Identification of Iron Species in Fe−BEA: Influence of the Exchange Level

A series of Fe−zeolite-beta (Fe−BEA and 57 Fe−BEA) has been prepared either by exchanging BEA (Si/Al = 12.5) with Fe(NO 3 ) 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 Mössbauer and DRIFT spectroscopies after various pretreatments. These pretreatments consisted of the calcination by O 2, the reduction by H 2, and the calcination by N 2 O of the prereduced sample. After calcination in O 2, Fe 2 O 3 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 N 2 O 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 O 2 . It is postulated that these specific oxocations would mainly be composed of mononuclear Fe species.