CATALYTIC DECOMPOSITION OF AMMONIUM NITRATE IN SUPERHEATED AQUEOUS SOLUTIONS

The decomposition of aqueous ammonium nitrate at elevated temperatures and pressures is examined as a function of chloride, nitrate, and total acidity. Catalysis requiring both chloride and acid was observed in solutions containing 20% (w/w) NH4NO3 at 180 °C. Nitrous oxide and dinitrogen were generated in a 4:1 ratio below 0.2 M H+. Dinitrogen formation correlated with the production of additional acidity by the reaction 5NH4NO3 → 4N2 + 2HNO3 + 9H2O. The second-order dependence of the decomposition reaction on [H+] is consistent with the reversible formation of NO2+. Incorporation of 18O into the N2O product, as well as the inverse deuterium isotope effect, supports this conclusion. A novel mechanism based on the intermediacy of NO2Cl is proposed for the chloride catalysis and contrasted to the radical-based pathways operational in molten NH4NO3 decompositions. Isotope-labeling experiments using 15NH4NO3 lead to the formation of 15NNO-labeled nitrous oxide and the dinitrogen products 15N⋮15N and N⋮15N in ...