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

Abstract

N 2O 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 FeO x -like crystallite were verified by means of H 2-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 deN 2O activity was observed for Fe-beta samples with iron contents higher than 1%. Two kinds of reaction mechanism, with respective formation of oxygen (O 2) or nitrogen oxide (NO x ) intermediate, for the direct decomposition of N 2O over Fe-beta zeolite (noted as Fe-Z) were proposed according to the N 2O-TPD, NO 2-TPD, N 2-TPD, N 2O-TPSR, and in situ DRIFTS investigation and density functional theory (DFT) study. The corresponding energy calculations for O 2-formation mechanism revealed that O 2 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.