Activating dinitrogen for chemical looping ammonia Synthesis: Mn nitride layer growth modeling

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 (H-2) to produce ammonia (NH3). Here, the dynamic process of N atoms penetrating into solid Mn has been investigated. Nitride layer growth was modeled to quantitate and predict 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 x 10(-11) m(2)/s and 4.1 +/- 3.5 x 10(-4) 1/s, respectively, at atmospheric pressure and 700 degrees C. Assuming spherical particles of Mn with a diameter of < 10 mu m, about 56.8 metric tons of Mn is sufficient to produce a metric ton of NH3 per day using CLAS. (C) 2021 Elsevier Ltd. All rights reserved.