Abstract
A series of Fe-zeolite-beta (Fe-BEA and 57Fe-BEA) has been prepared either 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 H2 or CO and Mo¨ssbauer and DRIFT spectroscopies after various pretreatments. These pretreatments consisted of the calcination by O2, the reduction by H2, and the calcination by N2O of the prereduced sample. After calcination in O2, Fe2O3 aggregates are only present when the exchange level exceeded 100%. At an exchange level lower than 100%, Fe would mainly be present as binuclear oxocations of the type [(OH)FeOFe(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 great difference stands in the formation of different Fe oxocations, much more easily reducible than those formed upon calcination in O2. It is postulated that these specific oxocations would mainly be composed of mononuclear Fe species.