Identification of iron species in Fe-BEA: Influence of the exchange level

A series of Fe-zeolite-beta (Fe-BEA and Fe-57-BEA) has been plt pared eithe r by exchanging BEA (Si/Al = 12.5) with Fe(NO3)(3) or by impregnation. The identification of Fe species in Fe-BEA has been carried out by temperature- programmed reduction (TPR) with H-2 or CO and Mossbauer and DRIFT spectrosc opies after various pretreatments. These pretreatments consisted of the cal cination by O-2, the reduction by H-2, and the calcination by N2O of the pr ereduced sample. After calcination in O-2, Fe2O3 aggregates are only presen t when the exchange level exceeded 100%. At an exchange level lower than 10 0%, Fe would mainly be present as binuclear oxocations of the type [(OH)FeO Fe(OH)](2+), with the proportion decreasing as Fe content decreases. There are some unreducible Fe atoms, possibly in tetrahedral coordination in the zeolite framework. After the calcination in N2O of prereduced Fe-BEA, the g reat difference stands in the formation of different Fe oxocations, much mo re easily reducible than those formed upon calcination in O-2. It is postul ated that these specific oxocations would mainly be composed of mononuclear Fe species.