Fe-saponite pillared and impregnated catalysts: II. Nature of the iron species active for the reduction of NOx with propene

A study of the NOx reduction with propene in the absence/presence of oxygen over Fe-saponite clay catalysts with different iron loadings (ca. 1–28 wt.%) has been performed. The catalysts were prepared by pillaring and impregnation methods and the iron active phases were characterized by using X-ray absorption spectroscopies and electron paramagnetic resonance. The samples display significant activity in the NOx reduction in the absence of oxygen with a maximum for a Fe content close to 10 wt.%. A strong decay of catalytic activity was observed with the introduction of increasing quantities of oxygen in the feed. Iron is mostly present in all catalysts as Fe(III) with a slightly distorted local octahedral symmetry. The catalytic behavior was explained in terms of the nature and properties of the Fe existing phases.