Characterisation and catalytic activity in de-NOx reactions of Fe-ZSM-5 zeolites prepared via ferric oxalate precursor

This paper deals with the spectroscopic characterisation and catalytic activity of Fe-ZSM-5 samples prepared by aqueous exchange with ferric oxalate and Mohr salt as precursors. NH4+-ZSM-5 zeolites with different Si/Al ratios were employed as starting materials, as such and after Na+-exchange. The catalytic activity of the samples was tested in the selective catalytic reduction of NO with propane in the 473–773 K range, and the nature of extraframework Fe species was investigated by UV–vis and FTIR spectroscopies, using NO as a probe molecule. The catalytic activity was found to be dependent upon the exchange method, the Si/Al ratio and the presence of Na+ ions. The results are discussed in terms of the relative concentration of isolated and clustered sites, as estimated by spectroscopic analysis. We propose that isolated sites are active in SCR, while clustered sites favour propane oxidation, having a detrimental effect on the activity for NO activation.