Phase cooperation between the ZnFe2O4 and α-Fe2O3 phases of ferrite catalysts in the oxidative dehydrogenation of n-butenes

Detailed characterizations and catalytic properties of pure ZnFe2O4, α-Fe2O3 and the biphasic catalysts are reported. It has been found that the biphasic catalysts containing ZnFe2 O4 and α-Fe2O3 exhibit remarkably improved catalytic activity with respect to each component. The observed phenomenon can be explained in terms of a synergetic effect. The results of the oxidative dehydrogenation of n-butenes over the pure phases and the biphasic catalyst at O2–C4H8 ratios ranging from conditions of oxygen deficiency to excess oxygen suggest that there may be a possible function distribution between ZnFe2O4 and α-Fe2O3 of the ferrite catalyst. The results of the oxidation reaction of n-butenes in the absence of gas-phase oxygen over the pure phases and the biphasic catalyst containing 55.5%α-Fe2O3 indicate that the biphasic catalyst exhibits a longer active life than each of the two pure phases. Characterization of the pure phases and biphasic catalyst by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and Mossbauer spectroscopy before and after the oxidation reaction of butenes in the absence of gas-phase oxygen reveals that α-Fe2O3 in the biaphasic catalyst was more easily reduced by butene than pure α-Fe2O3. With the catalytic behaviour of the pure phases and the biphasic catalyst taken into account, a synergetically catalytic mechanism for the ferrite biphasic catalyst is proposed.