Ammonium Nitrate Temperature-Programmed Decomposition on Fe–Zeolite Catalysts: Effect of Deposition Method

Abstract

The N2O formation during NOx selective catalytic reduction by NH3 is often attributed to NH4NO3 intermediate decomposition. Thermal decomposition of NH4NO3 has been extensively studied owing to the combination of its wide use as fertilizer and its dangerous properties. However, the decomposition of NH4NO3 in the presence of a catalyst has generated less attention. The decomposition of NH4NO3 may yield NxOy-type products such as NO, NO2, N2O, N2 as well as HNO3 and H2O. This work focuses on the emissions of N2O. The deposition of NH4NO3 onto a Fe–zeolite catalyst was carried out by dry impregnation, by using a dilute solution of NH4NO3, and by a mechanical mixture. In the absence of catalyst, the release of N2O strongly depends on the conditions of the experiment (static or dynamic). The presence of a catalyst and the method of mixing ammonium nitrate into it affects its decomposition. Nitrogen formation is much more significant for the impregnated sample. For the mechanically mixed sample, the ammonium nitrate is mainly decomposed into N2O and NO2. N2O from ammonia oxidation was also detected in the presence of a catalyst.