SYNERGISTIC CATALYSIS OF AMMONIUM NITRATE DECOMPOSITION

Chloride and various transition metal ions, notably chromium and copper, exhibit an unexpectedly large synergistic effect in the catalysis of the thermal decomposition of ammonium nitrate. Mechanisms are proposed for these reactions. In the case of copper and chloride, the proposed mechanism involves the operation of redox cycles in which reactions occur by electron transfer in chloro-bridged activated states. NH4+ and NH3 are oxidized to NH3+ and NH2, and NH2Cl is produced by reaction of NH2. The original cupric catalysts are then regenerated through oxidation by NO2+ and NO+. The proposed mechanism for chromium catalysis depends on the participation of dichromate in a fused-salt acid-base reaction with nitrate in which nitronium and chromate ions are formed. Both mechanisms produce intermediates which also occur in the mechanism proposed in previous publications for the simple chloride-catalyzed decomposition of ammonium nitrate. A su vey of the effects of 23 metals indicates that synergistic catalysis with chloride generally requires a metal capable of forming chloro complexes of reasonable stability in two oxidation states differing by one electron unit. Chromium is a special case in which oxo complexes are believed to be involved. © 1969, American Chemical Society. All rights reserved.