摘要
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 activeα-iron sites on zeolites.ICP-OES,N_2 adsorption–desorption test,X-ray diffraction,solid-state^(27)Al NMR,N_2O titration,TEM,EPR and^(57)Fe M?ssbauer 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_2O_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_3OH)selectivity of 6.5% at 375°C can be eventually obtained.
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 activeα-iron sites on zeolites.ICP-OES,N2 adsorption–desorption test,X-ray diffraction,solid-state27Al NMR,N2O titration,TEM,EPR and57Fe M？ssbauer 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.
基金
Support by the National Key R&D Program of China(2016YFA0202900)
the National Natural Science Foundation of China(21622606)
the Natural Science Foundation of Zhejiang Province(LR18B060001)
Basic Research Project of Sinopec Group(415025)
the Fundamental Research Funds for the Central Universities
