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 (N2) 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 (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 × 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 μm, about 56.8 metric tons of Mn is sufficient to produce a metric ton of NH3 per day using CLAS

Chemical Looping of Manganese to Synthesize Ammonia at Atmospheric Pressure: Sodium as Promoter

Affordable synthetic ammonia (NH3) enables the production of nearly half of the food we eat and is emerging as a renewable energy carrier. Sodium-promoted chemical looping NH3 synthesis at atmospheric pressure using manganese (Mn) is here demonstrated. The looping process may be advantageous when inexpensive renewable hydrogen from electrolysis is available. Avoiding the high pressure of the Haber-Bosch process by chemical looping using earth-abundant materials may reduce capital cost, facilitate intermittent operation, and allow operation in geographic areas where infrastructure is less sophisticated. At this early stage, the data suggest that 0.28 m3 of a 50 % porosity solid Mn bed may suffice to produce 100 kg NH3 per day by chemical looping, with abundant opportunities for improvement