Chemical Transformation of Fe, Air & Water to Ammonia: Variation of Reaction Rate with Temperature, Pressure, Alkalinity and Iron

The rate of ammonia production by the chemical oxidation of iron, N 2 (from air or as pure nitrogen) and water is studied as a function of (1) iron particle size, (2) iron concentration, (3) temperature, (4) pressureand (5) concentration of the alkaline reaction medium. The reaction meduium consists of an aqueous solution of equal molal concentrations of NaOH and KOH (Na 0.5 K 0.5 OH). We had previously reported on the chemical reaction of iron and nitrogen in alkaline medium to ammonia as an intermediate step in the electrochemical synthesis of ammonia by a nano-sized iron oxide electrocatlyst. Here, the intermediate chemical reaction step is exclusively explored. The ammonia production rate increases with temperature (from 20 to 250°C), pressure (from 1 atm to 15 atm of air or N 2 ), and exhibits a maximum rate at an electrolyte concentration of 8 molal Na 0,5 K 0,5 OH in a sealed N 2 reactor. 1-3 µm particle size Fe drive the highest observed ammonia production reaction rate. The Fe mass normalized rate of ammonia production increases with decreasing added mass of the Fe reactant reaching a maximum observed rate of 2.2x10 -4 mole of NH 3 h -1 g -1 for the reaction of 0.1 g of 1-3 µm Fe in 200°C 8 molal Na 0.5 K 0.5 OH at 15 atm. Under these conditions 5.1 wt% of the iron reacts to form NH 3 via the reaction N 2 + 2Fe + 3H 2 O ®2NH 3 + Fe 2 O 3 .