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The earth-abundant transition metal manganese (Mn) has been shown to activate dinitrogen (N 2) and store nitrogen (N) as nitride for subsequent chemical reaction, for example, to produce ammonia (NH3). Chemical looping ammonia synthesis (CLAS) is a practical way to use Mn nitride by contacting nitride with gaseous hydrogen (H2 ) to produce ammonia (NH 3). Here, the dynamic process of N atoms penetrating into solid Mn has been investigated. Nitride layer growth was modeled to quantitate and pre- dict the storage of activated N in Mn towards designing CLAS systems. The N diffusion coefficient (DN ) and reaction rate constant K for the first-order nitridation reaction were estimated at 6.2 ± 5.5 10-11 m2/s and 4.1 ± 3.5 10-4 1/s, respectively, at atmospheric pressure and 700 °C. Assuming spherical particles of Mn with a diameter of < 10 lm, about 56.8 metric tons of Mn is sufficient to produce a metric ton of NH 3 per day using CLAS
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Activating dinitrogen for chemical looping ammonia synthesis: nitridation of manganese
The earth-abundant transition metal manganese (Mn) has been shown to be useful to activate dinitrogen at atmospheric pressure and elevated temperature by forming bulk Mn nitrides. Mn nitrides could then be used, for example, for ammonia (NH3) synthesis in a chemical looping process by contacting nitride with gaseous hydrogen (H2). Here, we present an investigation of the morphology and local time-dependent composition of micrometer-scale Mn plates during nitridation in dinitrogen (N2) near atmospheric pressure at 700 C. The main motivation was to obtain design data for chemical looping synthesis of NH3 and to add to the somewhat sparse literature on nitridation of Mn. The morphology and elemental compositional variation of the nitrided specimens were studied with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), wide angle X-ray diffraction (WAXD), and mass balances. Three possible nitrogen (N) populations that may govern the Mn nitridation and later NH3 synthesis are identified. After four hours of nitridation, the N weight gain was found to be 9.4 ± 0.7 kgN to nMn-1 for the plates used here, resulting in a nitridation depth of 83 ± 8 lm.
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- Award ID(s):
- 1856084
- PAR ID:
- 10323579
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Journal of Materials Science
- Volume:
- 56
- Issue:
- 22
- ISSN:
- 0022-2461
- Page Range / eLocation ID:
- 12584 to 12595
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10853-021-06079-7
