Journal
ACS CATALYSIS
Volume 11, Issue 17, Pages 11005-11015Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.1c01934
Keywords
ammonia decomposition; CaNH; anion vacancy; Ni catalyst; Mars-van Krevelen mechanism
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Funding
- PRESTO grant from the Japan Science and Technology Agency (JST) [JPMJPR18T6]
- Kakenhi from the Japan Society for the Promotion of Science (JSPS) [JP21H00019, JP19H02512, 17H06153]
- Tokuyama Science Foundation
- JSPS fellowship [18J00745, P18361]
- [2019G503]
- Grants-in-Aid for Scientific Research [18J00745] Funding Source: KAKEN
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Ni-supported CaNH acts as a highly efficient catalyst for ammonia decomposition through an NH2- vacancy-mediated Mars-van Krevelen mechanism, exhibiting much greater activity than other Ni-based catalysts with a 100 degrees C lower operating temperature.
Nickel has been studied as an alternative catalyst to ruthenium for ammonia decomposition. However, high reaction temperatures are generally required to achieve good ammonia conversion because the weak interactions between nitrogen and the Ni surface reduce the frequency of the dehydrogenation reaction of ammonia. Here, we report Ni-supported CaNH as a highly efficient catalyst for ammonia decomposition through an NH2- vacancy-mediated Mars-van Krevelen mechanism. Ni/CaNH exhibited much greater ammonia decomposition activity than state-of-the-art Ni-based catalysts, and the operating temperature was 100 degrees C lower than those of the other Ni-based catalysts. Isotope-labeling experiments, NH3-pulse measurements, and density functional theory calculations suggested that two anionic electrons at the NH2- vacancy on the Ni/CaNH surface activated ammonia molecules to form intermediate NHx (x = 1, 2) species, even at 50 degrees C, and the supported Ni metal promoted the regeneration of NH2- vacancies on CaNH. These results demonstrate that NH2- vacancy sites on CaNH play an important role in overcoming the drawbacks of Ni-based catalysts in ammonia decomposition.
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