| Popis: |
Ammonium nitrate NH 4NO 3 (AN) is a proposed candidate for energetic ionic l iquids and solid propellants. The decomposition of aqueous NH 4NO 3 (50-55 wt-%), in the thermal condition and in the presence of various mono- and bimetallic catalysts, was investigated using thermal analysis (DTA-TGA), batch reactor and dynamic flow reactor with on-line MS analysis. The first results are as follows: heat ing in the absence of catalyst shows the quantitative only endothermic vaporization of water and AN have been evidenced into ammonia and nitric acid even at high temperature. In the presence of catalysts, a dramatic change is observed. All monometallic catalysts (sup ported Pt, Fe, Cu or Zn) present a true catalytic decomposition reaction linked to exothermic peaks. However, only Pt-based catalyst was able to trigger the decomposition at l ower temperature (210 °C). Nevertheless, tests in batch reactor reveals mediocre results ass ociated to very slow AN decomposition. Bimetallic catalysts M-M’/Al 2O3-Si (M, M’ = Fe, Cu, Zn, Pt) have been evaluated to o. The catalytic decomposition depends on the active phase and on the preparation method of the bimetallic catalysts. The addition of zinc or coppe r on non-reduced platinum catalyst (PtCuAl-NR and PtZnAl-NR) increases the catalytic effect of platinum and the results display a beneficial effect disclosed by a violent one-step decomposition. On the contrary, the addition of zinc or copper on reduced platinum metal leads to less active catalysts and the decomposition occurs in two steps. This activity di fference could be mainly related to the formation zinc-platinum and copper-platinum alloys when adding the second metallic precursor on non-reduced platinum, followed by a final reduction. Whatever the catalyst (PtAl, PtCuAl-NR or PtZnAl-NR), the results obtained using a dynamic reactor reveal the presence of the same gaseous and condensed products: major nitrogen and nitric acid and no oxygen; the formation of nitrogen oxides NO and N 2O depends on the catalyst nature: minor for PtAl and medium for PtCuAl-NR and PtZnAl-NR. |
