Mössbauer Spectroscopic Characterization of Iron Supported on Y Type Zeolites after Sulfiding

Abstract

Abstract Iron supported on zeolite catalysts, prepared by treating NH4Y with aqueous solutions containing Fe3+ or Fe2+ ions followed by calcination in air, were subjected to Mössbauer spectroscopic investigations before and after sulfiding treatments to elucidate the states and properties of Fe species supported. At least three types of Fe3+ species could be distinguished in the prepared samples. The first Fe3+ species were those located at the cation-exchange sites of zeolite. This type was reduced easily to Fe2+ species with the H2S treatment, but was resistant to aggregation to form Fe1−xS. The second Fe3+ species were those which had precipitated on the surface of zeolites as hydroxides. These were sulfided to crystalline Fe1−xS after H2S treatment. Finally, the third Fe3+ species were those which were quite resistant to both reduction to Fe2+ and sulfiding to Fe1−xS. These species were preferentially supported under the conditions where dealumination from zeolite framework took place simultaneously. Thus it was speculated that these species were bonded to zeolite framework to be stabilized. The distribution of the three Fe3+ species were quite different depending on the sample preparation. Comparison with the catalytic data clearly indicated that the third Fe3+ species acted as highly active sites for the toluene disproportionation reaction in the presence of H2S.