Fe-ZSM-11 magnetic properties: Its relation with the catalytic activity for NOx SCR with iso-butane and O2

Fen+-ZSM-11 zeolites, with Fe2+ and/or Fe3+ as active sites prepared by us by reproducible post-synthesis methods showed magnetic properties. Otherwise, they are very important in environmental catalysis for the reduction of NOx to N2 with hydrocarbons. The magnetic and catalytic properties of Fe-ZSM-11 samples with different contents of Fe2+ and Fe3+ were compared. The Fe2+-ZSM-11 sample (with 1.8 Fe2+ per unit cell) showed the best catalytic activity and greater saturation magnetization than the other samples. The proportion of Fe2+ per unit cell allows having higher amount of active sites for the reduction of NO when Fe2+ is bonded to the zeolite structure. These Fe2+ species bonded to the framework could generate ferromagnetic couples conferring the ferromagnetic behavior to the samples. The saturation magnetization of the other samples is smaller due to the lower amount of couples Fe2+–Fe2+. When the amount of Fe3+ increases, the Fe bonded to the structure as counter ion decreases, forming α-Fe2O3 as isolated clusters inactive for the reduction of NO. Mössbauer characterization of Fe2+-ZSM-11 showed that the Fe is forming couples (ferromagnetic) in an important amount. XANES studies of Fen+-ZSM-11 samples were performed in order to obtain the Fe2,3+composition.