6533b82bfe1ef96bd128df2c

RESEARCH PRODUCT

Steam-activated FeMFI zeolites. Evolution of iron species and activity in direct N2O decomposition

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Abstract In this paper the effect of the composition and steaming conditions of FeMFI catalysts on activity in direct N2O decomposition is investigated. MFI zeolites with different framework compositions (FeAlSi, FeGaSi, and FeSi) and without iron ( 100 mbar H2O in N2) favor the extraction of framework iron, enabling the application of lower activation temperatures. The optimum temperature during steam activation is that at which extraction of framework iron is complete without extensive clustering of extra-framework iron species into oxide particles, as was demonstrated by transmission electron microscopy and electrochemical characterization of the samples. Additional experiments showed an increase in activity as a function of decreasing crystal size of the zeolite, indicating the presence of intracrystalline transport limitations. Furthermore, higher N2O decomposition activities can be obtained by the application of a novel alkaline post-treatment of the steamed catalyst to further improve the catalyst accessibility by creation of mesopores. Implications of the results for the nature of the active Fe-site in direct N2O decomposition are discussed. Our observations suggest that small intrazeolitic iron species in extra-framework positions are crucial in direct N2O decomposition.