New precursor for the post-synthesis preparation of Fe-ZSM-5 zeolites with low iron content

Abstract

A new method for preparing ZSM-5 catalysts containing highly dispersed iron species is presented. Iron(III) oxalate was used as the iron precursor in an aerobic aqueous exchange process. The presence of different iron species inside the zeolite pores was investigated by IR spectroscopy of adsorbed NO, which revealed an excellent iron dispersion. The results were compared with those obtained on a Fe-ZSM-5 catalysts prepared by iron(II) chloride sublimation and on samples prepared by controlled migration of framework iron in isomorphously substituted samples.

Preparation and Pretreatment Temperature Influence on Iron Species Distribution and N2O Decomposition in Fe–ZSM-5

“…H 2 -TPR shows that at high temperatures (around 540°C) the FeO x species can be reduced and the 1856 cm )1 band is due to such reduced particles. This is further supported by the fact that such IR bands are observed over iron silicalite, which mainly consist of FeO x particles [6,7,29,[33][34][35][36][37][38][39][40][41]45,46]. No correlations are found between group 3, group 4, and group 5 iron nitrosyl bands and, therefore, these are considered as three different iron species.…”

“…NO forms various iron nitrosyls that are sensitive to the iron species coordination or location in the zeolite channels [32,33]. Therefore, the nature of iron species in zeolite can be effectively probed by characterising the NO stretching vibrations by IR [6,7,29,[33][34][35][36][37][38][39][40][41]. NO adsorption studies over auto-reduced Fe-ZSM-5 catalysts are presented in Ref.…”

“…Group 4 IR bands: Bands at 1815 and 1919 cm )1 are correlated to symmetric and asymmetric NO stretches of iron dinitrosyl species (Fe 2+ (NO) 2 ) and the shoulder at 1765 cm )1 is due to the mononitrosyl of the same iron species (figures 5-8) [41]. The iron dinitrosyl bands are observed over iron species present at zeolite ionexchanged positions as well as in FeO x containing samples [6,7,29,[33][34][35][36][37][38][39][40][41]46]. Due to high coordinative unsaturation of iron species (present in easily accessible straight channels) it is proposed to form di-, and even polynitrosyls [37,45].…”

The Effect of Different Active Sites on the Catalytic Activity of Fe-ZSM-5 Zeolite for N2O Direct Decomposition

“…Recently, Nechita et al [18] also prepared Fe-ZSM-5 zeolite with low iron loading through liquid ion-exchange In experiments, the results of catalytic evaluation showed that the catalytic activity enhanced with increasing the iron loading (Fig. 6).…”

Evidence for controlled insertion of Fe ions in the framework of clinoptilolite natural zeolites

“…The debate about the nature of the catalytically active sites, isolated Fe 2+ ions or dimeric-oligomeric species in extra-framework positions, has resulted in a incredibly high number of publications on the subject [12,13], as recently reviewed [14]. This interest has also leaded to the development of new ways to introduce Fe species in zeolitic frameworks in controlled manner [15,16]. This huge effort in understanding the structure and chemical reactivity of highly dispersed Fe sites has not been applied to natural zeolites up to now.…”