Thermochemical Synthesis of Ammonia and Syngas from Natural Gas at Atmospheric Pressure

Ammonia is a vital agricultural input and could be a carbon-free energy vector. An experimental proof-of-concept of a novel thermochemical cycle to produce NH3 and syngas (CO-H2) at atmospheric pressure from N2, steam, and shale gas (CH4) is demonstrated here: Mn was reacted with N2 forming Mn-nitride, corrosion of Mn-nitride with steam at 500 °C formed MnO and NH3, and finally MnO was reduced at 1150 °C in a 4 vol % CH4–96 vol % N2 stream to Mn-nitride, closing the cycle. Optimum nitridation at 800 °C and 120 min produced a Mn6N2.58-rich Mn-nitride mixture containing 8.7 ± 0.9 wt % nitrogen. NH3 yield was limited to 0.04 after 120 min during nitride corrosion, but addition of a NaOH promotor improved NH3 yield to 0.54. Mn6N2.58 yield was 0.381 ± 0.083 after MnO reduction for 30 min with CO and H2, but no CO2 detected in the product.