Inorganic Chemistry

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, N2(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 (Na0.5K0.5OH). 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 N2), and exhibits a maximum rate at an electrolyte concentration of 8 molal Na0,5K0,5OH in a sealed N2reactor. 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 2.2x10-4mole of NH3h-1g-1for the reaction of 0.1 g of 1-3 µm Fe in 200°C 8 molal Na0.5K0.5OH at 15 atm. Under these conditions 5.1 wt% of the iron reacts to form NH3via the reaction N2+ 2Fe + 3H2O ®2NH3+ Fe2O3.


Thumbnail image of Chem rxn of air and water to ammonia.pdf