Reactivity of binuclear Fe complexes in over-exchanged Fe/ZSM5, studied by in situ XAFS spectroscopy 2. Selective catalytic reduction of NO with isobutane

In situ XAFS spectroscopy was applied in order to determine the catalytically active sites in Fe/ZSM5, prepared by FeCl3 sublimation. The number of (inactive) spectators in this catalyst was minimized by using a specially dedicated calcination procedure. The catalytic activity of Fe/ZSM5 during the collection of the XAFS data was monitored via chemiluminescence analysis of the gas outlet. Binuclear Fe complexes with a FeOFe core were found to be catalytically active species in this material. During heat treatment in He to 350 °C the Fe complexes undergo auto-reduction, ascribed to the removal of oxygen from FeOFe bridges (closest FeO-coordination sphere) and the formation of Fe□Fe vacancies. Treatment with isobutane results in a further slight average reduction of iron, accompanied by an additional removal of oxygen from the FeOFe bridges. Fe in the binuclear complexes is readily oxidized when NO, NO+O2, or a typical HC-SCR mixture (NO, i-C4H10, O2) is fed to the Fe/ZSM5 catalyst. Reoxidation is accompanied by filling of the Fe□Fe vacancies. Under HC-SCR working conditions the average oxidation state of iron is 3+.