LAUSR

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 Mossbauer 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°C can be eventually obtained.