Abstract: Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH₄ to oxygenates have remained challenging topics so far. In this paper, we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene, which was conducted under water-free conditions followed by a series of calcination. Moreover, extra-framework dinuclear Fe²⁺ complexes are identified as so-called active α-iron sites on zeolites. ICP-OES, N₂ adsorption-desorption test, X-ray diffraction, solid-state ²⁷Al NMR, N₂O titration, TEM, EPR and ⁵⁷Fe Mössbauer spectra were carried out to characterize properties of sample structure, acid sites, as well as the supported iron species. Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites. Compared with catalysts synthesized by conventional impregnation, the samples prepared by the facile approach possess abundant dinuclear Fe²⁺ complexes but no Fe₂O₃ bulks and show weak acidity. These lead to a higher oxygenate selectivity in CH₄ oxidation to oxygenates. Remarkably, the oxygenate (HCHO and CH₃OH) selectivity of 6.5% at 375℃ can be eventually obtained.

Key words: Ferrocene, Iron-containing zeolites, Preparation, Distributions, Partial oxidation

摘要： Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH₄ to oxygenates have remained challenging topics so far. In this paper, we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene, which was conducted under water-free conditions followed by a series of calcination. Moreover, extra-framework dinuclear Fe²⁺ complexes are identified as so-called active α-iron sites on zeolites. ICP-OES, N₂ adsorption-desorption test, X-ray diffraction, solid-state ²⁷Al NMR, N₂O titration, TEM, EPR and ⁵⁷Fe Mössbauer spectra were carried out to characterize properties of sample structure, acid sites, as well as the supported iron species. Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites. Compared with catalysts synthesized by conventional impregnation, the samples prepared by the facile approach possess abundant dinuclear Fe²⁺ complexes but no Fe₂O₃ bulks and show weak acidity. These lead to a higher oxygenate selectivity in CH₄ oxidation to oxygenates. Remarkably, the oxygenate (HCHO and CH₃OH) selectivity of 6.5% at 375℃ can be eventually obtained.

关键词: Ferrocene, Iron-containing zeolites, Preparation, Distributions, Partial oxidation