Influence of extra-framework Al on the structure of the active iron sites in Fe/ZSM-35

The influence of extra-framework Al via AlCl3 deposition on the structure of the active Fe sites in Fe/ZSM-35 was investigated by Si-29 MAS NMR, UV-visible diffuse reflectance spectroscopy, infrared spectroscopy, UV Raman spectroscopy, and Fe-57 Mossbauer spectroscopy combined with catalytic decomposition of N2O. It is found that high-temperature treatment considerably modifies the iron speciation. UV-visible diffuse reflectance spectra and in situ infrared spectra of NO adsorption show that a significant amount of clustered and cationic Fe species is transformed into extra-framework Fe-O-Al mixed oxide species by high-temperature treatment. UV Raman spectra and Fe-57 Mossbauer spectra suggest the generation of a binuclear Fe site stabilized by extra-framework Al species with a feature Raman band at 875 cm(-1), which is associated with the high activity of N2O decomposition. A possible explanation is that the addition of extra-framework Al species is beneficial for the formation of binuclear active Fe sites bound to extra-framework Al. (C) 2013 Published by Elsevier Inc.