CH4 oxidation to oxygenates with N2O over iron-containing Y zeolites: Effect of preparation
Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH 4 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 Fe 2 + complexes are identified as so-called active α-iron sites on zeolites. ICP-OES, N 2 adsorption–desorption test, X-ray diffraction, solid-state 27 Al NMR, N 2 O titration, TEM, EPR and 57 Fe 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 Fe 2 + complexes but no Fe 2 O 3 bulks and show weak acidity. These lead to a higher oxygenate selectivity in CH 4 oxidation to oxygenates. Remarkably, the oxygenate (HCHO and CH 3 OH) selectivity of 6.5% at 375°C can be eventually obtained.
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