Oxydehydrogenation of C2–C4hydrocarbons over Fe-ZSM-5 zeolites with N2O as an oxidant

Abstract

Fe-ZSM-5 zeolites with a Si/Al ratio equal to 25 and 50, comprising 0.4 wt% of Fe and calcined at different temperatures, were used for oxidative dehydrogenation (ODH) of C₂–C₄ hydrocarbons. The calcination temperature (873 or 1173 K) slightly influenced hydrocarbon conversion, while it distinctly affected the selectivity towards respective olefins. It stems from the modification of acidic centers present in Fe-ZSM-5 samples. Calcination at 1173 K resulted in the decrease of total acidity, especially of strong Brønsted sites. UV-vis spectra evidenced the presence of very different iron(III) species, while the existence of Fe(II) ions was inferred from IR spectra of the adsorbed NO molecule. IR bands located at about 1840 and 1750 cm⁻¹ indicate the presence of isolated iron(II) species, particularly in Fe-ZSM-5(1173) samples.