Effect of iron impurities on the catalytic activity of BEA, MOR and MFI zeolites in the SCR of NO by ethanol

Abstract

The combined use of chemical analysis, XRD, EPR and Mössbauer techniques provides detailed information on the nature of iron impurities in commercial BEA, MOR and MFI zeolites. EPR and Mössbauer spectroscopies evidence that iron impurities are present mainly as tetrahedral Fe(III) species and to a minor extent as octahedral Fe(III) species, with relative amounts depending on the type of zeolite. Iron impurities present in commercial BEA, MOR and MFI zeolites are active in the selective catalytic reduction (SCR) of NO by ethanol, with NO conversion higher than 37, 43 and 50% for BEA, MOR and MFI, respectively, and with selectivity toward N2 higher than 90% for all zeolites in the temperature range 575–775K. The much higher activity of commercial BEA, MOR and MFI than that of FeSiBEA and CoSiBEA, both prepared by a two-step postsynthesis method, suggests that Fe(III) impurities in commercial zeolites are present in tetrahedral and/or octahedral environments, possibly close to lattice Al, which make them active in the SCR of NO by ethanol. The Brønsted and Lewis acidic sites in studied zeolites are determined by FTIR measurements of pyridine adsorption.