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Keywords:

  • density functional theory;
  • iron;
  • isotopes;
  • mass spectrometry;
  • zeolites

Abstract

The role of framework oxygen atoms in N2O decomposition [N2O(g)[RIGHTWARDS ARROW]N2(g) and 1/2O2(g)] over Fe-ferrierite is investigated employing a combined experimental (N218O decomposition in batch experiments followed by mass spectroscopy measurements) and theoretical (density functional theory calculations) approach. The occurrence of the isotope exchange indicates that framework oxygen atoms are involved in the N2O decomposition catalyzed by Fe-ferrierite. Our study, using an Fe-ferrierite sample with iron exclusively present as FeII cations accommodated in the cationic sites, shows that the mobility of framework oxygen atoms in the temperature range: 553 to 593 K is limited to the four framework oxygen atoms of the two AlO4 tetrahedra forming cationic sites that accomodate FeII. They exchange with the Fe extra-framework 18O atom originating from the decomposed N218O. We found, using DFT calculations, that O2 molecules facilitate the oxygen exchange. However, the corresponding calculated energy barrier of 87 kcal mol−1 is still very high and it is higher than the assumed experimental value based on the occurrence of the sluggish oxygen exchange at 553 K.