Study on the direct decomposition of nitrous oxide over Fe-beta zeolites: From experiment to theory

N2O direct decomposition over Fe-beta zeolite prepared by wet ion-exchange (WIE) was systematically investigated based on the experimental and theoretical studies in this paper. Both isolated iron ions in the charge compensation positions and highly dispersed FeOx-like crystallite were verified by means of H2-TPR. Catalytic performances of various Fe-BEA zeolites with diverse iron contents were thereafter studied. The results showed that: (1) the catalytic activity of bare beta zeolite was significantly promoted via ion-exchange; (2) no obvious further increase in deN2O activity was observed for Fe-beta samples with iron contents higher than 1%. Two kinds of reaction mechanism, with respective formation of oxygen (O2) or nitrogen oxide (NOx) intermediate, for the direct decomposition of N2O over Fe-beta zeolite (noted as Fe-Z) were proposed according to the N2O-TPD, NO2-TPD, N2-TPD, N2O-TPSR, and in situ DRIFTS investigation and density functional theory (DFT) study. The corresponding energy calculations for O2-formation mechanism revealed that O2 desorption was the rate determining step with an energy barrier of 63.20 kcal/mol. Another mechanism with NO formation was also simulated by DFT calculations, whose energy calculations indicated that the formation of Fe-Z-(NO)2 was the main pathway for NO generation with an energy barrier of 26.92 kcal/mol.

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► N2O catalytic decomposition over Fe-beta zeolites involves the formation of O2 and NOx molecules.
► O2 desorption is the rate determining step for an O2-formation mechanism.
► Fe-Z-(NO)2 formation determines the rate of reaction pathway undergoing a NO-formation mechanism.