve as an efficient and stable catalyst upon Ni loading. The catalytic activity of Ni/CeN reached 6.5 mmol.g(-1).h(-1) with an effluent NH3 concentration (E-NH3) of 0.45 vol %, reaching the thermodynamic equilibrium (E-NH3 = 0.45 vol %) at 400 degrees C and 0.1 MPa, thereby circumventing the bottleneck for N-2 activation on Ni metal with an extremely weak nitrogen binding energy. The activity far exceeds those for other Co- and Ni-based catalysts, and is even comparable to those for Ru-based catalysts. It was determined that CeN itself can produce ammonia without Ni-loading at almost the same activation energy. Kinetic analysis and isotope experiments combined with density functional theory (DFT) calculations indicate that the nitrogen vacancies in CeN can activate both N-2 and H-2 during the reaction, which accounts for the much higher catalytic performance than other reported nonloaded catalysts for ammonia synthesis.
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