REDUCTION AND SULFIDATION PROPERTIES OF IRON SPECIES IN IRON-SUPPORTED Y-ZEOLITE BY TEMPERATURE-PROGRAMMED REDUCTION AND SULFIDING

Temperature-programmed reduction (TPR) and temperature-programmed sulfiding (TPS) were used to characterize reduction and sulfiding properties of Fe-exchanged Y-zeolites and Fe-treated Y-zeolites, which were prepared by treating NH4Y-zeolite with an aqueous ferric nitrate solution (Fe-treatment). By considering their unique TPR and TPS patterns, it was confirmed that the Fe2+-species in the Fe-exchanged Y-zeolites are stabilized inside the sodalite cages and the hexagonal prisms. On the basis of the TPR and TPS characterizations, it was demonstrated that three types of the Fe-species are present in the Fe-treated Y-zeolites: ion-exchanged species, small Fe oxide clusters, and Fe oxide without interaction with the zeolite framework (including aggregated ferric oxide), the proportion of which is dependent on the extent of the Fe-treatment. Prolonged Fe-treatment weakens the interaction between the Fe-species and the framework oxygen atoms by hydrolysis, and leads to the aggregation of the Fe oxides and to the formation of bulk ferric oxide. The small Fe-oxide clusters, which are probably situated inside the supercages through a coordination with the framework oxygen atoms, are responsible for the high activity for toluene disproportionation in the presence of H2S. © 1993 Academic Press, Inc.