Characterization and activity of Fe-ZSM-5 catalysts prepared by ion exchange procedure in Fe-citrate and Fe-oxalate solutions

Abstract

The oxidation-reduction properties of iron cations exchanged into zeolites have been know for some time and zeolites that contain ion-exchanged iron are known to be catalytically active for several reduction-oxidation type reactions. Different methods are suited for preparing Fe-ZSM-5 catalysts like addition of iron during the hydrothermal synthesis of ZSM-5, ion exchange in the liquid phase, solid-state ion exchange, or sublimation (chemical vapor deposition) of FeCl3. The nature and local environment of iron species is strongly dependent on the synthetic route, which influences their catalytic performance. In the work presented here, Fe-ZSM-5 catalysts have been obtained from a hydrogen form of the zeolite ZSM-5, with Si/Al=15 purchased from Zeolyst International. Fe-ZSM-5 catalysts were prepared using Fe-citrate and Fe-oxalate solutions. The obtained samples were characterized by IR, TG, XRPD method and temperature programmed desorption (TPD) technique. The effect of ion exchange procedures on the activity of Fe-ZSM-5 catalysts was studied by n-hexane adsorption experiments. The main aim of this work was to evaluate and compare the influence of ion exchange procedure on the active sites for adsorption in the investigated samples.

Zeoliti koji poseduju jone gvožđa su vrlo važni katalizatori u oksidoredukcionim reakcijama, kako u gasovima, tako i u rastvorima. U ovom radu su napravljeni i okarakterisani uzorci Fe-ZSM-5 zeolita koji su sintetisani iz Fe-oksalatnog i po prvi put, Fe-citratnog rastvora. Pokazano je da stepen izmene jako zavisi od uslova sinteze i da se mehanizam izmene u prisustvu Fe-citrata i Fe-oksalata znatno razlikuje. Oba tipa uzoraka u hidratisanoj formi adsorbuju nepolarni molekul n-heksana. TPD-MS i TG rezultati ukazuju da se heksan različito vezuje na uzorcima dobijenim iz rastvora Fe-citrata u odnosu na uzorke dobijene iz Feoksalata.